Receptive field properties of rat ventral lateral geniculate cells projecting to the superior colliculus

Cells of the ventral lateral geniculate nucleus (LGV) in rats sending their axons to the superior colliculus (SC), were identified electrophysiologically as the ones responding antidromically to electrical stimulation of SC. They were located in the external part of LGV. Visual receptive fields of these cells were mostly of ON-tonic types and some of movement-sensitive ones. Evidence was presented supporting existence of the reciprocal fiber connection between the LGV and the SC.     

Afferent projections to the ventral lateral geniculate nucleus in the cat

Horseradish peroxidase (HRP) injections were made into the dorsal lateral geniculate nucleus (LGN_d) and ventral lateral geniculate nucleus (LGN_v) of the cat in order to define afferent projections to LGN_v. These were found from the superior colliculus, contralateral LGN_v, dorsal median raphe nucleus, locus coeruleus, ipsilateral pretectum, and various portions of visual cortex. While many cortical areas project to LGN_v (17, 18, 19, 21 and lateral suprasylvian), the heaviest input arises from areas 17 and 20. The cell bodies of origin are in layer 5 in contrast to layer 6 which projects to LGN_d.     

The visual field representation of the rat ventral lateral geniculate nucleus

The representation of the visual field in the ventral lateral geniculate nucleus (LGNv) was studied in rats anesthetized with urethane by recording the response of single units to visual stimulation. Receptive fields of LGNv units were plotted on a campimeter, 60 cm in diameter, which was placed 30 cm from the contralateral eye. LGNv neurons responded mainly to stimulation of the contralateral eye with on-tonic characteristics. Few neurons responded only to stimulation of the ipsilateral eye and no binocular interaction was observed. Retinotopic organization was clearly seen in the LGNv; the nasal visual fields were represented dorsally, the temporal fields ventrally, and the upper to lower visual fields were in the rostrolateral to caudomedial parts of the LGNv. A given point in the visual field is represented along a line running through the LGNv in a rostrocaudal direction. Almost the entire horizontal extent of the contralateral visual field was represented in the LGNv, whereas vertically the visual field between 40 degrees above and 20 degrees below the distribution axis was represented. The major axis of the strip of the visual field containing all the RF centers, which is referred to as the distribution axis, inclined nasally up and temporally down at an angle of 10.4 degrees to the 0 degree horizontal meridian line. The representation of the distribution axis in the retina was in accordance with the major axis of retinal ganglion cell distribution (Fukuda, '77; Schober and Gruschka, '77).     

Ground squirrel ventral lateral geniculate receives laminated retinal projections

Retinal projections to ground squirrel ventral lateral geniculate (VLG) nucleus were studied with anterograde axonal transport methods. Results indicate that VLG may be divided into 5 laminae: 3 contralateral projection fields are interleaved with 2 ipsilateral projections.     

Properties of cells responding to visual stimuli in the rat ventral lateral geniculate nucleus

Single-unit recordings were made of the ventral lateral geniculate nucleus (LGv) in the albino rat anesthetized with urethane. Visual receptive field properties as well as the characteristics of responses elicited by electrical stimuli to the optic tract and to the visual cortex were examined. Compared with the relay cells of the dorsal lateral geniculate nucleus (LGd), LGv cells were characterized by the following properties. (i) They responded to visual cortex stimuli orthodromically as well as to optic tract shocks. (ii) The postexcitatory inhibition they showed after single optic tract or visual cortex stimuli was only short-lasting, at most 100 ms. (iii) Conduction velocities of the optic nerve afferent fibers were mostly in the range of slow fibers, 2 to 10 m/s. (iv) The receptive fields were essentially homogeneous in type; about 90% of the sample of 53 cells were On-tonic. (v) Receptive field sizes were substantially large, from 6.3 to 45.6° (mean, 22.3°). (vi) On-tonic cells revealed a regular maintained discharge whose level changed monotonically as a function of the luminous intensity of the stimulating light. The functional implications of these findings were compared with those of the relay cells in the LGd.     

