Mice with a deletion of the major central myelin protein exhibit hypersensitivity to noxious thermal stimuli: involvement of central sensitization.

Null mutations in the gene encoding the major myelin protein of the central nervous system, proteolipid protein 1 (PLP1), cause an X-linked form of spastic paraplegia (SPG2) associated with axonal degeneration. While motor symptoms are the best known manifestations of this condition, its somatosensory disturbances have been described but poorly characterized. We carried out a longitudinal study in an animal model of SPG2 - mice carrying a deletion of the Plp1 gene (Plp-null mice). Plp-null mice exhibited severe early-onset thermal hyperalgesia, in the absence of thermal allodynia. We first performed an electrophysiological testing which showed an early decrease in peripheral and spinal conduction velocities in Plp null mice. Such as the abnormal sensitive behaviors, this slowing of nerve conduction was observed before the development of myelin abnormalities at the spinal level, from 3months of age, and without major morphological defects in the sciatic nerve. To understand the link between a decrease in nerve velocity and an increased response to thermal stimuli before the appearance of myelin abnormalities, we focused our attention on the dorsal horn of the spinal cord, the site of integration of somatosensory information. Immunohistochemical studies revealed an early-onset activation of astrocytes and microglia that worsened with age, associated later in age with perturbation of the expression of the sensory neuropeptides calcitonin-gene-related peptide and galanin. Taken together, these results represent complementary data supporting the hypothesis that Plp-null mice suffer from ganglionopathy associated with late onset central demyelination but with few peripheral nerve alterations, induced by the glial-cell-mediated sensitization of the spinal cord. The mechanism suggested here could underlie pain experiments in other leukodystrophies as well as in other non-genetic demyelinating diseases such as multiple sclerosis.

Mutation of Proteolipid Protein 1 Gene: From Severe Hypomyelinating Leukodystrophy to Inherited Spastic Paraplegia.

Pelizaeus-Merzbacher Disease (PMD) is an inherited leukodystrophy affecting the central nervous system (CNS)-a rare disorder that especially concerns males. Its estimated prevalence is 1.45-1.9 per 100,000 individuals in the general population. Patients affected by PMD exhibit a drastic reduction or absence of myelin sheaths in the white matter areas of the CNS. The Proteolipid Protein 1 (PLP1) gene encodes a transmembrane proteolipid protein. PLP1 is the major protein of myelin, and it plays a key role in the compaction, stabilization, and maintenance of myelin sheaths. Its function is predominant in oligodendrocyte development and axonal survival. Mutations in the PLP1 gene cause the development of a wide continuum spectrum of leukopathies from the most severe form of PMD for whom patients exhibit severe CNS hypomyelination to the relatively mild late-onset type 2 spastic paraplegia, leading to the concept of PLP1-related disorders. The genetic diversity and the biochemical complexity, along with other aspects of PMD, are discussed to reveal the obstacles that hinder the development of treatments. This review aims to provide a clinical and mechanistic overview of this spectrum of rare diseases.

Antioxidant effect of grape seed extract corrects experimental autoimmune encephalomyelitis behavioral dysfunctions, demyelination, and glial activation.

Background and purpose: Multiple sclerosis (MS), a multifactorial autoimmune disease of the central nervous system (CNS), is characterized by demyelination and chronic inflammation, as well as axonal and neuronal loss. There is no cure for MS, and despite a significant improvement in the therapeutic management of patients during the last 20 years, some symptoms are still resistant to treatment, and the evolution of the disease to progressive form seems still ineluctable. The etiology of MS is complex and still not fully understood. However, inflammation is a major driver of physiopathology and oxidative stress contributes to CNS lesions and promotes existing inflammatory response. Plant polyphenols are endowed with many therapeutic benefits through alleviating oxidative stress and inflammation, thus providing neuroprotection in MS. We presently evaluated the curative effect of grape seed extract (GSE) in an experimental autoimmune encephalomyelitis (EAE) mouse model of MS. Experimental approach: Six-week-old C57Bl/6J females were subjected to the EAE paradigm (using myelin oligodendrocyte glycoprotein peptide fragment (35-55), complete Freund's adjuvant, and pertussis toxin) and then chronically treated with GSE from day 10 to day 30 post-induction. Clinical score and body weight were monitored daily, while evaluation of sensitive, motor, cognitive, and anxiety-related behaviors was performed weekly. Then, the GSE effect was evaluated on whole brain and spinal cord samples through the evaluation of oxidative stress damage, antioxidant capacities, myelin alteration, astroglial and microglial proliferation, and sirtuin expression. Key results: Grape seed extract curative chronic treatment corrected the clinical course of EAE, as well as the mechanical hypersensitivity, and avoided the development of EAE mouse thermal cold allodynia. The neuropathological evaluation showed that GSE reduced oxidative stress in the brain and spinal cord by decreasing the lipid and protein oxidation through correction of the three main antioxidant enzyme activities, namely, superoxide dismutase, catalase, and glutathione peroxidase, as well as restoring normal myelin protein expression and correcting microglial and astroglial protein overexpression and sirtuin downregulation. Conclusion and implications: These data strongly support GSE as an effective therapeutic approach in MS treatment.

