Fluorescence Histochemical Studies on the Noradrenergic Innervation of the Canine Larynx

The origin and course of noradrenergic nerve fibers contained in laryngeal nerves and their destinations in the larynx of the dog were investigated using fluorescence histochemistry. The superior laryngeal nerve, including the internal and external branches and the recurrent laryngeal nerve were found to contain many noradrenergic nerve fibers and these laryngeal nerves were the only noradrenergic nerve supply channels for the larynx. The superior laryngeal nerve received noradrenergic nerve fibers from the superior cervical ganglion below the nodose ganglion. The recurrent laryngeal nerve is considered to receive noradrenergic nerve fibers originating from the middle cervical ganglion directly, and those originating from the superior cervical ganglion via the vagus nerve. The cricothyroid muscle received noradrenergic nerve fibers from the external branch of the superior laryngeal nerve and other intrinsic muscles received them from the internal branch of the superior laryngeal nerve and the recurrent laryngeal nerve. The submucosal glands in the supraglottic and epiglottic regions received the noradrenergic nerve fibers from the internal branch of the superior laryngeal nerve and those in the subglottic region were innervated by noradrenergic nerve fibers in the recurrent laryngeal nerve.