Effects of exercise training on dendritic morphology in the cardiorespiratory and locomotor centers of the mature rat brain

It has been shown that dendritic branching in neural cardiorespiratory and locomotor centers can be attenuated with exercise training (ET) initiated immediately after weaning. The purpose of this study was to determine whether neuroplastic changes occur within cardiorespiratory and locomotor centers due to ET after maturation. Male Sprague-Dawley rats (21 days old, n=28) were individually housed in standard cages. At 91 days of age, animals were divided into two groups: untrained (UN; n=14) and trained (TR; n=14). The TR group exercised spontaneously for 50 days on running wheels. ET indexes were obtained, including maximal O2 consumption, percent body fat, resting heart rate, and heart weight-to-body weight ratios. The brain was processed with a modified Golgi-Cox procedure. Impregnated neurons from the periaqueductal gray (PAG), posterior hypothalamic area (PH), nucleus of the tractus solitarius (NTS), cuneiform nucleus (CnF), rostral ventrolateral medulla, nucleus cuneatus, and cerebral cortex were examined. Neurons were traced and analyzed using the Sholl concentric ring analysis of dendritic branching. The mean total number of dendritic intersections with the concentric rings per neuron per animal were compared between UN and TR groups. There were significant differences between UN and TR groups in the PH, PAG, CnF, and NTS in the total number of intersections per animal. In some areas, the effect size was smaller when ET was initiated in mature animals, possibly related to their relatively reduced activity levels. In conclusion, the adult rat brain remains dynamic and adapts to chronic ET. However, some brain areas appear to be more affected if ET is initiated in early postnatal development.