Small-molecule-induced epigenetic rejuvenation promotes SREBP condensation and overcomes barriers to CNS myelin regeneration.

Remyelination failure in diseases like multiple sclerosis (MS) was thought to involve suppressed maturation of oligodendrocyte precursors; however, oligodendrocytes are present in MS lesions yet lack myelin production. We found that oligodendrocytes in the lesions are epigenetically silenced. Developing a transgenic reporter labeling differentiated oligodendrocytes for phenotypic screening, we identified a small-molecule epigenetic-silencing-inhibitor (ESI1) that enhances myelin production and ensheathment. ESI1 promotes remyelination in animal models of demyelination and enables de novo myelinogenesis on regenerated CNS axons. ESI1 treatment lengthened myelin sheaths in human iPSC-derived organoids and augmented (re)myelination in aged mice while reversing age-related cognitive decline. Multi-omics revealed that ESI1 induces an active chromatin landscape that activates myelinogenic pathways and reprograms metabolism. Notably, ESI1 triggered nuclear condensate formation of master lipid-metabolic regulators SREBP1/2, concentrating transcriptional co-activators to drive lipid/cholesterol biosynthesis. Our study highlights the potential of targeting epigenetic silencing to enable CNS myelin regeneration in demyelinating diseases and aging.

Reduced Concussion Symptom Burden in Early Adolescent Athletes Using a Head-Neck Cooling Device.

OBJECTIVE: To determine whether an investigational head-neck cooling device, Pro2cool, can better reduce symptom severity compared with standard postconcussion care in early adolescent athletes after a sports-related concussion. DESIGN: Prospective, longitudinal, randomized trial design conducted over a 28-day period. SETTING: Six pediatric medical centers in Ohio and Michigan. PARTICIPANTS: The study enrolled 167 male and female 12- to 19-year-old athletes who experienced a sports-related concussion within 8 days of study enrollment and registering a Sports Concussion Assessment Tool 5 (SCAT5) composite score >7. INTERVENTIONS: Pro2cool, an investigational head-neck cooling therapy device, was applied at 2 postinjury time points compared with postconcussion standard of care only. MAIN OUTCOME MEASURES: Baseline SCAT5 composite symptom severity scores were determined for all subjects. Sports Concussion Assessment Tool 5 scores for concussed athletes receiving cooling treatment were analyzed across 6 independent postenrollment time points compared with subjects who did not receive cooling therapy and only standard care. Adverse reactions and participate demographics were also compared. RESULTS: Athletes who received Pro2cool cooling therapy (n = 79) experienced a 14.4% greater reduction in SCAT5 symptom severity scores at the initial visit posttreatment, a 25.5% greater reduction at the 72-hour visit posttreatment, and a 3.4% greater reduction at the 10-day visit compared with subjects receiving only standard care (n = 88). Overall, 36 adverse events (increased blood pressure, decreased pulse, and dizziness) were reported, with 13 events associated with the device, of which 3 were classified as moderate in severity. CONCLUSIONS: This study demonstrates the efficacy and safety of head and neck cooling for the management of concussion symptoms in adolescent athletes of an age group for which little to no prior data are available.

Colony size buffers interactions between neonicotinoid exposure and cold stress in bumblebees.

Social bees are critical for supporting biodiversity, ecosystem function and crop yields globally. Colony size is a key ecological trait predicted to drive sensitivity to environmental stressors and may be especially important for species with annual cycles of sociality, such as bumblebees. However, there is limited empirical evidence assessing the effect of colony size on sensitivity to environmental stressors or the mechanisms underlying these effects. Here, we examine the relationship between colony size and sensitivity to environmental stressors in bumblebees. We exposed colonies at different developmental stages briefly (2 days) to a common neonicotinoid (imidacloprid) and cold stress, while quantifying behaviour of individuals. Combined imidacloprid and cold exposure had stronger effects on both thermoregulatory behaviour and long-term colony growth in small colonies. We find that imidacloprid's effects on behaviour are mediated by body temperature and spatial location within the nest, suggesting that social thermoregulation provides a buffering effect in large colonies. Finally, we demonstrate qualitatively similar effects in size-manipulated microcolonies, suggesting that group size per se, rather than colony age, drives these patterns. Our results provide evidence that colony size is critical in driving sensitivity to stressors and may help elucidate mechanisms underlying the complex and context-specific impacts of pesticide exposure.

