[The role on the analgesia of entopeduncular nucleus]

L-glutamic acid, bicuculline (a GABA receptor antagonist), lidocaine and GABA were injected into entopeduncular and habenular nuclei respectively in rats. Pain threshold was measured by the latency of avoidance response (tail-flick) elicited by radiant heat exposure before and after intracerebral injection. Microinjection of different concentration of L-glutamic acid (25 nmol/L.0.5 microliter-1, 50 nmol/L.0.5 microliter-1, 100 nmol/L.0.5 microliter-1) into bilateral entopeduncular nuclei resulted in increases of pain threshold in a dose-dependent manner. Similar increase of pain threshold could also be observed by microinjection of 200 nmol/L GABA.0.5 microliter-1 into bilateral habenular nuclei. Both the effect of GABA and that of glutamate, could be antagonized by 0.2% bicuculline. The results mentioned above indicate that GABAergic fibers are involved in the analgesic effect of entopeduncular-habenular complex.