Arginine vasopressin does not contribute to seizures induced by intracerebroventricularly-injected pilocarpine

Arginine vasopressin (AVP) has been shown to contribute to the production of seizures. Here, we aimed to investigate the effects of AVP on seizures induced by intracerebroventricular (i.c.v.) injection of pilocarpine. Rats were treated with 0.2-2.4 mg/5 μl pilocarpine intracerebroventricularly, to obtain the dose-response relationship for behavioural seizures. 2.4 mg/5 μl pilocarpine induced status epilepticus in all rats and 0.2 mg/5 μl pilocarpine did not produce any sign of seizure in any of the rats. In the second step, AVP (0.01-1000 ng/2 μl; i.c.v.) was injected 5 min before i.c.v. injection of a low dose pilocarpine (0.4 mg/5 μl) and rats were observed for percentage of status epilepticus, status epilepticus latency and behavioural seizure scores. None of the applied doses of AVP had any significant effect on seizures induced by 0.4 mg/5 μl i.c.v. pilocarpine. Subcutaneous injection of 1000 ng AVP 1 h before 0.4 mg i.c.v. pilocarpine also did not produce significant difference with respect to the 0.4 mg pilocarpine group. Finally, pretreatment with neither an AVP V1 receptor antagonist (25, 125, 250 ng/5 μl; i.c.v.) nor an AVP V2 receptor antagonist (25, 125, 250 ng/5 μl; i.c.v.) prevented status epilepticus, induced by 2.4 mg/5 μl i.c.v. pilocarpine. We conclude that AVP does not act as a convulsant agent in centrally-induced pilocarpine seizures.