Nrg1 intracellular signaling regulates the development of interhemispheric callosal axons in mice.

Schizophrenia is associated with altered cortical circuitry. Although the schizophrenia risk gene NRG1 is known to affect the wiring of inhibitory interneurons, its role in excitatory neurons and axonal development is unclear. Here, we investigated the role of Nrg1 in the development of the corpus callosum, the major interhemispheric connection formed by cortical excitatory neurons. We found that deletion of Nrg1 impaired callosal axon development in vivo. Experiments in vitro and in vivo demonstrated that Nrg1 is cell-autonomously required for axonal outgrowth and that intracellular signaling of Nrg1 is sufficient to promote axonal development in cortical neurons and specifically in callosal axons. Furthermore, our data suggest that Nrg1 signaling regulates the expression of Growth Associated Protein 43, a key regulator of axonal growth. In conclusion, our study demonstrates that NRG1 is involved in the formation of interhemispheric callosal connections and provides a novel perspective on the relevance of NRG1 in excitatory neurons and in the etiology of schizophrenia.

ARID1B controls transcriptional programs of axon projection in an organoid model of the human corpus callosum.

Mutations in ARID1B, a member of the mSWI/SNF complex, cause severe neurodevelopmental phenotypes with elusive mechanisms in humans. The most common structural abnormality in the brain of ARID1B patients is agenesis of the corpus callosum (ACC), characterized by the absence of an interhemispheric white matter tract that connects distant cortical regions. Here, we find that neurons expressing SATB2, a determinant of callosal projection neuron (CPN) identity, show impaired maturation in ARID1B+/- neural organoids. Molecularly, a reduction in chromatin accessibility of genomic regions targeted by TCF-like, NFI-like, and ARID-like transcription factors drives the differential expression of genes required for corpus callosum (CC) development. Through an in vitro model of the CC tract, we demonstrate that this transcriptional dysregulation impairs the formation of long-range axonal projections, causing structural underconnectivity. Our study uncovers new functions of the mSWI/SNF during human corticogenesis, identifying cell-autonomous axonogenesis defects in SATB2+ neurons as a cause of ACC in ARID1B patients.

Dmd mdx mice have defective oligodendrogenesis, delayed myelin compaction and persistent hypomyelination.

Duchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene, resulting in the loss of dystrophin, a large cytosolic protein that links the cytoskeleton to extracellular matrix receptors in skeletal muscle. Aside from progressive muscle damage, many patients with DMD also have neurological deficits of unknown etiology. To investigate potential mechanisms for DMD neurological deficits, we assessed postnatal oligodendrogenesis and myelination in the Dmdmdx mouse model. In the ventricular-subventricular zone (V-SVZ) stem cell niche, we found that oligodendrocyte progenitor cell (OPC) production was deficient, with reduced OPC densities and proliferation, despite a normal stem cell niche organization. In the Dmdmdx corpus callosum, a large white matter tract adjacent to the V-SVZ, we also observed reduced OPC proliferation and fewer oligodendrocytes. Transmission electron microscopy further revealed significantly thinner myelin, an increased number of abnormal myelin structures and delayed myelin compaction, with hypomyelination persisting into adulthood. Our findings reveal alterations in oligodendrocyte development and myelination that support the hypothesis that changes in diffusion tensor imaging seen in patients with DMD reflect developmental changes in myelin architecture.

Reorganization of dopamine circuitry in the anterior corpus callosum between early adolescence and adulthood in the mouse.

