Characteristics of mucosal nociceptors in the rat oral cavity: an in vitro study

Characteristics of mucosal nociceptors were investigated by recording activities from single fibers in the lingual nerve in an in vitro jaw-nerve preparation of rats. We found four subtypes of nociceptors in the medial side gingival area of the oral mucosa in the lower jaw: 11 A delta-high threshold mechanonociceptors (A delta-HTMs), 7 A delta-mechanoheat nociceptors (A delta-MHs), 21 A delta-polymodal nociceptors (A delta-POLYs) and 28 C-polymodal nociceptors (C-POLYs). Thus the majority of the nociceptors was polymodal type (ca. 73% of the recorded fibers), ca. 43% of which consisted of A delta-POLYs scarcely found in the skin but commonly found in the deep tissue, muscle or colon. In contrast to the skin, the size of the receptive field of both A delta and C polymodal types was larger than that of either A delta-HTM or A delta-MH type. The von Frey threshold of all types of mucosal nociceptor was higher than that of the skin, though their heat threshold was almost the same as that of the skin nociceptors. These results show that the mucosal nociceptors are different from the skin nociceptors in the frequency distribution of their types and certain physiological properties.