Role of C-afferent fibres in the mechanism of action of sacral nerve root neuromodulation in chronic spinal cord injury

Objective To determine whether sacral root neuro-modulation (a promising therapeutic modality in patients with refractory voiding and storage problems) has its effect through the blockade of C-afferent fibres that form the afferent limb of a pathological reflex arc responsible for the dysfunction of bladder storage. Materials and methods The study comprised 39 female Sprague Dawley rats divided into three equal groups: normal controls (group 1); spinally transected at T10 (group 2); spinally transected and electrically stimulated bilaterally at S1 for 6 h daily (group 3). Three weeks after transection the rats were assessed using urodynamics; substance P, neurokinin A and calcitonin gene-related peptide (CGRP) were extracted from the dorsal root ganglia (DRG) of the L5 and L6 roots and quantified by radioimmunoassay. Results Spinally transected rats developed urinary bladder hyper-reflexia after 3 weeks. This was associated with a significant increase in the neuropeptide content of the DRG of L6. Electrostimulation of S1 significantly decreased the neuropeptide content of L6. In contrast, transection and S1 neurostimulation did not affect the neuropeptide content of the L5 DRG, except for CGRP, which increased after spinal transection and decreased with neurostimulation. Conclusions In spinally transected rats, sacral root neurostimulation abolished bladder hyper-reflexia and attenuated the rise in neuropeptide content of the L6 DRG. These results suggest that the blockade of C-afferent fibre activity is one of the mechanisms of action of sacral root neuromodulation.