The maturation of forebrain dopamine circuitry occurs over multiple developmental periods, extending from early postnatal life until adulthood, with the precise timing of maturation defined by the target region. We recently demonstrated in the adult mouse brain that axon terminals arising from midbrain dopamine neurons innervate the anterior corpus callosum and that oligodendrocyte lineage cells in this white matter tract express dopamine receptor transcripts. Whether corpus callosal dopamine circuitry undergoes maturational changes between early adolescence and adulthood is unknown but may be relevant to understanding the dramatic micro- and macro-anatomical changes that occur in the corpus callosum of multiple species during early adolescence, including in the degree of myelination. Using quantitative neuroanatomy, we show that dopamine innervation in the forceps minor, but not the rostral genu, of the corpus callosum, is greater during early adolescence (P21) compared to adulthood (>P90) in wild-type mice. We further demonstrate with RNAscope that, as in the adult, Drd1 and Drd2 transcripts are expressed at higher levels in oligodendrocyte precursor cells (OPCs) and decline as these cells differentiate into oligodendrocytes. In addition, the number of OPCs that express Drd1 transcripts during early adolescence is double the number of those expressing the transcript during early adulthood. These data further implicate dopamine in axon myelination and myelin regulation. Moreover, because developmental (activity-independent) myelination peaks during early adolescence, with experience-dependent (activity-dependent) myelination greatest during early adulthood, our data suggest that potential roles of dopamine on callosal myelination shift between early adolescence and adulthood, from a developmental role to an experience-dependent role.

Proteomic dissection of vanishing white matter pathogenesis.

Vanishing white matter (VWM) is a leukodystrophy caused by biallelic pathogenic variants in eukaryotic translation initiation factor 2B. To date, it remains unclear which factors contribute to VWM pathogenesis. Here, we investigated the basis of VWM pathogenesis using the 2b5ho mouse model. We first mapped the temporal proteome in the cerebellum, corpus callosum, cortex, and brainstem of 2b5ho and wild-type (WT) mice. Protein changes observed in 2b5ho mice were then cross-referenced with published proteomic datasets from VWM patient brain tissue to define alterations relevant to the human disease. By comparing 2b5ho mice with their region- and age-matched WT counterparts, we showed that the proteome in the cerebellum and cortex of 2b5ho mice was already dysregulated prior to pathology development, whereas proteome changes in the corpus callosum only occurred after pathology onset. Remarkably, protein changes in the brainstem were transient, indicating that a compensatory mechanism might occur in this region. Importantly, 2b5ho mouse brain proteome changes reflect features well-known in VWM. Comparison of the 2b5ho mouse and VWM patient brain proteomes revealed shared changes. These could represent changes that contribute to the disease or even drive its progression in patients. Taken together, we show that the 2b5ho mouse brain proteome is affected in a region- and time-dependent manner. We found that the 2b5ho mouse model partly replicates the human disease at the protein level, providing a resource to study aspects of VWM pathogenesis by highlighting alterations from early to late disease stages, and those that possibly drive disease progression.

5Z-7-Oxozaenol attenuates cuprizone-induced demyelination in mice through microglia polarization regulation.

INTRODUCTION: Demyelination is a key factor in axonal degeneration and neural loss, leading to disability in multiple sclerosis (MS) patients. Transforming growth factor beta activated kinase 1 (TAK1) is a critical molecule involved in immune and inflammatory signaling pathways. Knockout of microglia TAK1 can inhibit autoimmune inflammation of the brain and spinal cord and improve the outcome of MS. However, it is unclear whether inhibiting TAK1 can alleviate demyelination. METHODS: Eight-week-old male c57bl/6j mice were randomly divided into five groups: (a) the control group, (b) the group treated with cuprizone (CPZ) only, (c) the group treated with 5Z-7-Oxozaenol (OZ) only, and (d) the group treated with both cuprizone and 15 µg/30 µg OZ. Demyelination in the mice of this study was induced by administration of CPZ (ig) at a daily dose of 400 mg/kg for consecutive 5 weeks. OZ was intraperitoneally administered at mentioned doses twice a week, starting from week 3 after beginning cuprizone treatment. Histology, rotarod test, grasping test, pole test, Western blot, RT-PCR, and ELISA were used to evaluate corpus callosum demyelination, behavioral impairment, oligodendrocyte differentiation, TAK1 signaling pathway expression, microglia, and related cytokines. RESULTS: Our results demonstrated that OZ protected against myelin loss and behavior impairment caused by CPZ. Additionally, OZ rescued the loss of oligodendrocytes in CPZ-induced mice. OZ inhibited the activation of JNK, p65, and p38 pathways, transformed M1 polarized microglia into M2 phenotype, and increased brain-derived neurotrophic factor (BDNF) expression to attenuate demyelination in CPZ-treated mice. Furthermore, OZ reduced the expression of proinflammatory cytokines and increases anti-inflammatory cytokines in CPZ-treated mice. CONCLUSION: These findings suggest that inhibiting TAK1 may be an effective approach for treating demyelinating diseases.

