The physiology of opiate hedonic effects and the role of opioids in motivated behavior.

The topics discussed in this article are the neural mechanisms of opiate hedonic effects and the role of endogenous opioids in regulating motivational-affective responses of the organism. First, research on the mechanisms of opiate hedonic effects is briefly reviewed; evidence is discussed which suggests the existence of separate neural substrates for the mediation of opiate analgesia, amelioration of aversive emotion, and reward. In the remainder of the article, recent work of our laboratory is summarized which concerns the role of endogenous opioids in regulating feeding and reward elicited by electrical stimulation in the lateral hypothalamus; evidence is presented which indicates that opioid activity associated with the state of food motivation potentiates reward processes. In addition, evidence is discussed which suggests that this opioid activity may concurrently diminish the organism's emotional responsiveness to competing aversive stimuli. The relevance of this area of research to human opiate abuse is discussed.