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Effect of dark and light adaptation on the retina and pecten of chicken
Abstract
Retinae and pecten oculi of chickens were studied after 30 days of dark and light adaptation. Biochemically, glycogen and alkaline phosphatase activity increased 24 and 6%, respectively, in retina on dark adaptation, and decreased 15 and 17%, respectively, on light adaptation. Retinal RNA content increased 11% on light adaptation. DNA remained unaffected on dark and light adaptation of the retina. Alkaline phosphatase activity of pecten decreased 25% on dark adaptation.Histochemically, glycogen-rich paraboloids of accessory cones and hyperboloids of rods of the retina atrophied when subjected to light and hypertrophied on dark adaptation. On light adaptation, except for the outer plexiform layer, the alkaline phosphatase activity was negligible. Possible significance of these results in relation to sensory functions of the retina and retina-pecten interrelationship is discussed.
... In the capillary endothelial cells, specialized membranes greatly increase intracell membrane surfaces [18][19][20], which with the pleats and intracellular vesicles [19], have long suggested pectenial nutrition of the avascular avian retina [17,19,21] and an oxygen gradient from pecten to retina [21]. High pecten content of carbonic anhydrase [22] and alkaline phosphatase [23] indicates metabolic activity. However, absence of discernible endothelial cell boundaries, their clear, almost structureless cytoplasm and thick, hyaline membrane surrounding capillaries [18,19], are unexplained. ...
... The pecten contains much alkaline phosphatase and carbonic anhydrase [22,23]. Light increased alkaline phosphatase activity in the pecten [22]. ...
... The pecten contains much alkaline phosphatase and carbonic anhydrase [22,23]. Light increased alkaline phosphatase activity in the pecten [22]. Respiratory CO 2 converted by carbonic anhydrase to the HCO 3 necessary in anaplerotic b-carboxylation [73], would in turn stimulate recycling of nitrogen; readily available in migrating birds. ...
Pigments serve many visually obvious animal functions (e.g. hair, skin, eyes, feathers, scales). One is ‘melanin’, unusual in an absorption across the UV–visual spectrum which is controversial. Any polymer or macro-structure of melanin monomers is ‘melanin’. Its roles derive from complex structural and physical–chemical properties e.g. semiconductor, stable radical, conductor, free radical scavenger, charge-transfer. Clinicians and researchers are well acquainted with melanin in skin and ocular pathologies and now increasingly are with internal, melanized, pathology-associated sites not obviously subject to light radiation (e.g. brain, cochlea). At both types of sites some findings puzzle: positive and negative neuromelanin effects in Parkinsons; unexpected melanocyte action in the cochlea, in deafness; melanin reduces DNA damage, but can promote melanoma; in melanotic cells, mitochondrial number was 83% less, respiration down 30%, but development similar to normal amelanotic cells.
... Although the structure of the pecten has received a lot of attention (Bawa & YashRoy, 1974;Bhattacharjee, 1993;Braekevelt, 1993;Kiama et al., 1994) data on quantitative structural characteristics are scarce. Save for a preliminary morphometric study to determine the proportion of pectineal blood vessels in the cormorant Phalacrocorax carbo (Bhattacharjee & Maina, 1987), most other available data are based mainly if not exclusively on the number of pleats (Thomson, 1929;Meyer, 1977) and information concerning the precise size of the pectens is lacking. ...
... The role of pigmented tissue in the pecten oculi has been debated for a long time. The suggested roles include raising the metabolism of the pecten by increasing its temperature through light absorption (Bawa & YashRoy, 1974), providing structural support (Braekevelt, 1993), and protecting the pectineal capillaries from the harmful effects of ultraviolet radiation (Kiama et al., 1994). Although the pigmented tissue could be performing any or all of these roles, the present data suggest that there is an optimum fraction of the pigment component the pecten has to concede with, without its nutritive role being compromised. ...
The pecten oculi is a highly vascularized and pigmented organ that overlies the optic disc and projects into the vitreous body in the avian eye. First reported over 300 years ago, its function(s) remains a puzzle to ornithologists, ophthalmologists and anatomists. Morphometric study of this unique organ was undertaken in birds exhibiting apparently different visual acuities, namely two species of diurnal birds (the ground-dwelling domestic fowl Gallus gallus var. domesticus and a highly active predator bird, the black kite (Milvus migrans) and a nocturnal bird (the spotted-eagle owl Bubo bubo africanus). The volume of the owl's eye was 4.8 and 2.2 times larger than that of the fowl and the kite, respectively. However, the pecten of the fowl consisted of more pleats (16–18) compared to the kite (12–13) and the owl (5–6). The volume of the pecten of the kite was 1.4 and 2.7 times larger than that of the fowl and the owl, respectively (P < 0.05). Similarly, the surface area of the pecten of the kite was 2.6 and 4 times larger than that of the fowl and owl, respectively (P < 0.05). The volume density of blood vessels (lumen and wall) in the pecten of the kite, fowl and owl comprised 67.7%, 66.9% and 62.6%, respectively, the pigmented tissue constituting the rest. Both the volume density and the volume of the blood in the pecten were higher in the diurnal birds (kite, fowl) than the owl (P < 0.05). The surface area of the capillary luminal surface was 1.7 and 5.3 times higher in the kite than in the fowl and the owl, respectively (P < 0.05). These results suggest that the functional morphology of the pecten correlates with the life-style of the bird and with functional need, and lends further support to the nutritive role of the pecten.
... Vol. 11, Issue 6, December-2023 European Journal of Applied Sciences (EJAS) Several observations have been linked to the PO over the years: The PO has a high concentration of carbonic anhydrase and alkaline phosphatase [16,17,22,23], and the alkaline phosphatase activity of the PO decreases on dark adaptation by somewhere between 25% [24] and 100% [25]. Furthermore, the endothelium of the PO's capillaries shows a positive histochemical reaction for aminopeptidase, and negative reaction for succinic-acid dehydrogenase [23]. ...
Purpose: To summarize and evaluate the latest hypotheses on the function of the pecten oculi (PO). Methods: Review of relevant literature. Results: The PO is an organ present in all avian eyes. A similar structure, the conus papillaris (CP), is also found in terrestrial reptiles. Several reports have claimed the PO nourishes the avascular avian retina, but it has also been argued that the function is not primarily nutritive but instead may be related to intraocular pH-regulation, as the avian retina has an anaerobic metabolism. These conclusions are, at first glance, contradictory. However, a recent report indicated how these two views may be incorporated in a new and unifying hypothesis, with the common denominator being that the CP/PO evolved in tandem with increasing uric acid (UA) in serum. Discussion: According to Wingstrand and Munk, the PO leaks oxygen and nutrients to the retina, meaning that leakage of the small and heavily soluble component UA in serum could follow the same path. Protein-binding of the UA is not an option in the vitreous body, as the UA could crystalize intraocularly and harm the visual function. Two mechanisms countering this situation have been identified: 1) The inflow of the UA to the intraocular compartments (i.e.-vitreous body and anterior chamber) is reduced through selective barriers both in the PO and in the ciliary body. 2) The UA solubility is increased through alkalization of the vitreous body by the PO. Conclusion: During evolution vision was improved when the retinal vessels were collected in the PO. Two competing hypotheses on the PO's function have been summarized, and it is shown how these may be incorporated in a new unifying hypothesis.
