THE DISTRIBUTION OF AFFERENT NEURONS IN THE TRIGEMINAL MESENCEPHALIC NUCLEUS AND THE CENTRAL PROJECTION OF AFFERENT-FIBERS OF THE MYLOHYOIDNERVE IN THE RAT

Horseradish peroxidase conjugated to wheatgerm agglutinin (HRP:WGA) wa s injected into the proximal cut ends of three branches of the mylohyo id nerve in rats: the branch to the mylohyoid muscle (BrMh), the branc h to the anterior belly of the digastricus muscle (BrDg), and the cuta neous branch (BrCu). HRP-labeled cells were detected in the ipsilatera l caudal portion of the trigeminal mesencephalic nucleus (Vmes) and th e ipsilateral ventromedial division of the trigeminal motor nucleus, e xcept when HRP:WGA was applied to the BrCu. Morphologically, all label ed Vmes cells were of the pseudounipolar type. Projections of the prim ary afferents of the BrMh were observed in the ipsilateral trigeminal nucleus caudalis, the upper cervical dorsal horns of laminae I-III, an d the dorsolateral recticular formation (Rf), whereas the primary affe rents of the BrDg terminated in the ipsilateral trigeminal nucleus pri ncipalis and Rf. These observations suggest that the role of the affer ent inputs of the mylohyoid muscle differs from that of those of the a nterior belly of the digastricus muscle in terms of several functions associated with jaw-closing and infrahyoid muscles.