Laminar distribution of NMDA receptors in cat and monkey visual cortex visualized by [3H]-MK-801 binding

Glutamate is the major excitatory neurotransmitter of the mammalian central nervous system. Two major classes of glutamate receptors have been reported. The actions of glutamate on its N-methyl-D-aspartate (NMDA)-type receptor may underlie developmental and adult plasticity as well as neurotoxicity. The NMDA-type of glutamate receptor in cat and monkey visual cortex was visualized by means of in vitro receptor autoradiography with the noncompetitive NMDA-receptor antagonist [³H]-MK-801. The kinetics, performed on tissue sections, revealed an apparently single, saturable site with an approximate dissociation constant (KD) of 18.5 nM in cat and 15.9 nM in monkey visual cortex. Autoradiography, performed on frontal sections of cat and monkey visual cortex, revealed a heterogeneous laminar distribution of NMDA receptors. Cat areas 17,18,19, and the lateral suprasylvian areas exhibited a similar NMDA-receptor distribution. In these areas, NMDA receptors were most prominent in layer II and the upper part of layer III. In monkey striate cortex, NMDA receptors were primarily concentrated in layers II, upper III, IVc, V, and VI. In monkey secondary visual cortex, [³H]-MK-801 labeling was most prominent in layers II, V, and VI; whereas in the temporal visual areas included in this study layer II displayed the heaviest receptor labeling. In neither cat nor monkey could we observe significant differences in NMDA-receptor distribution between different retinotopic subdivisions within a single visual area. Neither did we detect any periodic changes in NMDA-receptor distribution that would correspond to the compartments defined by cytochrome-oxidase in monkey V1 and V2. © 1993 Wiley-Liss, Inc.     

Regional distribution of binding sites for neuropeptide Y in cat and monkey visual cortex determined by in vitro receptor autoradiography

The goal of this study was to elucidate the precise regional and laminar distribution of neuropeptide Y (NPY) binding sites in feline and primate visual cortex. By means of in vitro receptor autoradiography, NPY binding sites in primate and feline visual cortex were specifically labeled with 3H-NPY. In cat area 17, the highest density of NPY-binding sites was present in lamina I and the upper half of lamina II. The density then gradually decreased towards lamina VI. Areas 18 and 19 exhibited a similar binding site-density profile. The decrease in density from superficial to deep layers was more gradual in area 18 than in areas 17 and 19. In monkey primary visual cortex (V1), layer IVc presented a high concentration of NPY binding sites, in addition to a dense zone of binding sites in layer I. Monkey secondary visual cortex (V2) displays a similar dense zone in layer I, but lacks such high density of NPY binding sites in layer IV. Therefore, the border between primary and secondary visual cortex coincides with the abrupt disappearance of this latter high density in layer IV. In cat as well as in monkey visual cortex, no significant differences were found between regions representing central vision and those representing the peripheral parts of the visual field. Comparison of our results for NPY binding sites with the distribution of alpha 1-adrenergic receptors, as recently described by Rakic et al. (J. Neurosci. 8(10):3670-3690, 1988) for primate and Parkinson et al. (Brain Res. 457:70-78, 1988) for feline visual cortex, revealed that those two patterns are very similar.     

Laminar and regional distribution of galanin binding sites in cat and monkey visual cortex determined by in vitro receptor autoradiography.

The distribution of galanin (GAL) binding sites in the visual cortex of cat and monkey was determined by autoradiographic visualization of [125I]-GAL binding to tissue sections. Binding conditions were optimized and, as a result, the binding was saturable and specific. In cat visual cortex, GAL binding sites were concentrated in layers I, IVc, V, and VI. Areas 17, 18, and 19 exhibited a similar distribution pattern. In monkey primary visual cortex, the highest density of GAL binding sites was observed in layers II/III, lower IVc, and upper V. Layers IVA and VI contained moderate numbers of GAL binding sites, while layer I and the remaining parts of layer IV displayed the lowest density. In monkey secondary visual cortex, GAL binding sites were mainly concentrated in layers V-VI. Layer IV exhibited a moderate density, while the supragranular layers contained the lowest proportion of GAL binding sites. In both cat and monkey, we found little difference between regions subserving central and those subserving peripheral vision. Similarities in the distribution of GAL and acetylcholine binding sites are discussed.     

