Effect of morphine in combination with chlorpromazine and haloperiodol on operant behavior.

Using a discrete-trial avoidance-escape schedule in rats the interactions of morphine (M), chlorpromazine (C) and Haloperidol (H) were studied. All three drugs given alone or in combination disrupted operant behavior. At low doses C and H potentiated each other's effect, while at high doses antagonism could be observed. When combinations of M with C or H were tested, no antagonism or synergism was detected. Based on the statistical considerations used, it seems to be confirmed that the reflex inhibitory action of neuroleptics and M are mediated by independent receptor populations.