The effects of the medial and cortical amygdala lesions on post-stress analgesia in rats.

The role of the medial, and cortical nuclei of amygdala was studied in 54 Möll-Wistar rats under two modes of foot-shock analgesia. In all but control animals bilateral electrolytic lesions were performed. Pre- and post-stress pain reactivity were measured in the hot-plate and the tail-flick tests. The damage of the medial nucleus decreases animals' primordial pain reactivity. Four minutes of continuous foot-shock produced post-stress analgesia in all control and lesioned rats, but 20 min of regularly intermittent foot-shock failed to evoke analgesia in the lesioned rats, especially in subjects with the dorsal part of the medial nucleus injuries. The results indicate that the medial and cortical nuclei are important in regulation of the post-stress antinociceptive processes evoked only by prolonged intermittent shock action. It has been previously shown that the behaviour evoked by this stressor is related to opioid mechanisms, and modulated by the hypothalamic-pituitary-adrenocortical system. Present finding is in agreement with our concept of the dorsomedial amygdala involvement in painful and stressful stimuli processing.