Histochemical localization of synaptic zinc in the developing cat visual cortex

The terminal boutons of many neurons in the telencephalon are known to contain a vesicle-bound, chelatable pool of zinc (Zn²⁺) that can be selectively visualized with histochemical procedures. In this paper, the normal laminar, areal, and ultrastructural distribution of histochemically reactive zinc in the visual cortex of the adult cat as well as its development from birth are described. In the adult cat visual cortex, intense zinc staining was found in layers I, II, III, and V, with layer VI staining only lightly. The primary geniculostriate input zone, layer IV, was conspicuously distinguished by the relative absence of zinc. This distinct pattern was restricted only to areas 17 and 18 and differentiated them from adjacent cortical area 19 laterally and the subadjacent cingulate cortex. The earliest zinc-positive staining in visual cortical areas 17 and 18 was first apparent by postnatal day 2 (P2) and was characterized by staining of a thin layer at the bottom of the cortical plate. By P10, and continuing through P20, synaptic zinc formed a trilaminar pattern of dense staining in areas 17 and 18, which included the top of layer I, and layers III and V. The laminar pattern of synaptic zinc in visual cortex appeared mature by P30, except that the distribution of zinc in layer IV was not uniform. This was most apparent around P50 in tangential sections through layer IV from opened and flattened cortex, where columnar patches of increased zinc staining were apparent in area 17. These columns were approximately 400 μm in diameter, with a centre-to-centre spacing of approximately 900 μm. The distribution of synaptic zinc apparently reflects the process of synaptic maturity of the cat visual cortex and appears to demarcate a particular form of columnar organization in visual cortex. © 1993 Wiley-Liss, Inc.     

Immunocytochemical localization of somatostatin and cholecystokinin in the cat visual cortex

Immunocytochemistry was used to examine the morphology and distribution of cholecystokinin-like and somatostatin-like neurons in areas 17, 18 and 19 of cat visual cortex as a function of lamination. Immunoreactive cells of both peptides were observed in all layers of cat visual cortex. While somatostatin-like cells occurred mainly in layers II + III and VI, cholecystokinin-like cells were observed chiefly in the superficial layers (I + II + III). Somatostatin-like cells displayed morphological features of multipolar and bipolar varieties, and cholecystokinin-like cells displayed morphological features of multipolar and bitufted varieties. Similar results were obtained for all 3 areas.     

The distribution of the cells of origin of callosal projections in cat visual cortex

The distribution of neurons projecting through the corpus callosum (callosal neurons) was examined in retinotopically defined areas of cat visual cortex. As many callosal neurons as possible were labeled in a single animal by surgically dividing the posterior two-thirds of the corpus callosum and exposing the cut ends of callosal axons to horseradish peroxidase. The distribution of callosal neurons within a visual field representation was related to standard electrophysiological maps as well as to recording sites marked by electrolytic lesions. Callosal neurons were found in every retinotopically defined cortical area. The portion of the visual field representation that contained callosal neurons increased progressively from the area 17/18 border to area 19, to areas 20 and 21, and to the lateral suprasylvian visual areas. In area 17, the portion of the visual field representation containing callosal neurons extended from the vertical meridian out to a maximum of 10 degrees azimuth. In the posteromedial lateral suprasylvian visual area, callosal neurons were present in a region extending from the vertical meridian representation out to a representation of 60 degrees azimuth. Most callosal neurons were medium to large pyramids at the border of layers III and IV. A few layer IV stellates were among the callosal neurons of areas 17 and 18. In area 19 and even more so in the lateral suprasylvian visual areas, callosal neurons included pyramidal and fusiform-shaped cells in layers V and VI. The laminar distributions of callosal neurons in areas 20 and 21 were similar to those of area 19 and the lateral suprasylvian visual areas. The widespread distribution of callosal neurons in areas 20 and 21 and in the lateral suprasylvian visual areas suggests that the regions of peripheral visual field representation in cat cortex, as well as the representations of the vertical meridian, have access to the opposite cerebral hemisphere. This finding is significant in light of demonstrations of the importance of some of these cortical areas in the interhemispheric transfer of visual learning.     