Can chronopharmacology improve the therapeutic management of neurological diseases?

The importance of circadian rhythm dysfunctions in the pathophysiology of neurological diseases has been highlighted recently. Chronopharmacology principles imply that tailoring the timing of treatments to the circadian rhythm of individual patients could optimize therapeutic management. According to these principles, chronopharmacology takes into account the individual differences in patients' clocks, the rhythmic changes in the organism sensitivity to therapeutic and side effects of drugs, and the predictable time variations of disease. This review examines the current literature on chronopharmacology of neurological diseases focusing its scope on epilepsy, Alzheimer and Parkinson diseases, and neuropathic pain, even if other neurological diseases could have been analyzed. While the results of the studies discussed in this review point to a potential therapeutic benefit of chronopharmacology in neurological diseases, the field is still in its infancy. Studies including a sufficiently large number of patients and measuring gold standard markers of the circadian rhythmicity are still needed to evaluate the beneficial effect of administration times over the 24-hour day but also of clock modulating drugs.

In-Depth Characterization of Somatic and Orofacial Sensitive Dysfunctions and Interfering-Symptoms in a Relapsing-Remitting Experimental Autoimmune Encephalomyelitis Mouse Model.

Among the many symptoms (motor, sensory, and cognitive) associated with multiple sclerosis (MS), chronic pain is a common disabling condition. In particular, neuropathic pain symptoms are very prevalent and debilitating, even in early stages of the disease. Unfortunately, chronic pain still lacks efficient therapeutic agents. Progress is needed (i) clinically by better characterizing pain symptoms in MS and understanding the underlying mechanisms, and (ii) preclinically by developing a more closely dedicated model to identify new therapeutic targets and evaluate new drugs. In this setting, new variants of experimental autoimmune encephalomyelitis (EAE) are currently developed in mice to exhibit less severe motor impairments, thereby avoiding confounding factors in assessing pain behaviors over the disease course. Among these, the optimized relapsing-remitting EAE (QuilA-EAE) mouse model, induced using myelin oligodendrocyte glycoprotein peptide fragment (35-55), pertussis toxin, and quillaja bark saponin, seems very promising. Our study sought (i) to better define sensitive dysfunctions and (ii) to extend behavioral characterization to interfering symptoms often associated with pain during MS, such as mood disturbances, fatigue, and cognitive impairment, in this optimized QuilA-EAE model. We made an in-depth characterization of this optimized QuilA-EAE model, describing for the first time somatic thermal hyperalgesia associated with mechanical and cold allodynia. Evaluation of orofacial pain sensitivity showed no mechanical or thermal allodynia. Detailed evaluation of motor behaviors highlighted slight defects in fine motor coordination in the QuilA-EAE mice but without impact on pain evaluation. Finally, no anxiety-related or cognitive impairment was observed during the peak of sensitive symptoms. Pharmacologically, as previously described, we found that pregabalin, a treatment commonly used in neuropathic pain patients, induced an analgesic effect on mechanical allodynia. In addition, we showed an anti-hyperalgesic thermal effect on this model. Our results demonstrate that this QuilA-EAE model is clearly of interest for studying pain symptom development and so could be used to identify and evaluate new therapeutic targets. The presence of interfering symptoms still needs to be further characterized.

Longitudinal MRI monitoring of brain damage in the neonatal ventral hippocampal lesion rat model of schizophrenia.

