UC Riverside

Multiple Sclerosis (MS) is a T-Cell mediated autoimmune disease that leads to widespread CNS lesions due to progressively chronic demyelination. Prolonged demyelination is implicated in axonal damage leading to neuronal loss in the CNS. This loss of neurons manifests through clinical symptoms such as optic neuritis, ataxia, memory loss, dysarthria, and seizures due to disrupted neuronal networks and cortical circuitry. Using a chronic demyelination model of cuprizone (CPZ) diet, we have shown hyperexcitability in mice with a significant loss of parvalbumin (PV+) interneurons in the CA1 hippocampal region and widespread gliosis. This was similar to past results obtained from pathological studies of postmortem MS with seizure brains, where significant loss of PV neurons in hippocampus and cortical layers was observed. In addition, dysfunction in glutamate transport was also observed. How and when seizures arise in a demyelinating brain is difficult to study in postmortem brain, thus, we investigated the status of neuronal activity and glial activity in the demyelinating brain of CPZ diet mice. We attempted to identify excitatory activity in layer-specific neurons in various cortical regions and evaluate GABAergic neuronal function during demyelination. 6, 9, and 12 week CPZ diet fed mice brains were examined for c-Fos activity in the cerebral cortex including the hippocampus. We divided them as: Region A (sensory and motor cortex), Region B (parietal and visual cortex), Region C (Piriform cortex), and Region D (cortical amygdala). Brain sections were immunostained for cFos+NeuN to label active neurons; Iba1+ GFAP to assess activation of microglia and astrocytes; PLP+NFM to assess extent of demyelination and axon integrity. Quantification showed a significant increase in activity across the established regions, especially in closely analyzed Region B. A significant increase in cFos+NeuN in regions correlated with decreased PV and increased glia activation response was observed. Hyperactivity of neurons and the loss of PV+ cells in identified regions could be a major contributing factor in initiation of demyelination-associated hyperexcitability. This could be due to perturbation of the expansive inhibitory network that raises physiologic resistance to seizures via the coordination of glutamatergic activity. Because MS patients are up to 3-5 times more likely to develop epileptic seizures than the general population, understanding hyperexcitability during inflammatory demyelination will help us design better therapeutics for MS patients with seizures.