Honeycomb-like mosaic at the border of layers 1 and 2 in the cerebral cortex

In this report, we present evidence of a small-scale modularity (<100 microm) at the border of layers 1 and 2 in neocortical areas. The modularity is best seen in tangential sections, with double-labeling immunohistochemistry to reveal overlapping or complementary relationships of different markers. The pattern is overall like a reticulum or mosaic but is described as a "honeycomb," in which the walls and hollows are composed of distinct afferent and dendritic systems. We demonstrate the main components of the honeycomb in rat visual cortex. These are as follows: (1) zinc-enriched, corticocortical terminations in the walls, and in the hollows, thalamocortical terminations (labeled by antibody against vesicular glutamate transporter 2 and by cytochrome oxidase); (2) parvalbumin-dense neuropil in the walls that partly colocalizes with elevated levels of glutamate receptors 2/3, NMDAR receptor 1, and calbindin; and (3) dendritic subpopulations preferentially situated within the walls (dendrites of layer 2 neurons) or hollows (dendrites of deeper neurons in layers 3 and 5). Because the micromodularity is restricted to layers 2 and 1b, without extending into layer 3, this may be another indication of a laminar-specific substructure at different spatial scales within cortical columns. The suggestion is that corticocortical and thalamocortical terminations constitute parallel circuits at the level of layer 2, where they are segregated in association with distinct dendritic systems. Results from parvalbumin staining show that the honeycomb mosaic is not limited to rat visual cortex but can be recognized at the layer 1-2 border in other areas and species.

In vivo 31P magnetic resonance spectroscopy of human brain at 7 T: an initial experience

In vivo (31)P spectra were acquired from the human primary visual cortex at 7 T. The relaxation times of the cerebral metabolites, intracellular pH, rate constant (k(f)) of the creatine kinase (CK) reaction, and nuclear Overhauser enhancement (NOE) on the detected phosphorus moieties from irradiation of the water spins were measured from normal subjects. With a 5-cm-diameter surface coil, 3D (31)P chemical shift imaging was performed with a spatial resolution of 7.5 ml and an acquisition resolution of 8 min, resulting in a signal-to-noise ratio (SNR) for phosphocreatine (PCr) resonance of 32. The apparent T(1) and T(2) of PCr measured at 7 T were 3.37 +/- 0.29 s and 132.0 +/- 12.8 ms, respectively, which were considerably longer than those of adenosine triphosphate (ATP) (T(1): 1.02-1.27 s; T(2): 25-26 ms). The NOE measured in this study was 24.3% +/- 1.6% for PCr, and 10% for ATP. The k(f) measured in the human primary visual cortex was 0.24 +/- 0.03 s(-1). The results from this study suggest that ultra-high-field strength is advantageous for performing in vivo (31)P magnetic resonance spectroscopy (MRS) in the human brain.

Neurochemical comparison of synaptic arrangements of parvocellular, magnocellular, and koniocellular geniculate pathways in owl monkey (Aotus trivirgatus) visual cortex

As in other primates, the lateral geniculate nucleus (LGN) of owl monkeys contains three anatomically and physiologically distinct relay cell classes, the magnocellular (M), parvocellular (P), and koniocellular (K) cells. M and P LGN cells send axons to the upper and lower tiers of layer IV, and K cells send axons to the cytochrome oxidase (CO) blobs of layer III and to layer I of primary visual cortex (V1). Our objective was to compare the synaptic arrangements made by these axon classes. M, P, and K axons were labeled in adult owl monkeys by means of injections of wheat germ agglutinin-horseradish peroxidase into the appropriate LGN layers. The neurochemical content of both pre- and postsynaptic profiles were identified by postembedding immunocytochemistry for gamma-aminobutyric acid (GABA) and glutamate. Our key finding is that the synaptic arrangements made by M, P, and K axons in owl monkey exhibit more similarities than differences. They are exclusively presynaptic, contain glutamate and form asymmetric synapses mainly with glutamate-positive dendritic spines. The majority of the remaining axons synapse with glutamatergic dendritic shafts. There are also differences between LGN pathways. M and P terminals are significantly larger and more likely to make multiple synapses than K axons, although M and P axons do not differ from each other in either of these characteristics. Of interest, a larger percentage of M and K axons than P axons make synapses with GABAergic dendritic shafts. Cells directly postsynaptic to M and K axons are known to exhibit orientation selectivity and, in some cases, direction selectivity. Cells postsynaptic to P axons do not show these properties, but instead tend to reflect their LGN inputs more faithfully; therefore, it is possible that these physiologic differences seen in the cortical cells postsynaptic to different LGN pathways reflect the differential involvement of inhibitory circuits.

