Adult ciliary neurotrophic factor receptors help maintain facial motor neuron choline acetyltransferase expression in vivo following nerve crush

Exogenous ciliary neurotrophic factor (CNTF) administration promotes the survival of motor neurons in a wide range of models. It also increases the expression of the critical neurotransmitter enzyme choline acetyltransferase (ChAT) by in vitro motor neurons, likely independent of its effects on their survival. We have used the adult mouse facial nerve crush model and adult-onset conditional disruption of the CNTF receptor (CNTFR) gene to directly examine the in vivo roles played by endogenous CNTF receptors in adult motor neuron survival and ChAT maintenance, independent of developmental functions. We have previously shown that adult activation of the CreER gene construct in floxed CNTFR mice depletes this essential receptor subunit in a large subset of motor neurons (and all skeletal muscle, as shown in this study) but has no effect on the survival of intact or lesioned motor neurons, indicating that these adult CNTF receptors play no essential survival role in this model, in contrast to their essential role during embryonic development. Here we show that this same CNTFR depletion does not affect ChAT labeling in nonlesioned motor neurons, but it significantly increases the loss of ChAT following nerve crush. The data suggest that, although neither motor neuron nor muscle CNTF receptors play a significant, nonredundant role in the maintenance of ChAT in intact adult motor neurons, the receptors become essential for ChAT maintenance when the motor neurons are challenged by nerve crush. Therefore, the data suggest that the receptors act as a critical component of an endogenous neuroprotective mechanism. J. Comp. Neurol. 525:1206-1215, 2017. (c) 2016 Wiley Periodicals, Inc.