Biomedical subjects

K Zilles

Publications and source records attributed to K Zilles.

At least 127 records · Page 7Linked to original sources

PubMed1999

Current-source-density profiles associated with sharp waves in human epileptic neocortical tissue.

In human neocortical slices obtained during epilepsy surgery, sharp waves have been described to appear spontaneously, the shape of which met all criteria of epileptiform field potentials. In the present investigation, the current sinks and sources underlying these potentials were analysed. The cortical tissue used in the present study was a small portion of the tissue blocks excised for treatment of pharmacoresistant focal epilepsy. The tissue came from the temporal (n = 26), frontal (n = 1) and parietal (n = 1) lobes. Slices of 500 microm thickness were cut in the frontal plane perpendicular to the pial surface. Field potentials were recorded using a linear array of eight wire electrodes (diameter: 33 microm) with interelectrode distances of 300 microm. To scan a slice for sharp field potentials, this array was placed perpendicular to the pial surface at the midsection of each preparation, and consecutively at the respective midsections of the resulting halves of the slice. Each of these locations was termed a recording line. Depending on the appearance of spontaneous potentials, recording lines and slices were classified as either spontaneous or non-spontaneous. With both spontaneous and zero Mg(2+)-induced interictal discharges, in spontaneous slices, current sinks were preferentially located in layers II and III. In non-spontaneous slices, current sinks associated with interictal potentials could be found throughout all cortical laminae. With zero Mg(2+)-induced ictal activity, in spontaneous slices, the initial sinks were preferentially located in cortical laminae II and IIIa, and were shifted to lower ones after additional application of bicuculline. In non-spontaneous slices, no ictal-type discharges could be induced with omission of Mg2+ from the superfusate. Only addition of bicuculline elicited ictal-type activity, and sinks associated with this were preferentially located in layers II and IIIa. The results suggest that the supragranular layers, especially layer II, change qualitatively in functional organization in slices showing spontaneous discharges. We think that this special feature represents the function of the upper layers and can be blocked by bicuculline. This interpretation is supported by the observation that ictal discharges normally started in the upper layers in spontaneous and non-spontaneous slices, except for spontaneous slices with bicuculline, where the zone initiating discharges was translocated to deeper layers.

Adolescent↗

PubMed1999

Ionotropic glutamate and GABA receptors in human epileptic neocortical tissue: quantitative in vitro receptor autoradiography.

Since a disturbed balance between excitatory and inhibitory amino acid receptors is suggested to be an important condition for epileptogenic cortical activity, the present study has focused on the analysis of the densities of (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), N-methyl-D-aspartate, kainate and GABA subtype A receptors in neocortical tissue surgically removed from patients with focal epilepsy. The mean densities (collapsed over cortical layers I-VI) and the laminar distribution patterns of [3H]AMPA, [3H]MK-801, [3H]kainate and [3H]muscimol binding to AMPA, N-methyl-D-aspartate, kainate and GABAA receptors were determined with quantitative receptor autoradiography in the neocortex of patients with focal epilepsy and controls. The tissue probes used in the present study were functionally characterized by parallel electrophysiological investigations. From that, the different probes could be subdivided into a spontaneously spiking and a non-spontaneously spiking group. The mean density of [3H]AMPA binding sites was significantly increased (+37%) in the group of epileptic brains (n = 10) compared with controls (n = 10), but the mean densities of [3H]MK-801, [3H]kainate and [3H]muscimol binding sites were not significantly altered (-8%, +/-0% and -7%, respectively). The relation between the densities of all four binding sites were simultaneously displayed as polar plots in each single brain ("receptor fingerprints"). The consistent up-regulation of [3H]AMPA binding sites in all epileptic brains was found to be associated with a down-regulation of the N-methyl-D-aspartate receptor in four of the five non-spontaneously spiking cases, and an associated up-regulation of the N-methyl-D-aspartate receptor was seen in all spontaneously spiking cases. Finally, the laminar distribution of binding site densities was analysed, since the mean densities collapsed over all neocortical layers may obscure layer-specific alterations. Layer- and receptor- specific up- or down-regulations were found in epileptic tissue compared with controls. Moreover, the laminar distribution pattern of current sinks associated with epileptiform potentials in a spontaneously spiking cortical slice was found to be co-localized with local maxima of AMPA receptor densities. The present analysis of four ionotropic glutamate and GABA receptor subtypes demonstrates a consistent and significant up-regulation of [3H]AMPA binding sites in all cases of human focal epilepsy, which co-localizes with the occurrence of sinks in current-source-density analysis. The receptor fingerprint analysis suggests a subdivision of focal epilepsy into two subtypes on the basis of neurochemical/functional correlations: (i) a spontaneously spiking subtype with increased N-methyl-D-aspartate receptor density, and (ii) a non-spontaneously spiking subtype with decreased N-methyl-D-aspartate receptor density.