Corticothalamic cells in layers 5 and 6 of primary and secondary sensory cortex express GAP-43 mRNA in the adult rat

The expression of a presynaptic phosphoprotein, growth-associated protein (GAP)-43, is associated with synaptogenesis during development and synaptic remodeling in the adult. This study examined GAP-43 mRNA expression and distribution in primary and secondary areas of visual, auditory, and somatosensory cortex of the adult rat, by in situ hybridization with a digoxigenin-coupled mRNA probe, focusing particularly on the corticothalamic cells in layers 5 and 6. In the six cortical areas studied, GAP-43 mRNA was expressed predominantly in layers 5 and 6 and was greater in secondary than primary areas. There were densely labeled cells in layers 5 and 6 of all areas, which showed a restricted sublaminar distribution in primary areas and more even distribution in secondary areas. Combining retrograde transport of rhodamine beads with in situ hybridization in visual and auditory cortex showed that corticothalamic cells in layers 5 and 6 express GAP-43 mRNA. There are more of these GAP-43 mRNA positive corticothalamic cells in layer 5 of secondary areas than in primary areas. The evidence suggests that in the adult rat, plasticity related to GAP-43 is present in primary and secondary sensory cortex and more so in secondary areas.

Fos immunoreactivity in rat subcortical visual shell in response to illuminance changes

Immediate early gene expression has been used frequently as a marker of activity in the circadian visual system. Recent evidence suggests that the pretectum participates in orchestrating sleep and circadian responses to light. Lesions of the pretectum eliminate dark shift-induced rapid eye movement sleep triggering in albino rats, and compromise circadian phase shifts in hamsters. We hypothesized that regions of the pretectum respond to light with robust and region-specific Fos activation, similar to the suprachiasmatic nucleus and intergeniculate leaflet. We used Fos expression, the protein product of the immediate early gene c-fos, as a functional marker to measure the responses of neurons following acute lighting changes. Rats maintained on a 12:12 light-dark cycle were subjected to a shift from light-to-dark or from dark-to-light at midday (Zeitgeber time 6) or midnight (Zeitgeber time 18). Fos expression was visualized with immunocytochemistry and quantified with an automated scoring system. We found three regions in the pretectum (the olivary pretectal nucleus, posterior limitans, and a region homologous to the hamster commissural pretectal nucleus), and two regions in the lateral geniculate complex (the intergeniculate leaflet and ventral lateral geniculate nucleus) that demonstrated significant Fos activation in response to light. Furthermore, the olivary pretectal nucleus, the posterior limitans, and the ventral lateral geniculate nucleus showed preferential Fos activation after acute light onset rather than following chronic exposure to light at midday, whereas at midnight these nuclei showed Fos activation following both chronic light exposure and acute light onset. Given the extensive anatomical connections between pretectal nuclei and other nuclei in the subcortical visual shell, as well as with centers for sleep and arousal, it is highly plausible that these pretectal nuclei integrate information about changes in illuminance, and aid in the coordination of acute behavioral responses to light.

Different mechanisms for loss and recovery of binocularity in the visual cortex

Diverse molecular mechanisms have been discovered that mediate the loss of responses to the deprived eye during monocular deprivation. cAMP/Ca2+ response element-binding protein (CREB) function, in particular, is thought to be essential for ocular dominance plasticity during monocular deprivation. In contrast, we have very little information concerning the molecular mechanisms of recovery from the effects of monocular deprivation, even though this information is highly relevant for understanding cortical plasticity. To test the involvement of CREB activation in recovery of responses to the deprived eye, we used herpes simplex virus (HSV) to express in the primary visual cortex a dominant-negative form of CREB (HSV-mCREB) containing a single point mutation that prevents its activation. This mutant was used to suppress CREB function intracortically during the period when normal vision was restored in two protocols for recovery from monocular deprivation: reverse deprivation and binocular vision. In the reverse deprivation model, inhibition of CREB function prevented loss of responses to the newly deprived eye but did not prevent simultaneous recovery of responses to the previously deprived eye. Full recovery of cortical binocularity after restoration of binocular vision was similarly unaffected by HSV-mCREB treatment. The HSV-mCREB injections produced strong suppression of CREB function in the visual cortex, as ascertained by both DNA binding assays and immunoblot analysis showing a decrease in the expression of the transcription factor C/EBPbeta, which is regulated by CREB. These results show a mechanistic dichotomy between loss and recovery of neural function in visual cortex; CREB function is essential for loss but not for recovery of deprived eye responses.

