Contribution of cranial nerve ganglia to innervation of the walls of the rat external acoustic meatus

The retrograde neuronal tracer, fluorogold, was used to determine the relat ive contributions of neurons in selected cranial nerve ganglia to the somat osensory innervation of the external acoustic meatus in the rat. Frozen sec tions from the trigeminal (semilunar), facial (geniculate), glossopharyngea l (superior petrosal) and vagal (jugular) nerve ganglia were examined by ep ifluoresence microscopy 10 to 14 days after application of the tracer dye f luorogold to the superior, inferior, anterior and posterior walls of the ex ternal acoustic meatus. The anterior wall of the canal makes a large contri bution to the trigeminal ganglion and a lesser contribution to the other 3 ganglia. The trigeminal ganglion is also a major recipient from the posteri or wall with smaller contributions from that wall to the geniculate and vag al ganglia. The superior wall projects a relatively constant supply to all 4 ganglia while the inferior wall primarily relays to the trigeminal and ge niculate ganglia sending smaller contributions to the vagal and glossophary ngeal ganglia. In conclusion, neurons in these 4 cranial nerve ganglia cont ribute an overlapping supply to the 4 walls of the external ear meatus, and there is no evidence of a preferential distribution of nerve supply from o ne particular ganglion or nerve to specific walls of the external acoustic meatus.