Neddylation in the chronically hypoperfused corpus callosum: MLN4924 reduces blood-brain barrier injury via ERK5/KLF2 signaling.

Blood-brain barrier (BBB) breakdown and cerebrovascular dysfunction may contribute to the pathology in white matter lesions and consequent cognitive decline caused by cerebral hypoperfusion. Neddylation is the process of attaching a ubiquitin-like molecule NEDD8 (neuronal precursor cell-expressed developmentally downregulated protein 8) to specific targets. By modifying protein substrates, neddylation plays critical roles in various important biological processes. However, whether neddylation influences the pathogenesis of hypoperfused brain remains unclear. In the present study, cerebral hypoperfusion-induced white matter lesions were produced by bilateral common carotid artery stenosis in mice. The function of the neddylation pathway, BBB integrity, cerebrovascular dysfunction, myelin density in the corpus callosum and cognitive function were determined. We show that NEDD8 conjugation aberrantly amplified in microvascular endothelium in the corpus callosum following cerebral hypoperfusion. MLN4924, a small-molecule inhibitor of NEDD8-activating enzyme currently in clinical trials, preserved BBB integrity, attenuated glial activation and enhanced oligodendrocyte differentiation, and reduced hypoperfusion-induced white matter lesions in the corpus callosum and thus improved cognitive performance via inactivating cullin-RING E3 ligase (CRL). Administration of MLN4924 caused the accumulation of ERK5 and KLF2. The ERK5 inhibitor BIX 02189, down-regulated MLN4924-induced activation of KLF2 and reversed MLN4924-mediated increase in pericyte coverage and junctional proteins. Furthermore, BIX 02189 blocked MLN4924-afforded protection against BBB disruption and white matter lesions in the corpus callosum. Collectively, our results revealed that neddylation impairs vascular function and thus exacerbated the pathology of hypoperfused brain and that inhibition of neddylation with MLN4924 may offer novel therapeutic opportunities for cerebral hypoperfusion-associated cognitive impairment.

Glutamate delta-1 receptor regulates oligodendrocyte progenitor cell differentiation and myelination in normal and demyelinating conditions.

In this study, we investigated the role of glutamate delta 1 receptor (GluD1) in oligodendrocyte progenitor cell (OPC)-mediated myelination during basal (development) and pathophysiological (cuprizone-induced demyelination) conditions. Initially, we sought to determine the expression pattern of GluD1 in OPCs and found a significant colocalization of GluD1 puncta with neuron-glial antigen 2 (NG2, OPC marker) in the motor cortex and dorsal striatum. Importantly, we found that the ablation of GluD1 led to an increase in the number of myelin-associated glycoprotein (MAG+) cells in the corpus callosum and motor cortex at P40 without affecting the number of NG2+ OPCs, suggesting that GluD1 loss selectively facilitates OPC differentiation rather than proliferation. Further, deletion of GluD1 enhanced myelination in the corpus callosum and motor cortex, as indicated by increased myelin basic protein (MBP) staining at P40, suggesting that GluD1 may play an essential role in the developmental regulation of myelination during the critical window period. In contrast, in cuprizone-induced demyelination, we observed reduced MBP staining in the corpus callosum of GluD1 KO mice. Furthermore, cuprizone-fed GluD1 KO mice showed more robust motor deficits. Collectively, our results demonstrate that GluD1 plays a critical role in OPC regulation and myelination in normal and demyelinating conditions.