Human-specific organization of primary visual cortex: alternating compartments of dense Cat-301 and calbindin immunoreactivity in layer 4A

There is evidence that the cortical anatomy of the magnocellular (M) visual pathway, which carries information about motion and luminance contrast, was modified in human evolution. Recent results indicate that layer 4A of humans contains a meshwork of tissue bands that stain densely for nonphosphorylated neurofilament (NPNF), a protein that is preferentially expressed in elements of the M pathway, whereas apes and monkeys lack a comparable pattern. Here we examined the distribution of staining for Cat-301 -- a monoclonal antibody well established to stain M-related structures preferentially -- in area V1 of humans, apes (chimpanzees, orangutan), Old World monkeys (macaques) and New World monkeys (spider monkeys, squirrel monkeys). Single-staining experiments, using a peroxidase-tetramethylbenzidine (TMB) reaction, revealed alternating zones of dark and light staining for Cat-301 in layer 4A of humans, similar to those observed with NPNF. Double-staining studies in humans revealed that Cat-301-immunoreactive somas and neuropil were localized within the same tissue bands that stained strongly for NPNF and, furthermore, that these bands alternated with irregularly shaped territories that stained very strongly for calbindin. Nonhuman primates, by contrast to humans, displayed weak Cat-301 and calbindin staining in layer 4A. The co-localization of Cat-301 and NPNF in human layer 4A, and the weak staining for these molecules in layer 4A of other primates, suggests that the cortical representation of the M channel was modified in recent human evolution. The calbindin-rich compartments in human layer 4A cannot be related to a particular geniculostriate pathway on neurochemical grounds; they may constitute an interneuronal population that increased in human evolution.

Postnatal expression and distribution of Refsum disease gene associated protein in the rat retina and visual cortex: effect of binocular visual deprivation

Previously, phytanoyl-CoA alpha-hydroxylase-associated protein 1 (PAHX-AP1) was isolated as a novel neuron-specific protein to interact with Refsum disease (RfD) gene PAHX. Its expression in the brain increased after eyelid opening, and the elevated level was maintained through adulthood. In this report, to verify the hypothesis that light could trigger this increase, we have examined the developmental distribution pattern of PAHX-AP1 in rat retina and visual cortex, and changes of its expression by binocular deprivation. Northern blot analyses demonstrated PAHX-AP1 expression reached its highest level in the visual cortex and eyeball at 4 weeks after birth, and these levels were maintained through adult life. Two weeks after visual deprivation, its expression in the eyeball and visual cortex decreased compared with the control. In situ hybridization analyses of the retina showed that PAHX-AP1 expression was limited to the ganglionic cell layer at 10 days after birth, but expressed in the inner nuclear cell layer and extended to the outer nuclear cell layer at 2 and 3 weeks after birth, respectively. Two weeks after visual deprivation, however, it decreased in the ganglionic and inner nuclear cell layer, and disappeared in the rod and cone cell layers. In the visual cortex, strong signals of PAHX-AP1 were detected in layers IV and VI, and II-VI at 10 days and 2 weeks after birth, respectively. Its expression decreased after 2 weeks of visual deprivation. These results indicate that visual stimulation is essential for the maintenance of PAHX-AP1 expressions in the retina, especially in the rod and cone cell layers, and visual cortex, and suggest that PAHX-AP1 may be involved in the developmental regulation of the photoreceptor's function.

