Central cardiovascular effects produced by the GABA receptor agonist drug, THIP

In chloralose-anesthetized cats, injection of THIP (30-1000 microgram) into the fourth ventricle produced dose-dependent decreases in blood pressure and heart rate. Administration of similar doses into either the lateral and third ventricle or administration of the largest dose intravenously did not produce these effects. Microinjection of THIP (1.95 microgram) into nucleus ambiguus reversed bradycardia evoked by microinjection of bicuculline methiodide (160 ng) into this nucleus. These results confirm previous findings indicating that activation of GABA receptors in the hindbrain produces hypotension and bradycardia as well as reversal of bicuculline-induced activation of cardiac parasympathetic nerves.