Autoradiography↗

PubMed1999

Different nitric oxide synthase inhibitors cause rapid and differential alterations in the ligand-binding capacity of transmitter receptors in the rat cerebral cortex.

Inhibitors of nitric oxide (NO) synthesis reduce postlesional neuronal death during reperfusion injury by reducing the NO-mediated increase in excitatory neurotransmitter-release. The protective effects of various NO-synthase (NOS) inhibitors differ due to their isoform selectivity. The effects of NO-mediated excessive neurotransmitter supply are transmitted via specific neurotransmitter receptors expressed by the target cells. We report changes in the ligand-binding of different excitatory and inhibitory neurotransmitter-receptors studied by in vitro receptor autoradiography after in vivo-application of NOS-inhibitors. Since the constitutively expressed neuronal NOS-I is area-specifically distributed within the rat cortex, numerous cortical areas were studied in non-lesioned rats, in order to analyze the area-specific effects of NOS-inhibitors. The results showed that the NOS-I-specific inhibitor 7-nitroindazole increased binding of 3H-muscimol, 3H-pirenzepine and 3H-kainate, whereas the less isoform-specific, general NOS-inhibitor L-nitroarginine increased binding of 3H-muscimol and 3H-AMPA in most cortical areas, leaving 3H-kainate binding almost unchanged. The water soluble L-nitroarginine-methylester caused similar effects to those of L-nitroarginine which changed over a period of chronic treatment. The inhibitory GABAA-receptors were increased after NOS-inhibition in most cortical areas, whereas binding of 3H-Oxotremorine-M (acetylcholine receptors), 3H-MK-801 (NMDA-receptors) and 3H-AMPA (AMPA receptors) was affected differently among the cortical areas. Strongest alterations of ligand-binding capacity after administration of NOS-inhibitors were seen in cortical areas known to contain the highest packing densities of NOS-I-positive interneurons such as the piriform and entorhinal cortices, indicating that, in normal animals, neurotransmission and probably cognitive information processing would be affected by the pharmacological modulation of nitric oxide production.

Animals↗

PubMed1999

Neuronal correlates of real and illusory contour perception: functional anatomy with PET.

Illusory contours provide a striking example of the visual system's ability to extract a meaningful representation of the surroundings from fragmented visual stimuli. Psychophysical and neurophysiological data suggest that illusory contours are processed in early visual cortical areas, and neuroimaging studies in humans have shown that Kanizsa-type illusory contours activate early retinotopic visual areas that are also activated by real contours. It is not known whether other types of illusory contours are processed by the same mechanisms, nor is it clear to what extent attentional effects may have influenced these results, as no attempt was made to match the salience of real and illusory stimuli in previous imaging studies. It therefore remains an open question whether there are any brain regions specifically involved in the perception of illusory contours. To address these questions, we have used 15O-butanol positron emission tomography (PET) and a novel kind of illusory contour stimulus that is induced only by aligned line ends. By employing a form discrimination task that was matched for attention and stimulus salience across conditions we were able to directly contrast perception of real and illusory contours. We found that the regions activated by illusory contour perception were the same as those activated by real contours. Only one region, located in the right fusiform gyrus, was significantly more strongly activated by perception of illusory contours than by real contours. In addition, a principal component analysis suggested that illusory contour perception is associated with a change in the correlation between V1 and V2. We conclude that different kinds of illusory contours are processed by the same cortical regions and that these regions overlap extensively with those involved in processing of real contours. At the regional level, perception of illusory contours thus appears to differ from perception of real contours by the degree of involvement of higher visual areas as well as by the nature of interaction between early visual areas.

