Neuropeptide Y-containing neurons are situated predominantly outside cytochrome oxidase puffs in macaque visual cortex

Seasonal Differences in Expression of Neuropeptide Y (NPY) in Visual Centers of Spotted Munia (Lonchura punctulata)

The visual perception of birds is an incredibly exciting subject of research. Birds have significantly higher visual acuity than most other animals, which helps them stay safe in flight and detect their prey. Understanding how the eyes send information to the brain for additional processing is crucial. The brain has sections (nuclei) that accept input from the retina. The key areas where information is processed are the hyperpallium apicale (HA), hippocampus (HP), optic tectum (TeO), nucleus rotundus (RoT), and the geniculatus lateralis ventralis (Glv); among these, the RoT is one of the most investigated nuclei for vision. This study looked at how the visual centers of non-photoperiodic songbirds (Spotted Munia) adapt in different life history stages by looking at NPY expression. We immunohistochemically quantified NPY expression in four different seasons, including pre-breeding (June), breeding (September), post-breeding (December), and regressed (March) in the brain of Spotted Munia. We evaluated changes in the expression levels of the peptide throughout the year, by determining the expression at four different periods throughout the year. Peptide expression levels were projected to fluctuate within photoperiod-induced seasons. It was discovered that the parts of the brain related to vision (RoT, HA, and HP) have a higher number of immunoreactive cells during their mating season, i.e., during the summer. The appearance of NPY, a non-photic marker, in brain areas linked with light perception, was fascinating. Indirectly, NPY aids avian reproduction in a variety of ways. These findings demonstrate the importance of these nuclei in the process of reproduction, as well as the involvement of NPY in the visual brain areas of Spotted Munia.

Cytochrome oxidase "blobs": a call for more anatomy

An ordered relation of structure and function has been a cornerstone in thinking about brain organization. Like the brain itself, however, this is not straightforward and is confounded both by functional intricacy and structural plasticity (many routes to a given outcome). As a striking case of putative structure-function correlation, this mini-review focuses on the relatively well-characterized pattern of cytochrome oxidase (CO) blobs (aka "patches" or "puffs") in the supragranular layers of macaque monkey visual cortex. The pattern is without doubt visually compelling, and the semi-dichotomous array of CO+ blobs and CO- interblobs is consistent with multiple studies reporting compartment-specific preferential connectivity and distinctive physiological response properties. Nevertheless, as briefly reviewed here, the finer anatomical organization of this system is surprisingly under-investigated, and the relation to functional aspects, therefore, unclear. Microcircuitry, cell type, and three-dimensional spatiotemporal level investigations of the CO+ CO- pattern are needed and may open new views to structure-function organization of visual cortex, and to phylogenetic and ontogenetic comparisons across nonhuman primates (NHP), and between NHP and humans.

Organization of Neuropeptide Y-Immunoreactive Cells in the Mongolian gerbil (Meriones unguiculatus) Visual Cortex

Neuropeptide Y (NPY) is found throughout the central nervous system where it appears to be involved in the regulation of a wide range of physiological effects. The Mongolian gerbil, a member of the rodent family Muridae, is a diurnal animal and has been widely used in various aspects of biomedical research. This study was conducted to investigate the organization of NPY-immunoreactive (IR) neurons in the gerbil visual cortex using NPY immunocytochemistry. The highest density of NPY-IR neurons was located in layer V (50.58%). The major type of NPY-IR neuron was a multipolar round/oval cell type (44.57%). Double-color immunofluorescence revealed that 89.55% and 89.95% of NPY-IR neurons contained gamma-aminobutyric acid (GABA) or somatostatin, respectively. Several processes of the NPY-IR neurons surrounded GABAergic interneurons. Although 30.81% of the NPY-IR neurons contained calretinin, NPY and calbindin-D28K-IR neurons were co-expressed rarely (3.75%) and NPY did not co-express parvalbumin. Triple-color immunofluorescence with anti-GluR2 or CaMKII antibodies suggested that some non-GABAergic NPY-IR neurons may make excitatory synaptic contacts. This study indicates that NPY-IR neurons have a notable architecture and are unique subpopulations of the interneurons of the gerbil visual cortex, which could provide additional valuable data for elucidating the role of NPY in the visual process in diurnal animals.

