The sensory trigeminal complex projects contralaterally to the facial motor and the accessory abducens nuclei in the rat.

Anterograde tracer injections in the rat sensory trigeminal complex are shown here to demonstrate projections to the contralateral facial motor (VII) and accessory abducens (VIacc) nuclei. Most of the trigeminal fibres originated within the pars oralis (5o) and contacted neurones in the medial and intermediate VII. Moderate projections from the pars caudalis (5c) and interpolaris (5i) reached the lateral and dorsolateral VII. Rare projections from the principal nucleus (5P) were found. Trigeminal projections to the contralateral VIacc originated mainly from the 5P and 5o. Few projections from the 5i and 5c to the contralateral VIacc were found. Retrograde tracer injections in the VII showed premotor neurones to the contralateral VII scattered throughout the 5o and in the ventromedial portion of the caudal 5i and the 5c. Double retrograde tracing experiments provide evidence that neurones in the 5o and 5c project to both the ipsi- and contralateral VII. Such collateralization would play a significant role in the co-ordination of the musculature of the face.