Decreased synaptophysin immunoreactivity of the anterior horns in motor neuron disease

This study concerns the synaptophysin expression in anterior horn neurons of 15 patients with amyotrophic lateral sclerosis and of 4 patients with lower motor neuron disease, who had no upper motor neuron and corticospinal tract involvement. Immunohistochemical procedures were employed and specimens from 13 patients without neurological disease served as controls. A decrease in synaptophysin expression was observed in the anterior horn neuropil of all motor neuron disease patients and this reduction was correlated with the degree of degeneration or neuronal loss of anterior horn cells. Synaptophysin immunoreactivity was preserved in the proximal dendrites and around the somata of the remaining normal-appearing neurons, but it was reduced around the somata and dendrite, especially the distal portion of the proximal dendrites of small degenerated neurons with central chromatolysis, pigmentary atrophy, or simple neuronal atrophy. These observations suggest that presynaptic terminal loss is not secondary to motor cortical neuronal loss, but that the synaptic alterations in anterior horns occur in the wake of motor neuron degeneration.