Kindled seizures activate both branches of the autonomic nervous system

Amygdaloid kindled seizures in the rat induce an abrupt elevation of blood pressure accompanied by a significant decrease in heart rate. The autonomic pharmacology of this response was examined in unanesthetized kindled rats. Muscarinic receptor blockade with atropine (1 mg/kg, intravenous (i.v.)) a bolished the seizure-induced bradycardia. The seizure-induced hypertension was unaffected by beta-adrenergic blockade with timolol (1 mg/kg, i.v.), bu t was reduced by phentolamine (5 mg/kg, subcutaneous (s.c.)), an alpha-adre nergic receptor antagonist. A chemical sympathectomy was induced with 6-hyd roxydopamine (100 mg/kg, i.v.), an agent that does not cross the blood-brai n barrier. This eliminated the presser response but did not completely bloc k the seizure-induced bradycardia. The effectiveness of 6-hydroxydopamine w as tested with tyramine (0.5 mg/kg, i.v.) an agent that releases endogenous catecholamines. These results indicate amygdaloid kindled seizures activat e both branches of the autonomic nervous system. The bradycardia was mediat ed by the parasympathetic system; the presser response was caused by an inc rease in peripheral resistance due to alpha-adrenergic receptor activation. More important, these findings show that kindling is a useful seizure mode l for future studies on the effect of seizures on cardiovascular function a nd possible mechanisms of seizure-related sudden unexplained death. (C) 199 9 Elsevier Science B.V. All rights reserved.