Comparative aspects of structural organization of astrocytes of the layer i of the human and rat brain cortex

Importance of study of astrocytes for fundamental biology and medicine is due to their key role in formation of the brain barrier system. On taking into consideration the controversial data on structure of the mammalian neocortex superficial layers, of great actuality are the comparative studies of the structural and cytochemical organization of astrocytes in human and in the laboratory animals used in the experimental studies connected with modeling of brain diseases and traumas. The goal of the present work was to study structural organization of astrocytes in the human and rat neocortical layer I. The work was carried out on the autopsy and experimental material from Wistar rats. Astrocytes were revealed immunocytochemically by using antibodies to GFAP, vimentin and nestin. The preparations were examined with aid of light and confocal laser microscopy. No significant difference in the sizes of perinuclear areas were established between the rat and human astrocytes. In the majority of cortex regions, the spectrum of intermediate filaments-forming proteins in these cells was identical. However, there were essential differences revealed in organization of the superficial glial limiting membrane (SGLM). The human SGLM is formed by interlacing of thin processes in the layer I processes, whereas the rat SGLM is represented by specialized astrocytes spread along the cortical surface and connected with the wide-blade processes. The human layer I astrocytes have translaminar processes passing via several cortical layers, whereas in rats such processes are located within the limits of one layer. The revealed differences in the astrocyte structural organization should be taken into account when interpreting results of experimental studies carried out on rats and extrapolating these results to human.     

Mapping the structural core of human cerebral cortex

Structurally segregated and functionally specialized regions of the human cerebral cortex are interconnected by a dense network of cortico-cortical axonal pathways. By using diffusion spectrum imaging, we noninvasively mapped these pathways within and across cortical hemispheres in individual human participants. An analysis of the resulting large-scale structural brain networks reveals a structural core within posterior medial and parietal cerebral cortex, as well as several distinct temporal and frontal modules. Brain regions within the structural core share high degree, strength, and betweenness centrality, and they constitute connector hubs that link all major structural modules. The structural core contains brain regions that form the posterior components of the human default network. Looking both within and outside of core regions, we observed a substantial correspondence between structural connectivity and resting-state functional connectivity measured in the same participants. The spatial and topological centrality of the core within cortex suggests an important role in functional integration.     

Immunocytochemical studies of astrocytes following injury to the cerebral cortex of the rat

The morphological change of cerebral cortex astrocytes from protoplasmic to glial fibrillary acidic protein (GFAP)-containing cells is induced by injury. Protoplasmic astrocytes that contain no detectable amount of GFAP become filled with GFAP and their processes extend to form the glial scar around the wound. It is hypothesized that this transformation is induced by cAMP and neurotransmitters released from damaged neuronal cells. A similar mechanism may be present in other brain regions following injury or disease.     

Tangential organization of the infragranular fiber plexus in rat cerebral cortex

Cylindrical lesions (diameter 300-500 microns) were formed by poking needles into various parts of the cerebral cortex of adult albino rats. Degenerating axons were visualized in horizontal sections through the 'flattened' cortex using the silver impregnation method of Gallyas et al. [Stain Technol. 55: 291-297 (1980)] which stains degenerating axoplasm. The density and distribution of tangentially oriented axons were evaluated in the infragranular layers by TV image analysis. The sampling fields were concentrically arranged around the lesion at distances of 200, 400, 700 and 1,100 microns. The results indicate that the distribution patterns of degenerating (associational) axons covary with the cytoarchitectonic regions into which the lesions were placed. In the motor cortex, the majority of axons run in the antero-posterior direction. The density is generally lower around lesions in frontal regions than in parietal regions. The most extended degeneration was found around lesions near the border of or within the retrosplenial cortex, indicating an exceptionally strong internal connectivity in this area. Since only few degenerating axons were seen around lesions in the center of area 17, the high density of myelinated axons in the primary visual cortex seems to be due to fibers that originate in peristrate areas. It is concluded that the number and extension of fibers that degenerate tends to covary with some aspects of cortical architecture, but it is not area-specific.     

