Sex differences in tolerance to morphine antinociception in intra-nucleus accumbens administration of morphine in rat

Introduction: Sex differences in analgesic responses and tolerance to morphine under the systemic and injection in some nuclei of the brain have been reported, although the direction of these differences varies across studies. The purpose of the present study was to determine whether development tolerance to the analgesic effect of morphine differ between male and female in intra-nucleus accumbens administration of morphine in rat. Materials and methods: In order to induce tolerance, adult male and female rats were injected with morphine (2.5, 5, 10 and 50 μg/0.5 μL; intra-accumbal infusions) for 4 consecutive days during which, non-tolerant group received a single dose of morphine (saline for 3 consecutive days and morphine on 4th day) and control vehicle group received saline (4 consecutive days). On day 4, tail flick and hotplate test was done for pain evaluation in seperated groups. Comparisons between the groups were carried out using the Analysis of Variance (ANOVA), and post hoc Tukey's test. P<0.05 was considered to represent a significant difference. Results: The results of study revealed 4 things. 1) No significant morphine antinociceptive effect by tail flick test in both sexes, while the significant antinociceptive effect of morphine were observed in the hotplate test. 2) No significant sex differences were observed in hotplate test after acute morphine injection to animals. 3) Rats showed significantly tolerance to morphine analgesic effects under protocol by hotplate test. 4) Female rats showed significantly more tolerance to morphine analgesic effects than males by hotplate test. Conclusion: These data demonstrated that there were sex differences in tolerance to morphine antinociception in intra-nucleus accumbens administration that is dependent, in part, on the nociceptive test

کلیدواژه ها:

Sex differences ، Nucleus accumbens ، Antinociception ، Tolerance ، Morphine ، Rats