Elsevier

Brain Research

Volume 249, Issue 2, 14 October 1982, Pages 265-270
Brain Research

Opiate analgesia: Evidence for circadian rhythms in mice

https://doi.org/10.1016/0006-8993(82)90060-9Get rights and content

Abstract

The effects of a 12-12 h light-dark (L-D) cycle and of constant light (L-L) on nociceptive thresholds and morphine-induced analgesia were studied in two strains of mice: C57BL/6 and SEC/1Re.

Under the L-D condition, a diurnal rhythm was observed in the responsivity of mice to nociceptive stimuli, and in the analgesic effects of morphine. Under the L-L schedule clear patterns of daily rhythmicity were evident in both strains for both nociceptive thresholds and responsivity to morphine. Finally, under the L-L schedule, the overall responsivity to pain and the antinociceptive effects of morphine were clearly increased in comparison to the patterns evident in the L-D condition. The administration of naloxone decreased the nociceptive thresholds, thus indicating an involvement of the endogenous opioid peptides.

These phenomena are discussed in terms of the different pacemaker mechanisms involved in the expression of various patterns of daily behavioral and neurochemical rhythmicity in these strains, and of the effects of light in controlling the release of endogenous opioids.

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