Some aspects of the modular organization of the primary visual cortex of the cat: patterns of cytochrome oxidase activity.

The distribution of the enzyme cytochrome oxidase (CO) in continuous series of parasagittal sections from field 17 and frontal sections of the dorsal nucleus of the lateral geniculate body (LGB) from normal kittens and adult cats was studied. In all cats apart from neonates, layer IV showed regularly alternating areas with above-background levels of CO activity ("spots"). There was a significant increase in the contrast of the "spots" from days 13 to 21, which was followed by a significant decrease from days 48 to 93. These changes coincided with ontogenetic changes in the level of visual system plasticity. There were no differences in CO activity between layers A and A1 of the dorsal nucleus of the LGB. It is suggested that the non-uniform distribution of the level of functional activity of neurons in field 17 reflects the formation of columnar cortical structures during the critical period of postnatal ontogenesis.

Neuronal death in the lateral geniculate nucleus of young ferrets following a cortical lesion: time-course, age dependence and involvement of caspases.

In humans and many other mammalian species, the behavioural consequences of a cortical lesion tend to be milder when it occurs early in life, and there is evidence that an important factor contributing to the behavioural sparing in the young is the formation of new thalamo-cortical connections by thalamic neurons initially connected with the lesioned area. However, this plasticity may be hindered by the secondary death of many of these neurons owing to the elimination by the primary lesion of their trophic support from the cortex. With the long-term aim of preventing this neuronal death, we have here characterised its timing in the lateral geniculate nucleus of ferrets following lesions of the visual cortex on postnatal days 5, 10, 20 or 35. After the earliest lesions (P5 or P10), this cell death began rapidly and occurred synchronously, being maximal at 48 h and declining to zero over the next few days. Following later lesions the cell death began more slowly and continued for longer. The dying neurons contained activated caspase-3 and fragmented DNA and their number 2 days after a P5 lesion was reduced by the broad-band caspase inhibitor z-VAD.fmk. These experiments open the way for a concerted effort to enhance adaptive plasticity by neuroprotection in the hours or days following a cortical lesion.

Identification of subdivisions in the medial geniculate body of the guinea pig.

The accurate and reliable identification of subdivisions within the auditory thalamus is important for future studies of this nucleus. However, in the guinea pig, there has been no agreement on the number or nomenclature of subdivisions within the main nucleus of the auditory thalamus, the medial geniculate body (MGB). Thus, we assessed three staining methods in the guinea pig MGB and concluded that cytochrome oxidase (CYO) histochemistry provides a clear and reliable method for defining MGB subdivisions. By combining CYO with acetylcholinesterase staining and extensive physiological mapping we defined five separate divisions, all of which respond to auditory stimuli. Coronal sections stained for CYO revealed a moderate to darkly-stained oval core. This area (the ventral MGB) contained a high proportion (61%) of V-shaped tuning curves and a tonotopic organisation of characteristic frequencies. It was surrounded by four smaller areas that contained darkly stained somata but had a paler neuropil. These areas, the dorsolateral and suprageniculate (which together form the dorsal MGB), the medial MGB and the shell MGB, did not have any discernable tonotopic frequency gradient and contained a smaller proportion of V-shaped tuning curves. This suggests that CYO permits the identification of core and belt areas within the guinea pig MGB.

Adenylate cyclase 1 as a key actor in the refinement of retinal projection maps.

cAMP occupies a strategic position to control neuronal responses to a large variety of developmental cues. We have analyzed the role of calcium-stimulated adenylate cyclase 1 (AC1) in the development of retinal topographic maps. AC1 is expressed in retinal ganglion cells (RGCs) from embryonic day 15 to adulthood with a peak during the first postnatal week. At that time, the other calcium-stimulated AC, AC8, is expressed in the superior colliculus (SC) but not in the RGCs. In mice of the barrelless strain, which carry an inactivating mutation of the AC1 gene, calcium-stimulated AC activity is reduced by 40-60% in the SC and retina. RGC projection maps were analyzed with a variety of anterograde and retrograde tracers. After an initially normal development until postnatal day 3, retinal fibers from the ipsilateral and contralateral eye fail to segregate into eye-specific domains in the lateral geniculate nucleus and the SC. Topographic defects in the fine tuning of the retinotectal and retinogeniculate maps are also observed with abnormalities in the confinement of the retinal axon arbors in the anteroposterior and mediolateral dimensions. This is attributable to the lack of elimination of misplaced axon collaterals and to the maintenance of a transient ipsilateral projection. These results establish an essential role of AC1 in the fine patterning of the retinal map. Calcium-modulated cAMP production in the RGCs could constitute an important link between activity-dependent changes and the anatomical restructuring of the retinal terminal arbors within central targets.

