Lateral Terminal Nucleus Research Articles

The termination of retinofugal fibers in the crab-eating monkey (Macaca irus): an autoradiographic study.

In the crab-eating monkey (Macaca irus), the subcortical projection from the retina was studied by means of the autoradiographic method. Retinofugal fibers terminated bilaterally in the suprachiasmatic, pregeniculate, lateral geniculate, olivary, pretectal, lateral terminal and dorsal terminal nuclei and the superior colliculi. In the ipsilateral lateral geniculate nucleus, the retinofugal fibers terminated on laminae 0, 2, 3, and 5; in the contralateral nucleus, they ended in laminae 1, 4, and 6. In the superior colliculi, retinal terminals were aggregated in the stratum griseum superficiale. The ipsilateral suprachiasmatic nucleus showed a heavier labeling than the contralateral nucleus.

Visual discrimination impairments after lesions in zona incerta or lateral terminal nucleus of accessory optic tract

Possible visual functions of zona incerta (ZI) and lateral terminal nucleus of the accessory optic tract (LTN) in rats were investigated by comparing the effects of localized lesions on a series of discrimination learning tasks. In Experiment 1 animals with ZI lesions were impaired on a simultaneous black versus white (BW) discrimination but not on a simultaneous horizontal versus vertical (HV) task. Animals with LTN lesions were impaired on HV but not on BW. Rats with ZI lesions were impaired on a successive bright versus dim but not a successive HV discrimination when subsequently tested in Experiment 2. Animals with LTN lesions were impaired on both tasks. The results are related to the possibility that visual intensity information gains access to the motor system through a pathway running from the ventral lateral geniculate nucleus to the basal ganglia via ZI. Since LTN lesions impaired acquisition of a HV discrimination, a task highly susceptible to the effects of geniculostriate ablation, it is suggested that such lesions impair the use of visual information without distroying the sensory channels mediating the discrimination.

Accessory optic system of rhesus monkey

The accessory optic system of the rhesus monkey ( Macaca mulatta) was investigated using the silver method of de Olmos-Ingram to determine the course and distribution of its degenerating fibers following retinal evisceration. Serial Niss 1 sections were used to relate the axonal degeneration to the brain stem cytoarchitecture. It is found that this system consists of a dorsal and a lateral terminal nucleus together with a superior fasciculus (posterior fibers). The retinal fibers within this superior fasciculus originate primarily from the contralateral and some from ipsilateral retina. These fibers leave the superior quadrigeminal brachium to course ventrally and anteriorly over the caudolateral aspects of the medial geniculate, the inferior brachium, and the dorsolateral portion of the cerebral peduncle to terminate within the dorsal and lateral terminal nuclei.

The Accessory Optic System and its Relation to the Vestibulocerebellum

The accessory optic system (AOS) is a visual system organized in vestibular coordinates. Recordings from neurons in the three terminal nuclei of the AOS have revealed that this visual system processes information about the speed and direction of movement of large parts of the visual world. Best modulation of terminal nuclei neurons requires use of large textured stimuli and occurs at low speeds with peak sensitivity at 0.1–1 degree/sec. For medial terminal nucleus and lateral terminal nucleus, the preferred directions in space are vertical, but with a posterior component. For dorsal terminal nucleus, preference is for horizontal movement from posterior to anterior. Taken collectively, the preferred directions for terminal nuclei neurons define three directions in visual space: anterior, up with a posterior component, and down with a posterior component. The speed and direction selectivity of neurons of the accessory optic terminal nuclei are identical to those of the on-direction selective class of rabbit retinal ganglion cells and to those of visually driven climbing fibers in the cerebellar flocculus. It is most likely that the AOS serves to signal self-motion; the sensitivity of AOS neurons to slow speeds makes the AOS an ideal complement to the vestibular system.

The Accessory Optic System in the Rat

Using the anterograde degeneration method, the accessory optic system was analized and divided into the inferior and superior accessory optic tracts in the rat. The inferior accessory optic tract terminal is sent bilaterally into the medial treminal nucleus. The superior accessory optic tract fibers are contralaterally projected into the lateral and dorsal terminal nuclei.

An autoradiographic investigation of the subcortical visual system in chimpanzee.

