Microglial staining with OX-42 immunohistochemistry in the spinal cord during three different stages of motor neuron disease progression. A, presymptomatic stage; inset shows early microglial fusion in spinal cord. B, disease onset; C, end stage; D, wild type control. Note the dramatic increase in microglial staining with OX-42 during onset (B) and its subsequent decline during end stage (C). Scale bar: 200 μm. E, morphometric quantification of microglial immunostaining with OX-42 during disease development; * p < 0.05 and ** p < 0.001 with respect to age-matched controls; # p < 0.05 with respect to onset group.