P2X3-immunoreactive nerve fibres in neurogenic detrusor overactivity and the effect of intravesical resiniferatoxin.

Objectives: The ATP-gated purinergic receptor P2X3 is expressed by small diameter sensory neurons and has been identified in normal and neurogenic human bladder suburothelial fibres. Animal models have shown that ATP is released by the urothelium during bladder distension, suggesting a mechanosensory role for P2X3 receptors in normal bladder function. Successful treatment of spinal neurogenic detrusor overactivity (NDO) with intravesical resiniferatoxin (RTX), which partly acts on suburothelial C fibres, provides evidence for the emergence of a C fibre-mediated spinal reflex. The aim of this study was to investigate the possible role of P2X3-positive innervation in this pathological voiding reflex by comparing suburothelial P2X3 immunoreactivity of controls and in patients with NDO before and after intravesical RTX.
Methods: Bladder biopsies were obtained from 8 controls and 20 patients with refractory NDO enrolled in a trial of intravesical RTX. P2X3 nerve fibre density and intensity were studied in the specimens by immunohistochemistry.
Results: P2X3-IR nerve fibres were significantly increased in patients with NDO compared to controls (p=0.014). Thirteen patients had pre- and post-RTX biopsies available for immunohistochemistry; 5 of them responded clinically and 8 were non-responders. In the 5 patients who responded to RTX, there was a significant decrease in P2X3-positive fibres (p=0.032), whereas in non-responders, P2X3-IR nerve fibre density did not change significantly.
Conclusions: In patients with NDO, the numbers of P2X3-IR nerve fibres were increased in the suburothelium. There was a significant decrease in P2X3 immunoreactivity in responders to RTX, indicating a potential pathophysiological role for the P2X3 expressing fibres.