Brain Research, 246 (1982) 285-291 285 Elsevaer Biomedical Press Trigeminal primary afferents project bilaterally to dorsal horn and ipsilaterally to cerebellum, reticular formation, and cuneate, solitary, supratrigeminal and vagal nuclei MARK F JACQUIN, KAZUE SEMBA, ROBERT W RHOADES and M DAVID EGGER Department of Anatomy, Umverstty of Medteme and Denttso y of New Jersey, Rutge~ s Medical School and Ne~ Jersev School of Osteopathic Medicine, P 0 Bo r 101, Plseataway, NJ 08854 ( U S A ) (Accepted May 18th, 1982) Ke) words mgemmal ganghon -- horseradash peroxadase -- anterograde transport -- primary afferents -- bramstem -- spanal cord Horseradash peroxadase (HRP) apphed to the transected mandibular davlslon of the mgemlnal ganghon was transported antero- gradely to prevmusly well known primary afferent terminal zones an the dorsal braanstem tngemmal nuclear complex of the rat, and retrogradely to cell bodies m the tngemmal motor, supratrlgemmal and mesencephahc nuclea Primary tngemmal afferents were also vasable m the apsalateral cerebellar cortex and paraflocculus, and the dentate, cuneate, sohtary, supramgemmal, and dorsal motor vagal nuclei, parvlcellular reticular formation, area postrema, and C1-C6 dorsal horn The contralateral medulla and cerva- cal dorsal horn were also innervated by primary afferents which crossed m the posterior commissure These projectmns were also labeled when HRP was apphed to mdlvadual sensory branches of the mandibular nerve The purpose of this note 1s to describe brlefl~y some previously unknown projections of the trlgemlnal nerve in the rat as revealed by the anterograde trans- port of HRP In the cat, HRP applied directly to the severed proximal stumps of the Inferior alveolar, mental, auriculotemporal (mandibular division), in- fraorbital (maxillary), corneal, supraorbltal, infra- trochlear, frontal, and lacrimal (ophthalmic) bran- ches of the trxgemlnal nerve2,m, 27, or directly In the cat's tooth pulp chamber2, 36 results m transport of HRP through the Gasserlan ganglion and sensory root to largely discontinuous terminations in the bralnstem trIgeminal nuclear complex and cervical dorsal horn Similar results have been obtained with the hngual and inferior alveolar nerves in the ratiO, it and the corneal and supraorbital nerves in the xab- bit 33 The consensus is that the projection of trlgeml- nal primary afferents IS organized somatotoplcally. with mandibular fibers terminating dorsally in the lpsllateral bralnstem trigemlnal nuclear complex, ophthalmic fibers terminating ventrally, and maxil- lary fibers Interposed A consensus does not exist. however, concerning the presence of a crossed trlge- mInal primary afferent projection or of the Innerva- tion of "non-trlgeminal' bralnstem structures The discrepancies may be due either to variability In transgangllonic HRP transport or to differences in projection patterns among the various trlgemlnal branches To Increase the Intensity and extent of an- terograde HRP transport we developed surgical techniques to gain direct access to the trlgemlnal ganghon, allowing for selective application of HRP directly to the cell bodies of either the mandibular or ophthalmic-maxillary portions of the ganglion Eighteen adult female Wlstar rats were anestheti- zed with Ketamlne-HC1 and secured in a stereotaxlc head holder The central processes of trlgeminal pri- mary afferent fibers were labeled with HRP in 6 groups (n = 3 each) in two groups. HRP was ap- plied directly to the mandibular dIwslon or the oph- thalmic-maxillary division of the trlgemlnal gang- hon, and in the remaining 4 groups, HRP was ap- phed respectively to the severed proximal ends of the hngual, inferior alveolar, mylohyold, and aurlculo- temporal nerves which constitute the peripheral pro- cesses of the mandibular cell bodies found in the trl- gemlnal ganglion The major findings to be reported here come from the first group, in which the entire 0006-8993/82/0000-0000/$02 75 © 1982 Elsevier Biomedical Press