Abstract
The vanilloid receptor 1-like receptor (VRL-1), a capsaicin receptor homologue, is activated by high temperatures with a threshold >52°C. By VRL-1 immunhisotchemistry, the distribution of high-threshold heat nociceptors was examined in the trigeminal ganglion (TG). In the rat TG, VRL-1-immunoreactive (ir) neurons were abundant (14%) and had medium-sized to large cell bodies. The development of VRL-1-ir neurons was also examined in knockout mice for neurotrophin receptors and Brn-3a, a member of the POU family of transcription factors. In the knockout mouse for trkA (nerve growth factor high-affinity receptor), VRL-1-ir neurons almost disappeared. In addition, the loss of trkC (neurotrophin-3 high-affinity receptor) decreased the number of VRL-1-ir neurons. However, such neurons were abundant in the knockout mouse for trkB (brain-derived neurotrophic factor and neurotrophin-4 high-affinity receptor). On the other hand, VRL-1-ir neurons disappeared in the Brn-3a knockout mouse.
These findings suggest that high-threshold heat nociceptors have medium-sized to large cell bodies in the TG. Their development probably depends on nerve growth factor, neurotrophin-3 and Brn-3a. [Jpn J Physiol 54 Suppl:S11 (2004)]