Rat with excitotoxic neonatal ventral hippocampal lesions (NVHL rats) is considered as a heuristic neurodevelopmental model for studying schizophrenia. Extensive study of this model is limited by the lack of clear validity criteria of such lesions and because ascertaining of the lesions is realized postmortem with histological examination after completing experiments. Here, in a first experiment, by assessing the locomotor response to amphetamine in adult NVHL rats, we further specify that the lesions must be bilateral and confined to the ventral hippocampus to obtain the validated behavioral phenotype. We then show a longitudinal magnetic resonance imaging (MRI) protocol suitable for the detection of brain structural changes in NVHL rats. The T(2)-weighted images acquired in adult NVHL rats reveal the same structural changes as those appraised with histological protocol. Moreover, we demonstrate that the lesion status in adulthood can be accurately predicted from the T(2)-weighted images acquired in the juvenile period. As technical advantages, our MRI protocol makes possible to select animals according to lesion criteria as soon as in the juvenile period before long-lasting experiments and gives access in vivo to a quantitative parameter indicative of the lesion extent. Finally, we show that the lesion size increases only slightly between juvenile and adult periods. These latter results are discussed in the context of the specific postpubertal emergence of the behavioral deficits in NVHL rats.

Characterisation of spinal cord in a mouse model of spastic paraplegia related to abnormal axono-myelin interactions by in vivo quantitative MRI.

In inherited neurodegenerative disorders the engineering of genetically modified mice for the causative genes have provided new insights in the understanding of axono-glial interactions. Patients lacking the major proteins of the central nervous system myelin, the proteolipoproteins (PLP1) exhibit an ascending axonopathy, named spastic paraplegia type 2. Our objective was to examine the interest of using quantitative MRI for non invasive detection of spinal cord (SC) consequences of the PLP1 defect in a mouse model of SPG2 (PLP1-/Y). For this purpose an MRI acquisition and retrospective correction chain was set up to map apparent diffusion coefficients (ADC) and T2 in the mouse cervical SC which improve the intra- and inter-animal homogeneity. This reliable imaging processing protocol allowed to detect significant changes between PLP1-/Y and wild type 15-month old SC, mainly no longer detected ex vivo after SC fixation. On the basis of ADC(//) and ADC( perpendicular) variations, white matter (WM) damages were characterised on both the myelin and axonal components. The microstructural changes observed in the Plp1 deficient grey matter (GM) were concomitantly related to the isotropic increase of GM ADC. The T2 reduction measured in the WM as well as the GM of the mutant SC seems to be also an interesting marker of the SC axono-glial dysfunction. The present study demonstrated the interest of quantitative MRI for phenotyping in vivo the WM and GM changes in SC neurodegenerative disorders related to myelin and impaired glia-axonal interaction.

[Pharmacological management of neuropathic pain]. / Les traitements pharmacologiques des douleurs neuropathiques.

Neuropathic pain is defined as pain caused by a lesion or a disease affecting the somatosensory nervous system. Development of neuropathic pain is induced by many pathophysiological mechanisms affecting pain pathways. Neuropathic pain has diverse origins, making its management difficult, hence, many patients with neuropathic pain do not receive appropriate treatment. In 2015, a revision of the Neuropathic Pain Special Interest Group's (NeuPSIG) previous recommendations, based on a systematic review and meta-analysis, evaluated the efficacy of systemic and topical treatments of neuropathic pain. Treatments lines were established using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE), which allows to rate the quality of evidence and the strength of recommendations. First line treatments are gabapentin and pregabalin, noradrenalin and serotonin reuptake inhibitors and tricyclic antidepressants. Capsaicin and lidocaine patches are second line treatments, tramadol and strong opioids are third line treatments. This work also highlighted molecules with inconclusive recommendations or non-recommended pharmacological treatments based on a low quality of evidence, a lack of efficacy or a bad safety profile. The objective of this paper is to present the different treatments and to detail their mechanisms of action.

Oxidative stress and mitochondrial dynamics malfunction are linked in Pelizaeus-Merzbacher disease.

Pelizaeus-Merzbacher disease (PMD) is a fatal hypomyelinating disorder characterized by early impairment of motor development, nystagmus, choreoathetotic movements, ataxia and progressive spasticity. PMD is caused by variations in the proteolipid protein gene PLP1, which encodes the two major myelin proteins of the central nervous system, PLP and its spliced isoform DM20, in oligodendrocytes. Large duplications including the entire PLP1 gene are the most frequent causative mutation leading to the classical form of PMD. The Plp1 overexpressing mouse model (PLP-tg66/66 ) develops a phenotype very similar to human PMD, with early and severe motor dysfunction and a dramatic decrease in lifespan. The sequence of cellular events that cause neurodegeneration and ultimately death is poorly understood. In this work, we analyzed patient-derived fibroblasts and spinal cords of the PLP-tg66/66 mouse model, and identified redox imbalance, with altered antioxidant defense and oxidative damage to several enzymes involved in ATP production, such as glycolytic enzymes, creatine kinase and mitochondrial proteins from the Krebs cycle and oxidative phosphorylation. We also evidenced malfunction of the mitochondria compartment with increased ROS production and depolarization in PMD patient's fibroblasts, which was prevented by the antioxidant N-acetyl-cysteine. Finally, we uncovered an impairment of mitochondrial dynamics in patient's fibroblasts which may help explain the ultrastructural abnormalities of mitochondria morphology detected in spinal cords from PLP-tg66/66 mice. Altogether, these results underscore the link between redox and metabolic homeostasis in myelin diseases, provide insight into the pathophysiology of PMD, and may bear implications for tailored pharmacological intervention.

