Radioautographic study of the symphathetic fibers in the cochlea

The noradrenergic fibers of the cochlea have been investigated by radioautography after an in vitro labeling by 3H-Noradrenalin (3H-NA). Unmyelinated, perivascular and non-perivascular fibers took up and retained 3H-NA. Non-perivascular fibers formed small bundles together with unmyelinated efferents in the intraganglionic spiral bundle and the osseous spiral lamina. No labeled fibers were detectable beyond the habenula inside the organ of Corti. The labeled fibers, which are probably noradrenergic, were characterized by numerous varicosities and discontinuous Schwann sheathes. These morphological characteristics could associate them with a general role in cochlear function. Sometimes, labeled fibers were also found very close to Ranvier's node of certain myelinated fibers, which could suggest a specific effect on these fibers.