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Schematic representation of the retinopetal and retinofugal labeling observed in the mesencephalon of the lamprey following iontophoretic deposit of horseradish peroxidase in the optic nerve (modified from Rio, 1996). Note the presence of two feedback loops (retina→optic tectum→RMA→retina and retina→TAOA→M5→retina). Abbreviations: M5, retinopetal neurons of the M5 nucleus of Schober; RMA, retinopetal neurons of the reticular mesencephalic area; TAOA, tegmental accessory optic area (modified from Rio, 1996).
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The present review is a detailed survey of our present knowledge of the centrifugal visual system (CVS) of vertebrates. Over the last 20 years, the use of experimental hodological and immunocytochemical techniques has led to a considerable augmentation of this knowledge. Contrary to long-held belief, the CVS is not a unique property of birds but a...
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Context 1
... retinopetal neurons in adults: morphology and neurochem- ical aspects. In adult lampreys, the morphologies of the periventricular retinopetal neurons of M5 and those of the more laterally situated centrifugal visual neurons of RMA and ventro-lateral optic tectum differ considerably (Fig. 2). The neurons of M5 are large, with pyramidal somata displaying minor diameters of 8-10 μm and major diameters of 18-25 μm. From the apical pole, a large dendrite without spines emerges perpendicularly to the wall of the mesencephalic tegmentum; some of these reach, latero-ventrally, the tegmental accessory optic area. The cells of RMA ...
Context 2
... et al., 1992Rio et al., , 1993Rio et al., , 1996Vesselkin et al., 1988Vesselkin et al., , 1989aVesselkin et al., ,b, 1996 have shown that, in L. fluviatilis, the centrifugal visual neurons are involved in two feedback loops: (1) retina→mesencephalic tegmental accessory optic area→ M5→retina, and (2) retina→superficial tectal layers→RMA→ retina (Fig. 2). Synapses have been observed between the labeled dendrites of M5 neurons and the retinal terminals of the mesencephalic tegmental accessory optic area ( Rio et al., 1993) and between the retino-tectal terminals and the distal segments of RMA cell dendrites that penetrate the retinor- ecipient tectal layers (Rio, 1996;Rio et al., ...
Context 3
... and nerve and others in the intermediate region between the olfactory bulb and ventral telencephalon corresponding to the GCTN. Retinopetal neurons have also been described in the optic tract (intrachiasmatic nucleus) of Pantodon (Gerwerzhagen et al., 1982), but this observation has not been confirmed by others (Butler and Saidel, 1991; Table 1, Fig. ...
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Citations
... Retrograde (centrifugal) fibres. Small numbers of retrograde fibres (also referred to as corticofugal, centrifugal, or 'efferent' fibres) have been demonstrated in the optic nerves of most nonhuman species, potentially arising from eight different locations in the brain [128,129]. Of course, any fibre which arises in the brain and passes through the optic nerves must also pass through some part of the chiasm. ...
A recent anatomical study of the human optic chiasm cast doubt on the widespread assumption that nerve fibres travelling in the human optic nerve and chiasm are arranged retinotopically. Accordingly, a scoping literature review was performed to determine what is known about the nerve fibre arrangement in these structures. Meta-analysis suggested that the average number of fibres in each optic nerve was 1.023 million with an inter-individual range of approximately 50% of the mean. Loss of nerve fibres with age (approximately 3,400 fibres/year) could not account for this variability. The review suggested that there might be a retinotopic arrangement of nerve fibres in the orbital portion of the optic nerve but that this arrangement is most likely to be lost posteriorly with a more random distribution of nerve fibres at the chiasm. Limited studies have looked at nerve fibre arrangement in the chiasm. In summary, the chiasm is more ‘H-shaped’ than ‘X-shaped’: nerve fibre crossings occur paracentrally with nerves in the centre of the chiasm travelling coronally and in parallel. There is interaction between crossed and uncrossed fibres which are widely distributed. The review supports the non-existence of Wilbrand’s knee. Considerable further work is required to provide more precise anatomical information, but this review suggests that the assumed preservation of retinotopy in the human optic nerve and chiasm is probably not correct.
... In the following experiments the authors studied the beneficial effect of long-term oral administration (90 days) of melatonin on the retina in glaucoma patients. It was found that melatonin alleviated the disturbance of the circadian rhythms caused by glaucoma with different effects of melatonin on systemic vs. local circadian rhythms [42]. ...