Human COX6A1 gene: promoter analysis, cDNA isolation and expression in the monkey brain.

The human COX6A1 gene encodes the ubiquitous isoform of cytochrome c oxidase (COX) subunit VIa (VIa-L), and is located in a CpG island on chromosome 12q24.2. We compared the COX6A1 gene with the published cDNA and several ESTs and concluded that subunit COX VIa-L is synthesized as a preprotein, as are other COX subunits. The same transcription start sites were identified by primer extension analysis of human brain and lymphoblastoid RNA. Analysis of the COX6A1 promoter revealed several conserved sequence elements found in other COX genes, namely binding sites for nuclear respiratory factor 1 (NRF-1), nuclear respiratory factor 2/GA binding protein (NRF-2/GABP), and ying-yang protein 1 (YY1). These conserved elements were shown to bind nuclear proteins from HeLa nuclear extracts. COX6A1 cDNA was isolated from a human brain cDNA library, and the sequence was identical to that of human liver. The expression of this gene was demonstrated by in-situ hybridization in monkey brain sections with our human brain cDNA. Monocular impulse blockade in adult monkeys induced a downregulation of COX6A1 expression in deprived visual neurons, suggesting that this subunit gene is regulated by neuronal activity.

Rearing with monocular lid suture induces abnormal NADPH-diaphorase staining in the lateral geniculate nucleus of cats.

We investigated the changes in NADPH-diaphorase staining that occur in the lateral geniculate nucleus of cats following rearing with monocular lid suture. This staining allows visualization of the synthesizing enzyme of nitric oxide, a neuromodulator associated with plasticity. In the lateral geniculate nucleus of normally reared cats, NADPH-diaphorase exclusively labels the axons and terminals of an input from the parabrachial region of the brainstem; no geniculate cells in the A-laminae are labeled. Early monocular lid suture has no obvious effect on the NADPH-diaphorase staining of parabrachial axons. However, this lid suture results in the abnormal appearance of NADPH-diaphorase staining for geniculate somata. These cells are located primarily in the nondeprived laminae. Double-labeling experiments indicate that these cells with abnormal NADPH-diaphorase reactivity are Y relay cells: NADPH-diaphorase staining is found in cells retrogradely labeled from visual cortex; it is found in cells labeled with a monoclonal antibody for CAT-301, which selectively targets Y cells; it is not found in cells labeled with an anti-GABA antibody, which targets interneurons. Also, NADPH-diaphorase labeled cells are among the largest cells in the nondeprived laminae, again suggesting that they are Y relay cells. We cannot suggest a specific mechanism for this induction of NADPH-diaphorase labeling, but it does not seem to be due to abnormal binocular competition induced by the monocular lid suture.

Transient expression of NADPH-diaphorase in the lateral geniculate nucleus of the ferret during early postnatal development.

Retinogeniculate projections in the ferret are refined during postnatal development so that inputs from the two eyes become segregated into eye-specific laminae, and each eye-specific lamina is further divided into sublaminae containing inputs from on-center or off-center afferents. Segregation into eye-specific laminae and on/off sublaminae is dependent on neuronal activity; sublamination depends on activation of N-methyl-d-aspartate (NMDA) receptors. By analogy with the suggested role of nitric oxide in NMDA-mediated long-term potentiation in the hippocampus, we investigated a possible role for nitric oxide in ferret retinogeniculate development. The expression of NADPH-diaphorase, a nitric oxide synthase, was examined histologically in the lateral geniculate nucleus of ferrets at several postnatal ages. At birth, neuropil is labeled in the nucleus, although no cell bodies are visible. After the first postnatal week, some labeled cells appear, predominantly in the C laminae. By three postnatal weeks, cell bodies are clearly labeled in all geniculate laminae. Staining reaches a peak in density at about four postnatal weeks, then declines such that by six postnatal weeks labeled cells are no longer visible. This transient expression of NADPH-diaphorase activity is consistent with a role for nitric oxide in the development of mature connections within the ferret lateral geniculate nucleus.