Adult↗

PubMed1999

Neurobiological bases of behavioral development in the second year.

We discuss selected psychological competences that develop and become noticeable between one and two years of age and are temporally correlated to structural, biochemical and physiological changes in the brain. The psychological competences are: Language development, a sense of "right" and "wrong", self-awareness, and the ability to make inferences. The accompanying changes in the brain involve the prefrontal cortex, language-related cortical areas, hippocampus, cerebellum, basal ganglia and an increase in the connectivity of the network. Of special interest are the maturational changes in layers III-IV of the prefrontal cortex. Layer III is the origin and target of callosal and commissural axons linking the two hemispheres and the target of associational axons linking ipsilateral areas within each hemisphere. Layer IV, the target for axons from the mediodorsal nucleus of the thalamus, conveys information from other associational cortices, cerebellum, basal ganglia, and the reticular and limbic systems. In the second year, intensive dendritic growth and synaptogenesis in these layers increase the linking of these two layers and form a neural basis for a more efficient convergence and integration of information from the two hemispheres, which are functionally asymmetric. It is our hypothesis that these changes, together with the maturational changes in the cortico-subcortical network, are a basis for the observed emergence of the psychological competences. We are aware that temporal correlations cannot prove firm causal relationships. However, knowledge of these correlations is useful in generating specific hypotheses that can be tested directly.

Axons↗

PubMed1999

The role of ventral medial wall motor areas in bimanual co-ordination. A combined lesion and activation study.

Two patients with midline tumours and disturbances of bimanual co-ordination as the presenting symptoms were examined. Both reported difficulties whenever the two hands had to act together simultaneously, whereas they had no problems with unimanual dexterity or the use of both hands sequentially. In the first patient the lesion was confined to the cingulate gyrus; in the second it also invaded the corpus callosum and the supplementary motor area. Kinematic analysis of bimanual in-phase and anti-phase movements revealed an impairment of both the temporal adjustment between the hands and the independence of movements between the two hands. A functional imaging study in six volunteers, who performed the same bimanual in-phase and anti-phase tasks, showed strong activations of midline areas including the cingulate and ventral supplementary motor area. The prominent activation of the ventral medial wall motor areas in the volunteers in conjunction with the bimanual co-ordination disorder in the two patients with lesions compromising their function is evidence for their pivotal role in bimanual co-ordination.

Adult↗

PubMed1999

Patterned distribution of immunoreactive astroglial processes in the striate (V1) cortex of New World monkeys.

The possibility of a modular organization of non-neuronal elements was analyzed in the opercular region of the striate neocortex in adult New World monkeys. For this purpose, and in order to follow possible correlations in the general organization of neuronal and astroglial elements, immunocytochemical procedures for Glial Fibrillary Acid Protein (GFAP) and Microtubule Associated Protein 2 (MAP-2), in addition to cytochrome oxidase (COX) histochemistry, were applied to tangential and coronal sections and analyzed by using computer-assisted procedures. Astroglial interlaminar processes stemming from superficial laminae did not traverse lamina IVA, and thus did not appear in deeper layers. Clearly definable interlaminar processes were predominantly concentrated in laminae II-III. A honeycomb- like lattice was observed in tangential sections, with a "cell" size distribution similar to the MAP-2-IR lattice, suggesting an intimate association with the pyramidal columns. Additionally, analysis of similar sections disclosed the periodic appearance of large patches with high density of interlaminar processes, indicating a nonhomogeneous distribution of GFAP-IR processes in the striate cortex. COX "blobs" appeared frequently to coincide with areas expressing high density of GFAP-IR elements. These findings add a new perspective to current concepts of astroglial organization in the striate cortex of primates and reveal the existence of a non-neuronal modular organization in the primate striate cerebral cortex, and suggest that possible correlations between relative distributions of neuronal and astroglial elements should be further analyzed in cortical areas with a clear modular organization such as the striate cortex.

