Independence of aversive and pain mechanisms in the dorsal periaqueductal gray matter of the rat.

Electrical stimulation of the dorsal periaqueductal gray (DPAG) elicits autonomic responses similar to those following peripheral pain stimulation. The present study analyzes the effects of morphine and midazolan applied to the same DPAG site on the autonomic responses induced by both types of stimulation. Both drugs attenuated the increase in heart rate and blood pressure induced by DPAG stimulation while attenuating only the increase in heart rate induced by pain stimulation. These results suggest that the neural substrates of the autonomic expression of the DPAG and pain stimulation are different although they may partially overlap.