Ventral lateral geniculate nucleus afferents to the suprachiasmatic nucleus in the cat

The lateral geniculate complex innervates the hypothalamic suprachiasmatic nucleus (SCN). The location of neurons in the cat ventral lateral geniculate nucleus (vLGN) that give rise to the geniculohypothalamic tract has not been described. In this study, retrogradely labeled neurons were noted throughout the rostrocaudal extent of the medial vLGN following tracer injection into the SCN region. In addition, neuropeptide Y immunoreactive processes were also observed in the vLGN in this same medial zone and in the SCN. The data suggest that the medial zone of the cat vLGN may be homologous to the rodent intergeniculate leaflet (IGL).     

Visual function in the ventral lateral geniculate nucleus of the cat

The visual receptive fields of 293 single units in the ventral lateral geniculate nucleus of the cat were studied. In addition to the wide variety of types described by others, a group of units responding differentially to color was identified that included units responding particularly to blue and others with opponent color properties. Some units with spontaneous firing and without definite visual receptive fields were inhibited by stimulation of the optic chiasm (OX). A study of latency of firing to OX stimulation suggested that these cells were driven by retinal ganglion cells of the W type. One-third of all units studied were binocularly driven.     

Double-labeling of neuropeptide Y-immunoreactive neurons which project from the geniculate to the suprachiasmatic nuclei

A projection from the ventral geniculate area to the suprachiasmatic nuclei (SCN) has been demonstrated in rats and hamsters. Large lesions in this area of the geniculate cause a dramatic decrease in neuropeptide Y-immunoreactivity in the SCN. Since numerous neuropeptide Y-immunoreactive neurons are found in the lateral geniculate area, we and others proposed that these immunoreactive neurons project to the SCN. In the present study, neurons in the lateral geniculate area of golden hamster brains were examined for both neuropeptide Y-immunoreactivity and a retrograde tracer transported from the SCN. Two days after a pressure injection of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) into the SCN of hamsters, labeled neurons were found in the intergeniculate leaflet and in the external lamina of the anterior ventral lateral geniculate nucleus (VLGN). These neurons were compared with similarly located neurons which showed immunoreactivity for neuropeptide Y. Morphometric comparisons of neuropeptide Y- and WGA-HRP-labeled neurons indicated that they were comparable in terms of soma size, number of dendrites, orientation and localization. In additional hamsters, neurons double-labeled with a retrograde tracer and neuropeptide Y-immunoreactivity were localized in the intergeniculate leaflet and in the external lamina of the anterior VLGN. These results demonstrate that many neuropeptide Y-immunoreactive neurons located in both the intergeniculate leaflet and in the external lamina of the anterior VLGN project to the SCN in hamsters.     

Origin of butyrylcholinesterase in the lateral geniculate nucleus of tree shrew

We examined the distribution and possible origins of pseudocholinesterase activity within the lateral geniculate nucleus (LGN) of the tree shrew. Butyrylcholinesterase (BuChE) activity was spread diffusely throughout the LGN and not localized to neuronal perikaryon. Lesions of the LGN eliminated this BuChE activity while not affecting acetylcholinesterase (AChE) activity; however, removal of retinal input by unilateral ocular enucleations failed to affect the BuChE activity within the denervated layers of the LGN. This lack of effect suggests that, unlike the macaque monkey, retinal terminals within the LGN of tree shrew are not the source of BuChE. Thus, in the tree shrew LGN it appears that BuChE is not metabolically related to or dependent upon AChE nor does it originate from retinal sources, but rather BuChE appears to represent an enzyme that is endogenous to the LGN.     

Contrast invariance of orientation tuning in the lateral geniculate nucleus of the feline visual system

Responses of most neurons in the primary visual cortex of mammals are markedly selective for stimulus orientation and their orientation tuning does not vary with changes in stimulus contrast. The basis of such contrast invariance of orientation tuning has been shown to be the higher variability in the response for low‐contrast stimuli. Neurons in the lateral geniculate nucleus (LGN), which provides the major visual input to the cortex, have also been shown to have higher variability in their response to low‐contrast stimuli. Parallel studies have also long established mild degrees of orientation selectivity in LGN and retinal cells. In our study, we show that contrast invariance of orientation tuning is already present in the LGN. In addition, we show that the variability of spike responses of LGN neurons increases at lower stimulus contrasts, especially for non‐preferred orientations. We suggest that such contrast‐ and orientation‐sensitive variability not only explains the contrast invariance observed in the LGN but can also underlie the contrast‐invariant orientation tuning seen at the level of the primary visual cortex.     

