The effects of subchronic social and isolation stresses on learning and memory trend in male rats

Introduction: Psychological stresses influence brain functions such as learning and memory. Environmental factors like types and durations of stress affect brain responsiveness. This study investigated the effects of two subchronic social and isolation stresses on learning, memory, adrenal glands weight and corticosterone levels in the hippocampus and frontal cortex. Methods: Eighteen male rats were randomly allocated into three experimental groups: control, social stress and isolation stress groups. Rats were under stresses for 7 days. Latency of entrance into the dark room was evaluated as brain function, using the passive avoidance test before inducing of electrical shock (as initial latency) and on days 1, 3, 5 and 7 after foot shock. In addition, corticosterone levels were measured in the homogenized hippocampus and frontal cortex. Results: The latencies of days 1, 3 and 5 were significantly lower in an isolation stress group than the control group. The latency of day 7 significantly decreased in social and isolation stress groups, compared to the control group. The adrenal glands weight showed significant enhancements in social and isolation stress groups, compared to the control group. Although, the weight of the adrenal glands significantly increased in an isolation stress group, compared to the social stress group. There was a significant enhancement in the corticosterone levels in the hippocampus, but not frontal cortex in isolation stress group. Conclusion: It was concluded that subchronic isolation stress severely deteriorated brain functions (learning and memory) compared to the subchronic social stress. In addition, isolation stress affected corticosterone levels in the hippocampus more than frontal cortex.