Differential regulation of perineuronal nets in the brain and spinal cord with exercise training.

Perineuronal nets (PNNs) are lattice like structures which encapsulate the cell body and proximal dendrites of many neurons and are thought to be involved in regulating synaptic plasticity. It is believed that exercise can enhance the plasticity of the Central Nervous System (CNS) in healthy and dysfunctional states by shifting the balance between plasticity promoting and plasticity inhibiting factors in favor of the former. Recent work has focused on exercise effects on trophic factors but its effect on other plasticity regulators is poorly understood. In the present study we investigated how exercise regulates PNN expression in the lumbar spinal cord and areas of the brain associated with motor control and learning and memory. Adult, female Sprague-Dawley rats with free access to a running wheel for 6 weeks had significantly increased PNN expression in the spinal cord compared to sedentary rats (PNN thickness around motoneurons, exercise=15.75±0.63μm, sedentary=7.98±1.29μm, p<0.01). Conversely, in areas of the brain associated with learning and memory there was a significant reduction in perineuronal net expression (number of neurons with PNN in hippocampus CA1-exercise 21±0.56 and sedentary 24±0.34, p<0.01, thickness-exercised=2.37±0.13μm, sedentary=4.27±0.21μm; p<0.01). Our results suggest that in response to exercise, PNNs are differentially regulated in select regions of the CNS, with a general decreased expression in the brain and increased expression in the lumbar spinal cord. This differential expression may indicate different regulatory mechanisms associated with plasticity in the brain compared to the spinal cord.