Distribution of acetylcholinesterase in the geniculo striate system of Galago senegalensis and Aotus trivirgatus: evidence for the origin of the reaction product in the lateral geniculate body.

This inquiry began with the discovery that just two layers of the lateral geniculate nucleus (GL) of Galago contain large amounts of acetylcholinesterase (AChE). These two layers (layers 3 and 6) are similar in cell size and Nissl-staining characteristics and project to the same layer in the striate cortex. To find out whether the pattern of staining is unique in the Galago, we examined the distribution of AChE in the lateral geniculate nucleus of the owl monkey, Aotus trivirgatus. In this species we found that the parvocellular layers (3 and 4) stained darkly for AChE while the magnocellular layers (1 and 2) were only slightly stained. The interlaminar zones as well as the "S" layers were also distinguished by a high level of AChE staining. In order to determine the source of the cholinesterase staining in layers 3 and 6 of Galago, we studied, in separate experiments, the effects of kainic acid injections into GL, of eye enucleation, and of lesions of the striate cortex. Injections of kainic acid, followed by survival times of 2 and 11 days, produced severe cellular destruction in GL, yet the AChE staining of layers 3 and 6 was undiminished. Eye enucleations had no effect upon the AChE staining of GL even after a survival period of 3 years. In contrast, a small lesion of the striate cortex, followed by a 9-day survival period, produced conspicuous gaps in the AChE staining of layers 3 and 6. These results indicate that the AChE in layers 3 and 6 is not attributable to the cells within the layers, or to retinal fibers, but is dependent upon descending projections from the striate cortex. Because of the dependence of the AChE reaction product in layers 3 and 6 of GL upon an intact striate cortex, we turned our attention to the distribution of AChE in the striate cortex. In Galago, cholinesterase-positive cells were found in layer VI of the striate cortex; and in both Galago and Aotus, the striate cortex was distinguished from other cortical areas by a prominent band of cholinesterase activity within layer IV. This band ended abruptly at the 17-18 border. The precise origin of this cholinesterase staining within layer IV of the striate cortex remains to be determined.

The localization of cytochrome oxidase in the LGN and striate cortex of postnatal kittens.

The distribution of cytochrome oxidase (C.O.) was examined in the lateral geniculate nucleus of the kitten during the first postnatal month and compared with the adult pattern. During the first week, most of the C.O. was localized within the perikarya of geniculate neurons. Perigeniculate neurons had darkly reactive dendrites as well as perikaya. A population of relatively large, darkly reactive neurons became distinguishable around the end of the first week, as the level of reactivity diminished to moderate-to-light within most medium and small neurons. On the basis of their relative size and pattern of distribution, most of the darkly reactive neurons are likely to represent ones that will later have class 1 morphology and develop Y receptive field properties. These cells normally undergo rapid growth earlier, and their growth is more adversely affected by early short-term monocular suture than other classes of less reactive geniculate neurons. Thus, in the LGN of developing kitten, C.O. histochemistry may be used as a functional marker for future class 1 Y-cells. The reactivity of the neuropil gradually increases as synapses with dendrites mature. At the electronmicroscopic level the increased reactivity of the neuropil is due mainly to an increase in the number of reactive mitochondria localized within the growing dendrites. In the developing striate cortex of postnatal kittens dark reactivity is localized in the outer part of layer II for the first 2 weeks and then disappears. Dark reactivity gradually increases in layer IV after the third week. The changes in C.O. reactivity accompany pathway-specific physiological and anatomical changes that occur during early postnatal development.

Differential effect of visual deprivation on cytochrome oxidase levels in major cell classes of the cat LGN.