Discontinuous distribution of senile plaques within striate cortex hypercolumns in Alzheimer's disease

Tangential sections of the primary visual (striate) cerebral cortex from five patients with histopathologically verified Alzheimer's disease were used to study the laminar and tangential disposition of senile plaques. These lesions were visualized with thioflavin S or the modified Bielschowsky method, and classified into four different, purely morphological types: "classical", (predominantly) "neuritic", (primarily amyloid) "core" and "diffuse", which were charted and analyzed using computer-assisted three- and two-dimensional reconstruction and mapping methods. These analyses reveal a tendency for a selective laminar disposition of the lesions (preferentially in layers II/III and V) which is generally consistent with previous reports performed at lower resolution, yet the specific pattern is highly variable among patients, and among plaque subtypes within individual patients. In addition, we observed a clustering of senile plaques in the tangential domain (i.e. parallel to the pial surface) in layers II/III, that suggests a selective involvement of iterated circuits within the "units", "modules", or "hypercolumns" that some believe compose this region of the cortex. These findings also imply an intriguing relative sparing of immediately adjacent components of the modular circuitry of the cerebral cortex, in the same cytoarchitectonic layers. Taken together, these findings indicate that: (1) senile plaques may arise in functionally and anatomically distinct subsets of iterated neuronal circuits that cannot be reduced to schemes based on traditional cytoarchitectonic layers; and (2) that individual variability in the patterns of striate cortex involvement and clinical manifestations must be taken into consideration when addressing the specific mechanisms underlying visual dysfunction in Alzheimer's disease.

Early divergence of magnocellular and parvocellular functional subsystems in the embryonic primate visual system

In both human and Old World primates visual information is conveyed by two parallel pathways: the magnocellular (M) and parvocellular (P) streams that project to separate layers of the lateral geniculate nucleus and are involved primarily in motion and color/form discrimination. The present study provides evidence that retinal ganglion cells in the macaque monkey embryo diverge into M and P subtypes soon after their last mitotic division and that optic axons project directly and selectively to either the M or P moieties of the developing lateral geniculate nucleus. Thus, initial M projections from the eyes overlap only in prospective layers 1 and 2, whereas initial P projections overlap within prospective layers 3-6. We suggest that the divergence of the M and P pathways requires developmental mechanisms different from those underlying competition-driven segregation of initially intermixed eye-specific domains in the primate visual system.

Effects of aging on numbers and sizes of neurons in histochemically defined subregions of monkey striate cortex

BACKGROUND

In addition to its horizontal layers, primate striate cortex has a vertical modular organization. Among the vertical modules are histochemically defined areas of high and low cytochrome oxidase labeling in the supragranular layers, referred to, respectively, as blobs and interblobs. Cytochrome c oxidase (CO) blobs and interblobs differ in their inputs from the magnocellular and parvocellular visual pathways, their physiological properties, and many aspects of their neurochemistry. The present study investigated whether aging differentially affects neuron numbers or sizes in the supragranular blobs or interblobs.

METHODS

The right hemisphere from three young adult (5.2-12.4 years) and four old (24.0-26.7 years) rhesus monkeys was used. Tangential sections through the central visual-field representation were stained for CO and counterstained with cresyl violet. Montages were constructed through cortical layers 2 and 3, and neuron counts and size measurements were made in blob and interblob regions using stereological procedures that yield unbiased estimates. Blob density also was calculated.

RESULTS

CO blob density was 3.76/mm2 in young adults and 3.95/mm2 in old animals, a difference that was not statistically significant. Neuron soma sizes also did not differ significantly between young adult and old animals or between blob and interblob regions. In addition, neuron density was not significantly different between young adult and old animals. However, independent of age, neuron density was significantly higher in the center of interblobs (394,058 cells/mm3) than in the center of blobs (333,638/mm3).

CONCLUSIONS

Our results and those of previous studies (Vincent et al. 1989. Anat. Rec. 223:329-341; Peters and Sethares. 1993. Anat. Rec. 236:721-729) suggest that aging has little or no effect on the densities or sizes of the different functional or morphological types of neurons that exist in the different cortical layers or in the different vertical modules marked by CO blobs and interblobs. These findings are consistent with the results of our previous anatomical and physiological studies of the rhesus monkey retina and lateral geniculate nucleus. These results suggest that the retinogenic-ulostriate pathways are relatively unaffected by aging in the rhesus monkey.

