Involvement of opioid mechanisms in the dorsal periaqueductal gray in drug abuse.

Abstract

The opiate abstinence syndrome is comprised of motivational symptoms and physical correlates. In rats, physical correlates have been characterized as intense hyperactivity together with jumping, ptosis, teeth chattering, wet dog shakes, and diarrhea. Motivational symptoms have often been associated with the development of place aversions. The search for the neural substrates for the motivational symptoms and physical correlates of the opiate withdrawal syndrome has not reached a consensus as to the existence of a common or separate neural basis responsible for them. In our laboratory, we have gathered evidence that microinjection of morphine into the DPAG inhibits defensive behaviors. However, DPAG microinjections of high doses may produce a 'fearful' hyperactivity as measured in a circular arena or produce anxiogenic-like effects as measured in the elevated plus maze. The antiaversive effects of morphine result from its action on mu receptors and the aversive ones may be associated with its action on other opiate receptors. These findings implicate the PAG as an important structure of the neurobiological substrate of the emotional and physical correlates of the opiate abstinence syndrome.