Multiple sclerosis (MS) is a debilitating affliction of the central nervous system (CNS) that involves demyelination of neuronal axons and neurodegeneration resulting in disability that becomes more pronounced in progressive forms of the disease. The involvement of neurodegeneration in MS underscores the need for effective neuroprotective approaches necessitating identification of new therapeutic targets. Herein, we applied an integrated elemental analysis workflow to human MS-affected spinal cord tissue utilising multiple inductively coupled plasma-mass spectrometry methodologies. These analyses revealed shifts in atomic copper as a notable aspect of disease. Complementary gene expression and biochemical analyses demonstrated that changes in copper levels coincided with altered expression of copper handling genes and downstream functionality of cuproenzymes. Copper-related problems observed in the human MS spinal cord were largely reproduced in the experimental autoimmune encephalomyelitis (EAE) mouse model during the acute phase of disease characterised by axonal demyelination, lesion formation, and motor neuron loss. Treatment of EAE mice with the CNS-permeant copper modulating compound CuII(atsm) resulted in recovery of cuproenzyme function, improved myelination and lesion volume, and neuroprotection. These findings support targeting copper perturbations as a therapeutic strategy for MS with CuII(atsm) showing initial promise.

Demyelination within the central nervous system (CNS) is a significant feature of debilitating neurological diseases such as multiple sclerosis and administering the copper-selective chelatorcuprizone to mice is widely used to model demyelination in vivo. Conspicuous demyelination within the corpus callosum is generally attributed to cuprizone's ability to restrict copper availability in this vulnerable brain region. However, the small number of studies that have assessed copper in brain tissue from cuprizone-treated mice have produced seemingly conflicting outcomes, leaving the role of CNS copper availability in demyelination unresolved. Herein we describe our assessment of copper concentrations in brain samples from mice treated with cuprizone for 40 d. Importantly, we applied an inductively coupled plasma mass spectrometry methodology that enabled assessment of copper partitioned into soluble and insoluble fractions within distinct brain regions, including the corpus callosum. Our results show that cuprizone-induced demyelination in the corpus callosum was associated with decreased soluble copper in this brain region. Insoluble copper in the corpus callosum was unaffected, as were pools of soluble and insoluble copper in other brain regions. Treatment with the blood-brain barrier permeant copper compound CuII(atsm) increased brain copper levels and this was most pronounced in the soluble fraction of the corpus callosum. This effect was associated with significant mitigation of cuprizone-induced demyelination. These results provide support for the involvement of decreased CNS copper availability in demyelination in the cuprizone model. Relevance to human demyelinating disease is discussed. Graphical Abstract Cuprizone-induced demyelination in the mouse corpus callosum involves depletion of copper in the soluble fraction of this vulnerable brain region. Pharmacological copper delivery to the brain is protective.

Background: The implications on the choice of donor side when using the free fibula flap for reconstruction of unilateral maxillectomy defects has not been discussed in the literature so far. Methods: A unilateral maxillectomy reconstruction was replicated using a 3D-printed skull model and fresh cadaveric dissections of left and right osteomyocutaneous fibula flaps for comparison. Detailed photo documentation was conducted to analyze and illustrate the anatomical differences of performing a reconstruction using the ipsilateral or contralateral sides and their relative benefits and risks. Results: A more favorable lie of the septum and skin paddle and flexor hallucis longus muscle is attainable depending on which donor side is used and the planned direction of the pedicle. Conclusion: This study demonstrates why it is preferable to use the ipsilateral fibula if anastomosis is to the ipsilateral facial or neck recipient vessels, or the contralateral fibula where the contralateral recipient vessels are preferred.