Cytochrome oxidase histochemistry was used to examine the effects of visual deprivation on the development of neurons in the lateral geniculate nucleus of the kitten. Early postnatal monocular suture results in a decrease in reactivity within the neuropil of visually deprived binocular laminae A, A1, magnocellular C, and medial interlaminar nucleus. Within these regions, monocular suture has a greater effect on the relative numbers of, and the growth of darkly reactive (normally large), presumed Y-cells than on other less reactive geniculate neuronal classes. The decreases in the reactivity of the neuropil may be attributed to the decreases in the number of mitochondria, the number of darkly reactive mitochondria, and/or the number of darkly reactive mitochondria localized within dendrites. Although all classes of dendrites appear to be adversely affected, the decrease in C.O. reactivity was most dramatic within the presumed proximal dendrites of class 1 Y-cells. These dendrites were identified by the type of synaptic contacts they formed with retinal terminals (Rapisardi and Miles, '84, J. Comp. Neurol. 223:515-534; Wilson et al., '84, Proc. R. Soc. Lond. [Biol.] 221:411-436). As with Y-cells, the effects of monocular suture on the large darkly reactive cells were not as dramatic at sites where binocular interactions were either absent or where they had been experimentally eliminated. Based on the present and previously reported findings from several laboratories, it is likely that the selective physiological and morphological effects of monocular suture on Y-cells are accompanied by metabolic deficits involving both dendrites and perikarya. These effects appear to be due more to binocular interactions than to visual deprivation per se.

Brain nitric oxide synthase expression in the developing ferret lateral geniculate nucleus: analysis of time course, localization, and synaptic contacts.

Nitric oxide (NO) is a diffusible neurotransmitter that has been implicated in key developmental events, including the refinement of retinogeniculate axons into ON/OFF sublayers in the ferret lateral geniculate nucleus (LGN), and in the formation of eye-specific laminae in other species. To understand the role of NO in the LGN, it is critical to fully characterize the pattern of brain nitric oxide synthase (bNOS) expression within the nucleus, including the phenotype of the neural elements that express it. We have examined the temporal and spatial pattern of bNOS expression in the ferret LGN during the first 6 weeks of postnatal development, and in the adult, by detecting bNOS with a monoclonal antibody as well as beta-nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry. We have found that bNOS is expressed in neurons in the A laminae of the LGN as early as postnatal day 7 (P7), a time coincident with eye-specific segregation of retinal axons. This expression continues through P35, with peak somatodendritic expression at P21. Fluorescent double labeling using antibodies to bNOS and glutamic acid decarboxylase indicate that bNOS is expressed in gamma-aminobutyric acid-ergic interneurons within the A laminae. Electron microscopic examination of bNOS-labeled cells showed synaptic contacts from terminals with two distinct morphologic profiles. Expression of bNOS within interneurons that receive contacts from multiple sources indicates that the synaptic circuitry associated with bNOS activation and the potential targets of NO may be more complex than originally thought and supports a potential new role for interneurons as cellular intermediaries in the refinement of pathways in the LGN. Our findings broaden the window of time that bNOS may be active within the developing LGN, suggesting an expanded role for NO during early postnatal development.

Immunocytochemistry and distribution of parabrachial terminals in the lateral geniculate nucleus of the cat: a comparison with corticogeniculate terminals.

We used immunohistochemistry in cats to demonstrate the presence of brain nitric oxide synthase (BNOS) in cholinergic fibers within the A-laminae of the lateral geniculate nucleus. We used a double labeling procedure with electron microscopy and found that all terminals labeled for choline acetyltransferase (ChAT) in the geniculate A-laminae were double labeled for BNOS. Also, some interneuron dendrites, identified by labeling for gamma-aminobutyric acid (GABA), contained BNOS, but relay cell dendrites did not. We then compared parabrachial and corticogeniculate terminals, identifying the former by BNOS/ChAT labeling and the latter by orthograde transport of biocytin injected into cortical area 17, 18, or 19. All corticogeniculate terminals and most BNOS- or ChAT-positive brainstem terminals displayed RSD morphology, whereas some brainstem terminals exhibited RLD morphology. However, parabrachial terminals were larger, on average, than corticogeniculate terminals. We also found that parabrachial terminals were located both inside and outside of glomeruli, and they always contacted relay cell dendrites proximally among retinal terminals (the retinal recipient zone). In contrast, the cortical terminals were limited to peripheral dendrites (the cortical recipient zone). Thus, little if any overlap exists in the distribution of parabrachial and corticogeniculate terminals on the dendrites of relay cells.

