Decreased thermal tolerance in Mus musculus with melatonin and chlorpromazine.

Adult Mus musculus, previously acclimatized for two weeks to 25 degrees C and an LD 12:12 photoperiod, were injected (i.p.) with daily doses of melatonin (4.0 mg) or chlorpromazine (20.0 mg kg-1) for 2 days. Both drugs significantly reduced the critical thermal maximum (CTM) and the elevated defended temperature (EDT). Melatonin significantly increased the length of EDT but chlorpromazine had no effect on EDT. Both drugs reduce thermal tolerance in ectotherms, but this is apparently the first demonstration that melatonin and chlorpromazine increase sensitivity to high temperature in an endotherm.