Disruption of neuroendocrine stress responses to acute ferret odor by medial, but not central amygdala lesions in rats

Investigations of the neural pathways associated with responses to predators have implicated the medial amygdala (MeA) as an important region involved in defensive behaviors. To our knowledge, however, the involvement of the MeA in neuroendocrine responses to predator odor exposure has not been investigated. Therefore, the present study examined the effects of MeA disruption in rats exposed to ferret or control odor on hypothalamo-pituitary-adrenocortical (HPA) axis activation. Bilateral lesions of the MeA were made in Sprague–Dawley rats with the neurotoxin ibotenic acid (10 μg/μl; 0.3 μl / side). As a control for regional specificity, additional groups of rats were given lesions in the central amygdala (CeA). One week after recovery, the rats were exposed to ferret or strawberry control towels in small cages to examine HPA axis responses as determined by plasma corticosterone and adrenocorticotropin hormone (ACTH) levels. Rats with complete bilateral MeA but not CeA lesions displayed significantly less corticosterone and ACTH release compared to sham-operated control rats only in the ferret odor conditions. These results suggest that the MeA is an important structure involved in the HPA axis responses to predator odors, in support of previous studies investigating behavioral responses under similar conditions.