EFFECTS OF MOTOR EXPERIENCE ON MOUSE INFERIOR OLIVE NEURON MORPHOLOGY

The inferior olive (IO) is an evolutionarily conserved structure in the caudal medulla of jawed vertebrates that sends projections to cerebellar Purkinje cells in the form of climbing fibers (CF). Several characteristics of the IO suggest that plasticity in this brain region may differ from traditional models. IO neurons lack chemical synapses and communicate via gap junctions on their dendritic spines, contributing to electrical coupling and synchronized oscillatory activity. Although the IO is considered important in most theories of cerebellar learning, little is known about its intrinsic plasticity. Here, we examine the structural changes that emerge in the IO neuropil in response to a 14-day high-speed treadmill running paradigm in adult male mice. C57BL/6J mice were trained daily in voluntary, unrestrained treadmill running to their maximum speeds. The control group had no or limited experience running. Dendrites immunohistochemically stained for MAP2 and imaged using confocal laser scanning microscopy for morphological analysis. An increase in IO neuropil density was observed in motor-experienced mice relative to controls. Namely, skeleton density and fractal dimension were all higher in the group with motor experience (n = 3) compared to the limited-to-no-experience group (n = 6) (median (IQR): density 0.48 (0.25–0.86) vs. 0.43 (0.21–0.75), p = 0.007; fractal dimension 1.20 (1.10–1.29) vs. 1.18 (1.07–1.27), p = 0.004, Mann–Whitney U tests). These findings suggest that motor experience may be associated with morphological alterations in the IO.