Endogenous opioid system down-regulation during hibernation in amphibians.
In late summer, Northern grass frogs, Rana pipiens, intraspinally administered dynorphin produces a potent, dose-dependent antinociceptive action as measured by the acetic acid test used to evoke a hindlimb wiping response. Surprisingly, in fall, frogs which have entered hibernation, intraspinal dynorphin produces no antinociception action. Intraspinal morphine shows a decreased effect in fall frogs while systemic morphine is equi-effective in summer and fall frogs. Immobilization stress, previously shown to be mediated by endogenous opioid systems in this amphibian, produces a robust increase in nociceptive thresholds in summer frogs while the nociceptive thresholds of fall frogs are unaffected by this procedure. Summer frogs adapted to cold room (4 degrees C) show a significant decrease in nociceptive thresholds compared to cohorts kept at room temperature, and cold-adapted frogs returned to room temperature show a naloxone-attenuated increase in nociceptive threshold. Collectively, these data suggest that endogenous opioid systems in these northern frogs are down-regulated during fall hibernation.
Stevens
C W
CW
Department of Biological Sciences, University of Illinois, Chicago 60680.
Pezalla
P D
PD
D000818:Animals; D004399:Dynorphins / Q000494:pharmacology*; D004723:Endorphins / Q000378:metabolism* / Q000502:physiology; D006605:Hibernation; D007278:Injections, Spinal; D011894:Rana pipiens / Q000378:metabolism / Q000502:physiology*; D012149:Restraint, Physical; D012621:Seasons; D013312:Stress, Physiological / Q000378:metabolism* / Q000503:physiopathology
D004723:Endorphins; D004399:Dynorphins