Chronic Social Isolation Stress and Crowding in Rats Have Different Effects on Learning an Operant Behavior and the State of the Hypothalamo-Hypophyseal-Adrenocortical System

Social stress is a widely experienced problem in the contemporary world; it is diverse and is determined by specific living conditions in both humans and animals. Isolation stress and crowding stress are chronic states which are actively and effectively modeled in rodents. The aim of the present work was to study the influences of these types of social stress in rats on the rate of learning to complete an operant food-procuring behavior alone and in cooperation with a conspecific. Blood corticosterone and ACTH levels were measured to assess the state of the stress-mediating hypothalamo-hypophyseal-adrenocortical system (HHACS); neurotrophins and proinflammatory cytokines were also estimated. Isolation stress, in contrast to crowding, decreased learning effectiveness – formation of a new skill – in both individual and cooperative behavior. No increases in HHACS functioning were seen in stressed animals of either group. Furthermore, animals in crowded conditions showed significant reductions in corticosterone and increases in the proinflammatory cytokine IL-1β. These results suggest that the mechanisms of action of chronic isolation and crowding stress are different both at the level of the stress-mediating system of the body and at the level of their influences on integrative brain activity. © 2022, Springer Nature Switzerland AG.