Thermoregulatory and locomotor effects of DSIP: paradoxical interaction with d-amphetamine

A low dose (0.1 mg/kg) of peripherally administered delta sleep-inducing peptide (DSIP) caused hypothermia in rats maintained at 4 degrees C but larger doses (1.0 or 3.0 mg/kg) did not. At 22 degrees C all 3 doses of DSIP caused hyperthermia. The interaction of d-amphetamine with DSIP was dependent on ambient temperature; at 4 degrees C DSIP had no effect on d-amphetamine-induced hypothermia, but at 22 degrees C DSIP reversed the usual d-amphetamine-induced effect of hyperthermia to hypothermia. At 4 degrees C, DSIP also potentiated the hypermotility effects of d-amphetamine but blocked it at 22 degrees C. Many rats receiving DSIP (0.1 mg/kg) and d-amphetamine (15.0 mg/kg) at 22 degrees C paradoxically exhibited what appeared to be sleep. This sleep-like effect was not found after several other doses of DSIP and d-amphetamine, chlorpromazine, or at a cold ambient temperature. Sodium methohexital caused apparent sleep in animals treated with DSIP alone or with DSIP and d-amphetamine, but was unable to induce this effect in rats receiving d-amphetamine alone. The results suggest that the effects of peripherally injected DSIP on body temperature are independent from its effects on locomotion and that both effects are dependent upon ambient temperature.