Ventral Lateral Geniculate Nucleus Research Articles

The effects of neonatal monocular enucleation on the organization of ipsilateral and contralateral retinothalamic projections in the rabbit

Autoradiographic methods were used to compare the ipsilateral and contralateral retinothalamic projections in pigmented Dutch-Belted rabbits that had neonatal monocular enucleation with the projections found in normally reared rabbits. In the normal adult rabbit, there is dense label throughout the dorsal lateral geniculate nucleus (LGd) except for a decreased label density in the region corresponding to the ipsilateral input. Following neonatal monocular enucleation, the contralateral projection fills in the part of the LGd corresponding to the ipsilateral input. Our data indicate that following monocular enucleation, two processes occur: an arrest of the segregation process and an expansion of the contralateral projection into the space normally containing the terminals of the ipsilateral projection. In addition, this filling in of the terminal space occurs relatively rapidly and is completed by day 14. No changes, however, were observed in the ipsilateral projection to the LGd. Unlike the LGd, the ventral lateral geniculate nucleus and the intergeniculate leaflet showed increases in the size of the ipsilateral projection region, and no changes in the contralateral projection. The present findings suggest that there may be different mechanisms governing whether alterations in the distribution of retinothalamic projections will occur in either the ipsilateral or contralateral nucleus.

Circadian variation in sensitivity of suprachiasmatic and lateral geniculate neurones to 5-hydroxytryptamine in the rat.

Extracellular single-unit recordings were obtained from neurones in the suprachiasmatic nuclei (s.c.n.) of the rat (a putative circadian pace-maker), the ventral lateral geniculate nucleus (v.l.g.n.) and the hippocampus. These areas receive a 5-hydroxytryptamine (5-HT) innervation from the raphe nuclei. Recording of neuronal activity in the s.c.n., v.l.g.n. and the hippocampus revealed a diurnal variation in the response to the ionophoresis of 5-HT. This variation was manifest as a 2-3-fold increase in post-synaptic sensitivity to 5-HT during the subjective dark (active) phase of the circadian cycle. In contrast there was no apparent circadian variation in the sensitivity of s.c.n., v.l.g.n. or hippocampal neurones to ionophoresed gamma-aminobutyric acid (GABA). Neuronal activity recorded in the s.c.n., v.l.g.n. and hippocampus also exhibited a circadian variation in the recovery from 5-HT-induced suppression of firing. This may reflect reuptake processes as recovery can be prolonged by ionophoresis of uptake blockers (imipramine or fluoxetine). Rats (n = 15) expressing circadian arrhythmicity in their rest-activity behaviour induced by long-term continuous illumination (150-200 lx) showed no apparent circadian variation in 5-HT sensitivity. This loss was accompanied by either the development of a 5-6-fold subsensitivity to ionophoresed 5-HT (eleven out of fifteen rats) or a 2-3-fold supersensitivity to ionophoresed 5-HT (four out of fifteen rats). A similar loss of circadian variation and the development of a subsensitivity to ionophoresed 5-HT was also found in three rats sustaining complete electrolytic lesions of the s.c.n. These changes were not found in rats (n = 4) with partial s.c.n. lesions. These results implicate the s.c.n., or fibres passing through it, in the circadian modulation of 5-HT sensitivity in neurones both intrinsic to the s.c.n. circadian pace-maker itself and in the hippocampus and lateral geniculate nucleus (regions remote from the s.c.n.).

Control of cell number in the developing visual system. I. Effects of monocular enucleation

Monocular enucleation of hamsters on the day of birth caused an increase in cellular degeneration and a corresponding loss of cells in the dorsal lateral geniculate nucleus contralateral to the enucleation over the first 12 postnatal days. The superficial layers of the contralateral superior colliculus showed a similar increase in cell degeneration, except rostrally where the remaining ipsilateral projection is found. No changes in degeneration were found in either the ipsi- or contralateral ventral lateral geniculate nuclei, the intermediate and deep layers of the superior colliculus, or in the dorsal lateral geniculate and superficial superior colliculus ipsilateral to the enucleation, even though all were denervated to some degree. The disparities in the incidence of degenerating cells normally seen in the central and peripheral regions of the superior colliculus and dorsal lateral geniculate were preserved following the monocular enucleation. The incidence of degenerating cells in early development correlates well with known alterations in adult cell number. Only major denervations of retinal targets appear to be adequate to produce measurable changes in early cellular degeneration.

