Increase of low-affinity neurotrophin receptor p75 and growth-associated protein-43 immunoreactivities in the rat urinary bladder during experimentally induced nerve regeneration

Purpose: Nerve regeneration in the urinary bladder after pelvic nerve plexus injury remains uncertain. The objectives were to establish a rat model of nerve regeneration in the bladder and to examine possible changes of low-affinity neurotrophin receptor p75 and growth-associated protein-43 (GAP-43) immunoreactivities during denervation and nerve regeneration. Materials and Methods: Adult male rats were divided into 3 groups: controls, crush of the nerve bundles from the right major pelvic ganglion (MPG) to the bladder (nerve crush group) and removal of the right MPG (MPG removal group). Bladders were collected at 3, 7, 14, 30 and 60 days, and immunohistochemically stained for protein gene product 9.5 (PGP9.5: an axonal marker), p75 and GAP-43. Results: In the nel-ve crush group, PGP9.5 positive nerves were decreased in number at 3 and 7 days, and then increased after 14 days in the muscle layer of the operated side. By 60 days, the density returned to control levels. However, MPG removal resulted in a decrease of the density of PGP9.5 positive nerves throughout the experimental periods. These findings indicate that nerve regeneration occurred in the nerve crush group. The density of p75 labeled fibers was significantly increased at 3 to 30 days postoperatively in the nerve crush group. p75 immunoreactivity showed smooth surface and cytoplasmic staining, indicating that Schwann cells were p75 positive. GAP-43 labeled fibers showed significantly greater density at 3 to 14 days postoperatively. Schwann cells were GAP-43 immunoreactive and, in particular, regenerating nerve fibers appeared to be GAP-43 positive at 14 days. Conclusion: The present study suggests that p75 and GAP-43 are involved in the mechanism(s) of nerve regeneration in the urinary bladder.