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At least 1,117 records · Page 62Linked to original sources
PubMed1995

Persistence of early-generated neurons in the rodent subplate: assessment of cell death in neocortex during the early postnatal period.

In the rat, the deepest neocortical layer forms a conspicuous cell band known as layer Vlb. Cells in layer Vlb are among the first to differentiate, and it has been regarded as an homolog to the subplate of primates and carnivores. Cell death has been considered a universal feature of subplate cells. In order to assess the validity of this assertion, we examined the sequence of generation and the extent of cell death in layer Vlb. This was achieved using injections of 3H-thymidine and two methods for the direct visualization of apoptotic figures. Single injections of 3H-thymidine were performed between E12 and E15 (E0 is the day of insemination), and brains were examined at different postnatal ages between P1 and P63. The number of heavily labeled cells were counted in layer Vlb in six standard, equally spaced coronal sections in each brain. Single injections at E12 labels about 3% of the entire population of layer Vlb cells, 17% at E13, 30% at E14, and < 1% at E15. Our results indicate that the absolute number of heavily labeled cells in layer Vlb remains constant. The analysis of variance (one-way ANOVA) showed that the difference among the group means was not significant from P1 to P63 after injections at either E12, E13, or E14. In order to confirm these results, we evaluated the distribution of pyknotic (apoptotic) cell bodies in the neocortex. Apoptotic cells were visualized in Nissl preparations and by histochemical staining using an in situ apoptosis detection kit. The analysis was performed in rats from E18 to P15. Both methods gave comparable results. We found that the amount of cell death in layer Vlb is neither particularly prominent nor significantly different from that which occurs in the remaining neocortical layers, apart from layer II and in the white matter of the corpus callosum. We conclude that neuronal death does not play any significant role in the rodent subplate.

Aging↗
PubMed1995

Different forms of synaptic plasticity in somatosensory and motor areas of the neocortex.

We have studied vertical synaptic pathways in two cytoarchitectonically distinct areas of rat neocortex--the granular primary somatosensory (SI) area and the agranular primary motor (MI) area--and tested their propensity to generate long-term potentiation (LTP), long-term depression (LTD), and related forms of synaptic plasticity. Extracellular and intracellular responses were recorded in layer II/III of slices in vitro while stimulating in middle cortical layers (in or around layer IV). Under control conditions, 5 Hz theta-burst stimulation produced LTP in the granular area, but not in the agranular area. Agranular cortex did generate short-term potentiation that decayed within 20 min. Varying the inter-burst frequency from 2 Hz to 10 Hz reliably yielded LTP of 21-34% above control levels in granular cortex, but no lasting changes were induced in agranular cortex. However, the agranular cortex was capable of generating LTP if a GABAA receptor antagonist was applied locally at the recording site during the induction phase. In contrast to LTP, an identical form of homosynaptic LTD could be induced in both granular and agranular areas by applying low frequency stimulation (1 Hz for 15 min) to the middle layers. Under control conditions, both LTP and LTD were synapse-specific; theta-burst or low-frequency stimulation in the vertical pathway did not induce changes in responses to stimulation of a layer II/III horizontal pathway. Application of the NMDA receptor antagonist D-2-amino-5-phosphonovaleric acid (AP5) blocked the induction of both LTP and LTD in granular and agranular cortex. In the presence of AP5, low-frequency conditioning stimuli yielded a short-term depression in both areas that decayed within 10-15 min. Nifedipine, which blocks L-type, voltage-sensitive calcium channels, slightly depressed the magnitudes of LTP and LTD but did not abolish them. Synaptic responses evoked during theta-burst stimulation were strikingly different in granular and agranular areas. Responses in granular cortex were progressively facilitated during each sequence of 10 theta-bursts, and from sequence-to-sequence; in contrast, responses in agranular cortex were stable during an entire theta-burst tetanus. The results suggest that vertical pathways in primary somatosensory cortex and primary motor cortex express several forms of synaptic plasticity. They were equally capable of generating LTD, but the pathways in somatosensory cortex much more reliably generated LTP, unless inhibition was reduced. LTP may be more easily produced in sensory cortex because of the pronounced synaptic facilitation that occurs there during repetitive stimulation of the induction phase.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Distribution of NADPH-diaphorase-positive neurons in the opossum neocortex.