Identification of retinal ganglion cells projecting to the lateral hypothalamic area of the rat

The objective of the present study was to identify the retinal ganglion cells projecting to the lateral hypothalamic area of the rat. The retinohypothalamic tract has been divided into a medial and a lateral component on anatomical and developmental grounds. The medial component projects to the suprachiasmatic nucleus and adjacent structures such as the anterior hypothalamic and retrochiasmatic areas. The lateral component terminates in the lateral hypothalamic area dorsal to the supraoptic nucleus. Injections of the retrograde tracer FluoroGold were made into the retinorecipient region of the lateral hypothalamic area and retinal whole mounts were immunohistochemically processed for retrogradely labeled retinal ganglion cells. With FluoroGold injections confined to the lateral hypothalamic area, retrogradely labeled retinal ganglion cells are located almost exclusively in the superior temporal quadrant of the retina. Their size and morphology indicates that they are a homogenous subset of type III cells, but a definitive classification would require a more complete fill of dendritic arbors than is available in our retrograde material. In contrast, injections involving fibers of passage in the optic tract, or centered in the medial terminal nucleus of the accessory optic system, label cells distributed across the entire retinal surface. Unlike the retinal ganglion cells projecting to the suprachiasmatic nucleus [Moore et al., J. Comp. Neurol., 352 (1995) 351–366], the cells labeled after restricted lateral hypothalamic injections are not distributed evenly across the retinal surface. The difference in location of the retinal ganglion cells projecting to the lateral hypothalamic area supports the view that this retinohypothalamic projection is anatomically and functionally distinct from the projection to the suprachiasmatic nucleus and adjacent medial hypothalamus.     

Monosynaptic excitation of principal cells in the lateral geniculate nucleus by corticofugal fibers

Electrical stimulation of the primary visual cortex evoked long latency EPSPs in X and Y principal cells of the cat's lateral geniculate nucleus. An extrapolation procedure was used to reveal that these EPSPs were mediated monosynaptically to principal cells by slowly conducting corticogeniculate fibers. A similar type of excitation was observed in intrageniculate interneurons.     

Identification of ventral lateral geniculate nucleus cells projecting to the pretectum and superior colliculus in the cat

Among 235 histologically identified cells of the ventral lateral geniculate nucleus (LGV) in the cat, 66 responded antidromically to electrical stimulation of the pretectum (PT) and/or superior colliculus (SC): 22 projected to PT, 22 to SC and 22 to both sites. The LGV cells were innervated by optic tract fibers corresponding to axons of X- as well as W-type retinal ganglion cells.     

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 organization of retinal maps within the dorsal and ventral lateral geniculate nuclei of the rabbit

The cytoarchitectonic subdivisions in the rabbit's dorsal and ventral lateral geniculate nuclei have been related to the several retinal maps that can be defined in terms of the distribution of retinal axons within these nuclei. Destruction of different retinal sectors was combined with intravitreal injections of ³H-proline, so that the distribution of fiber degeneration and autoradiographic label in the geniculate nuclei could be used to define the retinal maps in each nucleus, and to compare the two nuclei with each other. The two nuclei show surprisingly similar patterns of organization. Each is made up of a laminated alpha sector that curves around a relatively cell-sparse beta sector. Two morphologically distinct layers of each alpha sector receive contralateral retinal afferents and between these there is a small region in receipt of ipsilateral afferents. In each nucleus, the lines of projection that represent single points in visual space pass perpendicular to the layers of the alpha sector and continue an almost straight course into the beta sector. Quantitative comparisons of the retinal maps show that the relative volumes devoted to the representation of segments of the visual field are approximately the same in the two nuclei.     

