Influence of lisuride on morphine withdrawal signs in the rat: a dopamine-mimetic effect.

The influence of lisuride on naloxone-induced withdrawal signs (wet shakes, escape attempts) was studied in morphine-dependent rats. Lisuride, injected IP at doses of 12.5 and 25 micrograms/kg, inhibited wet shakes while not significantly altering escape attempts induced by naloxone (4 mg/kg IP). At higher doses (50 and 100 micrograms/kg IP), lisuride's inhibitory effect on wet shakes persisted while escape attempts were actually potentiated with respect to control withdrawal rats. Increases in aggressive behavior were seen at all doses, and were dose-related. Haloperidol (0.3 mg/kg IP), administered 40 min before lisuride, did not modify the antagonistic effect on wet shakes, unlike sulpiride (40 mg/kg IP 30 min before lisuride), but at the same time blocked the increase in escape attempts and aggressiveness induced by lisuride. We suggest that lisuride modulates withdrawal signs by stimulation of dopamine receptors in the CNS. The effect of the dopamine mimetic N-n-propylnorapomorphine (NPA) on the same variables is reported as well as the influence of haloperidol on NPA, and a comparison between the effects of the two drugs is made.