Different radiant heat intensities differentiate intracerebroventricular morphine- from beta-endorphin-induced inhibition of the tail-flick response in the mouse.
The antinociceptive effects of morphine and beta-endorphin given intracerebroventricularly (i.c.v.) or intrathecally (i.t.) were evaluated by inhibition of the tail-flick and hot-plate paw-licking responses evoked by three different intensities of heat stimulation (low, intermediate and high) in male ICR mice. Morphine given i.c.v. was more potent in inhibiting the tail-flick response evoked by low than high intensity of heat stimulus. beta-Endorphin given i.c.v., on the other hand, was equally potent in inhibiting the tail-flick response evoked by different intensities of heat. This differential effect of morphine and beta-endorphin was not shown when morphine and beta-endorphin were given i.t. Morphine and beta-endorphin given i.c.v. or i.t. were equally potent in inhibiting the paw-licking response at different intensities of hot-plate temperature. Our results suggest that morphine given i.c.v. may inhibit high intensity heat-evoked tail-flick response spinally and inhibits low intensity heat-evoked tail-flick response supraspinally. Our results also provide additional evidence for different neural mechanisms of antinociceptive action of morphine and beta-endorphin.
Suh
H H
HH
Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee 53226.
Fujimoto
J M
JM
Tseng
L F
LF
D000698:Analgesia; D000818:Animals; D006358:Hot Temperature; D007276:Injections, Intraventricular; D007278:Injections, Spinal; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009020:Morphine / Q000494:pharmacology*; D009619:Nociceptors / Q000187:drug effects; D010147:Pain Measurement / Q000187:drug effects* / Q000379:methods; D001615:beta-Endorphin / Q000494:pharmacology*
D001615:beta-Endorphin; D009020:Morphine