BILATERAL LESIONS OF THE AMYGDALA ATTENUATE ANALGESIA INDUCED BY DIVERSE ENVIRONMENTAL CHALLENGES

This study was designed to evaluate the role of the amygdala, particul arly its central nucleus, in the induction of analgesia elicited by en vironmental challenges. Rats with large, radiofrequency lesions center ed in the central nucleus were found to display significantly attenuat ed analgesic responses to three different challenges: cat exposure, ac ute footshock, and re-exposure to an environment associated with foots hock. These findings show that the amygdala plays an important role in the elicitation of analgesia by each of the environmental challenges tested. Since the amygdala has been shown to play a critical role in f ear, these findings suggest that the analgesia elicited by these chall enges involves a substantial fear component. Moreover, the finding tha t amygdala lesions significantly reduced the analgesia elicited by a n on-noxious unconditional stimulus (cat exposure) strongly suggests tha t these lesions disrupt the expression of analgesia rather than produc ing a learning impairment. And finally, the findings of this study sup port the suggestion that fear-elicited analgesia is triggered by activ ation of a projection from amygdala to periaqueductal gray which forms one component of an integrated 'defensive behavioral system.'