Differential glutamatergic innervation in cytochrome oxidase-rich and -poor regions of the macaque striate cortex: quantitative EM analysis of neurons and neuropil

One of the hallmarks of the primate striate cortex is the presence of cytochrome oxidase (CO)-rich puffs and CO-poor interpuffs in its supragranular layers. However, the neurochemical basis for their differences in metabolic activity and physiological properties is not well understood. The goals of the present study were to determine whether CO levels in postsynaptic neuronal compartments were correlated with the proportion of excitatory glutamate-immunoreactive (Glu-IR) synapses they received and if Glu-IR terminals and synapses in puffs differed from those in interpuffs. By combining CO histochemistry and postembedding Glu immunocytochemistry on the same ultrathin sections, the simultaneous distribution of the two markers in individual neuronal profiles was quantitatively analyzed. As a comparison, adjacent sections were identically processed for the double labeling of CO and GABA, an inhibitory neurotransmitter. In both puffs and interpuffs, most axon terminals forming asymmetric synapses (84%)--but not symmetric ones, which were GABA-IR--were intensely immunoreactive for Glu. GABA-IR neurons received mainly Glu-IR synapses on their cell bodies, and they had three times as many mitochondria darkly reactive for CO than Glu-rich neurons, which received only GABA-IR axosomatic synapses. In puffs, GABA-IR neurons received a significantly higher ratio of Glu-IR to GABA-IR axosomatic synapses and contained about twice as many darkly CO-reactive mitochondria than those in interpuffs. There were significantly more Glu-IR synapses and a higher ratio of Glu- to GABA-IR synapses in the neuropil of puffs than of interpuffs. Moreover, Glu-IR axon terminals in puffs contained approximately three times more darkly CO-reactive mitochondria than those in interpuffs, suggesting that the former may be synaptically more active. Thus, the present results are consistent with our hypothesis that the levels of oxidative metabolism in postsynaptic neurons and neuropil are positively correlated with the proportion of excitatory synapses they receive. Our findings also suggest that excitatory synaptic activity may be more prominent in puffs than in interpuffs, and that the neurochemical and synaptic differences may constitute one of the bases for physiological and functional diversities between the two regions.

Contrast sensitivity and spatial frequency response of primate cortical neurons in and around the cytochrome oxidase blobs

The striate cortex of macaque monkeys contains an array of patches which stain heavily for the enzyme cytochrome oxidase (CO blobs). Cells inside and outside these blobs are often described as belonging to two distinct populations or streams. In order to better understand the function of the CO blobs, we measured the contrast sensitivity and spatial frequency response of single neurons in and around the CO blobs. Density profiles of each blob were assessed using a new quantitative method, and correlations of local CO density with the physiology were noted. We found that the CO density dropped off gradually with distance from blob centers: in a typical blob the CO density dropped from 75% to 25% over 100 microns. Recordings were confined to cortical layers 2/3. Most neurons in these layers have poor contrast sensitivity, similar to that of the parvocellular neurons in the lateral geniculate nucleus. However, in a small proportion of layers 2/3 neurons we found higher contrast sensitivity, similar to that of the magnocellular neurons. These neurons were found to cluster near blob centers. This finding is consistent with (indirect) parvocellular input spread uniformly throughout layers 2/3, and (indirect) magnocellular input focused on CO blobs. We also measured spatial tuning curves for both single units and multiple unit activity. In agreement with other workers we found that the optimal spatial frequencies of cells near blob centers were low (median 2.8 c/deg), while the optimal frequencies of cells in the interblob regions were spread over a wide range of spatial frequencies. The high cut-off spatial frequency of multi-unit activity increased with distance from blob centers. We found no correlation between spatial bandwidth and distance from blob centers. All measured physiological properties varied gradually with distance from CO blob centers. This suggests that the view of blob cells subserving visual functions which are entirely distinct from non-blob cells may have to be reevaluated.