Noradrenergic innervation of the developing and mature visual and motor cortex of the rat brain: a light and electron microscopic immunocytochemical analysis

The noradrenergic (NA) innervation of the developing and adult visual and motor cortex of the rat was examined with light and electron microscopic immunocytochemistry by using antibodies against dopamine-beta-hydroxylase. At birth, NA fibers were present in both cortical areas, appearing as two tangential streams, one above and the other below the cortical plate. During the subsequent weeks, these two streams arborized gradually innervating all cortical layers. The adult pattern of distribution was attained by postnatal day 14, but the density of innervation, which was higher in the motor than in the visual cortex, appeared similar to the adult by the end of the third postnatal week. Electron microscopic analysis revealed that a low proportion of NA varicosities (the highest value was 12% in the adult motor cortex in single sections) were engaged in synaptic contact, throughout development, in both areas examined. The overwhelming majority of these synapses were symmetrical, involving predominantly small or medium dendrites. This evidence suggests that transmission by diffusion is the major mode of NA action in the developing and adult cerebral cortex. Noradrenaline released in the rare synaptic junctions may act mainly to reduce the activity of its cortical targets. The results altogether provide morphologic evidence for an involvement of noradrenaline in the development of the neocortex and, along with earlier data on the serotonergic system, indicate that the monoaminergic systems are endowed with a specific anatomic organization in various areas of the brain.

Visual cortical organization at the single axon level: a beginning

Single axon analysis of visual cortical connections is an important extension of previous anterograde studies using 3H-amino acids or wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). The higher resolution tracers-Phaseolus vulgaris-leucoagglutinin (PHA-L), biocytin, biotinylated dextran amine (BDA) and dextran-conjugates-have already produced new results, simply by providing improved visualization, concerning laminar definition and possible subtypes of connections, as well as the beginning of a database of morphometrics and microstructure. The comparative approach, comparing geniculocortical terminations and cortical connections across several areas, has suggested both specific structural-functional correlations (for example, in extrastriate area MT/V5) and more subtle, possibly gradient-wise variations. Likely future directions for this line of research include more direct correlations of axon geometry with functional architectures, investigations of microcircuitry at the level of electron or confocal microscopy, anatomical and functional investigations of connectional convergence and interactions, and, not least, a more comprehensive database.

Expression of the nerve growth factor receptors TrkA and p75NTR in the visual cortex of the rat: development and regulation by the cholinergic input

Several lines of evidence have shown that nerve growth factor (NGF), the progenitor of the neurotrophin family of growth factors, plays a fundamental role in the developmental plasticity of the rat visual cortex. However, the expression of NGF receptors (NGFRs) TrkA and p75(NTR) and the possible sites of NGF action in the visual cortex remain to be elucidated so far. Using a highly sensitive ECL immunoblot analysis, we have been able to show, in the present study, that the TrkA protein is expressed in the rat visual cortex and that it is developmentally upregulated during the critical period for cortical plasticity. In contrast, the expression level of the low-affinity NGF receptor p75(NTR) seems to remain nearly constant throughout development. In the analysis of possible pathways involved in the regulation of NGFR expression, we found that neither blockade of the visual input nor NGF administration to the visual cortex resulted in a modulation of NGFR levels of expression. On the other hand, the selective destruction of cholinergic afferents to the visual cortex caused a dramatic, but not complete, reduction of the cortical NGFRs, which suggests that these receptors are located on cholinergic terminals predominantly. At the functional level, we found that, after the elimination of the cholinergic afferents to the visual cortex, the NGF-induced increase of both acetylcholine and glutamate release from cortical synaptosomes was strongly impaired. These results indicate that the cholinergic input is an important mediator of visual cortex responsiveness to NGF action.

Multimodal characterisation of cortical areas by multivariate analyses of receptor binding and connectivity data

Cortical areas are regarded as fundamental structural and functional units within the information processing networks of the brain. Their properties have been described extensively by cyto-, myelo- and chemoarchitectonics, cortical and extracortical connectivity patterns, receptive field mapping, activation properties, lesion effects, and other structural and functional characteristics. Systematic integrative approaches aiming at multimodal characterisations of cortical areas or at the delineation of global features of the cortical network, however, are still scarce and usually limited to a single data modality, such as cytoarchitectonical or tract tracing data. Here we describe a methodological framework for the systematic evaluation, comparison and integration of different data modalities from the brain and demonstrate its practical application and significance in the analysis of receptor binding and connectivity data within the motor and visual cortices of macaque monkeys. The framework builds on algorithmic methods to convert data between different cortical parcellation schemes, as well as on statistical techniques for the exploration of multivariate data sets comprising data of different types and scales. Thereby, we establish a relationship between intrinsic area properties as expressed by quantitative receptor binding, and extrinsic inter-area communication, which relies on anatomical connectivity. Our analyses provide preliminary evidence for a good correspondence of these two data types in the motor cortex, and their partial discrepancy in the visual cortex, raising hypotheses about the different organisational aspects highlighted by receptors and connectivity. The methodological framework presented here is flexible enough to accommodate a wide range of further data modalities, and is specific enough to permit novel insights and predictions concerning brain organisation. Thus, this approach promises to be very useful in the endeavour to characterise multimodal structure-function relationships in the brain.

