Cytoarchitecture, probability maps and functions of the human frontal pole.

The frontal pole has more expanded than any other part in the human brain as compared to our ancestors. It plays an important role for specifically human behavior and cognitive abilities, e.g. action selection (Kovach et al., 2012). Evidence about divergent functions of its medial and lateral part has been provided, both in the healthy brain and in psychiatric disorders. The anatomical correlates of such functional segregation, however, are still unknown due to a lack of stereotaxic, microstructural maps obtained in a representative sample of brains. Here we show that the human frontopolar cortex consists of two cytoarchitectonically and functionally distinct areas: lateral frontopolar area 1 (Fp1) and medial frontopolar area 2 (Fp2). Based on observer-independent mapping in serial, cell-body stained sections of 10 brains, three-dimensional, probabilistic maps of areas Fp1 and Fp2 were created. They show, for each position of the reference space, the probability with which each area was found in a particular voxel. Applying these maps as seed regions for a meta-analysis revealed that Fp1 and Fp2 differentially contribute to functional networks: Fp1 was involved in cognition, working memory and perception, whereas Fp2 was part of brain networks underlying affective processing and social cognition. The present study thus disclosed cortical correlates of a functional segregation of the human frontopolar cortex. The probabilistic maps provide a sound anatomical basis for interpreting neuroimaging data in the living human brain, and open new perspectives for analyzing structure-function relationships in the prefrontal cortex. The new data will also serve as a starting point for further comparative studies between human and non-human primate brains. This allows finding similarities and differences in the organizational principles of the frontal lobe during evolution as neurobiological basis for our behavior and cognitive abilities.

Stereotaxic probabilistic maps of the magnocellular cell groups in human basal forebrain.

The basal forebrain contains several interdigitating anatomical structures, including the diagonal band of Broca, the basal nucleus of Meynert, the ventral striatum, and also cell groups underneath the globus pallidus that bridge the centromedial amygdala to the bed nucleus of the stria terminalis. Among the cell populations, the magnocellular, cholinergic corticopetal projection neurons have received particular attention due to their loss in Alzheimer's disease. In MRI images, the precise delineation of these structures is difficult due to limited spatial resolution and contrast. Here, using microscopic delineations in ten human postmortem brains, we present stereotaxic probabilistic maps of the basal forebrain areas containing the magnocellular cell groups. Cytoarchitectonic mapping was performed in silver stained histological serial sections. The positions and the extent of the magnocellular cell groups within the septum (Ch1-2), the horizontal limb of the diagonal band (Ch3), and in the sublenticular part of the basal forebrain (Ch4) were traced in high-resolution digitized histological sections, 3D reconstructed, and warped to the reference space of the MNI single subject brain. The superposition of the cytoarchitectonic maps in the MNI brain shows the intersubject variability of the various Ch compartments and their stereotaxic position relative to other brain structures. Both the right and left Ch4 regions showed significantly smaller volumes when age was considered as a covariate. Probabilistic maps of compartments of the basal forebrain magnocellular system are now available as an open source reference for correlation with fMRI, PET, and structural MRI data of the living human brain.

Mapping auditory cortex in the La Plata dolphin (Pontoporia blainvillei).

This study deals with the mapping of the primary and secondary auditory cortex. Due to their important role in echolocation they were the first areas to be examined [P.J. Morgane, M.S. Jacobs, in: R.J. Harrison (Ed.), Functional Anatomy of Marine Mammals, Comparative Anatomy of the Cetacean Nervous System, vol. 1, Academic Press, London, 1972, pp. 117-144]. We analysed the brain of a La Plata dolphin (Pontoporia blainvillei), which had been fixed in formaldehyde, embedded in paraffin, cut in sections of 20mum thickness and stained with cresyl violet. The experimental approach being impossible, we used cytoarchitectonic variations in the neocortex. Former electrophysiological data [T.F. Ladygina, A.Y. Supin, Localization of the projectional sensory areas in the cortex of the porpoise Tursiops truncates, Zh. Evol. Biokhim. Fiziol. 13 (1978) 712-718] [Sokolov, T.F. Ladygina, A.Y. Supin, Location of sensory zones in cerebral cortex of dolphin, Dokl. Biol. Sci., Russian Original 202 (1-6) (1972)] provided the framework for the exact determination of borders between functional cortical areas. We used a stereological observer-independent procedure based on changes in volume density of cell bodies throughout the neocortex [A. Schleicher, et al., Stereological approach to human cortical architecture: Identification and delineation of cortical areas, J. Chem. Neuroanat. 20 (2000) 31-47]. Due to the computer program's high sensitivity to changes in volume density it was possible to analyse the poorly laminated dolphin cortex. The 3D-reconstruction of the auditory cortex was processed using the AMIRA 3.0 Graphics software package comparing the main primary gyri in the histological sections with those in coronal magnetic resonance imaging scans of another intact Pontoporia brain.