Distribution of the AMPA2 glutamate receptor subunit in adult cat visual cortex

In this study, we revealed the distribution of the AMPA2 glutamate receptor subunit (AMPA2) in the visual cortical areas 17 and 18 of the adult cat by means of different techniques. In situ hybridization, with a cat-specific radioactively labeled oligonucleotide probe, showed that AMPA2 mRNA was expressed mainly in cortical layers II/III and V/VI with a lower expression in layer IV and practically no signal in layer I. Immunocytochemistry, using a polyclonal AMPA2 subunit-specific antibody, showed immunoreactivity almost exclusively in the somata and dendrites of pyramidal neurons in cortical layers II/III and V/VI. Only a very faint signal was detected in layer IV. Neurons with little or no AMPA2 have AMPA receptors that are highly permeable to calcium. By determining the location of AMPA2, this study therefore provides a clear examination of the distribution of Ca²⁺-impermeable AMPA receptors over the supra- and infragranular layers of cat visual cortex. The functional implication of the absence of AMPA2 in cortical layer IV and thus the presence of Ca²⁺-permeable AMPA receptors in this layer, is still speculative and has yet to be elucidated.     

The distribution of acetylcholinesterase in the lateral geniculate nucleus of the cat and monkey

The distribution of acetylcholinesterase (AChE) has been examined histochemically in the lateral geniculate nucleus (LGN) of the cat and the monkey, and in the cat visual cortex. It was found that in the cat, AChE is most concentrated in laminae A and A₁. Lamina C-proper possessed a weak band of AChE in its ventral part. Only restricted patches of activity were observed in the medial interlaminar nucleus. Laminae C_1–3 and the central interlaminar nucleus possessed very little AChE. This pattern of enzyme distribution suggests that in the cat LGN, AChE activity coincides with the sites of neurophysiologically recorded X-cells, which are predominantly found in laminae A and A₁ and are scarce in the C laminae and the medial interlaminar nucleus. The presence of AChE over neurones in layer VI of both areas 17 and 18 of the cerebral cortex in the cat suggests the corticothalamic pathway as one possible source of geniculate AChE activity.In the monkey LGN, AChE activity was observed in the parvocellular and magnocellular layers. The activity was greatest in the magnocellular layers, which are believed to contain neurons driven predominantly by retinal Y-cells. Thus, for this species the correlation between AChE activity and X-cells does not seem to hold.     

Numbers and proportions of GABA-immunoreactive neurons in different areas of monkey cerebral cortex

