Thermoregulation in the rabbit following intracranial injection of norepinephrine

The release of norepinephrine (NE) from nerve terminals in the anterior hypothalamic/preoptic area (AH/POA) of the rabbit may serve to raise body temperature. To further examine the putative neurotransmitter role of NE, bilateral microinjections of 5 or 10 mug NE were made into or near the AH/POA of 44 conscious rabbits exposed to an ambient temperature of 15 degrees C. Microinjections into the AH/POS did not cause fever; they either had no influence on thermoregulation or rapidly induced ear vasocilation and increased ear temperature accompanied by slight falls in rectal temperature. The latter averaged 0.32 degrees C (range: 0.16-0.45 degrees C) in 18 rabbits in which the effects were prominent. In contrast, the injection of 100 or 250 mug NE into the lateral cerebral ventricles of conscious rabbits in the 15 degrees C environment caused mean fevers of 0.62 +/- 0.0, and 1.04 +/- 0.14 degrees C (+/- SE, n equals 6), respectively, within 70 min. The febrile response to intraventricular injection of NE may be due to an action of the drug at a site other than the AH/POA. Alternatively, the response may depend critically on the particular distribution of NE that results from its diffusion from the third ventricle into the AH/POA.