A digitally driven manufacturing process for high resolution patterning of cell formations.

This paper presents the engineering and validation of an enabling technology that facilitates new capabilities in in vitro cell models for high-throughput screening and tissue engineering applications. This is conducted through a computerized system that allows the design and deposition of high-fidelity microscale patterned coatings that selectively alter the chemical and topographical properties of cell culturing surfaces. Significantly, compared to alternative methods for microscale surface patterning, this is a digitally controlled and automated process thereby allowing scientists to rapidly create and explore an almost infinite range of cell culture patterns. This new capability is experimentally validated across six different cell lines demonstrating how the precise microscale deposition of these patterned coatings can influence spatiotemporal growth and movement of endothelial, fibroblast, neuronal and macrophage cells. To further demonstrate this platform, more complex patterns are then created and shown to guide the behavioral response of colorectal carcinoma cells.

The eyes reflect an internal cognitive state hidden in the population activity of cortical neurons.

Decades of research have shown that global brain states such as arousal can be indexed by measuring the properties of the eyes. The spiking responses of neurons throughout the brain have been associated with the pupil, small fixational saccades, and vigor in eye movements, but it has been difficult to isolate how internal states affect the eyes, and vice versa. While recording from populations of neurons in the visual and prefrontal cortex (PFC), we recently identified a latent dimension of neural activity called "slow drift," which appears to reflect a shift in a global brain state. Here, we asked if slow drift is correlated with the action of the eyes in distinct behavioral tasks. We recorded from visual cortex (V4) while monkeys performed a change detection task, and PFC, while they performed a memory-guided saccade task. In both tasks, slow drift was associated with the size of the pupil and the microsaccade rate, two external indicators of the internal state of the animal. These results show that metrics related to the action of the eyes are associated with a dominant and task-independent mode of neural activity that can be accessed in the population activity of neurons across the cortex.

Idiosyncratic neural coding and neuromodulation of olfactory individuality in Drosophila.

Innate behavioral biases and preferences can vary significantly among individuals of the same genotype. Though individuality is a fundamental property of behavior, it is not currently understood how individual differences in brain structure and physiology produce idiosyncratic behaviors. Here we present evidence for idiosyncrasy in olfactory behavior and neural responses in Drosophila We show that individual female Drosophila from a highly inbred laboratory strain exhibit idiosyncratic odor preferences that persist for days. We used in vivo calcium imaging of neural responses to compare projection neuron (second-order neurons that convey odor information from the sensory periphery to the central brain) responses to the same odors across animals. We found that, while odor responses appear grossly stereotyped, upon closer inspection, many individual differences are apparent across antennal lobe (AL) glomeruli (compact microcircuits corresponding to different odor channels). Moreover, we show that neuromodulation, environmental stress in the form of altered nutrition, and activity of certain AL local interneurons affect the magnitude of interfly behavioral variability. Taken together, this work demonstrates that individual Drosophila exhibit idiosyncratic olfactory preferences and idiosyncratic neural responses to odors, and that behavioral idiosyncrasies are subject to neuromodulation and regulation by neurons in the AL.

A Stable Population Code for Attention in Prefrontal Cortex Leads a Dynamic Attention Code in Visual Cortex.

Attention often requires maintaining a stable mental state over time while simultaneously improving perceptual sensitivity. These requirements place conflicting demands on neural populations, as sensitivity implies a robust response to perturbation by incoming stimuli, which is antithetical to stability. Functional specialization of cortical areas provides one potential mechanism to resolve this conflict. We reasoned that attention signals in executive control areas might be highly stable over time, reflecting maintenance of the cognitive state, thereby freeing up sensory areas to be more sensitive to sensory input (i.e., unstable), which would be reflected by more dynamic attention signals in those areas. To test these predictions, we simultaneously recorded neural populations in prefrontal cortex (PFC) and visual cortical area V4 in rhesus macaque monkeys performing an endogenous spatial selective attention task. Using a decoding approach, we found that the neural code for attention states in PFC was substantially more stable over time compared with the attention code in V4 on a moment-by-moment basis, in line with our guiding thesis. Moreover, attention signals in PFC predicted the future attention state of V4 better than vice versa, consistent with a top-down role for PFC in attention. These results suggest a functional specialization of attention mechanisms across cortical areas with a division of labor. PFC signals the cognitive state and maintains this state stably over time, whereas V4 responds to sensory input in a manner dynamically modulated by that cognitive state.SIGNIFICANCE STATEMENT Attention requires maintaining a stable mental state while simultaneously improving perceptual sensitivity. We hypothesized that these two demands (stability and sensitivity) are distributed between prefrontal and visual cortical areas, respectively. Specifically, we predicted attention signals in visual cortex would be less stable than in prefrontal cortex, and furthermore prefrontal cortical signals would predict attention signals in visual cortex in line with the hypothesized role of prefrontal cortex in top-down executive control. Our results are consistent with suggestions deriving from previous work using separate recordings in the two brain areas in different animals performing different tasks and represent the first direct evidence in support of this hypothesis with simultaneous multiarea recordings within individual animals.

