title: A comparison of antinociception induced by foot shock and morphine.
abstract: We compared the antinociception produced by brief intermittent foot shock (0.8-1.0 mA for 20 sec) and morphine by measuring the peak and duration of the effect, the consequences of spinalectomy and the sensitivity to antagonism by naloxone and d- and l-pentazocine and cyclazocine. Foot shock produced a peak antinociception (FSIA) equal to 10 mg/kg of morphine but the duration of FSIA was much shorter. Naloxone antagonized FSIA but a much larger dose (10 mg/kg) was required than for antagonism of morphine. The d-isomers of pentazocine and cyclazocine reduced FSIA but had no effect on morphine antinociception, whereas the l-isomers increased the peak and duration of FSIA and antagonized morphine-induced antinociception. Spinalectomy, which is known to block morphine antinociception, also blocks FSIA. Foot-shock stress did not produce an increase in tail-flick latency in morphine or methadone-tolerant animals demonstrating cross-tolerance between FSIA and morphine and methadone. The similarities between FSIA and morphine-induced antinociception suggest that similar opioid systems may be involved in both. However, the differences suggest that antinociception produced by brief FSIA involves a nonopiate as well as an opiate mechanism, perhaps with multiple opioid receptor sites having different affinities for the isomers of the antagonists.
mesh_terms: D000818:Animals; D003496:Cyclazocine / Q000494:pharmacology; D004597:Electroshock; D005528:Foot; D008297:Male; D008691:Methadone / Q000494:pharmacology; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology*; D010146:Pain / Q000503:physiopathology*; D010423:Pentazocine / Q000494:pharmacology; D010465:Perception / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology; D013997:Time Factors
chemical_list: D011957:Receptors, Opioid; D009270:Naloxone; D009020:Morphine; D003496:Cyclazocine; D010423:Pentazocine; D008691:Methadone