Juvenile Stress: A Sensitive Period of Vulnerability on Hippocampal CA2 and Social Recognition Memory

Social memory is the ability to discriminate between two or more conspecifics. The hippocampal CA2 is essential for social memory; dysfunction leads to social memory impairments. Early life stress has been found to cause social memory impairments. We examined whether social memory impairments observed after juvenile stress were due to CA2 dysfunction. Long-Evans rats were exposed to juvenile stress during P19-21. Social memory was recorded in early adulthood (P60/P61). Tissue was collected to determine CA2 cFos expression using nickel-enhanced 3,3'-Diaminobenzidine (DAB) immunohistochemistry. Adults exposed to stress did not differ from controls in sociability. However, they displayed social memory deficits, with a greater deficit in females. We also determined that juvenile stress significantly decreased cFos-positive cell density within the CA2, exhibiting reduced neuronal activity. These findings indicate that the CA2 is vulnerable to stress during the juvenile period, with long-term effects that persist throughout adulthood.