Afferent Projections to Pharynx and Soft Palate Motoneurons: A Light and Electron Microscopical Tracing Study in the Cat JOSE BOERS, 1 ANTOINETTE C. HULSHOFF, 2 HENK DE WEERD, 1 LEONORA J. MOUTON, 1 RUTGER KUIPERS, 1 AND GERT HOLSTEGE 1 * 1 Department of Anatomy and Embryology, Faculty of Medicine, University of Groningen, 9700 AD Groningen, The Netherlands 2 Department of Otorhinolaryngology, University Hospital Groningen, 9700 RB Groningen, The Netherlands ABSTRACT Pharynx and soft palate are muscles for respiration, vocalization, swallowing, and vomiting. In cat, motoneurons innervating pharynx/soft palate are located in the dorsal group of the nucleus ambiguus (dgNA) in the medulla oblongata. In cat, dgNA is the only part of nucleus ambiguus that can be distinguished as a separate cell group, which makes it possible to study its afferent input. In two cats, WGA-HRP injections in dgNA and surrounding tegmentum resulted in retrogradely labeled cells at several levels of the neuraxis. In 170 cases anterograde tracers were injected in areas in which the cells of origin were identified. Results demonstrate that dgNA afferents originate from the tegmentum dorsolateral to the superior olivary complex, medullary ventromedial tegmentum, caudal raphe nuclei, medul- lary lateral tegmental field, nucleus retroambiguus (NRA), and adjoining tegmentum, ex- tending into the first cervical segment of the spinal cord. In order to determine whether periaqueductal gray (PAG) and parabrachial nuclei (PB) make synaptic contacts with dgNA, ultrastructural studies combined anterograde tracing from PAG, PB, and NRA with retro- grade tracing of pharyngeal and soft palate motoneurons. The results showed that PB, but not PAG, projects to the dgNA and that NRA afferent synapses are three times as numerous as those from PB. The morphology of PB and NRA synapses is consistent with excitatory input. In conclusion, pharyngeal and soft palate motoneurons receive their afferents almost exclusively from the pontine and medullary tegmentum and first cervical spinal segment. J. Comp. Neurol. 486:18 –38, 2005. © 2005 Wiley-Liss, Inc. Indexing terms: nucleus ambiguus; vocalization; respiration; parabrachial nuclei; periaqueductal gray; nucleus retroambiguus The pharynx and soft palate play a crucial role in res- piration (Lunteren and Dick, 1996), swallowing (Doty and Bosma, 1956; Miller, 1972), vomiting (Gre ´lot and Miller, 1997), and vocalization (Thoms and Ju ¨ rgens, 1987; Saka- moto et al., 1996). Both groups of muscles are innervated by motoneurons located in the so-called dorsal group of the nucleus ambiguus (dgNA; Lawn, 1966; Yoshida et al., 1981; Holstege et al., 1983; Davis and Nail, 1984). In cat, the nucleus ambiguus (NA) is located in the medullary lateral tegmental field, extending from just caudal to the facial nucleus rostrally to the level of the obex caudally (Holstege et al., 1983; Davis and Nail, 1984). At most levels the NA is difficult to recognize, because in each transverse section only a few scattered NA motoneurons are present. In contrast, the dgNA is the only part of NA that can be recognized as a distinct nucleus in Nissl- stained sections. Despite the great importance of pharynx *Correspondence to: Gert Holstege, Dept. Anatomy and Embryology, Univ. Groningen, A. Deusinglaan 1, 9700 AD Groningen, The Netherlands. E-mail: g.holstege@med.rug.nl Received 4 June 2004; Revised 4 October 2004; Accepted 4 December 2004 DOI 10.1002/cne.20530 Published online in Wiley InterScience (www.interscience.wiley.com). THE JOURNAL OF COMPARATIVE NEUROLOGY 486:18 –38 (2005) © 2005 WILEY-LISS, INC.