Topographic Distribution of Laryngeal Motor Neurons in the Nucleus Ambiguus of the Guinea Pig Studied by Horseradish Peroxidase (HRP) Technique

Abstract

The topographic distribution of Nucleus Ambiguus (NA) motor neurons innervating the intrinsic laryngeal musculature in the guinea pig has not been studied previously. We used 25 guinea pigs anaesthetized by Penthrane (Methoxyflurane) inhalation. Horseradish peroxidase type VI (40%) was used. The motor neurons traced are distributed in cellular groups elongated rostro-caudally in a tract of the brain stem situated between a rostral plane compatible with the location of the retrofacial nucleus, and a caudal plane some millimetres below the obex. The motor neurons observed do not exhibit differential morphology in relation to the different muscles studied.

Somatotopy of the Neurons Innervating the Cricothyroid, Posterior Cricoarytenoid, and Thyroarytenoid Muscles of the Rat's Larynx

“…Second, some authors maintain that laryngeal neurons innervating individual laryngeal muscles are diffusely distributed along nucleus ambiguus while others maintain that a clear somatotopic organization can be seen. Most studies are in agreement in locating the neurons innervating the CT more rostral in the nucleus ambiguus than the remaining laryngeal muscles neurons (Szentagothai, ; Lawn, ; Hinrichsen and Ryan, ; Yoshida et al, ; Pásaro et al, ; Hisa et al, ; Davis and Nail, ; Basterra et al, ; Núñez‐Abades et al, ; Hirasugi et al, ) in the semicompact formation of the nucleus ambiguus (Bieger and Hopkins, ). On the other hand, other published studies established that the neurons of the loose formation that innervate intrinsic laryngeal muscles of the larynx, but the CT, are intermingled within the nucleus ambiguus (Gacek, ; Hinrichsen and Ryan, ; Pásaro et al, ; Davis and Nail, ; Hisa et al, ; Basterra et al, ; Flint et al, ; Nahm et al, ).…”

“…First, a number of studies describe laryngeal neurons as being located as a discrete single column of neurons extending along the rostrocaudal axis of the nucleus ambiguus in the brainstem (Szentagothai, ; Kalia and Mesulam, ; Hinrichsen and Ryan, ; Pásaro et al, ; Yoshida et al, ; Davis and Nail, ; Basterra et al, ; Okubo et al, ; Portillo and Pásaro, ; Van Daele and Cassell, ; Weissbrod et al, ; Pascual‐Font et al, ). Other studies describe laryngeal neurons as being clustered along the nucleus ambiguus into several defined columns each columns being separated by gaps where no laryngeal neurons are present (Lawn, ; Gacek, ; Wetzel et al, ; Hisa et al, ; Bieger and Hopkins, ; Okubo et al, ; Patrickson et al, ; Núñez‐Abades et al, ; Hirasugi et al, ).…”

Innervation of the larynx, pharynx, and upper esophageal sphincter of the rat

“…Labeling in the DMV after SLN and laryngeal injections has been observed previously. Basterra et al (1987) found labeling in the DMV in guinea pig after intralaryngeal HRP injection and attributed it to labeling of the visceromotor component of the larynx. Altschuler et al (1989) dealt mainly with the sensory components of the vagus nerve and their projections to NTS subdivisions; however, they do illustrate a few retrogradely labeled cells in the DMV after injection of the SLN and after injection of the esophagus.…”