Microtubule stabilizer ameliorates synaptic function and behavior in a mouse model for schizophrenia.

BACKGROUND: Recent data suggest that cytoskeletal defects may play a role in schizophrenia. We previously imitated features of schizophrenia in an animal model by disrupting gene coding for a microtubule-associated protein called STOP. STOP-null mice display synaptic defects in glutamatergic neurons, hyper-dopaminergy, and severe behavioral disorders. Synaptic and behavioral deficits are amended by neuroleptic treatment in STOP-null mice, providing an attractive model to test new antipsychotic agents. We examined the effects of a taxol-related microtubule stabilizer, epothilone D. METHODS: Mice were treated either with vehicle alone or with epothilone D. Treatment effects on synaptic function were assessed using electron-microscopy quantification of synaptic vesicle pools and electrophysiology in the CA1 region of the hippocampus. Dopamine transmission was investigated using electrochemical assays. Behavior was principally assessed using tests of maternal skills. RESULTS: In STOP-null mice, treatment with epothilone D increased synaptic vesicle pools, ameliorated both short- and long-term forms of synaptic plasticity in glutamatergic neurons, and had a dramatic beneficial effect on mouse behavior. CONCLUSIONS: A microtubule stabilizer can have a beneficial effect on synaptic function and behavior, suggesting new possibilities for treatment of schizophrenia.

Post-pubertal emergence of alterations in locomotor activity in stop null mice.

Overt schizophrenia is preceded by a prodromal phase during which juvenile patients display attenuated schizophrenia-related symptoms. Here, we have looked for evidence of a prodromal phase in juvenile STOP null mice, which, during adulthood, imitate features of schizophrenia. We have principally examined locomotor activity, which is abnormal in adult STOP null mice, and its apparent relationship with perturbed glutamatergic and dopaminergic transmission. When compared to corresponding wild-type mice, juvenile STOP null mice did not exhibit the basal hyperlocomotion or locomotor hypersensitivity to mild stress observed in adult mice. Juvenile STOP null mice also lacked disturbed locomotor sensitivity to MK-801, which was evident in adult mice. In contrast, juvenile STOP null mice exhibited a similar hypersensitivity to amphetamine as that found in adult mice. Thus, STOP null mice exhibited both a progression of locomotor activity defects over time and subtle alterations in the prepubertal period. We suggest that the pattern of locomotor disturbances observed in this study is related to altered dopaminergic reactivity in juvenile mice without major disturbance in glutamatergic transmission, whereas both neurotransmitter systems are impaired in adult mice.

Dopaminergic transmission in STOP null mice.

Neuroleptics are thought to exert their anti-psychotic effects by counteracting a hyper-dopaminergic transmission. Here, we have examined the dopaminergic status of STOP (stable tubule only polypeptide) null mice, which lack a microtubule-stabilizing protein and which display neuroleptic-sensitive behavioural disorders. Dopamine transmission was investigated using both behavioural analysis and measurements of dopamine efflux in different conditions. Compared to wild-type mice in basal conditions or following mild stress, STOP null mice showed a hyper-locomotor activity, which was erased by neuroleptic treatment, and an increased locomotor reactivity to amphetamine. Such a behavioural profile is indicative of an increased dopaminergic transmission. In STOP null mice, the basal dopamine concentrations, measured by quantitative microdialysis, were normal in both the nucleus accumbens and the striatum. When measured by electrochemical techniques, the dopamine efflux evoked by electrical stimulations mimicking physiological stimuli was dramatically increased in the nucleus accumbens of STOP null mice, apparently due to an increased dopamine release, whereas dopaminergic uptake and auto-inhibition mechanisms were normal. In contrast, dopamine effluxes were slightly diminished in the striatum. Together with previous results, the present study indicates the association in STOP null mice of hippocampal hypo-glutamatergy and of limbic hyper-dopaminergy. Such neurotransmission defects are thought to be central to mental diseases such as schizophrenia.