Reorganization of the facial motor nucleus after peripheral nerve regeneration. An HRP study in the rat.

The normal function of the mimetic muscles may depend on the somatotopic organization in the facial motor nucleus (FMN). The horseradish peroxidase (HRP) technique has been used to examine whether this organization is maintained after facial nerve (FN) transection, epineurial suture and subsequent reinnervation of the mimetic muscles in the rat. Eleven months after nerve repair, HRP was applied bilaterally to the zygomatic or buccal rami. The distribution of HRP-labelled neurons in the operated FMN was compared with that in the unoperated FMN. On the unoperated side, HRP-labelled neurons were located in discrete subdivisions of the FMN. Ipsilateral to operation, however, somatotopic organization of the FMN was no longer present. The possible significance of these findings for the development of mass movements of the mimetic muscles after peripheral FN injury of varying origin is discussed.