Elsevier

Brain Research Bulletin

Volume 57, Issues 3–4, February–March 2002, Pages 313-315
Brain Research Bulletin

Efferent connections of the vestibular nuclei in the rat: a neuromorphological study using PHA-L

https://doi.org/10.1016/S0361-9230(01)00726-2Get rights and content

Abstract

The efferent connections of the superior, medial, lateral, and descending vestibular nuclei were studied with anterograde tracing methods in rats. The following areas of termination could be discerned: (1) In the diencephalon, labeled terminals were detected in the thalamus. (2) In the mesencephalon, the red nucleus and motor nuclei involved in eye movements were richly supplied by the vestibular nuclei. (3) In the rhombencephalon, extensive intrinsic connections of all vestibular nuclei were demonstrated. Strong commissural connections were found among the medial, superior, and descending vestibular nuclei. The inferior olive received labeled fibers exclusively from the lateral vestibular nuclei. Individual differences were demonstrated in the termination areas in the reticular formation. (4) In the spinal cord, most of the descending vestibular fibers were found in the ipsilateral anterior funiculus.

Introduction

The dorsolateral part of the brainstem contains the superior (SVN), medial (MVN), lateral (LVN), and descending (DVN) vestibular nuclei, which receive fibers from the labyrinthine organs. In a series of experiments, we have studied the efferent connections of the individual vestibular nuclei in the rat with anterograde method. A detailed map of the fiber connections of these nuclei may contribute to the understanding of their specific roles within general vestibular functions. We were especially interested in the interconnections of the vestibular nuclei and knowing whether the intensity of interconnection can explain the vestibular compensation observed after labyrinthectomy. Parts of the results presented here have been published as a preliminary note [1].

Section snippets

Materials and methods

The experiments were carried out on adult Wistar rats in accordance with state regulations. Under urethan anaesthesia, the cranial cavity was opened and a glass micropipette filled with a 2.5% solution of Phaseolus vulgaris leucoagglutinin (PHA-L) was introduced into the appropriate vestibular nucleus (Fig. 1a–d) according to the coordinates of Paxinos and Watson [3]. After 14 days, the animals were transcardially perfused with a fixative of 2.5% glutaraldehyde, 0.5% paraformaldehyde, and 0.2%

Results

The rostralmost projection from all vestibular nuclei was detected in the diencephalon bilaterally. Most of the fibers originated in the MVN and SVN and terminated in the ventral posteromedial nucleus, the parafascicular nucleus, and the zona incerta.

In the midbrain, the strongest projection was demonstrated onto the oculomotor and trochlear nuclei, the nucleus of Darkschewisch, and the interstitial nucleus of Cajal after injection of the MVN, SVN, and DVN. The projection of the LVN was

Discussion

The results presented here showed a significant overlap in the central projections of the individual vestibular nuclei, albeit individual differences exist in their projections. The similar termination areas of the SVN, MVN, and DVN indicate that they are working in concert in maintaining the normal function of the vestibular system. The intensity of their interconnections suggests the essential bilaterality of vestibular reflexes and a possible role in the compensation of vestibular deficits.

Acknowledgements

The authors thank Dr. George Szekely for the valuable consultation, and Mrs. B. Szanitter, Mrs. D. Á. and Mikló Á. Nagy for technical assistance. The study was supported by FKFP 0425/99, MTA-F 226/98, and OTKA T 034376.

References (5)

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