Expression of TRPV4 in the stimulated rat oral mucous membrane--nociceptive mechanisms of lingual conical papillae.

The study was supported by 2006-2007 Aid Program for Overseas Training of the Promotion and Mutual Aid Corporation for Private School of Japan and International Exchange Grant, Osaka Dental University. We studied the function of TRPV4 expression and its neuronal activation in response to noxious stimulation of oral mucosa. The intermolar region of dorsal lingual eminence (IDLE) of rats was stimulated with 10 microl of either normal saline or 5% formalin. Immunohistological studies of the TRPV4, pERK and serotonin (5HT) expression in designated regions of tongues and brainstems were performed for studying the descending pain modulatory system in response to nociception. Specimens of the experimental IDLE demonstrated a significant increase of TRPV4 activity in particular in stratum basale of conical papillae (p < 0.01). pERK-IR positive neurons were significantly increased in the RMg (p < 0.05), Sp5C (p < 0.05) and Md (p < 0.01); TRPV4-IR neurons were found to show a similar distribution with pERK-IR cells in the peripheral Sp5C (p < 0.05). A significant increase of 5HT expression was observed in the RMg (p < 0.01), RPa (p < 0.01) and ROb (p < 0.05). The results suggest that TRPV4 in the oral mucosa is nociceptor of peripheral hyperalgesia, and pERK expression in the Sp5C is closely related with central hyperalgesia of the nociception. Furthermore, pERK-IR cells of the central 5HT nervous system are activated to accelerate 5HT release for neuronal modulation of the descending pain modulatory system in response to nociception.