Sex related differences in the response of mice, rats and cats to administration of picrotoxin.

Picrotoxin, 2.5 mg/kg, which was subconvulsive in male rats was 92% convulsive in female rats. Four mg/kg of picrotoxin, a dose which did not produce death in the male rats, was 75% lethal in the female rats. Picrotoxin also produced a significantly greater increase in the frequency of the spinal motoneurons discharge in the female than in male rats (444% of control compared to 222% of control). A similar significant difference to the analogous treatment was obtained in the female and male cats (439% of control compared to 368% of control). To counteract the picrotoxin-induced increased frequency of the spinal motoneurons discharge a double dose of diazepam had to be given to females of both species. A sex related difference in the occurrence of convulsions, latency and death following picrotoxin administration was also present in mice. However, mice responded in an opposite direction to rats and cats. Three mg/kg of picrotoxin was 100% convulsive and 27% lethal in male mice, while only 40% convulsive and 0% lethal in female mice. In male mice treated with a 100% lethal dose of picrotoxin, diazepam, 3.0 mg/kg, did not diminish the occurrence of convulsions but reduced the incidence of death to 70%. In equally treated female mice the same dose of diazepam reduced the occurrence of convulsions from 100 to 70% and the incidence of death to 10%. The existence of sex related differences in the response of mice, rats and cats to administration of picrotoxin might have its origin in the dimorphisms of the GABA system in these animal species.