Effects of cold acclimation and central opioid processes on thermoregulation in rats.
Two experiments, using centrally administered [D-Ala2-MePhe4-Gly(ol)5]enkephalin (DAMGO), a selective mu-opioid agonist, assessed the thermoregulatory consequences of cold acclimation. Experiment 1 assessed whether cold acclimation influenced DAMGO hyperthermia at room temperature. Sialo-adenectomized rats were implanted with ICV cannulae and IP Mini-Mitters. After 3 weeks of exposure to 5 degrees C (cold acclimation) or 22 degrees C (non-cold acclimation) rats were pretreated with IP naltrexone HCl (2 mg/kg b.wt.) or vehicle (0.15 M saline) and later administered a 5-microliters ICV injection of 0.15 M saline, 0.1, or 1.0 microgram DAMGO. Cold acclimation exerted little effect on core temperature but potentiated DAMGO hyperthermia in a dose-dependent, naltrexone-reversible, activity-independent manner. Experiment 2 assessed the effect these same manipulations exerted on operant escape from a convective source of mild heat (37 degrees C). Duration of heat escape increased with cold acclimation in a naltrexone-resistant manner, yet was not influenced by DAMGO in either non-cold-acclimated or cold-acclimated rats. These findings suggest that two central adaptations occur with cold acclimation: A non-mu-opioid process that increases heat sensitivity and a mu-opioid process that potentiates hyperthermia but fails to alter heat escape due to mu-opioid-mediated analgesia.
Wilson
J R
JR
Department of Psychology, University of Manitoba, Winnipeg, Canada.
Howard
B A
BA
D000064:Acclimatization / Q000502:physiology*; D000700:Analgesics / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001831:Body Temperature / Q000187:drug effects / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D003080:Cold Temperature; D003216:Conditioning, Operant / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004745:Enkephalins / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D006120:Grooming / Q000187:drug effects; D007276:Injections, Intraventricular; D008297:Male; D009043:Motor Activity / Q000502:physiology; D009271:Naltrexone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000037:antagonists & inhibitors / Q000187:drug effects*; D012469:Salivary Glands / Q000502:physiology; D013686:Telemetry
D000700:Analgesics; D004745:Enkephalins; D009292:Narcotic Antagonists; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009271:Naltrexone