Multimodal architectonic mapping of human superior temporal gyrus.

Although it is generally accepted that human superior temporal gyrus is activated by a huge variety of auditory and linguistic tasks, little is known about the exact positions and extents of cortical areas that are located on the lateral convexity of the gyrus (e.g., Brodmann's area 22). Such information, however, is relevant for a rigorous testing of structural-functional relationships in both normal volunteers and patients suffering from disorders of auditory and language perception. The present combined cytoarchitectonic and receptorarchitectonic study identifies a distinct area (Te3) in the lateral bulge of the superior temporal gyrus by using an algorithm-based approach for the detection of cortical borders. Our mapping data show that, in contrast to Brodmann's area (BA) 22, only small portions of Te3 reach the dorsal and ventral banks of the gyrus. Therefore, we labelled the newly defined area as "Te3" and not as "BA 22". The cytoarchitectonically defined borders of Te3 coincide with abrupt changes in the receptorarchitecture of several classical neurotransmitters, suggesting that Te3 represents a functionally relevant area of the human superior temporal gyrus. Since position and extent of area Te3 varied considerably between subjects, probability maps were created that show for each voxel of the standard references space, the frequency with which Te3 was present in it. These maps, in combination with previously published maps of the primary auditory cortex, can directly be compared with functional imaging data, and may open new perspectives for the analysis of structural-functional correlations in the human auditory and language systems.

Quantitative architectural analysis: a new approach to cortical mapping.

Recent progress in anatomical and functional MRI has revived the demand for a reliable, topographic map of the human cerebral cortex. Till date, interpretations of specific activations found in functional imaging studies and their topographical analysis in a spatial reference system are, often, still based on classical architectonic maps. The most commonly used reference atlas is that of Brodmann and his successors, despite its severe inherent drawbacks. One obvious weakness in traditional, architectural mapping is the subjective nature of localising borders between cortical areas, by means of a purely visual, microscopical examination of histological specimens. To overcome this limitation, more objective, quantitative mapping procedures have been established in the past years. The quantification of the neocortical, laminar pattern by defining intensity line profiles across the cortical layers, has a long tradition. During the last years, this method has been extended to enable a reliable, reproducible mapping of the cortex based on image analysis and multivariate statistics. Methodological approaches to such algorithm-based, cortical mapping were published for various architectural modalities. In our contribution, principles of algorithm-based mapping are described for cyto- and receptorarchitecture. In a cytoarchitectural parcellation of the human auditory cortex, using a sliding window procedure, the classical areal pattern of the human superior temporal gyrus was modified by a replacing of Brodmann's areas 41, 42, 22 and parts of area 21, with a novel, more detailed map. An extension and optimisation of the sliding window procedure to the specific requirements of receptorarchitectonic mapping, is also described using the macaque central sulcus and adjacent superior parietal lobule as a second, biologically independent example. Algorithm-based mapping procedures, however, are not limited to these two architectural modalities, but can be applied to all images in which a laminar cortical pattern can be detected and quantified, e.g. myeloarchitectonic and in vivo high resolution MR imaging. Defining cortical borders, based on changes in cortical lamination in high resolution, in vivo structural MR images will result in a rapid increase of our knowledge on the structural parcellation of the human cerebral cortex.

Changes in the expression of neurotransmitter receptors in Parkin and DJ-1 knockout mice--A quantitative multireceptor study.

