Localisation of recurrent laryngeal nerve motoneurons in the sheep by means of retrograde fluorescent labelling

The purpose of this investigation was to determine the central distribution of the efferent neurons of the recurrent laryngeal nerve (RLN) in the sheep by the use of the retrograde transport of the fluorescent tracer Fast Blue. The distribution of the RLN neurons was also compared with that of the neurons simultaneously labelled by injection of another tracer, Diamidino Yellow dihydrochloride, into the cervical trunk of the vagus nerve (CTV). Injections of the tracer into the CTV resulted in heavy retrograde labelling of neurons in the ipsilateral dorsal motor nucleus of the vagus nerve, in the nucleus ambiguus, in the nucleus retroambigualis and in the reticular formation surrounding the nucleus ambiguus. Following injections of the tracer into the RLN, labelling of neurons was seen over a wide area of the ipsilateral nucleus ambiguus and in the nucleus retroambigualis. Species differences in the distribution of the efferent component of the RLN are discussed, in particular ruminants compared to nonruminants.