Dorsal Lateral Geniculate Body Research Articles

Afferent connections of fields 17 and 18 of the cat cerebral cortex formed by neurons of the dorsal lateral geniculate body.

Horseradish peroxidase (HRP) was applied microiontophoretically to nine individual columns in fields 17 and six columns in field 18 of the cat cerebral cortex. Most labeled cells in the dorsal lateral geniculate body were identified in layer A. The ratio of number of labeled cells in layer A to the number of labeled cells in layer A1 was assessed (the A/A1 ratio). Application of HRP to columns in field 17 yielded A/A1 ratios of 0.5 to 2.5; application to field 18 gave ratios ranging from 0.2 to 0.9. This suggests that the fields studied here contained columns which were afferent in relation to the ipsilateral eye and the contralateral eye.

Adenosine A 1 and Benzodiazepine Receptors and Glucose Metabolism in the Visual Structures of Rats Monocularly Deprived by Enucleation or Eyelid Suture at a Sensitive Period

Purpose: To determine the changes in the adenosine A 1 and benzodiazepine receptor density and in glucose metabolism in the visual centers of the rat brain following monocular enucleation or eyelid suture on postnatal day 10 (PN10). Methods: Following monocular enucleation or eyelid suture on PN10 rats, the alterations in adenosine A 1 and benzodiazepine receptor density, and in glucose metabolism were evaluated in the superior colliculus (SC), the dorsal lateral geniculate body (DLG), and the visual cortex (VC) by ex vivo autoradiography with [ 11C]MPDX, [ 11C]flumazenil and [ 14C]2-deoxyglucose, respectively. Results: Enucleation reduced the [ 11C]MPDX binding in the SC and DLG, and enhanced the [ 11C]flumazenil binding in the SC. Eyelid suture reduced the [ 11C]flumazenil binding in the VC at day 20. [ 14C]2-deoxyglucose uptake was not decreased by enucleation in any region except in the SC and DLG at day 1, but was decreased by eyelid suture in the SC at days 20 and 55 and in the VC at day 55. Conclusions: The decrease in the presynaptic adenosine A 1 receptors in the SC following enucleation is coupled with an upregulation of postsynaptic benzodiazepine receptors. These neural reactions are completely different from those following eyelid suture. The development of neural architecture for visual functions is not completed at PN10 in rats.

Exercise increases blood flow to locomotor, vestibular, cardiorespiratory and visual regions of the brain in miniature swine.

1. The purpose of these experiments was to use radiolabelled microspheres to measure blood flow distribution within the brain, and in particular to areas associated with motor function, maintenance of equilibrium, cardiorespiratory control, vision, hearing and smell, at rest and during exercise in miniature swine. Exercise consisted of steady-state treadmill running at intensities eliciting 70 and 100 % maximal oxygen consumption (V(O(2),max)). 2. Mean arterial pressure was elevated by 17 and 26 % above that at rest during exercise at 70 and 100 % V(O(2),max), respectively. 3. Mean brain blood flow increased 24 and 25 % at 70 and 100 % V(O(2),max), respectively. Blood flow was not locally elevated to cortical regions associated with motor and somatosensory functions during exercise, but was increased to several subcortical areas that are involved in the control of locomotion. 4. Exercise elevated perfusion and diminished vascular resistance in several regions of the brain related to the maintenance of equilibrium (vestibular nuclear area, cerebellar ventral vermis and floccular lobe), cardiorespiratory control (medulla and pons), and vision (dorsal occipital cortex, superior colliculi and lateral geniculate body). Conversely, blood flow to regions related to hearing (cochlear nuclei, inferior colliculi and temporal cortex) and smell (olfactory bulbs and rhinencephalon) were unaltered by exercise and associated with increases in vascular resistance. 5. The data indicate that blood flow increases as a function of exercise intensity to several areas of the brain associated with integrating sensory input and motor output (anterior and dorsal cerebellar vermis) and the maintenance of equilibrium (vestibular nuclei). Additionally, there was an intensity-dependent decrease of vascular resistance in the dorsal cerebellar vermis.

