Music-based interventions have shown promise in aiding recovery in individuals with brain damage (BD), including acquired and traumatic brain injury (ABI and TBI). To investigate the underlying molecular mechanisms, we conducted a study integrating transcriptomic and epigenomic data. We compared gene expression changes driven by musical stimuli in healthy individuals exposed to music with transcriptomic data from TBI patients, identifying 154 common differentially expressed genes (DEGs) affected in TBI and impacted by music, including STK35, HNRNPA0. These genes are notably involved in synaptic plasticity, and neurodegenerative processes. Epigenomic analysis revealed that 92 of these DEGs also exhibited significant differential methylation in TBI samples, particularly in genes associated with neurodevelopment, neuroinflammation, and mood regulation. Pathway enrichment and cross-validation in independent datasets of TBI patients highlighted the cGMP-PKG signaling pathway, a key regulator of memory and plasticity. Co-expression network analysis further revealed six gene modules significantly associated with TBI, including modules centered on TXNIP and ALG13 genes, previously implicated in neuroinflammation and epilepsy, two conditions commonly associated with TBI. Interestingly, several hub genes from these modules also showed sensitivity to musical stimuli, suggesting that music may target biologically relevant networks involved in TBI pathology. These findings reveal intriguing molecular parallels between signatures associated with TBI and the biological response to music exposure, providing a proof-of-concept for future investigation. This molecular insight suggests a potential role for music as a biologically grounded component of neurorehabilitation. However, future studies should directly assess transcriptomic and epigenomic responses to music-based interventions in BD patients.
Mathematics is a complex skill requiring the coordination of distributed gray matter brain regions connected by white matter tracts. Diffusion tensor imaging (DTI) studies have revealed a network of white matter tracts that support math processing, but the specific microstructural features driving this relationship remain unclear. Other magnetic resonance imaging (MRI) methods-neurite orientation dispersion and density imaging (NODDI), inhomogeneous magnetization transfer (ihMT), multicomponent driven-equilibrium single-pulse observation of T1 and T2 (mcDESPOT), and g-ratio imaging-can probe microstructural features like axon packing, fiber orientation, and myelin more specifically than DTI. We applied these methods alongside DTI to evaluate links between white matter microstructure and math in a longitudinal cohort of 33 6-16 year olds (66 datasets total). Partial correlations between metrics of white matter microstructure and math skill, controlling for age and gender, were carried out in the left superior longitudinal and inferior longitudinal fasciculi, corticospinal tract, and the splenium. Cross-sectionally, fiber coherence of the corticospinal tract and superior longitudinal fasciculus correlated to mathematics performance. Longitudinally, change in markers of axonal packing and myelin were linked to changes in both math skill and fluency in a regionally-specific manner, with links to myelin-sensitive metrics most prevalent. Notably, decreases in myelin were linked to improvements in mathematics over time, suggesting ongoing refinement of the math network. Findings presented here did not survive multiple comparisons corrections, but provide insight for future work elaborating upon these associations in larger samples.
Neonatal hypoxic-ischemic brain damage (HIBD) is a major cause of neurological disability. This study investigated the role of the transcription factor specificity protein 1 (SP1) and its target, Acyl-CoA Synthetase Long-Chain Family Member 4 (ACSL4), in regulating ferroptosis in neonatal HIBD. Using a neonatal mouse HIBD model and an in vitro neuronal oxygen-glucose deprivation/reperfusion (OGD/R) model, we applied gene knockdown/overexpression and pharmacological tools, analyzed via molecular and histological techniques. Ferroptosis was activated in HIBD. Hypoxic-ischaemic injury upregulated SP1, which transcriptionally activated ACSL4 by binding its promoter. SP1 knockdown attenuated neuronal and brain injury, reducing lipid peroxidation and iron accumulation while improving cell viability and cognitive function. These protections were abolished by ACSL4 overexpression or erastin co-treatment, and were associated with suppression of the ACSL4-dependent ferroptotic pathway. The SP1/ACSL4 axis critically aggravates neonatal hypoxic-ischaemic brain damage by promoting ferroptosis, representing a promising therapeutic target.
