Chronic immobilization stress alters aspects of emotionality and associative learning in the rat

Abstract

Chronic stress significantly alters limbic neuroarchitecture and function, and potentiates emotionality in rats. Chronic restraint stress (CRS) increases aggression among familiar rats, potentiates anxiety, and enhances fear conditioning. Chronic immobilization stress (CIS) induces anxiety behavior and dendritic hypertrophy in the basolateral amygdala, which persist beyond a recovery period. However, little else is known about the emotional impact of CIS as a model of chronic stress or depression. Therefore, the authors present two experiments examining emotional and learned responses to CIS. In Experiment I, the authors examine individual differences in behaviors during and after CIS, specifically: struggling, aggression, learned helplessness, inhibitory avoidance, and escape behavior. In Experiment II, the authors confirm the effects of CIS on aggression and struggling during immobilization, and correlate individual responses with aspects of conditioned fear. Here the authors report significant effects of CIS on aggression, inhibitory avoidance, escape, as well as learned aspects of fear (i.e., fear conditioning) and inescapable stress (i.e., struggling and helplessness). These results emphasize the emotional and learned responses to CIS evident during and after the stress treatment, as well as the importance of individual differences.