Expression of the TRPM8-immunoreactivity in dorsal root ganglion neurons innervating the rat urinary bladder

The neurochemical phenotypes of the transient receptor potential melastatin-8 (TRPM8)-immunoreactive afferent neurons innervating the rat urinary bladder were examined by using a highly sensitive tyramide signal amplification method, combined with wheat-germ agglutinin-horseradish peroxidase (WGA-HRP) retrograde tracing. TRPM8-immunoreactivity was detected in a small proportion of the WGA-HRP-labeled bladder afferent neurons in the dorsal root ganglia of the Th13-L1 (1.14%) and the L6-S1 (1.27%). and these neurons were small in size (< 600 mu m(2)). The 82.6 +/- 3.8% of the TRPM8-immunoreactive bladder afferent neurons and 80.9 +/- 1.5% of the total population of the TRPM8-immunoreactive afferent neurons in the observed dorsal root ganglia expressed NF200 On the other hand, the proportions of the co-expression of TRPM8 and nociceptive markers such as calcitonin gene-related peptide(CGRP), transient receptor potential vanilloid-1 (TRPV1). and isolectin B4(IB4) in the bladder afferent neurons (81.5 +/- 5.2% for CGRP, 36.1 +/- 4.0% for TRPV1. and 15.8 +/- 5.5% for IB4) were higher in comparison to those in the total population of the TRPM8-immunoreactive afferent neurons (21.9 +/- 2.4% for CGRP, 16.6 +/- 1.7% for TRPV1, and 5.4 +/- 0.5% for IB4). although no significant difference existed for IB4 Our results suggest that the TRPM8-expressing bladder afferents should be classified as A delta-fibers and C-fibers. while some of these afferents; may be involved in nociceptive sensations (C) 2009 Elsevier Ireland Ltd and the Japan Neuroscience Society All rights reserved.