Microglia contribute to central nervous system homeostasis and neuroprotection partly through the release of small extracellular vesicles (sEVs) carrying regulatory cargoes such as microRNAs. Interleukin-4 (IL-4) alters microglial state and secretory output; however, whether sEVs released from IL-4-treated microglia protect neurons against toxic injury, and which cargoes mediate these effects, remains unclear. Here, we investigated the protective effects of sEVs derived from the IL-4-treated HMC3 human microglial cell line in a rotenone-induced injury model in the SH-SY5Y cell line and examined the contribution of microRNA-191-5p to neuroprotection. Small RNA sequencing revealed a distinct miRNA profile in IL-4-sEVs, with microRNA-191-5p emerging as the most statistically significant upregulated candidate. Its enrichment was confirmed by RT-qPCR. PKH67-labeled sEV-associated fluorescence was detected in SH-SY5Y cells, indicating uptake of microglia-derived sEVs by recipient cells. Functionally, pretreatment with IL-4-sEVs significantly reduced rotenone-induced cell death and preserved cell morphology compared with untreated and control sEV-treated cells. To assess the contribution of microRNA-191-5p, IL-4-sEVs were loaded with a microRNA-191-5p antagomir, which reduced microRNA-191-5p levels and partially attenuated the protective effect of IL-4-sEVs. Together, these findings suggest that sEVs derived from the IL-4-treated HMC3 microglial cell line mitigate rotenone-induced injury in the SH-SY5Y cell line in vitro and that microRNA-191-5p contributes, at least in part, to this effect.
Oxidative stress and neuroinflammation are critical contributors to hypoxic-ischemic brain injury. Microglia, the CNS-resident immune cells, undergo rapid activation in response to hypoxic stress. Endothelin-1 (ET-1), a vasoconstrictor implicated in cerebrovascular pathology, is upregulated by hypoxia; however, its role in microglial activation remains poorly understood. HMC3 human microglial cells were exposed to hypoxia (1% O2) for 4 hours. Reactive oxygen species (ROS) were quantified by flow cytometry. ET-1 and interleukin-6 (IL-6) protein concentrations were measured by ELISA and mRNA levels by qPCR. Mitogen-activated protein kinase (MAPK) activation and ET-1 localization were assessed by flow cytometry and immunofluorescence, respectively. The endothelin B receptor (ETBR) antagonist BQ788 was used to assess ET-1 signaling in hypoxia-induced responses. Hypoxia significantly upregulated ET-1 gene expression (5.0-fold increase, p < 0.001, n = 4) and elevated ET-1 protein production by 1.4-fold (p < 0.01, n = 4). IL-6 expression and secretion increased 1.5-fold under hypoxic conditions (p < 0.01, n = 4), an effect that was attenuated by BQ788 pretreatment. ROS levels increased 1.9-fold in hypoxic HMC3 cells (p < 0.01, n = 4) but were significantly reduced by ETBR inhibition. Additionally, hypoxia elevated the percentage of MAPK-activated cells compared to both normoxic and BQ788-treated groups (p < 0.01). These findings demonstrate that hypoxia induces ET-1 overexpression, ROS generation, MAPK activation, and IL-6 production in microglia, establishing a self-perpetuating cycle of neuroinflammation. ETBR blockade with BQ788 disrupts this cascade, suggesting that ET-1 signaling is a promising therapeutic target to mitigate secondary injury in hypoxic-ischemic brain conditions.
Border-associated macrophages (BAMs) represent a specialized population of tissue-resident immune cells strategically positioned at the critical interfaces between the central nervous system (CNS) and peripheral circulation, including the meninges, choroid plexus, and perivascular spaces. As frontline sentinels of the neuroimmune system, BAMs perform essential functions in immune surveillance, barrier integrity maintenance, and homeostatic regulation, yet their unique biology and disease-associated roles remain incompletely characterized compared to parenchymal microglia. This review aims to synthesize current knowledge on BAM ontogenetic origins, compartment-specific heterogeneity, transcriptional programs, and functional outputs in both health and neurological disorders. We conducted a comprehensive literature analysis integrating findings from lineage tracing studies, single-cell RNA sequencing, spatial transcriptomics, and functional interrogation in animal models of disease. The results reveal that BAMs exhibit remarkable cellular diversity shaped by distinct ontogenetic origins-primarily yolk sac-derived erythro-myeloid progenitors with variable contributions from fetal liver and postnatal monocytes depending on anatomical compartment. Compartment-specific marker combinations (CD206, LYVE1, CD163, MHCII) define functionally distinct subsets, and core transcriptional regulators including PU.1 and IRF8 maintain BAM identity while CSF-1/IL-34-CSF1R signaling governs survival and renewal. In neurological disorders including ischemic stroke, Alzheimer's disease, multiple sclerosis, and brain tumors, BAMs display pronounced double-edged roles, transitioning from protective homeostatic guardians to pathogenic drivers depending on disease stage and microenvironmental context. This comprehensive analysis establishes a unified framework for understanding BAM biology and identifies critical opportunities for developing subset-specific therapeutic strategies targeting these interface macrophages in neurological diseases.
