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On the Occurrence of an Intracranial Ganglion upon the OculoMotor Nerve in Scyllium Canicula, with a Suggestion as to Its Bearing upon the Question of the Segmental Value of Certain of the Cranial Nerves
Thesis (M.A.)--University of Kansas, Anatomy, 1923. Includes bibliographical references.
The results of the previous experiments confirm May and Horsley's conclusions that the mesencephalic trigeminal root contains both ascending and descending fibers. The former take origin from sensory cells in the semilunar ganglion and the latter from globular, unipolar cells in the alar (sensory) plate of the mesencephalon, and from a caudal continuation of these cells, known as the locus. coeruleus, which extend downward into the motor area of the pons.
Although the distribution of cholinergic cells is remarkably similar across the vertebrate species, no data are available on more primitive species, such as cartilaginous fishes. To extend the evolutionary analysis of the cholinergic systems, we studied the distribution of cholinergic neurons in the brain and rostral spinal cord of Scyliorhinus canicula by immunocytochemistry using an antibody against the enzyme choline acetyltransferase (ChAT). Western blot analysis of brain extracts of dogfish, sturgeon, trout, and rat showed that this antibody recognized similar bands in the four species. Putative cholinergic neurons were observed in most brain regions, including the telencephalon, diencephalon, cerebellum, and brainstem. In the retrobulbar region and superficial dorsal pallium of the telencephalon, numerous small pallial cells were ChAT-like immunoreactive. In addition, tufted cells of the olfactory bulb and some cells in the lateral pallium showed faint immunoreactivity. In the preoptic-hypothalamic region, ChAT-immunoreactive (ChAT-ir) cells were found in the preoptic nucleus, the vascular organ of the terminal lamina, and a small population in the caudal tuber. In the epithalamus, the pineal photoreceptors were intensely positive. Many cells of the habenula were faintly ChAT-ir, but the neuropil of the interpeduncular nucleus showed intense ChAT immunoreactivity. In the pretectal region, ChAT-ir cells were observed only in the superficial pretectal nucleus. In the brainstem, the somatomotor and branchiomotor nuclei, the octavolateral efferent nucleus, and a cell group just rostral to the Edinger-Westphal (EW) nucleus contained ChAT-ir neurons. In addition, the trigeminal mesencephalic nucleus, the nucleus G of the isthmus, some locus coeruleus cells, and some cell populations of the vestibular nuclei and of the electroreceptive nucleus of the octavolateral region exhibited ChAT immunoreactivity. In the reticular areas of the brainstem, the nucleus of the medial longitudinal fascicle, many reticular neurons of the rhombencephalon, and cells of the nucleus of the lateral funiculus were immunoreactive to this antibody. In the cerebellum, Golgi cells of the granule cell layer and some cells of the cerebellar nucleus were also ChAT-ir. In the rostral spinal cord, ChAT immunoreactivity was observed in cells of the motor column, the dorsal horn, the marginal nucleus (a putative stretch-receptor organ), and in interstitial cells of the ventral funiculus. These results demonstrate for the first time that cholinergic neurons are distributed widely in the central nervous system of elasmobranchs and that their cholinergic systems have evolved several characteristics that are unique to this group. J. Comp. Neurol. 420:139–170, 2000. © 2000 Wiley-Liss, Inc.
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In lambs, chronic section of the oculomotor nerve at the base of the skull just proximally to the cavernous sinus induced degeneration of some fibers in the central stump, although the peripheral stump contained some normal fibers. On the other hand, chronic section of the ophthalmic branch just distally to the semilunar ganglion was followed by degeneration of a certain number of medium and large caliber fibers in the ipsilateral oculomotor nerve. The presence of trigeminal afferent fibers in the trunk of an oculomotor nerve is supported by electrophysiologic experiments. Single-shock electrical stimulation of the frontal and nasociliary nerves and of the conjunctiva of the superior and inferior eyelids elicited short-latency evoked potentials, not only in the semilunar ganglion but also in the ipsilateral oculomotor nerve at the base of the skull. Such responses did not appear in those animals in which the ipsilateral ophthalmic and maxillary branches of the trigeminal nerve had been chronically cut. Thus, we can affirm that afferent trigeminal impulses enter the brain stem also through the third nerve. The perikarya of such a pathway are localized in the semilunar ganglion; the peripheral processes attain the conjunctiva of the superior and inferior eyelids through the ophthalmic and maxillary branches, and the central processes enter the oculomotor nerve by anastomoses between IIIrd and Vth cranial nerves after a short passage in the two trigeminal branches. The trigeminal nature of these fibers is also shown by the fact that electrical stimulation of the central stump of the IIIrd nerve can influence the dorsal neck muscles in the same way as other trigeminal afferents.
This research attempted to verify the hypothesis that the ganglion cells along the eye-muscle nerves innervate eye-muscle spindles. Our investigations were performed on calves. The intracranial portion of the oculomotor nerve sometimes contains a rather large number of ganglion cells in comparison with the peripheral part. Therefore, intracranial and peripheral parts of the left oculomotor nerve in 9 calves were chronically separated at the base of the skull before the nerve entered the orbit. Responses to stretching individual eye muscles either of the left or of the right side were recorded from the ipsilateral trigeminal ganglion. They were of the type induced by muscle-spindle excitation elsewhere. However, no responses were obtained from the intracranial course of the right oculomotor nerve. The spindles innervated by the left oculomotor nerve were normal in seven calves whose central oculomotor stump contained few ganglion cells. However, very few degenerated spindles were found in the extraocular muscles of two calves in which the intracranial stump of the nerve exhibited more than 100 ganglion cells. Thus, we conclude that the trigeminal ganglion of the calf contains the soma of the afferents from the eye-muscle spindles, as is the case for the lamb and pig. The ganglion cells in the oculomotor nerve can play only an accessory and negligible role in innervating the eye-muscle spindles.
The oculomotor nerves (3rd, 4th and 6th) of some species of fish and mammals have been studied to establish the presence, number, true topography and probable functional role of the ganglion cells located along the trunk. The finding of typical pseudo-unipolar ganglion cells is always unpredictable and extremely variable, from an inter- and intra-specific point of view, in members of the two zoological classes studied.
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