The co-expression of ASIC3 with calcitonin gene-related peptide (CGRP) or parvalbumin (PV) was examined in the trigeminal ganglion (TG) by a double immunofluorescence method. ASIC3-immunoreactivity (IR) was detected in 23% of TG neurons. These neurons were of various sizes (range=43-1768 μm2, mean±S.D.=651±356 μm2); 26% and 14% of ASIC3-immunoreactive (IR) neurons co-expressed CGRP- and PV-immunoreactivity (IR), respectively; 33% and 13% of the TG neurons retrogradely labeled from the tooth pulp and facial skin, respectively, exhibited ASIC3-IR; 36% of CGRP-IR TG neurons which innervate these tissues co-expressed ASIC3-IR. Only 4% of ASIC3-IR cutaneous TG neurons showed PV-IR, while 25% of ASIC3-IR tooth pulp neurons were also immunoreactive for PV. The present study suggests that ASIC3-IR TG neurons supply the tooth pulp and facial skin with unmyelinated or finely myelinated axons. ASIC3-IR neurons which have large myelinated axons may be common in the tooth pulp but not the facial skin. The axonal morphology of ASIC3-IR TG neurons may depend on the variety of their receptive fields.
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