Identification of a novel truncated isoform of trkB in the kitten primary visual cortex

Neurotrophins have been shown to play important roles in development and plasticity of the visual cortex (VC). Since signal transduction of neurotrophins is mediated through neurotrophin receptors, we attempted to analyze neurotrophin receptors in the VC. In this study, we isolated cDNAs encoding the intracellular regions of truncated isoforms of the trkB receptor from 30-d-old kitten primary VC. Two distinct truncated isoforms of trkB were isolated and characterized by sequence analyses. One of the isoforms corresponds to the previously described truncated trkB in several mammalian species. The second isoform represents a novel truncated trkB variant form in the kitten VC. Sequence analysis revealed that this contains a sequence that has not yet been reported in any species. This novel isoform, designated trkB.T4, results from alternative splicing 189-bp (63 amino acids) downstream from the splice site giving rise to the first known truncated isoforms of trkB. In the context of recent hypotheses regarding the function of truncated trkB receptors, sequence analysis indicates that trkB.T4 may bear putative signaling/internalization sequences.

Electron microscopic immunocytochemical detection of PSD-95, PSD-93, SAP-102, and SAP-97 at postsynaptic, presynaptic, and nonsynaptic sites of adult and neonatal rat visual cortex

Membrane-associated guanylate kinases (MAGUKs) assemble protein complexes at sites of cell-cell contact. At excitatory synapses in brain, MAGUKs localize to the postsynaptic density (PSD) and interact with N-methyl-D-aspartate (NMDA) glutamate receptors and downstream signaling proteins. However, NMDA receptors are not restricted to the PSDs, as electron microscopic immunocytochemical (EM-ICC) results indicate that NMDA receptors also occur at nonsynaptic portions of dendrites, perhaps functioning as reserves for rapid insertion into synaptic membranes in response to appropriate synaptic activity. NMDA receptors also occur in axons, at least in part to support glutamate-dependent enhancement of transmitter release. In this study, a systematic EM-ICC survey was performed to determine whether the distributions of four neuronal MAGUKs-PSD-95, PSD-93, SAP-102, and SAP-97-resemble that of NMDA receptors. Quantitative analysis revealed that the density of PSD-95 over thick PSDs of asymmetric axo-spinous synaptic junctions is 2-3-fold the level in the immediately adjacent cytoplasm of spines and terminals, while symmetric synapses show no association with PSD-95. Similarly, all four MAGUKs occur over PSDs of spines. However, we also detected MAGUK immunoreactivity, albeit more diffusely, along presynaptic membranes and in the cytoplasm of axons and dendritic shafts. In fact, the overall distribution of PSD-95 within the neuropil is equally prevalent along plasma membranes (including synaptic portions) as in the cytoplasm, away from plasma membranes. These results suggest that MAGUKs have dual roles: to maintain receptors at synapses and to regulate shuttling of receptors between nonsynaptic and synaptic sites.

Developmental changes in the expression of GABA(A) receptor subunits (alpha(1), alpha(2), alpha(3)) in the cat visual cortex and the effects of dark rearing

The present study used Western blots and Northern slot blots to determine changes in the level of expression of GABA(A) receptor subunits alpha(1), alpha(2), and alpha(3), in relation to the "critical period" in cat visual cortex. Levels of the GABA(A) alpha(1) subunit were lowest at 1 week, increased four-fold to a maximum at 10 weeks, and declined slightly (35%) into adulthood. Levels of the GABA(A) alpha(2) and alpha(3) subunits were highest at 1 week of age, decreased two-fold by 10 weeks of age and were constant thereafter. Comparison between visual cortex from normal and dark-reared cats at 5 weeks and 20 weeks showed that alpha(1) and alpha(3) subunit expression was elevated in dark-reared animals by approximately 50% at both ages. alpha(2) expression was not affected. These results implicate the importance of a shift from putative immature to mature GABA(A) receptor subunits during the critical period of visual cortex and in conjunction with parallel analysis of NMDA receptor subunit maturation, further support the notion that a changing excitatory/inhibitory balance is critical for neuronal plasticity.