The ubiquity of circadian rhythms in living organisms has generally been accepted by researchers over the last century. Indeed, morphology and molecular biology of the circadian clock were described during the last fifty years. This main biological clock is located in the suprachiasmatic nucleus of the hypothalamus. This nucleus is connected with the retina by the retinohypothalamic tract. This way, light regulates the functioning of the biological clock and biological rhythms such as the sleep-wake cycle and other cyclic functions by releasing melatonin from the pineal body (PB) into the general circulation. Melatonin reaches the retina via the bloodstream as humoral feedback. More than a hundred years ago a reverse neuronal connection between the central nervous system and the retina was hypothesized. This so-called centrifugal visual or retinopetal system has been explored in detail in birds, but less information is available in mammals. In this work, the morphology and physiology of mammalian centrifugal visual pathways are reviewed. It is generally accepted that the centrifugal (retinopetal) fibers terminate mainly on the amacrine cells of the retina. Histaminergic fibers terminate on dopaminergic amacrine cells. Serotoninergic synapses were identified on ganglion cells. In addition, serotoninergic fibers were also associated with photoreceptor terminals. Luteinizing hormone releasing hormone fibers have been observed in birds, but not in mammalian retinas. In summary, based on the data available in the literature, it seems that the retinopetal system has a mandatory role in lower vertebrates, but a modulatory role in mammals. There is currently no adequate way to eliminate the centrifugal visual system that would better explain its true function.
... Retinal ganglion cells also contain 5 HT and may possibly exert their influence at the central level by a sero toninergic mechanism. 5 HT is also found in the structures of the vertebrate retinopetal system and, thus, possibly mediates the modulatory effect of the brain on retinal functions [27]. ...
Labeling of 5-HT-immunoreactive structures was performed on eye slices of freshwater molluscs Lymnaea stagnalis and Pomacea canaliculata. In the periocular region of both species an increased density of 5-HTergic fibers forming structurally distinct plexuses and partially penetrating into the retina was detected. Transcription of serotonin receptor genes was detected in eye tissues: two types in L. stagnalis and three in P. canaliculata. Its relative level is significantly upregulated compared with central ganglia of the nervous system and tentacles. Additionally transcription of the 5HT transporter gene was recorded in P. canaliculata tissues.The obtained results are discussed in terms of a possible serotonergic mechanism of modulation of processes in the retina of gastropods.
... Retinal ganglion cells also contain 5 HT and may possibly exert their influence at the central level by a sero toninergic mechanism. 5 HT is also found in the structures of the vertebrate retinopetal system and, thus, possibly mediates the modulatory effect of the brain on retinal functions [27]. ...
Labeling of 5-HT-immunoreactive structures was performed on eye slices of freshwater molluscs Lymnaea stagnalis and Pomacea canaliculata. In the periocular region of both species an increased density of 5-HTergic fibers forming structurally distinct plexuses and partially penetrating into the retina was detected. Transcription of serotonin receptor genes was detected in eye tissues: two types in L. stagnalis and three in P. canaliculata. Its relative level is significantly upregulated compared with central ganglia of the nervous system and tentacles. Additionally transcription of the 5HT transporter gene was recorded in P. canaliculata tissues.The obtained results are discussed in terms of a possible serotonergic mechanism of modulation of processes in the retina of gastropods.
... Nevertheless, half of all optic lobe neurons receive 5 or more synapses from VCNs, showing that much early visual processing incorporates feedback from the central brain. Centrifugal inputs to the retina are found in many vertebrate species, including humans (Repérant et al. 2006). ...
Connections between neurons can be mapped by acquiring and analyzing electron microscopic (EM) brain images. In recent years, this approach has been applied to chunks of brains to reconstruct local connectivity maps that are highly informative, yet inadequate for understanding brain function more globally. Here, we present the first neuronal wiring diagram of a whole adult brain, containing 5x10^7 chemical synapses between ~130,000 neurons reconstructed from a female Drosophila melanogaster. The resource also incorporates annotations of cell classes and types, nerves, hemilineages, and predictions of neurotransmitter identities. Data products are available by download, programmatic access, and interactive browsing and made interoperable with other fly data resources. We show how to derive a projectome, a map of projections between regions, from the connectome. We demonstrate the tracing of synaptic pathways and the analysis of information flow from inputs (sensory and ascending neurons) to outputs (motor, endocrine, and descending neurons), across both hemispheres, and between the central brain and the optic lobes. Tracing from a subset of photoreceptors all the way to descending motor pathways illustrates how structure can uncover putative circuit mechanisms underlying sensorimotor behaviors. The technologies and open ecosystem of the FlyWire Consortium set the stage for future large-scale connectome projects in other species.