Idiosyncratic learning performance in flies.

Individuals vary in their innate behaviours, even when they have the same genome and have been reared in the same environment. The extent of individuality in plastic behaviours, like learning, is less well characterized. Also unknown is the extent to which intragenotypic differences in learning generalize: if an individual performs well in one assay, will it perform well in other assays? We investigated this using the fruit fly Drosophila melanogaster, an organism long-used to study the mechanistic basis of learning and memory. We found that isogenic flies, reared in identical laboratory conditions, and subject to classical conditioning that associated odorants with electric shock, exhibit clear individuality in their learning responses. Flies that performed well when an odour was paired with shock tended to perform well when the odour was paired with bitter taste or when other odours were paired with shock. Thus, individuality in learning performance appears to be prominent in isogenic animals reared identically, and individual differences in learning performance generalize across some aversive sensory modalities. Establishing these results in flies opens up the possibility of studying the genetic and neural circuit basis of individual differences in learning in a highly suitable model organism.

Transient receptor potential vanilloid 4 channel deletion regulates pathological but not developmental retinal angiogenesis.

Transient receptor potential vanilloid 4 (TRPV4) channels are mechanosensitive ion channels that regulate systemic endothelial cell (EC) functions such as vasodilation, permeability, and angiogenesis. TRPV4 is expressed in retinal ganglion cells, Müller glia, pigment epithelium, microvascular ECs, and modulates cell volume regulation, calcium homeostasis, and survival. TRPV4-mediated physiological or pathological retinal angiogenesis remains poorly understood. Here, we demonstrate that TRPV4 is expressed, functional, and mechanosensitive in retinal ECs. The genetic deletion of TRPV4 did not affect postnatal developmental angiogenesis but increased pathological neovascularization in response to oxygen-induced retinopathy (OIR). Retinal vessels from TRPV4 knockout mice subjected to OIR exhibited neovascular tufts that projected into the vitreous humor and displayed reduced pericyte coverage compared with wild-type mice. These results suggest that TRPV4 is a regulator of retinal angiogenesis, its deletion augments pathological retinal angiogenesis, and that TRPV4 could be a novel target for the development of therapies against neovascular ocular diseases.

Histone deacetylase 8 inhibition suppresses mantle cell lymphoma viability while preserving natural killer cell function.

Mantle Cell Lymphoma (MCL) is a non-Hodgkin lymphoma with a median survival rate of five years. Standard treatment with high-dose chemotherapy plus rituximab (anti-CD20 antibody) has extended overall survival although, the disease remains incurable. Histone deacetylases (HDAC) are a family of enzymes that regulate multiple proteins and cellular pathways through post-translational modification. Broad spectrum HDAC inhibitors have shown some therapeutic promise, inducing cell cycle inhibition and apoptosis in leukemia and non-Hodgkin's lymphoma. However, the therapeutic effects of these broad-spectrum HDAC inhibitors can detrimentally dampen Natural Killer (NK) cell cytotoxicity, reduce NK viability, and downregulate activation receptors important for NK mediated anti-tumor responses. Impairment of NK function in MCL patients during therapy potentially limits therapeutic activity of rituximab. Thus, there is an unmet need to decipher specific roles of individual HDACs in order to preserve and/or enhance NK function, while, directly impairing MCL viability. We investigated the impact of HDAC8 in MCL cell lines. Inhibition or genetic loss of HDAC8 caused MCL cells to undergo apoptosis. In contrast, exposure of primary human NK cells to an HDAC8 inhibitor does not alter viability, receptor expression, or antibody dependent cellular cytotoxicity (ADCC). However, an increase in effector cytokine interferon-gamma (IFNγ) producing NK cells was observed in response to HDAC8 inhibition. Taken together these data suggest that selective HDAC8 inhibitors may simultaneously preserve NK functional activity, while impairing MCL tumor growth, establishing a rationale for future clinical evaluation.

