Correlation between different types of retinal ganglion cells and their projection pattern in the albino rat

Injecting Fluoro-Gold (FG) and Evans-Blue (EB) into the right dLGN and SC in the adult albino rat, ipsilaterally projecting double-labeled retinal ganglion cells were mainly seen in the ventrotemporal crescent. They were mainly large sized cells. The ipsilaterally projecting double-labeled cells tended to have larger somata than the single- and double-labeled cells projecting to the contralateral superior colliculus and/or dorsal nucleus of the lateral geniculate body.     

The ventral lateral geniculate nucleus of the albino rat morphological and histochemical observations

The ventral lateral geniculate nucleus (vLGN) of albino rats (Wistar strain) has been described histologically and histochemically. Special attention was paid to the identification of cell classes in Nissl and Golgi preparations, the afferent and efferent connections of vLGN cells and the demonstration of enzymes of energy and transmitter metabolism. Topographical aspects were taken into consideration, too. The main results can be summarized as follows: In the rat vLGN, three subnuclei can be distinguished: the lateral and medial subnucleus and the intergeniculate leaflet. In the rostral vLGN, the lateral and medial subnucleus is separated by a vertical fibre bundle which contains retinal axons. Our own experiments and findings of other groups revealed that the rat vLGN is connected with numerous brain structures. There is no efferent projection to cortical regions. Afferent fibres reach the vLGN from retina, visual cortex, superior colliculus, pretectal region, zona incerta, contralateral vLGN, dorsal raphe nucleus, locus coeruleus, mesencephalic reticular formation, vestibular and dorsal tegmental nuclei. An efferent projection has been found to superior colliculus, pretectal region, dorsal lateral geniculate nucleus, contralateral vLGN, zona incerta, pontine nuclei, suprachiasmatic nucleus, lateral terminal nucleus of the accessory optic system and intralaminar nucleus of thalamus. Comparative findings suggest that the lateral subnucleus is involved in "specific projections", whereas the medial subnucleus projects to "unspecific zones". For detailed information see text. Five classes of neurons can be distinguished in Golgi and Nissl preparations. Class 1 cells are medium-sized to large with smooth thick proximal but branched spiny distal dendrites. They are confined to the lateral subnucleus and the intergeniculate leaflet. In the lateral subnucleus, class 1 cells could be identified as geniculo-tectal relay neurons (Brauer and Schober, 1982). All other classes of neurons are spineless or sparsely spined. Class 2 cells (giant neurons) of unknown function could be found in the lateral and medial subnucleus. Class 3 cells (medium-sized multipolar neurons) can mainly be found in the medial subnucleus. They are good candidates for neurons projecting to the contralateral vLGN. Class 4 cells (bipolar neurons) occupy the ventromedial part of the medial subnucleus and are very similar to cells localized in the adjacent zona incerta. Cells belonging to this type could found to be labelled by the HRP reaction product after injection of this enzyme in the pontine region.(ABSTRACT TRUNCATED AT 400 WORDS)     

The morphology, number, distribution and central projections of Class I retinal ganglion cells in albino and hooded rats

Class I retinal ganglion cells have been identified in wholemounts of rat retinae following injections of horseradish peroxidase (HRP) into retino-recipient nuclei. Class I cells are characterized by relatively large somata, 3-7 fairly frequently branching large-gauge primary dendrites and relatively thick axons. Cells with a very similar morphology have been visualized in the ganglion cell layer of retinal wholemounts using a neurofibrillar stain. The size of the somata and dendritic trees of Class I cells is affected by the density of all classes of ganglion cells: both somata and dendritic trees of Class I cells located in the region of peak density are smaller than those located in medium- and low-density ganglion cell regions. The mean numbers of Class I ganglion cells labelled following massive injections of HRP into retino-recipient nuclei were 876 (in albino rats) and 944 (in hooded rats), while the mean number of cells stained with the neurofibrillar method in albino retinae was 791. Thus, with the total number of positively identified retinal ganglion cells being 110,000-115,000 [Potts et al., 1982; Perry et al., 1983], Class I cells in both strains of rat constitute less than 1% of all retinal ganglion cells. Nevertheless the dendritic fields of Class I cells cover the entire retina. Although Class I cells are distributed relatively evenly across the retina, the density is slightly greater in the lower temporal retina where the bulk of the ipsilaterally projecting fibres originates. While Class I cells represent up to 10% of ipsilaterally projecting retinal ganglion cells in both strains of rat, fewer Class I cells project ipsilaterally in albinos than in hooded rats. All contralaterally projecting Class I cells appear to send branching axons to the superior colliculus and dorsal lateral geniculate nucleus. Class I cells represent a larger proportion of the ganglion cells projecting to the dorsal lateral geniculate nucleus (4-5%) than that of ganglion cells projecting to the superior colliculus (about 1%). The morphology, numbers, distribution and the pattern of the central projections of Class I retinal ganglion cells in rats suggest that they are likely to be homologues of the alpha-type ganglion cells distinguished in carnivores.     

