Physical exercise can reverse the deficit in fear memory induced by maternal deprivation

Maternal deprivation during the first 10 days of life induces significant behavioral alterations in rodents which persist through adulthood. Physical exercise reduces the cognitive deficits associated with pharmacologic and pathological conditions. Here we investigated whether forced physical exercise alters memory deficits caused by postnatal maternal deprivation. Male rats were divided into four groups: (1) control, (2) deprived, (3) exercised, and (4) deprived+exercised. In groups 2 and 4, pups were deprived from their mothers for 3h/day during the first 10 days post-birth. In groups 3 and 4, from postnatal day 45 (PND-45) on, animals were submitted to forced treadmill exercise. At adulthood, animals were submitted to four different behavioral tasks: open field, Morris water maze (MWM), object recognition (OR) and inhibitory avoidance (IA). Maternal deprivation had no effect on open field behavior, but disrupted memory in the three other tasks. Physical exercise alone had no effect, except for a slight enhancement of MWM learning. Importantly, physical exercise reversed the deficit of IA and reduced the deficit of spatial memory but not that of OR seen in deprived animals. It is possible that physical exercise may counteract the influence of maternal deprivation on neurohumoral or hormonal memory modulatory systems related to stress. Indeed, the decreasing order of the effect of exercise on the memory disturbances induced by deprivation roughly follows the descending degree of stress associated with each task (IA>MWM>OR). Maternal deprivation is known to hinder hormonal mechanisms involved in coping with stress.