Double labeling of GABA and cytochrome oxidase in the macaque visual cortex: quantitative EM analysis

In the primate striate cortex, cytochrome oxidase (CO)-rich puffs differ from CO-poor interpuffs in their metabolic levels and physiological properties. The neurochemical basis for their metabolic and physiological differences is not well understood. The goal of the present study was to examine the relationship between the distribution of gamma aminobutyric acid (GABA)/non-GABA synapses and CO levels in postsynaptic neuronal profiles and to determine whether or not a difference existed between puffs and interpuffs. By combining CO histochemistry and postembedding GABA immunocytochemistry on the same ultrathin sections, the simultaneous distribution of the two markers in individual neuronal profiles was quantitatively analyzed. In both puffs and interpuffs, GABA-immunoreactive (GABA-IR) neurons were the only cell type that received both non-GABA-IR (presumed excitatory) and GABA-IR (presumed inhibitory) axosomatic synapses, and they had three times as many mitochondria darkly reactive for CO than non-GABA-IR neurons, which received only GABA-IR axosomatic synapses. GABA-IR neurons and terminals in puffs had a larger mean size, about twice as many darkly reactive mitochondria, and a higher ratio of non-GABA-IR to GABA-IR axosomatic synapses than those in interpuffs (2.3:1 vs. 1.6:1; P < 0.01). There were significantly more synapses of both non-GABA-IR and GABA-IR types in the neuropil of puffs than of interpuffs; however, the ratio of non-GABA-IR to GABA-IR synapses was significantly higher in puffs (2.86:1) than in interpuffs (2.08:1; P < 0.01). Our results are consistent with the hypothesis that the level of oxidative metabolism in postsynaptic neurons and neuronal processes is tightly governed by the strength and proportion of excitatory over inhibitory synapses. Thus, the present results suggest that (1) GABA-IR neurons in the macaque striate cortex have a higher level of oxidative metabolism than non-GABA ones because their somata receive direct excitatory synapses and their terminals are more tonically active; (2) the higher proportion of presumed excitatory synapses in puffs imposes a greater energy demand there than in interpuffs; and (3) excitatory synaptic activity may be more prominent in puffs than in interpuffs because puffs receive a greater proportion of excitatory synapses from multiple sources including the lateral geniculate nucleus, which is not known to project to the interpuffs.

Effect of retinal impulse blockage on cytochrome oxidase-poor interpuffs in the macaque striate cortex: quantitative EM analysis of neurons

One of the hallmarks of the primate striate cortex is the presence of cytochrome oxidase-rich puffs in its supragranular layers. Neurons in puffs have been classified as type A, B, and C in ascending order of cytochrome oxidase content, with type C cells being the most vulnerable to retinal impulse blockade. The present study aimed at analysing cytochrome oxidase-poor interpuffs with reference to their metabolic cell types and the effect of intraretinal tetrodotoxin treatment. The same three metabolic types were found in interpuffs, except that type B and C neurons were smaller and less cytochrome oxidase-reactive in interpuffs than in puffs. Type A neurons had small perikarya, low levels of cytochrome oxidase, and received exclusively symmetric axosomatic synapses. The largest neurons were pyramidal, type B cells with moderate cytochrome oxidase activity and were also contacted exclusively by symmetric axosomatic synapses. Type C cells medium-sized with a rich supply of large, darkly reactive mitochondria and possessed all the characteristics of GABAergic neurons. They were the only cell type that received both symmetric and asymmetric axosomatic synapses. Two weeks of monocular tetrodotoxin blockade in adult monkeys caused all three major cell types in deprived interpuffs to suffer a significant downward shift in the size and cytochrome oxidase reactivity of their mitochondria, but the effects were more severe in type B and C neurons. In nondeprived interpuffs, all three cell types gained both in size and absolute number of mitochondria, and type A cells also had an elevated level of cytochrome oxidase, indicating that they might be functioning at a competitive advantage over cells in deprived columns. However, type B and C neurons showed a net loss of darkly reactive mitochondria, indicating that these cells became less active. Thus, mature interpuff neurons remained vulnerable to retinal impulse blockade and the metabolic capacity of these cells remains tightly regulated by neuronal activity.