Breastfeeding promotes oligodendrocyte precursor cells division and myelination in the demyelinated corpus callosum.

Demyelination alters the conduction of neuronal signals and hampers sensory-motor functions. Experimental and clinical evidence suggest that breastfeeding exerts a promyelinating impact on the maternal brain. The mechanism underlying this neuroprotective effect is not well-understood. In the present paper, we assessed the impact of rat lactation on lysolecithin-induced demyelination injury within the corpus callosum of lactating and non-lactating postpartum rats. We show that lactation enhanced the cell density of oligodendrocyte precursor cells (OPCs), but not that of activated microglia and astrocytes, within the demyelination lesion. Lactation also increased the expression of myelin markers involved in the initial stage of myelin recovery (Myelin-associated glycoprotein and 2',3'-cyclic nucleotide 3'-phosphodiesterase) and reduced the demyelination injury. Altogether, these data suggest that lactation creates a conducive promyelinating environment through increased OPCs cell division, enhanced expression of select myelin proteins, and reduced number of non-myelinated axons.

Development of nanoRibo-seq enables study of regulated translation by cortical neuron subtypes, showing uORF translation in synaptic-axonal genes.

Investigation of translation in rare cell types or subcellular contexts is challenging due to large input requirements for standard approaches. Here, we present "nanoRibo-seq" an optimized approach using 102- to 103-fold less input material than bulk approaches. nanoRibo-seq exhibits rigorous quality control features consistent with quantification of ribosome protected fragments with as few as 1,000 cells. We compare translatomes of two closely related cortical neuron subtypes, callosal projection neurons (CPN) and subcerebral projection neurons (SCPN), during their early postnatal development. We find that, while translational efficiency is highly correlated between CPN and SCPN, several dozen mRNAs are differentially translated. We further examine upstream open reading frame (uORF) translation and identify that mRNAs involved in synapse organization and axon development are highly enriched for uORF translation in both subtypes. nanoRibo-seq enables investigation of translational regulation of rare cell types in vivo and offers a flexible approach for globally quantifying translation from limited input material.

Generation and characterization of a knock-in mouse model for spastic tetraplegia, thin corpus callosum, and progressive microcephaly (SPATCCM).

Solute carrier family 1 member 4 (SLC1A4), also referred to as Alanine/Serine/Cysteine/Threonine-preferring Transporter 1 (ASCT1), is a sodium-dependent neutral amino acid transporter. It is expressed in many tissues, including the brain, where it is expressed primarily on astrocytes and plays key roles in neuronal differentiation and development, maintaining neurotransmitter homeostasis, and N-methyl-D-aspartate neurotransmission, through regulation of L- and D-serine. Mutations in SLC1A4 are associated with the rare autosomal recessive neurodevelopmental disorder spastic tetraplegia, thin corpus callosum, and progressive microcephaly (SPATCCM, OMIM 616657). Psychomotor development and speech are significantly impaired in these patients, and many develop seizures. We generated and characterized a knock-in mouse model for the most common mutant allele, which results in a single amino acid change (p.Glu256Lys, or E256K). Homozygous mutants had increased D-serine uptake in the brain, microcephaly, and thin corpus callosum and cortex layer 1. While p.E256K homozygotes showed some significant differences in exploratory behavior relative to wildtype mice, their performance in assays for motor coordination, endurance, learning, and memory was normal, and they showed no significant differences in long-term potentiation. Taken together, these results indicate that the impact of the p.E256K mutation on cognition and motor function is minimal in mice, but other aspects of SLC1A4 function in the brain are conserved. Mice homozygous for p.E256K may be a good model for understanding the developmental basis of the corpus callosum and microcephaly phenotypes observed in SPATCCM patients and assessing whether they are rescued by serine supplementation.

