Topographic organization of central terminal region of different sensory branches of the rat mandibular nerve.
The central projection of primary neurons comprising the auriculotemporal nerve, cutaneous branch of the mylohyoid nerve, inferior alveolar nerve, mental nerve, lingual nerve, and buccal nerve was investigated using transganglionic transport of HRP in young rats. In view of the topographic organization of central projection fields, the nerves were divided into two groups; i.e., those projecting to the dorsolateral margin of the trigeminal nucleus principalis, subnucleus oralis, and interpolaris (the auriculotemporal, mylohyoid, and mental nerves) and those projecting more medially (the inferior alveolar, lingual, and buccal nerves). The former group of nerves projected more caudally than the latter in the medullary and spinal dorsal horn complex rostral to the 3rd cervical segment, in general. Furthermore, the latter group projected to the nucleus of the solitary tract and the supratrigeminal and paratrigeminal nuclei, whereas the other nerves did not. The data indicate the following points: Primary neurons innervating the intraoral structures terminate medial (in trigeminal nucleus principalis and subnucleus oralis) and ventral (in subnucleus interpolaris) to the terminal fields of those innervating the facial skin. Primary neurons innervating the intraoral structures project to the nucleus of the solitary tract and the supra- and paratrigeminal nuclei, whereas those innervating the facial skin do not. Primary neurons innervating the periphery of the face project to the spinal dorsal horn and those innervating the intra/perioral region project to medullary dorsal horn, though this segregation from the medulla to the 3rd cervical segment is relatively loose. Only those trigeminal primary neurons, whose receptive fields extend to or beyond the midline, project to the contralateral dorsal horn from the medulla to the 3rd cervical segment.