An analysis of the cellular localization of cytochrome oxidase in the lateral geniculate nucleus of the adult cat.

The distribution of cytochrome oxidase (C.O.) was examined in the normal adult cat lateral geniculate nucleus at the cellular and electron-microscopic levels. The darker reactivity of the X- and/or Y-receptive laminae (A, A1, magnocellular lamina C [Cm], and medial interlaminar nucleus [MIN]) compared with the lightly reactive W-receptive parvicellular lamina C (Cp) indicates that there are pathway-specific histochemical differences in the visual system of the cat. At the cellular level, darkly reactive large cells in the lateral geniculate nucleus (LGN) closely resemble class 1, Y-cells, in relative size and distribution, thus indicating that C.O. histochemistry may be used as a functional marker for these cells. Perigeniculate neurons are also darkly reactive. Neuronal classes 2, 4, and 3 (presumed X-cells, W-cells, and/or interneurons) have moderate to lightly reactive perikarya. The darkly reactive neuronal classes tend to receive relatively stronger proximal excitatory synaptic input than do the less reactive neuronal classes. Since all neuronal classes appeared to have darkly (or moderately) reactive dendrites, C.O. reactivity must differ between dendrite and soma of some neuronal classes. At the electron-microscopic level, distinct components of the neuropil tend to have specific levels of C.O. reactivity. The predominance of darkly reactive mitochondria in dendrites indicates that dendrites are metabolically very active. RLD and may F's, but few large axon terminals with round vesicles (RL) or small axon terminals with round vesicles (RS) profiles are darkly reactive, implying that specific classes of presynaptic structures are more active than others. Thus C.O. histochemistry may be useful for distinguishing not only functionally active neuronal classes such as Y-cells and perigeniculate (PG) neurons from less active neuronal classes, but also functionally more or less active parts of the same neuron including its dendrites, axons, and/or axon terminals.

Histochemical localization of cytochrome oxidase activity in the visual system of the tree shrew:normal patterns and the effect of retinal impulse blockage.

The tree shrew Tupaia belangeri has three functional pathways (ON-center, OFF-center, and W-like cells) that arise in the retina and proceed through separate LGN laminae to separate cortical targets. To determine whether these pathways have consistent differences in activity, cytochrome oxidase (C.O.) patterns were examined in the retina, LGN, and striate cortex. In six normal tree shrews the outer and inner plexiform layers of the retina were highly reactive for C.O. A pale, vascularized cleft zone separated the a (OFF) and b (ON) inner plexiform sublaminae, which seemed about equally reactive for C.O. In the LGN, laminae 1 and 2 (ON-center cells) and laminae 4 and 5 (mostly OFF-center cells) were highly reactive for C.O. LGN lamina 3 and 6 are part of an W-like afferent pathway. Lamina 3 was distinctly paler than laminae 1, 2, 4, and 5 while lamina 6 was intermediate. In the striate cortex, layer IV was the most reactive layer. Sublayer IVb (predominantly an OFF region) was consistently more reactive than sublayer IVa (predominantly ON). The middle portion, layer IVm, was paler than either IVa or IVb. This paler region includes, but extends above and below, the cell-sparse "cleft" region. Thus, considering all three levels of the retinogeniculostriate pathway, the ON and OFF systems were equally active until they reached the striate cortex, where the OFF system appeared to be more active than the ON. The W-cell laminae in the LGN exhibited the lowest level of activity. The contribution of ganglion cell activity to these patterns was assessed by intravitreal administration of tetrodotoxin (TTX) blockade either monocularly (three animals) or binocularly (two animals). In the TTX-treated retinae, the inner plexiform a and b sublaminae were paler for C.O., although visible, and were still separated by the pale cleft. The ganglion cell layer was very pale in comparison to the normal. In the LGN, monocular TTX blockade reduced the C.O. reactivity in the ON and OFF laminae that received input from the treated eye but had little effect on the W-like cell laminae. The ipsilaterally innervated ON and OFF laminae were more affected than were the contralaterally innervated laminae. Binocular TTX treatment resulted in a decrease of C.O. activity in the binocular segment of the ON and OFF LGN laminae. In the striate cortex, the most marked changes following TTX treatment occurred in layer IV.(ABSTRACT TRUNCATED AT 400 WORDS)

