More severe neurologic deficits in SJL/J male than female mice following Theiler's virus-induced CNS demyelination

Potential biological contributers to the sex difference in multiple sclerosis progression

Multiple sclerosis (MS) is an immune-mediated disease that targets the myelin sheath of central nervous system (CNS) neurons leading to axon injury, neuronal death, and neurological progression. Though women are more highly susceptible to developing MS, men that develop this disease exhibit greater cognitive impairment and accumulate disability more rapidly than women. Magnetic resonance imaging and pathology studies have revealed that the greater neurological progression seen in males correlates with chronic immune activation and increased iron accumulation at the rims of chronic white matter lesions as well as more intensive whole brain and grey matter atrophy and axon loss. Studies in humans and in animal models of MS suggest that male aged microglia do not have a higher propensity for inflammation, but may become more re-active at the rim of white matter lesions as a result of the presence of pro-inflammatory T cells, greater astrocyte activation or iron release from oligodendrocytes in the males. There is also evidence that remyelination is more efficient in aged female than aged male rodents and that male neurons are more susceptible to oxidative and nitrosative stress. Both sex chromosome complement and sex hormones contribute to these sex differences in biology.

Theiler’s virus-induced demyelinating disease as an infectious model of progressive multiple sclerosis

Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disease of unknown etiology. However, several studies suggest that infectious agents, e.g., Human Herpes Viruses (HHV), may be involved in triggering the disease. Molecular mimicry, bystander effect, and epitope spreading are three mechanisms that can initiate immunoreactivity leading to CNS autoimmunity in MS. Theiler’s murine encephalomyelitis virus (TMEV)-induced demyelinating disease (TMEV-IDD) is a pre-clinical model of MS in which intracerebral inoculation of TMEV results in a CNS autoimmune disease that causes demyelination, neuroaxonal damage, and progressive clinical disability. Given the spectra of different murine models used to study MS, this review highlights why TMEV-IDD represents a valuable tool for testing the viral hypotheses of MS. We initially describe how the main mechanisms of CNS autoimmunity have been identified across both MS and TMEV-IDD etiology. Next, we discuss how adaptive, innate, and CNS resident immune cells contribute to TMEV-IDD immunopathology and how this relates to MS. Lastly, we highlight the sexual dimorphism observed in TMEV-IDD and MS and how this may be tied to sexually dimorphic responses to viral infections. In summary, TMEV-IDD is an underutilized murine model that recapitulates many unique aspects of MS; as we learn more about the nature of viral infections in MS, TMEV-IDD will be critical in testing the future therapeutics that aim to intervene with disease onset and progression.

Biological Sex As a Critical Variable in CD4+ Effector T Cell Function in Preclinical Models of Multiple Sclerosis

Significance: T cells play a pivotal role in maintaining adaptive immune responses against pathogens. However, misdirected T cell responses against self-tissues may lead to autoimmune disease. Biological sex has profound effects on T cell function and is an important determinant of disease incidence and severity in autoimmune diseases such as multiple sclerosis (MS). Recent Advances: Many autoimmune diseases skew toward higher female incidence, including MS; however, it is has become increasingly more accepted that men living with MS are more prone to developing a progressive disease course and to having worsened disease outcomes. Critical Issues: In this review, we discuss what is known about the role of biological sex on T cell development and differentiation, examining evidence that male sex can augment T helper 17 (Th17) responses. Next, we outline what is known about sex differences in animal models of MS, and about the distinct roles played by sex hormones versus sex chromosomes in pathogenesis in these models. Finally, we discuss recent advances that examine the molecular basis for worsened disease outcomes in males, with a particular focus on the role played by Th17 cells in these models. Future Directions: Better understanding the role of biological sex in T cell function may pave the way to effective personalized treatment strategies in MS and other autoimmune diseases. Antioxid. Redox Signal. 37, 135-149.

