Vanilloid receptor homologue, VRL1, is expressed by both A- and C-fiber sensory neurons

The capsaicin receptor (VR1) homologue, VRL1, is thought to be responsible for transducing high-threshold heat responses in Aδ-fiber neurons. In the present study, the expression of VRL1 by A- or C-fiber sensory neurons in rats was investigated by using a VRL1 and 200 kDa neurofilament (NF200, an A-fiber marker) double immunohistochemical staining method. Approximately 46% of VRL-positive neurons were NF200 positive. Though double-labeled neurons tended to be medium to large, many VRL1 single-labeled neurons were large. Dense VRL1 immunoreactivity was also found in laminae I and II of the spinal dorsal horn, where nociceptive Aδ- and C-fibers normally terminate. These results suggest that both C-fiber and Aδ-fiber primary sensory neurons express VRL1, and VRL1 may play an important role in nociception.