Distribution of calcitonin gene-related peptide-like immunoreactivity in the nucleus ambiguus of the cat

The distribution of calcitonin gene-related peptide (CGRP) in the cat nucleus ambiguus was examined by means of a combination of horseradish peroxidase (HRP) tracing and immunohistochemical techniques. Vagal motoneurons in the nucleus ambiguus were identified by applying HRP to either the thoracic vagus or the superior laryngeal nerve or the cervical vagus. Motoneurons in the nucleus ambiguus labelled with HRP from the thoracic vagus did not contain CGRP-like immunoreactivity although CGRP-like immunoreactive cells were present in this nucleus on the same sections. In contrast, a large proportion of the motoneurones labelled from the superior laryngeal nerve and a smaller proportion of cells labelled from the cervical vagus did contain CGRP-like immunoreactivity. It is concluded that CGRP-like immunoreactivity is absent from vagal preganglionic motoneurones projecting to structures in the thorax and abdomen but is present in vagal motoneurones projecting to striated muscle of the larynx and pharynx.