Immune Cell Contributors to the Female Sex Bias in Multiple Sclerosis and Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is a chronic, autoimmune, demyelinating disease of the central nervous system (CNS) that leads to axonal damage and accumulation of disability. Relapsing-remitting MS (RR-MS) is the most frequent presentation of MS and this form of MS is three times more prevalent in females than in males. This female bias in MS is apparent only after puberty, suggesting a role for sex hormones in this regulation; however, very little is known of the biological mechanisms that underpin the sex difference in MS onset. Experimental autoimmune encephalomyelitis (EAE) is an animal model of RR-MS that presents more severely in females in certain mouse strains and thus has been useful to study sex differences in CNS autoimmunity. Here, we overview the immunopathogenesis of MS and EAE and how immune mechanisms in these diseases differ between a male and female. We further describe how females exhibit more robust myelin-specific T helper (Th) 1 immunity in MS and EAE and how this sex bias in Th cells is conveyed by sex hormone effects on the T cells, antigen presenting cells, regulatory T cells, and innate lymphoid cell populations.

Antecedent presentation of neurological phenotypes in the Collaborative Cross reveals four classes with complex sex-dependencies

Antecedent viral infection may contribute to increased susceptibility to several neurological diseases, such as multiple sclerosis and Parkinson’s disease. Variation in clinical presentations of these diseases is often associated with gender, genetic background, or a combination of these and other factors. The complicated etiologies of these virally influenced diseases are difficult to study in conventional laboratory mouse models, which display a very limited number of phenotypes. We have used the genetically and phenotypically diverse Collaborative Cross mouse panel to examine complex neurological phenotypes after viral infection. Female and male mice from 18 CC strains were evaluated using a multifaceted phenotyping pipeline to define their unique disease profiles following infection with Theiler’s Murine Encephalomyelitis Virus, a neurotropic virus. We identified 4 distinct disease progression profiles based on limb-specific paresis and paralysis, tremors and seizures, and other clinical signs, along with separate gait profiles. We found that mice of the same strain had more similar profiles compared to those of different strains, and also identified strains and phenotypic parameters in which sex played a significant role in profile differences. These results demonstrate the value of using CC mice for studying complex disease subtypes influenced by sex and genetic background. Our findings will be useful for developing novel mouse models of virally induced neurological diseases with heterogenous presentation, an important step for designing personalized, precise treatments.

Host genetic background influences diverse neurological responses to viral infection in mice

Infection by Theiler's murine encephalomyelitis virus (TMEV) is a model for neurological outcomes caused by virus infection because it leads to diverse neurological conditions in mice, depending on the strain infected. To extend knowledge on the heterogeneous neurological outcomes caused by TMEV and identify new models of human neurological diseases associated with antecedent infections, we analyzed the phenotypic consequences of TMEV infection in the Collaborative Cross (CC) mouse population. We evaluated 5 different CC strains for outcomes of long-term infection (3 months) and acute vs. early chronic infection (7 vs. 28 days post-infection), using neurological and behavioral phenotyping tests and histology. We correlated phenotypic observations with haplotypes of genomic regions previously linked to TMEV susceptibility to test the hypothesis that genomic diversity within CC mice results in variable disease phenotypes in response to TMEV. None of the 5 strains analyzed had a response identical to that of any other CC strain or inbred strain for which prior data are available, indicating that strains of the CC can produce novel models of neurological disease. Thus, CC strains can be a powerful resource for studying how viral infection can cause different neurological outcomes depending on host genetic background.