... This provides strong evidence that the pecten absorbs light and shields the eye from UV light's damaging effects (Braekevelt, 1998;Kiama et al., 1994). This was done in an effort to suggest that the pecten's function was analogous to the light baffles in the camera (Bawa & YashRoy, 1972;Venkateshan & Ramesh, 2006). According to certain theories, the melanocytes help hold the pecten firmly straight in the vitreous humor by acting as a structural support (Braekevelt, 1991b). ...
There is scanty data about the comparative morphological features between the pecten oculi of two carnivorous birds with different visual active clock hours: the diurnal common kestrel and the nocturnal little owl. This study illustrated the comparative gross, scanning electron microscopy, and histological characteristics between pecten oculi of kestrel and little owl. This study first attempts to describe the scanning electron microscopy‐energy dispersive x‐ray (SEM–EDX) elemental analysis at the parts (apex, middle, and base) of the pecten oculi of these two birds. The present study results observed the same position, origin, directions, parts, convoluted outer pleat surfaces, and SEM–EDX elemental analysis, but there were some minor variations due to the different visual active clock hours. These minor variations were summarized in the following points: pleat number (21–23 in the kestrel and 10–11 in the owl), shape (fan rhomboid in the kestrel and accordion in the owl), inter‐pleat spaces (wider in the kestrel than in the owl), pigmentations (highly black pigmented in the owl than in the kestrel), hyalocyte cell aggregations (highest in the middle and dwindling at the apex and base in the kestrel, while highest in the middle and base and dwindling at the apex in the owl), and SEM–EDX elemental analysis percentage. SEM/EDX elemental analysis confirmed the presence of oxygen (the highest one), carbon, nitrogen (the second one), nitrogen (the third one), and aluminum (the lowest one) in varying percentages within the pecten oculi; these findings contribute to our understanding of its structural, adaptations with different visual active clock hours, and functional characteristics.
Research Highlights
This study compared the pecten oculi of two carnivorous birds with different visual active clock hours: the diurnal common kestrel and the nocturnal little owl.
Anatomically, the characteristic features were similar in both the birds, but some minor variations were observed adapted to their visual active clock hours.
The pecten oculi of both birds were analyzed using SEM–EDX for elemental analysis, and it revealed that oxygen was the highest elemental concentration, followed by carbon and nitrogen. Aluminum concentrations were small as per SEM–EDX analysis.
The study suggested that the pecten oculi of these birds are related to their active visual clocks and adaptive nutritional mechanisms.
... Thus, the alkaline environment created in the vitreous body by the carbonic anhydrase in PO is favourable both for the alkaline phosphatase activity and the solubility of UA [19]. In addition, the activity of alkaline phosphatase in PO decreases 25% on dark adaptation [89]. ...
... There are some previously published data describing the gross morphological appearance especially the retina of different avian species (Alix, Segovia, & García, 2017;Bawa & YashRoy, 1972;Braekevelt & Thorlakson, 1993;El-Beltagy, 2015;Hossler & Olson, 1984;Segovia, García, G omez-Torres, & Mengual, 2016). However, the cornea, iris, and choroid received little attention from researchers (Meyer, 1977). ...
The present study was designed to provide a complete morphological description of the eye of the migratory Garganey duck (Anas querquedula) and its visual adaptation with the different surrounding environmental conditions during its migration journeys using a stereomicroscope, scanning electron microscope (SEM), and light microscope. The current work depends on six adult Garganey ducks that were captured from the area near and on the shores of Edku city. The obtained results revealed that the eye of the migratory Garganey duck has the features of both diurnal and nocturnal birds. The histological examination reveals that the pigmented epithelium of the retina has long prolongations filled with melanin. The cone is the dominant photoreceptor, but simple rods are present. The inner nuclear and ganglion cell layers are thick. SEM examination shows that the arrangement of the collagen fibrils on the external surface was reticular in shape. The radial folds present as pledged structures on the pigmented epithelium covered with circular structures. The main lens body has flat with hexagonal outlines fibers. The edges and surfaces of these hexagonal fibers were studded with protrusions or elevations (balls) and depressions (sockets). The sockets and balls were either rounded or ellipsoid in shape. The balls were more on the edges and the sockets on the surface. In conclusion, our findings indicated a higher degree of functional adaptation between the morphological structure of the eye and the surrounding environmental conditions. The obtained results revealed that the eye had the features of both diurnal and nocturnal birds. The pigmented epithelium of the retina had long prolongations filled with melanin. The cone is the dominant photoreceptors, but simple rods are present. The radial folds present as pledged structures on the pigmented epithelium covered with circular structures.
... The primary role of melanocytes in the pectineal tissue is to protect blood vessels from the adverse effects of ultraviolet light and to provide structural support to the pecten oculi so that it maintains a tight vertical position in the gel-like vitreous body. Furthermore, the absorption of the light that enters the eye by the melanocytes results in an increase in the temperature of the pectineal tissue, which in return increases the metabolic rate (Bawa & Yashroy, 1972). Similar to reports available for other avian species, in the present study, it was observed that, in the pecten oculi of the Gerze chicken, melanocytes were localized to the periphery of the blood vessels and were present at a higher level in the apex of the pecten, compared to its base. ...
The pecten oculi is a highly vascularized and pigmented organ that projects from the optic disc into the vitreous body in the avian eye. In this study, the pecten oculi of Turkey's native Gerze chicken was examined by light and scanning electron microscopy. Furthermore, the localization of some adherens junction components (E‐cadherin and pan‐cadherin) in intact vessels of the blood–retina barrier was investigated by immunohistochemistry. In the Gerze chicken, the pecten oculi was a thin structure, which was located over the head of the discus nervi optici and projected from the retina into the corpus vitreum. The pecten oculi consisted of 18–21 highly vascularized pleats, joined apically by a bridge and resembled an accordion in appearance. Hyalocytes and melanocytes were observed around the small and large vessels. The morphometric data of the pecten oculi showed that there were no statistical differences in terms of sex. The immunohistochemical analysis of the pecten oculi, which is used as a model for the investigation of the formation and maturation of the barrier properties in the central nervous system, revealed cytoplasmic E‐cadherin and pan‐cadherin immunoreactivity in the endothelial cells of the small, large and capillary vessels. These observations suggest that while the morphological and histological structure of the Gerze chicken's pecten oculi was generally similar to that of other diurnal domestic birds, the pecten oculi, a model system for vascular differentiation and the blood–retina barrier, expressed different cadherins.
... That directed to propose that pecten's function equivalent to the light baffles in the camera [23,24]. ...
Objective: As pecten oculi had great functional significances for ornithology, pecten oculi of Baladi duck was well-deserving of intensive morphological study. So, the aim of this study was to throw light on some anatomical and histological formation of the pecten oculi of Baladi ducks as well as use of scanning electron microscopy.
Materials and Methods: Twenty eyeballs of 10 adult Baladi ducks were used to fulfill this work. Ten eyes were used to study the gross anatomy of pecten oculi, including the location, shape, and numbers of pleats. Five samples were embedded at 10% neutral buffered formalin. The speci¬mens were examined by regular histological procedures. The latter five samples were applied for electron microscopy.
Results: Grossly, the pecten oculi is formed of three portions: the base, emerged from the optic disk; the pleats, sorted in fan shape; and the bridge. The essential histological ingredients of Baladi ducks pecten oculi are the blood vessels, lymph vessels, pigment cells, and hyalocytes.