The organization of subcortical projections of the hamster's visual cortex

The subcortical projections of the hamster's visual cortex were determined by use of injections of tritiated proline and heat lesions placed in different cortical loci. The brains were processed for autoradiography and silver impregnation of degenerating axons. Striate cortex was shown to project ipsilaterally to the dorsocaudal region of the caudate nucleus, a dorsolateral area within the thalamic reticular nucleus (RT), a laterodorsal region of the nucleus lateralis anterior (LA), the rostral half of nucleus lateralis posterior (LP), the whole territory of the dorsal (dLGN) and ventral (vLGN) geniculate nuclei, the anterior (PA) and posterior (PP) pretectal nuclei, the superior colliculus (SC), and the precerebellar pontine nuclei. In addition, the medial visual area (18b) was shown to project to a medial band of LA and part of the caudal half of LP, while the adjoining parietal cortex was seen to terminate in a lateral part of the caudate, a ventral band of LA, and the ventral half of rostral LP. Segregation of different cortical inputs was clear in LA, LP, caudate, and pons. The projections to dLGN, vLGN, SC, LP, and PA were retinotopically organized. Clear evidence of some topography was found within RT, PP, and the pons, although a consisten map could not be derived from the data.     

Retinal projections and functional architecture of cortical areas 17 and 18 in the tyrosinase-negative albino cat

The visual field representation and functional architecture of cortical areas 17 and 18 in albino cats were studied. In the same animals the distributions of ipsilaterally and contralaterally projecting retinal ganglion cells were determined by injecting horseradish peroxidase into the dorsal lateral geniculate nucleus or optic tract. All cats were tyrosinase-negative albinos (cc), not deaf white cats (W). The proportion of ipsilaterally projecting ganglion cells in the temporal retina of the albino cat was found to be much smaller than in the normal cat or in the Siamese cat. In the albino cat less than 5% of ganglion cells in temporal retina project ipsilaterally. Recordings from areas 17 and 18 provided evidence of a substantial representation of the ipsilateral hemifield in albino visual cortex; cells representing the contralateral and ipsilateral hemifields were often segregated into alternating zones in area 17 and were always segregated in area 18. Cells recorded at the borders of zones representing the ipsilateral and contralateral hemifields often had abnormal properties. Some border cells had two receptive fields separated by as much as 60 degrees of azimuth; one field subserved the contralateral hemifield (contralateral nasal retina) and the other subserved the mirror-symmetric part of ipsilateral hemifield (contralateral temporal retina). Receptive fields of cells subserving the two hemifields did not differ in size. The preferred orientations, preferred velocities, and other characteristics of the two fields were approximately the same; preferred orientation changed gradually and systematically across the borders of zones representing the two hemifields. Our results indicate that afferents representing nasal and temporal regions of retina of the same eye can segregate and form "hemiretina" domains in albino visual cortex. These afferents can also converge upon individual cortical cells in a fashion reminiscent of convergence of afferents from the two eyes upon binocular cells in the normal cortex. The organization of albino visual cortex is therefore different from the organization of Siamese visual cortex. This may be because, in the albino cat but not the Siamese cat, nearly all cells in temporal retina project contralaterally; afferents representing contralateral temporal retina are not at a significant competitive disadvantage in the albino.     

