Effect of maternal separation on mitochondrial function and role of exercise in a rat model of Parkinson's disease.

Early life stress, such as maternal separation, causes adaptive changes in neural mechanisms that have adverse effects on the neuroplasticity of the brain in adulthood. As a consequence, children who are exposed to stress during development may be predisposed to neurodegenerative disorders in adulthood. A possible mechanism for increased vulnerability to neurodegeneration may be dysfunctional mitochondria. Protection from neurotoxins, such as 6-hydroxydopamine (6-OHDA), has been observed following voluntary exercise. The mechanism of this neuroprotection is not understood and mitochondria may play a role. The purpose of this study was to determine the effects of maternal separation and exercise on mitochondrial function in a rat model of Parkinson's disease. Maternally separated (pups separated from the dam for 3 h per day from postnatal day (P) 2-14) and non-separated rats were placed in individual cages with or without attached running wheels for 1 week prior to unilateral infusion of 6-OHDA (5 μg/4 μl, 0.5 μl/min) into the left medial forebrain bundle at P60. After 2 h recovery, rats were returned to their cages and wheel revolutions recorded for a further 2 weeks. On P72, the rats' motor function was assessed using the forelimb akinesia test. On P74, rats were sacrificed for measurement of mitochondrial function. Exercise increased the respiratory control index (RCI) in the non-lesioned hemisphere of 6-OHDA-lesioned rats. This effect was evident in the striatum of non-separated rats and the prefrontal cortex of maternally separated rats. These results suggest that early life stress may reduce the adaptive response to exercise in the striatum, a major target of dopamine neurons, but not the prefrontal cortex in this model of Parkinson's disease.