Animals↗

PubMed1998

Bihemispheric reduction of GABAA receptor binding following focal cortical photothrombotic lesions in the rat brain.

Focal brain lesions may lead to neuronal dysfunctions in remote (exofocal) brain regions. In the present study, focal lesions were induced in the hindlimb representation area of the parietal cerebral cortex in rats using the technique of photothrombosis. Photothrombosis occurs after illumination of the brain through the intact skull following intravenous injection of the photosensitive dye Rose Bengal. This resulted in cortical lesions with a diameter of about 2 mm. Quantitative receptor autoradiography was used to study alterations in the density of [3H]muscimol binding sites to GABAA receptors seven days after lesion induction. A reduced GABAA receptor binding (-13 to -27% of the control value) was found in layers II and III of remote exofocal regions in the ipsi- and contralateral cortex. The reduction was consistently more intense in the ipsilateral cortical areas than in those of the contralateral hemisphere. Using extracellular recordings, significant correlations between GABAA receptor binding and paired pulse inhibition could be demonstrated. The present investigation demonstrates that focal brain lesions cause a widespread, functionally effective down-regulation of GABAA receptors. These postlesional changes may result from lesion-induced alterations in cortical connectivity.

Animals↗

PubMed1998

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.

Animals↗

PubMed1998

Limbic frontal cortex in hominoids: a comparative study of area 13.

The limbic frontal cortex forms part of the neural substrate responsible for emotional reactions to social stimuli. Area 13 is one of the cortical areas long known to be part of the posterior orbitofrontal cortex in several monkey species, such as the macaque. Its presence nevertheless in the human brain has been unclear, and the cortex of the frontal lobe of the great and lesser apes remains largely unknown. In this study area 13 was identified in human, chimpanzee, bonobo, gorilla, orangutan, and gibbon brains, and cortical maps were generated on the basis of its cytoarchitecture. Imaging techniques were used to characterize and quantify the microstructural organization of the area, and stereological tools were applied for estimates of the volume of area 13 in all species. Area 13 is conservative in its structure, and features such as size of cortical layers, density of neurons, and space available for connections are similar across hominoids with only subtle differences present. In contrast to the homogeneity found in its organization, variation is present in the relative size of this cortical area (as a percentage of total brain volume). The human and the bonobo include a complex orbitofrontal cortex and a relatively smaller area 13. On the contrary the orangutan stands out by having a shorter orbitofrontal region and a more expanded area 13. Differences in the organization and size of individual cortical areas involved in emotional reactions and social behavior can be related to behavioral specializations of each hominoid and to the evolution of emotions in hominids.

Anatomy, Comparative↗

PubMed1998

Structural divisions and functional fields in the human cerebral cortex.

The question of what is a cortical area needs a thorough definition of borders both in the microstructural and the functional domains. Microstructural parcellation of the human cerebral cortex should be made on multiple criteria based on quantitative measurements of microstructural variables, such as neuron densities, neurotransmitter receptor densities, enzyme densities, etc. Because of the inter-individual variations of extent and topography of microstructurally defined areas, the final microstructurally defined areas appear as population maps. In the functional domain, columns, patches and blobs signifying synaptically active parts of the cortex appear as cortical functional fields. These fields are the largest functional entities of the cerebral cortex according to the cortical field hypothesis. In its strong version, the cortical field hypothesis postulates that all neurons and synapses within the fields perform a co-operative computation. A number of such fields together provide the functional contribution of the cerebral cortex. The functional parcellation of the human cerebral cortex must be based on field population maps, which after intersection analysis appear as functional domains. The major structural-functional hypothesis to be examined is whether these functional domains are equi-territorial to the microstructurally defined meta-maps. The cortical hypothesis predicts that, if two brain tasks make use of one or several identical or largely overlapping fields, they cannot be performed simultaneously without errors or increases in latency. Evidence for such interference is presented. This evidence represents a restriction in the parallel processing of the human brain. In the posterior part of the brain not only visual cortical areas may qualify for parallel processing, but also the somatosensory cortices appear to have separate functional streams for the detection of microgeometry and macrogeometry.