Multiple types of nitrogen monoxide synthase-/NADPH diaphorase-containing neurons in the human cerebral neocortex

Nitrogen monoxide (NO) synthase (NOS)-containing neurons (NOSN) were identified by means of reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry in nine areas of the human cerebral neocortex from patients 9-74 years of age. Labeled neurons were analyzed according to their disposition in the various layers of the cortical gray and immediately subjacent white matter, and classified according to their cytological features. The vast majority of NOSN (about 80%) are situated in the subcortical white matter and not in the cortical gray proper. Nevertheless, these NOSN extend their processes into the cortical gray and thus appear to participate in intracortical circuits, along with the minority of NOSN situated in all cortical layers. Although many NOSN are small aspiny local circuit neurons, as reported previously, additional distinct cytological types of NADPH diaphorase-positive neurons were also identified, including: (a) local circuit neurons in layer I; (b) granule cells in layer II, and (c) non-pyramidal neurons with densely spinous dendrites in the white matter immediately under the cortical gray. Processes fulfilling light microscopic criteria for axons were seen in many of the above cell types originating from proximal dendrites and, less frequently, from a presumed axon hillock. Taken together, these observations indicate that NOSN belong to several distinct morphological and presumably functional classes, some of which have a unique or restricted laminar location, raising the possibility that some of these various classes of neurons may be selectively affected or spared in neurodegenerative disorders.

Neurochemical compartmentation of monkey and human visual cortex: similarities and variations in calbindin immunoreactivity across species

The compartmental organization of visual cortical neurons was examined across species of primates by directly comparing the pattern of immunoreactivity for the 28-kD vitamin D-dependent calcium-binding protein (calbindin) in area 17 of squirrel monkeys, macaques, and neurologically normal adult humans. Area 17 of macaques and squirrel monkeys was similar in that somata and processes intensely immunoreactive for calbindin were present in the same layers (II-III, IVB, and V) and in both species formed a well-stained matrix that surrounded the CO-rich puffs in layer III. These intensely calbindin-immunoreactive neurons were identified as subpopulations of GABA-immunoreactive neurons. Among the most obvious differences in the two monkey species was the distribution of calbindin-positive elements outside of layer III: a dense immunostained matrix surrounded the puffs in layers II, IVB, V, and VI of squirrel monkeys but the immunostained neurons adopted no regular pattern outside layer III in macaques. In addition, although somata lightly immunoreactive for calbindin were present in both species, they were much more abundant in squirrel monkeys than macaques. The pattern of calbindin immunostaining in human area 17 resembled that of macaques in forming an intense matrix that surrounded puffs only in layer III, yet also resembled that of squirrel monkeys by including large numbers of light immunoreactive somata. These lightly immunostained somata included a very dense population forming a prominent band in layer IVA of human visual cortex. We conclude that for layer III of primary visual cortex, a similar pattern of neuronal chemistry exists across species of primates which is related to this layer's compartmental organization. Yet for other layers, the expression of calbindin immunoreactivity varies from one species to the next, perhaps reflecting variations in other neuronal properties.

Nitric oxide synthase in the visual cortex of monocular monkeys as revealed by light and electron microscopic immunocytochemistry

Recent results indicate that nitric oxide (NO) can play an important role in neuronal excitability by modifying the strength of activated synapses and regulating local cerebral blood flow. We sought to determine whether the level of NO synthase (NOS) could, in turn, also be regulated by neural activity. Results using a polyclonal anti-NOS antibody showed that, in cortical area V1 of monocular monkeys, NOS-immunoreactivity is diminished in lamina 4C neuropil of the deprived ocular dominance columns relative to the immediately adjacent non-deprived columns. Closer examination of lamina 4C indicated that the intercolumnar difference in NOS-immunoreactivity does not reflect differences in the distribution of NOS-labeled perikarya, since relatively few neurons were immunoreactive for NOS in lamina 4C of either monocular or normal binocular monkeys. Electron microscopy revealed that the majority (> 80%) of NOS-immunoreactive profiles in lamina 4C are axon terminals. NOS-immunoreactive spines and dendritic shafts also are present but these are more prevalent in the superficial laminae. In order to determine whether the intercolumnar differences in lamina 4C neuropil correspond to altered densities of NOS cells in the superficial laminae, we performed a series of quantitative analyses. In the superficial laminae, NOS-cells occur as two distinguishable classes: a few that are large and intensely NOS-immunoreactive and many more (ca. 24-fold) that are small and lightly immunoreactive. Analysis of the distribution of 559 small and 105 large NOS-immunoreactive cells within 40-microns-thick tangential sections spanning laminae 2-3 showed that the number of cells (large and small together) associated with each blob is approximately 14 for both deprived (lighter) and non-deprived (darker) blobs. These cells are distributed evenly from the center to periphery of columns. Analysis of the distribution of NOS-cells in the infragranular laminae also did not reveal any columnar differences. These observations suggest that local neural activity may be coupled to NO release via alteration of NOS protein levels specifically within distal axonal processes of neurons. This mechanism could operate in conjunction with the more instantaneous catalytic activation of NOS. Ultrastructural analyses further suggest that NO may act as an anterograde and retrograde messenger arising from terminals in addition to its proposed role as a retrograde messenger arising from dendrites.