Conclusion: The current work explains the primary macro- and micro-morphological features of pecten oculi in Baladi duck and collates these features to those formerly explained in other birds. Generally, pecten oculi of Baladi duck was analogous to that of the diurnal birds. [J Adv Vet Anim Res 2019; 6(4.000): 456-462]
... The alkaline phosphatase activity was observed by Tsugio (1982) in the pecten of dark adapted eye in chick and demonstrated no activity. He mentioned that darkness may make the exchange of metabolites between pecten and less active vitreous humour with the similar observations by Bawa and Roy (1972) in chicken. However in the present study also it was similar with them, but when the day active i.e. diurnal birds were chosen for detecting the strength of alkaline phosphatase activity in their pecten oculi and when it revealed a very weak activity then it was required to be noted that alkaline and acid phosphatase were those enzymes which hydrolyzes the phosphate group and act as catalyst to speed up the chemical reaction in cell at basic and acidic environment with optimum pH of 10.5 and 5.3 respectively. ...
The study was conducted on 18 eyes, which revealed that dark black velvety pecten oculi has 13 to 17 number of accordion (pectineal) folds. These accordion folds were initiated from cauda of optic nerve and travelled via fundus distally into the vitreous humour in the manner of undulated natured pathway of snake. Macroscopically the shape of pecten oculi was observed without much difference of the sail board. The maximum average length and height of pecten oculi was found on the tune of 3.378±0.061 mm and 5.913±0.074 mm respectively. Histomorphologically the pecten oculi showed an organization as the festoon of blood capillaries with their elastic, collagen and reticular fibers which correspond with the structure of spring diving board. Its working principle was also being matched with Hook’s law, how the diving spring board work. Melanocytes, melanosomes and melanin granules were observed in and around blood capillaries of pecten oculi. The highest concentration of melanin was observed in the apex. Histochemically the pecten oculi was shown very weak activity of acid phosphatase and alkaline phosphatase. It has shown a strong activity of glycogen at optic nerve and collagen fibers of pectineal capillaries. Ultrastructurally, the nucleated erythrocytes were witnessed at luminal area of pectineal blood capillary and the endothelium was elaborating tight intercellular junction. The primary and secondary lamellae were observed in the luminal region of pectineal capillary wherein pigment depositing globules were discovered. Pecten oculi of Guinea fowl (Numida meleagris) perform various functions, after which it is identified as the organ of haemostatic function, support system to retina to get visual acuity, phagocytic, immunity shield and the source of energy for vitreous humour by performing process of diffusion.
... The alkaline phosphatase activity was observed by Tsugio (1982) in the pecten of dark adapted eye in chick and demonstrated no activity. He mentioned that darkness may make the exchange of metabolites between pecten and less active vitreous humour with the similar observations by Bawa and Roy (1972) in chicken. However in the present study also it was similar with them, but when the day active i.e. diurnal birds were chosen for detecting the strength of alkaline phosphatase activity in their pecten oculi and when it revealed a very weak activity then it was required to be noted that alkaline and acid phosphatase were those enzymes which hydrolyzes the phosphate group and act as catalyst to speed up the chemical reaction in cell at basic and acidic environment with optimum pH of 10.5 and 5.3 respectively. ...
The study was conducted on 18 eyes, which revealed that dark black velvety pecten oculi has 13 to 17 number of accordion (pectineal) folds. These accordion folds were initiated from cauda of optic nerve and travelled via fundus distally into the vitreous humour in the manner of undulated natured pathway of snake. Macroscopically the shape of pecten oculi was observed without much difference of the sail board. The maximum average length and height of pecten oculi was found on the tune of 3.378?0.061 mm and 5.913?0.074 mm respectively. Histomorphologically the pecten oculi showed an organization as the festoon of blood capillaries with their elastic, collagen and reticular fibers which correspond with the structure of spring diving board. Its working principle was also being matched with Hook?s law, how the diving spring board work. Melanocytes, melanosomes and melanin granules were observed in and around blood capillaries of pecten oculi. The highest concentration of melanin was observed in the apex. Histochemically the pecten oculi was shown very weak activity of acid phosphatase and alkaline phosphatase. It has shown a strong activity of glycogen at optic nerve and collagen fibers of pectineal capillaries. Ultrastructurally, the nucleated erythrocytes were witnessed at luminal area of pectineal blood capillary and the endothelium was elaborating tight intercellular junction. The primary and secondary lamellae were observed in the luminal region of pectineal capillary wherein pigment depositing globules were discovered. Pecten oculi of Guinea fowl (Numida meleagris) perform various functions, after which it is identified as the organ of haemostatic function, support system to retina to get visual acuity, phagocytic, immunity shield and the source of energy for vitreous humour by performing process of diffusion.
... It is interesting that the amount of enfolding of the apical and basal plasmalemmal of the capillary endothelium in both the pectin and the ciliary body increased greatly in both the pectin and the ciliary body after administration of acetazolamide. The alkaline phosphatase activity of pectin tissues changes markedly upon dark adaptation [38]. ...
The development and evolution of eyes is ancient and difficult problem in biology. Darwin postulated a prototype eye which can evolve under natural selection. Neo-Darwinists, based in morphological criteria, have postulated a polyphyletic origin that has evolved independently in the various animal phyla. Molecular phylogenetic analyses and developmental genetic experiments, cast serious doubts on both theories. The study of the development of the eye in the amphibian embryo has been a formidable tool research to experimental embryology and evolutionary biology as early as 1901. The embryonic induction, the interactions between different embryonic tissues (organizers); and the role of genes, were conceived as result of reciprocal transplantation experiments. The classical description is that the eye in vertebrates develops from the neural plate, as an evagination from the brain, forming the optic vesicle; which subsequently invaginates to form the optic cup. The inner layer of the optic cup forms the retina with its photoreceptor layers, whereas the outer layer gives rise to the pigment epithelium which absorbs the light in the back of the retina. However, failed to recognize the importance of melanin pigment. The mammalian eye consists of several layers that contain melanin, 40 % more than skin in average. Retinal, Iris and ciliary pigment epithelial cells are derived from neural ectoderm, oppositely, the uveal melanocytes, placed in choroid, iris and ciliary body stroma, are developed from the neural crest. The photo screening protective effects of melanin, the biophysical and biochemical also protective effects and biologic and photo biologic effects; have been extensively studied, but so far, researchers have been considered melanin merely as a sun block with difficult-to-explain properties. Therefore, the unsuspected intrinsic property of melanin to transforms visible and invisible light, into chemical energy, through water dissociation, as chlorophyll in plants, founded in our research facility in 2002 break the ground in regards our concepts about the biology and physiology of the body and therefore the eye. Melanin is a fundamental molecule in bioenergetic pathways, wherever is placed, and the ocular globe is not an exception. Thereby, the main function of melanin in the eye, is chemical energy production through water dissociation, as chlorophyll in plants.
... Furthermore, the choroidal lacunae become smaller and less numerous near the optic nerve, pecten oculi, and iridotrabecular angle, and therefore are not a part of a Schlemm's canal (De Stefano and Mugnaini, 1997). Several other observations made on the pecten oculi also give support to the hypothesis of a secretory function, including 1) extrusion of dye from the pecten accompanying each heart beat during fluorescein angiography (Bellhorn and Bellhorn, 1975), 2) the pecten´s high content of carbonic anhydrase and alkaline phosphatase (Bawa and YashRoy, 1972;Amemiya, 1982), 3) evidence that the pecten acts as an agitator to propel perfusate towards the central retina (Pettigrew et al., 1990), and 4) evidence of the pecten having a crucial role in maintaining retinal health (appearance of retinal damage after pectin oculi ablation (Wingstrand and Munk, 1965). In this study, we showed that Doppler imaging is capable of successfully enabling characterization of the http: //www.openveterinaryjournal.com W. de Moraes et al. ...
