We propose to continue our investigations into the neural mechanism of pain perception and analgesia in the rat. We will also continue studies related to the role of endorphins in mechanisms of epilepsy and reward and will initiate an investigation of a model of chronic pain in this species. A major objective of our work is to dissect the brain stem pain inhibitory system into its functional and structural component parts by examining which brain regions, when electrically stimulated, mediate an opiate-like analgesia, which ones mediate effects involving descending monoaminergic paths, and which ones may be endogenously involved in the phenomenon of stress-induced pain inhibition. Anatomical methods aimed at disclosing especially descending paths within this system will also be employed. Other proposed studies will employ a method of autoradiography to examine the natural circumstances which lead to endorphin release and the types of opiate receptors involved. Still others will apply pharmacological tools to investigate the nature of opiate seizures and reward. The dorsal rhizotomy model of chronic pain will be studied in an attempt to learn more about the quality of the sensations which are associated with this phenomenon, including a comparison with experimentally induced itch. We hope that advances in these areas will elucidate the basic neural and neurochemical processes which underlie pain perception and that the progress we make will prove significant as well in relation to human pain disorders.