Estrogen has well-documented neuroprotective effects in a variety of clinical and experimental disorders of the CNS, including autoimmune inflammation, traumatic injury, stroke, and neurodegenerative diseases. The beneficial effects of estrogens in CNS disorders include mitigation of clinical symptoms, as well as attenuation of histopathological signs of neurodegeneration and inflammation. The cellular mechanisms that underlie these CNS effects of estrogens are uncertain, because a number of different cell types express estrogen receptors in the peripheral immune system and the CNS. Here, we investigated the potential roles of two endogenous CNS cell types in estrogen-mediated neuroprotection. We selectively deleted estrogen receptor-α (ERα) from either neurons or astrocytes using well-characterized Cre-loxP systems for conditional gene knockout in mice, and studied the effects of these conditional gene deletions on ERα ligand-mediated neuroprotective effects in a wellcharacterized model of adoptive experimental autoimmune encephalomyelitis (EAE). We found that the pronounced and significant neuroprotective effects of systemic treatment with ERα ligand on clinical function, CNS inflammation, and axonal loss during EAE were completely prevented by conditional deletion of ERα from astrocytes, whereas conditional deletion of ERα from neurons had no significant effect. These findings show that signaling through ERα in astrocytes, but not through ERα in neurons, is essential for the beneficial effects of ERα ligand in EAE. Our findings reveal a unique cellular mechanism for estrogen-mediated CNS neuroprotective effects by signaling through astrocytes, and have implications for understanding the pathophysiology of sex hormone effects in diverse CNS disorders.multiple sclerosis | astrogliosis | conditional knockout T he female sex hormone, estrogen, is neuroprotective in many clinical and experimental CNS disorders, including autoimmune conditions such as multiple sclerosis (MS), neurodegenerative conditions such as Alzheimer's and Parkinson diseases, and traumatic injury and stroke (1-4). Estrogen treatment has been shown to ameliorate clinical disease and decrease neuropathology in these disease models (1-4). Pharmacological studies have suggested roles for different estrogen receptors, but the cell types that mediate neuroprotective effects of estrogen are not known for any experimental or clinical condition. Identifying cells that bear specific estrogen receptor subtypes and are essential for specific estrogen-mediated effects is fundamental to elucidating and therapeutically exploiting the mechanisms that underlie estrogen-mediated neuroprotection. Toward this end, we used a genetic loss-of-function strategy. We selectively deleted estrogen receptor-α (ERα) from two different CNS cell types, neurons and astrocytes, and then determined the effects of these conditional gene deletions on the ability of ERα-ligand treatment to ameliorate disease severity of experimental autoimmune encephalomyelitis (EAE) in mice.EAE i...

Sex differences in brain function and behavior are regularly attributed to gonadal hormones. Some brain sexual dimorphisms, however, are direct actions of sex chromosome genes that are not mediated by gonadal hormones. We used mice in which sex chromosome complement (XX versus XY) and gonadal sex (ovaries versus testes) were independent, and found that XX mice showed faster food-reinforced instrumental habit formation than XY mice, regardless of gonadal phenotype.

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.

In animal studies of nociception, females are often more sensitive to painful stimuli, whereas males are often more sensitive to analgesia induced by μ agonists. Sex differences are found even at birth, and in adulthood are likely caused, at least in part, by differences in levels of gonadal hormones. Here we investigate nociception and analgesia in neonatal mice, and assess the contribution of the direct action of sex chromosome genes in hotplate and tail withdrawal tests. We used the four core genotypes mouse model, in which gonadal sex is independent of the complement of sex chromosomes (XX vs. XY). Mice were tested at baseline and then injected with μ-opioid agonist morphine (10mg/kg), or with the κ-opioid agonist U50,488H (U50, 12.5mg/Kg) with or without the N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 (0.1mg/kg). On the day of birth, XX mice showed faster baseline latencies than XY in tail withdrawal, irrespective of their gonadal type. Gonadal males showed greater effects of morphine than gonadal females in the hotplate test, irrespective of their sex chromosome complement. U50 and morphine were both effective analgesics in both tests, but MK-801 did not block the U50 effect. The results suggest that sex chromosome complement and gonadal secretions both contribute to sex differences in nociception and analgesia by the day of birth. Perspective: Sex differences in pain may stem not only from the action of gonadal hormones on pain circuits, but from the sex-specific action of X and Y genes. Identification of sex chromosome genes causing sex differences could contribute to better pain therapy in females and males.