Effects of intrathecal capsaicin on autonomic and behavioral heat loss responses in the rat.
Capsaicin and Tween 80 were injected into the lumbar subarachnoid space of rats via a chronic cannula, and the thermoregulatory effects compared. The rats were placed in a climatic chamber at an ambient temperature (Ta) of 20 and 30 degrees C. In the first series of experiments the rats had no access to the fan lever. Intrathecal (IT) capsaicin injection produced a fall in rectal temperature, with a rise in cutaneous temperatures due to vasodilation. On the contrary, IT or the intraperitoneal (IP) Tween 80 injection route had no effect on body temperature. In addition capsaicin-administered IP induced a fall in spinal cord temperature (Tsp). In the second series of experiments the rats had access to a lever activating a fan that drew cool outside air into the climatic chamber. After IT capsaicin injection, the rats increased bar-pressing behavior for fresh air. This was significant at both Ta 20 and 30 degrees C. The results tend to support the hypothesis of capsaicin action somewhere on the thermal afferent pathways. Furthermore, it is possible that the action of capsaicin on thermoregulatory behavior is mediated by the release of substance P from primary afferent terminals.
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C.N.R.S. Faculte de Medecine Lyon-Sud Universite Claude Bernard, Oullins, France.
D000818:Animals; D001341:Autonomic Nervous System / Q000187:drug effects*; D001522:Behavior, Animal / Q000187:drug effects*; D001831:Body Temperature / Q000187:drug effects; D001833:Body Temperature Regulation / Q000187:drug effects*; D002211:Capsaicin / Q000008:administration & dosage / Q000494:pharmacology*; D003216:Conditioning, Operant / Q000187:drug effects; D007274:Injections, Intraperitoneal; D007278:Injections, Spinal; D011136:Polysorbates / Q000008:administration & dosage / Q000494:pharmacology; D051381:Rats
D011136:Polysorbates; D002211:Capsaicin