Chronic stress impairs learning and hippocampal cell proliferation in senescence-accelerated prone mice.

Chronic stress can induce cognitive impairment. It is unclear whether a higher susceptibility to chronic stress is associated with the progression of pathological brain aging. Senescence-accelerated prone mouse 8 (SAMP8) is a naturally occurring animal model of accelerated brain aging. Senescence-accelerated resistant mouse 1 (SAMR1) is usually used as the normal control. In this study, we examined the effects of chronic restraint stress (CRS) on learning in the Y-maze, hippocampal cell proliferation, and the expression of brain-derived neurotrophic factor (BDNF) in the hippocampus of 4-month-old SAMP8 and SAMR1. The results showed that exposure to CRS impaired learning and hippocampal cell proliferation in SAMP8 and SAMR1 but to a much greater extent in SAMP8. Furthermore, CRS significantly decreased the expression of BDNF protein and mRNA in the hippocampus of SAMP8 and SAMR1. These data indicated that SAMP8 is more sensitive to the deleterious effects of CRS on learning than SAMR1. A greater decrease in hippocampal cell proliferation caused by chronic stress may be part of the underlying mechanism for the more severe learning deficit observed in SAMP8. In addition, our findings suggested a role of BDNF in the stress-induced impairment of learning and hippocampal cell proliferation in both strains.