The number and proportion of neurons displaying GABA immunoreactivity were determined for 50-micron-wide columns through the thickness of 10 areas of monkey cerebral cortex, including the precentral motor area (area 4), 3 cytoarchitectonic fields of the first somatic sensory area (areas 3b, 1, and 2), 2 areas of parietal association cortex (areas 5 and 7), the first and second visual areas (areas 17 and 18), area 21 of the temporal lobe, and areas of the orbital and lateral frontal cortex. Methods of fixation and immunocytochemical processing were designed to maximize the number of stained cells in 15-micron-thick frozen sections and 1-micron-thick plastic sections. In 8 of the 10 areas the number and proportion of GABA-immunoreactive neurons per 50-micron-wide column were found to be the same (34-43 cells/column; 25% of the total neuronal population). Areas 17 and 3b differed. Area 17 contained 50% more GABA-immunoreactive neurons (52-66 cells/column) but more than twice the total number of neurons, so that the GABA cells made up less than 20% of the total. In 3 monkeys, the number and proportion of GABA-positive neurons per 50-micron-wide column in area 3b were smaller than in adjacent areas of sensorimotor cortex (26-42 cells/column; 19-22%). In 2 other monkeys, the number and proportion (34-43 cells/column; 24-26%) were the same as in adjacent areas. Despite the similarity among most areas of monkey cortex, within some areas, the number of GABA-positive neurons per 50-micron-wide column varied as much as 30%. These variations form a significant, repeating pattern only in area 18, where narrow bands (150-200 micron wide) of relatively few stained cells alternated with either narrow or wide bands (600-700 micron wide) in which columns contained more cells. The GABA-immunoreactive neurons were unevenly distributed across layers, with every area containing large numbers and proportions of stained cells in layer II, and every area but area 4 displaying a second concentration in the principal thalamocortical recipient layers. In area 4, the number of GABA-positive neurons declined sharply from layer II to layer III and remained low through layer VI. For areas displaying the greatest intra-areal variability, only 1 or 2 layers contributed significantly to that variability (layer IV in area 3b, layers III and V in area 18, and layers II and III in area 17).(ABSTRACT TRUNCATED AT 400 WORDS)     

Laminar distribution of GABA (gamma-aminobutyric acid) in the dorsal lateral geniculate nucleus, Area 17 and Area 18 of the visual cortex, and the superior colliculus of the cat

The laminar distribution of gamma-aminobutyric acid (GABA) was studied in certain structures of the visual system of the adult cat. A microassay method to measure GABA (10(-12) mol) was established using enzymatic cycling of NADP-NADPH. In the dorsal lateral geniculate nucleus, GABA concentration was highest in lamina A (average concentration 23 mmol/kg dry weight) and lowest in lamina C. In the visual cortex (Areas 17 and 18), the concentration of GABA was 10-12 mmol/kg dry weight in layers I-IV and 5-8 mmol/kg dry weight in layers V and VI. No significant difference was found in the GABA distribution in Areas 17 and 18. In the superior colliculus, the highest level of GABA was found in the upper part of the superficial gray layer (40 mmol/kg dry weight), whereas the deep layers contained GABA at a concentration of 23-28 mmol/kg dry weight. The results of the GABA distribution measurements revealed an orderly, layer-specific disposition of the neurotransmitter in the cat visual system. GABA may play an important role in the function of the visual system.     

Distribution and morphological characterization of phosphate-activated glutaminase-immunoreactive neurons in cat visual cortex

Phosphate-activated glutaminase (PAG) is the major enzyme involved in the synthesis of the excitatory neurotransmitter glutamate in cortical neurons of the mammalian cerebral cortex. In this study, the distribution and morphology of glutamatergic neurons in cat visual cortex was monitored through immunocytochemistry for PAG. We first determined the specificity of the anti-rat brain PAG polyclonal antibody for cat brain PAG. We then examined the laminar expression profile and the phenotype of PAG-immunopositive neurons in area 17 and 18 of cat visual cortex. Neuronal cell bodies with moderate to intense PAG immunoreactivity were distributed throughout cortical layers II-VI and near the border with the white matter of both visual areas. The largest and most intensely labeled cells were mainly restricted to cortical layers III and V. Careful examination of the typology of PAG-immunoreactive cells based on the size and shape of the cell body together with the dendritic pattern indicated that the vast majority of these cells were pyramidal neurons. However, PAG immunoreactivity was also observed in a paucity of non-pyramidal neurons in cortical layers IV and VI of both visual areas. To further characterize the PAG-immunopositive neuronal population we performed double-stainings between PAG and three calcium-binding proteins, parvalbumin, calbindin and calretinin, to determine whether GABAergic non-pyramidal cells can express PAG, and neurofilament protein, a marker for a subset of pyramidal neurons in mammalian neocortex. We here present PAG as a neurochemical marker to map excitatory cortical neurons that use the amino acid glutamate as their neurotransmitter in cat visual cortex.     

