THE IMPLICATION OF CENTRAL SEROTONIN IN ELECTRO-ACUPUNCTURE TOLE

Electro-acupuncture (EA) applied to both legs for 30min raised the tail flick latencyof the rat significantly. This effect of EA analgesia became attenuated and finally disap-peared after repeated EA stimulations, which was termed EA tolerance. EA tolerance and itscross tolerance to morphine analgesia were found to be partially reversed by intracerebro-ventricular injection of 5-hydroxytryptophan (5-HTP), the precursor of 5-hydroxytryptamine(5-HT). However, there was no depletion in cerebral 5-HT, nor was there decrease ofthe number of 5-HT receptors in the brain of the EA tolerant animals. Results obtainedfrom different lines of analysis point to the conclusion that development of tolerance toprofoundly released 5-HT during prolonged EA stimulation may constitute one of themechanisms for EA tolerance.