Impact of dorsolateral periaqueductal gray lesions on shock-induced hyperalgesia

Abstract

Prior exposure to shock lowers vocalization thresholds to heat and facilitates the acquisition of conditioned fear when training is conducted in a different context. These observations have been taken as evidence that shock exposure increases the affective impact of subsequent aversive stimuli, a phenomenon known as hyperalgesia. The present study explores whether this hyperalgesia depends on neurons within the dorsolateral periaqueductal gray (dlPAG). Experiment 1 showed that lesioning either the rostral or caudal dlPAG prevented the shock-induced reduction in vocalization thresholds. Experiment 2 showed that lesioned subjects also failed to exhibit facilitated learning after shock exposure. Taken together, these results suggest that the dlPAG plays a critical role in the production of shock-induced hyperalgesia.