An immunohistochemical and morphometric study on astrocytes and microvas culature in the human cerebral cortex

In this study, astrocytes and microvessels of the human cerebral cortex were analysed morphometrically with the aim of acquiring quantitative information on the glio-vascular relationships, considered to be of great importance in the formation and functioning of the blood--brain barrier. Immunohistochemistry for the astrocytic marker, glial fibrillary acidic protein, was used with a computerized image analysis system. The brain tissue was embedded using the progressive lowering of temperature method, and the image analyser was applied to semithin sections subjected to immunogold--silver staining and viewed by epipolarization microscopy. The results show that, in the human cerebral cortex, astrocytes cover 11.4% of the cortex area and that their perivascular processes are nearly as extensive as the vascular bed (0.8% versus 1.72% of the cortex area). These processes form a virtually continuous sheath around the vascular walls, only 11% of the vessel perimeter lacking this astrocytic glia covering. The present results, compared with previous unpublished data obtained by conventional immunocytochemical procedures on wax sections, indicate that low-temperature methods combined with gold--silver immunolabelling on semithin sections significantly improve the detection of immunoreactivity and the performance of the image analyser. This revised version was published online in November 2006 with corrections to the Cover Date.     

Functional expression of metabotropic GABAB receptors in primary cultures of astrocytes from rat cerebral cortex

GABA(B) receptor subunits are widely expressed on neurons throughout the central nervous system (CNS), at both pre- and postsynaptic sites, where they mediate the late and slow component of the inhibitory response to the major inhibitory neurotransmitter GABA. Recently, GABA(B) receptors have been reported to be expressed in astrocytes and microglia in the rat CNS by immunocytochemistry. However, there are few reports available for the functional characterization of GABA(B) receptors on astrocytes. In the present study, we therefore investigated the functional expression and characteristics of GABA(B) receptors in primary cultures of astrocytes from rat cerebral cortex. In the presence of 10 microM GTP, forskolin concentration-dependently increased adenylylcyclase (AC) activity in membranes prepared from rat astrocytes. The selective GABA(B) agonist (R)-baclofen concentration-dependently reduced forskolin-stimulated AC activity in the presence of 10 microM GTP. This effect was reversed by the selective GABA(B) antagonists, CGP-55845 and CGP-54626, and was completely abolished by treatment of astrocytic membranes with pertussis toxin. In addition, RT-PCR, Western blotting, and immunocytochemistry clearly showed that metabotropic GABA(B) receptor isoforms (GABA(B)R1 and GABA(B)R2) are expressed in rat cerebrocortical astrocytes. Taken collectively, these results demonstrate that functionally active metabotropic GABA(B) receptors are expressed in rat cerebrocortical astrocytes.     

Area and layer patterning in the developing cerebral cortex

Two anatomical patterns characterize the neocortex, and both are essential for normal cortical function. First, neocortex is divided into anatomically distinct and functionally specialized areas that form a species-specific map. Second, neocortex is composed of layers that organize cortical connectivity. Recent studies of layer and area development have used time-lapse microscopy to follow cortical cell division and migration, gene arrays to find layer- or area- specific regulatory genes, time- and region- specific manipulations of candidate genes, and optical imaging to compare area maps in wild type with genetically altered mice. New observations clarify the molecular and cellular mechanisms that generate each pattern, and stress the links between layer and area formation.     