Development of acetylcholinesterase activity in the lateral geniculate nucleus.

The pattern of acetylcholinesterase activity in the tree shrew (Tupaia belangeri) lateral geniculate nucleus (LGN) undergoes a number of striking changes during postnatal development. The adult tree shrew LGN is made up of six cellular layers divided by relatively cell-free interlaminar zones. At birth, however, the nucleus appears unlaminated when processed with conventional Nissl-staining techniques. The cellular lamination appears during the first postnatal week. The eyes open much later, typically at the end of the third week after birth. In the adult tree shrew, acetylcholinesterase (AChE) activity is found throughout the nucleus (both within and between the six cellular layers). In most sections examined, reaction product is slightly more intense in the lateral cell layers (4, 5, and 6). This is in sharp contrast to the pattern at birth (postnatal day zero, or P0). The detectable AChE activity at this age is apparently found in inchoate layers 1-2 and 4-5. Within these pairs, areas innervated by the ipsilateral eye (i.e., incipient layers 1 and 5) appear to contain more reaction product. From P0 to P4, the density of AChE activity increases in layers 1-2 and 4-5 and becomes detectable in the barely evident layers 3 and (usually) 6 at this age. By the middle of the second postnatal week, after laminae are clearly apparent with a Nissl stain, AChE activity has increased and is mainly associated with each cellular layer in the nucleus. During the third week after birth this pattern undergoes a radical shift. The most intense AChE activity is now in the interlaminar zones. Finally, as the adult pattern emerges, AChE activity increases in the cellular layers and all areas of the nucleus exhibit relatively high levels of AChE activity. Superimposed on this changing laminar pattern of AChE activity are changes related to the retinotopic map within the nucleus. Portions of the LGN representing central vision develop their characteristic pattern of activity several days ahead of the regions representing more peripheral visual field locations. AChE activity is also found transiently in the optic tract near the LGN during the first 3 postnatal weeks. Two (possibly three) groups of AChE-carrying fibers can be traced from the optic chiasm to their apparent sites of termination (or origin) in the parabigeminal nucleus, ventral lateral geniculate nucleus, and dorsal LGN. The activity present in the optic tract disappears shortly after eye opening.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructure of cholinergic synaptic terminals in the thalamic anteroventral, ventroposterior, and dorsal lateral geniculate nuclei of the rat.

The principal relay nuclei of the thalamus receive their cholinergic innervation from two midbrain cholinergic groups: the pedunculopontine tegmental nucleus and the laterodorsal tegmental nucleus. The different thalamic nuclei exhibit populations of cholinergic axons which vary in density and morphology when examined at the light microscopic level. However, the ultrastructure of the cholinergic terminals in different thalamic nuclei has not been described. This study was undertaken to confirm that synaptic contacts are formed by cholinergic axons in several principal thalamic relay nuclei, to describe their ultrastructural morphology, and to identify the types of postsynaptic elements contacted by cholinergic synaptic terminals. The thalamic nuclei examined in this study are the dorsal lateral geniculate nucleus, ventroposteromedial nucleus, ventroposterolateral nucleus, and anteroventral nucleus. Our results confirm that cholinergic axons form synaptic terminals in these thalamic nuclei. Cholinergic synaptic terminals contact structures outside the characteristic synaptic glomeruli, are never postsynaptic, and have morphologies and postsynaptic targets which differ among the thalamic nuclei. In the ventroposterior nuclei, cholinergic terminals form asymmetric synaptic contacts onto larger dendrites in the extraglomerular neuropil. In the anteroventral nucleus, cholinergic terminals form both symmetric and asymmetric synaptic contacts onto dendrites and somata. Cholinergic terminals in the anteroventral nucleus are larger than those in other nuclei. In the dorsal lateral geniculate nucleus, cholinergic terminals contact both somata and dendrites in the extraglomerular neuropil, but the synaptic contacts in this nucleus are symmetric in morphology.