Brain Mapping↗

PubMed1998

Transient changes in the presence of nitric oxide synthases and nitrotyrosine immunoreactivity after focal cortical lesions.

Since ischemic insults lead to a deregulation of nitric oxide production which contributes to delayed neuronal death, we investigated changes in the distribution and amount of nitric oxide synthases I and II and in the appearance of nitrotyrosine caused by small, well-defined photothrombic lesions (2 mm in diameter) in the somatosensory cortex of rats. Four hours after lesioning, cell loss was evident in the core of the lesion and no nitric oxide synthase was present within this area, indicating that neurons expressing nitric oxide synthase I were lost or that nitric oxide synthase I was degraded. No increase in the number of neurons expressing nitric oxide synthase I was visible in the area surrounding the lesion, nor in other parts of the brain. One day after lesioning, NADPH-diaphorase- and nitric oxide synthase II-positive leucocytes had invaded the perilesional cortex and were accumulated in injured blood vessels. By two to three days post-lesion, layer V and VI pyramidal neurons, microglia, astrocytes and invading leucocytes had become strongly immunoreactive for nitric oxide synthase II within a perilesional rim. The number of cells expressing nitric oxide synthase I remained stable. Nitric oxide synthase II immunoreactivity and related NADPH-diaphorase had decreased by seven days post-lesion in most animals. However, the number of activated microglia or macrophages and astrocytes, as revealed by other markers, remained elevated. In addition, nitrotyrosine immunoreactivity was evident in the blood vessels close to the lesion, as well as in the ipsilateral hippocampus and thalamus. These findings indicate that no perilesional changes in the number of neurons expressing nitric oxide synthase I occur, but that a transient increase in nitric oxide synthase II does take place in the aftermath of small cortical lesions. The results suggest that increased nitric oxide production is limited to certain post-lesional intervals in this experimental model. It is also obvious that the vast majority of nitric oxide synthase-positive cells are nitric oxide synthase II-containing astrocytes three days after lesioning, suggesting that astrocyte-derived nitric oxide plays a significant role in delayed neuronal death. Such a condition points to an important aspect of post-lesional astrocytosis.

Animals↗

PubMed1998

Structural alterations and changes in cytoskeletal proteins and proteoglycans after focal cortical ischemia.

