DORSOLATERAL PERIAQUEDUCTAL GRAY LESIONS ELIMINATE SHOCK-INDUCED HYPERALGESIA IN RATS. S. McLemore*, E. D. Crown, J. W. Grau, M. W. Meagher. Dept. of Psychology, Texas A&M University, College Station, TX 77843.
Exposure to a few moderately intense (1-mA) tailshocks has been shown to lower vocalization thresholds to both heat and subsequent shock, and facilitates the acquisition of conditioned fear (measured by freezing) when training is conducted in a different context. These observations have been taken as evidence that shock exposure induces a general state of hyperalgesia.
The present study explored whether this shock-induced hyperalgesia depends on neurons within the dorsolateral periaqueductal gray (dlPAG). Rats received either rostral dlPAG lesions, caudal dlPAG lesions, or sham operations. Two weeks later, they were placed in restraining tubes and half of the rats in each condition received three 1-mA (0.75-s) tailshocks while the other half received an equivalent period of restraint. Experiment 1 showed that tailshock lowered vocalization thresholds to heat in sham operated, but not lesioned subjects. Experiment 2 examined the impact of dlPAG lesions on the acquisition of conditioned fear. Sham operated rats demonstrated enhanced acquisition after shock exposure, while both rostral and caudal lesions eliminated this effect. Taken together, these results suggest that the dlPAG plays a critical role in the production of shock-induced hyperalgesia. Supported by MH54557 to J. W. G. and M. W. M.
Society for Neuroscience Abstracts, 24 (1998), 1901.