Cortical projections to the superior colliculus in the macaque monkey: A retrograde study using horseradish peroxidase

The topical and laminar distribution of corticotectal cells, as well as their size and morphology, were studied in the macaque monkey with the horseradish peroxidase (HRP) technique. After HRP injections restricted primarily to the superficial layers of the colliculus, labelled cells were found in visual cortex (areas 17, 18, and 19) and both in the frontal eye field (area 8) and the adjacent part of premotor cortex (area 6). The clustering of labelled cells in visual cortex indicated that each of the anatomically and functionally distinct visual areas has its own set of collicular projections. When intermediate and deeper layers of the colliculus were injected, labelled cells were found also in posterior parietal cortex (area 7) where they were concentrated mainly on the posterior bank of the intraparietal fissure, in inferotemporal cortex (areas 20 and 21), in auditory cortex (area 22), in the somatosensory representation SII (anterior bank of sylvian fissure, area 2), in upper insular cortex (area 14), in motor cortex (area 4), in premotor cortex (area 6), and in prefrontal cortex (area 9). In the motor and premotor cortex, labelled cells formed a continuous band which appeared to stretch across finger-hand-arm-shoulder-neck representation. Similarly, the cluster of labelled cells in area 2 may correspond to the finger-hand representation of SII. The cortical regions not containing labelled cells were the somatosensory representation SI (areas 3, 1 and 2) and the infraorbital cortex. Labelled cells were restricted to layer V of all cortical areas except in the primary visual cortex, where labelled cells were found in both layer V and layer VI. The size spectrum of corticotectal cells ranged from 14.8 μm (average diameter) in area 17 to 27.8 μm in area 6, comprising cells as small as 8 μm and as large as 45 μm. Labelled cells in posterior parietal (area 7), in auditory (area 22), and in motor cortex (area 4) were small and distributed over only a narrow range of sizes. Those in premotor cortex (area 6) were often large and had a wide range in size distribution. The differences in size and morphology of corticotectal neurons suggest that they do not form a uniform class of neurons.     

Interconnections of the visual cortex with the frontal cortex in the rat

Horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) and autoradiography of tritiated leucine were used to trace the cortical origins and terminations of the connections between the visual and frontal cortices in the rat. Ipsilateral reciprocal connections between each subdivision of the visual cortex (areas 17, 18a and 18b) and the posterior half of the medial part of the frontal agranular cortex (PAGm), and their laminar organizations were confirmed. These connections did not appear to have a significant topographic organization. Although in areas 17 and 18b terminals or cells of origin in this fiber system were confined to the anterior half of these cortices, in area 18a they were observed spanning the anteroposterior extent of this cortex, with in part a column like organization. No evidence could be found for the participation of both the posterior parts of areas 17 and 18b and the anterior half of this frontal agranular cortex in these connections. Fibers from each subdivision of the visual cortex to the PAGm terminated predominantly in the lower part of layer I and in layer II. In area 17, this occipito-frontal projection was found to arise from the scattered pyramidal cells in layer V and more prominently from pyramidal cells in layer V of area 17/18a border. In area 18a, the fibers projecting to the PAGm originated mainly from pyramidal cells primarily in layer V and to a lesser extent in layers II, III and VI. Whereas in area 18b, this projection was found to arise mainly from pyramidal cells in layers II and III, to a lesser extent in layers V and VI, and less frequent in layer IV. On the other hand, the reciprocal projection to the visual cortex was found to originate largely from pyramidal cells in layers III and V of the PAGm. In areas 17 and 18a, these fibers terminated in layers I and VI, and in layers I, V and VI, respectively. Whereas in area 18b, they were distributed throughout all layers except layer II.     

