The clinical benefits of intravesical electrical stimulation (IVES) in patients with increased residual urine or reduced bladder capacity have been reported. However, studies on the underlying mechanism of IVES has been limited to the A δ afferent and parasympathetic neurons. This study investigated the changes in the calcitonin gene-related peptide (CGRP), substance P (SP), and nitric oxide synthase (NOS) expression in the thoracolumbar and lumbosacral dorsal root ganglia (DRG) of spinalized rats to determine the effect of IVES on the C fiber afferent nerve. Forty Sprague-Dawley rats were divided into normal controls (n = 10); IVES treated normal rats (n = 10), spinalized rats (n = 10), and IVES treated spinalized rats (n = 10). IVES was performed for 2 weeks (5 days a week). IVES was started 3 weeks after spinalization in the spinalized animals. All animals had the DRG removed at the thoracolumbar (T13-L2) and lumbosacral (L5-S1) level. Changes in the CGRP, SP and n-NOS levels at the DRG were measured by western-blot analysis. The relative density of the CGRP and SP following spinalization was significantly higher compared to the controls in both the T13-L2 and L5-S1 DRG. However, IVES in the spinalized rat significantly decreased the relative density of the CGRP and SP compared to the rats with spinalization alone. A significant increase in the relative density of n-NOS was detected in the L5-S1 DRG following spinalization. However, the density of n-NOS was significantly lower after IVES in both the T13-L2 and L5-S1 DRGs. In conclusion, IVES significantly reduced the CGRP, SP and n-NOS levels in the DRG of spinalized rats. CGRP, SP and n-NOS are the main factors that contribute to the hyper-excitability of the micturition reflex after spinal cord injury. These results suggest that the bladder C fiber afferent is also involved in modulating the micturition reflex by IVES.
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