An immunohistochemical study of neurotransmitter profiles in developing human visual cortex

The temporal pattern of development and distribution of gamma aminobutyric acid, serotonin, substance P and neuropeptide Y immunoreactive profiles was studied in the human visual cortex from 16 to 26 weeks of gestation, using an immunohistochemical technique. The immunoreactive profiles showed an increase in number and a change in their morphology and distribution pattern over the time period studied. A large number of neurons, fibers and terminals were stained with GABA antibody at 17-18 weeks and were distributed throughout the five zones of the developing visual cortex. GABA neurons were non-pyramidal and bipolar in form at 17-18 weeks while at 18-19 and 20-21 weeks the cells of subplate and intermediate zones were multipolar. Substance P and serotonin immunopositive fibers were present mainly in the intermediate zone at 16 and 17-18 weeks, where they were oriented in a horizontal manner. At subsequent ages they invaded the other zones also. Substance P positive neurons could be visualized only at 26 weeks of gestation in the intermediate, subventricular and ventricular zones; no cell bodies, however, stained with serotonin antibody. Neuropeptide Y immunoreactive cells and fibers were first seen in the intermediate zone but later were found to be distributed in other zones too. The observations indicate that the intermediate zone of the visual cortex in which the transmitters and peptides appear earlier assumes importance in the normal development as also noted in other mammals.

A comparison of the development of neuropeptide and MAP2 immunocytochemical labeling in the macaque visual cortex during pre- and postnatal development

The appearance of Substance P (SP) and Neuropeptide Y (NPY) has been studied using light microscopic immunocytochemical labeling throughout the complete developmental span of Macaca nemestrina monkey striate cortex. In the adult, 80% of the NPY+ neurons occur in the white matter (WM) and most of the remainder are medium to large multipolar neurons in layer 2. Fibers occur in all layers except 4C and are very numerous, given the relatively small number of NPY+ cell bodies. NPY+ neurons first were seen at embryonic day (E) 75. Most neurons were in the intermediate zone (IZ), but a few were in the immature cortical plate (CP). An adult-like distribution was present by E125 for neurons and by birth for fibers, but fiber staining intensity and number increased to postnatal year 1 (P1yr). In adult cortex, numerous SP+ nonpyramidal neurons were present in layers 2-6 and WM, but SP+ fibers were surprisingly infrequent. During development, significant numbers of SP+ neurons were not seen in the CP until E113-125. Later prenatal ages had a prominent plexus of SP+ cell bodies and fibers at the layer 5/6 border. This plexus disappeared by P12wk due to either down-regulation of SP or cell death. SP+ neurons in IZ/WM were very sparse until birth after which they increased in number and staining intensity up to P1yr, suggesting a postnatal up-regulation of SP in a preexisting WM subpopulation. Cell densities were determined for SP, NPY, and the neuron-specific marker microtubule-associated protein 2 (MAP2) to clarify the developmental dynamics of IZ/WM neurons. MAP2+ cell densities in WM peaked around birth and then declined 20% in the outer half and 77% in the inner half of WM. SP+ cell density rose 57% from birth to P20wk and then declined 20% into adulthood. NPY+ cell density was fairly constant prenatally and then rose 300% by adulthood. Neuropeptide cell density changes took place predominantly in the outer WM. These data indicate that cell death does occur in the general population of monkey striate cortical WM neurons. In contrast, both SP+ and NPY+ cells are characterized by minimal cell death and a late expression of neuropeptides which causes an increase in neuropeptide+ cell density in postnatal WM.