The distribution of NADPH-diaphorase reactive cells were evaluated both in horizontal sections of a flattened cortex and in transversal sections of the opossum (Didelphis marsupialis) neocortex. The tangential distribution of labeled cells behind the orbitalis fissure was denser in the rostral vs caudal regions and in the lateral vs medial regions. Transversal sections revealed that most of the positive neurons are in the grey matter, although 1/4 of this population is located in the underlying white matter. This pattern of neuronal distribution is similar to that previously described in rodents, but quite different from that observed in higher mammals such as the cat and primates.

Animals↗
PubMed1995

Localization of superoxide dismutases in Alzheimer's disease and Down's syndrome neocortex and hippocampus.

Abnormalities in the cellular regulation and expression of antioxidant enzymes may have a role in mechanisms of central nervous system aging and neurodegeneration. We therefore examined, using isozyme-specific antibodies and immunohistochemistry, the localization of copper, zinc-superoxide dismutase and manganese-superoxide dismutase in the frontal and temporal neocortices and hippocampi of aged controls and individuals with Alzheimer's disease or Down's syndrome. Two different antibodies to copper, zinc-superoxide dismutase and one antibody to manganese-superoxide dismutase were evaluated by immunoblotting of homogenates of human brain before use in immunohistochemistry. The copper, zinc-superoxide dismutase antibodies recognized a single band of proteins at 16 kd. The manganese-superoxide dismutase antibody detected a single band of proteins at 25 kd. Immunohistochemically, copper, zinc-superoxide dismutase and manganese-superoxide dismutase immunoreactivities were localized predominantly to neocortical and hippocampal pyramidal neurons and scarcely seen in glial cells in controls. In Alzheimer's disease and Down's syndrome, the distributions and intensities of these two forms of superoxide dismutase immunoreactivities were different as compared with controls. Copper, zinc-superoxide dismutase was enriched in pyramidal neurons undergoing degeneration, whereas manganese-superoxide dismutase was more enriched in reactive astrocytes than in neurons. In senile plaques, copper, zinc-superoxide dismutase-positive globular structures were surrounded by astrocytes highly enriched in manganese-superoxide dismutase. By double label immunohistochemistry, some pyramidal neurons coexpressed superoxide dismutases and tau, and a few copper, zinc-superoxide dismutase-positive structures in senile plaques colocalized with tau. Amyloid cores, diffuse plaques, and microglia scarcely showed colocalization with superoxide dismutase-positive structures. The observed changes in the cellular localization of superoxide dismutases in neocortex and hippocampus in cases of Alzheimer's disease and Down's syndrome support a role for oxidative injury in neuronal degeneration and senile plaque formation. The differential localization of copper, zinc-superoxide dismutase and manganese-superoxide dismutase in cerebral sites of degeneration suggests that cellular responses to oxidative stress is antioxidant enzyme specific and cell type specific and that these two forms of superoxide dismutase may have different functions in antioxidant mechanisms.

Adult↗
PubMed1993

Brn-5 is a divergent POU domain factor highly expressed in layer IV of the neocortex.

We have identified rat cDNA clones that encode a POU domain protein, referred to as brain-5 (Brn-5). During embryogenesis in the rat, Brn-5 is widely expressed with highest levels in the developing brain and spinal cord from embryonic day 12.5. In the adult, Brn-5 mRNA is most abundant in the brain, where it is diffusely expressed with the exception of an enrichment in layer IV of the neocortex. However, Brn-5 is also found in multiple adult tissues outside the central nervous system, including kidney, lung, heart, adrenal, skin, testis, and anterior pituitary. This expression pattern contrasts with that of most other POU domain genes that are expressed predominantly in the developing nervous system and are progressively restricted to discrete regions of the brain. The predicted amino acid sequence of Brn-5 is considerably divergent from previously described POU domains and thus defines a new POU domain subclass (class VI). Consistent with its divergent sequence, the DNA-binding characteristics of Brn-5 overlap with, but are clearly distinct from, that of Oct-2. Although Brn-5 can bind to non-octamer sites, a random site selection indicates that its preferred binding site contains a variant octamer core motif. Finally, we show that the amino terminus of Brn-5 contains a transactivation domain.

Amino Acid Sequence↗
PubMed1994

Presynaptic depression of synaptic transmission mediated by activation of metabotropic glutamate receptors in rat neocortex.

