Possible involvement of 5-hydroxytryptamine and cyclic-AMP in tolerance to tremorine analgesia in mice

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Abstract
The phenomenon of tolerance to the analgesic action of tremorine in mice was studied by the hot-plate and tail-clip methods. Reduction in 5-HT levels in brain by parachlorophenylalanine pretreatment decreased the ED50 of tremorine analgesia in tremorine tolerant mice. 5-Hydroxytryptophan, l-Dopa or α-methyl-para-tyrosine did not influence the analgesic response to tremorine in tremorine tolerant animals. However, theophylline was found to enhance the tolerance to tremorine analgesia. Brain 5-HT and cAMP are probably involved in tremorine tolerance, whereas neither noradrenaline nor dopamine is involved in the phenomenon.