Visual System Labeled by c-Fos Immunohistochemistry after Light Exposure in the ‘Blind’ Subterranean Zambian Mole-Rat (Cryptomys anselli)

The Zambian mole-rat (Cryptomys anselli) is a rodent that lives and forages underground, and under natural conditions is rarely, if ever, exposed to light. Its eye is organized as in other rodents and is prominent but minuscule. The animals do not seem to react to light behaviorally or to orient visually, although exact physiological and/or behavioral experiments have not been conducted to date. Nuclear expression of transcriptional regulatory protein (c-Fos) as a marker of cell activity was studied immunohistochemically in five mole-rats exposed to bright light for 1 h after 3 days in constant darkness, and in four non-stimulated control animals that were kept in darkness for three days and then killed under deep anesthesia. The retinae and retino-recipient areas of non-stimulated animals remained unlabeled, but many of these structures showed strong c-Fos expression bilaterally [retina, dorsal lateral geniculate body (DLG), olivary pretectal nucleus, retrosplenial cortex, neocortex] in light-exposed animals. In contrast, the suprachiasmatic nucleus did not seem to be affected by light stimuli during the experiment. In both light-stimulated and control animals the rudimentary superior colliculus exhibited slight immunoreactivity. Interestingly, the olivary pretectal nucleus, which in mammals is involved in light/dark discrimination, as well as the DLG as part of the image-forming visual system were consistently labeled by c-Fos after light stimulation, indicating that vision in Cryptomys possibly plays a more significant role than previously assumed.

Anatomical characteristics and three‐dimensional model of the dog dorsal lateral geniculate body

The morphological and laminar characteristics of the dorsal lateral geniculate nucleus (LGN) and medial interlaminar nucleus (MIN) of the domestic dog (Canis familiaris) were studied by three-dimensional computer reconstruction of labeled retinal afferents following intraocular HRP injections. As previously reported, the dog LGN consisted of layers A, A1, C, C1, C2, and C3. Layers A, C, and C2 receive contralateral-eye inputs, and layers A1 and C1 ipsilateral inputs. The dog MIN was found to have four orderly interdigitating layers; layers 1, 2, 3, and 4, medial to lateral. MIN layers 1 and 3 received contralateral inputs, and layers 2 and 4 ipsilateral inputs. Layer 1 had the largest soma of all LGN/MIN layers. LGN layer A was partially separated into medial and lateral subdivisions by a cleft free of somata. The overall three-dimensional shape of the lateral geniculate body was like the letter C, with the convex part of the C directed posteriorly. The relative volume of the MIN was smaller than in the cat; the canine MIN comprised 8.3% of the combined volume of layers A, A1 and the MIN, while that of the cat comprised 14.2% as estimated from Sanderson's map. The volume of all contralateral-eye layers, combining both LGN and MIN, was 31.2 mm3 (78%), and that for ipsilateral layers was 8.6 mm3 (22%). The ratio of ipsilateral to contralateral laminar volumes is much lower in the dog than in the cat. Anat Rec 256:29–39, 1999. © 1999 Wiley-Liss, Inc.

Acute and chronic D-fenfluramine treatments have different effects on serotonin synthesis rates in the rat brain: an autoradiographic study.

The effects of acute and chronic treatments with D-fenfluramine on the regional rates of serotonin (5-hydroxy-tryptamine; 5-HT) synthesis were investigated using the alpha-[14C]methyl-L-tryptophan (alpha-[14C]MTrp) autoradiographic method. In the first series of experiments, acute D-fenfluramine treatment (5 mg/kg; i.p.) given 20 min before the tracer injection significantly (p<0.05) decreased 5-HT synthesis in the dorsal raphe, and significantly (p<0.05) increased the rates in the cerebral cortices and caudate nucleus, when compared to the rates in the control rats (saline treated). In a second series of experiments, following a 7-day treatment with D-fenfluramine (5 mg/kg/day; i.p.), a significant (p<0.05) decrease of 5-HT synthesis, in the dorsal raphe was observed, and significant (p<0.05) increases were observed in the hypothalamus, the dorsal thalamus, the medial and lateral geniculate body and some brain stem regions (locus ceruleus, inferior and superior colliculus). No significant changes were observed in the cerebral cortices.