The development of somatostatin immunoreactive neurons in cat visual cortical areas

The development of somatostatin immunoreactive (SOM-ir) neurons in cat striate and extrastriate cortex was studied to determine whether temporal changes in the morphology, distribution and density of SOM-ir neurons during development would provide clues to the emergence of specific cortical areas. The visual cortical areas examined included areas 17–19 and 7, posteromedial lateral suprasylvian, posterolateral lateral suprasylvian cortex and splenial visual area. We observed that the pattern of SOM-ir neurons in the cortical plate reflects the maturation of the cortical plate. At 1 week of age, SOM-ir neurons were only found in layers V and VI of the developing cortex; by 2 weeks of age, SOM-ir neurons were found in layer IV; and by 3 weeks of age, SOM-ir neurons were located in all layers of the cortex except layer I. SOM-ir neurons in the subplate were much more numerous under lateral cortical areas than under medial areas. This difference decreased over the first 2 postnatal weeks and by the 14th day after birth (P14), the distribution and numbers of SOM-ir neurons in the subplate/white matter had reached the adult pattern. The timing of exuberant SOM expression in the subplate suggests a function in the formation of visual corticocortical connections which begin to develop during the first postnatal week in the kitten.     

Comparative distributions of dopamine D-1 and D-2 receptors in the cerebral cortex of rats, cats, and monkeys

The distributions and laminar densities of cerebral cortical dopamine D-1 and D-2 receptors were studied in rats, cats, and monkeys. Distributions were determined by using alternate, adjacent tissue sections processed for D-1 and D-2 receptor subtypes and compared to an adjacent, nearly adjacent, or similar sections stained for Nissl substance. [3H]-SCH 23390 and [3H]-spiroperidol (in the presence of 100 nM mianserin) were used to label the D-1 and D-2 receptors, respectively. The regional distribution and laminar density of dopamine receptors were determined by in vitro quantitative autoradiography and video densitometry of selected isocortical and peri-allocortical regions. Granular (prefrontal, primary somatosensory, and primary visual), agranular (primary motor and anterior cingulate), and limbic (entorhinal and perirhinal) cortices were examined. Where possible, homologous areas among the species were compared. The D-1 receptor was present in all regions and laminae of the cerebral cortex of rats, cats, and monkeys. The regional densities for the D-1 receptor were higher in the cat and monkey than in the rat. The rat D-1 receptor displayed a relatively homogeneous laminar pattern in most regions except that the deeper laminae (V and VI) contained more receptors than the superficial layers. The cats and monkeys, however, had distinctly heterogeneous laminar patterns in all regions of cortex that varied from one region to another and were quite different from that seen in the rat. The cats and monkeys had highest densities of the D-1 receptor in layers I and II and lowest densities in layers III and IV, whereas layers V and VI were intermediate. The density of D-1 receptors was greater than the density of D-2 receptors in all regions and laminae of cerebral cortex of the cat and monkey and greater in most regions and laminae of the rat cerebral cortex. The D-2 receptor was also distributed in all regions of the cerebral cortex of rats, cats, and monkeys. The D-2 receptor was very homogeneous in its regional distribution and laminar pattern compared to the D-1 receptor in all 3 species. The D-2 receptor was denser in the superficial layers (I and II) of the cortex than in the deeper layers in the rats, but more homogeneous in the different laminae of the cat and monkey cerebral cortex. The rat cortical D-2 receptor exceeded the D-1 receptor in restricted laminae of selective regions.(ABSTRACT TRUNCATED AT 400 WORDS)     

Ontogeny of somatostatin receptors in the rat somatosensory cortex.

The distribution and density of SRIF receptors (SRIF-R) were studied during development in the rat somatosensory cortex by in vitro autoradiography with monoiodinated [Tyr0-DTrp8]S14. In 16-day-old fetuses (E16), intense labeling was evident in the intermediate zone of the cortex while low concentrations of SRIF-R were detected in the marginal and ventricular zones. The highest density of SRIF-R was measured in the intermediate zone at E18. At this stage, labeling was also intense in the internal part of the developing cortical plate; in contrast, the concentration of binding sites associated with the marginal and ventricular zones remained relatively low. Profound modifications in the distribution of SRIF-R appeared at birth. In particular, a transient reduction of receptor density occurred in the cortical plate. During the first postnatal week, the density of receptors measured in the intermediate zone decreased gradually; conversely, high levels of SRIF-R were observed in the developing cortical layers (II to VI). At postpartum day 13 (P13), a stage which just precedes completion of cell migration in the parietal cortex, the most intensely labeled regions were layers V-VI and future layers II-III. From P13 to adulthood, the concentrations of SRIF-R decreased in all cortical layers (I to VI) and the pattern of distribution of receptors at P21 was similar to that observed in the adults.(ABSTRACT TRUNCATED AT 250 WORDS)     

