Organisation of reciprocal connections between trigeminal and vestibular nuclei in the rat

In order to study the connection patterns between the sensory trigeminal an d the vestibular nuclei (VN), injections of anterogradely and/or retrograde ly transported neuronal tracers were made in the rat. Trigeminal injections resulted in anterogradely labelled fibres, with an ipsilateral preponderan ce, within the VN: in the ventrolateral part of the inferior nucleus (IVN), in the lateral part of the medial nucleus (MVN), in the lateral nucleus (L VN) with a higher density in its ventral half, and in the superior nucleus (SVN), more in the periphery than in the central part. Moderate trigeminal projections were observed in the small vestibular groups f, x and y/l and i n the nucleus prepositus hypoglossi. Additional retrogradely labelled neuro nes were seen in the NN, MVN, and LVN, in the same regions as those receivi ng trigeminal afferents. Morphological analysis of vestibular neurones demo nstrated that vestibulo-trigeminal neurones are relatively small and belong to a different population than those receiving projections from the trigem inal nuclei. The trigemino-vestibular and vestibulo-trigeminal relationship s were confirmed by tracer injections in the VN. The results show that, in the VN, there is sensory information from facial receptors in addition to those reported from the neck and body. These facia l afferents complement those from the neck and lower spinal levels in suppl ying important somatosensory information from the face and eye muscles. The oculomotor connections of the respective zones of the VN receiving trigemi nal afferents suggest that sensory inputs from the face, including extraocu lar proprioception, may, through this pathway, influence the vestibular con trol of eye and head movements. (C) 1999 Wiley-Liss, Inc.