Analgesia induced by brief footshock: blockade by fenfluramine and 5-methoxy-N,N-dimethyltryptamine and prevention of blockade by 5-HT antagonists.

Analgesia induced by footshock (2 mA, 30 s) is decreased by the 5-HT releaser, fenfluramine, and the rapidly acting 5-HT agonist, 5-methoxy-N,N-dimethyltryptamine (5-MeODMT). These decreases are blocked by the 5-HT antagonists, cyproheptadine and methiothepin. However, the antagonists when given alone do not influence shock-induced analgesia. Therefore, analgesia induced by brief footshock in the absence of drugs may not involve 5-HT-dependent mechanisms even though it may be influenced by pharmacologically provoked changes of 5-HT release or by 5-MeODMT. This drug was also able to attenuate the analgesia after its induction, possibly reflecting a disruption of memory processes rather than of nociceptive mechanisms per se.