Nucleus Of The Optic Tract Research Articles

Oculomotor areas in the rabbit's midbrain and pretectum

The role of some meso- and diencephalic structures in eye movements was investigated by ablation and stimulation experiments. Optokinetic nystagmus was abolished by small lesions in the lateral pretectum, but not by complete removal of the superior colliculi. Stimulation of the superior colliculus and other visual centers was effective in eliciting nystagmus (slow phase ipsilateral), but the most efficient trigger zones are found in the lateral pretectum and the midbrain tegmentum. Only from these areas could nystagmus still be elicited after degeneration of the primary optic fibers. The lateral pretectal trigger zone is probably identical with the nucleus of the optic tract. It is postulated that this nucleus is an essential station for horizontal optokinetic reactions. Saccades were obtained by stimulation of the mesencephalic central grey, but not for any visual centers such as the superior colliculus.

Corticofugal projections from the visual cortices to the thalamus, pretectum and superior colliculus in the cat.

AbstractSmall lesions were placed in visual cortical areas 17, 18, 19, 20, 21, 7, and Clare‐Bishop in the cat, and the sites of terminal degeneration seen with Fink‐Heimer technique were plotted in thalamus, pretectum and superior colliculus. No degeneration was found in these sites after area 20 lesions; lesions in the other cortical areas gave different patterns of degeneration. Two major patterns were present, one from lesions in 17–18, one from lesions in 21, 7 and C‐B, with degeneration from 19 forming a transition between the two groups.Areas 17, 18 and 19 project to the dorsolateral geniculate nuclear complex (LGNd); areas 21, C‐B and 7 do not. Area 17 projects to the laminar part, area 18 to both laminar and interlaminar (NIM) parts, and 19 only to NIM. The corticogeniculate projections from all three areas are topically organized anteroposteriorly, and at least that from area 17 is topically organized mediolaterally.Areas 17 and 18 project topically to a columnar locus of the medial pulvinar (=lateral posterior) nucleus which ventrally includes that area known as the posterior nucleus. Area 19 has a double columnar projection to this part of the thalamus, one in the medial and one in the lateral pulvinar area. The medial column lies medial to that from 17–18, and appears to overlap the termination of the ascending projection from the superior colliculus. Cortical areas 21, C‐B and 7 also have a double projection to the pulvinar.These findings indicate that the corticorecipient neurons in both medial and lateral sectors of the pulvinar are organized so that dorsal neurons are activated by stimuli in upper visual fields (lower retina) and ventral neurons by stimuli in lower fields (upper retina).Areas 17 and 18 project to the external layer of the ventrolateral geniculate (LGNv) nucleus, 19 to both external and internal layers, and 21, C‐B and 7 to internal layer only.The pretectal projection from 17–18 is limited to its caudal pole chiefly in the posterior pretectal nucleus (NPP), and also in the nucleus of the optic tract (NOT). Area 19 fibers terminate in NPP, NOT and also in the reticular part of the anterior pretectal nucleus (NPAr). Those from 21 and C‐B end primarily in NPAr, and from area 7 in both reticular and compact parts of NPA. These corticopretectal systems all appear to be organized topically.Areas 17, 18 and 19 have a double termination in the superior colliculus, a focal pattern in the superficial layers (chiefly lamina II), and a diffuse pattern in deeper layers (laminae IV, V, VI). The superficial pattern only provides the retinotopical matching with the optic afferents. All other cortical areas project diffusely to the deep layers. After lesions in 21 and C‐B, the superficial foci are larger and centered in lamina III; after area 7 lesions this focal degeneration is centered in laminae III and IV and spread over much of the width of the colliculus. Degeneration to pontine nuclei and inferior olive was not examined.

An electron microscope study of the dorsal cap of the inferior olive in the rabbit, with special reference to the pretecto-olivary fibers

Synaptic organization in the dorsal cap of the inferior olive has been studied electron microscopically in the rabbit. Axosomatic synaptic knobs were so sparse that the entire contour of a somatic profile often no synaptic contact. About 70% of axosomatic knobs were filled with round synaptic vesicles, and 30% with pleomorphic ones. Axodendritic synaptic knobs were most frequently encountered upon small or medium-sized dendritic profiles. About 60% of them were filled with round synaptic vesicles, and 40% with pleomorphic ones. The crest synapses with subjunctional bodies were frequently encountered. One or more dark-cored vesicles were often seen in both axosomatic and axodendritic knobs (20–30%). After placing lesions in the pretectal areas around the nucleus of the optic tract, electron-dense degenerated synaptic knobs were observed in the dorsal cap ipsilateral to the lesion. The great majority of degenerated knobs were in synaptic contact with small or medium-sized dendrites. Degenerated axodendritic knobs, however, comprised only a small proportion of the total synaptic population (0.43% in a rabbit with a survival period of 3 days). No unequivocal signs of degeneration were found in axosomatic synaptic knobs.