Irisin treatment lowers levels of phosphorylated tau in the hippocampus of pre-symptomatic female but not male htau mice.

AIMS: Irisin is a hormone cleaved from fibronectin type-III domain-containing protein 5 in response to exercise and may be therapeutic in Alzheimer's disease (AD). Irisin is shown to repair damage caused by midlife cardiometabolic risk factors for AD (i.e., diabetes mellitus; hypertension), prevent neural amyloid beta aggregation and reduce neuroinflammation. However, there are no investigations of irisin's effect on AD-associated tauopathy in the brain. This study begins to address this gap in knowledge. METHODS: Transgenic htau mice that selectively develop age-related tauopathy were treated with recombinant irisin (100 µg/kg weekly i.p.) beginning at a pre-symptomatic age (4 months) to determine if irisin could prevent emergence of early neuropathology. One month later, mice were sacrificed to collect brain tissue and serum. Protein levels of ptau (serine 202), inflammatory cytokine tumour necrosis factor alpha (TNFα) and FNDC5 were quantified using capillary-based western blotting (Wes). RESULTS: Our data show that irisin treatment significantly reduced ptau and TNFα in the hippocampus and serum of female htau mice compared to vehicle-treated controls. Irisin treatment did not alter ptau levels in male htau hippocampus and appeared to enhance both neural and systemic TNFα levels. CONCLUSIONS: This study provides the first evidence that enhancing the endogenous hormone irisin may be therapeutic against emerging neuropathology in a tauopathy-selective AD model. This is important because there are currently no disease-modifying therapeutics available for AD, and few agents in development address the multiple disease targets irisin appears to-making irisin an intriguing therapeutic candidate for further investigation.

Interplay between intraocular and intracranial pressure effects on the optic nerve head in vivo.

Intracranial pressure (ICP) has been proposed to play an important role in the sensitivity to intraocular pressure (IOP) and susceptibility to glaucoma. However, the in vivo effects of simultaneous, controlled, acute variations in ICP and IOP have not been directly measured. We quantified the deformations of the anterior lamina cribrosa (ALC) and scleral canal at Bruch's membrane opening (BMO) under acute elevation of IOP and/or ICP. Four eyes of three adult monkeys were imaged in vivo with OCT under four pressure conditions: IOP and ICP either at baseline or elevated. The BMO and ALC were reconstructed from manual delineations. From these, we determined canal area at the BMO (BMO area), BMO aspect ratio and planarity, and ALC median depth relative to the BMO plane. To better account for the pressure effects on the imaging, we also measured ALC visibility as a percent of the BMO area. Further, ALC depths were analyzed only in regions where the ALC was visible in all pressure conditions. Bootstrap sampling was used to obtain mean estimates and confidence intervals, which were then used to test for significant effects of IOP and ICP, independently and in interaction. Response to pressure manipulation was highly individualized between eyes, with significant changes detected in a majority of the parameters. Significant interactions between ICP and IOP occurred in all measures, except ALC visibility. On average, ICP elevation expanded BMO area by 0.17 mm2 at baseline IOP, and contracted BMO area by 0.02 mm2 at high IOP. ICP elevation decreased ALC depth by 10 µm at baseline IOP, but increased depth by 7 µm at high IOP. ALC visibility decreased as ICP increased, both at baseline (-10%) and high IOP (-17%). IOP elevation expanded BMO area by 0.04 mm2 at baseline ICP, and contracted BMO area by 0.09 mm2 at high ICP. On average, IOP elevation caused the ALC to displace 3.3 µm anteriorly at baseline ICP, and 22 µm posteriorly at high ICP. ALC visibility improved as IOP increased, both at baseline (5%) and high ICP (8%). In summary, changing IOP or ICP significantly deformed both the scleral canal and the lamina of the monkey ONH, regardless of the other pressure level. There were significant interactions between the effects of IOP and those of ICP on LC depth, BMO area, aspect ratio and planarity. On most eyes, elevating both pressures by the same amount did not cancel out the effects. Altogether our results show that ICP affects sensitivity to IOP, and thus that it can potentially also affect susceptibility to glaucoma.