Based on one adult chimpanzee monocularly injected with radioactive proline, retinofugal fibers were found to terminate bilaterally in the suprachiasmatic, pregeniculate, lateral geniculate, olivary, pretectal and lateral terminal nuclei, and the superior colliculi; the existence of a dorsal terminal nucleus of the accessory optic system is in doubt. In the ipsilateral geniculate nucleus, the fibers terminate in layers 2, 3 and 5; in the contralateral nucleus, they end in layers 1, 4 and 6. Midway through the geniculate nucleus, layers 3 and 4 split medially into two daughter layers each. In the superior colliculi, most of the retinal terminals are aggregated superficially in a band located in the stratum griseum superficiale. The contralateral band is interrupted by gaps; the ipsilateral band has fewer gaps, is slightly thicker and located more deeply. There is a limited second tier of terminals in the contralateral superficial gray.

The accessory optic system of the ferret.

The accessory optic system of the ferret has been studied both by silver degeneration staining and by autoradiography after intraocular 3H leucine injections. There is no anterior accessory optic tract but a posterior tract containing only crossed fibres leaves the brachium of the superior colliculus and ends in the two nuclei, the medial and lateral terminal nuclei, lying either side of the cerebral peduncle. Both suprachiasmatic nuclei receive retinal fibres visible only on autoradiographs; most fibres end in the contralateral nucleus. No other area in the hypothalamus appears to receive retinal fibres demonstrated by these methods.

An autoradiographic study of the projections from the lateral geniculate body of the rat

The projections from the lateral geniculate body of the rat were followed using the technique of autoradiography after injections of [ 3H]proline into the dorsal and/or ventral nuclei of this diencephalic structure. Autoradiographs were prepared from either frozen or paraffin coronal sections through the rat brain. The dorsal nucleus of the lateral geniculate projected via the optic radiation to area 17 of the cerebral cortex. There was also a slight extension of label into the zones of transition between areas 17, 18 and 18a. The distribution of silver grains in the various layers of the cerebral cortex was analyzed quantitatively and showed a major peak of labeling in layer IV with minor peaks in outer layer I and the upper half and lowest part of layer VI. The significance of these peaks is discussed in respect to the distribution of geniculocortical terminals in other mammalian species. The ventral nucleus of the lateral geniculate body had 5 major projections to brain stem structures both ipsilateral and contralateral to the injected nucleus. There were two dorsomedial projections: (1) a projection to the superior colliculus which terminated mainly in the medial third of the stratum opticum, and (2) a large projection via the superior thalamic radiation which terminated in the ipsilateral pretectal area; a continuation of this projection passed through the posterior commissure to attain the contralateral pretectal area. The three ventromedial projections involved: (1) a geniculopontine tract which coursed through the basis pedunculi and the lateral lemniscus to terminate in the dorsomedial and dorsolateral parts of the pons after giving terminals to the lateral terminal nucleus of the accessory optic tract, (2) a projection via Meynert's commissure to the suprachiasmatic nuclei of both sides of the brain stem as well as to the contralateral ventral lateral geniculate nucleus and lateral terminal nucleus of the accessory optic tract, and (3) a medial projection to the ipsilateral zona incerta. The results obtained in these experiments are contrasted with other data on the rat's central visual connections to illustrate the importance of these connections in many subcortical visual functions.

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.

The primary optic projections in pigmented and albino guinea pigs: an experimental degeneration study

Summary An eye was enucleated in each of 6 pigmented and 6 albino guinea pigs. Six to 8 days later the animals were killed and their brains were prepared by the Nauta and Nissl methods in order to study the course and terminal distribution of the degenerating optic fibers. Several major differences were demonstrated between the pigmented and albino guinea pigs in the terminal distribution of the crossed and uncrossed optic fibers. First, it was shown that in the pigmented animals the ventral and dorsal lateral geniculate nuclei, the nucleus tractus opticus, the nuclei praetectalis anterior and posterior, and the superior colliculus all receive inputs from both retinae; whereas in the albino animals these same nuclei could be found to receive organized inputs only from the contralateral retina. Second, it was found that the pattern of the contralateral retinal input to the ventral and dorsal lateral geniculate nuclei, but not to the pretectal nuclei, the superior colliculus and the terminal accessory optic nuclei, differs between the two strains of animals. In both the pigmented and albino guinea pigs it was shown that the accessory optic system is composed entirely of crossed optic fibers and consists of two fiber groups (inferior and superior fasciculi) and 3 terminal nuclei (dorsal, lateral and medial terminal nuclei). It was also shown that in both strains of animals the degenerating optic fibers that lie in and adjacent to the ventral and dorsal lateral geniculate nuclei and the pretectal nuclei course within two distinct fiber systems oriented perpendicularly to each other.

