Gene expression in trigeminal ganglion neurons in temporomandibular joint inflamed rats

Abstract

   In order to evaluate the neuronal mechanisms of abnormal pain following TMJ inflammation, the expression of Transient Receptor Potential (TRP) channels in trigeminal ganglion neurons (TRG neurons) were precisely analyzed in rats with temporomandibular joint (TMJ) inflammation.
   The facial skin temperature was significantly increased at 1 and 3 days after complete Freund's adjuvant (CFA) injection into the TMJ and that was decreased at 7 days after that. On the other hand, we could not observe any facial skin temperature changes in sham-operated rats. Many inflammation mediated cells were observed in the TMJ region at 3 days after CFA injection.Furthermore, the small number of inflammation mediated cells was distributed in the TMJ region at 7 days after CFA injection. TRPV1 mRNA was expressed in small TRG neurons (≤ 200 µm²) 3 days after CFA injection. On the other hand, the number of TRG neurons expressed TRPM8 mRNA was significantly larger at 7 days after CFA injection in 201 - 300 µm² and 401 - 500 µm² TRG cells. TRPA1 mRNA was expressed in 101 - 200 µm² TRG cells at 3 days after CFA injection.
   The present findings revealed that TRPV1 and TRPA1 in TRG cells and inflammation-medicated cells in TMJ region expressed with similar time-course associated with facial temperature change after CFA injection, suggesting that these channels are involved in the trigeminal neuropathic pain following TMJ inflammation.