Influence of social interaction on nociceptive-induced changes in locomotor activity in a mouse model of acute inflammatory pain: Use of novel thermal assays

Most acute and chronic animal models of pain rely heavily on reflexive assays for evaluating levels of nociception, which involves removing the animal from its normal social environment. Here, we examine and characterize the influence of social interactions on inflammatory pain-evoked changes in movement in two different mouse strains. To produce inflammatory nociception, we injected CFA bilaterally into the hind paws of Balb/c and C3H mice and then recorded exploratory locomotor activity using an automated detector system to first evaluate the effects of social behavior on nociception. Secondly, we determined if carprofen administration altered the effects of social behavior on nociceptive-evoked movement. This methodology was expanded to create a novel thermal activity assay to objectively measure the effect of heat and cold on CFA-evoked animal movement in paired animals. Paired Balb/c and C3H mice exhibited significant hyper-locomotion that lasted for 3h post-injection in Balb/c, but only 1h post-injection in C3H. Single Balb/c mice only showed increased activity for 1h post-injection, while single C3H mice showed no increase. This CFA-induced increase in activity in paired animals was highly inversely correlated with mechanical allodynia as measured using standard Von Frey filaments. Carprofen administration completely blocked this CFA-induced hyperlocomotor activity. Both heat and cold induced a significant increase in locomotor activity in paired mice injected with CFA, while having no effect on activity in control mice injected with saline. The results presented here indicate that social interactions greatly influence inflammatory pain-induced changes in locomotor activity and indicate that the use of movement-based assays to evaluate nociception in paired mice may provide an alternative and more sensitive method to quantify nociception and characterize novel analgesic effects over time in the context of social interactions in rodent models of pain.

Mice repeatedly exposed to Group-A β-Haemolytic Streptococcus show perseverative behaviors, impaired sensorimotor gating, and immune activation in rostral diencephalon

Repeated exposure to Group-A β-Haemolytic Streptococcus (GAS) may constitute a vulnerability factor in the onset and course of pediatric motor disturbances. GAS infections/colonization can stimulate the production of antibodies, which may cross the blood brain barrier, target selected brain areas (e.g. basal ganglia), and exacerbate motor alterations. Here, we exposed developing SJL male mice to four injections with a GAS homogenate and evaluated the following domains: motor coordination; general locomotion; repetitive behaviors; perseverative responses; and sensorimotor gating (pre-pulse inhibition, PPI). To demonstrate that behavioral changes were associated with immune-mediated brain alterations, we analyzed, in selected brain areas, the presence of infiltrates and microglial activation (immunohistochemistry), monoamines (HPLC), and brain metabolites (in vivo Magnetic Resonance Spectroscopy). GAS-exposed mice showed increased repetitive and perseverative behaviors, impaired PPI, and reduced concentrations of serotonin in prefrontal cortex, a brain area linked to the behavioral domains investigated, wherein they also showed remarkable elevations in lactate. Active inflammatory processes were substantiated by the observation of infiltrates and microglial activation in the white matter of the anterior diencephalon. These data support the hypothesis that repeated GAS exposure may elicit inflammatory responses in brain areas involved in motor control and perseverative behavior, and result in phenotypic abnormalities.

Hormone and immune system interactions in demyelinating disease

The immune, endocrine and nervous systems communicate with each other through a myriad of molecules including cytokines, hormones and neurotransmitters. Alterations in the balance of the products of these systems affect susceptibility to autoimmune disease and also the progression of disease. One of the most intensely studied autoimmune diseases is multiple sclerosis (MS). The purpose of this review is to explore the relationships between sex hormones and MS disease progression and to attempt to understand the paradox that although women are more likely to develop MS, female sex hormones appear to be beneficial in symptom amelioration. The proposed mechanisms of the therapeutic action of estrogens will be discussed with respect to T cell polarization and also on CNS cell populations. Investigations into the pathogenesis of multiple sclerosis (MS) and animal models of MS have given insights into the interactions between the neuroendocrine systems and provide important potential therapeutic venues that may be expanded to other autoimmune and neurodegenerative conditions.