Cell signaling heterogeneity is modulated by both cell-intrinsic and -extrinsic mechanisms: An integrated approach to understanding targeted therapy.

During the last decade, our understanding of cancer cell signaling networks has significantly improved, leading to the development of various targeted therapies that have elicited profound but, unfortunately, short-lived responses. This is, in part, due to the fact that these targeted therapies ignore context and average out heterogeneity. Here, we present a mathematical framework that addresses the impact of signaling heterogeneity on targeted therapy outcomes. We employ a simplified oncogenic rat sarcoma (RAS)-driven mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase-protein kinase B (PI3K-AKT) signaling pathway in lung cancer as an experimental model system and develop a network model of the pathway. We measure how inhibition of the pathway modulates protein phosphorylation as well as cell viability under different microenvironmental conditions. Training the model on this data using Monte Carlo simulation results in a suite of in silico cells whose relative protein activities and cell viability match experimental observation. The calibrated model predicts distributional responses to kinase inhibitors and suggests drug resistance mechanisms that can be exploited in drug combination strategies. The suggested combination strategies are validated using in vitro experimental data. The validated in silico cells are further interrogated through an unsupervised clustering analysis and then integrated into a mathematical model of tumor growth in a homogeneous and resource-limited microenvironment. We assess posttreatment heterogeneity and predict vast differences across treatments with similar efficacy, further emphasizing that heterogeneity should modulate treatment strategies. The signaling model is also integrated into a hybrid cellular automata (HCA) model of tumor growth in a spatially heterogeneous microenvironment. As a proof of concept, we simulate tumor responses to targeted therapies in a spatially segregated tissue structure containing tumor and stroma (derived from patient tissue) and predict complex cell signaling responses that suggest a novel combination treatment strategy.

Distinct Sources of Variability Affect Eye Movement Preparation.

The sequence of events leading to an eye movement to a target begins the moment visual information has reached the brain, well in advance of the eye movement itself. The process by which visual information is encoded and used to generate a motor plan has been the focus of substantial interest partly because of the rapid and reproducible nature of saccadic eye movements, and the key role that they play in primate behavior. Signals related to eye movements are present in much of the primate brain, yet most neurophysiological studies of the transition from vision to eye movements have measured the activity of one neuron at a time. Less is known about how the coordinated action of populations of neurons contribute to the initiation of eye movements. One cortical area of particular interest in this process is the frontal eye fields, a region of prefrontal cortex that has descending projections to oculomotor control centers. We recorded from populations of frontal eye field neurons in macaque monkeys engaged in a memory-guided saccade task. We found a variety of neurons with visually evoked responses, saccade-aligned responses, and mixtures of both. We took advantage of the simultaneous nature of the recordings to measure variability in individual neurons and pairs of neurons from trial-to-trial, as well as the moment-to-moment population activity structure. We found that these measures were related to saccadic reaction times, suggesting that the population-level organization of frontal eye field activity is important for the transition from perception to movement.SIGNIFICANCE STATEMENT The transition from perception to action involves coordination among neurons across the brain. In the case of eye movements, visual and motor signals coexist in individual neurons as well as in neighboring neurons. We used a task designed to compartmentalize the visual and motor aspects of this transition and studied populations of neurons in the frontal eye fields, a key cortical area containing neurons that are implicated in the transition from vision to eye movements. We found that the time required for subjects to produce an eye movement could be predicted from the statistics of the neuronal response of populations of frontal eye field neurons, suggesting that these neurons coordinate their activity to optimize the transition from perception to action.

Dynamic shifts of visual and saccadic signals in prefrontal cortical regions 8Ar and FEF.

