Synergistic effects of age and stress in a rodent model of stroke

Ageing and stress represent critical influences on stroke risk and outcome. These variables are intricately linked, as ageing is frequently associated with gradual dysregulation of the hypothalamic-pituitary-adrenal axis. This study determined the effects of stress on motor function in aged rats, and explored possible interactions of age and stress on motor recovery following stroke in a rat model. Young adult (4 months) and aged (18 months) male Wistar rats were tested in skilled and non-skilled movement before and after focal ischemia in motor cortex. One group of each age received restraint stress starting seven days pre-lesion until three weeks post-lesion. Aged rats were less mobile and stress further diminished their overall exploratory activity. Aged rats were also less proficient in motor skill acquisition and slower to improve after lesion. Stress diminished post-lesion improvement and prevented recovery of endpoint measures. The larger functional loss in aged rats vs. young rats was accompanied by greater damage of cortical tissue and persistent elevations in corticosterone levels. The behavioural and physiological measures suggest limited ability of aged animals to adapt to chronic stress. These findings show that age or stress alone can modulate motor performance but may have greater influence by synergistically affecting stroke recovery.