Afferents to the lateral reticular nucleus from the oculomotor region. II. The oculomotor nucleus, the interstitial nucleus of Cajal and the nucleus of the posterior commissure.

By means of retrograde transport of the wheat germ agglutinin-horseradish peroxidase complex, afferent fibres to the lateral reticular nucleus from the oculomotor and accessory oculomotor nuclei were demonstrated in the cat. Small iontophoretic ejections were made into the main part of the lateral reticular nucleus from a ventral approach. Significant numbers of retrogradely labelled neurons were found bilaterally in all parts of the oculomotor nucleus. The majority was of small size and distributed along the dorsal and lateral boundaries of the nucleus. Some labelled neurons were located just outside these boundaries, in the periaqueductal gray and the adjacent mesencephalic reticular formation. Retrogradely labelled neurons were also found in the accessory oculomotor nuclei: The interstitial nucleus of Cajal featured a substantial number of labelled neurons. Some labelled neurons were consistently found also in the nucleus of the posterior commissure, but no labelled neurons were found in the nucleus of Darkschewitch. The labelled neurons in the interstitial nucleus of Cajal were of different sizes and located bilaterally, mainly in its rostral part. Caudal as well as rostral parts of the main lateral reticular nucleus appear to receive the descending afferents from the oculomotor region, but higher numbers of labelled neurons were found subsequent to ejections in the rostral part. The findings are discussed and some comments are made concerning the lateral reticular nucleus as a possible relay nucleus for oculomotor input to the cerebellum.