Analysis of facial nerve axon, DRG, and sympathetic neuron (superior cervical ganglion, SCG) numbers in GDF-15 deficient mice and wild-type littermates at 6 months of age. a, Significant 13% decrease of axon numbers in the facial nerve of GDF-15 deficient mice, as compared to wild-type littermates. b, Numbers of neurons in the SCG of GDF-15 deficient mice and wild-type littermates are not significantly different. (c) Significant neuron losses in L4 (-22%) and L5 (-25%) DRG in GDF-15 deficient mice as compared to wild-type littermates.