Optic tectum of the eastern garter snake, Thamnophis sirtalis. I. Efferent pathways.

Extracellular, iontophoretic injections of horseradish peroxidase were used to anterogradely fill axons efferent from the optic tectum in garter snakes. The tectal efferent pathways consist of six axon types with distinct projections and terminal morphologies. Tectogeniculate axons pass into the diencephalon via the optic tract, bearing collaterals that form spatially restricted, rodlike arbors in the pretectum, the ventral lateral geniculate nucleus, and the ventrolateral nucleus. Tectoisthmi axons exit the tectum as a thin-caliber component of the ventral tectobulbar tract. They form spatially restricted, spherical arbors within nucleus isthmi. Tectoisthmobulbar axons also give rise to small, spherical arbors within nucleus isthmi, but the parent axons continue caudally into the pontine and medullary reticular formation issuing many short collateral branches. Tectorotundal axons reach the diencephalon via the tectothalamic tract and give rise to fine terminal collaterals in the nucleus of the tectothalamic tract ipsilaterally and in nucleus rotundus bilaterally. Single axons form sheetlike terminal fields that span the rostrocaudal extent of nucleus rotundus. Ipsilateral tectobulbar axons descend into the midbrain tegmentum where they issue several thick collaterals that terminate widely throughout the nucleus lateralis profundus mesencephali. The parent axon continues caudally giving off several widely spreading collaterals within the pontine and medullary reticular formation. Crossed tectobulbar axons enter the dorsal tectobulbar tract and cross the midline to form the predorsal bundle. Single axons give rise to terminal collaterals in the nucleus lateralis profundus mesencephali bilaterally, the contralateral pontine and medullary reticular formation, and the intermediate gray of the cervical spinal cord.

Subcortical afferent and efferent connections of the superior colliculus in the rat and comparisons between albino and pigmented strains.

Subcortical connections of the superior colliculus were investigated in albino and pigmented rats using retrograde and anterograde tracing with horseradish peroxidase (HRP), following unilateral injection of HRP into the superior colliculus. Afferents project bilaterally from the parabigeminal nuclei, the nucleus of the optic tract, the posterior pretectal region, the dorsal part of the lateral posterior-pulvinar complex and the ventral nucleus of the lateral lemniscus; and ipsilaterally from the substantia nigra pars reticulata, the pars lateralis of the ventral lateral geniculate nucleus, the intergeniculate leaflet, the zona incerta, the olivary pretectal nucleus, the nucleus of the posterior commissure, the lateral thalamus, Forel's field H2, and the ventromedial hypothalamus. Collicular efferents terminate ipsilaterally in the anterior, posterior and olivary pretectal nuclei, the nuclei of the optic tract and posterior commissure, the ventrolateral part of the dorsal lateral geniculate nucleus, the pars lateralis of the ventral lateral geniculate nucleus, the intergeniculate leaflet, and the zona incerta; and bilaterally in the parabigeminal nuclei and lateral posterior-pulvinar complex (chiefly its dorsal part). The general topographical patterns of some of the afferent and efferent projections were also determined: the caudal and rostral parts of the parabigeminal nucleus project to the caudal and rostral regions, respectively, of the superior colliculus; caudal superior colliculus projects to the most lateral, and lateral superior colliculus to the most caudal part of the terminal field in the dorsal lateral geniculate nucleus; caudolateral superior colliculus projects to the caudal ventrolateral part of the ventral lateral geniculate nucleus, while rostromedial parts of the colliculus project more rostrally and dorsomedially. Following comparable injections in pigmented and albino animals, fewer retrogradely labelled cells were found in subcortical structures in the albino than in the pigmented rats. The difference was most marked in nuclei contralateral to the injected colliculus. Thus, the effects of albinism on the nervous system may be more widespread than previously thought.

Anatomical studies on the nucleus reticularis tegmenti pontis in the pigmented rat. II. Subcortical afferents demonstrated by the retrograde transport of horseradish peroxidase.

