Innervation of the rat external auditory meatus: a retrograde tracing study

The innervation of the rat external auditory meatus has contributions from several nerves. Fluoro-gold, a retrograde neuronal tracer, was used to determine the relative contributions from neurons in cranial and spinal ganglia, and to distinguish any difference in the sensory and motor innervation between the outer cartilaginous and inner bony portions. The following ganglia were examined: the trigeminal, geniculate, glossopharyngeal, vagal, superior cervical, and dorsal root (C2-C4) ganglia. All selected ganglia demonstrated innervation of the external ear canal, particularly the trigeminal, glossopharyngeal, facial, and vagal ganglia. The geniculate and glossopharyngeal ganglia contributed more innervation to the inner osseous portion than to the outer cartilaginous portion of the external ear canal, and the vagal ganglion contributed relatively equally.