Morphologic analysis of rat retinocollicular neuron terminals containing monoamine oxidase

The retino-collicular neuron terminals containing type A monoamine oxidase (MAO-A) in the stratum griseum superficiale of the rat superior colliculus were analyzed to provide a morphologic basis for the physiologic role of these neurons in the visual pathway. A computer-assisted, three-dimensional re-construction of the terminal complex associated with the MAO-A-positive terminals was performed. MAO-A-positive terminals originated in the retina and terminated in the stratum griseum superficiale. This was confirmed by tract tracing and enucleation experiments. The terminals were densely grouped in clusters of irregularly shaped swellings. Electron microscopy revealed that the MAO-A-positive terminals were located in a glomerulus-like structure. In this terminal complex, a significant proportion of the axonal profiles (42.96%) synapsed with the MAO-A-positive terminals. Most of the profiles (24.16%) resembled presynaptic dendrites, which represent intermediate elements between the retinal terminals and conventional dendrites. Unlike the glomerulus in the dorsal lateral geniculate body, the MAO-A-positive terminal swellings were not located in the central part of the terminal complex. The terminals had an irregular shape and were located in the complex. The terminal complex was partially ensheathed by glial processes. Furthermore, the membrane surfaces exhibiting synaptic specializations were very small compared with the total surface of the terminal swellings. The membrane length of the synaptic specialization was 5.38% of the total perimeter of the MAO-A-positive terminals.

Cholecystokinin affects the neuronal discharge mode in the rat lateral geniculate body

Neurons of the dorsal lateral geniculate body (dLGB) discharge either continuously with single spikes or in bursts, that is, groups of action potentials with an interspike interval ≤ 4 ms. The influence of the sulphated octapeptide of cholecystokinin (CCK-8S) on the discharge mode of dLGB neurons was studied in rats anesthetized with urethane. Unit activity was recorded during repeated stimulation with diffuse light. The occurrence of bursts was determined during control conditions and during iontophoretic administration of CCK-8S and its antagonists. CCK-8S frequently increased the number of bursts. The percentage of spikes involved in bursts was mainly aug-mented in neurons that responded after short latency to light or were excited by light-off. It was predominantly reduced in units responding to light attar long latency with a primary excitation. CCK A receptors seem to contribute to burst induction, since CCK-8S reduced bursting in the presence of the CCK A receptor antagonist Go 410 and increased bursting when applied with the CCK@ receptor antagonist PD 135,158. These bursts were frequently related to fight stimuli.

Cholinergic, Monoaminergic and Peptidergic Innervation of the Primary Visual Centers in the Brain of the Lizards &lt;i&gt;Gekko gecko&lt;/i&gt; and &lt;i&gt;Gallotia galloti&lt;/i&gt; (Part 2 of 2)

In order to study the relationship between retinal projections and immunohistochemically identified neurotransmitter systems in the primary visual centers of the brain in lizards, intraocular injections of horseradish peroxidase were combined with immunohistochemistry. Antibodies raised against six substances were applied: choline acetyltransferase (ChAT), serotonin (5-HT), tyrosine hydroxylase (TH), dopamine (DA), substance P (SP), and leu-enkephalin (LENK). In the primary visual centers of the lizards <i>Gekko gecko </i>and <i>Gallotia galloti, </i>notable overlap was observed between retinofugal fibers with: 1) ChAT-immunoreactive fibers in almost all primary visual centers; 2) 5-HT-immuno-reactive fibers in the ventral lateral geniculate body and the basal optic nucleus; 3) TH-immunoreactive fibers in the nucleus ovalis and the dorsal lateral geniculate body; 4) SP- and LENK-immunoreactive fibers in the perirotundal belt; and 5) TH- and SP-immunoreactive fibers in the pretectal posterodorsal nucleus. The latter nucleus also contains dopaminergic cell bodies that lie outside the retinal target area but have dendrites extending into it. Several differences were noted in the distribution of 5-HT-, TH-, DA-, and LENK-immunoreactive fibers in the tectum of the midbrain in the two species studied. Distinct laminae of 5-HT-immunoreactive fibers (layer 9) and TH- and DA-immunoreactive fibers (layers 9 and 11) are present in G. <i>gecko </i>but absent or, at least, less distinct in G. <i>galloti. </i>On the contrary, the optic layers in the tectum of G. <i>galloti </i>show a rather dense plexus of LENK immunoreactive fibers, whereas the corresponding layers in G. <i>gecko </i>are devoid of LENK-immunoreactivity. Since only a very few ChAT immunoreactive fibers were observed in the optic nerve of G. <i>galloti, </i>most of the observed immunoreactive fibers in the primary visual centers are considered to have an extraretinal origin. Putative sources of the cholinergic, the monoaminergic, and the peptidergic innervation of the primary visual centers in reptiles include the isthmic nucleus, the raphe nuclei, the substantia nigra and the nucleus of the posterior commissure, as reported in other amniotes.