Single thalamic neurons project to both lateral suprasylvian visual cortex and area 17: a retrograde fluorescent double-labeling study

Area 17 and the posteromedial lateral suprasylvian (PMLS) visual cortex receive inputs from three thalamic nuclei in common: the lateral division of the lateral posterior nucleus (LPl), the C-laminae of the lateral geniculate nucleus (LGNd), and the medial interlaminar nucleus (MIN). The present study determined whether these projections originate from the same cells via bifurcating axons or from separate populations of cells. Double-label retrograde transport techniques were used to label cells projecting to area 17 with one fluorescent dye and to label cells projecting to PMLS cortex with a different dye. The two dyes used were fast blue and Evans blue. Following injections into the two cortical areas, some cells were double labeled and some were single labeled in all three thalamic nuclei studied. However, the relative number of double- and single-labeled cells, as well as the relative number of cells single-labeled following injections into each cortical area, differed among the three thalamic nuclei. In both MIN and the C-laminae of the LGNd, the number of double-labeled cells was small. Similarly, the number of cells single labeled with the dye placed in PMLS cortex was small in these two nuclei. In contrast, a relatively large number of cells were single labeled with the dye placed in area 17, especially in the C-laminae of the LGNd. These results suggest that in both MIN and the C-laminae of the LGNd, few cells project to both area 17 and the PMLS cortex, few cells project only to PMLS cortex, and a relatively greater number of cells project only to area 17. In LPl, many cells were labeled after the cortical injections. In fact, when the areas of densest labeling for both dyes overlapped, almost every labeled cell in LPl was double labeled. This indicates that almost all LPl cells that project to one cortical area also project to the other via a bifurcating axon.     

Collateral projections from the supramammillary nucleus to the medial septum and hippocampus

Previous reports have shown that the supramammillary nucleus projects to the medial septum and to the hippocampus, and specifically to the dentate gyrus and the CA2/CA3a region of the hippocampus. The aim of the present study was to examine collateral projections from the supramammillary nucleus to the septum and hippocampus. The fluorescent retrograde tracers, Fluororuby and Fluorogold, were injected into regions of the septum and hippocampus, respectively, and the supramammillary nucleus was examined for the presence of single- and double-labeled neurons. The main findings were: 1) pronounced numbers of single-labeled cells (about 40-60/section) were present in the supramammillary nucleus following retrograde tracer injections in either the septum or hippocampus; 2) single and double retrogradely labeled neurons were intermingled within the supramammillary nucleus and mainly localized to the lateral two-thirds of the supramammillary nucleus; 3) approximately 5-10% of supramammillary cells were double-labeled, ipsilaterally, and 2-4%, contralaterally, with injections in medial or lateral parts of the medial septum and the dentate gyrus of the hippocampus; and 4) approximately 3-5% of supramammillary cells were double-labeled, ipsilaterally, and 1-2%, contralaterally, with injections in the medial septum and CA2/CA3a of the dorsal hippocampus. Cells of the supramammillary nucleus have been shown to fire rhythmically in bursts synchronous with the hippocampal theta rhythm and have been implicated in the generation of the theta rhythm. The supramammillary cells that we identified with collateral projections to the septum and hippocampus may be directly involved in generation of the theta rhythm.     

Modulation of visually evoked responses in units of the ventral lateral geniculate nucleus of the rat by somatic stimuli

Single unit activity was recorded from the ventral part of the lateral geniculate nucleus (vLGN) in rats anaesthetized with urethane. Most of the cells located laterally in the nucleus were excited by light. The studied vLGN neurones did not respond to electrical stimulation of the tail, but about half of them changed their response to light significantly when the light flash was paired with the electrical stimulation. When the tail stimulus preceded the light, the changes consisted in a pronounced facilitation of flash-evoked activity. When the electrical stimulus was applied after the flash in a forward conditioning paradigm, facilitations were less pronounced and responses of some neurones were suppressed. These results are in contrast to those of similar experiments on the dorsal LGN, neurones of which were mainly facilitated by the conditioning paradigm. Thus, light-evoked activity of ventral geniculate cells can be enhanced by arousal-related processes.     