A Variant in TBCD Associated with Motoneuronopathy and Corpus Callosum Hypoplasia: A Case Report.

Mutations in the tubulin-specific chaperon D (TBCD) gene, involved in the assembly and disassembly of the α/ß-tubulin heterodimers, have been reported in early-onset progressive neurodevelopment regression, with epilepsy and mental retardation. We describe a rare homozygous variant in TBCD, namely c.881G>A/p.Arg294Gln, in a young woman with a phenotype dominated by distal motorneuronopathy and mild mental retardation, with neuroimaging evidence of corpus callosum hypoplasia. The peculiar phenotype is discussed in light of the molecular interpretation, enriching the literature data on tubulinopathies generated from TBCD mutations.

Krüppel-like factor 7 deficiency disrupts corpus callosum development and neuronal migration in the developing mouse cerebral cortex.

Krüppel-like Factor 7 (KLF7) is a zinc finger transcription factor that has a critical role in cellular differentiation, tumorigenesis, and regeneration. Mutations in Klf7 are associated with autism spectrum disorder, which is characterized by neurodevelopmental delay and intellectual disability. Here we show that KLF7 regulates neurogenesis and neuronal migration during mouse cortical development. Conditional depletion of KLF7 in neural progenitor cells resulted in agenesis of the corpus callosum, defects in neurogenesis, and impaired neuronal migration in the neocortex. Transcriptomic profiling analysis indicated that KLF7 regulates a cohort of genes involved in neuronal differentiation and migration, including p21 and Rac3. These findings provide insights into our understanding of the potential mechanisms underlying neurological defects associated with Klf7 mutations.

Comparative examination of the pons and corpus callosum as reference regions for quantitative evaluation in positron emission tomography imaging for Alzheimer's disease using 11C-Pittsburgh Compound-B.

OBJECTIVES: Standardised uptake value ratio (SUVR) is usually obtained by dividing the SUV of the region of interest (ROI) by that of the cerebellar cortex. Cerebellar cortex is not a valid reference in cases where amyloid ß deposition or lesions are present. Only few studies have evaluated the use of other regions as references. We compared the validity of the pons and corpus callosum as reference regions for the quantitative evaluation of brain positron emission tomography (PET) using 11C-PiB compared to the cerebellar cortex. METHODS: We retrospectively evaluated data from 86 subjects with or without Alzheimer's disease (AD). All subjects underwent magnetic resonance imaging, PET imaging, and cognitive function testing. For the quantitative analysis, three-dimensional ROIs were automatically placed, and SUV and SUVR were obtained. We compared these values between AD and healthy control (HC) groups. RESULTS: SUVR data obtained using the pons and corpus callosum as reference regions strongly correlated with that using the cerebellar cortex. The sensitivity and specificity were high when either the pons or corpus callosum was used as the reference region. However, the SUV values of the corpus callosum were different between AD and HC (p < 0.01). CONCLUSIONS: Our data suggest that the pons and corpus callosum might be valid reference regions.

24-hydroxycholesterol replacement rate measured in blood is a non-invasive biomarker of brain demyelination and remyelination in cuprizone-treated mice.