Invasion of visual cortex by the auditory system in the naturally blind mole rat

Previously we have shown that the dorsal lateral geniculate body (LGB), which is strictly visual in sighted mammals, receives a strong auditory input in the naturally blind mole rat (Spalax ehrenbergi). Here we show with the 2-deoxyglucose technique and with single-unit recordings that in this species the initially non-degenerated visual cortex, as defined by its connection with LGB, is also activated by the auditory modality. These findings suggest that cross-modal compensation may occur as a natural consequence of the degeneration of a sense organ.

Differential alterations of second messenger systems and cerebral glucose use following excitotoxic lesion of rat cerebral cortex

Quantitative autoradiography of [ 3H]forskolin and [ 3H]phorbol 12,13 dibutyrate (PDBu) binding was examined 21 days after unilateral lesioning of the rat visual cortex using ibotenic acid. In the same animals, the functional deficit was assessed using quantitative [ 14C]-2-deoxyglucose autoradiography. [ 3H]Forskolin binding was significantly reduced in each layer of the lesioned visual cortex by at least 40% compared to the contralateral hemisphere. Significant reductions in [ 3H]forskolin binding were observed in the superior colliculus (−15%) and dorsal lateral geniculate body (−12%) ipsilateral to the lesioned cortex. [ 3H]PDBu binding was significantly reduced in the lesioned visual cortex (layers V–VI) by 34%, compared with the control hemisphere. There were no significant alterations in [ 3H]DPBu binding in any other brain regions. Following ibotenate-induced lesioning of the visual cortex, glucose use was significantly reduced throughout the lesioned cortex by at least 25% with minor alterations in glucose use in the ipsilateral dorsal lateral geniculate body and superior colliculus. The present study highlights the relative robustness of [ 3H]PDBu binding compared to [ 3H]forskolin binding after excitotoxic damage to the cerebral cortex and suggests that [ 3H]forskolin binding sites are present on cortical efferent fibres.

Alterations of functional glucose use and ligand binding to second messenger systems following unilateral orbital enucleation

Quantitative autoradiography was used to examine the effect of lesioning a well-defined glutamatergic system (retinofugal fibres) on [ 3H]forskolin binding to G s-adenylate cyclase and [ 3H]PDBu (phorbol-12,13-dibutyrate) binding to protein kinase C (PKC) in the rat visual system at 1, 5, 10 and 20 days after unilateral orbital enucleation. Local cerebral glucose utilisation was determined in the same animals using quantitative [ 14C]2-deoxyglucose autoradiography. At 5 days post-lesion, [ 3H]forskolin binding sites were significantly reduced in the visually-deprived superior colliculus (−14 ± 1%) and dorsal lateral geniculate body (−8 ± 2%), and these reductions persisted until 20 days post-lesion. There were no significant alterations in the amount of [ 3H]PDBu binding in any region in the visually-deprived hemisphere following enucleation. Function-related glucose use was significantly reduced throughout the visual pathway after enucleation. In this study, there was no conclusive evidence of plastic modifications of second messenger systems in the rat visual system despite a general depression of visual function following lesion of retinofugal fibres.

