ANTIDEPRESSANT DRUG-INDUCED HYPOTHALAMIC COOLING IN SYRIAN-HAMSTERS

Antidepressant drugs have been reported to alter the circadian pattern of body temperature, but specific effects an the amplitude or on aver age body temperature are not consistent, and there have been no specif ic studies to examine chronic drug effects on brain temperature. To ad dress these issues, hypothalamic temperature (T-hy) was monitored tele metrically in hamsters treated with three antidepressant drugs, the mo noamine oxidase inhibitor (MAOI), clorgyline; the 5HT reuptake inhibit or, fluoxetine; and the alkali metal, lithium. For comparison, hamster s were also treated with two neuroleptic drugs, chlorpromazine and hal operidol. Each of the three antidepressant drugs, but neither of the n euroleptic drugs, produced a chronic decrease in diurnal (vest-phase) hypothalamic temperature. The T-hy-decreasing effect of clorgyline was not prevented by pinealectomy, and T-hy decreased more than peritonea l temperature (T-p), thus reducing the temperature difference between the hypothalamus and the peritoneal cavity. Less general effects of th e antidepressants were also observed. Clorgyline and fluoxetine, but n ot lithium, delayed the 24-hour rhythm of T-hy. Clorgyline and lithium , but not fluoxetine decreased the average 24-hour T-hy. The neurolept ics chlorpromazine and haloperidol decreased the amplitude of the 24-h our T-hy rhythm. The fact that chronic antidepressant drugs, but not n euroleptic drugs, decrease T-hy is consistent with their different neu rotransmitter effects and clinical applications, and raises the possib ility that their antidepressant property might be related to their cap acity to decrease T-hy during sleep.