Effects of central gaba receptor agonism and antagonism on evoked diencephalic cardiovascular responses

Abstract

The administration of the GABA agonists diazepam (0.3 mg/kg i.v.) and muscimol (0.3 μg/kg, i.c.v.) to chloralose-anaesthetized cats caused significant inhibition of the pressor responses elicited by electrical diencephalic stimulation. The inhibition was apparently a result of a reduction in centrally emanating sympathetic discharge to vasoconstrictor nerves. The GABA antagonist bicuculline (0.5 mg/kg i.v.) reversed the inhibition caused by muscimol but not by diazepam; however, pretreatment with bicuculline prevented the inhibition caused by diazepam. Muscimol caused significant and marked reductions in blood pressure and heart rate by decreasing central sympathetic nerve discharge; this action was also completely reversed by bicuculline. It is suggested that central activation of GABA receptors results in an inhibition of centrally evoked cardiovascular responses by preventing increases in sympathetic outflow. Furthermore, basal as well as evoked blood pressure, heart rate and sympathetic nervous discharge can be reduced by small doses of the directly acting GABA receptor stimulant muscimol.