Active vision is a fundamental process by which primates gather information about the external world. Multiple brain regions have been studied in the context of simple active vision tasks in which a visual target's appearance is temporally separated from saccade execution. Most neurons have tight spatial registration between visual and saccadic signals, and in areas such as prefrontal cortex (PFC), some neurons show persistent delay activity that links visual and motor epochs and has been proposed as a basis for spatial working memory. Many PFC neurons also show rich dynamics, which have been attributed to alternative working memory codes and the representation of other task variables. Our study investigated the transition between processing a visual stimulus and generating an eye movement in populations of PFC neurons in macaque monkeys performing a memory guided saccade task. We found that neurons in two subregions of PFC, the frontal eye fields (FEF) and area 8Ar, differed in their dynamics and spatial response profiles. These dynamics could be attributed largely to shifts in the spatial profile of visual and motor responses in individual neurons. This led to visual and motor codes for particular spatial locations that were instantiated by different mixtures of neurons, which could be important in PFC's flexible role in multiple sensory, cognitive, and motor tasks.NEW & NOTEWORTHY A central question in neuroscience is how the brain transitions from sensory representations to motor outputs. The prefrontal cortex contains neurons that have long been implicated as important in this transition and in working memory. We found evidence for rich and diverse tuning in these neurons, which was often spatially misaligned between visual and saccadic responses. This feature may play an important role in flexible working memory capabilities.

A neural network for online spike classification that improves decoding accuracy.

Separating neural signals from noise can improve brain-computer interface performance and stability. However, most algorithms for separating neural action potentials from noise are not suitable for use in real time and have shown mixed effects on decoding performance. With the goal of removing noise that impedes online decoding, we sought to automate the intuition of human spike-sorters to operate in real time with an easily tunable parameter governing the stringency with which spike waveforms are classified. We trained an artificial neural network with one hidden layer on neural waveforms that were hand-labeled as either spikes or noise. The network output was a likelihood metric for each waveform it classified, and we tuned the network's stringency by varying the minimum likelihood value for a waveform to be considered a spike. Using the network's labels to exclude noise waveforms, we decoded remembered target location during a memory-guided saccade task from electrode arrays implanted in prefrontal cortex of rhesus macaque monkeys. The network classified waveforms in real time, and its classifications were qualitatively similar to those of a human spike-sorter. Compared with decoding with threshold crossings, in most sessions we improved decoding performance by removing waveforms with low spike likelihood values. Furthermore, decoding with our network's classifications became more beneficial as time since array implantation increased. Our classifier serves as a feasible preprocessing step, with little risk of harm, that could be applied to both off-line neural data analyses and online decoding.NEW & NOTEWORTHY Although there are many spike-sorting methods that isolate well-defined single units, these methods typically involve human intervention and have inconsistent effects on decoding. We used human classified neural waveforms as training data to create an artificial neural network that could be tuned to separate spikes from noise that impaired decoding. We found that this network operated in real time and was suitable for both off-line data processing and online decoding.

Fully Automated Protein Proximity Assay in Formalin-Fixed, Paraffin-Embedded Tissue Using Caged Haptens.

The ability to interrogate for the presence and distribution of protein-protein complexes (PPCs) is of high importance for the advancement of diagnostic capabilities such as determining therapeutic effects in the context of pharmaceutical development. Herein, we report a novel assay for detecting and visualizing PPCs on formalin-fixed, paraffin-embedded material using a caged hapten. To this end, we synthetically modified a nitropyrazole hapten with an alkaline phosphatase (AP)-responsive self-immolative caging group. The AP-labile caging group abrogates antibody binding; however, upon exposure to AP, the native hapten is regenerated. These caged haptens were applied in a proximity assay format by the use of a first antibody labeled with caged haptens that can be uncaged by AP conjugated to the second antibody. Only when the two epitopes of interest are in close proximity to one another will the AP interact with the caged hapten and uncage it. The native hapten, which represents the population of PPCs, was then visualized by an anti-hapten antibody conjugated to horseradish peroxidase, followed by diaminobenzidine detection. We provide proof of concept for the detection of protein proximity pairs (ß-catenin-E-cadherin and EGFR-GRB2), and confirm assay specificity through technical controls involving reagent omission experiments, and biologically by treatment with small-molecule kinase inhibitors that interrupt kinase-adaptor complexes.

Structural and Functional Rescue of Chronic Metabolically Stressed Optic Nerves through Respiration.