The sphingolipids galactosylceramide (GalCer), sulfatide (ST) and sphingomyelin (SM) are essential for myelin stability and function. GalCer and ST are synthesized mostly from C22-C24 ceramides, generated by Ceramide Synthase 2 (CerS2). To clarify the requirement for C22-C24 sphingolipid synthesis in myelin biosynthesis and stability, we generated mice lacking CerS2 specifically in myelinating cells (CerS2ΔO/ΔO ). At 6 weeks of age, normal-appearing myelin had formed in CerS2ΔO/ΔO mice, however there was a reduction in myelin thickness and the percentage of myelinated axons. Pronounced loss of C22-C24 sphingolipids in myelin of CerS2ΔO/ΔO mice was compensated by greatly increased levels of C18 sphingolipids. A distinct microglial population expressing high levels of activation and phagocytic markers such as CD64, CD11c, MHC class II, and CD68 was apparent at 6 weeks of age in CerS2ΔO/ΔO mice, and had increased by 10 weeks. Increased staining for denatured myelin basic protein was also apparent in 6-week-old CerS2ΔO/ΔO mice. By 16 weeks, CerS2ΔO/ΔO mice showed pronounced myelin atrophy, motor deficits, and axon beading, a hallmark of axon stress. 90% of CerS2ΔO/ΔO mice died between 16 and 26 weeks of age. This study highlights the importance of sphingolipid acyl chain length for the structural integrity of myelin, demonstrating how a modest reduction in lipid chain length causes exposure of a denatured myelin protein epitope and expansion of phagocytic microglia, followed by axon pathology, myelin degeneration, and motor deficits. Understanding the molecular trigger for microglial activation should aid the development of therapeutics for demyelinating and neurodegenerative diseases.

Small molecular weight functional mimetics of brain-derived neurotrophic factor (BDNF) which act via the TrkB receptor have been developed to overcome the pharmacokinetic limitations of BDNF as a therapeutic for neurological disease. Activation of TrkB on oligodendrocytes has been identified as a potential strategy for myelin repair in demyelinating conditions. Here, we tested the efficacy of intracerebroventricular infusion of TrkB agonist 7,8-dihydroxyflavone (DHF) to promote myelin repair in the cuprizone model and alter the course of experimental autoimmune encephalomyelitis (EAE). In these two distinct mouse models used for the preclinical testing of remyelinating therapeutics, we found that DHF infusion increased the percentage of myelin basic protein and density of oligodendrocyte progenitor cells (OPCs) in the corpus callosum of female C57BL/6 mice after cuprizone demyelination. However, DHF did not alter the percentage of axons myelinated or increase the density of post-mitotic oligodendrocytes in this model. Direct cerebrospinal fluid infusion of DHF also had no effect on the clinical course of EAE, and examination of the lumbar spinal cord after 21 days of treatment revealed extensive demyelination. These results indicate that direct cerebrospinal fluid infusion of DHF is ineffective at promoting myelin repair in toxin-induced and inflammatory models of demyelination.

The authors regret the inclusion of a calculation error, in results section 3.6 (Fig. 5a and b), regarding cortical and hippocampal tissue volumes. This calculation error affected all data equally (actual values are 10-fold higher than reported), such that statistical analyses and interpretations remain accurate. The correct version of the figure is provided below.

Small molecular weight functional mimetics of brain-derived neurotrophic factor (BDNF) which act via the TrkB receptor have been developed to overcome the pharmacokinetic limitations of BDNF as a therapeutic agent for neurological disease. Activation of TrkB signalling on oligodendrocytes has been identified as a potential strategy for promoting myelin repair in demyelinating conditions such as Multiple Sclerosis (MS). Here, we tested the efficacy of intracerebroventricular infusion of TrkB agonist 7,8-dihydroxyflavone (DHF) to promote myelin repair in the cuprizone model of de- and remyelination and alter the course of experimental autoimmune encephalomyelitis (EAE), after the onset of clinical signs. In these two distinct, but common mouse models used for the preclinical testing of MS therapeutics, we found that DHF infusion increased the percentage of myelin basic protein and density of oligodendrocyte progenitor cells (OPCs) in the corpus callosum of female C57BL/6 mice after cuprizone demyelination. However, DHF did not alter the percentage of axons myelinated or increase the density of post-mitotic oligodendrocytes in this model. Direct central nervous system infusion of DHF infusion also had no effect on the clinical course of EAE in male and female C57BL/6 mice, and examination of the lumbar spinal cord after 21 days of treatment revealed extensive demyelination, with active phagocytosis of myelin debris by Iba1+ macrophages/microglia. These results indicate that direct central nervous system infusion of DHF is ineffective at promoting myelin repair in toxin-induced and inflammatory models of demyelination.

