Bemerkungen zum Ursprung der labyrinth�ren Efferenz bei Vertebraten. Eine Evolutionshypothese

Abstract

In our comparative study in all classes of vertebrates we determined the cells of origin of efferent acoustic and efferent vestibular fibers by the use of retrograde axonal transport of horseradish peroxidase (HRP). In fish we investigated the goldfish, in the amphibians the green tree frog, in reptiles a turtle and the Caiman. In birds we studied the chicken and in mammals the guinea pig. If one compares the origin of efferent labyrinthine fibers there seems to be a shift from a medial position in the brain stem (lateral to the fasciculus longitudinalis medialis) in the fish to a more lateral position in the amphibians. In reptiles the parent cells stretch more ventral in the direction of the superior olive. While in turtles efferent acoustic neurons are intermingled with efferent vestibular neurons, it is in the evolutionary stage of Crocodilia that efferent acoustic neurons separate from efferent vestibular neurons. In birds there is a similar finding as in the Caiman. In mammals, efferent vestibular neurons shift dorsally to a position lateral to the genu of the facial nerve. Efferent acoustic neurons are located throughout the superior olivary complex.