CHRONIC SOCIAL STRESSES OF ISOLATION AND CROWDING DIFFERENTLY AFFECT INSTRUMENTAL BEHAVIOR LEARNING AND THE HYPOTHALAMIC-PITUITARY-ADRENOCORTICAL SYSTEM IN RATS
Social stress is a widespread problem in the modern world; it is diverse and is determined by the specific features of the living conditions of both humans and animals. The chronic conditions vigorously and effectively modeled on adult rodents are isolation stress and crowding stress. The aim of this work was to study the effect of these types of social stress in rats on the rapidity of learning to perform the same instrumental food-obtaining behavior alone and in cooperation with a conspecific. Corticosterone and ACTH levels were determined in the blood of animals to assess the state of the stress-implementing hypothalamic-pituitary-adrenocortical system (HPACS), as well as neurotrophins and proinflammatory cytokines. Isolation stress, in contrast to crowding, caused a decrease in the effectiveness of learning (the formation of new experiences), both in individual and cooperative behavior. At the same time, there was no increase in the functioning of HPACS in stressed animals of both groups. Moreover, the level of corticosterone significantly decreased and the level of the pro-inflammatory cytokine IL-1beta increased in animals under crowded conditions. The results suggest that the mechanisms of action of chronic isolation and crowding stress are different both at the level of stress-implementing systems of the body, and at the level of their influence on the integrative function of the brain.