Low cerebral blood flow is a non-invasive biomarker of neuroinflammation after repetitive mild traumatic brain injury

Neuroinflammation increases oxygen extraction in a mouse model of Alzheimer's disease

BACKGROUND

Neuroinflammation, impaired metabolism, and hypoperfusion are fundamental pathological hallmarks of early Alzheimer's disease (AD). Numerous studies have asserted a close association between neuroinflammation and disrupted cerebral energetics. During AD progression and other neurodegenerative disorders, a persistent state of chronic neuroinflammation reportedly exacerbates cytotoxicity and potentiates neuronal death. Here, we assessed the impact of a neuroinflammatory challenge on metabolic demand and microvascular hemodynamics in the somatosensory cortex of an AD mouse model.

METHODS

We utilized in vivo 2-photon microscopy and the phosphorescent oxygen sensor Oxyphor 2P to measure partial pressure of oxygen (pO2) and capillary red blood cell flux in cortical microvessels of awake mice. Intravascular pO2 and capillary RBC flux measurements were performed in 8-month-old APPswe/PS1dE9 mice and wildtype littermates on days 0, 7, and 14 of a 14-day period of lipopolysaccharide-induced neuroinflammation.

RESULTS

Before the induced inflammatory challenge, AD mice demonstrated reduced metabolic demand but similar capillary red blood cell flux as their wild type counterparts. Neuroinflammation provoked significant reductions in cerebral intravascular oxygen levels and elevated oxygen extraction in both animal groups, without significantly altering red blood cell flux in capillaries.

CONCLUSIONS

This study provides evidence that neuroinflammation alters cerebral oxygen demand at the early stages of AD without substantially altering vascular oxygen supply. The results will guide our understanding of neuroinflammation's influence on neuroimaging biomarkers for early AD diagnosis.

Co-administration of dl-3-n-butylphthalide and neprilysin is neuroprotective in Alzheimer disease associated with mild traumatic brain injury

dl-3-n-Butylphthalide is a potent synthetic Chinese celery extract that is highly efficient in inducing neuroprotection in concussive head injury (CHI), Parkinson's disease, Alzheimer's disease, stroke as well as depression, dementia, anxiety and other neurological diseases. Thus, there are reasons to believe that dl-3-n-butylphthalide could effectively prevent Alzheimer's disease brain pathology. Military personnel during combat operation or veterans are often the victims of brain injury that is a major risk factor for developing Alzheimer's disease in their later lives. In our laboratory we have shown that CHI exacerbates Alzheimer's disease brain pathology and reduces the amyloid beta peptide (AβP) inactivating enzyme neprilysin. We have used TiO2 nanowired-dl-3-n-butylphthalide in attenuating Parkinson's disease brain pathology exacerbated by CHI. Nanodelivery of dl-3-n-butylphthalide appears to be more potent as compared to the conventional delivery of the compound. Thus, it would be interesting to examine the effects of nanowired dl-3-n-butylphthalide together with nanowired delivery of neprilysin in Alzheimer's disease model on brain pathology. In this investigation we found that nanowired delivery of dl-3-n-butylphthalide together with nanowired neprilysin significantly attenuated brain pathology in Alzheimer's disease model with CHI, not reported earlier. The possible mechanism and clinical significance is discussed based on the current literature.

Profiling the neuroimmune cascade in 3xTg mice exposed to successive mild traumatic brain injuries

Repetitive mild traumatic brain injuries (rmTBI) sustained within a window of vulnerability can result in long term cognitive deficits, depression, and eventual neurodegeneration associated with tau pathology, amyloid beta (Aβ) plaques, gliosis, and neuronal and functional loss. However, we have limited understanding of how successive injuries acutely affect the brain to result in these devastating long-term consequences. In the current study, we addressed the question of how repeated injuries affect the brain in the acute phase of injury (<24hr) by exposing the 3xTg-AD mouse model of tau and Aβ pathology to successive (1x, 3x, 5x) once-daily weight drop closed-head injuries and quantifying immune markers, pathological markers, and transcriptional profiles at 30min, 4hr, and 24hr after each injury. We used young adult mice (2-4 months old) to model the effects of rmTBI relevant to young adult athletes, and in the absence of significant tau and Aβ pathology. Importantly, we identified pronounced sexual dimorphism, with females eliciting more differentially expressed proteins after injury compared to males. Specifically, females showed: 1) a single injury caused a decrease in neuron-enriched genes inversely correlated with inflammatory protein expression as well as an increase in AD-related genes within 24hr, 2) each injury significantly increased expression of a group of cortical cytokines (IL-1α, IL-1β, IL-2, IL-9, IL-13, IL-17, KC) and MAPK phospho-proteins (phospho-Atf2, phospho-Mek1), several of which were co-labeled with neurons and correlated with phospho-tau, and 3) repetitive injury caused increased expression of genes associated with astrocyte reactivity and immune function. Collectively our data suggest that neurons respond to a single injury within 24h, while other cell types including astrocytes transition to inflammatory phenotypes within days of repetitive injury.

