Using a sensitive double immunostaining technique with unconjugated cholera-toxin B subunit as a retrograde tracer, the authors determined the nuclei of origin of monoaminergic, peptidergic, and cholinergic afferent projections to the cat facial nucleus (FN). The FN as a whole receives substantial afferent projections, with relative subnuclear differences, from the following areas: (1) the perioculomotor areas, the contralateral paralemniscal region, and the mesencephalic reticular formation dorsal to the red nucleus; (2) the ipsilateral parabrachial region and the nucleus reticularis pontis, pars ventralis; and (3) the nuclei reticularis parvicellularis, magnocellularis, ventralis, and dorsalis of the medulla.
In addition, the present study demonstrated that the lateral portion of the FN receives specific projections from the contralateral medial and olivary pretectal nuclei and the ipsilateral reticular formation of the pons. It was also found that the FN receives: (1) serotoninergic inputs mainly from the nuclei raphe obscurus, pallidus, magnus, and the caudal ventrolateral bulbar reticular formation; (2) catecholaminergic afferent projections from the A7 noradrenaline cell group located in the Kölliker-Fuse, parabrachialis lateralis, and locus subcoeruleus nuclei; (3) methionin-enkephalin-like inputs originating in the pretectal complex, the nucleus paragigantocellularis lateralis and the caudal raphe nuclei; (4) substance P-like afferent projections mainly from the Edinger-Westphal complex and the caudal raphe nuclei; and (5) cholinergic afferents from an area located ventral to the nucleus of the solitary tract at the level of the obex.
In the light of these anatomical data, the present report discusses the physiological significance of FN inputs relevant to tonic and phasic events occurring at the level of the facial musculature during the period of paradoxical sleep in the cat.