Lesions of the periaqueductal gray disrupt input to the rostral ventromedial medulla following microinjections of morphine into the medial or basolateral nuclei of the amygdala.

Microinjections of morphine into the basolateral (BLa) and medial (MEa) nuclei of the amygdala differentially affect rostral ventromedial medulla (RVM) neuronal activity and nocifensive behaviors. PAG lesions attenuated or blocked the effects of both BLa and MEa morphine on RVM cell activity, and interfered with the behavioral antinociception produced by BLa infusions. These results demonstrate that the influences from both the BLa and MEa to the RVM are relayed via the PAG.