... Afferent innervation of the retina has been studied for over a century and reported in all classes of vertebrates (Repérant et al., 1989(Repérant et al., , 2006(Repérant et al., , 2007. The site of origin of retinal centrifugal fibers varies considerably among vertebrate species: mostly from the preoptic retinopetal nucleus and olfactory bulb in fish; anterior hypothalamus, lamina terminalis and pretectal region in amphibian; ventral thalamus, caudal mesencephalic tegmentum and telencephal in reptile; and the isthmo-optic nucleus and caudal mesencephalon in birds. ...
... Several neurotransmitters (5-HT) and peptides (i.e. FMRFamide, gonadotropin releasing hormone, substance P, met-enkephalin, histamine) have been detected in their synaptic endings (Repérant et al., 1989(Repérant et al., , 2006(Repérant et al., , 2007Gastinger et al., 2006). ...
Circadian (24-h) clocks are cell-autonomous biological oscillators that orchestrate many aspects of our physiology on a daily basis. Numerous circadian rhythms in mammalian and non-mammalian retinas have been observed and the presence of an endogenous circadian clock has been demonstrated. However, how the clock and associated rhythms assemble into pathways that support and control retina function remains largely unknown. Our goal here is to review the current status of our knowledge and evaluate recent advances. We describe many previously-observed retinal rhythms, including circadian rhythms of morphology, biochemistry, physiology, and gene expression. We evaluate evidence concerning the location and molecular machinery of the retinal circadian clock, as well as consider findings that suggest the presence of multiple clocks. Our primary focus though is to describe in depth circadian rhythms in the light responses of retinal neurons with an emphasis on clock control of rod and cone pathways. We examine evidence that specific biochemical mechanisms produce these daily light response changes. We also discuss evidence for the presence of multiple circadian retinal pathways involving rhythms in neurotransmitter activity, transmitter receptors, metabolism, and pH. We focus on distinct actions of two dopamine receptor systems in the outer retina, a dopamine D4 receptor system that mediates circadian control of rod/cone gap junction coupling and a dopamine D1 receptor system that mediates non-circadian, light/dark adaptive regulation of gap junction coupling between horizontal cells. Finally, we evaluate the role of circadian rhythmicity in retinal degeneration and suggest future directions for the field of retinal circadian biology.
... In this case, interactions, or "connections", between the system's components are asymmetric (e.g., interactions between neurons via chemical synapses) and no component receives connections back from the components that it connects to (no such feedback is present either via direct back-connections or indirectly via a chain of connections with other nodes). This is illustrated in Figure 4. Examples of feedforward systems include sensory inputs to the brain such as the inputs from retina to the thalamus (although some amount of feedback to the retina from the rest of the brain exists [76]) and some of the most successful deep neural networks currently in widespread use [77]. ...
A hypothesis is presented that non-separability of degrees of freedom is the fundamental property underlying consciousness in physical systems. The amount of consciousness in a system is determined by the extent of non-separability and the number of degrees of freedom involved. Non-interacting and feedforward systems have zero consciousness, whereas most systems of interacting particles appear to have low non-separability and consciousness. By contrast, brain circuits exhibit high complexity and weak but tightly coordinated interactions, which appear to support high non-separability and therefore high amount of consciousness. The hypothesis applies to both classical and quantum cases, and we highlight the formalism employing the Wigner function (which in the classical limit becomes the Liouville density function) as a potentially fruitful framework for characterizing non-separability and, thus, the amount of consciousness in a system. The hypothesis appears to be consistent with both the Integrated Information Theory and the Orchestrated Objective Reduction Theory and may help reconcile the two. It offers a natural explanation for the physical properties underlying the amount of consciousness and points to methods of estimating the amount of non-separability as promising ways of characterizing the amount of consciousness.
... It carries out these transformations with very little feedback from higher brain centers; in the mouse there are only 150 axons providing feedback from the brain. This represents only 0.2% of the axons in the optic nerve (Gastinger et al., 2006;Repérant et al., 2006). These axons are from modulatory centers including histaminergic fibers from hypothalamus and serotonergic fibers from the dorsal raphe. ...