Retinal projections in domestic ungulates. II. The retinal projections in the horse and the ox

A unilateral eye enucleation was performed on 7 horses and 6 oxen. The animals were sacrificed after a 6–14-day survival period and their brains were processed by the Nauta-Gygax and the Fink-Heimer methods to determine the distribution of retinal projections in the primary optic centres, as well as by the Klu¨ver-Barrera method for a study of the nuclear configuration. In both the horse and ox, bilateral retinal projections were traced to the dorsal as well as the ventral nucleus of the lateral geniculate body (LGs, LGv), to the medial interlaminar nucleus (MI), the nucleus of the optic tract (NTO), the nucleus pretectalis posterior (PRp) and the superior colliculus (SC). In neither species did the LGd show any distinct lamination. In the LGv, only the lateral sector presented terminal degeneration. This nucleus is larger and better developed in the ox than in the horse. No evidence of retinal-fibre termination was found in the nucleus pretectalis anterior (PRa) and in the area pretectalis medialis (PRm). A crossed accessory optic tract, composed of the posterior fibres of the superior fasciculus of Hayhow, was identified in both species. Degenerating fibres of this tract were traced to the dorsal (DTN), lateral (LTN) and medial (MTN) terminal nucleus in the horse; the last-mentioned nucleus could not be identified in the ox. No evidence of a retinohypothalamic projection could be found in either species.

Pretectal region and the pupillary light reflex. An anatomical analysis in the monkey.

AbstractThe effects of discrete lesions in the pretectal region of the monkey upon the pupillary light reflex were studied, using infrared pupillography. Resulting degeneration was studied by silver impregnation methods.The nucleus of the optic tract (NOT) and the sublentiform nucleus (SL) project fibers to the nuclei of the posterior commissure (NPC) and to portions of the ipsilateral inferior pulvinar, pregeniculate nucleus and dorsal lateral geniculate body. NPC gives rise to the bulk of the fibers in the posterior commissure (PC) which largely terminate upon contralateral cells of NPC. Some fibers arising from NPC enter the ipsilateral central gray and terminate bilaterally primarily upon cells of the medial visceral columns of the oculomotor complex (OMC). These fibers partially decussate ventral to the aqueduct.Fibers from the olivary nucleus (ON) cross in the PC and project to terminations upon: (1) large cells of the opposite ON and (2) the anterior median nuclei and the contralateral lateral visceral cell column of OMC. NOT, and possibly ON, give rise to fibers crossing in PC that project to the contralateral accessory optic tract nucleus (AOTN).Unilateral lesions that fairly selectively destroy parts of NOT, ON, SL, NPC, central fibers of PC or the nucleus of the pretectal area (NPA), produce neither miosis, mydriasis, anisocoria, nor do they impair direct or consensual pupillary light reflexes. Unilateral lesions, which impair pupillary light reflexes, involve multiple structures, such as NPC, PC and lateral regions of the central gray.

Conduction velocity in pathways from retina to superior colliculus in the cat: a correlation with receptive-field properties.

Conduction velocity in pathways from retina to superior colliculus in the cat: a correlation with receptive-field properties.

Retinal projections in domestic ungulates. I. The retinal projections in the sheep and the pig