Gender differences in autoimmunity associated with exposure to environmental factors

Autoimmunity is thought to result from a combination of genetics, environmental triggers, and stochastic events. Gender is also a significant risk factor with many diseases exhibiting a female bias. Although the role of environmental triggers, especially medications, in eliciting autoimmunity is well established less is known about the interplay between gender, the environment and autoimmunity. This review examines the contribution of gender in autoimmunity induced by selected chemical, physical and biological agents in humans and animal models. Epidemiological studies reveal that environmental factors can be associated with a gender bias in human autoimmunity. However many studies show that the increased risk of autoimmunity is often influenced by occupational exposure or other gender biased activities. Animal studies, although often prejudiced by the exclusive use of female animals, reveal that gender bias can be strain specific suggesting an interaction between sex chromosome complement and background genes. This observation has important implications because it argues that within a gender biased disease there may be individuals in which gender does not contribute to autoimmunity. Exposure to environmental factors, which encompasses everything around us, adds an additional layer of complexity. Understanding how the environment influences the relationship between sex chromosome complement and innate and adaptive immune responses will be essential in determining the role of gender in environmentally-induced autoimmunity.

Characterization of dysferlin deficient SJL/J mice to assess preclinical drug efficacy: fasudil exacerbates muscle disease phenotype

The dysferlin deficient SJL/J mouse strain is commonly used to study dysferlin deficient myopathies. Therefore, we systematically evaluated behavior in relatively young (9-25 weeks) SJL/J mice and compared them to C57BL6 mice to determine which functional end points may be the most effective to use for preclinical studies in the SJL/J strain. SJL/J mice had reduced body weight, lower open field scores, higher creatine kinase levels, and less muscle force than did C57BL6 mice. Power calculations for expected effect sizes indicated that grip strength normalized to body weight and open field activity were the most sensitive indicators of functional status in SJL/J mice. Weight and open field scores of SJL/J mice deteriorated over the course of the study, indicating that progressive myopathy was ongoing even in relatively young (<6 months old) SJL/J mice. To further characterize SJL/J mice within the context of treatment, we assessed the effect of fasudil, a rho-kinase inhibitor, on disease phenotype. Fasudil was evaluated based on previous observations that Rho signaling may be overly activated as part of the inflammatory cascade in SJL/J mice. Fasudil treated SJL/J mice showed increased body weight, but decreased grip strength, horizontal activity, and soleus muscle force, compared to untreated SJL/J controls. Fasudil either improved or had no effect on these outcomes in C57BL6 mice. Fasudil also reduced the number of infiltrating macrophages/monocytes in SJL/J muscle tissue, but had no effect on muscle fiber degeneration/regeneration. These studies provide a basis for standardization of preclinical drug testing trials in the dysferlin deficient SJL/J mice, and identify measures of functional status that are potentially translatable to clinical trial outcomes. In addition, the data provide pharmacological evidence suggesting that activation of rho-kinase, at least in part, may represent a beneficial compensatory response in dysferlin deficient myopathies.

Chronic restraint stress during early Theiler's virus infection exacerbates the subsequent demyelinating disease in SJL mice: II. CNS disease severity

Theiler's murine encephalomyelitis virus (TMEV) infection is a well-characterized model of multiple sclerosis (MS). Previous research has shown that chronic restraint stress (RS) during early TMEV infection exacerbates behavioral signs of the disease. The present data suggest that RS-induced increases in CNS inflammation, demyelination, and axonal degeneration may underlie this exacerbation. In addition, we report that males exhibit greater CNS inflammation and higher numbers of demyelinating lesions while females show greater susceptibility to RS-induced exacerbation. These findings indicate that RS during early TMEV infection increases CNS lesion formation during the late phase and suggest that the effects of RS are sex-dependent.

Impact of sex steroids on neuroinflammatory processes and experimental multiple sclerosis

Synthetic and natural estrogens as well as progestins modulate neuronal development and activity. Neurons and glia are endowed with high-affinity steroid receptors. Besides regulating brain physiology, both steroids conciliate neuroprotection against toxicity and neurodegeneration. The majority of data derive from in vitro studies, although more recently, animal models have proven the efficaciousness of steroids as neuroprotective factors. Indications for a safeguarding role also emerge from first clinical trials. Gender-specific prevalence of degenerative disorders might be associated with the loss of hormonal activity or steroid malfunctions. Our studies and evidence from the literature support the view that steroids attenuate neuroinflammation by reducing the pro-inflammatory property of astrocytes. This effect appears variable depending on the brain region and toxic condition. Both hormones can individually mediate protection, but they are more effective in cooperation. A second research line, using an animal model for multiple sclerosis, provides evidence that steroids achieve remyelination after demyelination. The underlying cellular mechanisms involve interactions with astroglia, insulin-like growth factor-1 responses, and the recruitment of oligodendrocytes.

