Cardiovascular responses following injection of picrotoxin into the lateral cerebral ventricle of rabbits

Summary Experiments are presented to show that injections of small doses of picrotoxin into the lateral cerebral ventricles of rabbits induce a rise in blood pressure and cardiac arrhythmias (bradycardia, tachycardia, extrasystoles, ventricular fibrillation). The bradycardia is largely abolished by bilateral vagotomy. Both the pressor response and other cardiac arrhythmias are markedly diminished or abolished by previous injections of reserpine, phenoxybenzamine, and by spinal C2 section, but not by adrenalectomy or spinal T4-5 section. Pretreatment with LSD did not prevent these changes. The convulsant action of picrotoxin does not appear to contribute to these cardiovascular responses. It is concluded that picrotoxin can stimulate central sympathetic mechanisms leading to increased sympathetic outflow affecting the cardiovascular system, although the specific brain areas involved remain to be determined.