The subcortical nuclear groups projecting to the nucleus reticularis tegmenti pontis (NRTP) were studied in pigmented rats with the aid of the retrograde horseradish peroxidase (HRP) technique. Small iontophoretic injections of HRP were placed in the medial regions of the NRTP, an area that has been shown in several species to be involved in eye movements. Other large injections in the NRTP or small injections placed just outside the nucleus were used to clarify the projections to the NRTP. Results indicate that the NRTP receives afferents from visual relay nuclei, including the nucleus of optic tract, the superior colliculus, and the ventral lateral geniculate nucleus; oculomotor-associated structures including the zona incerta, the H1 and H2 fields of Forel, the nucleus subparafasciculus, the interstitial nucleus of Cajal, the visual tegmental relay zone of the ventral tegmental area of Tsai, the mesencephalic, pontine, and medullary reticular formations, the nucleus of the posterior commissure, and a portion of the periaqueductal gray termed the supra-oculomotor periaqueductal gray; cerebellar and pontomedullary nuclei, including the superior, lateral, and medial vestibular nuclei, the deep cerebellar nuclei, and NRTP interneurons, and nuclei related to limbic functions including the lateral habenula, the mammillary nuclei, the hypothalamic nuclei, the preoptic nuclei, and the nucleus of diagonal band of Broca. A surprisingly large number of afferents to the medial regions of the NRTP arise from visual- or eye-movement-related nuclei. The projection from the nucleus of the optic tract (NOT) confirms previous anatomical and physiological studies on the pathways involved in horizontal optokinetic nystagmus, but the number of NOT afferents is small in relation to other areas potentially related to visuomotor pathways such as the zona incerta, ventral lateral geniculate nucleus, fields of Forel, perirubral area, and subparafasciculus. The NRTP may also relay information related to vertical visuomotor reflexes (e.g., vertical optokinetic nystagmus) given the strong projections from the medial terminal nucleus of the accessory optic system, visual tegmental relay zone, supra-oculomotor periaqueductal gray, interstitial n. of Cajal, and midbrain reticular formation. The presence of significant NRTP projections from the superior colliculus and the mesencephalic and pontine reticular formations suggests that these nuclei may provide the pathways for the noted saccade-related activity of NRTP neurons. In addition, projections from the vestibular nuclei were found that provide the anatomical basis for head velocity signals recorded in NRTP neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Visual response properties of ventral lateral geniculate nucleus cells projecting to the pretectum and superior colliculus in the cat

The visual properties of cells in the cat ventral lateral geniculate nucleus (LGV) identified antidromically from the pretectum and/or superior colliculus (projection cells) were studied in comparison with those of LGV neurons which could not be activated antidromically (non-projection cells). ON-plasic receptive fields (RFs) were relatively predominant in 27 projection cells, whereas On-tonic RFs were found more commonly in the non-projection group. The distribution of the RF centers revealed a centroperipheral gradient of the visual field representation within the LGV that the central visual field was more densely organized.

The thalamic connections of the ventral lateral geniculate nucleus in the cat: Intralaminar projections and commissural connections

The thalamic connections of the ventral lateral geniculate nucleus in the cat: Intralaminar projections and commissural connections

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.

Neuropeptide Y immunoreactivity in the hamster geniculo-suprachiasmatic tract

The distributions of neuropeptide Y (NPY) and avian pancreatic polypeptide (APP) immunoreactivity were examined in the suprachiasmatic nucleus and the geniculate area of male golden hamster brains. In some cases, colchicine was injected intraventricularly to aid in visualization of immunoreactive cell bodies. A group of hamsters were given bilateral or unilateral radiofrequency lesions of the geniculate area and neuropeptide Y immunoreactivity was examined in the suprachiasmatic nucleus after survival times varying between 8 and 300 days. Another group of hamsters received unilateral intraocular injections of anterograde tracers and the overlap of NPY-immunoreactive cells in the geniculate area and labeled retinal afferents was assessed. It was found that NPY- and APP-immunoreactive fibers formed a dense plexus in the ventro-lateral suprachiasmatic nucleus. NPY-immunoreactive cell bodies were observed in the intergeniculate leaflet as well as in the external lamina of the anterior portion of the ventral lateral geniculate nucleus. Unilateral lesions of the geniculate produced a relative reduction in neuropeptide Y immunoreactivity in the ipsilateral suprachiasmatic nucleus whereas bilateral lesions produced a reduction of neuropeptide Y immunoreactivity in both suprachiasmatic nuclei. All NPY-immunoreactive cells in the intergeniculate leaflet were overlapped by bilateral retinal afferents. In the ventral lateral geniculate nucleus, all NPY-immunoreactive cells were overlapped by contralateral retinal afferents; however, not all such cells were in areas receiving ipsilateral retinal afferents. These results indicate that the hamster geniculo-suprachiasmatic tract originates in part from NPY-immunoreactive cell bodies and that these cells lie in areas receiving direct retinal afferents.