Anatomy of glutamic acid decarboxylase immunoreactive neurons and axons in the rat medial geniculate body.

This is a study of the form, density, and distribution of glutamic acid decarboxylase (GAD) immunoreactive neurons and puncta (axon terminals) in the adult rat medial geniculate complex. GAD-positive elements were stained by either the peroxidase-antiperoxidase or avidin-biotin procedures. Thalamic architectonic subdivisions were defined independently in Golgi, Nissl, plastic-embedded semi-thin, and fiber-stained preparations, and from investigations of medial geniculate connectivity. GAD-positive neurons represent only approximately 1% of medial geniculate neurons. They occur in the three major medial geniculate subdivisions (ventral, dorsal, and medial). There is variability between subdivisions in the form and number of such neurons, and among the puncta. In the ventral division, immunopositive somata may have sparsely branched dendrites as long as 300-400 microns and capped with varicose expansions or bouton-like sprays of appendages. These closely appose the somata or primary dendrites of other cells; the axons of these GAD-positive neurons are also immunostained. In the dorsal division there are fewer GAD-positive neurons and their structure is different. Their dendrites are rarely immunoreactive for more than 100-150 microns; nor can their immunostained axons be traced very far. In the medial division the number of GAD-positive neurons, considering the relatively small size of this division, was high. These neurons rarely have immunostained dendrites, and more than one type of neuron is immunoreactive. The average somatic diameter of GAD-positive neurons is about 60% of that of non-immunostained cells in semi-thin material; however, the range of somatic area and the dendritic variability of these neurons suggest that cells representing more than one population are immunopositive and include all but the largest neurons. The puncta also show regional differences. Small (0.5-2 microns in diameter), medium (2-3 microns), or large (greater than 3 microns) puncta occur. In the ventral division, the predominantly medium-sized puncta are about four times as numerous on a unit/area basis than in the dorsal division, where they are far smaller and more delicate; medial division puncta are as numerous as those in the ventral division, but are much larger and coarser, and may form perisomatic arrangements. Controls were devoid of specific immunostaining.(ABSTRACT TRUNCATED AT 400 WORDS)

The distribution of glutamic acid decarboxylase immunoreactivity in the diencephalon of the opossum and rabbit.

We have examined the distribution of neurons and terminals immunoreactive for glutamic acid decarboxylase (GAD) in the thalamus and adjacent structures of the opossum (Didelphis virginiana) and the rabbit and have compared this distribution with the distributions we described previously for the cat and bushbaby (Galago senegalensis). The significance of these experiments depends, first, on the fact that GAD is the synthetic enzyme for GABA, and therefore that GAD immunoreactivity is a marker for GABAergic inhibitory neurons, and second, on previous findings that suggest that GABAergic neurons in the dorsal thalamus are local circuit neurons. In both cat and Galago, GAD-immunoreactive neurons are distributed essentially throughout the entire thalamus. In the opossum, GAD neurons are chiefly confined to the dorsal lateral geniculate nucleus and the lateral extremity of the lateral posterior nucleus. The distribution of GAD neurons in the rabbit is intermediate between that found in the opossum on the one hand and cat and Galago on the other. Like opossum, about 25% of the neurons in the lateral geniculate nucleus of rabbit are GAD immunoreactive. Unlike opossum, however, as many as 18% of the cells in the ventral posterior nucleus of the rabbit are GAD immunoreactive, and scattered cells are also labeled in other thalamic areas, such as the medial geniculate and the lateral group. Aside from the findings in the dorsal thalamus, the chief observation is that GAD-immunoreactive neurons and/or terminals densely fill all principal targets of the optic tract, including the ventral lateral geniculate nucleus; the superficial gray layer of the superior colliculus; the anterior, posterior, and olivary pretectal nuclei; the nucleus of the optic tract; and the medial and lateral terminal nuclei of the accessory optic tract. These results support the idea first put forward by Cajal that local circuit neurons increase in number during the course of the evolution of complex mammalian brains. If we can assume that the conservative opossum retains characteristics reflecting an early stage of mammalian evolution, the results suggest that thalamic local circuit neurons arose first in the visual system and only later in evolution spread throughout the thalamus.