The Development of Retinal Ganglion Cell Decussation Patterns in Postnatal Pigmented and Albino Ferrets

The decussation patterns of retinal ganglion cells in postnatal pigmented and albino ferrets were examined by using retrograde axonal tracers. Following unilateral injections into the optic pathway of newborn pigmented ferrets, ∼ 13 000 cells were labelled in the ipsilateral retina. The majority (11 500) of these were located in temporal retina. Postnatally, the numbers of cells projecting ipsilaterally from temporal retina fell by 49%. High rates of loss were observed in both the smaller uncrossed projection from nasal retina (92%) and also in the crossed projection from temporal retina (84%). After injections on the day of birth, a decussation line was not obvious in the crossed projection: ≥ 14 000 labelled cells were found in temporal retina. Double tracer studies showed that very few of these cells had axons which projected bilaterally. The numbers of ipsilaterally projecting cells labelled in neonatal albino ferrets was dramatically reduced. Only ∼ 2500 were labelled in temporal retina following injections at birth. As in pigmented ferrets, about half of these cells subsequently died. The reduced uncrossed projection in albino neonates was asociated with an increase in the crossed projection from temporal retina, in which ∼ 21 000 cells were labelled following injections at birth. These results suggest that differential postnatal ganglion cell death establishes the adult decussation pattern in the contralateral retinal projection but merely refines the pattern already established in the uncrossed projection. Postnatal ganglion cell death plays no significant role in generating the abnormal projections found in albino ferrets.     

Neurons in the superficial dorsal horn of the rat spinal cord projecting to the medullary ventrolateral reticular formation express c-fos after noxious stimulation of the skin

The nociceptive nature of the neurons of the superficial dorsal horn (laminae I–III) which project to the medullary ventrolateral reticular formation is studied in the rat. Medullary injections of Fluoro-Gold showed exclusive retrograde labeling of laminae I–III cells when the tracer filled a zone intermediate between the lateral tip of the lateral reticular nucleus and the spinal trigeminal nucleus, pars caudalis. This zone is here called VLMlat. Following noxious mechanical or thermal stimulation of the skin, double-labeled neurons, which stained retrogradely and were Fos-immunoreactive, prevailed in laminae I and IIo. Double-labeled neurons were few in lamina IIi after thermal stimulation and entirely lacking in lamina III after the two kinds of stimulation. Findings in lamina I confirm previous electrophysiological data (see Menétrey et al.,J. Neurophysiol., 52 (1984) 595–611) showing that lamina I cells projecting to the ventrolateral reticular medulla convey noxious messages. The occurrence of numerous double-labeled cells in lamina IIo suggests that this lamina is also involved in nociceptive transmission to the VLMlat.     

Localization of parabrachial nucleus neurons projecting to the thalamus or the amygdala in the cat using horseradish peroxidase.

Topographical localization of parabrachial nucleus (PBN) neurons projecting directly to the thalamus or the amygdala was examined in the cat by the horseradish peroxidase (HRP) method. After HRP injection in the central nucleus of the amygdala, PBN neurons labeled with the enzyme were seen ipsilaterally in the ventral portion of the lateral PBN as well as in the medial PBN. When the HRP injections were centered on the parvocellular portion of the posteromedial ventral nucleus of the thalamus (VPMpc), HRP-labeled neurons were observed ipsilaterally in the dorsal portion of the lateral PBN as well as in the medial PBN. Within the medial PBN, the distribution of neurons projecting to the amygdala overlapped that of neurons projecting to VPMpc; the cell bodies of the former neurons, however, tended to be more elongated than the latter, and the mean of the average soma diameters of the former was significantly larger than the latter. On the other hand, in the lateral PBN no significant differences were noted between the means of the average soma diameters of neurons projecting to VPMpc and those projecting to the amygdala. The PBN neurons in the cat were presumed to transmit gustatory and general visceral information ipsilaterally to the thalamic taste region and the limbic areas in the basal forebrain.     

Retinal ganglion cell death and terminal field retraction in the developing rodent visual system

The anterograde and retrograde transport of HRP has been employed in neonatal rats and adult rats which were unilaterally enucleated at various stages during the first week after birth. In neonatal animals given unilateral thalamic implants of horseradish peroxidase, the number of labelled retinal ganglion cells in the ipsilateral eye declines over the first week. This is considered to be a consequence of cell death. At the same time unilateral intraocular injections of the same tracer reveals that the terminal field of ipsilaterally projecting retinal axons in the dorsal lateral geniculate nucleus is retracting to form the adult pattern. It is proposed that retraction and ganglion cell death are related. In the monocular adult animals it is shown that fewer ipsilaterally projecting ganglion cells are found the later enucleation takes place. But the number of ipsilaterally projecting cells found in the adult animal enucleated at birth is not as great as the number found in the newborn rat. In spite of this the proportion of the dorsal lateral geniculate nucleus occupied by ipsilaterally projecting ganglion cells is similar in neonates of a given age and adults that were enucleated at that age.     