Young children have a high risk of sustaining a traumatic brain injury (TBI), which can have debilitating life-long consequences. Importantly, the young brain shows particular vulnerability to injury, likely attributed to ongoing maturation of the myelinating nervous system at the time of insult. Here, we examined the effect of acute treatment with the partial tropomyosin receptor kinase B (TrkB) agonist, LM22A-4, on pathological and neurobehavioral outcomes after pediatric TBI, with the hypothesis that targeting TrkB would minimize tissue damage and support functional recovery. We focused on myelinated tracts-the corpus callosum and external capsules-based on recent evidence that TrkB activation potentiates oligodendrocyte remyelination. Male mice at postnatal day 21 received an experimental TBI or sham surgery. Acutely post-injury, extensive cell death, a robust glial response and disruption of compact myelin were evident in the injured brain. TBI or sham mice then received intranasal saline vehicle or LM22A-4 for 14 days. Behavior testing was performed from 4 weeks post-injury, and brains were collected at 5 weeks for histology. TBI mice showed hyperactivity, reduced anxiety-like behavior, and social memory impairments. LM22A-4 ameliorated the abnormal anxiolytic phenotype but had no effect on social memory deficits. Use of spectral confocal reflectance microscopy detected persistent myelin fragmentation in the external capsule of TBI mice at 5 weeks post-injury, which was accompanied by regionally distinct deficits in oligodendrocyte progenitor cells and post-mitotic oligodendrocytes, as well as chronic reactive gliosis and atrophy of the corpus callosum and injured external capsule. LM22A-4 treatment ameliorated myelin deficits in the perilesional external capsule, as well as tissue volume loss and the extent of reactive gliosis. However, there was no effect of this TrkB agonist on oligodendroglial populations detected at 5 weeks postinjury. Collectively, our results demonstrate that targeting TrkB immediately after TBI during early life confers neuroprotection and preserves myelin integrity, and this was associated with some improved neurobehavioral outcomes as the pediatric injured brain matures.

Oligodendrocyte production and central nervous system (CNS) myelination is a protracted process, extending into adulthood. While stimulation of neuronal circuits has been shown to enhance oligodendrocyte production and myelination during development, the extent to which physiological stimuli induces activity-dependent plasticity within oligodendrocytes and myelin is unclear, particularly in the adult CNS. Here, we find that using environmental enrichment (EE) to physiologically stimulate neuronal activity for 6-weeks during young adulthood in C57Bl/6 mice results in an enlargement of callosal axon diameters, with a corresponding increase in thickness of pre-existing myelin sheaths. Additionally, EE uniformly promotes the direct differentiation of pre-existing oligodendroglia in both corpus callosum and somatosensory cortex, while differentially impeding OPC homeostasis in these regions. Furthermore, results of this study indicate that physiologically relevant stimulation in young adulthood exerts little influence upon the de novo generation of new myelin sheaths on previously unmyelinated segments and does not enhance OPC proliferation. Rather in this context, activity-dependent plasticity involves the coincident structural remodeling of axons and pre-existing myelin sheaths and increases the direct differentiation of pre-existing oligodendroglia, implying constraints on maximal de novo production in the adult CNS. Together, our findings of myelinated axon remodeling and increased pre-existing oligodendroglial differentiation constitute a previously undescribed form of adaptive myelination that likely contributes to neuronal circuit maturation and the maintenance of optimum cognitive function in the young adult CNS.Main points ### Competing Interest StatementThe authors have declared no competing interest.

