Evaluation of immunoreactive for glial fibrillary acidic protein astrocytes in the periaqueductal gray matter of rats treated with monosodium glutamate.

Abstract

The aim of this study was to evaluate the glial fibrillary acidic protein immunoreactive (GFAP-IR) astrocytes in the periaqueductal gray matter (PAG) of rats treated with monosodium glutamate (MSG). This study was performed on PAG sections of rats treated subcutaneously with MSG (2 g/kg b.w. (group I) and 4 g/kg b.w. (group II)) and saline (group C). Immunohistochemical reactions were performed by peroxidase-antiperoxidase method using an antibody against GFAP protein. In animals receiving MSG in dorsomedial (dm) and dorsolateral (dl) parts of PAG the majority of astrocytes had GFAP-IR bodies and few thin, poorly branched protuberances. In lateral (l) and ventrolateral (vl) parts of PAG cells with numerous, branched protuberances with GFAP expression were observed. Some astrocytes in vl PAG of group II rats were characterized by strongly stained cytoplasmic bodies and thick, multiple branched protuberances. Statistically significant differences in the number of GFAP-IR astrocytes were shown between control animals and group II in dm PAG and dl PAG. All MSG-treated animals revealed statistically significantly fewer immunonegative structures for GFAP as well as all cells in the PAG.In the PAG of rats receiving MSG, especially at high dose, there is an increase in GFAP immunoreactivity in astrocytes. The hypertrophy of GFAP-IR cells and the probable lack of their proliferation may indicate isomorphic astroglia in response to increased extracellular glutamate concentrations. However, the decrease in their number in dm PAG and dl PAG may be related to MSG cytotoxicity.