Protein ubiquitination is a type of posttranslational modification that occurs in all cells to regulate numerous biological processes. Ubiquitination of proteins is carried out by an enzymatic cascade where E3 ubiquitin ligases facilitate the final step in the transfer of ubiquitin to substrates. This review focuses on the role of E3 ubiquitin ligases in the regulation of oligodendrocytes, a glial cell type in the central nervous system that is critical for axon myelination and overall neuronal health. Here we focus on how protein ubiquitination dominantly driven by E3 ubiquitin ligase enzymes alters the development, maintenance, and disease pathogenesis in oligodendrocytes.
Repair after peripheral nerve injury (PNI) faces major obstacles due to microenvironmental imbalance and neuronal loss. Ferroptosis, an iron-dependent cell death driven by lipid peroxidation, has emerged as a key pathological event in PNI, linking oxidative stress, mitochondrial dysfunction, and inflammation to regenerative failure. Targeting ferroptosis protects vital cells-such as Schwann cells and neurons-and ameliorates the regenerative niche, offering a promising therapeutic strategy. This review elucidates the mechanisms of ferroptosis in PNI, detailing its roles in Schwann cells, dorsal root ganglion neurons, and macrophages via core pathways including Nrf2/HO-1/GPX4 and ACSL4. We further evaluate current intervention strategies and their therapeutic efficacy. This synthesis provides novel insights into PNI pathology and guides the development of innovative treatments.
The deubiquitinase Ataxin-3 causes spinocerebellar ataxia type 3 (SCA3) upon polyglutamine (polyQ) expansion. While expressed in the nervous system, the function of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel therein remains unclear, as does its potential regulation by Ataxin-3. This study reveals that Ataxin-3 interacts with and promotes CFTR degradation in human microglia by its K63-linked polyubiquitination, thereby shortening CFTR's half-life. Paradoxically, K63-linked polyubiquitin chains also promote the degradation of Ataxin-3 itself, suggesting a complex feedback mechanism. The pathogenic Ataxin-3Q80 mutant exerts a stronger effect than the wild-type protein. Consequently, this Ataxin-3-CFTR axis drives microglial polarization toward a pro-inflammatory phenotype and amplifies neuroinflammation. We thus identify a novel "Ataxin-3-K63 ubiquitin chain-CFTR" pathway that controls microglial activation, offering new mechanistic insight and therapeutic targets for SCA3. Abbreviations: MJDM: achado-Joseph disease; SCA3: spinocerebellar ataxia type 3; PolyQ: polyglutamine; CNS: central nervous system; CFTR: cystic fibrosis transmembrane conductance regulator; CF: cystic fibrosis; UIMs: ubiquitin-interacting motifs; MEM: Minimum Essential Medium; FBS: fetal bovine serum; P/S: penicillin/streptomycin; siRNA: small interfering RNA; BSA: bovine serum albumin; Co-IP: Co-immunoprecipitation; LPS: lipopolysaccharide; WT-CFTR: wild-type CFTR; CHX: Cycloheximide; 3-MA: 3-Methyladenine; IF: Immunofluorescence; IB: immunoblot; Ub: ubiquitin
The use of antiretroviral (ART) treatment during pregnancy has dramatically reduced rates of perinatally-acquired human immunodeficiency virus 1 (HIV-1) infection to <1% in the United States. Despite this success, we have limited knowledge of how ART drugs that cross the placental barrier affect fetal development, particularly in the central nervous system (CNS). During gestation, large populations of oligodendroglia are produced that are responsible for critical postnatal CNS myelination enabling appropriate neurological function. Previous studies have shown that antiretrovirals impair oligodendrocyte (OL) differentiation leading us to hypothesize that OL maturation might be inhibited by exposure to a frontline ART drug cocktail (Triumeq®) prescribed during pregnancy containing dolutegravir (DTG), abacavir (ABC), and lamivudine (3TC). In this study, we demonstrated that exposing primary rat oligodendrocyte precursor cells (OPCs) and OLs to the Triumeq drug combination decreased OL maturation and myelin protein production in a concentration-dependent manner, and that DTG was solely responsible. Regardless of the timing of exposure during OL development, a high concentration of DTG inhibited OL maturation. Bulk RNA sequencing revealed transcriptional changes after DTG exposure related to a variety of cellular mechanisms, including cellular responses to stress pathways, amino acid starvation, and mitochondrial dysfunction. Although we found that DTG robustly activated the integrated stress response (ISR), attempted rescue experiments showed that DTG primarily inhibits OL maturation independently of the ISR. Collectively, our novel data on DTG underscore the necessity of investigating how ART drugs that are administered during pregnancy and cross the placental barrier can affect fetal CNS development.