In order to study structural alterations which occur after a defined unilateral cortical infarct, the hindlimb region of the rat cortex was photochemically lesioned. The infarcts caused edema restricted to the perilesional cortex which affected allocortical and isocortical areas differently. Postlesional changes in cytoskeletal marker proteins such as microtubule-associated protein 2, non-phosphorylated (SMI32) and phosphorylated (SMI35, SMI31 and 200,000 mol. wt) neurofilaments and 146,000 mol. wt glycoprotein Py as well as changes in proteoglycans visualized with Wisteria floribunda lectin binding (WFA) were studied at various time points and related to glial scar formation. The results obtained by the combination of these markers revealed six distinct regions in which transient, epitope-specific changes occurred: the core, demarcation zone, rim, perilesional cortex, ipsilateral thalamus and contralateral homotopic cortical area. Within the core immunoreactivity for microtubule-associated protein 2 and SMI32 decreased and the cellular components showed structural disintegration 4 h post lesion, but partial recovery of somatodendritic staining was seen after 24 h. Microtubule-associated protein 2 and SMI32 persisted up to days 7 and 5 respectively in the core, whereas the number of glial fibrillary acidic protein- and WFA-positive cells decreased between days 7 and 14. The demarcation zone showed a dramatic loss of immunoreactivity for all epitopes 4 h post lesion which was not followed by a phase of recovery. In the inner region of the demarcation zone there was an invasion and accumulation of non-neuronal WFA-positive cells which formed a tight capsule around the core. Neuronal immunoreactivities for microtubule-associated protein 2, SMI31 and Py as well as astrocytic glial fibrillary acidic protein increased strongly within an approximately 0.4-1.0 mm-wide rim region directly bordering the demarcation zone. Py immunoreactivity increased significantly in the perilesional cortex, whereas glial fibrillary acidic protein-positive astrocytes became transiently more numerous in the entire lesioned hemisphere including strongly enhanced immunoreactivity in the thalamus by days 5-7 post lesion. Glial fibrillary acidic protein immunoreactivity increased in the corpus callosum and the homotopic cortical area of the unlesioned hemisphere by days 5-7. In this homotopic area additional changes in SMI31 immunoreactivity occurred. Our results showed that a cortical infarct is not only a locally restricted lesion, but leads to a variety of cytoskeletal and other structural changes in widely-distributed functionally-related areas of the brain.

Animals↗

PubMed1998

Modular distribution of vasoactive intestinal polypeptide in the rat barrel cortex: changes induced by neonatal removal of vibrissae.

The distribution of vasoactive intestinal polypeptide-immunoreactive neuronal structures in the barrel cortex (posteromedial barrel subfield) of adult rats was analysed after unilateral removal of the vibrissal follicles of row C in neonatal rats. The hypothesis was tested whether the distribution of vasoactive intestinal polypeptide-immunoreactive structures depends on the normal anatomical organization of the specific sensory input. After three months survival the distribution of the vasoactive intestinal polypeptide-immunoreactive structures was morphometrically evaluated. This approach revealed alterations in the contralateral posteromedial barrel subfield, where the disappearance of barrel row C and a substantial increase in size mainly of barrel row D, but also of other rows could be detected. Increase in row D included both barrels and the interspace (septal segments between barrels in one row). As vasoactive intestinal polypeptide immunoreactivity of the barrel field was found previously to be localized in synaptic boutons involved in symmetric synapses, our present findings suggest that (i) the interspace is enriched in inhibitory vasoactive intestinal polypeptide-immunoreactive synapses as opposed to the excitatory thalamocortical input reaching the barrel hollow, (ii) the spatial distribution of the vasoactive intestinal polypeptide system in the barrel cortex is closely associated with the neuronal organization of the sensory input and reacts with a considerable plasticity to lesion-induced changes of the input, and (iii) the compensatory barrel hypertrophy in a row neighbouring the deafferented row involves an increasing number of vasoactive intestinal polypeptide-immunoreactive synapses per barrel.

Afferent Pathways↗

PubMed1998

Long-term cellular dysfunction after focal cerebral ischemia: in vitro analyses.

The long-term (< or = six months) functional consequences of permanent middle cerebral artery occlusion were studied with in vitro extra- and intracellular recording techniques in adult mouse neocortical slices. After survival times of one to three days, 28 days and six months, intracellular recordings from layers II/III pyramidal cells in the vicinity of the infarct did not reveal any statistically significant changes in the intrinsic membrane properties when compared to age-matched control animals. However, a pronounced hyperexcitability could be observed upon orthodromic synaptic stimulation in neocortical slices obtained from mice 28 days after induction of ischemia. Low-intensity electrical stimulation of the afferents elicited particularly in this group epileptiform extracellular field potential responses and intracellular excitatory postsynaptic potentials, that were longer in duration as compared to the controls. When the N-methyl-D-aspartate receptor-mediated excitatory postsynaptic potential was pharmacologically isolated in a bathing solution containing 0.1 mM Mg2+ and 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione, the synaptic responses were longer and larger in the ischemic cortex as compared to the controls. Higher stimulus intensities evoked in normal medium a biphasic inhibitory postsynaptic potential, that contained in the 28 days post-ischemia group a prominent amino-phosphonovaleric acid-sensitive component, indicating a strong concurrent activation of a N-methyl-D-aspartate receptor-mediated excitatory postsynaptic potential. This pronounced co-activation could only be observed in the 28 days ischemic group, and neither after one to three days or six months post-ischemia nor in the controls. The quantitative analysis of the efficiency of stimulus- evoked inhibitory postsynaptic potentials recorded in amino-phosphono-valeric acid revealed a reduction of GABA-mediated inhibition in ischemic cortex. Although this reduction in intracortical inhibition may already contribute to an augmentation of N-methyl-D-aspartate receptor-mediated excitation, our results do also indicate that the function of N-methyl-D-aspartate receptors is transiently enhanced in the ischemic cortex. This transient hyperexcitability does not only cause cellular dysfunction in the vicinity of the infarct, but may also contribute to neuronal damage due to excitotoxicity.