Neuronal organization and plasticity in adult monkey visual cortex: immunoreactivity for microtubule-associated protein 2

Immunocytochemical staining for microtubule-associated protein 2 (MAP 2) was used to examine the morphology of neurons, the organization of neuronal groups, and the neurochemical plasticity of cells in adult monkey area 17. MAP 2-immunostained neurons are present through the depth of area 17 but are most intensely immunoreactive in layers IVB and VI. From layer IVB, separate groups of MAP 2-positive cells invade layers IVA and IVC alpha. Clusters of cells protrude upward from superficial layer IVB and occupy the central core regions of the cytochrome oxidase (CO)-stained honeycomb in layer IVA, while large neurons typical of layer IVB are distributed in irregular clusters in the subjacent layer IVC alpha. The somata in the layer IVA honeycomb cores give off immunostained dendrites which remain largely within the core regions. Patches of MAP 2-positive neurons are also present in layers II and III, where they coincide with the CO-stained puffs. Intravitreal injections of tetrodotoxin (TTX) into one eye of adult monkeys produce stripes of alternating light and dark MAP 2 immunostaining in layer IVC. Stripes of light immunostaining coincide with stripes of light CO staining, and correspond to reduced MAP 2 immunoreactivity within cortical neurons dominated by the TTX-injected eye. In layers II and III, the MAP 2 immunostaining of patches overlying the injected-eye columns is similarly reduced. No change occurs in the MAP 2 immunostaining of layer IVA. These data suggest that the anatomical and physiological heterogeneity of layers IVA and IVC alpha arises from the periodic invasion of neurons characteristic of layer IVB, that the neurons in layer IVA have dendrites confined to thalamocortical-recipient or nonrecipient zones and that the expression of MAP 2 changes in adult cortical neurons following the loss of retinal input.

Morphology and laminar distribution of neuropeptide Y immunoreactive neurons in the human striate cortex

The morphology, laminar distribution, and distribution relative to cytochrome oxidase patches of neuropeptide-Y immunoreactive (NPY-ir) neurons were studied in the human striate cortex. The density of NPY-ir cells was highest in the white matter. NPY-ir neurons were sparsely distributed within the cortical layers. NPY-ir neurons were located in both cytochrome oxidase dense patch and interpatch regions. However, the paucity of NPY-ir neurons in layer III, where cytochrome oxidase patches are most clearly demonstrated, precluded establishing a clear relationship of NPY-ir neurons to cytochrome oxidase patches. NPY-ir neurons exhibited a variety of nonpyramidal morphologies, and many of them had axons with recurrent or looped trajectories. A dense plexus of NPY-ir axons was located just beneath the pia, and these axons were concentrated at the entry points of pial blood vessels. Other NPY-ir neurons had cell bodies or processes in close proximity to cerebral capillaries. These results suggest a role of NPY in cortical metabolism, control of cerebral circulation, or activity-related changes in local blood flow.

Organization and plasticity of GABA neurons and receptors in monkey visual cortex

The GABA neurons of monkey area 17 are a morphologically and chemically heterogeneous population of interneurons that are normally distributed most densely within the geniculocortical recipient zones of the visual cortex. In adult monkeys deprived of visual input from one eye, the levels of immunoreactivity for GABA and GAD within neurons of these geniculocortical zones is reduced. Similar changes are seen in the levels of proteins that make up the GABAA receptor sub-type. The effects of monocular deprivation on other substances suggest that specific types of GABA neurons, such as those in which the tachykinin neuropeptide family and parvalbumin coexist with GABA, are greatly influenced by changes in visual input. That some proteins remain normal within deprived-eye neurons and that other proteins are increased indicates the changes in the GABA cells of the cortex are not the result of a general reduction in protein synthesis. Comparisons of what is known about the morphological and synaptic features of GABA cells in area 17 and the characteristics of cells affected by monocular deprivation suggests that certain classes, such as the clutch cell, may be preferential targets of deprivation. Such a selective loss of certain GABA neurons would have broad implications for the possible physiological plasticity of cortical cells, for if ongoing studies determine that specific receptive field properties are affected by monocular deprivation in adults, the correlation of functional properties and classes of GABA cells would be possible.

