The effect of exercise on spatial learning and hippocampal proteins in maternally separated adult rats

Includes bibliographical references.Repeated maternal separation (MS) has been reported to induce changes in hypothalamic-pituitary- adrenal (HPA) axis activity leading to abnormal stress responses later in life. Such alterations have also been linked to poor cognitive function. In contrast, exercise enhances cognitive function. Previously, we reported that MS improved object location memory. However, exercise had no effect on object location memory despite increases in levels of synaptophysin and phospho-extracellular signal-regulated protein kinase (pERK) in the hippocampus of non-separated-exercised rats. In the current study, the same MS technique and three-week voluntary exercise regimen were tested to determine their effect on spatial learning in young adult Sprague-Dawley (SD) rats. A total of 144 rats were either maternally separated from postnatal day 2 to 14 or designated as controls. At postnatal day 50, rats were transferred to cages with attached running wheels. Approximately half of the rats were allowed to exercise voluntarily in the wheels whilst the wheels attached to the cages of the remaining non-exercising rats were immobilised. Rats were divided into 3 cohorts. Cohort 1 provided baseline levels of pERK, mitogen-activated protein kinase phosphatase-1 (MKP-1) and brain derived neurotrophic factor (BDNF) after exercise. Cohorts 2 and 3 were trained in the Morris Water Maze (MWM) 1 and 15 days post-exercise, respectively. Consistent with our previous findings, pERK was increased in non-separated-exercised rats post-exercise. MKP-1, the regulator of pERK, was also increased in the non-separated-exercised group. BDNF was decreased in the MS non-exercised group but augmented by exercise. All groups trained immediately after exercise performed similarly in the MWM but MS rats from cohort 3 had better reversal spatial memory. According to these results, repeated MS decreased neurotrophic factors but did not alter the plasticity-related proteins measured in this study. However, this phenomenon was not associated with performance in the spatial learning and memory task in the MWM. These current observations support our previous findings that MS can cause adaptations that lead to improved learning and memory in adulthood