Sex differences in behavioral and thermal responses to pargyline and tryptophan

The effects of parenterally injected pargyline and tryptophan on rectal temperature and behavior have been studied in male and female rats. Pargyline alone (50 mg/kg) produced hypothermia in both sexes. Pargyline (50 mg/kg) followed by low doses (20--50 mg/kg) of tryptophan caused a behavioral syndrome consisting of tremor, hindlimb abduction, forepaw treading, and straub tail. In females, but not in males, hypothermia was potentiated. The same dose of pargyline followed by higher doses (60--150 mg/kg) of tryptophan produced a short hypothermia followed by a dose-dependent behavioral syndrome, hyperthermia, and mortality. On all of these measures, females responded following shorter latencies and lower doses of tryptophan. Both hypothermia and hyperthermia were observed in treated animals following pretreatment with a peripheral decarboxylase inhibitor. The results suggest a complex role for serotonin in thermoregulation. The sex differences observed suggest higher activity of serotonin in female rat brains following the drug treatment, which may be accounted for by a higher utilization rate of tryptophan.