Introduction

Functional and morphological changes in bladder afferent pathways are reportedly involved in neurogenic detrusor overactivity (DO) after spinal cord injury (SCI). The present study examined the morphological changes in different populations of bladder afferent neurons in mice after SCI using an HSV vectors encoding mCherry fluorescent protein that is driven by cell type-specific promoters using mice.

Methods

SCI was induced by Th8/9 spinal cord transection in female C57BL/6N mice. Mice were divided into 8 groups; 1. spinal intact (SI) with CMV promoter (CMVp)-mCherry, 2. SI with CGRPp-mCherry, 3. SI with NF200p-mCherry, 4. SI with TRPV1p-mCherry, 5. SCI with CMVp-mCherry, 6. SCI with CGRPp-mCherry, 7. SCI with NF200p-mCherry and 8. SCI with TRPV1p-mCherry. Two weeks after vector inoculation into the bladder wall, L1 and L6 dorsal root ganglia (DRGs) were removed bilaterally for immunofluorescent staining using anti-mCherry antibody.

Results

The number of CMVp vector-labeled neurons was not altered after SCI. The numbers of CGRPp and TRPV1p vector-labeled neurons significantly increased compared to those of SI mice (p<0.001). The number of NF200p vector-labeled neurons significantly decreased compared to SI mice (p<0.001). Cell size distributions of CGRPp vector-labeled C-fiber and NF200p vector-labeled A-fiber neurons showed an increase in the number of C-fiber neurons and a decrease in the number of A-fiber neurons in L6 DRGs after SCI. The median cell size of CGRPp vector-labeled neurons shifted to a larger size (p<0.05) from 247.0 (SI) to 271.3 µm² (SCI), while the median cell size of TRPV1p vector-labeled neurons shifted to a smaller size (p<0.01) from 245.2 (SI) to 216.5 µm² (SCI).

Conclusions

Using an HSV vector-mediated novel neuronal labelling technique, we found that SCI induces morphological changes in bladder afferent pathways, including expansion of the C-fiber cell population that expresses CGRP and TRPV1, which could contribute to C-fiber afferent hyperexcitability and DO, after SCI. _x000D_ _x000D_

Funding

NIH P01 DK093424