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

Introduction. The astrocytic S100β 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 S100β protein immunoreactive (S100β-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 S100β protein. Results. The analyses showed the presence of the S100β-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 S100β-IR cells with numerous, thicker and branched processes were observed. A decrease in the number of the S100β-IR cells was found in PAG in the MSG-treated animals, particularly with the larger dose. The number of cells with the S100β expression was comparable in vl PAG in all rats. Conclusions. MSG administered parenterally to the higher dose to adult rats affects the immunoreactivity of S100β 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.