Vibrissaeless mutant rats with a modular representation of innervated sinus hair follicles in the cerebral cortex

Specialized areas in the cerebral cortex are essential to mediate the various sensory modalities and are crucial to their recovery in disease. We recently observed that prenatal photoreceptor cues are not indispensable for the development of the elaborate modular organization of the primate primary visual (striate) cortex (Kuljis, R. O. and P. Rakic. 1990. Proc. Natl. Acad. Sci. USA 87: 5303-5306). By contrast, the elegant experiments of Woolsey, Van der Loos, and collaborators (Van der Loos, H., and T. A. Woolsey. 1973. Science 179: 395-398; Van der Loos, H. and J. Dörfl. 1978. Neurosci Lett. 7: 23-30; Woolsey, T. A. 1967. John Hopkins Med. J. 121: 91-112; Woolsey, T. A. and H. Van der Loos. 1970. Brain Res. 17: 205-242) indicate that postnatal vibrissal receptor input is necessary for the development of modular organization in the posteromedial barrel subfield (PMBSF) of the rodent somatosensory cortex. The present report is part of a series of studies designed to address the variables that result in seemingly different results in these two models. Here, I address the role of pre- and postnatal tactile experience in the development of the rat homologue of the mouse PMBSF using mutants that lack vibrissae. Mutants exhibit cytoarchitectonic units in layer IV similar to those in controls, as revealed by NissI stains and histochemistry for succinate dehydrogenase and cytochrome oxidase. Sections from flat mounts of the vibrissal pad reveal that all mutants contain vibrissal follicles with stumps of sinus hairs in a geometric array and number similar to that in controls, and that the follicles are innervated heavily by fascicles of fibers from the infraorbital nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypercolumns in primate visual cortex can develop in the absence of cues from photoreceptors

The visual cortex in primates consists of an array of anatomically and chemically identifiable cellular modules (hypercolumns) with distinct physiological properties. For example, layers II/III in the macaque monkey contain a regular array of cytochrome oxidase-rich blobs. Furthermore, the surrounding cytochrome oxidase-poor interblob regions have a higher density of neuropeptide Y-positive aspiny stellate cells. Neurons in the blobs are thought to mediate predominantly low spatial frequencies and color vision, while those in the interblobs appear to be engaged in pattern vision and high spatial frequency analysis. In this study we examined the role of the retina in the development of hypercolumns. A bilateral retinal ablation was performed in embryos at midgestation, before any photoreceptors had established contacts with other retinal neurons and before layers II/III of the cortex--or their synaptic connection--had been generated. We found that the cortex in operated animals had cytochrome oxidase blobs and that their size and spacing were normal. In addition, neuropeptide Y-containing neurons were preferentially distributed in the interblob region as in control animals. Our findings indicate that some basic aspects of the cyto- and chemoarchitectonic organization of the cerebral cortex, which presumably evolved for the analysis of form and color, can emerge in the absence of cues from the retinal photoreceptors that mediate these attributes of vision.

Distribution of neuropeptide Y-containing perikarya and axons in various neocortical areas in the macaque monkey

The laminar and areal distribution of neuropeptide Y (NPY)-containing perikarya and their processes was analyzed immunocytochemically in Brodmann's neocortical areas 17, 18, 7, 22, 3, 4, 24, and 9 (Walker's area 46) in seven macaque monkeys. Most NPY-containing cells are distributed in two broad bands in layers II-III and V-VI in all areas; relatively few cells can be found in layer I and virtually none in layer IV. Numerous NPY-containing cells are situated in the white matter immediately subjacent to the cortical gray. Severalfold regional and individual differences in the density of NPY-positive somata were found in supra- and infragranular layers. However, the interareal variations in the density of NPY-containing somata do not conform to a universal pattern, because of either individual variability or inherent difficulties in standardizing immunocytochemical labeling. In contrast, the laminar differences in the distribution of NPY-containing axons among cortical areas are consistent in all animals. In general, primary sensory and motor areas have a lesser density of NPY-containing axons than association and limbic areas. Within the general pattern, area-specific laminar segregation of NPY-containing axons occurs. The regional differences in the distribution of NPY-like immunoreactivity in the neocortex may reflect innate characteristics of local neuronal circuits serving specialized functions.