The olivary pretectal nucleus: experimental anatomical studies in the rat.

The olivary pretectal nucleus: experimental anatomical studies in the rat.

Efferent connections of area 20 in the cat: HRP-WGA and autoradiographic studies.

Following injections of horseradish peroxidase-wheat germ agglutinin conjugate (HRP-WGA) and tritiated leucine into area 20 of the cat, terminal labeling was observed in visual areas 19, 21, the splenial visual area, the lateral suprasylvian area as well as in premotor, association and limbic related cerebral cortical regions. Labeled terminals in the subcortex were distributed in the caudate nucleus, the claustrum, the putamen, the anterior ventral nucleus, the intralaminar nuclei, the caudal division of the intermediate lateral nucleus, the lateralis posterior-pulvinar complex, the parvocellular C laminae of the dorsal lateral geniculate nucleus and the ventral lateral geniculate nucleus. In HRP-WGA preparations, retrogradely labeled somata were observed in these regions with the exception of certain subcortical structures. The projections are discussed with respect to the possible role area 20 plays in the cortical control of pupillary constriction.

Depression and recovery of metabolic activity in rat visual system after eye removal

To examine the anterograde metabolic effects of visual system damage, unilateral eye enucleation was carried out in 19 black-hooded rats, and the animals were injected with 2-deoxy[ 14C]glucose at postoperative survival times ranging from 1 h to 91 days. Metabolic depression followed by recovery to near-normal resting levels of activity was seen contralateral to the enucleation in the superior colliculus and the dorsal and ventral lateral geniculate nucleus (primary effects), and in the lateral posterior nucleus, in layer IV, and the infragranular layers of visual cortex (secondary effects). Diaschisis, defined as a temporary depression in neural activity after denervation, appears to be a characteristic response of the damaged visual system.

Central projections of cat retinal ganglion cells.

The central projections of different groups of cat retinal ganglion cells were studied following small iontophoretic injections of horseradish peroxidase (HRP) into physiologically characterized sites. Analysis was restricted to labeled cells in the upper periphery of the nasal retina, contralateral to the injection site. Injections were made to the A lamina and C lamina of the dorsal lateral geniculate nucleus (LGNd-A,C), the geniculate wing (LGNd-W), the ventral lateral geniculate nucleus (LGNv), the pretectum (PT), and the superior colliculus (SC). The dendritic fields of alpha, beta, and epsilon cells were well labeled by the procedures we employed. A group, termed "g1," had somal sizes within the range of the smaller beta and epsilon cells, but dendritic morphologies distinct from either class. The g1 group may consist of a number of types, but our material provided no basis for further distinguishing them. Many cells were observed that had smaller somas; all had thin axons, and few had dendritic fields that labeled to any significant extent. We were not able to further distinguish these cells, and refer to this group, which may include a number of types, as "g2" cells. From the peripheral nasal retina, alpha cells project to LGNd-A, LGNd-C, PT, and SC. Beta cells project to LGNd-A, LGNd-C, and PT. Epsilon and g1 cells project to the LGNd-C, LGNd-W, LGNv, PT, and SC. We determined the total spatial density of cells in the region of the retina analyzed, using a Nissl-stained preparation. We then estimated the relative fraction of cells in each of the above groupings by injecting HRP throughout a cross section of the optic tract. Multiplying this relative fraction by the total spatial density gave an estimate of the spatial density of each of these groupings. From the spatial density of cells labeled from the injection site, we were able to estimate the fraction of cells of each retinal grouping that project to each of the zones investigated. By these calculations, almost all alpha cells from the upper nasal retina project to LGNd-A and LGNd-C; most project to SC, and about a third to PT. Beta cells, by contrast, project almost exclusively to LGNd-A, with about 10% going to LGNd-C, and about 1% to the PT. The great majority of epsilon cells, if not all, project to LGNd-W, and up to half of this population also project to the other zones noted above.(ABSTRACT TRUNCATED AT 400 WORDS)

Classification of retinal ganglion cells and their axon terminals in the target areas in teleosts (sebastiscus and navodon)

