The feline oculomotor nucleus: morphological subdivisions and projection to the cerebellar cortex and nuclei.

The cytoarchitecture of the feline oculomotor nucleus was examined in sections stained with thionin and neutral red. Five different subdivisions (caudal central, paramedian, ventral, dorsomedial and dorsolateral divisions) can be identified on each side of the midline. This observation is discussed, and our findings are compared to previous studies of the cytoarchitecture or central muscular representation of the oculomotor nucleus in which different subgroups have been distinguished. Implants or injections of the wheat germ agglutinin-horseradish peroxidase complex have revealed that all five subdivisions project to different parts of the cerebellar cortex and nuclei. Retrogradely labelled cells were found in the oculomotor nucleus in 18 cases following deposition of tracer in the fastigial and interposed nuclei and certain regions of the anterior, posterior and flocculonodular lobes. The projection is bilateral and appears to have its main termination in flocculus. It originates from small neurons, especially from those located along the dorsal border of the oculomotor nucleus.