Six sheep and 5 pigs were subjected to unilateral eye enucleation; after a 14-day survival period their brains were treated by the Nauta-Gygax and the Klüver-Barrera methods, to determine the distribution of retinal efferents in the primary optic centres. In both the sheep and the pig the retina projects bilaterally to both the dorsal and ventral nuclei of the lateral geniculate body (LGd, LGv), to the medial interlaminar nucleus (MI), to the nucleus of the optic tract (NTO), to the nucleus pretectalis posterior (PRp), and to the colliculus superior (SC). A concealed type of lamination was found to exist in the LGd of both species. In the LGv, preterminal degeneration was found in the lateral sector only. This nucleus is relatively larger in the pig than in the sheep. In the NTO degenerating preterminals were found to be diffusely distributed, while in the PRp they appeared in the dorsal part of the nucleus only. No degenerating preterminals were found in the pulvinar, the nucleus pretectalis anterior (PRa) or the area pretectalis medialis (PRm). In both species a crossed accessory optic tract corresponding to the posterior fibres of the superior fasciculus of Hayhow could be identified, and the degenerating fibres of this bundle could be treced to the dorsal and the lateral terminal nuclei of the accessory optic system (DTN, LTN). No evidemce of a retinohypothalamic projection was found in either species.

The termination of retinal axons in the pretectal region of mammals.

AbstractThe retinopretectal projection was investigated in the rat, mouse, rabbit and tree shrew primarily by means of the Fink‐Heimer technique. The experimental animals survived for varying periods of time following unilateral eye removal. The retinopretectal projection in each species was predominantly contralateral. A dense field of terminal degeneration was observed in the nucleus of the optic tract and in the olivary pretectal nucleus in each of the species. A less dense projection was observed for the posterior pretectal nucleus in each species. A sparse projection to the anterior pretectal nucleus was observed in the rabbit and tree shrew but not in the rat or mouse. A dense, ipsilateral projection to the olivary pretectal nucleus was observed in the rat, mouse and tree shrew. A sparse, ipsilateral projection was found in the anterior end of the posterior pretectal nucleus in the rat, mouse and tree shrew and in the posterior part of this nucleus in the rabbit. In the tree shrew, a small amount of terminal degeneration was found in the ipsilateral anterior pretectal nucleus. The nomenclature used here is uniformly applicable among the species described.

An analysis of the posterior group of thalamic nuclei on the basis of its afferent connections.

AbstractThe distribution of the axonal and terminal degeneration in the posterior group and principal nuclei of the thalamus of the cat has been studied with the Nauta technique following lesions of the major ascending sensory pathways and of most areas of the cerebral cortex. The cellular changes occurring in the same parts of the thalamus after damage of the cortex of the somatic, auditory and visual sensory areas have also been investigated.It has been found that the posterior group receives fibers from all parts of the cortex on the lateral surface of the hemisphere caudal to area 4, with the exception of areas 17, 18 and 19 of the visual cortex, and that cellular degeneration occurs in the posterior group after damage of the same areas of cortex. Both fiber and cellular degeneration can be found in the posterior group after a lesion confined to either the somatic sensory or auditory cortex.Experiments with smaller lesions have shown that all areas of the cortex which have been studied send fibers to parts of three distinct types of thalamic nuclei — to the relevant principal nucleus, to a part of the intralaminar group of nuclei or the posterior group, and to a part of the reticular nucleus. After larger lesions of the cortex cellular degeneration is always found in parts of these three types of nuclei. Ascending fibers in the somatic and auditory sensory pathways also terminate in the principal nuclei and in one or other part of the intralaminar nuclei‐posterior group system but not in the reticular nucleus.There is a definite interrelationship in the somatic and auditory sensory systems between the site of termination of the ascending fibers of these pathways, the principal nuclei and parts of the posterior group in which these two pathways end, and the area of cortex to which these principal nuclei project and which, in turn, sends fibers back to them and to the posterior group. It is suggested that there is a similar relationship between the site of termination in the intralaminar nuclei of afferent fibers from subcortical structures, the principal nuclei in which the same afferent pathways end, and the area of cortex with which these principal nuclei are related. This appears to be true at least for the pathways from the cerebellum and globus pallidus to the ventrolateral nucleus and the relevant components of the intralaminar nuclei.On the basis of the experimental findings it is suggested that the posterior group should be included with the intralaminar group of nuclei, and that the region equivalent to the intralaminar nuclei‐posterior group system for the visual cortex is the pretectum (either the whole or a part) or the nucleus of the optic tract. If this hypothesis is correct there is a continuous, well‐organized projection of the neocortex upon the entire extent of the intralaminar nuclei‐posterior group‐pretectal area complex: prefrontal and limbic cortex being related to rostral intralaminar nuclei, areas 6 and 4 to the parafascicular, centre median and central lateral nuclei, the somatic sensory cortex to the medial division of the posterior group, the auditory cortex to the lateral division of the posterior group, the supra‐sylvian cortex to the suprageniculate nucleus and intermediate division of the posterior group and the visual cortex to the pretectum and adjoining regions.

