This study evaluated the time-course changes in bladder and external urinary sphincter (EUS) activity and the expression of mechanosensitive channels in lumbosacral dorsal root ganglia (DRG) after spinal cord injury (SCI). Female C57BL/6N mice in the SCI group underwent transection of the Th8/9 spinal cord. Spinal intact mice and SCI mice at 2, 4, and 6 wk post-SCI were evaluated by single-filling cystometry and EUS-electromyography (EMG). In another set of mice, the bladder and L6-S1 DRG were harvested for protein and mRNA analyses. In SCI mice, nonvoiding contractions were confirmed at 2 wk post-SCI and did not increase over time to 6 wk. In 2-wk SCI mice, EUS-EMG measurements revealed detrusor sphincter dyssynergia, but periodic EMG reductions during bladder contraction were hardly observed. At 4 wk, SCI mice showed increases of EMG activity reduction time with increased voiding efficiency. At 6 wk, SCI mice exhibited a further increase in EMG reduction time. RT-PCR of L6-S1 DRG showed increased mRNA levels of transient receptor potential vanilloid 1 and acid-sensing ion channels (ASIC1-ASIC3) in SCI mice with a decrease of ASIC2 and ASIC3 at 6 wk compared with 4 wk, whereas Piezo2 showed a slow increase at 6 wk. Protein assay showed SCI-induced overexpression of bladder brain-derived neurotrophic factor with a time-dependent decrease post-SCI. These results indicate that detrusor overactivity is established in the early phase, whereas detrusor sphincter dyssynergia is completed later at 4 wk with an improvement at 6 wk post-SCI, and that mechanosensitive channels may be involved in the time-dependent changes.NEW & NOTEWORTHY This is the first paper to evaluate the time-course changes of bladder dysfunction associated with mechanosensitive channels in a mouse model.
Keywords: brain-derived neurotrophic factor; detrusor overactivity; detrusor sphincter dyssynergia; mechanosensitive channel; spinal cord injury.