In mice, dietary cuprizone causes brain demyelination with subsequent spontaneous remyelination upon return to normal chow. Heavy water (2H2O) labeling with mass spectrometric analysis can be used to measure brain de novo synthesis of several myelin components including cholesterol, phospholipids, galactocereboside (GalC) and myelin-associated proteins. 24-hydroxycholesterol (24-OHC), the major metabolite of brain cholesterol, is detected in blood and is believed to be specifically derived from CNS cholesterol metabolism. We assessed changes in syntheses of myelin components in brain and of blood sterols during cuprizone-induced experimental demyelination and remyelination, with and without thyroid hormone (T3) treatment. Mice were fed cuprizone for 4 weeks, then returned to control diet and treated with either placebo or T3 (0.005 mg/day). 2H2O was administered for the last 14 days of cuprizone diet, and for either 6, 12 or 19 days of treatment during recovery from cuprizone, after which blood and corpus callosum (CC) samples were collected (n = 5/time point/treatment). 2H incorporation into cholesterol and 24-OHC in blood and CC, and incorporation into phospholipid (PL)-palmitate, GalC, myelin basic protein (MBP) and 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase) in CC were measured. Cuprizone significantly (p < 0.05) decreased syntheses of cholesterol, 24-OHC, GalC, MBP, CNPase and PL-palmitate in the CC and these effects were all reversed during recovery. T3 treatment significantly (p < 0.05) increased syntheses of cholesterol, 24-OHC and palmitate compared to placebo. 24-OHC and cholesterol turnover rates in brain and blood were nearly identical and 24-OHC rates in blood paralleled rates in CC, indicating that blood 24-OHC derives primarily from the brain and reflects oligodendrocyte function. In summary, changes in synthesis of several lipid and protein components in brain during cuprizone-induced demyelination and remyelination are measurable through stable isotope labeling. Blood 24-OHC turnover rates closely reflect flux rates of brain cholesterol in response to cuprizone and T3, which alter oligodendrocyte function. Labeling of blood 24-OHC has potential as a non-invasive marker of brain de novo cholesterol synthesis and breakdown rates in demyelinating conditions.

Microglial aryl hydrocarbon receptor enhances phagocytic function via SYK and promotes remyelination in the cuprizone mouse model of demyelination.

Multiple sclerosis (MS) is an inflammatory-mediated demyelinating disease of the central nervous system (CNS). Although studies have demonstrated that microglia facilitate remyelination in demyelinating diseases, the underlying mechanisms are still not fully characterized. We found that aryl hydrocarbon receptor (AhR), an environment sensor, was upregulated within the corpus callosum in the cuprizone model of CNS demyelination, and upregulated AhR was mainly confined to microglia. Deletion of AhR in adult microglia inhibited efficient remyelination. Transcriptome analysis using RNA-seq revealed that AhR-deficient microglia displayed impaired gene expression signatures associated with lysosome and phagocytotic pathways. Furthermore, AhR-deficient microglia showed impaired clearance of myelin debris and defected phagocytic capacity. Further investigation of target genes of AhR revealed that spleen tyrosine kinase (SYK) is the downstream effector of AhR and mediated the phagocytic capacity of microglia. Additionally, AhR deficiency in microglia aggravated CNS inflammation during demyelination. Altogether, our study highlights an essential role for AhR in microglial phagocytic function and suggests the therapeutic potential of AhR in demyelinating diseases.

TrkB-dependent EphrinA reverse signaling regulates callosal axon fasciculate growth downstream of Neurod2/6.

Abnormal development of corpus callosum is relatively common and causes a broad spectrum of cognitive impairments in humans. We use acallosal Neurod2/6-deficient mice to study callosal axon guidance within the ipsilateral cerebral cortex. Initial callosal tracts form but fail to traverse the ipsilateral cingulum and are not attracted towards the midline in the absence of Neurod2/6. We show that the restoration of Ephrin-A4 (EfnA4) expression in the embryonic neocortex of Neurod2/6-deficient embryos is sufficient to partially rescue targeted callosal axon growth towards the midline. EfnA4 cannot directly mediate reverse signaling within outgrowing axons, but it forms co-receptor complexes with TrkB (Ntrk2). The ability of EfnA4 to rescue the guided growth of a subset of callosal axons in Neurod2/6-deficient mice is abolished by the co-expression of dominant negative TrkBK571N (kinase-dead) or TrkBY515F (SHC-binding deficient) variants, but not by TrkBY816F (PLCγ1-binding deficient). Additionally, EphA4 is repulsive to EfnA4-positive medially projecting axons in organotypic brain slice culture. Collectively, we suggest that EfnA4-mediated reverse signaling acts via TrkB-SHC and is required for ipsilateral callosal axon growth accuracy towards the midline downstream of Neurod family factors.

