Structure of the neocortex of the Baikal ringed seal (Pusa sibirica Gm.)]

The sulci and gyri of the neocortex, as well as cyto-, synaptoarchitectonics and neuronal composition of the sensomotor (brain area) have been studied in the Baikal ringed seal. The structure of the sulci and gyri have been found to be similar to that in carnivores. The following specific features have been revealed in the brain of this endemic species: a thick layer I, presence of giant pyramidal cells in the layer III, large mitochondria in the presynaptic parts and dendrites. The results obtained are discussed concerning adaptation to semiaqueous way of life and to diving.     

Spatial organization and interneuronal relations in various areas of the neocortex in Cetacea

The data on pyramidal neurons joining in the parietal and temporal areas of the dolphin neocortex by means of apical dendrites fasciculi are presented. The fasciculi also contain dendrites of spindle-like and stellate cells. The vertical fasciculi of the dendrites unite neurons of the layer V and of the sublayer III2. In the sublayer III1, after dichotonic division of the apical dendrites, fasciculi of the second order are formed, to them the dendrites of the pyramidal neurons of the sublayer III1 and the layer II join. Several forms of the interneuronal contacts have been revealed: axo-dendritic, axo-spinous and dendro-dendritic. Synaptic complexes of the converged and divergent types have been shown. A suggestion is made on formation of larger neuronal modules++, having common afferent entrance and demonstrating selectivity to the stimulus properties.     

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.     

Comparative aspects of structural organization of astrocytes of the first layer of the human and rat cerebral cortex

Importance of study of astrocytes for fundamental biology and medicine is due 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 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 specter of proteins forming intermediate filaments in these cells was identical. However, there were essential differences revealed in organization of the superficial glial bordering lamina (SGBL). The human SGBL is formed by interlacing of thin processes in the layer I processes, whereas the rat SGBL 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.     

Structural basis of the intracortical synchronization of epileptic potentials in the sensomotor region of the rat neocortex

In control rats, penicillin-induced epileptiform discharges were completely synchronous in the neocortex sites at a distance of up to 4 mm from each other. Number of the cells decreased by 45.5% during 90 days in isolated cortical slabs and the synchronisation disappeared. The data obtained show that the loss of large pyramidal neurones of the layer V entailed a loss of the spatial synchronisation. The main axonal collaterals of large pyramidal neurones of the layer V could be followed horizontally for a distance of up to 2 mm in the somatosensory cortex. The neuronal network formed by the large pyramidal neurones of the layer V seems to provide a spatial synchronisation in the neocortex.     

Annexin 6 immunoreactivity in select cell populations in the rat brain.

We examined the distribution of annexin 6 (ANX6) in rat brain with immunohistochemistry (IHC). Several neuronal cell populations were intensely labeled with the ANX6 monoclonal antibody (MAb), including layer 5 of neocortex, the lateral septum, the lateral hypothalamic area, the red nucleus, and the Purkinje cell layer in cerebellum. Neuronal immunolabeling was localized to the nucleus and the cytosol. Darkly stained ANX6-immunoreactive glia, with the morphology characteristic of astrocytes, were abundant in the hippocampus, substantia nigra reticulata, and cerebellum. Evidence suggests that ANX6 may function in neuronal and glial calcium-dependent processes.     

Immunohistochemistry and nerve lesion experiments on the methionine-enkephalin immunopositive neurons in the small intestine of the bullfrog (Rana catesbeiana)

Summary Nerve elements in the small intestine of the bullfrog. Rana catesbeiana, were studied by immunohistochemistry with anti-methionine enkephalin antisera and by nerve lesion experiments, using laser irradiation. Methionine-enkephalin immunopositive nerve fibers occur in the myenteric plexus, circular muscle layer, submucosa, and mucosa. Immunopositive nerve cell bodies in the myenteric plexus have dendrite-like and a long axon-like processes. In the froglet (3 months after metamorphosis), these axon-like processes lead posteriorly in the nerve strand of the myenteric plexus. Some bifurcate, one branch continuing posteriorly, the other doubling back to lead anteriorly; both form terminal varicose fibers in the circular muscle layer. Nerve lesion experiments, in the adult bullfrog, resulted in accumulations of methionine-enkephalin immunoreactivity at the oral and hinder edges of the laser-irradiated necrotic area; there were sprouting and nonsprouting immunopositive stumps. It is suggested that bidirectional flow of methionine-enkephalin in the myenteric plexus is mediated via the anterior and posterior branches of the axon-like process. The difference in sprouting behavior of immunopositive nerve fiber stumps, after nerve lesion, is discussed with reference to regional differences of the axon-like process.     

