Contrasting roles of 5-hydroxytryptamine and noradrenaline in fever in rats.

1. We have investigated the effects of endogenous monoamine depletion on the development of fever in rats. 2. Fever was produced in rats by a single intraperitoneal injection of Salmonella typhosa endotoxin or leucocyte pyrogen manufactured from ox blood. 3. Depletion of brain 5-hydroxytryptamine (5-HT) by pretreatment with p-chlorophenylalanine prevented the rise in rectal temperature produced both by bacterial endotoxin and by leucocyte pyrogen. 4. On the other hand depletion of noradrenaline (NA) by 6-hydroxydopamine pretreatment resulted in a potentiation of the fever produced by bacterial endotoxin. 5. These results suggest that 5-HT is involved in mechanisms responsible for the rise in temperature during fever and that NA is involved in mechanisms which serve to attenuate the rise.