The role of the amygdala in controlling acute stress, and adaptation to repeated stress

• Main Author: Carter, Roderick Nicholas
• Published: University of Cambridge 2004
• Subjects: 612.8
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597337

The experiments described in this thesis sought to test two putative functions of the amygdala. The first set of experiments was aimed at asking whether small and large amygdala lesions are capable of blocking responses to acute unconditioned stress. The second set of experiments sought to determine what role the amygdala may play in adapting to stress. The bulk of previous literature on the amygdala show its role in gaining emotional responses to situations. A role in adaptation to stress would require the amygdala to be able to drive less and less response to a repeated stimulus over time. In order to model stress in the laboratory, restraint stress of Lister Hooded rats was employed in these studies. Stress was measured experimentally by a variety of measures. Plasma levels of the stress hormone corticosterone was measured by radio-immuno-assay. Expression of <i>c-fos </i>mRNA measured by in situ hybridisation was used as a non-specific marker of neuronal activation in the brain. Expression of corticotropin releasing hormone (CRH) and arginine vasopressin (AVP), peptides critical in controlling corticosterone secretion and known to be modulated by stress, were measured in the paraventricular hypothalamic nucleus (PVN) also by <i>in situ </i>hybridisation. Telemetry was used to measure heart rate an indicator of the autonomic response to stress. Two types of lesion were studied, neurotoxic lesions of the central nucleus of the amygdala (CeA), and neurotoxic lesions of the entire amygdaloid complex including the central nucleus, lateral, basolateral, basomedial, medial and cortical nuclei (AMY). In all experiments, lesioned animals were compared with sham operated animals. Lesions were assessed as to their affect on acute stress, and also on adaptation to repeated stress.