Somatotopic representation within the facial motor nucleus of the chicken studied by means of horseradish peroxidase.

Abstract

The distribution in the chicken of motoneurons innervating the hyolingual muscles, i.e. the M. branchiomandibularis (BM), M. ceratoglossus (CG), M. interceratobranchialis (CB), M. serpihyoideus (PH), M. stylohyoideus (YH) and one of the mandibular muscles, M. depressor mandibulae (DM), was examined by retrograde transport of horseradish peroxidase conjugated with wheatgerm agglutinin. Labelled motoneurons are found in the three subnuclei of the facial (VII) nucleus, as well as hypoglossal (XII) nucleus. The distribution of motoneurons projecting to the DM are observed in the three subnuclei, those of the BM, PH and YH in the intermediate and ventral subnuclei and those of the CB and CG in the intermediate subnucleus. Motoneurons projecting to the PH, YH, CB and CG are also distributed in the XII nucleus. The ratio of labelled motoneurons of the VII to XII nuclei decreases the PH, YH, CB and CG in that order, and the ratio of labelled ones of the ventral to intermediate subnuclei decreases the BM, PH and YH in that order. The topographical and functional aspects of the subdivision of the motor nucleus are discussed.