Omega-3 polyunsaturated fatty acids (ω3 PUFAs) are critical structural components of neuronal membranes, yet the molecular specificity of their incorporation within neural cells remains incompletely defined. We integrated untargeted and targeted lipidomics with lipid ontology analysis and coarse-grained membrane simulations to characterize remodeling in primary rat cortical neurons and neuron-astrocyte co-cultures following supplementation with docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), or docosapentaenoic acid (DPA). Each ω3 PUFA produced a distinct lipidomic signature. DHA showed the most consistent incorporation, selectively enriching phosphatidylethanolamine (PE) species-particularly PE(18:0/22:6) and PE(18:1/22:6)-associated with membrane curvature and organelle organization. Ontology analysis linked DHA supplementation to intrinsic curvature-related membrane features, and membrane simulations demonstrated enhanced collective bilayer bending without substantial changes in overall membrane thickness. EPA preferentially increased EPA-containing PE species without elevating DHA levels, whereas DPA effects were variable and culture-dependent, indicating selective metabolic handling of individual ω3 species. Differences between neurons and neuron-astrocyte co-cultures underscore the importance of cellular context in ω3-driven remodeling. By resolving ω3 incorporation at molecular species resolution and linking compositional changes to predicted membrane behavior, this study provides a structural framework for understanding how dietary ω3 fatty acids may influence neuronal membrane organization and cellular resilience.
The loss of brain noradrenergic neurons is one of the earliest alterations observed in Alzheimer's disease and other neurodegenerative pathologies. The consequent reduction of brain noradrenaline levels facilitates the progression of neuroinflammatory processes that can be fatal for neurons and other brain cells. For this reason, compensating for noradrenaline deficit through different means constitutes an interesting therapeutic strategy. Drugs that inhibit the reuptake of noradrenaline are used to elevate the extracellular concentrations of this neurotransmitter and potentiate this way its effects. These drugs are approved for the treatment of depression or attention deficit hyperactivity disorder, among other indications, but their repurposing and use in Alzheimer's disease could be of interest given the beneficial effects observed for noradrenaline in numerous studies. Based on this, we previously showed the beneficial effects of reboxetine, a noradrenaline reuptake inhibitor, on 5xFAD mice that accumulate amyloid beta in their brains and reproduce some of the typical alterations of Alzheimer's disease. In this study we have analyzed the effects of reboxetine on P301S mice, a different model of Alzheimer's disease based on the expression of mutant forms of human microtubule-associated protein tau. We observed that the administration of reboxetine with osmotic pumps for 28 days to 9-month-old mice reduced the accumulation and activation of microglia and astrocytes in different areas of the hippocampus. These findings indicate that reboxetine treatment prevents the neuroinflammatory response known to cause brain damage in Alzheimer's disease even when the treatment is initiated at an advanced stage of the disease.
This study demonstrates that electroacupuncture (EA) produces robust antidepressant effects in a rat model of methamphetamine (METH) withdrawal. Behavioral tests showed that EA applied at GV20, PC6, and HT7 significantly reduced immobility in the forced swim test and enhanced exploratory activity in the open field test. Mechanistically, EA repaired blood-brain barrier (BBB) disruption, as shown by reduced hippocampal water content, decreased Evans Blue leakage, and restored expression of tight-junction proteins (Occludin, Claudin-5, ZO-1). EA also inhibited neuronal apoptosis, suppressed microglial activation, and lowered pro-inflammatory cytokines IL-6 and TNF-α. Multi-omics analyses revealed that EA reversed METH-induced alterations in 32 differentially expressed genes related to the NLRP3 inflammasome pathway (Nlrp3, Pycard, Il1b) and BBB function, while metabolomic profiling identified 13 key metabolites involved in glutamate metabolism, TCA cycle, and tryptophan pathways. Crucially, the therapeutic benefits of EA were abolished by intracerebroventricular administration of the NLRP3 activator nigericin, confirming the essential role of NLRP3 inflammasome inhibition in EA's mechanism of action. In summary, EA represents a promising non-pharmacological approach for treating METH withdrawal-induced depression by coordinating BBB protection, suppression of neuroinflammation, and metabolic network regulation.