By surgically dividing the region of the presumptive optic chiasm in chick embryos on the third day of incubation (around stage 15), we have been able to induce substantial numbers of optic nerve fibers to grow aberrantly into the ipsilateral optic tract. As a result, many of the visual centers that are normally innervated only by fibers from the contralateral retina received fibers from both eyes. The proportion of fibers going to each tectal lobe varied from case to case, but in about one-third of the animals the tectal lobes received approximately equal numbers of fibers from each eye.In animals that survived until embryonic days 17–19 (which is beyond the period of retinal ganglion cell death) labeling of the two eyes with WGA-HRP and [3H]proline respectively, revealed a pattern of sharply defined eye dominance stripes or patches in the stratum griseum et fibrosum superficiale (SGFS) of the optic tectum, and in the ventral lateral geniculate nucleus. Less clearly segregated eye dominance zones were seen in the ectomammillary nucleus and the nucleus externus. The size and distribution of the stripes varied depending on the number of fibers projecting from each eye to a given tectal lobe; the minimum size was about 75 μm, while the maximum was large enough to occupy almost the entire tectal lobe. In animals in which the tectal input from the two eyes was roughly equal, the stripes varied in width between 75 μm and about one-third of the surface of the tectal lobe. The orientation of the stripes was consistently orthogonal to the direction of fiber ingrowth from the optic tract. From the earliest stages of optic fiber ingrowth, the fibers from the two eyes are completely intermixed in the stratum opticum (SO). However, on embryonic day 12, shortly after they have begun to penetrate into the SGFS, they are already segregated into stripes, although the stripe borders are very fuzzy. This suggests that the fibers from the two eyes may overlap at this stage. The phase of stripe formation coincides with that of naturally occurring retinal ganglion cell death, and we suggest that the two processes are interlinked.

Serotonergic innervation of the forebrain in the North American opossum.

The forebrain distribution of axons showing serotonin-like immunoreactivity was studied in the North American opossum. Serotonergic innervation of the hypothalamus was extensive, particularly within the ventromedial nucleus, the periventricular nucleus and the rostral supraoptic nucleus. Serotonergic axons were also present within the fields of Forel and zona incerta, but they tended to avoid parts of the subthalamic nucleus. In the thalamus serotonergic innervation was dense within the midline nuclei (e.g. the central, intermediate dorsal and rhomboid nuclei) and the ventral lateral geniculate nucleus, but relatively sparse in some of the nuclei more readily associated with specific functions (e.g. the ventrobasal nucleus). Serotonergic axons innervate most areas of the rostral and dorsal forebrain. Areas containing the heaviest innervation included the interstitial nucleus of the stria terminalis and the lateral septal nucleus. Serotonergic innervation of the neocortex varied markedly from region to region and within different layers of the same regions. The retrograde transport of True Blue combined with immunofluorescence for localization of serotonin revealed that serotonergic axons within the forebrain arise mainly within the dorsal raphe and superior central nuclei, but that some originate within the midbrain and pontine reticular formation and the locus coeruleus, pars alpha. Neurons of the raphe magnus and obscurus also innervate the forebrain, but few of them are serotonergic. The use of horseradish peroxidase as a retrograde marker provided evidence that raphe projections to the forebrain are topographically organized. Our results suggest that serotonergic projections to the forebrain, like those to the spinal cord, are connectionally heterogeneous.

Serotonergic Innervation of the Forebrain in the North American Opossum; pp. 213–228

The forebrain distribution of axons showing serotonin-like immunoreactivity was studied in the North American opossum. Serotonergic innervation of the hypothalamus was extensive, particularly within the ventromedial nucleus, the periventricular nucleus and the rostral supraoptic nucleus. Serotonergic axons were also present within the fields of Forel and zona incerta, but they tended to avoid parts of the subthalamic nucleus. In the thalamus serotonergic innervation was dense within the midline nuclei (e.g. the central, intermediate dorsal and rhomboid nuclei) and the ventral lateral geniculate nucleus, but relatively sparse in some of the nuclei more readily associated with specific functions (e.g. the ventrobasal nucleus). Serotonergic axons innervate most areas of the rostral and dorsal forebrain. Areas containing the heaviest innervation included the interstitial nucleus of the stria terminalis and the lateral septal nucleus. Serotonergic innervation of the neocortex varied markedly from region to region and within different layers of the same regions. The retrograde transport of True Blue combined with immunofluorescence for localization of serotonin revealed that serotonergic axons within the forebrain arise mainly within the dorsal raphe and superior central nuclei, but that some originate within the midbrain and pontine reticular formation and the locus coeruleus, pars alpha. Neurons of the raphe magnus and obscurus also innervate the forebrain, but few of them are serotonergic. The use of horseradish peroxidase as a retrograde marker provided evidence that raphe projections to the forebrain are topographically organized. Our results suggest that serotonergic projections to the forebrain, like those to the spinal cord, are connectionally heterogeneous.