Ultrastructure of the synapses of the initial axonal segment of the pyramidal neuron

Ultrastructure of the proximal part of the axon in the neurons, identified according to a number of morphological signs as pyramidal, has been studied in the layer III of the cat cerebral hemisphere sensomotor cortex. In sections, tangential to the cortical surface, in the initial axonal segment, a submembranous osmophilic layer and fasciculi of microtubules are revealed. On the initial segment spines are found, they contain cysterns resembling by their structure the spine system of the dendritic spines. Axonal terminals revealed along the axonal distribution are in contact both with the axonal trunk and with the spines. Regarding the initial segment, they are presynaptic, contain oval synaptic vesicles and form symmetric axo-axonal synapses only. In transversal sections axonal terminals are detected, arranging on the surface of the initial segment mostly as single ones, in longitudinal sections they are seen as clusters. Analysing the author's data and those from the literature, a conclusion is made that in intact animals the synaptic contacts at the initial segment of the axon are the only form of axo-axonal synapses in the neocortex.     

Neural recognition molecules CHL1 and NB-3 regulate apical dendrite orientation in the neocortex via PTP alpha

Apical dendrites of pyramidal neurons in the neocortex have a stereotypic orientation that is important for neuronal function. Neural recognition molecule Close Homolog of L1 (CHL1) has been shown to regulate oriented growth of apical dendrites in the mouse caudal cortex. Here we show that CHL1 directly associates with NB-3, a member of the F3/contactin family of neural recognition molecules, and enhances its cell surface expression. Similar to CHL1, NB-3 exhibits high-caudal to low-rostral expression in the deep layer neurons of the neocortex. NB-3-deficient mice show abnormal apical dendrite projections of deep layer pyramidal neurons in the visual cortex. Both CHL1 and NB-3 interact with protein tyrosine phosphatase alpha (PTPalpha) and regulate its activity. Moreover, deep layer pyramidal neurons of PTPalpha-deficient mice develop misoriented, even inverted, apical dendrites. We propose a signaling complex in which PTPalpha mediates CHL1 and NB-3-regulated apical dendrite projection in the developing caudal cortex.     

Microglia with an Endothelin ETB Receptor Aggregate in Rat Hippocampus CA1 Subfields Following Transient Forebrain Ischemia

Abstract: We examined endothelin (ET) receptors in the hippocampus CA1 subfields of stroke-prone spontaneously hypertensive rats subjected to a 10-min bilateral carotid occlusion and reperfusion. When delayed neuronal death had occurred in the pyramidal cell layer at 7 days after transient forebrain ischemia, the quantitative receptor autoradiographic method we used revealed a dramatic increase in number of ¹²⁵I-ET-1 binding sites in the hippocampus CA1 subfields. The highest number of de novo binding sites appeared in the area corresponding anatomically to the pyramidal cell layer with neuronal death. These binding sites were characteristically the ET_B receptor. The de novo ¹²⁵I-ET-1 binding was mainly present on microglia aggregating with a high density in the damaged pyramidal cell layer. As ET-1- and ET-3-like immunoreactivities were highly expressed within astrocytes in damaged neural tissue, the possibility that microglia with the ET_B receptor are activated to participate in the pathophysiology of ischemia-related neural tissue damage by astrocytic ET-1 and ET-3 produced in response to transient forebrain ischemia would have to be considered.     

