Effect of GABA Analogues on Blood Pressure and Central GABA Metabolism in the Rat

Gamma aminobutyric acid (GABA) and different GABA analogues were examined for their cardiovascular actions and their influence on striatal dopamine (DA) levels and GABA accumulation after aminooxyacetic acid (AOAA). Gamma hydroxybutyric acid (GHBA) and baclofen caused hypertension and tachycardia after systemic as well as intracerebroventricular administration, while the opposite was true for GABA and muscimol. The hypertension after GHBA and baclofen was not reduced by picrotoxin or bicuculline and was not influenced by varying GABA levels by 3-mercaptopropionic acid (3-MPA) or AOAA. GHBA and muscimol but not baclofen reduced GABA accumulation induced by AOAA. Picrotoxin in a subconvulsive dose increased GABA accumulation and antagonized the inhibition after GHBA or muscimol. Bicuculline and a moderate dose of picrotoxin tended to decrease GABA accumulation by themselves and if anything augmented the effects of GHBA and muscimol. GHBA and baclofen but not muscimol in combination with AOAA increased DA levels, which was not prevented by picrotoxin or bicuculline. We conclude that the cardiovascular actions of GHBA and baclofen are probably not mediated by mechanisms identical to those of muscimol or exogenous GABA. In view of the biochemical results their actions would however be compatible with a concept of different GABA receptors.