Lesions of the dorsomedial amygdala, but not the nucleus accumbens, reduce the aversiveness of morphine withdrawal in rats.

Small lesions of the dorsomedial amygdala reduced the magnitude of the conditioned place aversion produced by naltrexone-precipitated morphine withdrawal, whereas large lesions of the ventral nucleus accumbens had no effect. This finding that the dorsomedial amygdala, which has not been implicated in opiate reward, is involved in mediating the aversiveness of opiate withdrawal is consistent with data indicating that amygdala lesions reduce the aversiveness of a variety of aversive events. In contrast, the nucleus accumbens, which is involved in mediating the rewarding effects of opiates, does not appear to be critically involved in mediating the aversive effects of opiate withdrawal. Together, these findings suggest that the neural structures that mediate the rewarding effects of opiates may be at least partially distinct from the structures that mediate the aversive effects of opiate withdrawal.