Development of growth-associated protein-43 and neurotrophin receptor immunoreactivities in the rat urinary bladder

Little is known about how the prenatal innervation of the urinary bladder develops. The objective of this study was to define the timing and pattern of innervation of the developing rat bladder using growth-associated protein-43 (GAP-43) immunohistochemistry. In addition, we examined the development of two different classes of transmembrane receptor proteins, the Trk family of tyrosine kinases and neurotrophin receptor p75 immunoreactivities. GAP-43-positive nerves were first detected in the bladder at embryonic day (E) 16. They were growing rapidly to the bladder dome and covered the whole bladder by E18. The density of GAP-43-containing nerves increased in the muscle layer by postnatal day (P) 0. Both Trk receptor-positive and p75 neurotrophin receptor-positive fibers were also first seen at E16. The number of Trk immunoreactive nerves reached a peak at E18, and then decreased over the following days. In contrast, p75-labeled fibers were abundant at E18-P14. There were few GAP-43 or neurotrophin receptor-positive fibers in the adult. GAP-43 immunohistochemistry provided us with a picture of innervation in the developing rat bladder. Furthermore, the demonstration of neurotrophin receptors positive fibers in the prenatal and early postnatal bladders suggests that neurotrophins may contribute to the development of the peripheral nervous system in the urinary bladder.