An appraisal of the role of corticotropin-releasing hormone at the amygdala in the mediation of the stress response: Application of in vivo microdialysis in the assessment of neuropeptide release.

Abstract

Accumulating research suggest that an organism's response to psychological stressors includes an element of cognitive processing that is partially mediated through a change in the neurochemical milieu at the central nucleus of the amygdala (CeA). In this respect, corticotropin-releasing hormone (CRH) at the CeA may integrate the autonomic and behavioral effector systems of the stress response. Likewise, there is mounting evidence that bombesin-like peptides (BN-LPs) may act independently of, or through CRHergic systems to influence the stress response. Unfortunately, much of our knowledge regarding the precise role of CRH and BN-LPs has been disadvantaged by technical limitations that do not afford the direct assessment of neuropeptide release/utilization. The initial experiments presented in this thesis demonstrate the feasibility of using a novel in vivo microdialysis approach combined with a highly sensitive radioimmunoassay to assess the release of CRH and BN-LPs in freely behaving animals. This research demonstrates that CRH and BN-LPs are released at the CeA in response to both aversive and appetitive stimuli, signifying that these peptides represent two of the neurochemical signals involved in assigning emotional salience to stimuli, regardless of its valence. These findings challenge the widely held view that CRH at the CeA orchestrates the behavioral changes associated with stressor exposure. Based on the context and time-course of peptide release, it is suggested that CRH at the CeA might serve to maintain vigilance, direct attention, sub-serve memory formation, or represent a mechanism through which brain systems are sensitized to subsequent stressor exposure.