Demonstration of direct input from the retina to the lateral habenular nucleus in the albino rat

The projection from the retina to the habenular complex was studied using fluorescent retrograde tracers in the albino rat (Wistar, Japan Clea). Following separate unilateral injections of Fluoro-Gold (FG), Fluoro-Ruby (FR), or 4-acetamido,4′-isothiocyanostilbene-2,2′-disulfonic acid (SITS) into the lateral habenular nucleus (LHB), a small population of ganglion cells was labeled sporadically, predominantly those in the nasal retina contralateral to each injection site. Most of them were small cells, ranging from 9 to 16 μm in diameter, roughly corresponding to the type III ganglion cell in the rat retina. Additionally, all of the structures previously described as regions projecting to the LHB were confirmed. Upon re-examination of previous brain sections of albino rats which had undergone monocular enucleation, degenerating retinal nerve axons and/or their terminals, stained by a modified selective silver impregnation method, were observed in the well-documented end regions of retinal afferents as well as the LHB. The degenerating retino-habenular nerve terminals were distributed sparsely and restricted mainly to the caudal part of the LHB contralateral to the side of ocular enucleation. The present experimental data provide evidence for the existence of a non-image forming retino-habenular pathway in the albino rat. We suggest that, besides serving as a point of convergence for some of the major conduction channels of the limbic and striatal systems, the LHB may play more general integrative roles, including participation in the integration of visual information.     

Distribution of bulbospinal neurons supplying bilateral innervation to the phrenic nucleus in the rat.

The location of bulbospinal neurons with axon collaterals in both phrenic nuclei were determined by injecting two different fluorescent tracers into the right and left C4 cervical spinal cord. In contrast to single-labeled neurons that were found throughout the rostrocaudal extent of the medulla, the majority of double-labeled neurons were located in the rostral ventral respiratory group. Only a few double-labeled neurons were found in the ventrolateral nucleus of the solitary tract. The role of this bilateral pathway in synchronizing the activity of the phrenic nucleus is discussed.     

Organization of efferent projections from the internal segment of globus pallidus in primate as revealed by flourescence retrograde labeling method

The exact cellular origin and the degree of collaterlization of the major efferent projections from the internal segment of globus pallidus (GPi) in squirrel monkey (Saimiri sciureus) were studied using Evans blue (EB) and a mixture of DAPI-primuline (DP) as retrograde fluorescent tracers. After the conconmitant of EB in VA/VL thalamic nuclei and of DP in habenula on the same side, numerous EB-labeled cells were found in the central portion of GPi compared to a much smaller number of DP-labeled neurons mostly encountered at the periphery of GPi. Only very few double-labeled cells were visualized in these experiments indicating that the pallidohabenular and pallidothalamic pathways arise largely from two different cell populations, each having a preferential distribution in GPi. On the other hand, a multitude of both EB- and DP-labeled cells occurred in the central portion of GPi after the concomitant injection of EB in VA/VL nuclei and of DP in nucleus tegmenti pedunculopontinus of the midbrain tegmentum. Although the EB-labeled cells tend to be more abundant in the dorsolateral half, and the DP-labeled cells more numerous in the ventromedial half of GPi, about 70–75% of the cells in the core of GPi were double-labeled in such a case. This indicates that the pallidothalamic and pallidotegmental fibers arise largely from the same neurons in the core of GPi. A number of DP-labeled cells was also found in the contralateral GPi revealing that the pallidotegmental pathway is partly (15–20%) crossed. In addition, numerous DP-labeled cells (projecting to brain stem) occured in the medial two-thirds of the substantia nigra pars reticulata (SNr), whereas EB-labeled cells (projecting to the thalamus) abounded in the lateral third of SNr. A small number of double-labeled SNr cells were also encountered after thalamus-midbrain injection.These findings suggest that in regard to its output elements, the primate GPi is organized according to a complex pattern consisting of: (1) a central ‘motor’ zone where most neurons send axonal branches to both thalamus and midbrain; and (2) a peripheral ‘limbic’ zone which encroaches largely upon the lateral hypothalamus and whose cells project only to habenula. These two pallidal zones are furthermore embedded in a peripallidal neuronal network composed of large acetylcholinesterase-containing cells related to nucleus basalis and projecting diffusely to neocortex.     