Gender and sex hormones in multiple sclerosis pathology and therapy

Several lines of evidence indicate that gender affects the susceptibility and course of multiple sclerosis (MS) with a higher disease prevalence and overall better prognosis in women than men. This sex dimorphism may be explained by sex chromosome effects and effects of sex steroid hormones on the immune system, blood brain barrier or parenchymal central nervous system (CNS) cells. The well known improvement in disease during late pregnancy has also been linked to hormonal changes and has stimulated recent clinical studies to determine the efficacy of and tolerance to sex steroid therapeutic approaches. Both clinical and experimental studies indicate that sex steroid supplementation may be beneficial for MS. This could be related to anti-inflammatory actions on the immune system or CNS and to direct neuroprotective properties. Here, clinical and experimental data are reviewed with respect to the effects of sex hormones or gender in the pathology or therapy of MS or its rodent disease models. The different cellular targets as well as some molecular mechanisms likely involved are discussed.

MRI in experimental inflammatory and mitochondrial optic neuropathies

MRI is a powerful tool for evaluating structural and functional alterations in the optic nerve in experimental animal models of human disease. MRI-histopathological correlations have provided important insights into the pathogenesis of disease. Paramagnetic contrast agents have been used to serially visualize the foci and severity of disruption of the blood-optic nerve barrier and physiological neuronal alterations in living animals. Here I review the experience of our group in optic nerve imaging of experimental autoimmune encephalomyelitis and neurodegeneration induced by genetic manipulation of respiratory chain enzymes.

SJL mice exposed to cuprizone intoxication reveal strain and gender pattern differences in demyelination

The role of mouse strain and the influence of gender on demyelination were explored for the first time in SJL mice using the cuprizone intoxication model. We document here that SJL mice display a unique pattern of demyelination that did not follow the profile that is well-characterized in C57BL/6 mice. The SJL mice did not readily demyelinate at the midline within the corpus callosum but showed greater demyelination immediately lateral to midline. During continuous exposure to cuprizone, demyelination was not complete and appeared to plateau after week 7. Importantly, female mice were partially resistant to demyelination, whereas male mice were more severely demyelinated. Differences in the number of mature oligodendrocytes were consistent with the extent of demyelination; however, microglia, astrocyte and oligodendrocyte precursor cell populations did not differ between male and female mice. Thus, genetic factors and gender influence susceptibility to demyelinating disease in the cuprizone model, which may provide additional insights into the variability observed in human demyelinating diseases such as multiple sclerosis.

Decreased spinal cord opioid receptor mRNA expression and antinociception in a Theiler's murine encephalomyelitis virus model of multiple sclerosis

Multiple sclerosis patients typically experience increased pain that is relatively insensitive to opiate treatment. The mechanistic basis for this increased nociception is currently poorly understood. In the present study, we utilized the Theiler's murine encephalomyelitis virus (TMEV) model of MS to examine possible changes in spinal cord opioid receptor mRNA over the course of disease progression. TMEV infection led to significantly decreased mu, delta and kappa opioid receptor mRNA expression as analyzed by quantitative real-time PCR in both male and female mice at days 90, 150 and 180 post-infection (PI). Since opioid receptor mRNA expression decreased in TMEV mice, we examined whether opiate analgesia is also altered. TMEV infected female mice had significantly decreased opiate analgesia in thermal nociceptive tests beginning at day 90 PI, while TMEV-infected male mice did not display significantly decreased opiate analgesia until day 120 PI. The novel finding that opioid receptor expression is significantly decreased in the spinal cord of TMEV mice could explain the increased nociception and loss of opiate analgesia observed in both TMEV mice and multiple sclerosis patients.