Parvalbumin and calbindin D-28K immunoreactive neurons in area MT of rhesus monkey

The chemical characteristics of the neurons of the motion sensitive visual area, area MT, remain to be established. We studied the distribution pattern of two calcium binding proteins, parvalbumin (PV) and calbindin D28K (CB) in this area, using specific monoclonal antibodies and the peroxidase-antiperoxidase (PAP) immunohistochemical technique. Aldehyde fixed 30-micron-thick cryostat sections from area MT of five animals were processed free floating for immunohistochemical staining. Besides studying the morphological characteristics of PV and CB positive neurons, quantitative analysis was carried out to determine their (1) perikaryal area (Pa) and diameter, (2) numerical densities (NV)/mm3 cortical tissue, (3) absolute number (NC) in a column of cortex under 1 mm2 cortical surface along with (4) layerwise absolute number (NL) under 1 mm2 cortical surface and (5) laminar percentage distribution of immunoreactive (IR) neurons. Quantitative analysis was carried out using a Leica QMC 500 image analysis system connected to a DMRE microscope. The results showed that both types of IR neurons were localized to all cortical layers except layer I. The PV +ve neurons were equidistributed between the supra- and infragranular layers, with the highest percentage being present in layer III (45%) followed by layer V (21%). The CB +ve neurons, on the other hand, were predominantly localized in supragranular layers, with the highest percentage being in layer III (54%) and the next highest percentage in layer II (18%). The average Pa and diameter of PV +ve neurons were found to be 96.90 +/- 28.43 micron 2 and 11.01 +/- 1.61 microns respectively. The CB +ve neurons were significantly smaller in size than the PV +ve neurons, with average Pa and diameter of the former being 92.23 +/- 26.18 micron 2 and 10.39 +/- 1.23 microns respectively. The NV for PV and CB +ve neurons showed ranges of 3157-3894 and 2303-2585, with means of 3347 +/- 285 (+/- SD) and 3436 +/- 100 respectively. The values for NC showed ranges of 5230-5444 and 4020-4268 with means of 5378 +/- 85 and 4167 +/- 95 for PV and CB neurons respectively. Variations in size together with the differential distribution of these neurons in the cortical layers may indicate their involvement in different functional circuitaries.

Analysis of extracellular gamma-aminobutyric acid, glutamate and aspartate in cat visual cortex by in vivo microdialysis and capillary electrophoresis-laser induced fluorescence detection

To investigate the influence of a partial sensory deprivation on the extracellular concentration of amino acid neurotransmitters in cat visual cortex, a capillary electrophoresis method was developed for the quantification of gamma-aminobutyric acid (GABA), glutamate (Glu) and aspartate (Asp) in in vivo microdialysis samples of cat brain. Microdialysis samples from different regions of area 17 were obtained every 15-min using CMA 12 2-mm probes perfused with synthetic cerebrospinal fluid and derivatized using fluorescein isothiocyanate (FITC). Laser-induced fluorescence (LIF) detection was employed. Good selectivity was obtained with a borate buffer (20 mM, pH 10.25). The whole procedure, including the washing step takes only 15 min. The conditions for derivatization and separation were optimized. The parameters for validation such as linearity, precision and detection limit are also reported. The results are consistent with those of HPLC but, as the sample volumes needed are only 1--5 nl, a much better time resolution can be obtained.

Patterns of GABA(B)R1a,b receptor gene expression in monkey and human visual cortex