Parkinson's disease (PD) is a well-characterized neurological disorder with regard to its neuropathological and symptomatic appearance. At the genetic level, mutations of particular genes, e.g. Parkin and DJ-1, were found in human hereditary PD with early onset. Neurotransmitter receptors constitute decisive elements in neural signal transduction. Furthermore, since they are often altered in neurological and psychiatric diseases, receptors have been successful targets for pharmacological agents. However, the consequences of PD-associated gene mutations on the expression of transmitter receptors are largely unknown. Therefore, we studied the expression of 16 different receptor binding sites of the neurotransmitters glutamate, GABA, acetylcholine, adrenaline, serotonin, dopamine and adenosine by means of quantitative receptor autoradiography in Parkin and DJ-1 knockout mice. These knockout mice exhibit electrophysiological and behavioral deficits, but do not show the typical dopaminergic cell loss. We demonstrated differential changes of binding site densities in eleven brain regions. Most prominently, we found an up-regulation of GABA(B) and kainate receptor densities in numerous cortical areas of Parkin and DJ-1 knockout mice, as well as increased NMDA but decreased AMPA receptor densities in different brain regions of the Parkin knockout mice. The alterations of three different glutamate receptor types may indicate the potential relevance of the glutamatergic system in the pathogenesis of PD. Furthermore, the cholinergic M1, M2 and nicotinic receptors as well as the adrenergic α2 and the adenosine A(2A) receptors showed differentially increased densities in Parkin and DJ-1 knockout mice. Taken together, knockout of the PD-associated genes Parkin or DJ-1 results in differential changes of neurotransmitter receptor densities, highlighting a possible role of altered non-dopaminergic, and in particular of glutamatergic neurotransmission in PD pathogenesis.

Structural asymmetries in the human forebrain and the forebrain of non-human primates and rats.

Possible asymmetries of the following structures were studied: volumes of total human hemispheres, cortex and white matter volumes in post-mortem- (unknown handedness) and living brains (male right-handers); volumes of the rat primary visual cortex, its mon- and binocular subfields, its layer iv and the density of myelinated fibres in layer iv; transmitter receptor densities (NMDA, AMPA, kainate and GABAA receptors) in sensorimotor regions of the rat cortex; volume of the motor cortex and the 3D-extent of the central sulcus in the post-mortem- (unknown handedness) and living human brain (male right-handers); petalia of the hemispheres in human (male right- and left-handers) and chimpanzee brains. Histological, MRI and receptor autoradiographic techniques were used. With the notable exceptions of the transmitter receptors and the total primary visual cortex in rats and the hemispheres in chimpanzees, which do not show any significant directional asymmetry, all other parameters studied are asymmetrically distributed between the right- and left hemispheres. The regional distribution pattern and the degree of asymmetry of frontal and occipital petalia in living human brains differ between right- and left-handers.

Glucose utilization in rat hippocampus after long-term recovery from ischemia.

The influence on hippocampal glucose utilization of a transient 10-min forebrain ischemia was quantified in male Wistar rats after 2 and 3 weeks as well as after 3 months by application of the [14C]2-deoxyglucose technique. Ischemia was induced by occlusion of the carotid arteries and simultaneous lowering of the blood pressure to 40 mm Hg. For identification of the hippocampal architecture, sections were stained for perikarya (cresyl violet) and for acetylcholinesterase. The hippocampal regions clearly showed different responses to the ischemic insult. The necrotic pyramidal cells being almost completely removed, significant increases in glucose utilization occurred in most layers of the CA1 sector at 2 and 3 weeks post ischemia, while widespread reductions prevailed in all other sectors and the dentate gyrus. At 3 months after the ischemic insult, glucose utilization was reduced in all hippocampal structures including the CA1 region. The increases in glucose utilization in the CA1 sector are suggested to indicate long-lasting presynaptic hyperexcitation, while the widespread reductions in glucose utilization demonstrate that neuronal activity is also altered in hippocampal areas that do not show major histological damage.

Plasticity in the rat hippocampal formation following ibotenic acid lesion of the septal region: a quantitative [14C]deoxyglucose and acetylcholinesterase study.

