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At least 1,405 records · Page 78Linked to original sources
PubMed1988

Influence of narcotic antagonist drugs upon nitrous oxide analgesia in mice.

Nitrous oxide produced a concentration-related suppression of phenylquinone-induced abdominal constriction in mice. This analgesic effect was significantly reduced (but not abolished) by systemic pretreatment with (-)-naloxone or naltrexone but not (+)-naloxone. Systemic pretreatment with methylnaltrexone failed to appreciably influence nitrous oxide analgesia; however, methylnatrexone, administered centrally, significantly attenuated the drug effect. Furthermore, nitrous oxide analgesia was significantly reduced by MR-2266 (which is relatively selective for kappa-opioid receptors) but not by beta-funaltrexamine (which is selective for mu-opioid receptors) at the doses employed in this study. These findings suggest that nitrous oxide analgesia might involve an activation of kappa-opioid receptors in the central nervous system; however, a possible involvement of mu-opioid receptors is not absolutely precluded by this study.

Analgesia↗
PubMed1978

Lack of blockade of central dopaminergic receptors by narcotics: comparison with chlorpromazine.

d-Amphetamine and saline were used as discriminative stimuli in rats. After 0.6 mg/kg d-amphetamine administration, food reinforcement was contingent upon pressin 1 lever in 2-lever operant chamber. Responding on the other lever was reinforced only after saline injection of equal volume. The animals learned to discriminate between d-amphetamine and saline to a criterion of 85% correct. Administration of 2.5, 5.0 and 7.5 mg/kg morphine, and 0.02 and 0.04 mg/kg fentanyl produced saline-appropriate responses. Pretreatment with morphine and fentanyl had no significant effect on the d-amphetamine induced discriminative stimulus. In contrast, 1.25 and 2.5 mg/kg chlorpromazine antagonized d-amphetamine discrimination. These results indicate that despite their similar effect on brain dopamine turnover, morphine and fentanyl do not act on the same receptor site(s) as the neuroleptics, that is, they probably do not block brain dopamine receptors.

Animals↗
PubMed1980

The effect of phenobarbitone pretreatment on the narcotic antagonistic potency of naloxone in mice.

Pretreatment with phenobarbitone (5.0-20.0 mg/kg, s.c.) did not alter the antinociceptive effect (tail-flick assay) of morphine measured 4.5 h later. However, naloxone was more potent in antagonising this antinociceptive effect in phenobarbitone-pretreated mice than in saline-retreated animals. Concomitant administration of naloxone in the pretreatment regime did not alter the effect of phenobarbitone. The enhanced naloxone potency was related to the amount of phenobarbitone given, and was observable at 3.0 and 4.5 h after pretreatment. It was no longer apparent at 6.0 h. Because of a difference in time course and in the ability of naloxone to block the phenomenon, it is suggested that the mechanisms underlying the increase in naloxone potency induced by phenobarbitone pretreatment and morphine pretreatment may not be the same.

Analgesics↗
PubMed1984

Narcotic discrimination in pigeons: antagonism by naltrexone.

In pigeons trained to discriminate between morphine (10 mg/kg) and saline, both morphine and ethylketazocine produced dose-related morphine-appropriate responding. The maximum effect produced by meperidine, however, was only 60% of that produced by morphine or ethylketazocine. Naltrexone (0.1-1.0 mg/kg) produced dose-related shifts to the right in the dose-response curves for the discriminative stimulus and rate-decreasing effects of morphine and ethylketazocine without affecting the response produced by meperidine. Thus, in contrast to the effects observed in other species, morphine and ethylketazocine produce similar discriminative effects in the pigeon. In addition, the morphine-like discriminative effects and the rate-decreasing effects of meperidine in the pigeon are not mediated by the naltrexone-sensitive mechanisms which mediate these effects of morphine or ethylketazocine.

Animals↗