Alterations in neurotransmitter receptors and glucose use after unilateral orbital enucleation

Serotonin (5-hydroxytryptamine; 5-HT), acetylcholine and γ-aminobutyric acid (GABA) are neurotransmitters in the rat visual system. Using quantitative autoradiography, the effect of unilateral orbitral enucleationon [ 3H]5-HT, [ 3H]ketanserin, [ 3H]quinuclidinyl benilate (QNB) and [ 3H]muscimol binding to 5-HT 1, 5-HT 2, muscarinic and GABA A receptors has been examined within anatomical components of the visual pathway at 4 time points up to 20 days after the lesion. The functional deficit was assessed in the same animals using quantitative [ 14C]2-deoxyglucose autoradiography. At 1 day after unilateral orbital enucleation, there were no significant alterations in ligand binding although local cerebral glucose use was reduced in primary visual structures in the visually deprived hemisphere. At 5 days post-enucleation, however, [ 3H]5-HT binding was significantly reduced in both the visually deprived superior colliculus (by 17%) and dorsal lateral geniculate body (DLG) (by 33%). There were similar alterations in the binding of this ligand in these primary retinal projections areas at 10 and 20 days after orbital enucleation, but there were no changes in secondary areas (e.g. visual cortex) at any time point. [ 3H]Muscimol binding was significantly reduced in the visually deprived DLG (30%) and visual cortex (21%) only at 20 days post-lesion, whilst [ 3H]ketanserin and [ 3H]QNB were not altered in any region in the visually deprived hemisphere at any time point post-enucleation. At 10 and 20 days post-enucleation, the degree of [ 3H]5-HT, and [ 3H]muscimol binding deficits in visually deprived structures correlated significantly with the level of reduced metabolic activity in these areas ( r = 0.700andr = 0.543respectively). The specificity and regional and temporal heterogeneity of neurotransmitter receptor binding alterations provides evidence of selective adjustments within visual system component6s in response to orbital enucleation.

Effect of excision of occipital lobe tissue on about the 70th day of gestation on the growth and development of the sheep's brain

A unilateral occipital excision was performed on 14 fetal lambs at about the 70th day of gestation, and the brains were examined postnatally for gross morphological and histologic changes. Three operated brains revealed a posterior shift of the principal transverse sulcus in the ipsilateral hemisphere. This sulcus is remote from the area of excision, which was usually represented by a cystic cavity. Histologic examination showed that the dorsal lateral geniculate body was reduced in size in all but three of the operated brains. In two brains with the changed gyral pattern there was also a reduction in the size of the white fiber tracts of the frontal lobe. No evidence of neural regeneration was found in any of the brains. The implications of these findings from the point of view of possible neurosurgical intervention in the fetus are considered.

Auditory pathway and auditory activation of primary visual targets in the blind mole rat (Spalax ehrenbergi): I. 2-deoxyglucose study of subcortical centers.

The blind mole rat Spalax ehrenbergi is a subterranean rodent that shows striking behavioral, structural, and physiological adaptations to fossorial life including highly degenerated eyes and optic nerves and a behavioral audiogram that indicates high specialization for low-frequency hearing. A 2-deoxyglucose functional mapping of acoustically activated structures, in conjunction with Nissl/Klüver-Barrera-stained material, revealed a typical mammalian auditory pathway with some indications for specialized low-frequency hearing such as a poorly differentiated lateral nucleus and a well-developed medial nucleus in the superior olive complex. The most striking finding was a marked 2-deoxyglucose labeling of the dorsal lateral geniculate body and of cortical regions that correspond to visual areas in sighted rodents. The results render the blind mole rat a good model system for studying natural neural plasticity and intermodal compensation. In this report, we confine ourselves to the subcortical levels. The cortical level will be dealt comprehensively in a following paper.

Receptive-field properties and morphological characteristics of the superior collicular neurons that project to the lateral posterior and dorsal lateral geniculate nuclei in the hamster.

