Aims of the study: Sofar the topography of the vanilloid receptor in the bladder has only been studied with direct autoradiographical methods (1) or with indirect immunofluorescence studies of afferent nerves. These studies located the receptor on the afferent nerves. Moreover a higher concentration of the receptor was noted at the bladder neck in relation to the body of the bladder. Recently a rabbit anti-capsaicin receptor polyclonal antibody has become commercially available. The aim of the study was to confirm or to reject the current knowledge on the topography of the vanilloid receptor in the normal human bladder.

 

Methods:
Bladder tissue was taken from cystectomy specimens or transurethrally.In all cases a biopsy of the bladder neck or trigone was taken as well as a biopsy of the fundus of the bladder, includingthe muscularis. Immunohistochemstry was performed on frozen bladder specimens with a polyclonal anti-capsaicin-antibody (Chemicon Int.â), using a three-step unlabeled peroxidase-anti-peroxidase (PAP) method, as described previously (2). Colocalisation studies were performed for CGRP and Substance P using laser confocal microscopy.

 

Results:

1) The presence of the vanilloid receptor on unmyelinated nerves is confirmed.

2) Immunoreactivity was also noted on the Schwann cells (perineurium) of myelinated nerves.

3) Strong immunoreactivity was noted on the smooth muscle cells of the muscularis layer and of the lamina propria. The heterogeneity of the immunoreactivity in the muscular layer pleads against eventual background colouring.

 

4) The reported higher concentration at the level of the bladder neck is caused by the presence of more muscle fibers in the region and by the compactness and orientation of these fibers and not by a higher individual immunoreactivity.

 

Discussion: The presence of the receptor on the unmyelinated afferent nerves is confirmed. The presence on the perineurium and the abundant immunoreactivity of the smooth muscle is more puzzling. Possibly vanilloidreceptor blockade by intravesical capsaicin or resiniferatoxin not only results in an indirect smooth muscle relaxation by desensitisation of the afferent branch of a spinal C-fiber mediated reflex arc, but also in a direct relaxation by interaction with the smooth muscle itself.

 

References:

1)   Naunyn-Schmiedeberg’s Arch Pharmacol 347:624-629,1993.

2) Histopathology 23:519-525,1993.