Primary optic pathways in the echidna, Tachyglossus aculeatus: an experimental degeneration study.

AbstractThe retinofugal axons of Tachyglossus aculeatus were found to project to two diencephalic nuclei, disparate in size and location and designated provisionally as LGNa and b, and to the pretectum and superior colliculus. The primary optic pathways of the echidna are crossed except for a few fibers which pass to the ipsilateral large diencephalic nucleus (LGNa). Further work is required before the homologies of the two diencephalic nuclei can be determined. In addition, entirely crossed projections were also found to a large number of optic nuclei including a medial terminal nucleus, four cell groups interstitial to the optic tract, and a nucleus located within the brachium of the superior colliculus which may represent a dorsal terminal nucleus. The latter nucleus may, however, actually be the nucleus of the optic tract which is displaced from its usual close association with the pretectal area. Only an inferior fasciculus of the accessory optic tract was found.

The visual pathways of the lorisid lemurs (Nycticebus coucang and Galago crassicaudatus).

AbstractThe primary projections of the optic nerve were investigated in two species of lorisid lemurs (Nycticebus coucang and Galago crassicaudatus) following unilateral enucleation of an eye. In addition, the cytoarchitecture of the lateral geniculate body and of the pretectum is described. The lateral geniculate nucleus is composed of six cellular laminae – four magnocellular and two parvocellular. Optic nerve fibers from the retina of an eye terminate in laminae 1, 5 and 6 of the lateral geniculate body on the side opposite to the enucleated eye and laminae 2, 3 and 4 of the lateral geniculate body on the same side as the enucleated eye. Retinofugal fibers were also observed to project to the pregeniculate nucleus, nucleus of the optic tract, pretectal nucleus and superior colliculus on both the same side as and on the side opposite to the enucleated eye. A completely crossed accessory optic tract was noted. The lateral geniculate bodies of a Galago “borgne” (one blind atrophic eye) are also described.

Response characteristics of movement-detecting neurons in pretectal region of the cat

Single-unit responses to visual stimuli were recorded in the transitional region between optic tectum and thalamus; recording sites, marked by Prussian blue, were located in the nucleus of the optic tract, the deep pretectal nuclei, the pretectal area, and the nuclei of the posterior commissure. Most units were activated primarily by moving objects and a considerable proportion reacted in a directionally selective manner. Some units strongly preferred objects moving in a midsagittal plane towards the animal (Type I) or away from it (Type II). When tested with continuously increasing or decreasing sizes of stationary bright discs or shadows, Type I was primarily activated during increase, Type II during decrease of stimulus area. Increase or diminuition of stimulus intensity were ineffective. In another group of units visual angles of effective stimuli had to exceed 7 deg in small sized objects; threshold of visual angles increased with increasing object size. We suggest that these units require a minimum light flux to be excited. Selectivity for relatively low stimulus background contrasts was found in some units. Most neurons responded to stimulation of either eye. A considerable proportion did not react to diffuse illumination of their receptive field. Light spots flashed into the field center evoked in most cases phasic on-off reactions. Phasic-tonic responses occurred only in the nucleus of the optic tract. Receptive field sizes ranged from 2–120 deg. Only in the nucleus of the optic tract and in the pretectal area evidence of a retinotopic organization was obtained. Some neurons responded reliably to visual and tactile or visual and acoustic stimuli (multisensory convergence). Incidence of response properties varied with anatomical localization. Units of the nucleus of the optic tract were directionally unselective, frequently responsive to diffuse light and mostly excitable by one eye. The nucleus of the posterior commissure contained neurons which were directionally selective for vertical movements or for sagittal approach movements (Type I). Type II neurons were more laterally localized. Comparison of the present results with those of single unit studies in the optic tectum demonstrates many similarities but also definite differences.