Twenty harpy eagles (Harpia harpyja) without systemic or ocular diseases were examined to measure blood velocity parameters of the pectinis oculi artery using Doppler ultrasonography. Pectinate artery resistive index (RI) and pulsatility index (PI) were investigated using ocular Doppler ultrasonography. The mean RI and PI values across all eyes were 0.44±0.10 and 0.62±0.20 respectively. Low RI and PI values found in the harpy eagle´s pectinis oculi artery compared with the American pekin ducks one and other tissue suggest indeed a high metabolic activity in pecten oculi and corroborates the hypothesis of a nutritional function and/or intraocular pressure regulation.
... 13 This morphological observation and our results of similar RI and PI of the main branch of the pectinis oculi artery to the ciliary body arteries in dogs could signify that the pecten oculi has secretory functions as well. This is supported by the several lines of evidence and observations, such as that the pecten oculi acts as an agitator which propels perfusate toward the central retina, 39 the presence of an oxygen gradient from pecten to retina, 40 the large surface area produced by macroscopic folds, 41 and by microscopic infoldings of the luminal and external surfaces of the capillary endothelium, 9 extrusion of circulating fluorescein, 42 high content of carbonic anhydrase and alkaline phosphatase, 43,44 and retinal impairments after pectin oculi ablation. 40 In this study, we have demonstrated selected blood flow parameters of the main branch of the pectinis oculi artery. ...
Objective:
To measure blood velocity parameters of the main detectable branch of the pectinis oculi artery and compare with values found in other arteries in other species to form a hypothesis of the function of the pecten oculi in birds.
Methods:
Eleven American pekin ducks (Anas platyrhynchos domestica) without ocular diseases were examined with ocular Doppler ultrasonography. The pectinate artery resistive index (RI) and pulsatility index (PI) were calculated.
Results:
The mean of RI and PI values resulted, respectively, in: left eye (0.43 ± 0.07; 0.58 ± 0.13), right eye (0.37 ± 0.09; 0.47 ± 0.14), and both eyes (0.40 ± 0.08; 0.53 ± 0.14).
Discussion:
The low RI and PI values found in the main branch of the pectinis oculi artery compared with other arteries in other tissues suggest a high metabolic activity in the pecten oculi, and it could indicate a nutritional function and/or intraocular pressure regulation.
... It has suggested that pigmented cells provide the structural reinforcement to pecten oculi for keeping it firmly erectile within the gel-like vitreous and also protect the blood vessels against damage from ultraviolet light [1,7,17]. In addition the absorption of light by the pigmented cells probably raises the temperature within the pecten and hence the rate of metabolism within it [19]. ...
In this study was investigated the structure of pecten oculi in the ostrich, duck, pigeon, turkey, and starling. The pecten oculi of the ostrich was vaned type and made up primary, secondary, and few tertiary lamellae. However, duck, pigeon, turkey and starling had a pleated-type pecten oculi which displayed folded structure. The numbers of pleats of the pectens were 12, 13-14, 21-22, and 17 in duck, pigeon, turkey, and starling, respectively. Light microscopic investigation demonstrated that pecten oculi is basically composed of numerous capillaries, large blood vessels, and pigment cells in all investigating avian species. Capillaries were 20.23, 14.34, 11.78, 12.58, and 12.78 μ m in diameter in ostrich, duck, pigeon, turkey, and starling, respectively. The capillaries are surrounded by thick basal membrane, and pigmented cells were observed around the capillaries.
... Such a mechanism has not yet been reported in the retina; however, it is suspected that it may be one of the modes of synthesis of phospholipid from glucose on prolonged dark adaptation. I n our previous report (Bawa & YashRoy 1972) we have contended that during prolonged absence of light, the energy-requirement of the retina is less and a considerable part of the glucose supplied to the retina is converted to glycogen (glycogenesis). And it is plausible that a part of it (glucose) may be converted to phospholipid as is suggested by the findings of Day & Fidge (1965). ...
Chickens were adapted to dark and light for 30 days and their retinas were studied in comparison to the chickens kept in normal environments. Total phospholipid content and cholinesterase activity were determined biochemically in the retinas of each group of animals. An increase of approximately 22% was observed in the phospholipid content of the dark adapted retinas, whereas the light adapted retinas showed no significant change in comparison with the normal counterparts. Retinal cholinesterase activity decreases by about 64% on dark adaptation and increases by about 14% on light adaptation.
We studied the fine histological structures of pecten oculi of the Eurasian tree sparrow using various microscopy techniques. The pecten of the tree sparrow was found to be of a pleated type comprising of pleats, bridges, and base. The light microscopic study revealed further that the pleats consist of capillaries of varying sizes, blood vessels, and numerous pigmented cells that give them a black color. Histochemical studies of pecten showed a large deposition of lipid droplets, which were more abundant in the basal area. The transmission electron microscopy displayed capillaries and blood vessels that remain surrounded by a thick fibrous basal membrane. They are formed of endothelial cells having a large lumen and abluminal area with microfolds. Interstitial spaces were found filled with rounded melanocytes, electron-dense pigment granules, and mitochondria. Observations under the scanning electron microscope revealed the presence of a dense vascular network of capillaries and vessels. In addition, large hyalocytes were also observed on the surface of the pleats. The above observations suggest that the histological structure of the pecten of the tree sparrow resembles those present in the pecten of other diurnal birds. However, further investigation is required to ascertain its functional role in birds.
The avian eye is considered to be “supreme amongst all living creatures” and capable of attaining “an order of excellence unmatched in any other species not excepting man” (Duke-Elder, 1958). Many structural and functional adaptations have become involved in the perfection of visual processes in birds which, according to Pumphrey (1948a) represent the culmination of phylogenetic development toward diurnal vision. This chapter is concerned with several of these adaptations, the most obvious of which are the oil droplet inclusions and glycogen deposits within their photoreceptors, the well-developed areae and foveae within their retina and the highly vascularized pecten within their vitreous body. A detailed description of the avian eye is not intended; excellent sources are available on this subject: Wood (1914), Slonaker (1918), Franz (1934), Walls (1942), Rochon-Duvigneaud (1943), Polyak (1957), Duke-Elder (1958), and Hodges (1974)
Die Befunde werden mit denen am Conus papillaris anderer Echsen und Pecten oculi von Vögeln im Hinblick auf strukturelle Gemeinsamkeiten zwischen beiden Organen verglichen. DerChalcidesconus entspricht in Form, GefÄ\architektur, Innervation und Mastzellgehalt dem typischen Echsenconus, wÄhrend die relative Kapillarvermehrung und die Gestaltung ihrer EndotheloberflÄche mit den VerhÄltnissen im Pecten oculi vergleichbar ist. Der Conus papillaris vonChalcides chalcides nimmt somit hinsichtlich seiner Ultrastruktur eine gewisse Mittelstellung zwischen Conus und Pecten ein. Vermutlich dient auch der Conus der ErnÄhrung der avaskulÄren Echsennetzhaut bzw. dem Austausch der intraokulÄren Flüssigkeit.