In situ hybridization histochemistry and immunocytochemistry were used to examine GABA(B)R1a,b receptor mRNA and protein expression in areas 17 and 18 of the visual cortex of normal macaque monkeys and of monkeys that had been deprived of vision in one eye. In addition, the normal patterns of GABA(B)R1a,b protein expression were immunocytochemically studied in the human visual cortex. Overall levels of GABA(B)R1a,b transcript were higher in area 17 than in area 18. In area 17 GABA(B)R1a,b mRNA levels were highest in layers IVC and VI, moderate in layers II-IVA and low in layers I, IVB and V. In area 18 GABA(B)R1a,b transcript expression was high in layers II and III, moderate in layers IV and VI and low in layers I and V. Immunocytochemistry revealed nearly identical patterns of GABA(B)R1a,b protein expression in areas 17 and 18 in monkey and human. Both pyramidal and non-pyramidal neurons were GABA(B)R1a,b immunoreactive. The majority of intensely immunoreactive neurons in layers II, III, V and VI were pyramidal cells. Numerous non-pyramidal cells were intensely immunoreactive in layer IV of area 17 but layer IV cells were only lightly immunoreactive in area 18. Following 10 day periods of monocular deprivation, induced by intravitreal injections of tetrodotoxin, levels of GABA(B)R1a,b mRNA and protein were decreased in the deprived eye dominance columns of layers IVC and VI.

The occ1 gene is preferentially expressed in the primary visual cortex in an activity-dependent manner: a pattern of gene expression related to the cytoarchitectonic area in adult macaque neocortex

Marker molecules to visualize specific subsets of neurons are useful for studying the functional organization of the neocortex. One approach to identify such molecular markers is to examine the differences in molecular properties among morphologically and physiologically distinct neuronal cell types. We used differential display to compare mRNA expression in the anatomically and functionally distinct areas of the adult macaque neocortex. We found that a gene, designated occ1, was preferentially transcribed in the posterior region of the neocortex, especially in area 17. Complete sequence analysis revealed that occ1 encodes a macaque homolog of a secretable protein, TSC-36/follistatin-related protein (FRP). In situ hybridization histochemistry confirmed the characteristic neocortical expression pattern of occ1 and showed that occ1 transcription is high in layers II, III, IVA and IVC of area 17. In addition, occ1 transcription was observed selectively in cells of the magnocellular layers in the lateral geniculate nucleus (LGN). Dual labeling immunohistochemistry showed that the occ1-positive neurons in area 17 include both gamma-aminobutyric acid (GABA)-positive aspiny inhibitory cells and the alpha-subunit of type II calcium/calmodulin-dependent protein kinase (CaMKII alpha)-positive spiny excitatory cells. With brief periods of monocular deprivation, the occ1 mRNA level decreased markedly in deprived ocular dominance columns of area 17. From this we conclude that the expression of occ1 mRNA is present in a subset of neurons that are preferentially localized in particular laminae of area 17 and consist of various morphological and physiological neuronal types, and, furthermore, occ1 transcription is subject to visually driven activity-dependent regulation.

A light and electron microscopic analysis of the convergent retinal and visual cortical projections to the nucleus of the optic tract (NOT) in the pigmented rat

It is generally known that the nucleus of the optic tract (NOT) subserves visuomotor relations between the retina and preoculomotor structures as the only subcortical pathway mediating optokinetic responses (OKR) in mammals. We have examined the projections from the retina and visual cortical areas (areas 17, 18a and 18b) to NOT using tracers (wheat germ agglutinin-conjugated horseradish peroxidase, WGA-HRP and cholera toxin B subunit, CTB) in order to clarify how these two different functional inputs to OKR are organized. CTB injection into the vitreous body resulted in anterograde label almost exclusively in the contralateral NOT. Ultrastructually, the size of the retinal axon terminals was small (up to 0.7 micron in diameter), contained round synaptic vesicles and pale mitochondria, and made asymmetrical synaptic contacts with both GABA-positive and GABA-negative NOT neurons. Visual cortical area 17 and the transitional area between area 17 and 18a, or between area 17 and 18b projected their axons to the ipsilateral NOT. Ultrastructually, the size of the cortical axon terminals was small (up to 0.5 micron in diameter), contained round synaptic vesicles, and made asymmetrical synaptic contacts only with GABAnegative NOT neurons. With light and electron microscopical observation, there was a considerable overlap in the cortico-NOT and retino-NOT projection pattern: GABA-negative (presumably NOT projection) neurons simultaneously receive input from both cortical and retinal terminals. From these results, it seems reasonable to postulate that inputs from visual cortical areas in the pigmented rat cooperate with those from the retina in controlling OKR.