Conventional intracellular recordings were obtained from layer II-III neurons in adult rat neocortical brain slices. Excitatory and inhibitory (I) postsynaptic potentials (PSPs) were evoked prior to and during bath application of agonists and antagonists of metabotropic glutamate receptors (mGluRs). In the presence of the selective mGluR agonist 1S,3R-1-aminocyclopentane-1,3- dicarboxylic acid (1S,3R-ACPD; 5-200 microM), both excitatory and inhibitory components of the evoked PSPs were reversibly reduced. PSPs were significantly, but less effectively, decreased by L-2-amino-4-phosphonobutyric acid. Exposure to putative mGluR antagonists, alpha-methyl-4-carboxyphenylglycine or L-2-amino-3-phosphonopropionic acid, did not inhibit the 1S,3R-ACPD-mediated effect. In the presence of 6,7-dinitroquinoxaline-2,3-dione and D-2-amino-5-phosphonovaleric acid, 1S,3R-ACPD reversibly depressed directly evoked neocortical IPSPs; however, quisqualic acid (1-10 microM) did not mimic this effect. Analysis of spontaneous PSPs and paired-pulse facilitation indicated a presynaptic locus of action for 1S,3R-ACPD at mGluRs. These findings indicate that a specific mGluR subtype(s) may modulate both excitatory and inhibitory synaptic transmission in the adult rat neocortex via a presynaptic reduction of transmitter release.

Aminobutyrates↗
PubMed1975

[Problem of homologization of the cerebral neocortex in cetaceans].

Homologization of the cerebeal neocortex of the cetaceans was performed by comparison of macro- and micro-signs of the structural organization of the cerebral cortex of cetaceanson the one hand and comparison with the same data on the cerebral cortex of ungulates, carnivores and primates. The degree of homology of main fissures and convolutions of the brain of the cetaceans was shown to differ very markedly from the brain of carnivores and priimates. Besides, the complex of macroscopic and cytoarchitectonic characteristics as compared with earlier data on the structural organization of the new cortex of the dolphin (1969,1970) permitted identification of a new type of the cortex which is characteristic only of cetaceans andnot of the ground mammals.

Anatomy, Comparative↗
PubMed1993

Evolution of multiple areas and modules within neocortex.

There is compelling evidence that the number of cortical areas is variable across species, ranging from the order of 10 to 20 in species with little neocortex to perhaps a hundred or more in humans. The first mammals had few areas, and more fields evolved in several lines of descent. There are several general possibilities for how new cortical areas emerged in evolution, including the gradual differentiation of one area from another, the addition of new cortical tissue that became invaded by axons from other structures to create new fields, and the sudden duplication of existing areas as a result of mutation. A specific version of a "gradual differentiation" theory is presented. New areas might emerge as a result of a process in which classes of inputs to an area first segregate into modular groups of neurons, and then these modules coalesce to ultimately form totally separate populations. All stages allow expected functions to be mediated, and there might be different functional advantages for each stage. Thus, stages may be stable and change is not inevitable. As a result, all stages are represented in the organizations of existing fields of extant mammals.

Animals↗
PubMed1993

The astrocytic localization of protein kinase C in the neocortex, hippocampus and in vitro hippocampal slices of the guinea pig.

Immunohistochemical studies prove the most of the neurons of the central nervous system express one or more protein kinase C isoenzymes. However, there are only a few descriptions of the glial localization. In the present study, we detected protein kinase C immunohistochemically in guinea pig sensory neocortex, hippocampus and hippocampal slices following in vitro maintenance. Monoclonal antibodies against types II and III of protein kinase C were used. Consecutive sections were stained with polyclonal anti-glial-fibrillary-acidic protein serum. Scattered astrocytes contained protein kinase C in layers I and VI of the cerebral cortex, in the subcortical white matter, the subiculum, alveus and molecular layer of Ammon's horn, in the hilus and molecular layer of the dentate fascia. Ultrastructurally, immunostaining of glial processes in the neuropil and around blood vessels was observed. Strong staining of the endoplasmic reticulum and nuclear envelope was noted in glial cell bodies. The ultrastructural localization of protein kinase C suggests its participation in receptor-mediated processes, which may influence the shape and function of astrocytes.

Animals↗
PubMed1977

[Responses of neurons of the medial group of thalamic nuclei to stimulation of the fronto-basal portions of the neocortex].

Neuronal and focal responses of medial thalamic nuclei (mediodorsal, central lateral, parecentral, centrum medianum, parafascicular) to stimulation of frontobasal cerebral cortex (proreal, posterior orbital, basal temporal regions) were studied in acute experiments on cats narcotized by nembutal mixed with chloralose. Proceeding from the data on the number of neurons responding to cortical stimulation and on the duration of the response latent period, three functionally heterogeneous sections of medial nuclei were distinguished: the microcellular and magnocellular regions of the mediodorsal nucleus, and the intralaminar nuclei with the parafascicular complex. Neurons were recorded which could be activated antidromically during stimulation of another region. On this basis a suggestion is made on the integrating function of medial nuclei providing unification of the frontobasal regions of the neocortex.