A Disintegrin and Metalloproteinase 10 (ADAM10) Is Essential for Oligodendrocyte Precursor Development and Myelination in the Mouse Brain.

A disintegrin and metalloproteinase 10 (ADAM10) plays an essential role in the regulation of survival, proliferation, migration, and differentiation of various neural cells. Nevertheless, the role of ADAM10 in oligodendrocyte precursors (OPCs) and myelination in the central nervous system (CNS) of developing and adult mouse brains is still unknown. We generated ADAM10 conditional knockout (ADAM10 cKO) mice lacking the ADAM10 gene primarily in OPCs by crossing NG2-Cre mice with ADAM10 loxp/loxp mice. We found that OPCs expressed ADAM10 in the mouse corpus callosum and the hippocampus. ADAM10 cKO mice showed significant loss of back hair and reduction in weight and length on postnatal (30 ± 2.1) day, died at (65 ± 5) days after birth, and exhibited the "anxiety and depression-like" performances. Conditional knockout of ADAM10 in OPCs resulted in a prominent increase in myelination and a decrease in the number of OPCs in the corpus callosum at P30 owing to premyelination and lack of proliferation of OPCs. Moreover, the number of proliferating OPCs and mature oligodendrocytes (OLs) also decreased with age in the corpus callosum of ADAM10 cKO mice from P30 to P60. Western blot and RT-PCR results showed that the activation of Notch-1 and its four target genes, Hes1, Hes5, Hey1, and Hey2, was inhibited in the corpus callosum tissue of ADAM10 knockout mice. In our study, we provided experimental evidence to demonstrate that ADAM10 is essential for modulating CNS myelination and OPC development by activating Notch-1 signaling in the developing and adult mouse brain.

Influx of T cells into corpus callosum increases axonal injury, but does not change the course of remyelination in toxic demyelination.

Multiple sclerosis (MS) is a focal inflammatory and demyelinating disease. The inflammatory infiltrates consist of macrophages/microglia, T and B cells. Remyelination (RM) is an endogenous repair process which frequently fails in MS patients. In earlier studies, T cells either promoted or impaired RM. Here, we used the combined cuprizone/MOG-EAE model to further dissect the functional role of T cells for RM. The combination of MOG immunization with cuprizone feeding targeted T cells to the corpus callosum and increased the extent of axonal injury. Global gene expression analyses demonstrated significant changes in the inflammatory environment; however, additional MOG immunization did not alter the course of RM. Our results suggest that the inflammatory environment in the combined model affects axons and oligodendrocytes differently and that oligodendroglial lineage cells might be less susceptible to T cell mediated injury.

Neuronal nitric oxide synthase positive neurons in the human corpus callosum: a possible link with the callosal blood-oxygen-level dependent (BOLD) effect.

Brain functions have been investigated in the past decades via the blood-oxygen-level dependent (BOLD) effect using functional magnetic resonance imaging. One hypothesis explaining the BOLD effect involves the Nitric Oxide (NO) gaseous neurotransmitter, possibly released also by cells in the corpus callosum (CC). The eventual presence of NO releasing neurons and/or glial cells in the CC can be assessed by immunohistochemistry. Serial sections both from paraffin-embedded and frozen samples of CC obtained from adult human brains autopsy were studied with immunohistochemistry and immunofluorescence analysis, using an antibody against the neuronal isoform of Nitric Oxide Synthase (nNOS), the enzyme synthetizing the NO. The staining revealed the presence of many nNOS-immunopositive cells in the CC, shown to be neurons with immunofluorescence. Neuronal NOS-positive neurons presented different morphologies, were more numerous 4 mm apart from the midline, and displayed a peak in the body of the CC. In some cases, they were located at the upper boundary of the CC, more densely packed in the proximity of the callosal arterioles. The significant presence of nNOS-immunopositive neurons within the commissure suggests their probable role in the CC neurovascular regulation in the adult brain and could explain the BOLD effect detected in human CC.