Analysis of nociception, sex and peripheral nerve innervation in the TMEV animal model of multiple sclerosis

Although pain was previously not considered an important element of multiple sclerosis (MS), recent evidence indicates that over 50% of MS patients suffer from chronic pain. In the present study, we utilized the Theiler's murine encephalomyelitis virus (TMEV) model of MS to examine whether changes in nociception occur during disease progression and to investigate whether sex influences the development of nociception or disease-associated neurological symptoms. Using the rotarod assay, TMEV infected male mice displayed increased neurological deficits when compared to TMEV infected female mice, which mimics what is observed in human MS. While both male and female TMEV infected mice exhibited thermal hyperalgesia and mechanical allodynia, female mice developed mechanical allodynia at a faster rate and displayed significantly more mechanical allodynia than male mice. Since neuropathic symptoms have been described in MS patients, we quantified sensory nerve fibers in the epidermis of TMEV-infected and non-infected mice to determine if there were alterations in epidermal nerve density. There was a significantly higher density of PGP9.5 and CGRP-immunoreactive axons in the epidermis of TMEV-infected mice versus controls. Collectively these results indicate that the TMEV model is well suited to study the mechanisms of MS-induced nociception and suggest that alterations in peripheral nerve innervation may contribute to MS pain.

Castration of male C57L/J mice increases susceptibility and estrogen treatment restores resistance to Theiler's virus-induced demyelinating disease

Intracerebral inoculation of Theiler's murine encephalomyelitis virus (TMEV) results in immune-mediated demyelination in selective mouse strains. We have previously demonstrated that the males of C57L mice are significantly more susceptible to TMEV-induced demyelinating disease. To assess further the hormonal influence for this gender-associated differential susceptibility, estrogen-treated, castrated C57L mice were infected with TMEV and compared with sham-operated and/or placebo-treated mice. Interestingly, castration further elevated the susceptibility to virally induced demyelinating disease compared with sham-castrated control mice, and prolonged treatment of castrated mice with estrogen restored the resistance to the level of control mice. These results strongly suggest that sex hormone levels contribute to the gender-biased susceptibility to TMEV-induced demyelinating disease. Mice treated with estrogen showed a significantly decreased level of virus-specific Th1 responses both in the periphery and in the CNS. In addition, in vitro estrogen treatment was able to inhibit viral replication directly in macrophages, consistent with the lower level of viral RNA in microglia/macrophages in the CNS from castrated estrogen-treated mice compared with controls. Also, estrogen treatment inhibited VCAM-1 expression induced by tumor necrosis factor-alpha in cerebral vascular endothelial (CVE) cells via inhibition of nuclear factor-kappaB (NFkappaB), which is produced in various glial cells upon TMEV infection. Overall, estrogen treatment appears to exert its effects on viral replication, induction of immune responses, as well as infiltration of activated immune cells into the CNS via inhibition of NFkappaB function.

Gender issues in multiple sclerosis

Multiple sclerosis (MS) varies considerably in the way that it affects females and males. The prevalence of the disease is much greater in women and tends to follow a different clinical course than it follows in the affected male population. It is also well known that MS symptoms often are much less of a problem during pregnancy. This chapter discusses possible explanations for gender differences based on sex hormones as well as the effects of these hormones on cytokines and other factors that may influence the course of MS. Knowledge of these effects may hold some promise in other types of treatment for MS. Since MS is much more prevalent in women of child-bearing age, there are also implications for the use of disease-modifying agents as well as drugs and treatments that may be useful for treatment of MS. MS often causes symptoms of sexual dysfunction, but there may be effective treatment for many of these treatments.

