Projection from the facial nucleus to the auricular muscles of rabbits

Abstract

The auricular muscles correspond to the group of facial muscles that allows the auricle to move freely. The shape of the auricle and the location of the muscles on the head differs among species. The rabbit has eight auricular muscles that are innervated by motoneurons originating from the facial nucleus located on the ventral side of the medulla oblongata. However, the distribution within the facial nucleus of the motoneurons that innervate each auricular muscle has not been defined clearly. In the present study, retrograde transport of horseradish peroxidase was used to identify groups of facial motoneurons in the rabbit. Our results show that the medial subnucleus of the facial nucleus projects primarily to the auricular muscles, and that each auricular muscle is innervated by a specific group of motoneurons distributed in a particular region of the medial subnucleus. This motoneuron patterning appears to be a species-specific characteristic of the innervation of the auricular muscles.