Distribution and changes with age of calcitonin gene-related peptide- and substance P-immunoreactive nerves of the rat urinary bladder and lumbosacral sensory neurons

In the distal parts of the urinary tract, nerves containing calcitonin gene-related peptide (CGRP) or substance P (SP) are sensory with their cell bodies located in lumbosacral dorsal root ganglia. These two neuropeptides are recognised as being present in pelvic sensory nerves, and may be involved in the mediation of pain, stretch and/or vasodilatation. We have used indirect immunohistochemical techniques to examine the distribution and regional variation of nerves immunoreactive (-ir) for CGRP and SP in the urinary bladder and in neurons in lumbosacral dorsal root ganglia (L1-L2 & L6-S1) of young adult (3 months) and aged (24 months) male rats. Semi-quantitative estimations of nerve densities were made for CGRP-ir and SP-ir fibres innervating the dome, body and base of the urinary bladder. Quantitative studies were also used to examine the effects of age on the percentage of dorsal root ganglion neurons immunoreactive for CGRP and SP. There were very few immunoreactive axons in the dome and the overall density of innervation increased progressively towards the base of the bladder. The density of innervation in the aged rats revealed a slight reduction in CGRP and SP innervation of the detrusor muscle but was otherwise comparable to the young group. However, immunostaining of the lumbosacral dorsal root ganglia revealed that the percentage of CGRP- and SP-ir neuronal profiles showed a significant (P < 0.05) reduction from (mean +/- S.D) 44.5 +/- 2; 23.3 +/- 2 in young adult to 25.0 +/- 2.9; 14.8 +/- 1.6 in aged rats, respectively. These findings suggest that the involvement of CGRP and SP in urinary bladder innervation is relatively unchanged in old age, but their expression in dorsal root ganglion neurons is affected by age. The afferent micturition pathway from the pelvic region via these lumbosacral ganglia may be perturbed as a result.