Developmental changes in the expression of NMDA receptor subunits (NR1, NR2A, NR2B) in the cat visual cortex and the effects of dark rearing

The present study used Western blots to determine changes in the level of expression of the three major NMDA receptor subunits, NR1, NR2A, and NR2B, in relation to the 'critical period' in cat visual cortex. NR2A rose dramatically (10-fold) from very low levels at 1 week to a peak at 5 weeks and gradually declined into adulthood (twofold). NR2B showed a similar time course to NR2A, but the rise from 1 to 5 weeks was of lesser magnitude (twofold). NR1 was expressed at comparable levels at 1, 5, 10 weeks and declined markedly (fivefold) in older animals. No significant effects of dark rearing on the levels of NR2B and NR1 were found. However, NR2A expression was significantly elevated in normal compared to dark reared visual cortex (twofold) at 5 weeks and significantly elevated in dark reared compared to normal visual cortex at 20 weeks (twofold). The close agreement between NR2A expression and both the time course of the critical period and the effects of dark rearing on that time course further indicates a role of this subunit in visual cortical critical period plasticity.

Calcium-binding proteins calbindin D28K, calretinin, and parvalbumin immunoreactivity in the rabbit visual cortex

The distribution and morphology of neurons containing three calcium-binding proteins, calbindin D28K, calretinin, and parvalbumin in the adult rabbit visual cortex were studied. The calcium-binding proteins were identified using antibody immunocytochemistry. Calbindin D28K-immunoreactive (IR) neurons were located throughout the cortical layers with the highest density in layer V. However, calbindin D28K-IR neurons were rarely encountered in layer I. Calretinin-IR neurons were mainly located in layers II and III. Considerably lower densities of calretinin-IR neurons were observed in the other layers. Parvalbumin-IR neurons were predominantly located in layers III, IV, V, and VI. In layers I and II, parvalbumin-IR neurons were only rarely seen. The majority of the calbindin D28K-IR neurons were stellate, round or oval cells with multipolar dendrites. The majority of calretinin-IR neurons were vertical fusiform cells with long processes traveling perpendicularly to the pial surface. The morphology of the majority of parvalbumin-IR neurons was similar to that of calbindin D28K: stellate, round or oval with multipolar dendrites. These results indicate that these three different calcium-binding proteins are contained in specific layers and cells in the rabbit visual cortex.

GABAergic neurons in the rabbit visual cortex: percentage, layer distribution and cortical projections

6250 neurons yielding either callosal or inter-areal ipsilateral projections extrinsic to area 17 was GABAergic. Comparing these findings with those reported for other mammals, it seems that the incidence and distribution of GABAergic neurons in the visual cortex is similar in rabbits and rats. In contrast to rats but akin to higher mammals, no GABAergic neuron was found to furnish cortico-cortical connections to area 17 other than intrinsic connections.

Localisation of tachykinin NK1 and NK3 receptors in the human prefrontal and visual cortex

The distribution of tachykinin NK(1) and NK(3) receptors in the prefrontal (Brodmann area 9) and visual cortex (Brodmann area 17) of formalin-fixed postmortem human brain tissue was studied by immunohistochemistry. NK(1)-like immunoreactivity (NK(1)-LI) was observed as a thin band at the cortical surface and dots of NK(1)-LI localised on small non-pyramidal cells and in the neuropil (layers I-III). NK(3)-LI was found in beaded fibres and cells with astrocyte-like morphology in the superficial cortical layers and white matter. Dots of NK(3)-LI were prominent in the neuropil and on pyramidal (layers III/V) and non-pyramidal (layers V/VI) cells. The NK(3)-LI was more abundant and widespread than the NK(1)-LI. This is the first report of the distribution of the NK(1) receptor in the prefrontal and visual cortex of the human brain by immunohistochemistry.

PCR detection of host and HIV-1 sequences from archival brain tissue

Mutations in CCR5 and CCR2b have been recently shown to affect disease progression towards AIDS. A role for these host genotypes in AIDS dementia complex (ADC) has also been postulated but remains unclear. Additionally, brain-derived envelope sequences from HIV-1 have been associated with ADC but their specific contribution to pathogenesis remains uncertain. This study demonstrates the successful use of PCR techniques to isolate host CCR5 and CCR2b, and HIV-1 V3 sequences from paraffin embedded tissues from patients with and without ADC. PCR amplification from archival tissue offers a novel approach for studying the interactions between potential neuroprotective elements in the host and virulence determinants in HIV that may contribute to differences in susceptibility to ADC.