The local cerebral glucose utilization was measured in the hippocampal formation 3, 21, and 90 days after bilateral lesions of the medial septal nucleus and the nucleus of the diagonal band of Broca by multiple ibotenic acid injections. The CMRglc was determined in hippocampal areas and layers and various limbic and visual regions by quantitative [14C]2-deoxyglucose autoradiography using a computerized image-processing system. Three days after lesion, CMRglc was significantly decreased in 26 of the 38 structures examined. The most pronounced reductions were found in CA2 and CA3, the subiculum, and the parasubiculum. The CMRglc values of the 21- and 90-day postlesion groups did not differ significantly from control data when univariate statistics were used. However, by means of a factor analysis and subsequently a discriminant analysis as a multivariate test for group differences, significant lesion-induced CMRglc changes could be detected between the control group, the 3-day group, and the 90-day group. The 21-day group did not differ significantly from the controls. The data indicate that 90 days after lesion of the medial septum/diagonal band complex (MSDB), a considerable recovery of the mean CMRglc was found in the hippocampal region, although a normal level was not reached. In a parallel series, processing of sections for acetylcholinesterase (AChE) histochemistry revealed a severe destruction of AChE-positive fibers in the hippocampus at 3 days after lesion and a conspicuous recovery in the amount of stainable fibers and their staining intensity at 21 days postlesion. In the 90-day group, the AChE fibers recovered even further but did not reach the values of unlesioned sham-operated controls. The present study indicates that sprouting of surviving cholinergic afferents might be an important morphological substrate for CMRglc recovery in the hippocampus after MSDB lesion.

Quantitative analysis of the columnar arrangement of neurons in the human cingulate cortex.

The spatial organization of human cingulate (areas 24b, 23b, and 31) and pericingulate (areas 7 and 19) cortex was examined by using an image analyzer to measure characteristics of vertically oriented, translaminar columns of neurons in the cerebral cortex. Columns of 30-50 microns in diameter are hypothesized to be a general feature of cortical organization, but no quantitative analysis of different human cortical areas has been performed. Our results prove for the first time that a columnar organization was detectable in every area examined. The average width of cell columns was approximately 40 microns separated by a neuropil-rich fascicle of the same dimension. Because differences in the expression of a columnar organization were seen, the degree of columnization was subsequently expressed by a verticality index (VI) revealing specific changes in its dimension depending on the architectonic area. The VI was calculated by a linear combination of three variables derived from the measurement of cell density profiles in Nissl-stained sections at right angles to vertically oriented cell columns. Variables included the amplitude of profile peaks, the standard deviation of the width of those profile peaks, and the standard deviation of the distances between profile peaks. The index of verticality describes the deviation of a distinct area and layer from the mean degree of vertical organization of all cortical areas and layers examined. Thus, different degrees of columnar organization can be quantitatively described by the verticality index and can be used as criteria to characterize architectonic areas.

The monocular and binocular subfields of the rat's primary visual cortex: a quantitative morphological approach.

Primary visual cortex in the rat was studied by a variety of methods: transsynaptic transport of labelled amino acids, 2-deoxyglucose, and staining for perikarya, myelin, and acetylcholinesterase. The analysis was aided by a computer-controlled television image analyzer. The results obtained with different methods agree with one another in describing the position and extent of the entire primary visual cortex as well as its monocular (medial) and binocular (lateral) subareas.

Mapping of glial fibrillary acidic protein-immunoreactivity in the rat forebrain and mesencephalon by computerized image analysis.

Computer-assisted image analysis was used to map the regional distribution of glial fibrillary acidic protein-immunoreactive (GFAP-IR) astrocytes in the rat forebrain and mesencephalon. A complete survey of packing densities of GFAP-IR structures was performed. Computer maps revealed high values in the outer and inner layers of the cortex, some hippocampal and olfactory bulb layers, prepiriform cortex, dorsal part of the caudate-putamen, globus pallidus, lateral septum, reticular thalamic nucleus, lateral habenular nucleus, circumventricular organs, nuclei of the medial hypothalamus, substantia nigra, interpeduncular nucleus, and mamillary body. These correspond to regions of the embryonic pial and ventricular brain surfaces, which undergo developmental alterations including growth and various forms of internalization. From this we conclude that in the adult brain, astrocytes of high GFAP-IR are derivatives of surface-contact glia, whereas those located in areas having developed by the local thickening of the neural tube wall show reduced or no GFAP-IR.

