Defensive freezing evoked by electrical stimulation of the periaqueductal gray: comparison between dorsolateral and ventrolateral regions

Previous reports indicated that ventrolateral periaqueductal gray (vIPAG) plays a role in the expression of freezing behavior whereas dorsolateral periaqueductal gray (dIPAG) is involved on both freezing and active forms of defensive behaviors. In order to evaluate the role of each of these areas in the occurrence of defensive reactions, rats were electrically stimulated either in the dIPAG or vIPAG with different stimulus frequencies. Stepwise increases in the electrical stimulation of both dIPAG or VIPAG induced initially freezing and then a jumping response. Freezing induced by vIPAG stimulation had a tendency to disappear when the stimulation was turned off whereas freezing induced by clIPAG stimulation remained high in the absence of the stimulation. These results suggest that dIPAG and vIPAG are involved on defensive freezing probably through different neural circuitries. NeuroReport 12:4109-4112 (C) 2001 Lippincott Williams & Wilkins.