Identification and localization of the motor nuclei and sensory projections of the glossopharyngeal, vagus, and hypoglossal nerves of the cockatoo (Cacatua roseicapilla), Cacatuidae.

Abstract

Horseradish peroxidase (HRP) has been applied to the proximal severed ends of glossopharyngeal (N IX), vagus (NX), and hypoglossal (N XII) cockatoo in order to localize the motoneurons and sensory projections of these nerves which are involved in the control of the bird's feeding and phonatory behaviors. Application of HRP to N IX labeled four rhombencephalic nuclei: (1) a large-celled, retrofacial nucleus supplying M. geniohyoideus, the major tongue extensor; (2) a dorsal nucleus composed of medium-sized cells, projecting to most branches of N IX; (3) a ventrolateral nucleus supplying, amongst other structures, the floor of the pharynx and larynx; and (4) a ventral portion of the dorsal motor nucleus of the vagus. Neurons labeled by application of HRP to the cervical vagus comprise the classically defined dorsal motor nucleus and a ventrolateral medullary nucleus which is coextensive with that of the glossopharyngeus: together they probably constitute a nucleus ambiguus. Application of HRP to hypoglossal branches labeled a large nucleus intermedius (IM) and neurons ventral, ventrolateral, and caudal to it. The rostral third of IM supplies the lingual muscles, the caudal two-thirds the tracheosyringeal muscles. Many labeled neurons were found in the "jugular" ganglion following HRP treatment of each of the three nerves, especially N IX and N XII, which innervate the tongue. Central projections of these neurons are to nuclei of the descending trigeminus and to largely nonoverlapping portions of the principal trigeminal nucleus. It is hypothesized that these afferents provide sensory information necessary for the efficient processing and passage of food in the mouth.