An embedded subnetwork of highly active neurons in the neocortex

Unbiased methods to assess the firing activity of individual neurons in the neocortex have revealed that a large proportion of cells fire at extremely low rates (<0.1 Hz), both in their spontaneous and evoked activity. Thus, firing in neocortical networks appears to be dominated by a small population of highly active neurons. Here, we use a fosGFP transgenic mouse to examine the properties of cells with a recent history of elevated activity. FosGFP-expressing layer 2/3 pyramidal cells fired at higher rates compared to fosGFP(-) neurons, both in vivo and in vitro. Elevated activity could be attributed to increased excitatory and decreased inhibitory drive to fosGFP(+) neurons. Paired-cell recordings indicated that fosGFP(+) neurons had a greater likelihood of being connected to each other. These findings indicate that highly active, interconnected neuronal ensembles are present in the neocortex and suggest these cells may play a role in the encoding of sensory information. VIDEO ABSTRACT:     

Morphohistochemical analysis of secretory elements of the olfactory epithelium of marine fish

Morphohistochemical characteristics of various secretory elements of the olfactory lining have been analysed in sea fishes. In the investigation epithelium of Chondrostei and Teleostei has been used. For secrete formation, besides supporting cells, specialized secretory elements take part; among them cells of the I, II and III types can be revealed, as well as tubular and alveolar epithelial glands in some species of fishes. The secretory elements of the olfactory lining of the sea fishes produce substances of various chemical nature specific for the given type of formations and not depending on species-specific and ecological specialization. Essential species-specific differences are revealed in distribution, combinations, size and amount of the secretory elements per one unit of the olfactory lining surface. The analysis of these parameters in macro-, medio- and microsmatics, in fishes of various ecology and different systemic position, also demonstrates their differentiation.     

Cannabinoid receptors contribute to astroglial Ca2+-signalling and control of synaptic plasticity in the neocortex

Communication between neuronal and glial cells is thought to be very important for many brain functions. Acting via release of gliotransmitters, astrocytes can modulate synaptic strength. The mechanisms underlying ATP release from astrocytes remain uncertain with exocytosis being the most intriguing and debated pathway. We have demonstrated that ATP and d-serine can be released from cortical astrocytes in situ by a SNARE-complex-dependent mechanism. Exocytosis of ATP from astrocytes can activate post-synaptic P2X receptors in the adjacent neurons, causing a downregulation of synaptic and extrasynaptic GABA receptors in cortical pyramidal neurons. We showed that release of gliotransmitters is important for the NMDA receptor-dependent synaptic plasticity in the neocortex. Firstly, induction of long-term potentiation (LTP) by five episodes of theta-burst stimulation (TBS) was impaired in the neocortex of dominant-negative (dn)-SNARE mice. The LTP was rescued in the dn-SNARE mice by application of exogenous non-hydrolysable ATP analogues. Secondly, we observed that weak sub-threshold stimulation (two TBS episodes) became able to induce LTP when astrocytes were additionally activated via CB-1 receptors. This facilitation was dependent on activity of ATP receptors and was abolished in the dn-SNARE mice. Our results strongly support the physiological relevance of glial exocytosis for glia–neuron communications and brain function.     

The organization of double bouquet cells in monkey striate cortex

In previous publications we proposed a model of cortical organization in which the pyramidal cells of the cerebral cortex are organized into modules. The modules are centred around the clusters of apical dendrites that originate from the layer 5 pyramidal cells. In monkey striate cortex such modules have an average diameter of 23 μm and the outputs originating from the modules are contained in the vertical bundles of myelinated axons that traverse the deeper layers of the cortex. The present study is concerned with how the double bouquet cells in layer 2/3 of striate cortex relate to these pyramidal cell modules. The double bouquet cells are visualized with an antibody to calbindin, and it has been shown that their vertically oriented axons, or horse tails, are arranged in a regular array, such that there is one horse tail per pyramidal cell module. Within layer 2/3 the double bouquet cell axons run alongside the apical dendritic clusters, while in layer 4C they are closely associated with the myelinated axon bundles. However, the apical dendrites are not the principal targets of the double bouquet cell axons. Most of the neuronal elements post-synaptic to them are the shafts of small dendrites (60%) and dendritic spines, with which they form symmetric synapses. This regular arrangement of the axons of the double-bouquet cells and their relationship to the components of the pyramidal cells modules supports the concept that there are basic, repeating neuronal circuits in the cortex.     

