The role the hypothalamic defensive circuit and its main ascending targets on residual fear responses of animals bearing PAGDL lesions during predator exposure

Abstract

The periaqueductal gray, in particular its dorsolateral part (PAGdl) is known to be critically involved in the organization of innate and contextual fear responses to predatory threats. However, recent findings from our group has shown that PAGdl-lesioned animals exposed to a live predator showed clear fear responses, avoiding the predator and presenting a pattern of cautious exploration in the environment. Thus, suggesting the existence of residual fear responses in PAGdl-lesioned animals. Considering the central role the medial hypothalamic defensive circuit (formed by the anterior hypothalamic nucleus, dorsomedial part of the ventromedial nucleus and the dorsal premammillary nucleus) in processing predatory threats, in the present investigation, we propose a study of the potential role of the medial hypothalamic circuit and its main ascending targets (i.e., the lateral septum and the anteromedial nucleus of the thalamus) in mediating this residual fear responses in PAGdl-ledioned animals. To this end, animals bearing bilateral NMDA lesion in the PAGdl will receive bilateral muscimol injections in the medial hypothalamic circuit or its main ascending targets (i.e., the lateral septum or the anteromedial nucleus of the thalamus) to see how they affect fear responses during cat exposure. The major goal of this project is to unravel new paths potentially involved in mediating innate fear responses. (AU)