Effects of site-specific electrolytic and neurotoxic lesions on defensive responding in rodents

Abstract

The use of predator-related stimuli, such as cat fur/skin odors, has proven to be useful in eliciting defensive responses in both wild and laboratory rodents. These behaviors, including freezing, flight and risk assessment are innate responses and thus require no prior learning. While traditional approaches have focused on the role of the amygdala as a key structure responsible for these behaviors, more recent theories are beginning to shed light on a neural network involving many distinct forebrain, midbrain and hindbrain areas in the elicitation of defensive responses. One theory that has been gaining experimental support is one that involves the medial hypothalamic zone, consisting of the anterior, dorsomedial portion of the ventromedial and the dorsal premammillary nucleus. Tract tracing studies have shown that these three areas are highly interconnected and have numerous afferent and efferent projections to a variety of neural structures. One of these involves the vomeronasal pathway, a circuit consisting of the amygdala and the bed nucleus of the stria terminalis. While these structures have been hypothesized to playa role in defense, there is currently a dearth of studies that have directly manipulated specific structures within this system to examine its role in defensive behaviors. The aim of the present series of studies is to systematically examine key structures along this neural pathway by conducting site-specific lesions and exposing subjects to varying levels on predator threat stimuli, including cat fur/skin odors as well as a live cat.