Quantitative cytoarchitectonics of the posterior cingulate cortex in primates.

The cytoarchitecture of four cortical areas within the posterior cingulate region and the differences among them are quantitatively analyzed in 17 primate species. The transition from allocortex (area 29) to isocortex (areas 30, 23, and 31) is characterized by shifts in laminar proportions and cellular densities. The molecular layer and inner main lamina (layers V and VI) occupy a smaller proportion of the cortex in iso- than in allocortex, while conversely, the outer main lamina (layers II and III) makes up a larger proportion of the cortex in iso- than in allocortex. Layer IV is relatively larger in area 31 than in area 23. The packing densities of cell bodies were determined by gray-level index values. These values show that the isocortex has lower cell densities in the outer main lamina, but higher cell densities in the inner main layers. Furthermore, the granular layer of area 31 is more densely packed than it is in area 23. These results are discussed as structural correlates of a relative increase in the receptive and processing capacities of the isocortex over the adjacent allocortex.

Comparative aspects of the primate posterior cingulate cortex.

Cytoarchitecturally defined cortical areas of the posterior cingulate gyrus differ morphometrically among the major taxonomic divisions of primates. Prosimians and anthropoids have different laminar proportions in the isocortical regions (areas 30, 23, and 31); anthropoids have relatively larger outer main laminae and granular layers than prosimians. In the granular retrosplenial cortex (area 29), however, prosimians and anthropoids differ only in the proportion of the molecular layer to the rest of the cortex. On the other hand, the proportions of the inner and outer main laminae of area 29 differ between the infraorder divisions of Anthropoidea, the catarrhines, and the platyrrhines. The platyrrhines (New World monkeys) have apparently specialized by increasing the outer main lamina of area 29, which contains afferent and intracortical connections. Among all primates, the amount of neuropil in each cortical region changes as a function of brain weight, but within each area, the neuropil maintains a constant ratio between the outer and inner laminae. These observations suggest that neuropil ratios are conservative features in primates and that evolutionary changes more frequently involve shifts in volumetric proportions. Furthermore, the platyrrhine-catarrhine differences in area 29 likely evolved after the prosimian-anthropoid differences were established in the isocortical cingulate regions.

Receptor autoradiographic mapping of the mesial motor and premotor cortex of the macaque monkey.

This study analyzes regional and laminar distribution patterns of neurotransmitter binding sites in the motor areas of the macaque mesial frontal cortex. Differences in distribution patterns are compared with the cytoarchitectonic parcellation. Binding sites were analyzed with quantitative in vitro receptor autoradiography in unfixed brains of five macaque monkeys. Alpha-amino-3-hydroxy-5-methyl-4-isoxalone propionic acid (AMPA), kainate, and N-methyl-D-aspartate (NMDA) binding sites were labeled with [3H]AMPA, [3H]kainate, and [3H]MK-801, respectively, muscarinic binding sites with [3H]pirenzepine or [3H]oxotremorine-M, noradrenergic binding sites with [3H]prazosin or [3H]UK-14304, gamma-aminobutyric acid (GABA)A binding sites with [3H]muscimol, and serotoninergic binding sites with [3H]ketanserine. Adjacent sections were stained with a modified Nissl method for cytoarchitectonic analysis. In the motor areas F1, F3, and F6, [3H]AMPA, [3H]pirenzepine, and [3H]oxotremorine-M binding was maximal in layers II, III, and V, and [3H]kainate binding was maximal in layers V and VI. Clear-cut changes in laminar distribution patterns of [3H]AMPA, [3H]kainate, and [3H]oxotremorine-M binding sites very closely matched corresponding cytoarchitectonic borders. Mean areal binding densities of all ligands to F1, F3, and F6 were plotted as polar plots for each area. A polygon was obtained for each area ("neurochemical fingerprint") when all the density values belonging to one area were connected with each other. The "neurochemical fingerprints" of F1, F3, and F6 were virtually identical in shape but increased in size from F1 to F6. This result reflects the functional similarity of these motor-related areas and possibly correlates with their differential involvement in motor control. Areas F1, F3, and F6 can thus be grouped into one "neurochemical family" of areas.

Broca's region revisited: cytoarchitecture and intersubject variability.