The pecten oculi of the mallard duck (Anas platyrhynchos) has been examined by light and electron microscopy. In this species, the pecten is of the pleated type and 12–14 accordion folds are joined apically by a heavily pigmented bridge of tissue which holds the pecten in a fanlike shape, widest at the base. It is situated over the optic nerve head and extends out into the vitreous. The entire pecten is enclosed by a fine basal lamina and hyalocytes are often present on its outer surface. Within each fold are numerous capillaries, larger blood vessels, and melanocytes. The capillaries are surrounded by thick fibrillar basal laminae which often contain pericytes. These capillaries display extensive microfolds on both the luminal and abluminal borders. The endothelial cell bodies are extremely thin, with most organelles present in a paranuclear location. The melanocytes, which are most plentiful in the bridge region, form an incomplete sheath around the capillaries and other blood vessels. The morphology of the pecten in the mallard is indicative of a heavy involvement in the transport of materials.
The metabolism of glycogen was studied in sensory cells of the mormyrid fish, Gnathonemus petersii. Knollenorgans, specific cutaneous electroreceptor organs of the lateral line system, have a spontancous electrical activity and their resting discharge in the absence of stimulation is about 0.04 kHz. Various types of stimulation can produce an increase in frequency; the highest frequency (1.30 kHz) is obtained by moving the Knollenorgan above water level. Glycogen was visualized in ultrathin sections after fixation in a solution of potassium ferricyanide and osmium tetroxide. The density of glycogen particles was determined morphometrically in sensory cells before stimulation, after high-frequency activity, and after reimmersion in water. An increase in the electrical activity of the Knollenorgan resulted in a decrease of the glycogen content of sensory cells. The glycogen store was replenished to about 85% of control within 40 min after stimulation and subsequent reimmersion. The results demonstrate that glycogen in the sensory cells of the Knollenorgan represents an energy source which can be catabolized during high electrical activity and replenished during rest.
The pecten oculi of the domestic chicken was examined with light, scanning and transmission electron microscopy and with freeze-etching
techniques. Particular attention has been given to the capillary structure. The capillaries form an extensive anastomotic
network. Their endothelial cells have apical (luminal), as well as basal, longitudinally oriented microfolds. It is assumed
that the formation of apical differentiations of the endothelial surface is due to haemodynamic influences. Thus, sufficient
surface area for membrane bound enzymes is achieved. These enzymes are necessary for active transcellular transport processes
that require energy. In freeze-etched material, two different structures of the membrane surface of microfolds can be recognized.
These results are discussed in relation to transport functions through capillary endothelial cells of the pecten. It is assumed
that the pecten plays an important role in the nourishment of the retina and vitreous body.
Der Pecten oculi des Haushuhns wurde licht-, scanning- und transmissions-elektronenmikroskopisch sowie mit der Gefrierätz-Technik
unter besonderer Berücksichtigung seiner Kapillarstruktur untersucht. Die Kapillaren bilden ausgedehnte anastomosierende Netze.
Ihre Endothelzellen besitzen sowohl apikal (luminal) als auch basal längsorientierte Mikrofalten. Es wird angenommen, daß
die Ausbildung der apikalen endothelialen Oberflächendifferenzierung haemodynamisch bedingt ist. Hierbei wird gleichzeitig
ausreichend Platz für membrangebundene Fermente geschaffen, die für aktive energie-verbrauchende transzelluläre Transportprozesse
benötigt werden. Die Gefrierätzbefunde lassen unterschiedlich strukturierte Membranoberflächen an den Mikrofalten erkennen,
die im Zusammenhang mit Transportfunktionen der Kapillarendothelzellen des Pectenoculi diskutiert werden. Vermutlich spielt
der Pecten eine wichtige Rolle für die Ernährung von Retina und Glaskörper.
The pecten oculi is a highly vascular and pigmented organ placed in the vitreous body of the avian eye. As no data are currently available on the morphological organization of the pecten in the Psittaciformes, the pecten oculi of the budgerigar (Melopsittacus undulatus) was studied. The eyes from adult male budgerigars were examined by light, transmission, and scanning electron microscopy and a morphometric study on both light and transmission electron microscopy specimens was also performed in the different parts of the organ. In the budgerigar, the type of the pecten oculi was pleated. Its basal part had a cranio-caudal and postero-anterior course; its body consisted of 10-12-folds joined apically by a densely pigmented bridge. The pecten showed many capillaries, whose wall was thick and formed by pericytes and endothelial cells. These latter had a large number of microfolds, rectilinear on their luminal surface and tortuous on their abluminal surface. Interstitial pigment cells were placed among the capillaries, filled with melanin granules and showed many cytoplasmic processes. The morphometric analysis demonstrated significant differences among the three parts of the organ relative to the length of the endothelial processes and to the number and size of the pigment granules. The morphological and morphometric analysis showed that the bridge of the budgerigar, different from the other birds, had a large number of capillaries, so that this part of the organ could also play a trophic role for the retina in addition to the choriocapillaris.
The ultrastructure of the capillary endothelium of the conus papillaris within the vitreous body was studied in night, day, and mixed (night and day) active geckos (Homopholis wahlbergi •, Gekko gecko •, Pachydactylus bibronii
, Tarentola mauritanica
). Capillary endothelial cells were poorly developed in night and mixed active animals, whereas in day active animals they were highly organized. In particular the number and height of the luminal and basal microvilli and the frequency of micropinocytotic vesicles were distinctly increased in day active geckos. It is assumed that these structural mechanisms improve the transendothelial transportation capacity of metabolic substances.
When the thickness of the retinal layers was compared, we found that the inner retinal layers of those geckos in which the conus capillaries were poorly developed, were approximately 60 % of the thickness of the inner retina in the day active geckos. The results indicate that the structural organization of conal endothelial cells is related primarily to the retinal structure rather than to the animals' daytime behavior. Furthermore, our observations support the theory that the conus papillaris of lizards, like the pecten oculi of birds, has a primary function in the nutrition of the avascular retina and / or is involved in the exchange of fluid in the vitreous.
The pecten oculi of the red-tailed hawk (Buteo jamaicensis) has been examined by light and electron microscopy. In this species the pecten is very large and of the pleated type. It consists of 17-18 accordion folds which are joined apically by a heavily pigmented bridge of tissue which holds the pecten in a fan-like shape, widest at its base. It is situated over the optic nerve head and extends into the vitreous. Within each fold are numerous capillaries, larger supply and drainage vessels and melanocytes. The capillaries are specialized and display extensive microfolds on both the luminal and abluminal borders. The endothelial cell bodies are thin with most organelles present in a paranuclear location. The capillaries are surrounded by thick fibrillar basal laminae which are probably structurally important and which often enclose pericytes. The melanocytes which are most plentiful in the bridge region and peripherally in the pecten, form an incomplete sheath around the capillaries and other blood vessels. These melanocytes are also felt to be fulfilling a structural role within the pecten. The morphology of the pecten of the red-tailed hawk is indicative of a heavy involvement in the transport of materials to the avascular avian retina.
The pecten oculi of the great blue heron (Ardea herodias) has been examined by both light and electron microscopy. In this species the pecten is large and of the pleated type. It consists of 14-15 acordion folds that are joined apically by a more heavily pigmented bridge of tissue which holds the pecten in a fan-like shape widest at its base. As in other species it is situated over the optic nerve head and projects out into the vitreous. Within each fold are numerous capillaries, larger supply and drainage vessels and many melanocytes. The capillaries are extremely specialized vessels which display extensive microfolds on both their luminal and abluminal borders. The endothelial cell bodies are extremely thin with most organelles present in a paranuclear location. The capillaries are surrounded by thick fibrillar basal laminae which are felt to be structurally useful. Pericytes are a common feature of these capillaries. The numerous pleomorphic melanocytes which form an incomplete sheath around the capillaries and other blood vessels are also felt to be important in structural support of the pecten. The morphology of the pecten of the great blue heron is indicative of a heavy involvement in the transport of materials.
