Synantocytes: the fifth type of glia? In comparison with astrocytes.

To date four types of glial cells have been identified in central nervous system: astrocytes, oligodendrocytes, microglia, ependymocytes. The latest results indicate the existence of the fifth glial type-synantocytes from the Greek word synanto that is for contact. Synantocyte processes reach neurons, astrocytes, oligodendrocytes, microglia, synapses, myelin sheaths and nervous fibres' nodes of Ranvier. Morphologically, synantocytes are similar to astrocytes, but they do not contain, like astrocytes, glial fibrillary acidic protein and S-100 beta protein. Synantocytes show expression of NG2 surface chondroition sulphate proteoglycan. Moreover, these cells in contrast to astrocytes do not have membrane transporters for glutamate (Glu), but have receptors for Glu and gamma-aminobutyric acid, whose activation can contribute to keeping up ion balance in CNS. Synantocytes are components of synapses, participate in neuronal cytoskeleton stabilization and control myelin integrity, mediate oligodendrocytes answer to nervous fibres' damage and form glial scars. Thus, there are evidences that synantocytes and astrocytes make separate glial population, playing important functions in neuroprotection

Effects of monosodium glutamate treatment on calretinin-immunoreactive neurons in hippocampus of postnatal rats

Introduction. Calretinin (CR) is a protein, which is present in GABAergic neurons and belongs to the calcium-binding proteins family. It may reduce the excitotoxicity phenomenon through its Ca2+ buffering properties. This phenomenon is due to the increase of calcium ions levels caused by the excess of glutamate — the main excitatory neurotransmitter. The aim of the study was to investigate alterations of calretinin-immunoreactivity in neurons of hippocampal CA1 region and dentate gyrus with hilus in 10 day-old rats treated with monosodium glutamate (MSG). Material and methods. Ten 7 day-old Wistar rats were used. The MSG-group consisted of 5 MSG-treated rats at a dose of 4 g/kg b.w. for 3 consecutive days and the second group consisted of 5 control animals. After euthanasia the brains containing hippocampus were dissected and embedded in paraffin blocks. The immunohi­stochemical peroxidase-antiperoxydase reaction was performed on tissue sections. The morphometric analyses of CR-immunopositive neurons: density, percentage ratio to the density of all cells and an assessment of digital immunostaining intensity were performed. Results. The distribution of the CR-immunoreactive neurons in the hippocampus was irregular. In the MSG-group there were single cells, which were more intensely stained than in control animals. Some of cells contained processes of different length. The density of CR-immunopositive cells and their percentage ratio to the density of all cells did not change significantly after MSG treatment. However, there was a statistically significant increase in the staining intensity of CR-immunopositive cells. Conclusions. The obtained results indicate that CR-positive cells in P7–P10 rats are only slightly affected by MSG in CA1 region and dentate gyrus with hilus of the hippocampus

Investigations of hippocampal astrocytes in lipopolysaccharide-preconditioned rats in the pilocarpine model of epilepsy

The present paper is the first work to determine the effect of lipopolysaccharide (LPS) in the pilocarpine model of epilepsy on the morphology of rat hippocampal astrocytes in vivo. The study involved adult male Wistar rats, which 72 hours prior to administration of pilocarpine hydrochloride (PILO) were intraperitoneally (ip) preconditioned with LPS at a dose of 0.5 mg/kg b.w. The control animals were administered (ip) saline or LPS alone. The astrocytes in the control animals displayed characteristic stellate morphology. Examinations of the astrocytes were performed on days one, three and 21 of the pilocarpine model of epilepsy (i.e. in the acute, silent and chronic periods). The astrocytes of the CA1 and CA3 pyramidal layers of the hippocampus were observed and analyzed at the structural and ultrastructural levels. It was demonstrated that on days one and three, glial cells from both the nonpreconditioned and the LPS-preconditioned animals displayed similar reactive changes, manifesting themselves as swelling of cell bodies, glial processes, and astrocytosis. Moreover, reduction in cell organelles aggregated at one pole and the presence of vacuoles were observed. The most pronounced astrogliosis and cell swelling occurred on day 21. We conclude that LPS has no effect on the morphology of astrocytes in the pilocarpine model of epilepsy, unlike the results obtained by other authors in vitro. (Folia Histochemica et Cytobiologica 2011; Vol. 49, No. 2, pp. 219–224

Reactivity of astrocytes in the periaqueductal gray matter of rats treated with monosodium glutamate