Axon degeneration can arise from metabolic stress, potentially a result of mitochondrial dysfunction or lack of appropriate substrate input. In this study, we investigated whether the metabolic vulnerability observed during optic neuropathy in the DBA/2J (D2) model of glaucoma is due to dysfunctional mitochondria or impaired substrate delivery to axons, the latter based on our observation of significantly decreased glucose and monocarboxylate transporters in D2 optic nerve (ON), human ON, and mice subjected to acute glaucoma injury. We placed both sexes of D2 mice destined to develop glaucoma and mice of a control strain, the DBA/2J-Gpnmb+, on a ketogenic diet to encourage mitochondrial function. Eight weeks of the diet generated mitochondria, improved energy availability by reversing monocarboxylate transporter decline, reduced glial hypertrophy, protected retinal ganglion cells and their axons from degeneration, and maintained physiological signaling to the brain. A robust antioxidant response also accompanied the response to the diet. These results suggest that energy compromise and subsequent axon degeneration in the D2 is due to low substrate availability secondary to transporter downregulation.SIGNIFICANCE STATEMENT We show axons in glaucomatous optic nerve are energy depleted and exhibit chronic metabolic stress. Underlying the metabolic stress are low levels of glucose and monocarboxylate transporters that compromise axon metabolism by limiting substrate availability. Axonal metabolic decline was reversed by upregulating monocarboxylate transporters as a result of placing the animals on a ketogenic diet. Optic nerve mitochondria responded capably to the oxidative phosphorylation necessitated by the diet and showed increased number. These findings indicate that the source of metabolic challenge can occur upstream of mitochondrial dysfunction. Importantly, the intervention was successful despite the animals being on the cusp of significant glaucoma progression.

Altered functional interactions between neurons in primary visual cortex of macaque monkeys with experimental amblyopia.

Amblyopia, a disorder in which vision through one of the eyes is degraded, arises because of defective processing of information by the visual system. Amblyopia often develops in humans after early misalignment of the eyes (strabismus) and can be simulated in macaque monkeys by artificially inducing strabismus. In such amblyopic animals, single-unit responses in primary visual cortex (V1) are appreciably reduced when evoked by the amblyopic eye compared with the other (fellow) eye. However, this degradation in single V1 neuron responsivity is not commensurate with the marked losses in visual sensitivity and resolution measured behaviorally. Here we explored the idea that changes in patterns of coordinated activity across populations of V1 neurons may contribute to degraded visual representations in amblyopia, potentially making it more difficult to read out evoked activity to support perceptual decisions. We studied the visually evoked activity of V1 neuronal populations in three macaques (Macaca nemestrina) with strabismic amblyopia and in one control animal. Activity driven through the amblyopic eye was diminished, and these responses also showed more interneuronal correlation at all stimulus contrasts than responses driven through the fellow eye or responses in the control animal. A decoding analysis showed that responses driven through the amblyopic eye carried less visual information than other responses. Our results suggest that part of the reduced visual capacity of amblyopes may be due to changes in the patterns of functional interaction among neurons in V1.NEW & NOTEWORTHY Previous work on the neurophysiological basis of amblyopia has largely focused on relating behavioral deficits to changes in visual processing by single neurons in visual cortex. In this study, we recorded simultaneously from populations of primary visual cortical (V1) neurons in macaques with amblyopia. We found changes in the strength and pattern of shared response variability between neurons. These changes in neuronal interactions could impair the visual representations of V1 populations driven by the amblyopic eye.

What does scalp electroencephalogram coherence tell us about long-range cortical networks?

Long-range interactions between cortical areas are undoubtedly a key to the computational power of the brain. For healthy human subjects, the premier method for measuring brain activity on fast timescales is electroencephalography (EEG), and coherence between EEG signals is often used to assay functional connectivity between different brain regions. However, the nature of the underlying brain activity that is reflected in EEG coherence is currently the realm of speculation, because seldom have EEG signals been recorded simultaneously with intracranial recordings near cell bodies in multiple brain areas. Here, we take the early steps towards narrowing this gap in our understanding of EEG coherence by measuring local field potentials with microelectrode arrays in two brain areas (extrastriate visual area V4 and dorsolateral prefrontal cortex) simultaneously with EEG at the nearby scalp in rhesus macaque monkeys. Although we found inter-area coherence at both scales of measurement, we did not find that scalp-level coherence was reliably related to coherence between brain areas measured intracranially on a trial-to-trial basis, despite that scalp-level EEG was related to other important features of neural oscillations, such as trial-to-trial variability in overall amplitudes. This suggests that caution must be exercised when interpreting EEG coherence effects, and new theories devised about what aspects of neural activity long-range coherence in the EEG reflects.