Thermoregulatory effects of monoamine potentiators and inhibitors in the rat

Exogenously administered monoamines may elicit variable thermoregulatory responses dependent on dosage, species, site of administration, ambient temperature, etc. In an attempt to reconcile several inconsistencies, we have undertaken a series of studies related to monoaminergic control of temperature regulation. Thus, intraventricular administration of serotonin (2.64-26.4 mug) and norepinephrine (3.3-32.8 mug) in rats evoked acute (15-60 min) dose-dependent hypothermic responses (delta Tre = 2 degrees C) that were gradually superseded by significant, more persistent hyperthermia (delta Tre = 1 degreee C). Administration of chlorimipramine or imipramine (total dose 40 mug), even in monoamine-depleted animals, caused long-lasting hyperthermic responses, presumably by the prevention of reuptake of serotonin and norepinephrine at nerve terminals involved in thermoregulation. Pretreatment with the serotonin inhibitor cyproheptadine (4o mug) attenuated the hyperthermia achieved by central administration of chlorimipramine alone. We conclude that both monoamines can act as thermogenic agents under the conditions of these experiments.