Recent work has shown that physical inactivity versus activity alters neuronal structure in brain regions associated with cardiovascular regulation. For example, neurons in the rostral ventrolateral medulla (RVLM) are more responsive to excitation in sedentary compared to physically active animals. Mischel and colleagues hypothesized that enhanced functional responses in the RVLM may be due, in part, to changes in the structure of RVLM neurons that control sympathetic activity. Their results showed that dendritic arbors of spinally projecting tyrosine hydroxylase-positive neurons from sedentary rats were more branched than those of physically active rats. In sedentary rats, dendritic branching was greater in more rostral versus more caudal bulbospinal C1 neurons, whereas, in physically active rats, dendritic branching was consistent throughout the RVLM. In contrast, cell body size and the number of primary dendrites did not differ between active and inactive animals. Mischel and colleagues suggest that these structural changes provide an anatomical underpinning for the functional differences observed in physiological studies. They postulate that the inactivity-related structural and functional changes may enhance the overall sensitivity of RVLM neurons to excitatory stimuli and contribute to an increased risk of cardiovascular disease in sedentary individuals.
Mischel NA, Llewellyn-Smith IJ, Mueller PJ: Physical (in)activity-dependent structural plasticity in bulbospinal catecholaminergic neurons of rat rostral ventrolateral medulla. J. Comp. Neurology 522(3): 499-513 (2014); doi: 10.1002/cne.23464.