Localization of glutaminase-like and aspartate aminotransferase-like immunoreactivity in neurons of cerebral neocortex

The distribution of glutaminase (GLNase)- and aspartate aminotransferase (AATase)-immunoreactive cells was examined in the cerebral neocortex of rat and guinea pig and in the somatic sensorimotor and primary visual cortex of the Macaca fascicularis monkey. These enzymes are involved in the metabolism of glutamate and aspartate, two amino acids thought to be excitatory amino acid transmitters for cortical neurons. In each of the species examined a large percentage of layer V and VI pyramidal neurons have pronounced glutaminase-like immunoreactivity (GLNase IR). In contrast, neurons in layers I, II, and IV show little GLNase IR. Layer III in the rat and guinea pig contains only a few, densely labeled GLNase-like-immunoreactive (GLNase-Ir) pyramidal neurons, whereas in the monkey the number of GLNase-Ir cells in layer III varies between cytoarchitectonic fields. Area 3b of the primary somatic sensory cortex and area 17 (primary visual cortex) contain few GLNase-Ir cells in layer III. However, layer III contains moderate numbers of GLNase IR in cells in areas 3a, 1, 2, 5, and in the primary motor cortex. Within the motor cortex the largest pyramidal ("Betz") cells are not labeled. In marked contrast to the results with antibody to GLNase, antibody to AATase labels cells that appear nonpyramidal in form, and these cells are in all cortical layers in each of the species examined. This distribution is roughly similar throughout all areas of rodent neocortex, but in monkey visual cortex AATase-immunoreactive neurons are more numerous in layers II-III, IVc, and VI. When combined with the findings of other studies, our results suggest that GLNase IR marks pyramidal neurons that use an excitatory amino acid transmitter. Antibody to AATase appears to mark intrinsic cortical neurons. The AATase immunoreactivity of these cells could indicate that they use an excitatory amino acid transmitter. However, their form and distribution in cortex suggest that this antibody labels GABAergic neurons.     

Laminar cell counts and geniculo-cortical boutons in area 17 of cat and monkey

Counts have been made of the number of cells in individual laminae of the cortex in area 17 of the macaque monkey and cat, and degenerating terminals of geniculo-cortical axons have been studied with the electron-microscope in laminae IVab and IVc of the cortex of area 17 and lamina IV of area 18 of the visual cortex of the cat. The increase in number of cells through the depth of cortex in area 17 of the monkey compared with the cat would appear to involve about equally all laminae. In lamina IVab of area 17 of the cat the axon terminals of Y-type geniculo-cortical fibres make many more synapses per bouton than those of X-type fibres ending in lamina IVc. The geniculo-cortical axons ending in lamina IV of area 18 also make more multisynaptic boutons than those in lamina IVc of area 17. Thus, the terminals in the cortex of the X and Y functional types of fibre show comparable differences in both the cat and monkey.     

Morphology, distribution, and synaptic relations of somatostatin- and neuropeptide Y-immunoreactive neurons in rat and monkey neocortex

