Reduction of oxotremorine-induced analgesia after chronic but not acute restraint stress.

The analgesic response (tail-flick latency) induced by the muscarinic cholinergic agonist oxotremorine was investigated in DBA/2 mice exposed to acute (a single 2 h session) and chronic (2 h once daily for 10 days) restraint stress. While a single exposure to stress did not influence the antinociceptive effects of the cholinergic agonist, chronic stress induced a clear-cut reduction of the oxotremorine-induced analgesia. The results show an involvement of cholinergic mechanisms in the adaptive modulation of nociception after chronic stressful events.