QUANTITATIVE AND SOMATOTOPIC MAPPING OF NEURONS IN THE TRIGEMINAL MESENCEPHALIC NUCLEUS AND GANGLION INNERVATING TEETH IN MONKEY AND BABOON

Neurones of the trigeminal mesencephalic nucleus (Mes V) and ganglion innervating the periodontium of incisor, canine and molar teeth in 10 monkeys and 10 baboons were counted and mapped using the horseradish p eroxidase (Hrp), retrograde axonal transport method. Periodontal affer ent neurones of all these teeth were well represented in the Mes V, al though the incisors had a significantly higher number of labelled neur ones than the canines or molars. The primary cell bodies of the period ontal afferents were located mainly in the caudal part of the ipsilate ral Mes V from the level of the inferior colliculus to the floor of th e fourth ventricle in the pens. The caudal periodontal Mes V neurones may be favourably located to make collateral connections with the trig eminal motor nucleus for jaw reflexes. Incisors and canines had a larg e and predominantly ipsilateral representation of Hrp-labelled neurone s in the ganglion. In contrast, molar representation in the ganglion w as sparse and all labelled neurones supplied ipsilateral teeth. The ma xillary and mandibular teeth had a somatotopic distribution within the respective maxillary (middle) and mandibular (posterolaterai) compart ments of the trigeminal ganglion. It is suggested that the anterior te eth with greater connections to the Mes V and the ganglion may impart greater sensory perception and be involved in jaw reflexes to ensure a good occlusal relation during mastication. while the afferent connect ions of the molars may initiate complex jan reflexes during the occlus al phase of mastication. (C) 1997 Elsevier Science Ltd.