1. Intracellular recording, antidromic activation, and horseradish peroxidase (HRP) injection techniques were employed to characterize the receptive-field properties and morphology of the superior collicular (SC) neurons in the hamster that projected to the lateral posterior nucleus (LP) or the dorsal lateral geniculate body (LGNd). 2. Twenty-three tecto-LP and 21 tecto-LGNd cells were successfully characterized, filled with HRP, and recovered. Additional physiological information was obtained from four tecto-LP and five tecto-LGNd neurons in which HRP injections did not completely label the cell, but did provide information as to the laminar location of the soma. Recovered neurons were classified as wide-field or narrow-field vertical cells, marginal cells, stellate cells, or horizontal cells on the basis of their soma-dendritic morphology. They were categorized as stationary responsive (SR), movement sensitive (MV), or directionally selective (DS) on the basis of their physiological responses (3, 37). 3. The somas of the recovered tecto-LP cells were located, with two exceptions, in, or near, the borders of the stratum opticum (SO). Tecto-LGNd neurons, with two exceptions, had their cell bodies in the upper one-half of the stratum griseum superficiale (SGS). Fifty-two percent of the recovered tecto-LP cells were wide-field vertical cells, 22% were narrow-field vertical cells, 13% were stellate cells, 9% were horizontal cells, and 4% could not be classified according to the scheme that we employed. Twenty-four percent of the recovered tecto-LGNd cells were marginal cells, 24% were stellate cells, 38% were narrow-field vertical cells, 5% were horizontal cells, 5% were wide-field vertical cells, and 5% could not be classified. The difference between the distributions of morphological cell types that contributed to the tecto-LGNd and tecto-LP pathways was statistically significant (chi 2 = 15.8, P less than 0.01). 4. Sixty-seven percent of the tecto-LP cells had MV receptive fields, 11% were DS, 7% had SR fields, and 15% were unresponsive. The distribution of receptive-field types for tecto-LGNd cells was somewhat different: 54% had SR fields, 15% were MV, 19% were DS, 4% were somatosensory, 4% were unresponsive, and 4% were incompletely classified. These differences between tecto-LP and tecto-LGNd cells were statistically significant (chi 2 = 18.4, P less than 0.001). The strongest correlation between morphology and receptive-field type was observed for the wide-field vertical cells that projected to LP. All but one of these had MV receptive fields.(ABSTRACT TRUNCATED AT 400 WORDS)

Chapter 19: Influence of areas 17, 18, and 19 on receptive-field properties of neurons in the cat's posteromedial lateral suprasylvian visual cortex

This chapter focuses on the influence of areas 17, 18, and 19 on receptive-field properties of neurons in the cat's posteromedial lateral suprasylvian visual cortex. Besides extrastriate areas 18 and 19, ten extrastriate visual cortical areas are identified on the basis of pathway tracing and electrophysiological mapping studies. The posteromedial lateral suprasylvian (PMLS) visual area is the large and best studied of these extrastriate visual cortical areas. One of the features of PMLS cortex that makes it extremely useful for understanding how visual information is integrated in the brain is that it is the target of several parallel visual pathways. A second pathway to PMLS cortex arises from the superior colliculus and passes through the thalamus to PMLS cortex. The thalamic nuclei involved in this pathway are the lateral posterior nucleus (LP), the posterior nucleus of Rioch (PN), and the C layers of the dorsal lateral geniculate body (dLGB). Temporal frequency sensitivity of responses to the optimal spatial frequency also has been tested for many PMLS cells.

Behaviourally dependent modulation of lateral geniculate unit activity in the freely moving cat

In 120 neurons of the cat's dorsal lateral geniculate body (dLGB), spontaneous and light-evoked activity was analysed in order to obtain further information on firing characteristics during different behavioural states (quietly sitting, locomotion). Experiments were carried out in freely moving cats, using wireless methods for simultaneous registration of single unit activity and locomotion. During locomotion, an enhancement of neuronal single and pool activity was observed. During locomotor activity, flash-evoked responses were modulated, an increase of response amplitude and a decrease of peak latency in the peristimulus time histogram occurred. The results demonstrate a facilitatory influence on spontaneous and light-evoked activity of dLGB neurones during locomotion. They suggest a non-visual phasic modulation of retino-geniculo-cortical information transfer.