We have determined the extent of retinal cell damage and eye growth after treatment with different neurotoxins. Day-old chicks received an intraocular injection containing 2, 10, 50, 100 or 200 nmol of kainic acid (KA), an excitotoxic analogue of glutamate. After 21 days, with 2 nmol KA damage was confined to a small proportion of bipolar cells, whereas with 10–200 nmol KA there was dose-dependent damage to amacrine cells, ganglion cells and photoreceptors. There was an increase in eye weight and size of the vitreal chamber with 10 nmol KA or more. In a similar protocol using 5, 50 or 200 nmol quisqualic acid (QUIS), there was massive loss of amacrine cells and slight loss of horizontal cells, and a large increase in the anterior chamber depth. A single dose of 200 nmol N-methyl-D-aspartate lesioned amacrine cells, but did not alter eye size. Thus, excitotoxins which have different retinotoxic effects also have different effects on eye size.
The pecten oculi of the diurnally active pigeon (Columba livia) has been examined by light and electron microscopy. In this species the pecten is of the pleated type. It is situated over the optic nerve head and extends out into the vitreous. Fifteen to 17 accordion folds are joined apically by a heavily pigmented ridge of tissue which holds the pecten in a fan-like shape, widest at the base. The entire pecten is enclosed by a fine basal lamina. Within each fold are numerous capillaries, larger blood vessels and melanocytes. The capillaries are surrounded by thick fibrillar basal laminae which often contain pericytes. These capillaries display numerous microfolds on both the luminal and abluminal borders. The endothelial cell body is extremely thin with most organelles present in a paranuclear location. The melanocytes which are more plentiful in the bridge region form an incomplete sheath around the capillaries and other blood vessels. The morphology of the pecten in the pigeon is indicative of a heavy involvement in the transport of materials.
Intense alkaline phosphatase (ALPase) activity has been localized in the outer plexiform layer of the developing chick retina. To elucidate the functional significance of this enzymatic activity, we have injected an ALPase inhibitor, levamisole, into embryonic eyes on either the 13th or 15th day of incubation. The retina was fixed between the 15th and 20th day of incubation and examined by electron microscopy. Levamisole injection on the 13th day caused various morphological alterations in retinal development, including the appearance of solitary photoreceptor cells in the subretinal space as well as folding of both the outer plexiform and outer nuclear layers. Pedicles of photoreceptor cells in the outer plexiform layer displayed rather smooth configurations with a reduced number of invaginations by post-synaptic neurites. The outer plexiform layer was thinned and the neuritic extensions in this layer appeared much less developed than in the control (PBS-injected) retina. Photoreceptor outer segments were seldom observed. Besides these alterations, layers of optic fibers and ganglion cells were also affected, as shown by evidence of degeneration in the ganglion cells and thinning of the nerve-fiber layer. Injection of levamisole into day 15 embryonic eyes exerted less influence on retinal development, but some photoreceptor cells were still found in the subretinal space. Some of these observations have been reported in the retinas of aged normal animals or in retinas with hereditary or induced retinal dystrophy. It is suggested that ALPase activity in the outer plexiform layer of the developing chick retina may be important for the onset of normal development of synapses in the outer plexiform layer and differentiation of the photoreceptor cells.
The effect of elastase on alkaline phosphatase activity in the chick pecten capillaries was studied electron histochemically. The pecten was treated with elastase before incubation in the medium for alkaline phosphatase. Inactive alkaline phosphatase in the chick pecten capillary under dark adaptation could be demonstrated electron histochemically after treatment with elastase. Under light adaptation, the elastase-treated pecten demonstrated more intense alkaline phosphatase activity in the same localization as in the untreated pecten. Biochemical data also supported histochemically demonstrated enhancement effect of elastase on alkaline phosphatase activity in the chick pecten oculi. Elastase is expected to be useful for demonstrating enzymatic activity which is otherwise hard to detect.
The pecten of a nocturnally active bird, the nighthawk (Chordeiles minor) has been examined by light and electron microscopy. In this species the pecten consists of a pleated, highly vascular pigmented structure. It is situated over the optic nerve head and projects into the vitreous. Several accordion folds (4-5) are joined apically by a bridge of tissue which holds the pecten in a fan-like shape widest at the base. The entire pecten is enclosed in a fine basal lamina. Within each fold are numerous capillaries, larger blood vessels which could not be differentiated as to arterioles or venules and melanocytes. The capillaries are surrounded by extremely thick basal laminae composed of several fibrillar layers. These capillaries display extremely numerous microfolds on both the luminal and abluminal borders. The cell body is extremely thin with most organelles present in a paranuclear location. Pericytes are often associated with the capillaries. The melanocytes form an incomplete sheath around the capillaries and other blood vessels. The morphology of the pecten is indicative of a heavy involvement in the transport of materials.
The present paper describes ultrastructural localization of non-specific alkaline phosphatase (ALPase) activity in the chick retina during late embryonic development and after hatching. In the newly-hatched chick retina, intense ALPase activity was found in the outer plexiform layer (OPL), and a less intense reaction was found in the ganglion cell layer and at the outer limiting membrane. Electron microscopic histochemistry revealed that bipolar and horizontal dendrites within the OPL displayed intense reaction product along their plasma membranes. Only horizontal cells showed reaction product on almost their whole circumference. Müller cells also showed reaction product on the plasma membrane in the ganglion cell layer and on the microvilli at their apical portion. The reaction product in the OPL was first recognizable in the retina of the 13- to 14-day-old embryonic chick, and its intensity increased during further development. Little reaction product was found in Müller cells at the embryonic stage. The function of ALPase activity is discussed in relation to the development of the OPL and the nutrient supply for the neural retina.
Alkaline phosphatase activity in the pecten of chicks was studied electron histochemically. Alkaline phosphatase activity was located in the plasma membrane of the cytoplasmic processes in the luminal and basal portions of the endothelial cells of the capillary, in the plasma membrane of cells with pigmented granules and in the plasma membrane of cells in the vitreous in contrast with the basement lamina of the cells with pigmented granules. The cytoplasmic processes of the luminal and basal portions of the capillary endothelium and the plasma membrane of the cells with pigmented granules may play a role in the exchange of metabolites between the pecten and the vitreous. In the pecten of dark adapted eye, alkaline phosphatase activity could not be demonstrated histochemically. Thus, darkness may make the exchange of metabolites between the pecten and the vitreous less active.
The pecten oculi of the American crow (Corvus brachyrhynchos) has been examined by both light and electron microscopy. In this species the pecten is very large and of the pleated type. It consists of 22-25 accordion folds that are joined apically by a bridge of tissue which holds the pecten in a fan-like shape widest at its base. Within each fold are numerous capillaries, larger supply and drainage vessels and many melanocytes. The capillaries are extremely specialized for transport functions and display extensive microfolds on both their luminal and abluminal borders. Except for the nuclear region which contains most of the organelles, the endothelial cell bodies are extremely thin. These capillaries are surrounded by thick fibrillar basal laminae which are conjectured to be structurally important. Pericytes are a common feature of these capillaries. The numerous pleomorphic melanocytes interspersed between the capillaries are also felt to be important in structural support of the pecten. The pecten is considered to be comparable to the falciform process of some teleosts, the conus papillaris of reptiles, the supraretinal vessels of amphibians and teleosts and the intraretinal vessels of mammals which are all felt to be alternative methods of bringing nutrients to the inner retina.