The sizes of Brodmann's areas 44 and 45 (Broca's speech region) and their extent in relation to macroscopic landmarks and surrounding areas differ considerably among the available cytoarchitectonic maps. Such variability may be due to intersubject differences in anatomy, observer-dependent discrepancies in cytoarchitectonic mapping, or both. Because a reliable definition of cytoarchitectonic borders is important for interpreting functional imaging data, we mapped areas 44 and 45 by means of an observer-independent technique. In 10 human brains, the laminar distributions of cell densities were measured vertical to the cortical surface in serial coronal sections stained for perikarya. Thousands of density profiles were obtained. Cytoarchitectonic borders were defined as statistically significant changes in laminar patterns. The analysis of the three-dimensional reconstructed brains and the two areas showed that cytoarchitectonic borders did not consistently coincide with sulcal contours. Therefore, macroscopic features are not reliable landmarks of cytoarchitectonic borders. Intersubject variability in the cytoarchitecture of areas 44 and 45 was significantly greater than cytoarchitectonic differences between these areas in individual brains. Although the volumes of area 44 differed across subjects by up to a factor of 10, area 44 but not area 45 was left-over-right asymmetrical in all brains. All five male but only three of five female brains had significantly higher cell densities on the left than on the right side. Such hemispheric and gender differences were not detected in area 45. These morphologic asymmetries of area 44 provide a putative correlate of the functional lateralization of speech production.

Acetylcholinesterase activity and post-lesional plasticity in the hippocampus of young and aged rats.

Applying quantitative microscopic histochemistry, the activity of acetylcholinesterase was determined in the various layers of the rat hippocampus at three different levels along the rostrocaudal extent. Two age groups of animals were examined: young adults (two to three months old) and aged subjects (26 months old). Young adults were divided into controls, and animals killed eight and 35 days following bilateral ibotenate lesioning of the medial septum-diagonal band complex. Aged rats were divided into controls and animals 35 days post-lesion. Analysis of variance revealed that the mean acetylcholinesterase activities of the entire hippocampus of individuals were not significantly different between young and aged rats when averaged across controls and 35 days post-lesion. There was a significant decrease of acetylcholinesterase activity (-52%) in young adults eight days post-lesion as compared to controls, but a significant increase (+63%) took place until 35 days post-lesion as compared to eight days post-lesion. Significantly lower activities existed, however, in young (-22%) and aged rats (-18%) 35 days post-lesion as compared to controls. This decrease in mean activity was not age dependent. As acetylcholinesterase is considered to be a good cholinergic indicator in the hippocampus, the results suggest a homotypic collateral sprouting from spared cholinergic afferents following ibotenate lesion of the medial septum-diagonal band complex in young and aged rats. Based on the data obtained, it is reasonable to assume that there was no difference in the post-lesional plasticity of neuronal acetylcholinesterase between young adult and aged rats.

Quantitative autoradiography of 11 different transmitter binding sites in the basal forebrain region of the rat--evidence of heterogeneity in distribution patterns.

The distribution of 12 different binding sites for acetylcholine, L-glutamate, GABA, 5-hydroxytryptamine, dopamine and noradrenaline was measured with quantitative receptor autoradiography in four regions of the rat basal forebrain (medial septal nucleus including vertical and horizontal limbs of the diagonal band of Broca, magnocellular preoptic nucleus, substantia innominata and basal nucleus of Meynert, ventral pallidum). L-Glutamate binding sites represent the largest portion of the analysed receptors in all regions, followed by muscarinic2, 5-hydroxytryptamine1 and GABAA receptors. Muscarinic1, dopamine1, dopamine2 and 5-hydroxytryptamine2 receptors and alpha 1-, alpha 1A- and alpha 1B-adrenoceptors represent the minor receptor populations. The largest portion of the dopamine receptors is represented by the dopamine1 subtype, and the alpha 1B subtype dominates the alpha 1-adrenoceptor group. A heterogeneity of the distribution patterns of the different receptors throughout the basal forebrain regions is found. A comparison of the patterns shows that alpha 1-adrenoceptors have a similar regional distribution to that of the muscarinic2 receptors, but both receptor types have reciprocal distributions compared with the 5-hydroxytryptamine1 receptors. The results indicate that one transmitter may exert different effects in the basal forebrain regions depending on the densities of the respective receptor subtypes. Moreover, similar or reciprocal distribution patterns of some, but not all, analysed receptors point to a non-random association (co-distribution) of the different transmitter systems in the basal forebrain regions.

