An electrophysiological model of spinal transmission deficits in mouse experimental autoimmune encephalomyelitis

Therapeutic testosterone administration preserves excitatory synaptic transmission in the hippocampus during autoimmune demyelinating disease

Over 50% of multiple sclerosis (MS) patients experience cognitive deficits, and hippocampal-dependent memory impairment has been reported in >30% of these patients. While postmortem pathology studies and in vivo magnetic resonance imaging demonstrate that the hippocampus is targeted in MS, the neuropathology underlying hippocampal dysfunction remains unknown. Furthermore, there are no treatments available to date to effectively prevent neurodegeneration and associated cognitive dysfunction in MS. We have recently demonstrated that the hippocampus is also targeted in experimental autoimmune encephalomyelitis (EAE), the most widely used animal model of MS. The objective of this study was to assess whether a candidate treatment (testosterone) could prevent hippocampal synaptic dysfunction and underlying pathology when administered in either a preventative or a therapeutic (postdisease induction) manner. Electrophysiological studies revealed impairments in basal excitatory synaptic transmission that involved both AMPA receptor-mediated changes in synaptic currents, and faster decay rates of NMDA receptor-mediated currents in mice with EAE. Neuropathology revealed atrophy of the pyramidal and dendritic layers of hippocampal CA1, decreased presynaptic (Synapsin-1) and postsynaptic (postsynaptic density 95; PSD-95) staining, diffuse demyelination, and microglial activation. Testosterone treatment administered either before or after disease induction restores excitatory synaptic transmission as well as presynaptic and postsynaptic protein levels within the hippocampus. Furthermore, cross-modality correlations demonstrate that fluctuations in EPSPs are significantly correlated to changes in postsynaptic protein levels and suggest that PSD-95 is a neuropathological substrate to impaired synaptic transmission in the hippocampus during EAE. This is the first report demonstrating that testosterone is a viable therapeutic treatment option that can restore both hippocampal function and disease-associated pathology that occur during autoimmune disease.

Teriflunomide reduces behavioral, electrophysiological, and histopathological deficits in the Dark Agouti rat model of experimental autoimmune encephalomyelitis

Teriflunomide is an orally available anti-inflammatory drug that prevents T and B cell proliferation and function by inhibition of dihydroorotate dehydrogenase. It is currently being developed for the treatment of multiple sclerosis (MS). We report here for the first time the anti-inflammatory effects of teriflunomide in the Dark Agouti rat model of experimental autoimmune encephalomyelitis (EAE). Neurological evaluation demonstrated that prophylactic dosing of teriflunomide at 3 and 10 mg/kg delayed disease onset and reduced maximal and cumulative scores. Therapeutic administration of teriflunomide at doses of 3 or 10 mg/kg at disease onset significantly reduced maximal and cumulative disease scores as compared to vehicle treated rats. Dosing teriflunomide at disease remission, at 3 and 10 mg/kg, reduced the cumulative scores for the remaining course of the disease. Teriflunomide at 10 mg/kg significantly reduced inflammation, demyelination, and axonal loss when dosed prophylactically or therapeutically. In electrophysiological somatosensory evoked potential studies, therapeutic administration of teriflunomide, at the onset of disease, prevented both a decrease in waveform amplitude and an increase in the latency to waveform initiation in EAE animals compared to vehicle. Therapeutic dosing with teriflunomide at disease remission prevented a decrease in evoked potential amplitude, prevented an increase in latency, and enhanced recovery time within the CNS.

Glutamate receptor expression in multiple sclerosis lesions

Blockade of receptors for the excitatory neurotransmitter glutamate ameliorates neurological clinical signs in models of the CNS inflammatory demyelinating disease multiple sclerosis (MS). To investigate whether glutamate excitoxicity may play a role in MS pathogenesis, the cellular localization of glutamate and its receptors, transporters and enzymes was examined. Expression of glutamate receptor (GluR) 1, a Ca(++)-permeable ionotropic AMPA receptor subunit, was up-regulated on oligodendrocytes in active MS lesion borders, but Ca(++)-impermeable AMPA GluR2 subunit levels were not increased. Reactive astrocytes in active plaques expressed AMPA GluR3 and metabotropic mGluR1, 2/3 and 5 receptors and the GLT-1 transporter, and a subpopulation was immunostained with glutamate antibodies. Activated microglia and macrophages were immunopositive for GluR2, GluR4 and NMDA receptor subunit 1. Kainate receptor GluR5-7 immunostaining showed endothelial cells and dystrophic axons. Astrocyte and macrophage populations expressed glutamate metabolizing enzymes and unexpectedly the EAAC1 transporter, which may play a role in glutamate uptake in lesions. Thus, reactive astrocytes in MS white matter lesions are equipped for a protective role in sequestering and metabolizing extracellular glutamate. However, they may be unable to maintain glutamate at levels low enough to protect oligodendrocytes rendered vulnerable to excitotoxic damage because of GluR1 up-regulation.

T-cell-mediated disruption of the neuronal microtubule network: correlation with early reversible axonal dysfunction in acute experimental autoimmune encephalomyelitis

During the course of the central nervous system autoimmune disease multiple sclerosis (MS), damage to myelin leads to neurological deficits attributable to demyelination and conduction failure. However, accumulating evidence has indicated that axonal injury is also a predictor of MS clinical disease. Using the animal model of MS, experimental autoimmune encephalomyelitis (EAE), we examined whether axonal dysfunction occurred early in disease and correlated with disease symptoms. We tracked axons during EAE by using transgenic mice that express yellow fluorescent protein (YFP) in neurons. At the onset of disease, we observed a loss of YFP fluorescence in the spinal cord in areas that coincided with immune cell infiltration, before prominent demyelination. These inflammatory lesions also exhibited evidence of axonal injury but not axonal loss. During the recovery phase of EAE, the return of YFP fluorescence occurred in parallel with the resolution of inflammation. Using in vitro cultured neurons expressing YFP, we demonstrated that encephalitogenic T cells alone directed the destabilization of microtubules within neurites, resulting in a change in the pattern of YFP fluorescence. This study provides evidence that encephalitogenic T cells directly cause reversible axonal dysfunction at the onset of neurological deficits during an acute central nervous system inflammatory attack.