The pecten oculi of the barred owl (Strix varia) has been examined by light and transmission electron microscopy. The pecten in this species is of the pleated type and is small in comparison to the size of the ocular globe. The pecten consists of 8-10 accordion-like folds that are linked apically by a pigmented tissue bridge. Each fold contains numerous capillaries, larger supply and drainage vessels, and abundant pleomorphic melanocytes. Most of these capillaries are extremely specialized vessels that possess plentiful microfolds on both the luminal and abluminal surfaces. Some capillaries however display only a few microfolds. The endothelial cell bodies are extremely attenuated, with most organelles located near the nucleus. All capillaries are surrounded by a very thick fibrillar basal lamina, which is thought to provide structural support to these small vessels. Pericytes are commonly found within these thickened basal laminae. Numerous melanocytes are also present, with processes that form an incomplete sheath around the capillaries. These processes are also presumed to provide structural support for the capillaries. As in other avian species, the morphology of the barred owl pecten is indicative of extensive involvement in substance transport. When compared to the pecten of more visually-oriented species, this pecten is smaller, has fewer folds, and displays a reduced number of microfolds within the capillaries. In these and other features, the barred owl pecten is similar to the pecten of the great horned owl (Bubo virginianus).
The pecten oculi of the Australian galah (Eolophus roseicapillus) has been examined by both light and electron microscopy. In this species the pecten is large relative to the size of the eye and is of the pleated type. It consists of 20-25 accordion folds that are joined apically by a bridge of tissue which holds the pecten in a fan-like shape widest at its base. Within each fold are many melanocytes, numerous capillaries as well as larger supply and drainage vessels. The capillaries are extremely specialized for transport functions and display extensive microfolds on both their luminal (inner) and abluminal (outer) borders. Except for the nuclear region which also contains most of the organelles, the endothelial cell bodies are extremely thin. These capillaries are surrounded by thick fibrillar basal laminae which are felt to be structurally important. Pericytes are a common feature within the basal lamina of capillaries. The numerous pleomorphic melanocytes which more or less surround the capillaries are also presumed to be important in structural support of the pecten. The pecten represents a supplementary retinal circulation and is comparable to the falciform process of some teleosts, the conus papillaris of reptiles, the supraretinal vessels of amphibians and some teleosts and the intraretinal vessels of mammals, all of which are felt to be alternative methods of bringing nutrients to the inner retina.
The pecten oculi of the emu (Dromaius novaehollandiae) has been examined by light and electron microscopy. In this species the pecten is small relative to the size of the globe and is of a primitive pleated type. It consists of only 3-4 loose folds that are joined apically by a bridge of tissue which holds the pecten in a fan-like shape widest at its base. Each fold is quite thick (100-120 microns) and has a central core of mostly unpigmented cell processes. In this central region are supply or drainage vessels while numerous melanocytes and pecteneal capillaries are only located at the periphery of the folds. The capillaries are extremely specialized for transport functions and for the most part display extensive microfolds on both their luminal (inner) and abluminal (outer) borders although capillaries with very few microfolds are also noted. An unusual feature of some capillaries is luminal folds of the cell body with further luminal microfolds superimposed on them. Except for the nuclear region which contains most of the organelles, the endothelial cell bodies are extremely thin. These capillaries are surrounded by thick fibrillar basal laminae which are felt to be structurally important. Pericytes are a common feature within the basal lamina of these capillaries. The numerous peripherally located melanocytes which more or less surround the capillaries are also presumed to be important for structural support of the pecten. The large number of cell processes forming the central core of each fold are felt to be unpigmented processes of the melanocytes.
THE evolution of the eye is constrained by two conflicting requirements--good vascular perfusion of the retina, and an optical path through the retina that is unobstructed by blood vessels. Birds are interesting in that they have higher metabolic rates and thicker retinas than mammals, but have no retinal blood vessels. Nutrients and oxygen must thus reach the neurons of the inner retina either from the choroid through 300 micron of metabolically very active retina, or from the pecten, a pleated vascular structure protruding from the head of the optic nerve into the vitreous chamber, and more than a centimetre away from some retinal neurons. Despite the diffusional distance involved, several lines of evidence indicate that the pecten is the primary source of nutrients for the inner retina: the presence of an oxygen gradient from pecten to retina, the large surface area produced by macroscopic folds and by microscopic infoldings of the luminal and external surfaces of the capillary endothelium, extrusion of circulating fluorescein, high content of carbonic anhydrase and alkaline phosphatase, and retinal impairments after pecten ablation. Another peculiarity of birds, their saccadic oscillations, occur with a large cyclotor-sional component during every saccadic eye movement. In different species, saccades, which occur at intervals of 0.5-40 s, have up to 13 oscillations with frequencies of 15-30 Hz and ampliá-tudes of about 10 degrees. Therefore, as much as 12% of some birds' total viewing time may be subject to the image instability caused by the oscillations. Using fluorescein angiography, we show here that during every saccade, the pecten acts as an agitator which propels perfusate towards the central retina much more effectively than is observed during intersaccadic intervals.
The pecten oculi is a structure peculiar to the avian eye. Three morphological types of pecten oculi are recognized: conical type, vaned type and pleated type. The pleated type has been well studied. However, there exists only scanty data on the morphology of the latter two types of pectens. The structure of the vaned type of pecten of the ostrich, Struthio camelus was investigated with light and electron microscope. The pecten of this species consists of a vertical primary lamella that arises from the optic disc and supports 16-19 laterally located secondary lamellae, which run from the base and confluence at the apex. Some of the secondary lamellae give rise to 2 or 3 tertiary lamellae. The lamellae provide a wide surface, which supports 2-3 Layers of blood capillaries. Pigmentation is highest at the distal ends of the secondary and tertiary Lamella where blood capillaries are concentrated and very scanty on the primary and the proximal ends of the secondary lamella where the presence of capillaries is much reduced. In contrast to the capillaries of the pleated pecten, the endothelium of the capillaries in the pecten of the ostrich exhibits very few microvilli. These observations suggest that the morphology of the pecten of the ostrich, a flightless ratite bird is unique to the pleated pecten and is designed to meet the balance between optimal vision and large surface area for blood supply and yet ensuring it is kept firmly erect within the vitreous.
This article discusses the effects of stimulus deprivation on the development and atrophy of the visual sensory system. It presents effects of neural function upon neural structure. Quantitative changes in various regions of the central nervous system as shown by alterations in ribose nucleoprotein turnover in the cytoplasm and nucleus of neurons were definitely related to rate of stimulation. It was followed with the experiments which showed that exclusion of visual stimulation during the immediate postnatal period could result in varying degrees of arrested development and even atrophy of the ganglion cells and optic nerve fibers. The experimental problem of the present study was to determine the effects of the exclusion of light from the eye during early postnatal development in representative mammals. Anatomical studies of the receptor, cytochemical studies of the neural cells, and evaluation of the visual capacities of the individual animals were made. Experiment was performed on chimpanzees. Results shows the discernible differences between the ophthalmoscopic appearances of the eyes of the various groups of animals as related to degree and duration of light deprivation were seen in the chimpanzees. Nucleolar volume was consistently higher in the light-reared animals. (PsycINFO Database Record (c) 2013 APA, all rights reserved)
The ultrastructure of the bridge of the pecten oculi was studied in the newlyhatched chick. Whereas most of the bridge resembled the pleats in being composed of small blood vessels and intervening pigment cells, the distal portion of the bridge consisted of polarized pigment cells only. The processes of the pigment cells extended into the vitreous body and were covered by a discontinuous dense lamina, believed to be continuous with that of the internal limiting membrane of the retina. It did not form a complete separation between the bridge and the vitreous body. Intercellular spaces were not conspicuous, although the considerable structural variations dependent on the techniques employed need to be stressed.
