J. Neural Transmission52, 55--60 (1981) dotovlo/or by Springer-Verlag 1981 The Role of Consciousness in Stress-Induced Analgesia T. S. Jensen and D. F. Smith Department of Neurology,Aarhus UniversityHospital,Aarhus, and Psycho- pharmacologyResearchUnit PsychiatricHospital, Risskov,Denmark Received February 16, 1981 Summary Male rats received unavoidable footshock administered while either awake or under Halothane| anaesthesia. Tail-flick threshold was measured subsequently in awake rats. An elevation in pain threshold indicative of stress-induced analgesia (SIA) appeared in rats shocked while awake, but not in those shocked while anaesthetized. The findings suggest that conscious processes are necessary for the occurrence of SIA. Introduction Stress-induced analgesia (SIA) refers to the prompt, short-lasting reduction in pain sensitivity observed in animals subjected to certain types of stress (Madden, Akil, Patrick, and Barchas, 1977; Hayes, Bennett, Newlon, and Mayer, 1978; Bodnar, Kelly, and Glusman, 1978; Amir and Amit, 1978). SIA is considered to involve the release of endogenous opiate-like peptides under the control of supraspinal mechanisms (Madden, Akil, Patrick, and Barchas, 1977; Chance, White, Krynock, and Rosecrans, 1978; Lewis, Cannon, and Liebes- kind, 1980). While previous studies show SIA to depend on neuronal mechanisms originating in the brain (Hayes, Bennett, Newlon, and Mayer, 1978; Hayes, Price, Bennett, Wilcox, and Mayer, 1978; Millan, Przewlocki, and Herz, 1980), the role of consciousness in these processes remains to be elucidated. Therefore, the present study was carried out to determine whether consciousness is required for the occurrence of SIA in rats. 0300-9564/81/0052/0055/$ 01.20