RESUMO
The postnatal development of the innervation of the muscle layer in the rat urinary bladder was analysed in whole mount preparations using immunohistochemistry against protein gene-product 9.5 (PGP; general neuronal marker), growth-associated protein 43 (GAP), dopamine beta-hydroxylase (DBH), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP) and substance P (SP). Immunoreactive nerve fibres for all markers were already present at birth. The density of PGP- and GAP-positive nerve fibres was similar and remained constant throughout the postnatal development. The rank order of densities for the other markers relative to PGP was NPY (129-189%) > CGRP (20-63%) > SP (7-23%) > DBH (7-12%) > VIP (2-11%). While the density of presumably efferent VIP- and DBH-positive fibres did not change postnatally, NPY-positive fibres reached adult density at the fifth postnatal day. Sensory CGRP- and SP-positive nerve fibres approached adult levels at the end of the second week, shortly before the micturition reflex was completely developed. The data suggest that a sufficient relative density of sensory and certain efferent elements might be a prerequisite for the development of the mature micturition reflex.
