Cell size analysis of trigeminal primary afferent neurons comprizing individual peripheral branches of the rat mandibular nerve.

Cell bodies of primary afferent neurons comprizing individual peripheral branches of the rat mandibular nerve were labeled by retrograde transport of HRP and their sizes were measured. Approximately 60% of cell bodies of primary neurons innervating the intra and perioral structures through the inferior alveolar, lingual, mental, and buccal nerves were in the range between 300 and 600 micron 2 in cross-sectional area: mean +/- SD 509 +/- 243 micron 2, 420 +/- 181 micron 2, 469 +/- 200 micron 2, and 444 +/- 186 micron 2, respectively. Sixty-five percent of cell bodies of primary neurons innervating the periphery of the face through the cutaneous branch of the mylohyoid and auriculotemporal nerves were smaller than 300 micron 2 in cross-sectional area: 285 +/- 170 micron 2 and 286 +/- 172 micron 2, respectively. The data suggest that the intraoral/perioral region is different from the skin in the peripheral region of the face in terms of the mechanism by which sensory information is transmitted to the central nervous system. This difference may explain some of the formerly enigmatic phenomena such as the differential effects of spinal trigeminal tractotomy.