Ultrastructural organisation of the projection from the superior colliculus to the ventral lateral geniculate nucleus of the rat

Retinorecipient regions of the ventral lateral geniculate nucleus of the thalamus and the superior colliculus of the midbrain are linked by reciprocal axonal projections. In this study we have investigated the ultrastructural characteristics, the distribution, and the postsynaptic targets of the terminals of axons projecting to the ventral lateral geniculate nucleus from the superior colliculus. Horseradish peroxidase was injected into the superior colliculi of adult albino rats, and the Hanker-Yates method was used to visualize anterogradely and retrogradely transported peroxidase in the ventral lateral geniculate nuclei 24 hours following the injection. Labelled terminals were found in the lateral and ventrolateral parts of the external division of the ipsilateral ventral lateral geniculate nucleus. The labelled terminals were confined to areas of simple, nonglomerular neuropil. They were 0.45-1.5 micron in diameter; contained small, dark mitochondria and spherical synaptic vesicles; and established Gray type I (asymmetrical) synaptic contacts with the dendritic shafts, dendritic spines, and occasionally cell bodies of cells with the ultrastructural characteristics of projection cells. A few labelled terminals established synaptic contact with retrogradely labelled cells. Thus, in the rat, the projection from the superior colliculus gives rise to a uniform population of axon terminals in the nonglomerular neuropil of the lateral portion of the ventral lateral geniculate nucleus, which synapse with, and are probably excitatory to, geniculocollicular and other projection cells.     

Responsiveness of suprachiasmatic and ventral lateral geniculate neurons to serotonin and imipramine: a microiontophoretic study in normal and imipramine-treated rats

The suprachiasmatic nuclei (SCN) are a major pacemaker of circadian rhythms in mammals. The SCN receive a direct retinal projection and a second optic input via the ventral lateral geniculate nucleus (vLGN). Both visual pathways mediate the entrainment of circadian rhythms, whereas both the SCN and the vLGN receive serotonergic afferents from the raphe nuclei. We investigated the effects of microiontophoretically applied serotonin (5HT) on SCN and vLGN cells in normal rats and rats chronically treated with the 5HT reuptake blocker imipramine (IMI). In the SCN of both groups over 40% of all recorded cells (N = 80) responded to 5HT with a dose-dependent suppression of their spontaneous or glutamate-evoked discharge, while twenty percent were tonically light-responsive. Except for one cell with an inconsistent 5HT response, none of the visual SCN neurons were 5HT-sensitive. In the vLGN of normal and IMI-treated rats about 60% of the cells recorded (N = 42) were inhibited by 5HT. In IMI-treated rats a few cases of excitation by 5HT were encountered in the vLGN. Visual as well as non-visual vLGN cells were responsive to 5HT. Microiontophoretic application of IMI resulted in suppression of electrical activity in both brain regions and enhanced the response induced by 5HT. Chronic IMI-treatment produced a significant increase in the sensitivity of cells in the SCN and vLGN to iontophoresed 5HT, without affecting the relative magnitude of the inhibition. The recovery from 5HT-induced inhibition was slow in these animals. Interestingly, the spontaneous discharge rate of both 5HT-sensitive and 5HT-insensitive SCN and vLGN cells was significantly lower in the imipramine-treated group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution of neurons in the lateral pontine tegmentum projecting to thoracic, lumbar and sacral spinal segments in the cat