Sex-dependent effects of chronic restraint stress during early Theiler's virus infection on the subsequent demyelinating disease in CBA mice

Chronic restraint stress, administered during early infection with Theiler's virus, was found to exacerbate the acute CNS viral infection in male and female mice. During the subsequent demyelinating phase of disease (a model of multiple sclerosis), the effect of stress on disease progression was sex-dependent. Previously stressed male mice had less severe behavioral signs of the chronic phase, better rotarod performance and decreased inflammatory lesions of the spinal cord, while the opposite pattern was observed in females. In addition, mice in all groups developed autoantibodies to MBP, PLP139-151 and MOG33-55.

The genetics of the persistent infection and demyelinating disease caused by Theiler's virus

Theiler's virus causes a persistent and demyelinating infection of the central nervous system of the mouse, which is one of the best animal models to study multiple sclerosis. This review focuses on the mechanism of persistence. The virus infects neurons for a few weeks and then shifts to white matter, where it persists in glial cells and macrophages. Oligodendrocytes are crucial host cells, as shown by the resistance to persistent infection of mice bearing myelin mutations. Two viral proteins, L and L*, contribute to persistence by interfering with host defenses. L, a small zinc-finger protein, restricts the production of interferon. L*, a unique example of a picornaviral protein translated from an overlapping open reading frame, facilitates the infection of macrophages. Susceptibility to persistent infection, which varies among inbred mouse strains, is multigenic. H2 class I genes have a major effect on susceptibility. Among several non-H2 susceptibility loci, Tmevp3 appears to regulate the expression of important cytokines.

Gender bias in Theiler's virus-induced demyelinating disease correlates with the level of antiviral immune responses

Multiple sclerosis is an immune-mediated disease of the CNS and shows a sex-biased distribution in which 60-75% of all cases are female. A mouse model of multiple sclerosis, Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease, also displays a gender bias. However, in the C57L/J strain of mice, males are susceptible to disease whereas females are completely resistant. In this study we determined the gender differences in the TMEV-specific immune response, which may be responsible for the gender bias in clinical disease. Our data clearly demonstrate that female C57L/J mice induce significantly higher levels of TMEV-specific neutralizing Ab as well as a stronger peripheral T cell response throughout the course of viral infection. In contrast, male mice have a higher level of TMEV-specific CD4(+) and CD8(+) T cell infiltration into the CNS as well as viral persistence. These results suggest that a higher level of the initial antiviral immune response in female mice may be able to effectively clear virus from the periphery and CNS and therefore prevent further disease manifestations. Male mice in contrast do not mount as effective an immune response, thereby allowing for eventual viral persistence in the CNS and continuous T cell expansion leading to clinical symptoms.

Effects of gender on neurologic and functional recovery after spinal cord injury

OBJECTIVE

To assess gender differences in neurologic and functional outcome measures in persons with spinal cord injury (SCI).

DESIGN

Case series.

SETTINGS

Model Spinal Cord Injury Systems (MSCIS) throughout the United States.

PARTICIPANTS

People (N=14,433) admitted to an MSCIS within 30 days of injury.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Improvement in American Spinal Injury Association (ASIA) motor index score, ASIA Impairment Scale, level of injury, and FIM instrument scores after SCI.

RESULTS

When examining subjects grouped by severity of injury, changes in ASIA motor index total scores, from system admission to 1-year anniversary, were significantly greater for women than men with either complete ( P =.035) or incomplete ( P =.031) injuries. Functional comparison of men and women, using the FIM motor subscale, revealed that men had higher FIM motor scores at rehabilitation discharge among those with motor-complete injuries, except for those with C1-4 and C6 neurologic levels. Women with motor-incomplete high tetraplegia (C1-4 levels) had higher discharge FIM motor scores than did similarly afflicted men. There were no significant differences in FIM motor scores among men and women with other levels of motor incomplete SCI.

CONCLUSIONS

Gender differences in SCI were seen in several areas. Women may have more natural neurologic recovery than men; however, for a given level and degree of neurologic injury, men tend to do better functionally than women at time of discharge from rehabilitation. Future prospective study of the effects of estrogen on neurologic recovery and the effects of gender on functional potential are recommended.