On the formation of eye dominance stripes and patches in the doubly-innervated optic tectum of the chick

By surgically dividing the region of the presumptive optic chiasm in chick embryos on the third day of incubation (around stage 15), we have been able to induce substantial numbers of optic nerve fibers to grow aberrantly into the ipsilateral optic tract. As a result, many of the visual centers that are normally innervated only by fibers from the contralateral retina received fibers from both eyes. The proportion of fibers going to each tectal lobe varied from case to case, but in about one-third of the animals the tectal lobes received approximately equal numbers of fibers from each eye. In animals that survived until embryonic days 17–19 (which is beyond the period of retinal ganglion cell death) labeling of the two eyes with WGA-HRP and [ 3H]proline respectively, revealed a pattern of sharply defined eye dominance stripes or patches in the stratum griseum et fibrosum superficiale (SGFS) of the optic tectum, and in the ventral lateral geniculate nucleus. Less clearly segregated eye dominance zones were seen in the ectomammillary nucleus and the nucleus externus. The size and distribution of the stripes varied depending on the number of fibers projecting from each eye to a given tectal lobe; the minimum size was about 75 μm, while the maximum was large enough to occupy almost the entire tectal lobe. In animals in which the tectal input from the two eyes was roughly equal, the stripes varied in width between 75 μm and about one-third of the surface of the tectal lobe. The orientation of the stripes was consistently orthogonal to the direction of fiber ingrowth from the optic tract. From the earliest stages of optic fiber ingrowth, the fibers from the two eyes are completely intermixed in the stratum opticum (SO). However, on embryonic day 12, shortly after they have begun to penetrate into the SGFS, they are already segregated into stripes, although the stripe borders are very fuzzy. This suggests that the fibers from the two eyes may overlap at this stage. The phase of stripe formation coincides with that of naturally occurring retinal ganglion cell death, and we suggest that the two processes are interlinked.

The dorsal lateral geniculate nucleus in the mouse: a Golgi study

Summary The dorsal lateral geniculate nucleus (LGNd) in the mouse was studied using the rapid Golgi method. Two neuronal types were distinguished. The type I neurons were projection neurons which sent their axons into the superior thalamic radiation (STR). The vast majority of the type II neurons were intrinsic neurons, but a few of them sent their axons to the ventral lateral geniculate nucleus. Afferent fibers to the LGNd were traced ventrally from the optic tract (OT), ventromedially from the STR, and medially through the lateroposterior thalamic nucleus (LP). The OT fibers ran through the LGNd giving off many collaterals; some of these formed glomerular plexuses of fiber terminals within the LGNd. The STR fibers entering the LGNd from the ventromedial aspect constituted columnar plexuses of fiber terminals within the LGNd, the long axes of which ran mediolaterally in the LGNd. Some of the fibers running through the LP entered the LGNd from the medial aspect and terminated within the LGNd after giving off several collaterals. Thus, although no laminar pattern of neuronal arrangement was found in the LGNd of the mouse, the retinogeniculate and corticogeniculate fibers showed specific intranuclear organization.

Genesis of neurons in the dorsal lateral geniculate nucleus of the cat.

Neurons that will ultimately form the dorsal and ventral lateral geniculate nuclei, the medial interlaminar nucleus, the perigeniculate nucleus, and the nucleus reticularis of the cat undergo their final cell division beginning on, or slightly before, embryonic day 22 (E22) and ending on, or before, E32. Early in this period, neurogenesis proceeds for all of these geniculate nuclei, whereas only in the dorsal lateral geniculate nucleus does cell birth continue until E32. Distinct spatiotemporal gradients of cell birth are not obvious within any of the individual geniculate nuclei. For the dorsal lateral geniculate nucleus in particular, and for the other geniculate nuclei in general, neurons born early in this period exhibit a full range of adult soma sizes, including large and small neurons. Neurons born late in this period exhibit only small adult somas. The location and size of a neuron within the dorsal lateral geniculate nucleus provide clues to that cell's functional properties. On the basis of presently available information regarding the relationship between structure and function of neurons in the cat's dorsal lateral geniculate nucleus, the findings described here suggest that all functional classes of neurons in the dorsal lateral geniculate nucleus are born at the same time throughout most of this period.