Hypotension decreases GABA levels in brainstem regions of the rat

Concentrations of gamma-aminobutyric acid (GABA) and other amino acids were measured in microdissected areas of the rostral ventro-lateral medulla (RVL), nucleus tractus solitarii (NTS) and caudal ventrolateral medulla (CVL) of the rat, and effects on the amino acid levels, of hypotension induced by hexamethonium and nifedipine were examined. Hexamethonium and nifedipine decreased concentrations of GABA in all the regions studied, while concentrations of glycine, beta-alanine and taurine were not affected by these agents. Both agents caused a prolonged fall in blood pressure. These results strongly suggest that a decrease in blood pressure produces a decrease in GABA levels in the brainstem regions of the rat.