Some aspects of the structural organization of the arthropod ganglia

Summary This paper deals with the fine structure of the abdominal ganglia of several species of arthropods belonging to the classes Arachnida, Crustacea, Myriapoda and Insecta. The tissues were fixed in osmium tetroxide and embedded in n-butyl methacrylate or fixed in potasium permanganate and embedded in a mixture of X 133/2097 and Araldite.A comparative study was made in order to discriminate between those structural characteristics of the nervous system appearing only in determined taxonomic groups and those belonging to a fundamental plan common to the whole Phylum. This work covers the morphology of neurons, glial cells, neuropilic nerve fibers and neuronal connections.Most arthropod neurons are pear-shaped with only one prolongation and the nucleus is located in the center of the soma, enveloped by two membranes showing numerous pores. Cisternae of the ER have frequently been observed in continuity with this nuclear envelope. After osmic fixation the nuclear content appears to consist of small dense granules distributed at random in the nucleoplasm. In addition to these small perticles there are, in some species, large chromatin blocks. The use of Permanganate as fixative introduces important changes in the nuclear aspect; most of the nuclei look washed and the nuclear content acquires an homogeneous appearance.The cytoplasm of the neurons contains a complex system of internal membranes consisting of cisternae and tubuli of the ER system, lamellae of the Golgi complex and invaginations of the plasma membrane. In most species the elements of the ER system are distributed at random in the cytoplasm but in the neurons of Bothriurus bonariensis there are parallel aggregations of membranes similar to the Nissl bodies found in vertebrates.It was found in some of the species studied (Armadillidium vulgare and Lithobius Sp.) that the internal membrane system of the nerve cells is mainly represented by Golgi elements while the ER system seems to be poorly developed.Besides the membranous components, the neuronal cytoplasm contains mitochondria, multivesicular bodies and dense granules of neurosecretory material.Neuroglial cells are mainly characterized by their nuclear structure. After the action of osmium tetroxide, glial nuclei show irregular masses of chromatin inmersed in a nucleoplasm of low electron density. In permanganate fixed material these chromatin blocks appear as blank spaces.In the cytoplasm of these cells there are mitochondria, membranes pertaining to the ER system and elements of the Golgi complex but in some of the species studied gliofibrils and granules of pigment were found.Three main types of neuroglial cells have been recognized in an arthropod ganglia. These are: subcapsular glial cells, neuron satellites and nerve fiber satellites.The neuropile occupies the central region of the ganglion and consists of a great number of nerve fibers intermingled with glial processes. The neuropilic n. fibers consistently show profiles of ER membranes and tubuli pertaining to the ER system. In some of these fibers the ER reaches a high degree of development. In Armadillidium there is a special type of n. fiber containing a regular sequence of transversally oriented cisternae. Arthropod fibers sometimes contain thin parallel filaments as well as typical ER elements.Mitochondria, small vesicles and dense granules are commonly found within the neuroplasm of the neuropilic fibers. It is important to note that in arthropods, microvesicles are not restricted to the terminal region of the nerve fibers but that they may also occur all along the fibers.Arthropod neurons are enveloped by a glial insulating capsule and therefore interneuron contacts may only occur at neuropile level. These contacts are of three different morphological types: cross contacts, longitudinal contacts and end-knob contacts. At the level of longitudinal and cross contacts the neuroplasm shows no increase in the number of microvesicles or mitochondria. In the end-knob contacts, on the contrary, large numbers of microvesicles appear concentrated in the pre-synaptic fiber only, and occasionally in both fibers the pre-synaptic and the post-synaptic.It is maintained that funcional interneuron connections may result not only from contacts between fibers containing vesicles, but also between fibers in which vesicles are absent.     

Comparative aspects of DNA organization in metazoa

Data on sequence organization in metazoa are reviewed and tabulated. It is shown that the features of sequence organization previously observed in Xenopus DNA are extremely widespread. At least 70% of DNA fragments 2,000-3,000 nucleotides long contain both single copy and repetitive sequence in all the organisms examined except Drosophila.     

Space-time organization of recruitment in rabbit cerebral cortex

The spatio-temporal organization of the recruiting responses in the cerebral cortex was studied in an acute experiment on alert rabbits. Local low-frequency stimulation of the thalamic central medial nucleus leads to the appearance of both "generalized" and "local" spindles. Temporal shifts of 0.1--2 sec. occur in the appearance of the "generalized" spindles. The performed analysis permits the assumption that under local stimulation the spatio-temporal dynamics of the recruiting response is connected with the appearance of several spindle pacemakers which differ in their characteristics, e. g. in the speed of the excitability recovery and in their interrelations.     

Characteristics of the ensemble organization of the human cerebral cortex from birth to 20 years of age

When studying frontal, somatosensory and visual areas of the human cerebral cortex from birth up to 20 years of age in year-to-year intervals, it has been stated that by birth in neocortex all components of the neuron-glio-vascular ensembles are presented. They are not connected in their composition. During the first year of life the size of all types of neurons increases, long-axonal basket neurons differentiate, fasciculi of radial fibers become thick. By 3 years of life in the ensembles the neurons are definitely grouped as clusters. Sizes of spindle-like and satellite neurons increase; they distribute their axonal collaterals vertically, horizontally and in frontal-posterior direction. By 5-6 years of age the horizontal connection system becomes more complex at the expense of longitudinal growth and ramification of lateral and basal dendrites of the pyramidal neurons. In the section transversal areas occupied with cell groups increase. By 9-10 years of age the pyramidal neurons reach their greatest size. By 12-14 years of age the fibrillar component of the cortex increases considerably, inter- and intraensemble horizontal connections become more complex, the system of local connections becomes more plastic owing to development of short-axonal basket-like neurons. By 16-18 years of age the ensemble cortical organization in its main parameters of architectonics reaches the level specific for mature persons.