Chronic restraint stress during early Theiler's virus infection exacerbates the subsequent demyelinating disease in SJL mice

Chronic restraint stress, administered during early infection with Theiler's virus, was found to exacerbate the acute central nervous system (CNS) viral infection and the subsequent demyelinating phase of disease (an animal model of Multiple Sclerosis (MS)) in SJL male and female mice. During early infection, stressed mice displayed decreased body weights and spontaneous activity; while increased behavioral signs of illness and plasma corticosterone (CORT) levels. During the subsequent chronic demyelinating phase of disease, previously stressed mice had greater behavioral signs of the chronic phase, worsened rotarod performance, and increased inflammatory lesions of the spinal cord. In addition, mice developed autoantibodies to myelin basic protein (MBP), proteolipid protein peptide (PLP139-151), and myelin oligodendrocyte glycoprotein peptide (MOG33-55).

A new rodent model of hind limb penetrating wound injury characterized by continuous primary and secondary hyperalgesia

This article reports the development of a new hind limb pain model in which an incisional stab wound is placed on the front and back of the calf, causing both superficial and deep tissue injury. The injury causes primary mechanical hyperalgesia on the calf and secondary hind paw hyperalgesia, which served as the focus of the present study. Animals with unilateral stab wounds showed a significant increase in percent paw withdrawal (secondary mechanical hyperalgesia, reversed by morphine administration) from 2 to 48 hours after surgery, but no evidence of thermal hyperalgesia. In contrast, animals with bilateral leg injuries showed bilateral secondary mechanical and thermal hyperalgesia. Rats with unilateral leg incisional stab wounds showed a significant decrease in cage activity in both the horizontal and vertical directions, monitored by using a novel activity box approach, as compared to their 24-hour baseline levels or to the activity of naïve animals. Analysis of spinal cord Fos labeling demonstrated that calf injury significantly increased Fos expression in laminae I to VI of the L3-L5 cord segments. The data indicate that this model might be useful for evaluation of the mechanisms underlying penetrating injury-induced primary and secondary hyperalgesia or for testing the effect of analgesics on hyperalgesia induced by such injury.

PERSPECTIVE

Stab wounds and other types of penetrating wounds routinely encountered in emergency rooms and clinics are accompanied by pain associated with superficial and deep tissue injury. Here we present a rodent stab wound model that affords an opportunity to study the mechanisms of pain associated with traumatic injury.

A polymeric membrane dressing with antinociceptive properties: analysis with a rodent model of stab wound secondary hyperalgesia

The putative antinociceptive properties of a commercially available polymeric membrane dressing were tested by using a hind limb penetrating stab wound model in which secondary hyperalgesia could be evaluated from the hind paw. We examined the responses to mechanical and thermal stimuli applied to the hind paw remote to 2 small penetrating stab wounds of the calf. Application of the polymeric membrane dressing, but not gauze dressing, significantly reduced the development of both mechanical and thermal hyperalgesia induced by the penetrating stab wounds. In addition, animals with stab wounds showed a significant decrease in cage activity, and this decrease was prevented by application of the polymeric dressing. Analysis of spinal cord Fos expression demonstrated that the polymeric membrane, but not gauze, dressing significantly decreased stab wound-induced Fos expression in laminae I to VI of the ipsilateral L3-L5 cord segments. In addition, application of the polymeric membrane, but not gauze, dressing to the hind limb of naïve animals elicited Fos expression in laminae III and IV of the lumbar spinal cord. The data indicate that this model might be useful for evaluation of the mechanisms underlying deep tissue injury-induced secondary hyperalgesia, but they also demonstrate that the polymeric membrane dressing tested is capable of significantly reducing secondary hyperalgesia.

PERSPECTIVE

Surgery and other types of penetrating wounds cause pain that is not always relieved by opioids and/or less potent analgesics. The present results suggest that the polymeric membrane dressing tested here may be used alone or in conjunction with analgesics to relieve pain caused by penetrating tissue injury.