Reversibility of exercise-induced dendritic attenuation in brain cardiorespiratory and locomotor areas following exercise detraining

It has been shown previously that dendritic branching in cardiorespiratory and locomotor brain areas can be attenuated with exercise training (ET). It was not known whether this process was reversible. Twenty-three (n = 23) male Sprague-Dawley rats were individually caged and divided into two groups: untrained (UN; n = 11) and detrained (DTR; n = 12). DTR were provided with a running wheel at 21 days of age and exercised spontaneously. After 120 days (70 days of ET followed by 50 days of detraining), ET indexes were obtained, including maximal oxygen uptake, percent body fat, resting heart rate, and heart weight-to-body weight ratios. The brain was processed according to a modified Golgi-Cox procedure. Impregnated neurons from the periaqueductal gray (PAG), posterior hypothalamic area (PH), nucleus of the tractus solitarius (NTS), and cuneiform nucleus (CfN) were examined in coronal sections. Neurons were traced using a camera lucida technique and analyzed using the Sholl concentric ring analysis of dendritic branching. t-Tests compared the mean number of intersections per neuron by grouping inner rings, outer rings, and total number of intersections per animal. There were no significant differences between UN and DTR in PH, PAG, CfN, and NTS in the inner rings, outer rings, and total number of intersections per animal. A separate group of animals was used to show that a training effect in the CfN and NTS was present at 56 days of ET. Our results show that dendritic attenuation resulting from 70 days of ET in PH, PAG, CfN, and NTS is completely reversed with 50 days of detraining.