A dissociation between temperature regulation and fever in the rabbit.

1. The role of 5‐hydroxytryptamine (5‐HT) in temperature regulation and in fever in the rabbit has been investigated. 2. Intrahypothalamic microinjections of 5‐HT in the conscious rabbit alters body temperature in a dose‐dependent manner. 3. Low doses (5‐5nmol) of 5‐Ht and control saline injections produced a small, non‐significant increase in temperature, with a long latency. 4. Doses of 14 nmol 5‐HT produce a hyperthermia with a 45 min delay; while microinjections of 28 nmol result in a biphasic response; an initial short hypothermia is followed later by a hyperthermia. 5. Depleting the rabbit's brain of 5‐HT by pretreatment with p‐chlorophenylalanine (PCPA) fails to affect its body temperature at thermoneutral temperatures but significantly impairs the ability to thermoregulate against a cold stress. 6. PCPA pretreatment did not, however, impair the febrile response to bacterial pyrogen and prostaglandin E1. 7. These results reveal a dissociation between the effects of 5‐HT depletion on temperature regulation, and on fever. The site of action of 5‐HT in temperature regulation must be proximal to the fever input, but distal to the convengence of peripheral and hypothalamic temperature inputs.