Abstract:

Objective To examine the potential roles of estrogen in rostral ventromedial medulla (RVM) on visceral nociception. Methods The visceromotor responses (VMR) evoked by repeated colorectal distention (CRD) were monitored in lightly anesthetized adult female rats. Various doses of estrogen or morphine were applied by microinjection into RVM or cerebellomedullary cistern, and the changes of VMR were observed. Results Local administration of estrogen in RVM (0.01-1 μmol/L, 0.5 μL) resulted in dose-dependent increments in VMR evoked by CRD, with <2 min for the latency of this effect. Moreover, estrogen (0.1-1 μmol/L, 50 μL）applied intracisternally dose-dependently blocked the analgesia induced by microinjection of morphine into RVM. Conclusion Estrogen acting in RVM may not only enhance VMR, but also antagonize the analgesic action of morphine.

Key words: estrogen, rostral ventromedial medulla, visceromotor response, visceral pain