The relationship of optic nerve fiber groups activated by electrical stimulation to the consequent central postsynaptic events

A physiological analysis is described for the major central projections in the cat of the three fiber-size components of the optic tract compound action potential produced by electrical stimulation of the contralateral optic nerve. The first two waves, T1 and T2, both project to layers A and B of the lateral geniculate body, and thence to visual cortex. The superior colliculus response has three components: C1 is a response to direct projection of T1 axons; C2 is relayed via geniculate and striate cortex, and accordingly is influenced by both T1 and T2 tract fibers; C3, the largest response, is fired directly by the smallest diameter tract fibers, T3. The region of the nucleus of the optic tract and the lateral posterior nucleus of the thalamus can be activated by T1 and T2 tract fibers relayed by both cortical and subcortical mechanisms. Phylogenetic and functional considerations of the data are discussed.

Nuclear configuration of the diencephalon of Tamandua tetradactyla and Myrmecophaga jubata.

AbstractThe nuclear configuration of the diencephalon of Tamandua tetradactyla (lesser anteater) is figured, described and compared with that of Myrmecophaga jubata (greater anteater) and other mammals, particularly the cat. Their nuclear organization represents, in general, all the elements (or their homologues) found in the mammalian diencephalon.There is an unusually large nucleus centralis lateralis which penetrates into the nucleus medialis dorsalis from above. The size of the latter group, in the presence of a poorly developed orbitofrontal cortex, suggests that it is primarily dependent upon the marked development of the corpus striatum. The nuclei of the tractus habenulopeduncularis are displaced ventrally, apparently by the medial enlargement of the nucleus centralis lateralis. The nuclei parataeniales bear strong resemblance to those in the armadillo.There is no nucleus ventralis pars anterior in either Tamandua or Myrmecophaga. The nucleus ventralis medialis is much larger than that in carnivores. The presence of the nucleus submedius and its intimate relation to the nucleus anterior medialis of the anterior nuclear complex, accounts fairly well for questionable homologues in such forms as Tarsius.The existence of both the large‐celled nucleus of the optic tract and the nucleus limitans indicates the gradual incorporation, at least in part, of the former into the latter. Hypothalamic nuclei, except for the supraoptic and paraventricular groups, are rather poorly differentiated.

Sprouting of optic tract projections in the brain stem of the rat.

AbstractThe present experiments examine axonal sprouting of optic tract projections as a consequence of occipital cortex removal. Eyes were removed bilaterally in experimental rats 16 months following unilateral occipital cortex ablation. Seven animals survived this procedure. Controls included rats sacrificed 16 months after unilateral occipital cortex ablation, one week after unilateral occipital cortex destruction, and one week after bilateral or unilateral eye removal. Brains were serial‐sectioned and stained by the Nauta‐Gygax method for degenerating axons.Sprouting occurred only at two loci, the caudal half of the ventral lateral geniculate nucleus, pars lateralis, and the caudal portion of lateral nucleus of the optic tract and subjacent medial quarter of pretectal nucleus. These loci have in common that they are regions of convergence in a major fashion of the two fiber systems, the occipitofugal and retinofugal projections on which experiments were done. However, sprouting did not occur in other similarly deafferented regions. Explanations for this specificity of sprouting are discussed.Optic tract sprouting was observed only at paraterminal portions of the axon and not as collateral sprouts along its course.A suggested relationship between axonal sprouting and functional plasticity is discussed.

Distribution of optic fibers in the cat.

AbstractThis study undertook to investigate pathways and connections of optic tract fibers in the pulvinar, hypothalamus, ventral lateral geniculate, pretectal region and superior colliculus.Thirty‐five adult cats were utilized — 28 experimental subjects and seven controls. The right eye was removed and the cats allowed to survive for periods from three to 61 days. The chief method of investigation was the silver impregnation technique of Nauta‐Gygax ('54), supplemented by Marchi and luxol‐blue cresyl‐fast‐violet methods.Study of fiber patterns of degeneration in serial sections of the Nauta‐Gygax preparations revealed no preterminal axonal degeneration in the hypothalamus or pulvinar. Portions of a completely crossed accessory optic tract as described by Hayhow ('59) were identified. Preterminal degeneration of fine collaterals of the larger optic fibers was found in the dorsal one‐third of the lateral portion of the ventral lateral geniculate. Large areas of preterminal degeneration and many fibers of passage were observed in the pretectal region. Localized areas of pretermimal degeneration in this region were interpreted as belonging to the pretectal nucleus and to the nucleus of the optic tract. A large number of fine optic fibers was found terminating in the superficial stratum opticum of the superior colliculus. Two areas of preterminal degeneration lateral to the colliculus were interpreted as extension of the pretectal nucleus and as the nucleus olivaris colliculi.