Diabetic neuropathy has an incidence as high as 50% of diabetic patients and is characterized by damage to neurons, Schwann cells and blood vessels within the peripheral nervous system. The low-affinity neurotrophin receptor p75 (p75NTR ), particularly expressed by the Schwann cells in the peripheral nerve, has previously been reported to play a role in developmental myelination and cell survival/death. Increased levels of p75NTR , in the endoneurium and plasma from diabetic patients and rodent models of disease, have been observed, proposing that this receptor might be involved in the pathogenesis of diabetic neuropathy. Therefore, in this study, we addressed this hypothesis by utilizing a mouse model of selective nerve growth factor receptor (Ngfr) deletion in Schwann cells (SC-p75NTR -KO). Electron microscopy of sciatic nerves from mice with high fat diet induced obesity demonstrated how loss of Schwann cell-p75NTR aggravated axonal atrophy and loss of C-fibers. RNA sequencing disclosed several pre-clinical signaling alterations in the diabetic peripheral nerves, dependent on Schwann cell p75NTR signaling, specially related with lysosome, phagosome, and immune pathways. Morphological and biochemical analyses identified abundant lysosomes and autophagosomes in the C-fiber axoplasm of the diabetic SC-p75NTR -KO nerves, which together with increased Cathepsin B protein levels corroborates gene upregulation from the phagolysosomal pathways. Altogether, this study demonstrates that Schwann cell p75NTR deficiency amplifies diabetic neuropathy disease by triggering overactivation of immune-related pathways and increased lysosomal stress.

The p75 neurotrophin receptor (p75(NTR)) is required for maintaining peripheral sensory neuron survival and function; however, the underlying cellular mechanism remains unclear. The general view is that expression of p75(NTR)by the neuron itself is required for maintaining sensory neuron survival and myelination in the peripheral nervous system (PNS). Adopting a neuronal-specific conditional knockout strategy, we demonstrate the partial depletion of p75(NTR)in neurons exerts little influence upon maintaining sensory neuron survival and peripheral nerve myelination in health and after demyelinating neuropathy. Our data show that the density and total number of dorsal root ganglion (DRG) neurons in 2-month-old mice is not affected following the deletion of p75(NTR)in large-diameter myelinating neurons, as assessed by stereology. Adopting experimental autoimmune neuritis induced in adult male mice, an animal model of demyelinating peripheral neuropathy, we identify that deleting p75(NTR)in myelinating neurons exerts no influence upon the disease progression, the total number of DRG neurons, and the extent of myelin damage in the sciatic nerve, indicating that the expression of neuronal p75(NTR)is not essential for maintaining peripheral neuron survival and myelination after a demyelinating insultin vivo. Together, results of this study suggest that the survival and myelination of peripheral sensory neurons is independent of p75(NTR)expressed by a subtype of neuronsin vivo. Thus, our findings provide new insights into the mechanism underpinning p75(NTR)-mediated neuronal survival in the PNS.

As part of its programme of public talks the National Theatre in London hosted a panel event entitled ‘The Influence of Jacques Lecoq on UK Theatre’ in the Dorfman Theatre on 6 November 2018. The p...

The neurotrophin, brain-derived neurotrophic factor (BDNF) promotes central nervous system (CNS) myelination during development and after injury. This is achieved via activation of oligodendrocyte-expressed tropomyosin-related kinase (Trk) B receptors. However, while administration of BDNF has shown beneficial effects, BDNF itself has a poor pharmacokinetic profile. Here, we compare two TrkB-targeted BDNF-mimetics, the structural-mimetic, tricyclic dimeric peptide-6 (TDP6) and the non-peptide small molecule TrkB agonist LM22A-4 in the cuprizone model of central demyelination in female mice. Both mimetics promoted remyelination, increasing myelin sheath thickness and oligodendrocyte densities after one-week recovery. Importantly, LM22A-4 exerts these effects in an oligodendroglial TrkB-dependent manner. However, analysis of TrkB signaling by LM22A-4 suggests rather than direct activation of TrkB, LM22A-4 exerts its effects via indirect transactivation of Trk receptors. Overall, these studies support the therapeutic strategy to selectively targeting TrkB activation to promote remyelination in the brain.