Anatomical demonstration of ocular segregation in the retinogeniculocortical pathway of the New World capuchin monkey (Cebus apella).

We describe the architecture of the dorsal lateral geniculate nucleus and primary visual cortex (striate cortex; area 17) of the New World capuchin monkey (Cebus apella) on the basis of the distribution of cell bodies and cytochrome oxidase histochemistry. Changes in staining for cytochrome oxidase following unilateral enucleation served to indicate the organization of the representation of the two eyes in the retinogeniculocortical pathway. The number and disposition of eye-specific layers within the lateral geniculate nucleus of Cebus are consistent with the common plan of geniculate organization in anthropoid primates, and the radial organization of area 17 fits the pattern common to New World squirrel and Old World macaque monkeys, including the presence of cytochrome-oxidase-rich zones in supragranular and deeper cortical layers (Horton: Philos. Trans. R. Soc. Lond. [Biol.] 304:199-253, '84). Our principal finding is that cytochrome oxidase histochemistry following unilateral eye removal unequivocally reveals ocular dominance columns in the striate cortex of Cebus. As in the macaque (Hubel: Nature 292:762-764, '82), ocular dominance columns extend through the thickness of cortex and blobs are centered on columns, but the array of columns viewed tangentially is less orderly or more mosaic than in the macaque, and there is apparently significant overlap between columns. The presence of well-defined ocular dominance columns in Cebus, as in Ateles (Florence, Conley, and Casagrande: J. Comp. Neurol. 243:234-248, '86) but not in other New World monkeys examined previously, emphasizes the phylogenetic lability of binocular segregation in the primate visual cortex. In addition, the present results indicate significant differences with respect to the tangential organization of the ocular dominance domain between primate species in which ocular dominance columns are present.

Cell-specific expression of type II calcium/calmodulin-dependent protein kinase isoforms and glutamate receptors in normal and visually deprived lateral geniculate nucleus of monkeys.

In situ hybridization histochemistry and immunocytochemistry were used to map distributions of cells expressing mRNAs encoding alpha, beta, gamma, and delta isoforms of type II calcium/calmodulin-dependent protein kinase (CaMKII), alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate (AMPA)/ kainate receptor subunits, (GluR1-7), and N-methyl-D-aspartate (NMDA) receptor subunits, NR1 and NR2A-D, or stained by subunit-specific immunocytochemistry in the dorsal lateral geniculate nuclei of macaque monkeys. Relationships of specific isoforms with particular glutamate receptor types may be important elements in neural plasticity. CaMKII-alpha is expressed only by neurons in the S laminae and interlaminar plexuses of the dorsal lateral geniculate nucleus, but may form part of a more widely distributed matrix of similar cells extending from the geniculate into adjacent nuclei. CaMKII-beta, -gamma, and -delta isoforms are expressed by all neurons in principal and S laminae and interlaminar plexuses. In principal laminae, they are down-regulated by monocular deprivation lasting 8-21 days. All glutamate receptor subunits are expressed by neurons in principal and S laminae and interlaminar plexuses. The AMPA/kainate subunits, GluR1, 2, 5, and 7, are expressed at low levels, although GluR1 immunostaining appears selectively to stain interneurons. GluR3 is expressed at weak, GluR 6 at moderate and GluR 4 at high levels. NMDA subunits, NR1 and NR2A, B, and D, are expressed at moderate to low levels. GluR4, GluR6 and NMDA subunits are down-regulated by visual deprivation. CaMKII-alpha expression is unique in comparison with other CaMKII isoforms which may, therefore, have more generalized roles in cell function. The results demonstrate that all of the isoforms are associated with NMDA receptors and with AMPA receptors enriched with GluR4 subunits, which implies high calcium permeability and rapid gating.