Effects of acute and chronic stress on behavioral defensive responses

Abstract

The concept of stress is based on the observation that any environmental change, either external or internal, can disturb the maintenance of homeostasis/allostasis, causing a series of physiological alterations, the so-called "general adaptation syndrome". The purpose of the stress reaction is to maintain homeostasis/allostasis, which includes physiological reactions such as endocrine activation (in particular of the hypothalamo-pituitary-adrenal - HPA axis) and visceral changes, which per se, do not produce pathological consequences. Nevertheless, when the stimulation is prolonged or sustained, exceeding the body's capacity to maintain homeostasis, stress can have pathological sequelae. The purpose of the present study is to investigate if and how an acute stressor (restriction) and a chronic stressor (chronic unpredictable mild stress, CUMS) alter behavior of animals tested in the elevated T-maze model of anxiety. Male Wistar rats will be submitted to an acute stressor (30 min of restriction) or to CUMS for 14 days and subsequentelly (1 h later for the acute stressor and 24 h later for CUMS) exposed to the elevated T-maze, for avoidance and escape measurements. In terms of psychopathology, these responses have been related to generalized anxiety and panic, respectively. Corticosterone levels will always be measured after stress exposure and behavioral measurements. Additionally, to investigate the effects of stress on motricity, animals will also be tested in an open field immediately after T-maze exposure. At last, the study will also investigate the effects of stress on brain structures implicated with defense through the use of immunohistochemical and molecular biology analysis (c-fos expression and in situ hybridization of CRF mRNA). (AU)