Animals↗
PubMedDate not supplied

[The laminar distribution of the neuronal sources of afferent fibers to the neocortex in the caudal regions of the limbic cortex in rats and cats].

Laminar distribution of neurones in the caudal limbic cortex, which form projections to the neocortex, has been studied by axonal transport of HRP. It was shown that the associative parietal cortex (field 7) receives the greatest part of limbic afferents from neurones of layer V. It is suggested that field 7 is included in the limbic efferent system together with subcortical structures of the brain. Projections of the limbic cortex to the field 7 originate partly from associative neurones of layer III which are more numerous in cats than in rats.

Afferent Pathways↗
PubMed1996

Frequency and dendritic distribution of autapses established by layer 5 pyramidal neurons in the developing rat neocortex: comparison with synaptic innervation of adjacent neurons of the same class.

Synaptic contacts formed by the axon of a neuron on its own dendrites are known as autapses. Autaptic contacts occur frequently in cultured neurons and have been considered to be aberrant structures. We examined the regular occurrence, dendritic distribution, and fine structure of autapses established on layer 5 pyramidal neurons in the developing rat neocortex. Whole-cell recordings were made from single neurons and synaptically coupled pairs of pyramidal cells, which were filled with biocytin, morphologically reconstructed, and quantitatively analyzed. Autapses were found in most neurons (in 80% of all cells analyzed; n = 41). On average, 2.3 +/- 0.9 autapses per neuron were found, located primarily on basal dendrites (64%; 50-70 microns from the soma), to a lesser extent on apical oblique dendrites (31%; 130-200 microns from the soma), and rarely on the main apical dendrite (5% 480-540 microns from the soma). About three times more synaptic than autaptic contacts (ratio 2.4:1) were formed by a single adjacent synaptically coupled neuron of the same type. The dendritic locations of these synapses were remarkably similar to those of autapses. Electron microscopic examination of serial ultrathin sections confirmed the formation of autapses and synapses, respectively, and showed that both types of contacts were located either on dendritic spines or shafts. The similarities between autapses and synapses suggest that autaptic and synaptic circuits are governed by some common principles of synapse formation.

Animals↗
PubMedDate not supplied

[The development of transplants of human embryonic neocortex in the anterior chamber of the rat eye].

Dorsolateral regions of embryonic human neocortex at 9-11 weeks of development were transplanted into the eye anterior chamber of rat. Significant changes, leading to the complete destruction of the original cytoarchitectonies occured during the first three days. Intensive neuroblast degeneration in cortical and interstitial zones as well as decrease of mitotically deviding cell numder were observed 3-6 hours after the transplantation. Neuroepithelial cells form rosettes in ventricular zone by the end of the first day. Rosettes turned into the centres of proliferation, mitotic activity restored to the initial level. Cells migrated out of the rosettes in radial directions. By the end of the third day almost all the cells in cortical and interstitial zones degenerated, transplant was almost completely represented by the ventricular zone cells. Number of mitotic figures exceeded the initial level almost three times, transplant was enlarged, its blood supply was absent. Since the 4-th day mitotic activity decreased, transplant underwent lymphoid infiltration and its complete destruction occured by the end of the second week.

Animals↗
PubMed1996

Properties of convergent thalamocortical and intracortical synaptic potentials in single neurons of neocortex.

We explored differences in the properties of convergent afferent inputs to single neurons in the barrel area of the neocortex. Thalamocortical slices were prepared from mature mice. Recordings were made from neurons in layer V, and either thalamocortical afferents or horizontal intracortical axons were stimulated. Monosynaptic EPSPs from both sources had latencies shorter than 1.8 msec and low shape variance. Disynaptic thalamocortical IPSPs had latencies longer than 1.8 msec. All neuronal types, as defined by intrinsic firing patterns, received both thalamocortical and intracortical monosynaptic input. The shape parameters (rate of rise and half-width) of monosynaptic EPSPs from the two inputs did not differ significantly. The rate of rise of EPSPs varied considerably across cells, but the rates of rise of thalamocortical and intracortical EPSPs onto single cells were strongly correlated. The relative thresholds for activation of synaptic excitation and inhibition were strikingly different between the two tracts: thalamocortical stimulation induced GABAA-dependent IPSPs at stimulus intensities equal to or less than those required for evoking EPSPs in 35% (24 of 68) of the cells. In contrast, the threshold response to intracortical stimulation was always an EPSP, and only stronger stimuli could generate di- or polysynaptic IPSPs. We suggest that postsynaptic factors may tend to equalize the waveforms of EPSPs from thalamocortical and intracortical synapses onto single neurons. A major difference between the two convergent tracts is that the thalamocortical pathway much more effectively activates feedforward inhibitory circuits than does the horizontal intracortical pathway.

