Over half of multiple sclerosis (MS) patients experience cognitive deficits, including learning and memory dysfunction, and the mechanisms underlying these deficits remain poorly understood. Neuronal injury and synaptic loss have been shown to occur within the hippocampus in other neurodegenerative disease models, and these pathologies have been correlated with cognitive impairment. Whether hippocampal abnormalities occur in MS models is unknown. Using experimental autoimmune encephalomyelitis (EAE), we evaluated hippocampal neurodegeneration and inflammation during disease. Hippocampal pathology began early in EAE disease course, and included decreases in CA1 pyramidal layer volume, loss of inhibitory interneurons and increased cell death of neurons and glia. It is interesting to note that these effects occurred in the presence of chronic microglial activation, with a relative paucity of infiltrating blood-borne immune cells. Widespread diffuse demyelination occurred in the hippocampus, but there was no significant decrease in axonal density. Furthermore, there was a significant reduction in pre-synaptic puncta and synaptic protein expression within the hippocampus, as well as impaired performance on a hippocampal-dependent spatial learning task. Our results demonstrate that neurodegenerative changes occur in the hippocampus during autoimmune-mediated demyelinating disease. This work establishes a preclinical model for assessing treatments targeted toward preventing hippocampal neuropathology and dysfunction in MS.

Over 50% of multiple sclerosis (MS) patients experience cognitive deficits, and hippocampal-dependent memory impairment has been reported in over 30% of these patients. While post-mortem pathology studies and in vivo magnetic resonance imaging (MRI) 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 (post-disease 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 cornu ammonis 1 (CA1), decreased pre (Synapsin-1) and post (postsynaptic density 95; PSD-95) synaptic staining, diffuse demyelination, and microglial activation. Testosterone treatment administered either before or after disease induction restores excitatory synaptic transmission as well as pre- and postsynaptic protein levels within the hippocampus. Furthermore, cross-modality correlations demonstrate that fluctuations in excitatory postsynaptic potentials 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.

There are strong correlations between cortical atrophy observed by MRI and clinical disability and disease duration in multiple sclerosis (MS). The objective of this study was to evaluate the progression of cortical atrophy over time in vivo in experimental autoimmune encephalomyelitis (EAE), the most commonly used animal model for MS. Volumetric changes in brains of EAE mice and matched healthy controls were quantified by collecting high-resolution T2-weighted magnetic resonance images in vivo and labeling anatomical structures on the images. In vivo scanning permitted us to evaluate brain structure volumes in individual animals over time and we observed that though brain atrophy progressed differently in each individual animal, all mice with EAE demonstrated significant atrophy in whole brain, cerebral cortex, and whole cerebellum compared to normal controls. Furthermore, we found a strong correlation between cerebellar atrophy and cumulative disease score in mice with EAE. Ex vivo MRI showed a significant decrease in brain and cerebellar volume and a trend that did not reach significance in cerebral cortex volume in mice with EAE compared to controls. Cross modality correlations revealed a significant association between neuronal loss on neuropathology and in vivo atrophy of the cerebral cortex by neuroimaging. These results demonstrate that longitudinal in vivo imaging is more sensitive to changes that occur in neurodegenerative disease models than cross-sectional ex vivo imaging. This is the first report of progressive cortical atrophy in vivo in a mouse model of MS.

Cognitive deficits occur in over half of multiple sclerosis patients, with hippocampal-dependent learning and memory commonly impaired. Data from in vivo MRI and post-mortem studies in MS indicate that the hippocampus is targeted. However, the relationship between structural pathology and dysfunction of the hippocampus in MS remains unclear. Hippocampal neuropathology also occurs in experimental autoimmune encephalomyelitis (EAE), the most commonly used animal model of MS. Although estrogen treatment of EAE has been shown to be anti-inflammatory and neuroprotective in the spinal cord, it is unknown if estrogen treatment may prevent hippocampal pathology and dysfunction. In the current study we examined excitatory synaptic transmission during EAE and focused on pathological changes in synaptic protein complexes known to orchestrate functional synaptic transmission in the hippocampus. We then determined if estriol, a candidate hormone treatment, was capable of preventing functional changes in synaptic transmission and corresponding hippocampal synaptic pathology. Electrophysiological studies revealed altered excitatory synaptic transmission and paired-pulse facilitation (PPF) during EAE. Neuropathological experiments demonstrated that there were decreased levels of pre-and post-synaptic proteins in the hippocampus, diffuse loss of myelin staining and atrophy of the pyramidal layers of hippocampal cornu ammonis 1 (CA1). Estriol treatment prevented decreases in excitatory synaptic transmission and lessened the effect of EAE on PPF. In addition, estriol treatment prevented several neuropathological alterations that occurred in the hippocampus during EAE. Cross-modality correlations revealed that deficits in excitatory synaptic transmission were significantly correlated with reductions in trans-synaptic protein binding partners known to modulate excitatory synaptic transmission. To our knowledge, this is the first report describing a functional correlate to hippocampal neuropathology in any MS model. Furthermore, a treatment was identified that prevented both deficits in synaptic function and hippocampal neuropathology. More than 50% of MS patients experience cognitive deficits, 1,2 and hippocampal-dependent learning and memory is often impaired.3,4 Hippocampal atrophy has been shown in MS patients using in vivo MRI, 5,6 and this atrophy was correlated with impaired performance on visuospatial memory testing, a hippocampal-dependent function.7 Data from postmortem studies in MS have demonstrated that hippocampal demyelination and neuropathology occur. 8,9 This demyelination has been associated with changes in molecules modulating synaptic integrity, axonal transport and glutamate homeostasis.10 Although evidence from both in vivo MRI and post-mortem pathological studies indicates that hippocampal pathology occurs during MS, the relationship between such pathology and dysfunction remains unclear. Moreover, there are currently no treatments available to prevent hippocampal dysfunction during MS.Demyelination, axonal los...

Gray matter atrophy is an important correlate to clinical disability in multiple sclerosis (MS) and many treatment trials include atrophy as an outcome measure. Atrophy has been shown to occur in experimental autoimmune encephalomyelitis (EAE), the most commonly used animal model of MS. While the clinical severity of EAE is reduced in estrogen treated mice, it remains unknown whether estrogen treatment can reduce gray matter atrophy in EAE. In this study, mice with EAE were treated with either estrogen receptor (ER)-alpha ligand or ER-beta ligand, diffusion tensor images (DTI) were collected and neuropathology performed. DTI showed atrophy in the cerebellar gray matter of vehicle-treated EAE mice as compared to healthy controls, but not in ER-alpha or ER-beta ligand-treated EAE mice. Neuropathology demonstrated that Purkinje cell numbers were decreased in vehicle-treated EAE mice, while neither ER ligand-treated EAE groups showed a decrease. This is the first report of a neuroprotective therapy in EAE that unambiguously prevents gray matter atrophy while sparing a major neuronal cell type. Fractional anisotropy (FA) in the cerebellar white matter was decreased in vehicle-and ER-beta ligand-treated, but not in ER-alpha ligand-treated EAE mice. Inflammatory cell infiltration was increased in vehicle-and ER-beta ligand-treated, but not in ER-alpha ligand-treated EAE mice. Myelin staining was decreased in vehicle-treated EAE mice, and spared in both ER ligand-treated groups. This is consistent with decreased FA as a potential biomarker for inflammation rather than myelination or axonal damage in the cerebellum in EAE.