Distribution of the Vestibular Neurons Projecting to the Oculomotor and Trochlear Nuclei in Rabbits

Horseradish peroxidase and Fast Blue were injected into the oculomotor and trochlear nuclei of rabbits so as to study the distribution of vestibular neurons that project to these nuclei. After the oculomotor nucleus was injected, labelled neurons were found in the superior, medial, and descending vestibular nuclei as well as in cell group Y. In the superior nucleus, most of the neurons (510 ± 46) were ipsilateral to the injection, although contralaterally labelled neurons were also observed (104 ± 19) more peripherally. In cell group Y, 186 ± 24 contralaterally labelled neurons were observed, whereas hardly any (8 ± 3) were found on the ipsilateral side. The largest group of labelled neurons (811 ± 65) constituted a neuronal band located contralaterally in the medial nucleus and rostral part of the descending nucleus. This band rostromedially continued with the caudal part of the group of internuclear neurons of the abducens nucleus. Only 190 ± 31 neurons were labelled in the medial and descending nucleus ipsilateral to the injected oculomotor nucleus. After injection of the trochlear nucleus, labelled neurons were found in the ipsilateral superior nucleus and contralateral medial and descending nuclei; a few labelled cells were also observed in the ipsilateral medial and descending nuclei as well as in the contralateral cell group Y.