Identification of a Resilient Population of Axotomized Motoneurons within the Mouse Facial Motor Nucleus

Previous facial motoneuron (MN) survival studies have identified a facial MN population that is resilient to axotomy. Examination of the literature suggests two distinct populations of MN: one population vulnerable to axotomy and another population potentially resilient to axotomy. To identify potential differences in MN survival levels after target disconnection, we performed a facial nerve transection at the stylomastoid foramen in a number of different mouse strains, as well as models of immunodeficiency and MN disease. All mice were monitored for facial MN survival for up to 26 weeks post‐axotomy (wpa). We observed an 85% survival of facial MN at 4 wpa that was reduced to about 50% at 10 wpa in WT mice. In contrast, facial MN survival significantly dropped at 4 wpa to approximately 62% and 50% in immunodeficient and MN disease mice, respectively. Similar to WT mice, facial MN survival levels remained at about 50% for up to 18 wpa in both the immunodeficient and MN disease mice. Collectively, these data suggest that, despite target disconnection of similar MN populations by either axotomy or disease, there are inherent differences that may be exploited for therapeutic applications in the future.