Antidepressant drug-induced hypothalamic cooling in Syrian hamsters

Antidepressant drugs have been reported to alter the circadian pattern of body temperature, but specific effects on the amplitude or on average body temperature are not consistent, and there have been no specific studies to examine chronic drug effects on brain temperature. To address these issues, hypothalamic temperature (Thy) was monitored telemetrically in hamsters treated with three antidepressant drugs: the monoamine oxidase inhibitor (MAOI), clorgyline; the 5HT reuptake inhibitor, fluoxetine; and the alkali metal, lithium. For comparison, hamsters were also treated with two neuroleptic drugs, chlorpromazine and haloperidol. Each of the three antidepressant drugs, but neither of the neuroleptic drugs, produced a chronic decrease in diurnal (rest-phase) hypothalamic temperature. The Thy-decreasing effect of clorgyline was not prevented by pinealectomy, and Thy decreased more than peritoneal temperature (Tp), thus reducing the temperature difference between the hypothalamus and the peritoneal cavity. Less general effects of the antidepressants were also observed. Clorgyline and fluoxetine, but not lithium, delayed the 24-hour rhythm of Thy. Clorgyline and lithium, but not fluoxetine decreased the average 24-hour Thy. The neuroleptics chlorpromazine and haloperidol decreased the amplitude of the 24-hour Thy rhythm. The fact that chronic antidepressant drugs, but not neuroleptic drugs, decrease Thy is consistent with their different neurotransmitter effects and clinical applications, and raises the possibility that their antidepressant property might be related to their capacity to decrease Thy during sleep.