Galectin-3 (Gal-3) is a protein expressed by glia that belongs to an ancient family. Gal-3 recognises molecular patterns on pathogens due to the high degree of its binding specificity with carbohydrate recognition domains. Thus, in sponges as well as other invertebrates, galectins are an important component of the primitive innate immune system. Whereas Gal-3's function in driving mammalian inflammation is well known, its function in warding off bacterial and viral infections is not well appreciated. One route of brain infection is via the cerebrospinal fluid brain interface (CSFBI) which is primarily composed of ependymal cells (EC). ECs express high levels of Gal-3, and their motile cilia are compromised in Gal-3 KOs. In this mini-review, we discuss fundamentally important potential roles of Gal-3 in pathogen recognition at the CSFBI and suggest avenues of further study.
GABA receptors are classically known for driving neuronal hyperpolarization and modulating synaptic transmission. In glial cells, however, GABA induces depolarization and triggers calcium-dependent signaling pathways. Müller glia, the principal retinal glial population, maintain retinal homeostasis and are the major source of neuroretinal VEGF-A, a key angiogenic factor in development and disease. Although GABA receptor (GABAR) activity has been proposed to influence retinal VEGF-A, it remains unclear whether this regulation occurs through Müller glial cells (MGC) and which mechanisms are involved. Here, we investigated how GABAR activation modulates VEGF-A in primary mouse MGC cultures. Cells were exposed to GABA and selective agonists or antagonists of GABAA (muscimol, gabazine) and GABAB receptors (baclofen, CGP55845). VEGF-A expression and secretion were analyzed by immunofluorescence, western blot, RT-qPCR, and ELISA. To assess Ca2+ involvement, we used Ca2+-free Ringer-Krebs solution and the L-type channel blocker nimodipine, and examined MAPK signaling with the ERK1/2 inhibitor FR180204. Our findings show that GABA and muscimol increased VEGF-A fluorescence intensity after 48 hours while reducing VEGF-A secretion, without altering Vegfa mRNA. Both effects were abolished by extracellular Ca2+ removal or nimodipine, indicating a Ca2+-dependent mechanism. FR180204 also attenuated GABA- and GABAA-mediated effects, implicating MAPK signaling. Short-term assays revealed that GABA rapidly elevates VEGF-A protein and secretion within ∼30 minutes. Together, these findings identify a Ca2+- and GABAA-dependent pathway through which Müller glia regulate VEGF-A production and release, providing new insight into glial signaling and neurotransmitter-driven modulation of retinal angiogenic factors.
Cerebral ischemia is defined by insufficient blood supply to the brain and is a leading cause of mortality and neurological disability worldwide. Alpha-synuclein (α-Syn) is a protein associated with several neurodegenerative disorders, including Parkinson's disease, and has also been linked to the pathophysiology of cerebral ischemia. This narrative review provides a detailed overview of the current understanding of α-Syn in cerebral ischemia. We examine its impact on neuroinflammation, synaptic dysfunction, oxidative stress, and neuronal cell death, as well as its potential protective roles. Additionally, we explore therapeutic strategies targeting α-Syn, including pharmacological agents, gene knockdown models, and RNA-based therapies. We also discuss α-Syn expression changes in animal and human studies and its potential as a diagnostic biomarker. By clarifying the complex interplay between α-Syn and cerebral ischemia, this review aims to deepen our understanding of ischemic brain injury mechanisms and support the development of novel treatment approaches.
Vitamin D is a secosteroid hormone with myriad physiological functions, including pleiotropic effects in the central nervous system. Vitamin D deficiency has been linked to multiple neurodevelopmental and neurodegenerative diseases, including Rett syndrome, epilepsy, Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Over the past decades, vitamin D supplementation has been used as a preventative measure or a therapeutic intervention, often with inconsistent or variable responses. We discuss the known association between vitamin D deficiency and neurological disorder occurrence or progression for these disorders. Further, we assess the underlying causes for disruptions in vitamin D levels and the potential mechanisms of vitamin D-mediated improvements. We discuss disruptions in the vitamin D metabolism pathway, signaling, and/or feedback homeostasis that could underpin individual responses to vitamin D supplementation in these disorders. We further discuss the intersection between the vitamin D and cholesterol synthesis pathways and neuroinflammation, and the complex interactions that could contribute to the broad impact of vitamin D on neurological disorders.
