Radiation-induced changes in neuropeptides in the rat urinary bladder

Purpose: To determine whether there was a change in innervation in the rat urinary bladder following x-ray irradiation. Materials and Methods: The urinary bladders were obtained from rats irradiated 6 months previously with single doses of 15 Gy and 25 Gy x-radiation, and from nonirradiated (control) animals. They were examined immunohistochemically to localize neuropeptide Y (NPY), substance P (SP, vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), met-enkephalin (m-ENK), leu-enkephalin (1-ENK), somatostatin (SOM) and the enzyme, tyrosine-hydroxylase (TH). Computer assisted image analysis was used to assess the density of immunoreactive nerve fibres. Results: The greatest density of nerves observed in the bladder from control animals contained NPY, followed (in decreasing order) by CGRP, VIP, SP and TH. The nerves appeared to run predominantly along the longitudinal axis of the circular and longitudinal muscle fibres. SP-, CGRP-, TH- and occasionally VIP-immunoreactive nerves were observed in the lamina propria, at the base of the urothelium. Perivascular nerves containing neuropeptides and TH were observed throughout the bladder wall. There was an absence of m-ENK-, 1-ENK- and SOM-immunoreactive nerves in the control and irradiated rat urinary bladders. In the rat urinary bladder irradiated with 25 Gy x-radiation, there was a significant increase (P < 0.05) in the density of NPY-, TH- and SP- but not CGRP- and VIP-immunoreactive nerves. There were regional differences within the bladder, that is, there was an increase in VIP-, CGRP-and SP-immunoreactive nerves around and within the urothelium. NPY-immunoreactive nerves were seen in the connective tissue and elastic fibres of the lamina propria for the first time. An increase in the density or fluorescence intensity of perivascular TH- but not neuropeptide-containing nerves was observed. Conclusion: The increase in the density of NPY-, SP- and TH-immunoreactive nerves in the irradiated bladders may be due to axonal sprouting which contributes to the symptoms of radiation injury.