Steroid hormone effects on picrotoxin-induced seizures in female and male rats.

Picrotoxin (1 mg/kg, i.p.), evoked a single generalized seizure in 75% of ovariectomized rats. Pretreatment of matched pairs with silastic implants containing 100% estradiol had an anticonvulsant effect; it protected all rats against such seizures. Implants containing 10% estradiol in cholesterol were less effective in protecting against picrotoxin-induced seizures. With 2 mg/kg picrotoxin, 85% of the seizure-affected ovariectomized controls had multiple seizures. The incidence of seizures and the ratio of single to multiple seizures induced by the higher dose of picrotoxin were unaffected by estradiol silastic implants, intraperitoneal injections of progesterone (0.5 mg, 4-5 h before convulsant) or the combination of both hormones. At the 2 mg/kg dose, 8/8 intact males had no seizures while all paired ovariectomized females had seizures. By contrast, the incidence of seizures in pairs of gonadectomized males and females did not differ. Testosterone treatment improved the ratio of single to multiple seizures in males but not in females. Males had statistically fewer multiple seizures than did females after testosterone treatment. The distribution of latencies to a single seizure is statistically different from the distribution of latencies to the first of multiple seizures irrespective of dose, sex and hormone treatment. This suggests that the population of rats responding with a single seizure at the higher dose of picrotoxin have a higher threshold for acquiring multiple seizures and that testosterone predisposes males but not females to this population.