Interneurons of the motor region of the neocortex]

Interneurons of motor area in the brain cortex have been studied in cats and monkeys. The greatest attention has been paid to pyramidal interneurons, among which six cell types have been described according to their axonal composition. Unlike stellate interneurons, all types of pyramidal interneurons possess less developed axonal collaterals. Interneuronal contacts are situated on dendrites or cell bodies of middle and large long-axonal pyramids. Functional role of cortical interneurons seems to be different. Some of them are of inhibitory nature (basket cells and, perhaps, other types of long-axonal stellate neurons), others are exciting elements. The latter include short-axonal stellate neurons and, perhaps, pyramidal interneurons. While comparing the cortex in cats and monkeys, it is evident that the neocortex in monkeys, especially its lower layers, is rich in pyramidal interneurons.     

Comparative distribution of acid phosphatase and simple esterase in the mouse neocortex and hippocampal formation

The present study deals with the detailed distribution of acid phosphatase (AcP) and simple esterase (SE) in different layers of the neocortex and hippocampal formation of the mouse brain. The neurons, in general, had moderate to intense enzyme activity for AcP and mild to moderate activity for SE. The AcP activity dominated in the neuronal population as compared to the neuropil; the neuropil stained mildly for SE. The large pyramidal cells in the neocortex and cornu ammonis, and the granular cell layer of the gyrus dentatus, demonstrated strong enzyme activity both in AcP and SE preparations. The role of AcP and SE has been discussed in relation to various structures of the neocortex and hippocampal formation.     

Expression pattern of the maternally imprinted gene Gtl2 in the forebrain during embryonic development and adulthood

Recent work has uncovered a large number of imprinted genes, many of which are thought to play a role in neurodevelopment and behavior. In order to begin to understand the role of specific genes in these processes, their expression patterns will be key. In this study we used in situ hybridization to study the developmental expression of Gtl2 in the forebrain from E12.5 to adulthood, since preliminary data from a microarray study indicated differential expression between the ventral and dorsal telencephalon of the mouse at a critical time point in the generation and migration of cortical neuronal populations. Strong expression was observed in the diencephalon, ventral telencephalon, post mitotic cell layers of the neocortex and pyramidal cell layer of the hippocampus. Additionally, heavily labeled subpopulations of laminar restricted cells were seen in the latter two areas.     

Involvement of gap junctions in the development of the neocortex

Gap junctions play an important role during the development of the mammalian brain. In the neocortex, gap junctions are already expressed at very early stages of development and they seem to be involved in many processes like neurogenesis, migration and synapse formation. Gap junctions are found in all cell types including progenitor cells, glial cells and neurons. These direct cell-to-cell connections form clusters consisting of a distinct number of cells of a certain type. These clusters can be considered as communication compartments in which the information transfer is mediated electrically by ionic currents and/or chemically by, e.g., small second messenger molecules. Within the neocortex, four such communication compartments can be identified: (1) gap junction-coupled neuroblasts of the ventricular zone and gap junctions in migrating cells and radial glia, (2) gap junction-coupled glial cells (astrocytes and oligodendrocytes), (3) gap junction-coupled pyramidal cells (only during the first two postnatal weeks) and (4) gap junction-coupled inhibitory interneurons. These compartments can consist of sub-compartments and they may overlap to some degree. The compartments 1 and 3 disappear with ongoing develop, whereas compartments 2 and 4 persist in the mature neocortex. Gap junction-mediated coupling of glial cells seems to be important for stabilization of the extracellular ion homeostasis, uptake of neurotransmitters, migration of neurons and myelination of axons. Electrical synapses between inhibitory interneurons facilitate the synchronization of pyramidal cells. In this way, they contribute to the generation of oscillatory network activity correlated with higher cortical functions. The role of gap junctions present in neuroblasts of the ventricular zone as well as the role of gap junctions found in pyramidal cells during the early postnatal stages is less clear. It is assumed that they might help to form precursors of the functional columns observed in the mature neocortex. Although recent developments of new techniques led to the solution of many problems concerning gap junction-coupling between neurons and glial cells in the neocortex, there are many open questions which need to be answered before we can achieve a comprehensive understanding of the role of gap junctions in the development of the neocortex.