Neuropeptide Y- and vasoactive intestinal polypeptide-containing nerves in the intrinsic external urethral sphincter in the areflexic bladder compared to detrusor-sphincter dyssynergia in patients with spinal cord injury.

Specimens of urethra were obtained from patients with cervical and thoracic spinal cord lesion with detrusor-sphincter dyssynergia and from patients with lower motor neurone lesion with detrusor areflexia, undergoing transurethral sphincterotomy. Neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) in nerves associated with both the smooth and striated muscle components of the urethral sphincter were studied immunohistochemically and by immunoassay. In patients with detrusor-sphincter dyssynergia following cervical and thoracic spinal cord injury, NPY- and VIP-immunoreactive varicose nerve fibres were seen in both the smooth and striated muscle components of the urethral sphincter. In the smooth muscle, NPY- and VIP-immunoreactive nerves did not appear to have any particular orientation, but in the striated muscle region they were found to run along the length of individual muscle fibres. In patients with detrusor areflexia following lower motor neurone lesion, while the pattern, density and fluorescence intensity of NPY- and VIP-immunoreactive nerves in the smooth muscle of the sphincter mechanism appeared the same as seen in patients with detrusor-sphincter dyssynergia, there was a marked increase in the density of these nerves in the striated muscle region of the sphincter mechanism. Quantitation of the peptides by immunoassay was consistent with the histochemical findings, with significantly higher levels of both NPY and VIP in the striated muscle of patients with lower motor neurone lesion, compared to those with cervical and thoracic spinal cord lesion, p = 0.04. NPY and VIP levels in urethral smooth muscle were in the same range in lower motor neurone lesion patients and cervical and thoracic spinal cord lesion patients. We conclude that there are increased NPY- and VIP-containing fibres in striated muscle of the intrinsic external urethral sphincter in patients with areflexic bladder compared with those with detrusor-sphincter dyssynergia.