Fos-like immunoreactivity in the periaqueductal gray of rats exposed to a natural predator

IN the present study we examined, in rats exposed to a predator (cat), the distribution of neurons expressing Fos along the continuum formed by the ce ntral gray surrounding the caudal pole of the third ventricle and the peria queductal gray (PAG). After the predatory encounter, a distinct cluster of Fos-immunoreactive cells was observed in the precommissural nucleus. In the rostral two-thirds of the FAG, Fos expression was mostly seen in the dorso medial and dorsolateral regions. In contrast, at caudal levels of the FAG, most of the Fos-labelled neurons were distributed in the lateral and ventro lateral FAG. These results are discussed and compared with the pattern of t he FAG activation after fear conditioned to a context or elicited by aversi ve foot shock. (C) 1999 Lippincott Williams & Wilkins.