The extent of ultrastructural spinal cord pathology reflects disease severity in experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) has been studied for decades as an animal model for human multiple sclerosis (MS). Here we performed ultrastructural analysis of corticospinal tract (CST) and motor neuron pathology in myelin oligodendrocyte glycoprotein (MOG) peptide 35-55- and MP4-induced EAE of C57BL/6 mice. Both models were clinically characterized by ascending paralysis. Our data show that CST and motor neuron pathology differentially contributed to the disease. In both MOG peptide- and MP4-induced EAE pathological changes in the CST were evident. While the MP4 model also encompassed severe motor neuron degeneration in terms of rough endoplasmic reticulum alterations, the presence of intracytoplasmic vacuoles and nuclear dissolution, both models showed motor neuron atrophy. Features of axonal damage covered mitochondrial swelling, a decrease in nearest neighbor neurofilament distance (NNND) and an increase of the oligodendroglial cytoplasm inner tongue. The extent of CST and motor neuron pathology was reflective of the severity of clinical EAE in MOG peptide- and MP4-elicited EAE. Differential targeting of CNS gray and white matter are typical features of MS pathology. The MOG peptide and MP4 model may thus be valuable tools for downstream studies of the mechanisms underlying these morphological disease correlates.