Introduction. The astrocytic S100b calcium-binding protein performs numerous intra- and extracellular functions, promoting the survival of central nervous system (CNS) structures. Its increased synthesis and release are a manifestation of reactive glial behavior, crucial for the maintenance of proper neuronal function, particularly under the pathological conditions. The periaqueductal gray matter (PAG) is a mindbrain area composed of four parts dorsomedial (dm), dorsolateral (dl), lateral (l) and ventrolateral (vl)) which are involved in pain sensing and defensive reactions of the body. The aim of this study was to evaluate the S100b protein immunoreactive (S100b-IR) astrocytes in adult rats after administration of monosodium glutamate (MSG). Material and methods. The animals were administered the saline solution (group C), 2 g/kg b.w. MSG (group I) and 4 g/kg b.w. MSG (group II). The study was carried out on the brain sections stained by immunohistochemical peroxidase-antiperoxidase method with a primary mouse antibody against the S100b protein. Results. The analyses showed the presence of the S100b-immunoreactive cells in dm, dl, l, vl PAG of all animals. In the C and I group animals, the PAG astrocytes were characterized mainly by the presence of the studied protein in the nucleus and cytoplasm of the cell body. In the group II rats in all parts of PAG, the S100b-IR cells with numerous, thicker and branched processes were observed. A decrease in the number of the S100b-IR cells was found in dm, dl and l PAG in the MSG-treated animals, particularly with the larger dose. The number of cells with the S100b expression was comparable in vl PAG in all rats. Conclusions. MSG administered parenterally to the higher dose to adult rats affects the immunoreactivity of S100b protein in PAG. Phenotypic changes of the studied cells may indicate reactivity of glial cells and increased expression of the studied protein whereas a decrease in their number may result from the increased protein secretion into the extracellular space or cytotoxic death of glial cells

Synantocytes: the fifth type of glia? In comparison with astrocytes.

To date four types of glial cells have been identified in central nervous system: astrocytes, oligodendrocytes, microglia, ependymocytes. The latest results indicate the existence of the fifth glial type-synantocytes from the Greek word synanto that is for contact. Synantocyte processes reach neurons, astrocytes, oligodendrocytes, microglia, synapses, myelin sheaths and nervous fibres' nodes of Ranvier. Morphologically, synantocytes are similar to astrocytes, but they do not contain, like astrocytes, glial fibrillary acidic protein and S-100 beta protein. Synantocytes show expression of NG2 surface chondroition sulphate proteoglycan. Moreover, these cells in contrast to astrocytes do not have membrane transporters for glutamate (Glu), but have receptors for Glu and gamma-aminobutyric acid, whose activation can contribute to keeping up ion balance in CNS. Synantocytes are components of synapses, participate in neuronal cytoskeleton stabilization and control myelin integrity, mediate oligodendrocytes answer to nervous fibres' damage and form glial scars. Thus, there are evidences that synantocytes and astrocytes make separate glial population, playing important functions in neuroprotection

Reactivity of astrocytes in hippocampal CA1 area in rats after administration of habanero peppers

Introduction. Astrocytes react to microenvironmental changes. Their reactivity is manifested by an increase in glial fibrillary acidic protein (GFAP) and S100b protein levels, hypertrophy and hyperplasia. The aim of the study was to analyse immunoreactive GFAP (GFAP-IR) and S100b (S100b-IR) astrocytes of hippocampal CA1 area in adult rats intragastrically (i.g.) treated with habanero peppers. Material and methods. Brains from 10 control rats (group C) and 10 rats receiving oil suspension of habanero fruits for 7 days (group I-7) or 28 days (group II-28) were used. Antibodies against GFAP and S100b were used for immunohistochemistry. Morphology and distribution of astrocytes was evaluated under light microscope and their density was quantitatively analysed. Results. In the CA1 hippocampal area of group II-28 rats, GFAP-IR cells with numerous, branched processes were observed. S100b-IR astrocytes had delicate, single processes in comparison with cells without processes observed in groups I-7 and C. In groups I-7 and II-28, GFAP-IR astrocytes’ density significantly increased in SR — stratum radiatum of hippocampal CA1 area. In group I-7, a density of cells with the expression of S100b was significantly increased in SO — stratum oriens layer. In group II-28, the density of S100b-IR astrocytes was decreased. Conclusions. Habanero peppers administrated to rats, especially for a longer time, caused reactive changes in the astrocytes in hippocampal CA1 area, and thus these glial cells may protect neurons against excitotoxic damage