The pecten in the pigeon is a pleated lamina that consists of blood vessels and interstitial pigment cells. Arterioles with thin, unspecialized endothelium give origin to an exceedingly dense capillary network. The endothelial cells of the capillaries are provided on both the luminal and basal surfaces with thin lamellar processes, constricted at their origins from the cell body. Luminal lamellae are long, erect and have a prevailing longitudinal orientation. Basal lamellae are shorter, more irregularly oriented and more closely compressed. Besides the usual complement of cytoplasmic organelles, a moderate number of coated vesicles and of coated and uncoated inpocketings of the plasmalemma is present in the endothelial cells. A labyrinthine system of interstices surrounds the stalks of the basal lamellae and contains a material that resembles the substance of the basement lamina in density and texture. A similar material is found on the outer surface of the basal lamellae and imperceptibly merges with the ground substance of an unusually thick adventitial layer that is permeated by numerous unit fibrils of collagen. The capillary network is drained by venules, whose wall resembles the capillary wall. The pigment cells contain melanin granules, large mitochondria and many bundles of filaments. They are sandwiched between two basement laminae and separate the blood vessels from the vitreous body. The bridge of the pecten consists of pigment cells with a few interspersed capillaries.
The activity pattern of oxidative enzymes was studied in normal and light-damaged rat retina with histochemical methods. The epithelial cells and the inner segments of the photoreceptor cells showed high activities for both respiratory and glycolytic enzymes whereas the nerve cells with their processes were less active. The Müller neuroglial cells showed activity mainly in the glycolytie enzyme system. The outer segments of the photoreceptor cells showed no activity.
The first change, observed within a few hours, was a reduction of nicotinamide adenine dinncleotide diaphorase and cytochrome oxidase activity in the epithelial cells. Five hours after light exposure there was a marked reduction in these two enzymes as well as lactate dehydrogeuase.
The other retinal cell types remained unchanged initially. The inner segments of the photoreceptor cells gradually lost their enzyme activities after about 1 day. The debris formed by the disintegrated epithelium and photoreceptor cells was phagocytosed by cells with moderate enzyme activities. The Müller neuroglial cells showed a large increase in nicotinamide adenine dinncleotide daphorase and lactate dehydrogenase activity, especially next to the degenerating seleral half of the retina. There was a temporary increase in the activity of oxidative enzymes in the choroid during the retinal disintegration.
Apparently the epithelial cells are the first to be damaged. The changes observed are discussed in relation to similar retinal degenerations due to physical and chemical damage of the retina.
SEVERE damage to the retina by exposure to light has recently been demonstrated by Noell1,2 and by us.3,4 To establish the pathogenetic mechanisms, a series of electron microscopic studies of the retinas which had been exposed to lights under several conditions has been in progress in this laboratory. Depending on the duration of the light exposure and the nature of the light sources, the retinas show damage varying all the way from total degeneration of the whole retina to minimal changes in the photoreceptors.Upon exposure to relatively cold light at a brightness of approximately 750 foot-candles (ft-c), photoreceptic outer segments of the albino rat demonstrate remarkable membranous changes. The purpose of this paper is to describe such changes in the photoreceptic cells and to discuss the mechanisms of the damage.Materials and Methods
Albino rats were mainly used in the experiment. Ordinary wire mesh animal cages
In the present contribution an attempt has been made to study the changes in the distribution of alkaline phosphatase amongst the constituents of the eye of garden lizard, Colotes versicolor, under normal daylight and dark conditions. In the latter increase in the alkaline phosphatase activity in most of the layers is seen. This has been explained from the physiological and metabolic point-of-view.
Monocular light deprivation in new-born rats produces a significant decrease of acetylcholinesterase activity in the deprived retina and in the lateral geniculate nucleus connected with the closed eye; pseudocholinesterases are not affected. No differences in enzyme activity were detected in the superior colliculus and in the visual cortex. The results are briefly discussed with regard to the physiopathology of the functional amblyopia produced by chronic light deprivation.
The ultrastructure of the bridge of the pecten oculi was studied in the newlyhatched chick. Whereas most of the bridge resembled the pleats in being composed of small blood vessels and intervening pigment cells, the distal portion of the bridge consisted of polarized pigment cells only. The processes of the pigment cells extended into the vitreous body and were covered by a discontinuous dense lamina, believed to be continuous with that of the internal limiting membrane of the retina. It did not form a complete separation between the bridge and the vitreous body. Intercellular spaces were not conspicuous, although the considerable structural variations dependent on the techniques employed need to be stressed.
Rods, double cones which comprise a principal and an accessory cone, and two types of single cones occur in the chick retina. The rod is narrow and contains a paraboloid, a basal nucleus and a small synaptic body with long synaptic lamellae. The principal cone has a pale-staining oil droplet and is aligned against an accessory cone, which has a paraboloid, no oil droplet, but a small granular vesicle instead. The synaptic body of the principal cone is large and partly surrounds that of its associated accessory cone. The synaptic body of the accessory cone has a long process extending into the outer plexiform layer. Single cone type I has a dark oil droplet and the mitochondria in the ellipsoid are dense with cristae. Single cone type II has a lighter-staining oil droplet and fewer cristae. The synaptic bodies of both types of single cone lie vitreal to those of rods and double cones. Fibres connect the synaptic body to the nuclear region in single cones and accessory cones, but not in rods and principal cones. Another type of synaptic body, which is not that of a receptor, occurs in the outer plexiform layer. Groups of small vesicles, like those in the synaptic body, occur near the base of the inner segments; synaptic vesicles may originate here. Muller cells separate each receptor, except the members of a double cone, at the outer limiting membrane and may position the receptors in relation to the pigment epithelium to allow a radial orientation of the inner and outer segments.
The discovery that glycolytic enzymes in the retina are concentrated in Müller's fibers1 prompted an inquiry into the distribution of substrates for glycolysis. Glycogen is the most readily demonstrable of the substrates, and the present paper is a report of our studies on the histochemical distribution of retinal glycogen both in a variety of species and under various conditions. A preliminary report was presented at the meeting of the International Congress of Histochemistry and Cytochemistry in 1960.
The quantity and distribution of glycogen in the retina have been controversial since Ehrlich noted its presence in frog retinas as early as 1883.2 Thus, early investigators3 denied that the normal rabbit retina had sufficient glycogen to be histochemically demonstrable, at least by the methods then available (carmine and iodine). Subsequently others found traces in the rabbit retina4; others reported finding variable amounts5; and still others found what
Histochemkky, Theoretical and Applied, 2nd ed. pp. 832-833 and 400 (figs 103 and 105). J. and A
- A G E Pearse
Pearse, A. G. E. (1960). Histochemkky, Theoretical and Applied, 2nd ed. pp. 832-833 and 400 (figs 103 and 105). J. and A. Churchill Ltd., London. ADAPTATION STUDIES ON RETINA AND PECTEN 97
Ophthalmologiea (Basel) 159,460
- M Radnbt
- P Jobbbgyi
- I Henszberger
- B Lovas
- E Rasch
- R H Austin
- K L Chow
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