Dendritic ramifications of trigeminal motor neurons innervating jaw-closing muscles of rats.

A cholera toxin subunit conjugated horseradish peroxidase (CTHRP) was found to be very useful in labelling the dendrites of motoneurons. CTHRP was injected individually to jaw-closing muscles (temporalis, masseter, and medial pterygoid) of rats, and their motoneurons including the dendrites were labelled and studied. The results show that the motoneuron cell bodies innervating temporalis, masseter, and medial pterygoid muscles are located in the trigeminal motor nucleus in dorsal, ventromedial and ventrolateral position. The dendrites of these motoneurons extend radially into mesencephalic nucleus, supratrigeminal nucleus, pontine reticular formation, trigeminal sensory nucleus and even into the bundles of the ascending root of the facial nerve. These dendrites may serve as an extended surface for various synaptic contacts to the jaw closing motoneurons. The possibility that they may also have presynaptic influence on the input to the trigeminal motoneurons is also discussed.