The olfactory bulb is known to carry out computations for the olfactory perception of concentration invariance of odor recognition, a perception that is essential for life as we know it. However it is not known whether these computations require the extensive feedback to the bulb from the many brain regions which send this feedback. We have measured the concentration dependence of the mitral cell output of the bulb before and after blocking this feedback by lidocaine infusion into the medial olfactory peduncle. Surprisingly we found that the concentration dependence of the mitral cell output was unaffected by the lidocaine block of feedback. Furthermore the computation is rapid; it is complete within a single 250 msec inhalation. The computations for concentration invariance are most likely carried out within the olfactory bulb itself and they are carried out quickly.
... In this case, interactions, or "connections", between the system's components are asymmetric (e.g., interactions between neurons via chemical synapses) and no component receives connections back from the components that it connects to (no such feedback is present either via direct back-connections or indirectly via a chain of connections with other nodes). This is illustrated in Figure 4. Examples of feedforward systems include sensory inputs to the brain such as the inputs from retina to the thalamus (although some amount of feedback to the retina from the rest of the brain exists [67]) and some of the most successful deep neural networks currently in widespread use [68]. ...
A hypothesis is presented that non-separability of degrees of freedom is the fundamental property underlying consciousness in physical systems. The amount of consciousness in a system is determined by the extent of non-separability and the number of degrees of freedom involved. Non-interacting and feedforward systems have zero consciousness, whereas most systems of interacting particles appear to have low non-separability and consciousness. By contrast, brain circuits exhibit high complexity and weak but tightly coordinated interactions, which appear to support high non-separability and therefore high amount of consciousness. The hypothesis applies to both classical and quantum cases, and we highlight the formalism employing the Wigner function (which in the classical limit becomes the Liouville density function) as a potentially fruitful framework for characterizing non-separability and, thus, the amount of consciousness in a system. The hypothesis appears to be consistent with both the Integrated Information Theory and the Orchestrated Objective Reduction Theory and may help reconcile the two. It offers a natural explanation for the physical properties underlying the amount of consciousness and points to methods of estimating the amount of non-separability as promising ways of characterizing the amount of consciousness.
... Occasionally some fibers were observed in the tectum ipsilateral to the injected optic nerve. Some retrogradely labeled cell bodies projecting to the retina were also observed in the tegmentum ventral to the tectum, as reported in many vertebrate species (e.g., ventral brain in Figure 2(e), for review see Repérant et al. 2006Repérant et al. , 2007. Altogether, this indicates that the retina sends projections to the thalamus, pretectum and tectum, and receives projections from central neurons in the tegmentum, features that are well conserved from basal vertebrates to mammals (see discussion, Suryanarayana et al. 2020, Repérant et al. 2006. ...
... Some retrogradely labeled cell bodies projecting to the retina were also observed in the tegmentum ventral to the tectum, as reported in many vertebrate species (e.g., ventral brain in Figure 2(e), for review see Repérant et al. 2006Repérant et al. , 2007. Altogether, this indicates that the retina sends projections to the thalamus, pretectum and tectum, and receives projections from central neurons in the tegmentum, features that are well conserved from basal vertebrates to mammals (see discussion, Suryanarayana et al. 2020, Repérant et al. 2006. ...
The transformation of visual input into motor output is essential to approach a target or avoid a predator. In salamanders, visually guided orientation behaviors have been extensively studied during prey capture. However, the neural circuitry involved is not resolved. Using salamander brain preparations, calcium imaging and tracing experiments, we describe a neural substrate through which retinal input is transformed into spinal motor output. We found that retina stimulation evoked responses in reticulospinal neurons of the middle reticular nucleus, known to control steering movements in salamanders. Microinjection of glutamatergic antagonists in the optic tectum (superior colliculus in mammals) decreased the reticulospinal responses. Using tracing, we found that retina projected to the dorsal layers of the contralateral tectum, where the dendrites of neurons projecting to the middle reticular nucleus were located. In slices, stimulation of the tectal dorsal layers evoked glutamatergic responses in deep tectal neurons retrogradely labeled from the middle reticular nucleus. We then examined how tectum activation translated into spinal motor output. Tectum stimulation evoked motoneuronal responses, which were decreased by microinjections of glutamatergic antagonists in the contralateral middle reticular nucleus. Reticulospinal fibers anterogradely labeled from tracer injection in the middle reticular nucleus were preferentially distributed in proximity with the dendrites of ipsilateral motoneurons. Our work establishes a neural substrate linking visual and motor centers in salamanders. This retino-tecto-reticulo-spinal circuitry is well positioned to control orienting behaviors. Our study bridges the gap between the behavioral studies and the neural mechanisms involved in the transformation of visual input into motor output in salamanders.