An anterior component of the accessory optic system of the cat, with evidence for the absence of reticuloretinal fibers

A hitherto unreported component of the accessory optic system of the cat brain is described using the de Olmos-Ingram cupric silver method 1–3 weeks after unilateral intraorbital optic nerve section. This component crosses the optic chiasm and leaves the contralateral optic tract to pierce the lateral one-fifth of the cerebral peduncle and the reticular complex of the thalamus at the level where the cerebral peduncle joins the internal capsule. It then swings medially and caudoventrally along the junction between the cerebral peduncle and the substantia nigra. Most of its fibers enter the accessory optic tract (AOT) and its medial and lateral terminal nuclei as they are designated by Hayhow. A few fibers deviate from this path, coursing ventrally and slightly caudomedially through the cerebral peduncle to join the AOT along the route. The failure of this new fiber component to undergo Wallerian degeneration subsequent to the production of peduncular lesions coupled with other evidences indicates its centripetal rather than centrifugal (with respect to the brain) nature. The proposal of centrifugal (efferent) optic fibers orininating from the mesencephalic reticular formation (reticulo-retinal fibers) cannot be confirmed.

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.

Efferent projections of the superior colliculus in the opossum.

AbstractThe Fink and Heimer technique was used to study the ascending and descending fiber degenerations resulting from unilateral electrolytic lesions in the superior colliculus of sixteen adult opossums. The ascending fiber degeneration left the colliculus by way of a small parabrachial bundle or with the brachium of the superior colliculus. The former bundle contributed degenerating terminals to the suprageniculate, parabrachial, and magnocellular medial geniculate nuclei and appeared to terminate in the lateral terminal nucleus of Hayhow (Hayhow, '66). The latter bundle contributed fibers to the pretectal and posterolateral nuclei as well as discrete projections to the ventral lateral geniculate nucleus and ventral thalamus.Descending degenerating fibers in the brainstem were destributed along three tracts: (1) a medial predorsal bundle, (2) an intermediate tectoreticular, and (3) a lateral tectopontine. These tracts were seen to terminate mainly in tegmental and reticular centers as well as in the lateral basilar nucleus of the pons. Degenerating fibers of the predorsal bundle were followed to lower medullary levels but could not be traced to spinal levels.The present findings are descussed in relation to data reported for more developed mammalian species.

Lipid droplets in the lateral terminal nucleus of the accessory optic system in Galago (Primates)

Neuronal inclusions within the lateral terminal nucleus of the accessory optic system in Galago were identified as lipids. Intact L-fibers are essential for their formation. After eye enucleation, which interrupted the L-fibers, the number of cells containing lipid droplets decreased significantly.

The accessory optic system in Erinaceus (Insectivora) and Galago (primates).

AbstractAfter unilateral eye removal in Erinaceus and Galago, Nauta‐gygax and Fink‐Heimer silver impregnation methods were used to study the accessory optic system. In Erinaceus the accessory optic fibers terminate contralaterally in the dorsal lateral and medial terminal nuclei of the accessory optic system; in Galago only the dorsal and lateral terminal nuclei are seen.Hayhow's nomenclature of the accessory optic fibers in modified in such a way that they are now classified according to their terminations. The D‐fibers terminate in the dorsal terminal nucleus, the L‐fibers in the lateral terminal nucleus, and the M‐fibers in the medial terminal nucleus. Accordingly, D‐, L‐ and M‐fibers are found in Erinaceus, while only D‐ and L‐fibers are present in Galago.As in the two monkey species recently studied, but contrasting sharply with the findings in all non‐primate mammals, the M‐fibers and the medial terminal nucleus are absent in Galago. It is hypothetized that the accessory optic system is similarly reduced in all other primates.No retinal fibers terminate in the preoptic region, lamina terminalis, hypothalamus, subthalamic nucleus or substantia nigra.

The retinal projections of the tree shrew and hedgehog

Summary Retinal projections in the European hedgehog (Erinaceus europaeus) are primarily to the contralateral superior colliculus, pretectal complex and pars dorsalis and ventralis of the lateral geniculate body. Ipsilateral projections to the same sites are also present but are sparse in comparison. A crude form of differential projection to the dorsal lateral geniculate nucleus is present in which ipsilateral projections terminate primarily in the central portion of the nucleus while contralateral projections terminate primarily in the peripheral portions of the nucleus. The accessory optic system is entirely contralateral and consists of dorsal, lateral and medial accessory optic nuclei and a superior accessory optic fasciculus. An inferior accessory optic fasciculus appears to be lacking. In the three shrew (Tupaia glis) similar projections are found except that they are markedly greater in amount and there are differential projections to laminated dorsal lateral geniculate nuclei which are organized differently than in those few primates which have been studied. In addition, an inferior accessory optic fasciculus is present and the more anterior fibers of the superior fasciculus are well developed. The latter fact probably is correlated with the greater extent of the lateral terminal nucleus.