Neurons in the monkey and rat cerebral cortex immunoreactive for somatostatin tetradecapeptide (SRIF) and for neuropeptide Y (NPY) were examined in the light and electron microscope. Neurons immunoreactive for either peptide are found in all areas of monkey cortex examined as well as throughout the rat cerebral cortex and in the subcortical white matter of both species. In monkey and rat cortex, SRIF-positive neurons are morphologically very similar to NPY-positive neurons. Of the total population of SRIF-positive and NPY-positive neurons in sensory-motor and parietal cortex of monkeys, a minimum of 24% was immunoreactive for both peptides. Most cell bodies are small (8 to 10 micron in diameter) and are present through the depth of the cortex but are densest in layers II-III, in layer VI, and in the subjacent white matter. From the cell bodies several processes commonly emerge, branch two or three times, become beaded, and extend for long distances through the cortex. The fields formed by these processes vary from cell to cell; therefore, the usual morphological terms bipolar, multipolar, and so on do not adequately characterize the full population of neurons. Virtually every cell, however, has at least one long vertically oriented process, and most processes of white matter cells ascent into the cortex. No processes could be positively identified with the light microscope as axons. The processes of the peptide-positive neurons form dense plexuses in the cortex. In each area of monkey cortex, SRIF-positive and NPY-positive processes form a superficial plexus in layers I and II and a deep plexus in layer VI. These plexuses vary in density from area to area. All appear to arise from cortical or white matter cells rather than from extrinsic afferents. In some areas such as SI and areas 5 and 7, the superficial plexus extends deeply into layers III and IV; and in area 17, two very prominent middle plexuses occur in layers IIIB through IVB and in the upper one-third of layer V; these are separated by layer IVC, a major zone of thalamic terminations, which contains very few SRIF- or NPY-positive processes. The density of the plexuses is greater for NPY-positive processes than for SRIF-positive processes in all areas. In the rat, the plexuses do not display a strict laminar organization but generally are densest in the supragranular layers (I to III) and decline steadily in the deeper layers.(ABSTRACT TRUNCATED AT 400 WORDS)     

Neuronal populations stained with the monoclonal antibody Cat-301 in the mammalian cerebral cortex and thalamus

The monoclonal antibody Cat-301 was used to examine neurons in the cerebral cortex and dorsal thalamus of several mammalian species, including Old World monkeys, cats, bush babies, guinea pigs, and rats. In each species, subpopulations of cortical and thalamic neurons are stained along the surfaces of their somata and proximal dendrites. Cat-301-positive cortical neurons include specific groups of pyramidal cells (e.g., corticospinal but not corticobulbar or callosal neurons in the monkey sensory-motor areas) and certain GABA-immunoreactive nonpyramidal cells. In the thalamus, the relay neurons projecting to the cortex and not the intrinsic neurons are stained. The Cat-301-positive neurons are nonhomogeneously distributed in the cat and monkey cortex and thalamus. In the cortex, they are densely packed in 2 bands that in most areas include layers III and V, but that in primary sensory areas include layers IV and VI. Because the density of stained neurons, their distribution, and the intensity of their staining vary among cortical areas, the borders between neighboring areas can often be detected by the differences in Cat-301 staining. Broader, regional differences are also readily apparent, for areas in the parietal and occipital lobes contain large numbers of intensely stained cells, but most areas in the frontal and temporal lobes contain fewer, more lightly stained neurons. The same broad differences are seen within the thalamus: only those nuclei reciprocally connected with intensely stained cortical areas contain large numbers of Cat-301-positive neurons. Differences among species include variations in cell density and distribution when a given cortical area or thalamic nucleus is compared between cats and monkeys. Greater differences are seen among the other species. Immunoreactive neurons in the cerebral cortex are sparse and lightly stained in guinea pigs, are restricted to the hippocampal formation in rats, and are very rare and isolated in bush babies. Similarly, Cat-301-positive thalamic neurons are restricted to only one or 2 nuclei in the guinea pig and rat and are extremely rare in the bush baby. Cat-301 stains organized groups of neurons in the cat and monkey cortex and thalamus. In addition to the laminar organization of stained cells in all cortical areas (see above), the Cat-301-positive neurons of monkey areas 17 and 18 are grouped into radial arrays. In area 17, clusters of stained cells are present in layers above and below layer IVC. These clusters lie at the centers of ocular dominance columns, within patches stained for cytochrome oxidase (CO). Most of these cells are also GABA-immunoreactive.(ABSTRACT TRUNCATED AT 400 WORDS)