Fig. 8.
The effects of stopping exercise on postfracture gene expression of spinal cord inflammatory mediators (A–K). Figure 1 illustrates the reoccurrence of allodynia and unweighting in exercised mice after stopping exercise for 2 weeks. In this experiment a cohort of fracture mice (FX + wheel) were treated with 4 weeks ad lib access to a running wheel, starting at 3 weeks postfracture, and then the wheel was removed for 2 weeks; the animals were euthanized (9 weeks postfracture) and the skin collected. Control fracture mice not provided access to a running wheel (FX + no wheel) were euthanized (9 weeks postfracture) and the skin collected. Inflammatory mediator expression in the lumbar cord innervating the fracture limb was measured by real-time polymerase chain reaction. Interleukin 6 (IL-6, B), tachykinin precursor 1 (TAC1, F), tachykinin receptor 1 (TACR1, G), calcitonin-related polypeptide α (CALCA, I), calcitonin-related polypeptide β (CALCB, J), and calcitonin receptor-like receptor (CALCRL, K) messenger RNA (mRNA) levels were upregulated at 9 weeks postfracture, compared to nonfractured control mice. All these increases in inflammatory mediator gene express were reversed by 4 weeks wheel running (fig. 5), and this reversal persisted after stopping wheel running. There were no changes in the hind paw skin expression of interleukin 1β (IL-1β, A), tumor necrosis factor α (TNF-α, C), nerve growth factor (NGF, D), C-C motif chemokine ligand 2 (CCL2, E), and receptor activity-modifying protein 1 (RAMP1, H) at 9 weeks postfracture (no wheel), compared to nonfracture control mice, and exercise had no effects on the 9-weeks postfracture expression of these genes. Values are means ± SD, n = 8 per cohort. One-way ANOVA with Bonferroni post hoc testing. *P < 0.05, **P < 0.01, and ***P < 0.001 for fracture + no wheel or fracture + wheel versus control; #P < 0.05, ##P < 0.01, and ###P < 0.001 for fracture + wheel versus fracture + no wheel. CGRP = calcitonin gene-related peptide.