MPC-n (IgG) improves long-term cognitive impairment in the mouse model of repetitive mild traumatic brain injury

BACKGROUND

Contact sports athletes and military personnel who suffered a repetitive mild traumatic brain injury (rmTBI) are at high risk of neurodegenerative diseases such as advanced dementia and chronic traumatic encephalopathy (CTE). However, due to the lack of specific biological indicators in clinical practice, the diagnosis and treatment of rmTBI are quite limited.

METHODS

We used 2-methacryloyloxyethyl phosphorylcholine (MPC)-nanocapsules to deliver immunoglobulins (IgG), which can increase the delivery efficiency and specific target of IgG while reducing the effective therapeutic dose of the drug.

RESULTS

Our results demonstrated that MPC-capsuled immunoglobulins (MPC-n (IgG)) significantly alleviated cognitive impairment, hippocampal atrophy, p-Tau deposition, and myelin injury in rmTBI mice compared with free IgG. Furthermore, MPC-n (IgG) can also effectively inhibit the activation of microglia and the release of inflammatory factors.

CONCLUSIONS

In the present study, we put forward an efficient strategy for the treatment of rmTBI-related cognitive impairment and provide evidence for the administration of low-dose IgG.

Partial Depletion of Microglia Attenuates Long-Term Potentiation Deficits following Repeated Blast Traumatic Brain Injury in Organotypic Hippocampal Slice Cultures

Blast-induced traumatic brain injury (bTBI) has been a health concern in both military and civilian populations due to recent military and geopolitical conflicts. Military service members are frequently exposed to repeated bTBI throughout their training and deployment. Our group has previously reported compounding functional deficits as a result of increased number of blast exposures. In this study, we further characterized the decrease in long-term potentiation (LTP) by varying the blast injury severity and the inter-blast interval between two blast exposures. LTP deficits were attenuated with increasing inter-blast intervals. We also investigated changes in microglial activation; expression of CD68 was increased and expression of CD206 was decreased after multiple blast exposures. Expression of macrophage inflammatory protein (MIP)-1α, interleukin (IL)-1β, monocyte chemoattractant protein (MCP)-1, interferon gamma-inducible protein (IP)-10, and regulated on activation, normal T cell expressed and secreted (RANTES) increased, while expression of IL-10 decreased in the acute period after both single and repeated bTBI. By partially depleting microglia prior to injury, LTP deficits after injury were significantly reduced. Treatment with the novel drug, MW-189, prevented LTP deficits when administered immediately following a repeated bTBI and even when administered only for an acute period (24 h) between two blast injuries. These findings could inform the development of therapeutic strategies to treat the neurological deficits of repeated bTBI suggesting that microglia play a major role in functional neuronal deficits and may be a viable therapeutic target to lessen the neurophysiological deficits after bTBI.

The PI3K/AKT Signaling Pathway and Caspase-3 in Alzheimer's Disease: Which One Is the Beginner?

One of the main players in apoptosis during Alzheimer's disease progression are different members of caspase family of proteases. The most well-known member of this family is caspase-3, in which alterations of its levels have been detected in samples from Alzheimer's disease patients. There are numerous intracellular factors involved in regulation of cellular apoptosis through regulation of caspase-3 activity, the most important of which is the PI3K/AKT signaling pathway. This commentary tries to highlight the probable relations between PI3K/AKT signaling pathway and caspase-3 in Alzheimer's disease.

Reversal of spatial memory impairment by phosphodiesterase 3 inhibitor cilostazol is associated with reduced neuroinflammation and increased cerebral glucose uptake in aged male mice

The nucleotide second messenger 3', 5'-cyclic adenosine monophosphate (cAMP) and 3', 5'-cyclic guanosine monophosphate (cGMP) mediate fundamental functions of the brain, including learning and memory. Phosphodiesterase 3 (PDE3) can hydrolyze both cAMP and cGMP and appears to be involved in the regulation of their contents in cells. We previously demonstrated that long-term administration of cilostazol, a PDE3 inhibitor, maintained good memory performance in aging mice. Here, we report on studies aimed at determining whether cilostazol also reverses already-impaired memory in aged male mice. One month of oral 1.5% cilostazol administration in 22-month-old mice reversed age-related declines in hippocampus-dependent memory tasks, including the object recognition and the Morris water maze. Furthermore, cilostazol reduced neuroinflammation, as evidenced by immunohistochemical staining, and increased glucose uptake in the brain, as evidence by positron emission tomography (PET) with 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG). These results suggest that already-expressed memory impairment in aged male mice that depend on cyclic nucleotide signaling can be reversed by inhibition of PDE3. The reversal of age-related memory impairments may occur in the central nervous system, either through cilostazol-enhanced recall or strengthening of weak memories that otherwise may be resistant to recall.

