Effects of brain monoamine depletions on thermoregulation in rabbits

Biochemical analyses revealed that 5,7-dihydroxytryptamine- (5,7-DHT) treated and 6-hydroxydopamine- (6-OHDA) treated rabbits, respectively, had a significant reduction in diencephalic 5-hydroxytryptamine (5-HT) and norepinephrine (NE) with minimal alterations in the other monoamines. Both 5,7-DHT-treated and 6-OHDA-treated animals, although showing the maintenance of normal body temperatures, did exhibit specific alterations in the thermoeffector outputs. The 5-HT-depleted animals displayed an increase in ear skin blood flow, respiratory heat loss, and metabolism at both ambient temperatures (Ta) of 22 and 2 degrees C. The NE-depleted animals displayed a decrease in metabolism at all levels of Ta tested. Also, the peripheral temperature threshold for the onset of heat loss responses were displaced to higher values than in control animals. In addition, the prostaglandin E1-induced fever was attenuated after the pretreatment of rabbits with either 5,7-DHT or 6-OHDA. The data indicate that brain levels of 5-HT and NE alter, in an apparently reciprocal fashion, the thermoregulatory responses of rabbits. Also, the integrity of 5-HT and NE pathways in brain is vital for the full functioning of a prostaglandin in producing a fever.