Hippocampal Dentate Fascia Research Articles

Structural Organization of Astrocytes in the Subgranular Zone of the Rabbit Hippocampal Dentate Fascia

Neurogenesis in the subgranular zone (SGZ) of the mammalian hippocampus is well known to occur throughout the life span. Astrocytes in this specialized proliferative zone are supposed to have properties of progenitor cells. Structural features of these cells and their interspecies differences remain understudied, while data on the structural organization of the SGZ in the rabbit (order Lagomorpha, superorder Glires), which is widely used in medical and biological studies, are lacking at all. The present work was focused on the structural and cytochemical organization of astrocytes in the SGZ of the rabbit hippocampal dentate fascia as studied by laser confocal microscopy. The study was carried out on the brain of adult Chinchilla rabbits compared to that of adult Wistar rats. Two morphological astrocyte types were identified in the rabbit SGZ: radial gliocyte-like (type I) and atypical fibrous astrocyte-like (type II) cells. By contrast, the rat SGZ exhibited a predominance of type II astrocytes which lacked long unramified processes penetrating through the granular layer and reaching the molecular layer. SGZ astrocytes, both in the rabbit and rat, were characterized by intense immunoreactivity for glutamine synthetase, most pronounced in the processes that formed the perivascular glia limitans. Importantly, the peculiarities of the astrocyte organization in the dentate fascia of the rabbit hippocampus allowed SGZ delimitation, whereas astrocytes in the rat SGZ exhibited no local morphological distinctions. The latter finding indicates a more complex organization of the neurogenic zone in the hippocampus of lagomorphs in contrast to the same zone in rodents.

Structural organization of glial cells at the border between the neurotransplant and recipient brain.

Integration of fetal hippocampal dentate fascia neurotransplants with the neocortical somatosensory region in adult rats was studied by electron microscopy. The growth of nerve fiber through the neurotransplant/brain border formed by the glial cells was studied. The interface zone was organized by various astrocyte subpopulations and ependymocytes forming multilamellar accumulations in some sites of the interface. These conglomerations of the glial cells and their processes did not prevent the growth of axonal and axodendritic bundles; moreover, fibrous astrocyte axons accompanied them. Under conditions of immature nervous tissue transplantation to the focus of mature brain damage, the glial cells created a substrate in the interface permeable for nerve fibers, thus promoting the functional integration of the neurotransplant.

Structural changes in the hippocampal dentate fascia in rats after action of hypoxia at the perinatal period of development

Structural changes in the hippocampal dentate fascia in rats after action of hypoxia at the perinatal period of development

Frontotemporal dementia: evidence for impairment of ascending serotoninergic but not noradrenergic innervation. Immunocytochemical and quantitative study using a graph method.

A graph method was employed to analyze the spatial neuronal patterns of nuclear grays of the pontine tegmentum with ascending aminergic projections to the forebrain in 12 cases of frontotemporal dementia (FTD). The nuclear grays examined were the nucleus centralis superior (NCS), a part of the nucleus raphae dorsalis (NRD), and the locus coeruleus (LC). The results were compared with 30 cases of Alzheimer's disease (AD) and 35 non-demented controls. In addition to the graph evaluations, neuronal cytoplasmic inclusion bodies were stained by silver impregnation and ubiquitin (Ub) and tau immunohistochemistry. The FTD cases showed a significant, 40%, decline in number of neurons in the NCS and NRD, while the LC was spared. The magnitude of neuronal loss matched that of AD where, by contrast, the LC was also severely changed. Amyloid deposition and Alzheimer neurofibrillary tangles occurred in the aminergic nuclei almost exclusively in AD and, to a minor extent, in some aged controls. No cytoplasmic inclusion bodies were found in the aminergic nuclei of the FTD cases. However, 6 cases had Ub-positive but tau-negative neuronal inclusions in the hippocampal dentate fascia and in layer 2 of the prefrontal isocortex, and 3 showed clinical and histological signs of motor neuron disease. Our results suggest that the serotoninergic raphe nuclei with ascending projections to the forebrain, but not the LC, become directly or indirectly involved in frontotemporal dementia both with and without motor neuron disease.

Pick's disease immunohistochemistry: new alterations and Alzheimer's disease comparisons.

Pick's disease (PD) brains were examined immunohistochemically for the expression of antigens known to be associated with Alzheimer's disease (AD) lesions. Most antibodies which label intracellular neurofibrillary tangles (NFTs) in AD were found to stain Pick bodies (PBs). Among them was the monoclonal antibody A2B5, which is known to recognize neuronal surface gangliosides. This result indicates that membrane proteins are probably incorporated into PBs as into NFTs. However, PBs, in contrast to NFTs, showed a paucity of staining for heparan sulfate glycosaminoglycan and basic fibroblast growth factor (bFGF). Staining for midkine, seen in senile plaques in AD, was not seen in PD. The relative lack of staining for these two neurotrophic factors in PD brain may reflect underlying mechanisms which are distinct from those in AD. We also describe two glial abnormalities in PD: glial fibrillary tangles and clusters of granules positive for the complement protein C4d in the hippocampal dentate fascia. These are presumably related to complement-activated oligodendroglia, and both pathological structures are more abundant in advanced cases, suggesting that they may be hallmarks of the disease progression.

Elimination of granular cells after intrahippocampal colchicine injection causing disappearance of evoked potentials and deterioration of development of the conditioned avoidance reflex in rats

The aim of our work was to study the involvement, in the process of learning, of synapses between the perforant path and granular cells of the hippocampal dentate fascia for formation of a conditioned reflex (CR) of active avoidance elaborated in response to electrostimulation of the perforant path. To achieve this we used the property of the neurotoxin colchicine at a certain concentration of eliminating selectively the fascia cells. One month after colchicine injection we observed destruction of granular cells, disappearance of the dentate fascia focally evoked potentials, and considerable deterioration in the elaboration of active avoidance CR. Administration of saline solution in control experiments did not bring about such changes. The results obtained show the important role of the entorhinal input into the hippocampus in the learning model used.

Regional Metabolic Activity in the Rat Brain During Sleep-Wake Activity

[14C]2-Deoxyglucose autoradiography was used to demonstrate regional metabolic activity in the rat brain during wake, slow-wave sleep (SWS), and REM sleep. Data are expressed as values of relative metabolic activity (RMA, regional optic density/mean brain optic density), which show the level of metabolic activity in a region, relative to the mean level of the brain. Regions exhibiting obviously decreased RMA during SWS include the cerebellum, cortical layer IV, and most of the thalamus, including the massa intermedia and lateral geniculate nuclei. Low levels of RMA in sensory relay regions during SWS reflect functional deafference of the brain. In contrast, some limbic regions, including the hypothalamic core and hippocampal dentate fascia, exhibit increased RMA during SWS. Regions exhibiting increased RMA may have functions which are carried on at high levels during sleep. The metabolic appearance of the brain in REM is very different from that in SWS. The reticular core, substantia nigra, hippocampal dentate fascia, and stratum moleculare, and many regions associated with the extrapyramidal motor system, exhibit increased RMA. The cerebellum and ventral thalamic nucleus show decreased RMA, while the lateral thalamic nuclei and cortical layer IV show no metabolic state dependency. In sum, SWS is associated with a general decrease in RMA of sensory and motor areas, and with increased RMA in some limbic regions. RMA is similar in cerebellar and hippocampal regions during REM and SWS. In contrast, RMA in many sensory relay regions does not decrease during REM, and there is REM-specific increase of RMA in some pontomesencephalic regions associated with motor function.