The co-expression of P2X3 receptor with the vanilloid receptor subtype I (VR1) and vanilloid receptor 1-like receptor (VRL-1) was examined in the rat trigeminal ganglion (TG) by a double immunofluorescence method. P2X3 receptor-immunoreactive (it) neurons were predominantly small to medium-sized (range = 93.8-1844.4 mum(2), mean +/- S.D. = 503.8 +/- 286.5 mum(2)); 35% and 9% of P2X3 receptor-ir TG neurons were immunoreactive for VR1 and VRL-1, respectively. Small and medium-sized P2X3 receptor-ir neurons contained VR1-immunoreactivity (it), whereas medium-sized and large P2X3 receptor-ir neurons showed VRL-1-ir. The retrograde tracing and immunohistochemical methods revealed that 30% of the TG neurons retrogradely labeled from the facial skin and tooth pulp exhibited P2X3 receptor-ir. The co-expression of P2X3 receptor and VR1 was detected in 16% of cutaneous TG neurons and 6% of tooth pulp neurons. On the other hand, the co-expression of P2X3 receptor and VRL-1 was common in tooth pulp neurons (23%) and rare in cutaneous TG neurons (8%). In the tooth pulp, 95% of P2X3 receptor-ir TG neurons contained VRL-1-ir.
The present study indicates that P2X3 receptor-ir TG neurons, which co-express VR-ir, are abundant in the facial skin. The tooth pulp is probably innervated by TG neurons, which contain both P2X3-and VRL-1-ir. (C) 2003 Published by Elsevier B.V.