Long-term changes of ionotropic glutamate and GABA receptors after unilateral permanent focal cerebral ischemia in the mouse brain.

Long-term hyperexcitability was found after unilateral, permanent middle cerebral artery occlusion in exofocal neocortical areas of the adult mouse [Mittmann et al. (1998) Neuroscience 85, 15-27]. The aim of the present study was to test the hypothesis in an identical paradigm of ischemia. whether alterations in the densities of both excitatory and inhibitory amino acid receptors may underlie these pathophysiological changes. Alterations in densities of [3H]dizocilpine, [3H]D,L-amino-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, [3H]kainate and [3H]muscimol binding sites were demonstrated with quantitative in vitro receptor autoradiography. All binding sites were severely reduced in the core of the ischemic lesion. A completely different reaction was found in the exofocal, histologically inconspicuous parts of the somatosensory cortex and the more remote neocortical areas of both hemispheres. The [3H]muscimol binding sites were significantly reduced four weeks after ischemia in the motor cortex, hindlimb representation area and exofocal parts of the primary and secondary somatosensory cortices of both hemispheres. The focus of the reduction in [3H]muscimol binding sites was found in lower layer V and upper layer VI. Contrastingly, the densities of [3H]dizocilpine binding sites were found to be increased in these areas, whereas those of [3H]D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and [3H]kainate binding sites did not show significant changes. The [3H]dizocilpine binding site density increased predominantly in layers III and IV. All binding sites were also reduced in the retrogradely reacting, gliotic part of the ipsilateral ventroposterior thalamic nucleus, whereas the [3H]D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid binding sites were increased in the surround of the ipsilateral nucleus and no changes in binding sites were seen in the whole contralateral nucleus. We conclude that permanent local ischemia leads to a long-term and widespread impairment of the normal balance between binding sites of excitatory and inhibitory neurotransmitter receptors in neocortical areas far away from the focus of the post-ischemic tissue damage. The imbalance comprises an up-regulation of the [3H]dizocilpine binding sites in the ion channels of N-methyl-D-aspartate receptors and a down-regulation of [3H]muscimol binding sites of the GABA(A) receptors in the ipsi- and contralateral neocortex. These changes at the receptor level explain the previously observed hyperexcitability with the appearance of epileptiform field potentials and the long duration of excitatory postsynaptic potentials four weeks after ischemia.

Excitatory and inhibitory neurons express c-Fos in barrel-related columns after exploration of a novel environment.

Recent work has shown that behaviorally meaningful sensory information processing is accompanied by the induction of several transcription factors in the barrel cortex of rodents. It is now generally accepted that stimulus-transcription coupling is an important step in the sequence of events leading to long-term plastic changes in neuronal structure and function. Nevertheless, so far few data are available as to what types of neurons are involved in such a genomic response. Here, we determined the morphological and neurochemical identity of neurons in rat barrel cortex showing a c-Fos-immunoreactive nucleus after exploration of an enriched environment. Double stainings of c-Fos and glial fibrillary acidic protein excluded astrocytes as a possible cell type expressing this transcription factor. By morphological phenotyping with intracellular Lucifer Yellow injections, it was found that a large majority were probably excitatory pyramidal cells, but inhibitory interneurons were also found to contain c-Fos-immunoreactive nuclei. By neurochemical phenotyping of GABAergic interneurons with specific antibodies, a significant induction was found, in a layer-dependent manner, for the populations of glutamic acid decarboxylase-, parvalbumin-, calbindin- and vasoactive intestinal polypeptide-immunoreactive neurons but not for calretinin-immunoreactive cells in experimental compared to control columns. From these data we conclude that thalamic afferents effectively drive cortical excitatory as well as inhibitory intracortical circuits. Thus, the adaptations of receptive field properties of cortical neurons after different manipulations of the sensory periphery are likely to be caused by plastic changes in excitatory and inhibitory networks.