Neurogenesis in the dentate gyrus of the hippocampus is a conserved and highly regulated process throughout the lifespan. Hippocampal neural stem and progenitor cells (NSPCs) can either transition into an activated proliferative state or remain quiescent. Accumulating data suggests that mitochondrial fatty acid β-oxidation is important in maintaining NSPCs quiescence under normal physiological conditions; however, the contribution of this pathway in NSPCs following brain injury remains unknown. While severe traumatic brain injury (TBI) is characterized by increased NSPCs proliferation in the hippocampus, the extent of this proliferative response after mild TBI, the most prevalent form of TBI, has not been fully delineated. Using closed head injury as a model of mild TBI and a brain-specific knockout mouse of carnitine palmitoyltransferase 2 (CPT2; an obligate gene in mitochondrial fatty acid β-oxidation), we investigated the role of fatty acid oxidation in hippocampal NSPCs proliferation in naïve and injured male and female mice. Our results show that loss of CPT2 in the brain does not affect hippocampal proliferation in naïve mice. Furthermore, mild TBI upregulates proliferation at day 3 post-injury, and is further increased only in male CPT2-deficient mice. Despite the post-injury increase in hippocampal NSPCs proliferation in CPT2B-/- mice, long-term neurogenesis remained unchanged. Together, these data provides a new insight into the metabolic regulation of NSPCs neurogenesis in the hippocampus following mild traumatic brain injury.
Thy1, a synaptic protein, may support synaptic junction adherence. Thus, we hypothesized that loss of Thy1 may alter synaptic transmission. Our focus on the Thy1 knockout (KO) mouse model stems from the loss of Thy1 expression in individuals with Restless Legs Syndrome (RLS), a neurological disorder. This investigation aimed to determine: 1) if the absence of Thy1 affects synaptic function in the striatal region, 2) if the absence of Thy1 alters the synaptic response to dopamine and gabapentin, and 3) if the Thy1 loss can alter behavior modulated by the striatum. Network-level synaptic transmission was measured in corticostriatal slices from Thy1 KO and C57BL/6 control mice. In vivo, acoustic startle behavioral testing was used to measure startle reaction and prepulse inhibition in both groups. Raclopride, a D2 receptor antagonist, decreased population spike amplitude in control but not Thy1 KO slices. Quinpirole, a D2 receptor agonist, did not change spike amplitude in any group. Gabapentin, a Ca2+ channel blocker, reduced population spike amplitude in Thy1 KO slices more than in controls. The behavioral acoustic startle response was diminished in Thy1 KO mice and attributed to enhanced prepulse inhibition. Loss of Thy1 alters striatal synaptic function, affecting dopaminergic modulation of corticostriatal neurotransmission and resulting in disruption of the startle response and prepulse inhibition.
In contemporary myelin biology, there is a growing trend to prioritize faster, more convenient methodologies for evaluating white matter structure over quality of the analysis. This shift is often accompanied by less attention to the mechanistic foundations of the methods in preclinical and clinical research. To address such worrisome trends, the current article assesses three approaches for estimating the myelin g ratio from electron microscopy data, which is the gold standard approach to measure the impacts of neuropathology and treatment strategies on white matter integrity. Of the mathematical models examined, two are consistent with and equivalent to the linear relation defined by the axon versus fiber diameter plot (the principal data). The final model is the canonical almost universally accepted approach to measuring g ratios. This model is demonstrated to be internally inconsistent and discordant with the axon versus fiber diameter relation and can lead to inaccurate conclusions about myelin integrity. Furthermore, the increasing interest in non-invasive neuroimaging approaches to measure g ratios clinically in both physiologic and pathophysiologic studies necessitates calibration with electron microscopy-derived g ratios. In this vein, mathematical models applicable to these methodologies are concordant; thus, magnetic resonance imaging holds significant promise for accurate determination of myelin integrity in patients. On the other hand, the metrics measurable by this voxel-based technology may preclude application to gray matter myelin and perhaps limit its use to linearly-organized white matter tracts.
