Motherhood mitigates aging-related decrements in learning and memory and positively affects brain aging in the rat

The current work examined spatial learning and memory (i.e., latencies to find a baited food well) in age-matched nulliparous, primiparous and multiparous (NULL, PRIM and MULT, zero, one or two pregnancies and lactations, respectively). We tested at 6, 12, 18 and 24 months of age in a dry land version of the Morris water maze (Main task), and at 12, 18 and 24 months in the same task in which the original location of the baited well was changed (Reversal task). We show that PRIM/MULT rats, compared to the age-matched NULL females, learned the spatial tasks significantly better and exhibited attenuated memory decline, up to 24 months of age. Furthermore, at the conclusion of behavioral testing, we investigated levels of these animals' hippocampal (CA1 and dentate gyrus) immunoreactive amyloid precursor protein (APP), a marker of neurodegeneration and age-related cognitive loss. MULTs had significantly reduced APP in both CA1 and DG, relative to PRIMs and NULLs, and PRIMs had a trend (p < 0.06) toward a reduction in APP compared to NULLs in DG. Further, level of APP was negatively correlated with performance in the two tasks (viz., more APP, worse maze performance). Reproduction, therefore, with its attendant natural endocrine and postpartum sensory experiences, may facilitate lifelong learning and memory, and may mitigate markers of neural aging, in the rat. Combining natural hormonal exposure with subsequent substantial experience with stimuli from the offspring may preserve the aged parous female brain relative to that of NULL females.