Mesencephalic and pontine afferent fiber system to the facial neucleus in the cat: a study using the horseradish peroxidase and silver impregnation techniques.

The mesencephalic and pontine afferent fiber system to the medial or lateral part of the facial nucleus was examined in the cat by the horseradish peroxidase and the Fink-Heimer methods. The medial part of the facial nucleus was observed to receive afferent fibers mainly from the perioculomotor and the midbrain paralemniscal regions. The perioculomotor region, which included the oculomotor nucleus, the Edinger-Westphal nucleus, the interstitial nucleus of Cajal, the nucleus of Darkschewitsch, and the ventral part of the periaqueducatal gray, sent fibers to the facial nucleus bilaterally with a slight dominance of the ipsilateral distribution. The midbrain paralemniscal region, which was just medial to the dorsal part of the medial lemniscus at caudal levels of the superior colliculus, sent numerous fibers to the contralateral facial nucleus. In contrast, the lateral part of the facial nucleus received many afferent fibers from the ventral part of the parabrachial nuclei; the parabrachiofacial fibers were distributed bilaterally with a marked predominance of the ipsilateral distribution. The existence of crossed rubrofacial fibers was confirmed. Some neurons in the ventral part of the nucleus pontis centralis oralis were found to send fibers to the facial nucleus bilaterally with a predominance of the contralateral distribution.