Animals↗
PubMed1996

[Rosette formation in explants of human embryonic neocortex (an electron-microscopic study)].

Multiple invaginations and closed cavities (rosettes) were developed in 199 fragments of wall of human anterior cerebral vesicle. Contraction of neuroepithelial cells apexes after the principle of the gathered tobacco pouch was involved into the process. This confirms the previous suggestion of the authors on the similarity between the mechanisms of rosettes forming and neurulation. The participation of radial glia cells and neuroblasts in the reorganization of the neocortex germ was also studied.

Cells, Cultured↗
PubMed1997

Synchrony of clonal cell proliferation and contiguity of clonally related cells: production of mosaicism in the ventricular zone of developing mouse neocortex.

We have analyzed clonal cell proliferation in the ventricular zone (VZ) of the early developing mouse neocortex with a replication-incompetent retrovirus encoding human placental alkaline phosphatase (AP). The retrovirus was injected into the lateral ventricles on embryonic day 11 (E11), i.e., at the onset of neuronogenesis. Three days postinjection, on E14, a total of 259 AP-labeled clones of various sizes were found in 7 fetal brains. There are approximately 7 cell cycles between E11 and E14 (), and there is a 1-2 cell cycle delay between retroviral injection and the production of a retrovirally labeled "founder" cell; thus, we estimate that the "age" of the clones was about 5-6 cell cycles. Almost one-half of the clones (48.3%) identified were pure proliferating clones containing cells only in the VZ. Another 18.5% contained both proliferating and postproliferative cells, and 33.2% contained only postproliferative cells. It was striking that over 90% of the clonally related proliferating cells occurred in clusters of two or more apparently contiguous cells, and about 73% of the proliferating cells occurred in clusters of three or more cells. Regardless of the number of cells in the clone, these clusters were tightly packed and confined to a single level of the VZ. This clustering of proliferating cells indicates that clonally related cells maintain neighbor-neighbor relationships as they undergo interkinetic nuclear migration and progress through several cell cycles, and, as a result, the ventricular zone is a mosaic of small clusters of clonally related and synchronously cycling cells. In addition, cells in the intermediate zone and the cortical plate were also frequently clustered, indicating that they became postproliferative at a similar time and that the output of the VZ is influenced by its mosaic structure.

Animals↗
PubMed1996

[Vascularization of the human embryonic neocortex in the rat anterior chamber under cyclosporine A immunosuppression].

Fragments of 9 weeks hyman embryo neocortex were grafted into the rat eye anterior chamber. To prevent rejection cyclosporin A was introduced to the animals. Vascular network forming in transplants was studied for 5 weeks 3 days endothelial buds from the iris vessels appeared in transplants. After 10 days capillaries with erythrocytes appeared in the graft on the border with iris. 3 weeks later vascular network achieved its maximal development, occupying almost the entire graft thickness. The vessels developed diverged from the norm: they had variceal widenings, and focal distribution with significant non-vascular gaps.

Animals↗
PubMed1997

Synaptic connections of calretinin-immunoreactive neurons in the human neocortex.

Previous immunocytochemical studies in the cerebral cortex of various species have shown that the calcium-binding protein calretinin (CR) labels specific subpopulations of nonspiny nonpyramidal cells (interneurons). The present study attempts to characterize morphologically and chemically the microcircuitry of CR-immunoreactive (CR-ir) neurons in the human temporal neocortex. Postembedding immunocytochemistry for CR and GABA and combination immunocytochemistry for CR and nonphosphorylated neurofilament protein (NPNFP) or for CR and the calcium-binding proteins parvalbumin (PV) and calbindin (CB) showed CR multiterminal endings frequently innervating the distal apical dendrite or the cell body and proximal dendrites of NPNFP-ir or CB-ir pyramidal cells, respectively. Cell bodies of interneurons immunoreactive for CB or PV were innervated only occasionally by CR multiterminal endings, whereas certain GABA neurons were surrounded by them. Furthermore, CR-ir axon terminals formed either symmetrical (the majority) or asymmetrical synapses with a variety of postsynaptic elements. These results indicate that different subpopulations of CR interneurons exist that are specialized for selective innervation of somatic or dendritic regions of certain pyramidal and nonpyramidal neurons.

Adult↗