Connections of the vestibular nuclei in the rabbit

This thesis descnbes the afferent, efferent and intrinsic connections of the vestibular nuclei in the Dutch belted rabbit. Different anatomical tracing techniques were used to study these projections. A description of the vestibular complex was added, since recent data for the rabbit are scarce (Chapter 2). A comparison between cytoarchitecture and staining for acetylcholinesterase and cytochromoxidase supported the subdivision of the central magnocellular area of the vestibular complex into a dorsal region comprising the lateral vestibular nucleus of Deiters and the ventrally located magnocellular portion of the medial vestibular nucleus. Additional evidence supporting this distinction came from a detailed analysis of the primary vestibular input in the rabbit (Chapter 3). The central projections of the vestibular nerve were investigated with anterograde axonal transport of wheatgerm agglutinin conjugated horseradish peroxidase (WGA-HRP) and tritiated leucine following injection in the vestibular ganglion. Labeled fibers and terminal ramifications were observed throughout the vestibular complex, including the magnocellular part of the medial vestibular nucleus, but they were absent from lateral vestibular nucleus. The absence of a projection of the vesnbular nerve to lateral vestibular nucleus is in accordance with the findings in other mammals (Voogd, 1964, Korte, 1979, Carleton and Carpenter, 1984). Termination in the cortex was restricted to the vermis. Small numbers of mossy fiber terminals were present bilaterally, close to the midline in lobules I and II, and in the depth of the main fissures separating the lobules II- VI. In the posterior vermis labeled mossy fiber terminals were found in lobule X and the ventral aspect of lobule IXd. Here the entire ipsilateral hemivermis contained many terminals, while contralaterally fewer mossy fiber tenninals were present in the medial one-third of these lobules. Labeled mossy fibers and terminals were absent from the flocculus and adjacent ventral paraflocculus.