Animals↗

PubMed1998

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.

Animals↗

PubMed1998

Analysing functional connectivity in brain slices by a combination of infrared video microscopy, flash photolysis of caged compounds and scanning methods.

We evaluate a novel set-up for scanning functional connectivity in brain slices from the somatosensory cortex of the rat. Upright infrared video microscopy for targeted placement of electrodes is combined with rapid photolysis of bath-applied caged neurotransmitter induced by a xenon flash lamp. Flash photolysis of caged glutamate and electrical stimulation produce comparable field potential responses and demonstrate that the viability of the submerged slices exceeds several hours. Glutamate release leads to field potential responses whose two phases are differentially affected by selective blockade of N-methyl-D-aspartate- and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate-type glutamate receptors with DL-2-amino-5-phosphonovaleric acid and 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulphonamide, respectively. Rapid computer-controlled scanning of hundreds of distinct stimulation sites with simultaneous recordings at a fixed reference site allows construction of functional input maps from peak amplitudes and delays to peak of field potential responses. Selective laminar expansion of the functional input maps after bicuculline application demonstrates that the combination of this conveniently assembled set-up with pharmacological and physical manipulations can provide insights into the determinants of functional connectivity in brain slices.

2-Amino-5-phosphonovalerate↗

PubMed1998

Immunohistochemical evidence for dysregulation of the GABAergic system ipsilateral to photochemically induced cortical infarcts in rats.

Deficits of GABAergic transmission have been reported to occur in tissue surrounding ischemic cortical lesions between a few days and several weeks after the insult. In the present experiments, we used immunohistochemistry with antibodies against parvalbumin and two major subunits of the GABA(A) receptor (alpha1, alpha2) to characterize the events that underlie these changes at different levels of circuit organization. Neocortical infarcts (2 mm diameter) consistently affecting medial parts of the primary somatosensory cortex were induced photochemically in adult male Wistar rats; animals were allowed to recover for one week before perfusion-fixation. When compared to controls the pattern of immunoreactivity had changed for the al subunit of the GABA(A) receptor seven days after the insult. Ipsilateral to the ischemic lesions, we found a decrease in staining intensity reaching up to 4 mm laterally, resulting in a partial or complete absence of the normal laminar staining pattern. No consistent changes were observed for the alpha2 subunit. Parvalbumin staining revealed pathological alterations in a rim of tissue surrounding the infarct, measuring up to 1 mm from the border of the infarcts. Parvalbumin-positive interneurons in this region showed signs of degeneration; both a reduction of the number of dendrites and, to a lesser extent and only immediately adjacent to the ischemic lesions, a reduction of the number of parvalbumin-positive neurons was readily apparent. The results provide evidence for both a differential regulation of two GABA(A) receptor subunits and degenerative changes of parvalbumin-containing interneurons ipsilateral to cortical infarcts. The relevance of these findings for mechanisms underlying long-term recovery, transient functional deficits and postinfarct seizures warrants further investigation.

Animals↗