Elimination of neurons from the rhesus monkey's lateral geniculate nucleus during development

The timing, magnitude, and spatial distribution of neuron elimination was studied in the dorsal lateral geniculate nucleus of 57 rhesus monkeys (Macaca mulatta) ranging in age from the 48th day of gestation to maturity. Normal and degenerating cells were counted in Nissl-stained sections by using video-enhanced differential interference contrast optics and video-overlay microscopy. Before embryonic day 60 (E60), the geniculate nucleus contains 2,200,000 +/- 100,000 neurons. Roughly 800,000 of these neurons are eliminated over a 40- to 50-day period spanning the middle third of gestation. Neurons are lost at an average rate of 300 an hour between E48 and E60, and at an average rate of 800 an hour between E60 and E100. Very few neurons are lost after E100, and as early as E103 the population has fallen to the adult average of 1,400,000 +/- 90,000. Degenerating neurons are far more common in the magnocellular part of the nucleus than in the parvicellular part. In 20 of 29 cases, the number of neurons is greater on the right than on the left side. The right-left asymmetry averages about 8.5% and the difference is statistically significant (phi 2 = 38, p less than .001). The period of cell death occurs before the emergence of cell layers in the geniculate nucleus, before the establishment of geniculocortical connections, and before the formation of ocular dominance columns (Rakic, '76). Most important, the depletion of neurons in the geniculate nucleus begins long before the depletion of retinal axons. The number of geniculate neurons is probably a key factor controlling the number of the retinal cells that survive to maturity.     

Shrinkage of cells in undeprived laminae of the monkey lateral geniculate nucleus following late closure of one eye

Measurements of mean cell area have been made in the lateral geniculate nuclei of 16 normal rhesus monkeys as a control for changes following visual deprivation. There is little variability between animals and no significant growth between 8 days of age and adulthood in the parvocellular laminae. The magnocellular laminae show more variability and some continuing growth after 8 days of age.     

Quantitative analysis of the lateral geniculate nucleus in the mutant microphthalmic rat

A quantitative analysis of the lateral geniculate nucleus was carried out in the mutant microphthalmic rat. In the dorsal lateral geniculate nucleus (LGNd) of the microphthalmic rat we found the total volume and neuronal population were reduced by 45 and 68% of normal values, respectively. The size of normal LGNd neurons was 8 to 20 μm and that of mutant LGNd cells from 6 to 16 μm. Neurons of the normal LGNd were medium-size and round or oval, and their cell bodies were filled with Nissl substance. Microphthalmic LGNd neurons, on the other hand, had narrow cytoplasmic spaces with few Nissl granules, and pale cell nuclei. In the microphthalmic rat, the lateral part of the ventral lateral geniculate nucleus (LGNvl) also showed a marked reduction in the total volume and neuronal population which were 42 and 76% of normal values, respectively. The size of normal LGNvl neurons was 8 to 20 μm and that of the microphthalmic neurons from 6 to 16 μm. These findings suggested that a marked reduction in the size of the LGNd and LGNvl in the mutant can be attributed to a decrease in neuronal population to a diminution of cell size.     

Different distributions of large and small retinal ganglion cells in the cat after HRP injections of single layers of the lateral geniculate body and the superior colliculus

Retinal ganglion cells were labeled with HRP after injecting layers of GL or single strata within the stratum griseum superficiale (SGS). Only small cells were labeled after injecting small cell C layers and upper SGS. Only large cells were labeled after injecting lower SGS. Small and large cells were labeled after injecting medial interlaminar nucleus (MIN) and layers A and A₁.     

Retinal ganglion cells projecting to the dorsal raphe and lateral geniculate complex in Mongolian gerbils

Injections of rhodamine-B into the dorsal raphe nucleus (DRN) and Fluoro-Gold into the lateral geniculate nucleus (LGN) revealed double-labeled retinal ganglion cells (DL RGCs) projecting to both nuclei. The soma-size distribution of DL RGCs was compared with three other distributions: DRN-projecting RGCs, LGN-projecting RGCs, and a large sample of RGCs labeled via the optic nerve with DiI. DL RGC soma diameters fell primarily within the mid-to-upper size range of all three distributions. DL RGCs may provide information to both nuclei concerning comparable aspects of light and visual stimulation via collateralized axons.