Gamma-aminobutyrate-like immunoreactivity in the thalamus of the cat

Serial sections of the cat's thalamus were incubated with a purified antiserum raised against gamma-aminobutyric acid conjugated to bovine serum albumin by distilled glutaraldehyde. This serum has been extensively characterized and appears to react selectively with fixed gamma-aminobutyric acid in brain tissue treated with glutaraldehyde. Adjoining sections were stained with thionin and served as invaluable guides for a correct evaluation of the immunolabelling pattern. In the neuropil the intensity of the immunostaining varies considerably between thalamic nuclei and even between nuclear subdivisions. The neuropil staining appears particularly dense in the nuclei parataenialis, periventricularis, centralis medialis, reuniens, rhomboideus, habenularis lateralis, centrum medianum, parafascicularis, subparafascicularis, submedius, dorsal and ventral parts of the lateral geniculate body, the dorsal part of the medial geniculate body, the posterior complex, suprageniculate nucleus, pulvinar and parts of the lateral posterior nucleus. The pulvinar/lateralis posterior complex shows a particularly well-differentiated staining pattern which closely matches Updyke's [Updyke (1983) J. comp. Neurol. 219 143–181] parcellation of this region. In several thalamic nuclei or subareas—and notably in those relay nuclei which are known to project upon non-primary sensory cortical areas—the immunostained neuropil is characterized by many puncta encircling an unstained profile. With few exceptions all thalamic nuclei displayed immunoreactive nerve cell bodies. Several examples were found of a mismatch between the number of such cells and the staining intensity of the neuropil. Thus the nuclei periventricularis, parafascicularis, subparafascicularis, parataenialis, limitans and centrum medianum although being very rich in neuropil staining have practically no immunostained perikarya. Rough estimates were made of the size and the proportion of gamma-aminobutyric acid labelled neurons in all major—and some minor—thalamic nuclei and their subdivisions. In some thalamic nuclei, notably the nuclei reticularis, anterior dorsalis, lateralis dorsalis, centralis lateralis, ventralis posterior and the dorsal lateral geniculate body, the population of immunoreactive neurons is distinctly heterogeneous with regard to soma size. The findings are discussed with regard to previous immunocytochemical studies of the distribution of gamma-aminobutyric acid and its synthesizing enzyme in the thalamus. Particular emphasis is put on the great species differences which appear to exist in this respect.

Organization of geniculocortical connections following prenatal interruption of binocular interactions

The organization of geniculostriate connections in normal cats was compared with that of adult animals that were uniocularly enucleated before birth. In normal animals microelectrophoretic deposits of horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) into the A-lamina of the dorsal lateral geniculate body (LGd) resulted in anterograde label in layers IV and VI and labeled cells in layer VI of areas 17 and 18. The labeling pattern within both of these cortical areas consisted of alternating patches separated by zones of equivalent size that were relatively free of label. In the normal animals no reaction product was evident in any other cortical area. In the prenatally enucleated cats, the LGd both contralateral and ipsilateral to the remaining eye is comprised of only two distinct cell layers. The dorsal layer appears to be a composite of the normal A/A1-laminae, while the ventral layer appears to correspond to the C-laminae. Deposits of WGA-HRP into the superficial aspect of the A/A1 layer yielded a dense continuous band of label within layers IV and VI of areas 17 and 18. Additionally, such deposits in the prenatally enucleated cats also revealed an anomalous reciprocal connection with area 19. Punctate deposits of WGA-HRP into cortical area 19 of the fetal enucleates resulted in the labeling of two distinct populations of cells within the A/A1 layer of the LGd. No cells were labeled within the A-laminae following such deposits into area 19 of normal animals. The geniculocortical connections of the prenatally enucleated cats, including that to area 19, were found to be retinotopically organized. These results indicate that in utero interruption of binocular interactions prevents the formation of ocular dominance domains within areas 17 and 18 of the cat's visual cortex. This could reflect the maintenance of exuberant geniculocortical projections present at the time of prenatal eye removal as originally suggested by Rakic ( Science, 214 (1981) 928–931). The anomalous connection with area 19, on the other hand, could be due to the disruption of LGd cell migration resulting from the early eye removal.