The course of descending fibers projecting to the spinal cord and the arrangement of their parent cells located in various nuclei of the dorso-lateral pontine tegmentum were studied using the horseradish peroxidase (HRP) retrograde axonal transport technique. Retrogradely labeled neurons were found in the locus coeruleus (LC), subcoeruleus (SC), K?lliker-Fuse nucleus (KF) and in the lateral parabrachial nucleus (LPB) after HRP injections into various spinal segments. Neurons innervating the thoracic spinal cord were found to be arranged in the ventral portion of the LC and in the entire SC; their axons descended ipsilaterally. Neurons with descending axons to lumbar segments were seen mainly in the ventral portion of the LC and in the medial portion of SC. Most of their axons were also seen to descend ipsilaterally. Neurons projecting to sacral segments occurred in the entire LC and in the medial portion of the SC. Large part of descending fibers crossed the midline at the level of (or near) the termination site. Neurons of all portions of the KF and LPB projected to the thoracic spinal cord only ipsilaterally, while many descending fibers innervating the sacral segments crossed the midline.     

Class-specific cell death shapes the distribution and pattern of central projection of cat retinal ganglion cells

The development of the nasotemporal division in cat retina was studied. We find that in the normally pigmented neonatal cat significant numbers of ganglion cells of all types in temporal retina project to the contralateral dorsal lateral geniculate nucleus (LGNd); far fewer cells in temporal retina project contralaterally to the LGNd in the normal adult. Thus, most of these cells must be eliminated during development. Experimental interruption of one optic tract in the neonate results in the retrograde degeneration of the ipsilaterally projecting ganglion cells in the temporal retina ipsilateral to the lesion. Consequent to the loss of the ipsilaterally projecting cells in this hemiretina, many of the ganglion cells projecting to the intact contralateral LGNd, which are normally eliminated, survive. Also, unlike in the normal cat, in which very few of the small ganglion cells in temporal retina project contralaterally to the thalamus, in optic tract sectioned (OTX) cats, significant numbers of the smallest ganglion cells in the temporal retina ipsilateral to the lesion project contralaterally to the intact thalamus. In order to make a quantitative comparison of the distributions of ipsilaterally and contralaterally projecting cells in the temporal retinae of normal cats, OTX cats, and neonatal kittens, it was necessary to determine the position of the vertical meridian in all animals. We defined the vertical meridian as the median edge (Stone, 1966). The median edge was determined from the distribution of the most nasally located, ipsilaterally projecting cells in temporal retina. The results indicate that the angle of the vertical meridian (median edge) with respect to the area centralis and optic disc is specified before birth and does not differ in normal cats, OTX cats, or neonatal kittens. Since the location of the vertical meridian does not change with age in postnatal life and is not affected by optic tract section, corresponding regions of retina in the different groups could be compared. A quantitative analysis of ganglion cell density in the temporal retina contralateral to the section, ipsilateral to the intact hemisphere, indicated that there was a reduction in the population of ipsilaterally projecting ganglion cells that was complementary to the abnormally large number of contralaterally projecting cells surviving in the temporal retina ipsilateral to the lesion.(ABSTRACT TRUNCATED AT 400 WORDS)     

Retinal projections to the superior colliculus and dorsal lateral geniculate nucleus in the tammar wallaby (Macropus eugenii): I. Normal topography

The topography of retinal projections to the superior colliculus and dorsal lateral geniculate nucleus of a wallaby, the tammar (Macropus eugenii), was investigated by an anatomical method. Small laser lesions were made in the retinas of experimental animals, and the remaining retinal projections were visualized by means of horseradish-peroxidase histochemistry. The position of each lesion was correlated with the position of the filling defects in the terminal label. The whole of the retina projects to the contralateral superior colliculus. The nasal retina is represented caudally, and the temporal retina rostrally. The ventral retina is represented medially, and the dorsal retina laterally. There is a projection to the ipsilateral superior colliculus, but it is patchy and its topography could not be determined by this method. The retinotopic map in the contralateral dorsal lateral geniculate nucleus has the nasal retina represented rostrally and the temporal retina caudally in the nucleus. The dorsal retina is represented ventrally, and the ventral retina is represented dorsally. It appears that the whole of the retina projects contralaterally, and in addition the temporal retina projects ipsilaterally. The maps of visual space through the two eyes were shown to be in topographic register in the binocular region by making a deposit of HRP in the visual cortex. This resulted in a column of retrogradely labeled cells in the nucleus. This column crossed the laminae, which are innervated by the ipsilateral and contralateral eye at right angles.