Genetic deletion of Krüppel-like factor 11 aggravates traumatic brain injury

Background

The long-term functional recovery of traumatic brain injury (TBI) is hampered by pathological events, such as parenchymal neuroinflammation, neuronal death, and white matter injury. Krüppel-like transcription factor 11 (KLF 11) belongs to the zinc finger family of transcription factors and actively participates in various pathophysiological processes in neurological disorders. Up to now, the role and molecular mechanisms of KLF11 in regulating the pathogenesis of brain trauma is poorly understood.

Methods

KLF11 knockout (KO) and wild-type (WT) mice were subjected to experimental TBI, and sensorimotor and cognitive functions were evaluated by rotarod, adhesive tape removal, foot fault, water maze, and passive avoidance tests. Brain tissue loss/neuronal death was examined by MAP2 and NeuN immunostaining, and Cresyl violet staining. White matter injury was assessed by Luxol fast blue staining, and also MBP/SMI32 and Caspr/Nav1.6 immunostaining. Activation of cerebral glial cells and infiltration of blood-borne immune cells were detected by GFAP, Iba-1/CD16/32, Iba-1/CD206, Ly-6B, and F4/80 immunostaining. Brian parenchymal inflammatory cytokines were measured with inflammatory array kits.

Results

Genetic deletion of KLF11 worsened brain trauma-induced sensorimotor and cognitive deficits, brain tissue loss and neuronal death, and white matter injury in mice. KLF11 genetic deficiency in mice also accelerated post-trauma astrocytic activation, promoted microglial polarization to a pro-inflammatory phenotype, and increased the infiltration of peripheral neutrophils and macrophages into the brain parenchyma. Mechanistically, loss-of-KLF11 function was found to directly increase the expression of pro-inflammatory cytokines in the brains of TBI mice.

Conclusion

KLF11 acts as a novel protective factor in TBI. KLF11 genetic deficiency in mice aggravated the neuroinflammatory responses, grey and white matter injury, and impaired long-term sensorimotor and cognitive recovery. Elucidating the functional importance of KLF11 in TBI may lead us to discover novel pharmacological targets for the development of effective therapies against brain trauma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02638-0.

Systems Analysis of the Neuroinflammatory and Hemodynamic Response to Traumatic Brain Injury

Mild traumatic brain injuries (mTBIs) are a significant public health problem. Repeated exposure to mTBI can lead to cumulative, long-lasting functional deficits. Numerous studies by our group and others have shown that mTBI stimulates cytokine expression and activates microglia, decreases cerebral blood flow and metabolism, and impairs cerebrovascular reactivity. Moreover, several works have reported an association between derangements in these neuroinflammatory and hemodynamic markers and cognitive impairments. Herein we detail methods to characterize the neuroinflammatory and hemodynamic tissue response to mTBI in mice. Specifically, we describe how to perform a weight-drop model of mTBI, how to longitudinally measure cerebral blood flow using a non-invasive optical technique called diffuse correlation spectroscopy, and how to perform a Luminex multiplexed immunoassay on brain tissue samples to quantify cytokines and immunomodulatory phospho-proteins (e.g., within the MAPK and NFκB pathways) that respond to and regulate activity of microglia and other neural immune cells. Finally, we detail how to integrate these data using a multivariate systems analysis approach to understand the relationships between all of these variables. Understanding the relationships between these physiologic and molecular variables will ultimately enable us to identify mechanisms responsible for mTBI.

The Pathobiology of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: The Case for Neuroglial Failure

Although myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) has a specific and distinctive profile of clinical features, the disease remains an enigma because causal explanation of the pathobiological matrix is lacking. Several potential disease mechanisms have been identified, including immune abnormalities, inflammatory activation, mitochondrial alterations, endothelial and muscular disturbances, cardiovascular anomalies, and dysfunction of the peripheral and central nervous systems. Yet, it remains unclear whether and how these pathways may be related and orchestrated. Here we explore the hypothesis that a common denominator of the pathobiological processes in ME/CFS may be central nervous system dysfunction due to impaired or pathologically reactive neuroglia (astrocytes, microglia and oligodendrocytes). We will test this hypothesis by reviewing, in reference to the current literature, the two most salient and widely accepted features of ME/CFS, and by investigating how these might be linked to dysfunctional neuroglia. From this review we conclude that the multifaceted pathobiology of ME/CFS may be attributable in a unifying manner to neuroglial dysfunction. Because the two key features - post exertional malaise and decreased cerebral blood flow - are also recognized in a subset of patients with post-acute sequelae COVID, we suggest that our findings may also be pertinent to this entity.

Sex differences in the blood-brain barrier: Implications for mental health

Prevalence of mental disorders, including major depressive disorder (MDD), bipolar disorder (BD) and schizophrenia (SZ) are increasing at alarming rates in our societies. Growing evidence points toward major sex differences in these conditions, and high rates of treatment resistance support the need to consider novel biological mechanisms outside of neuronal function to gain mechanistic insights that could lead to innovative therapies. Blood-brain barrier alterations have been reported in MDD, BD and SZ. Here, we provide an overview of sex-specific immune, endocrine, vascular and transcriptional-mediated changes that could affect neurovascular integrity and possibly contribute to the pathogenesis of mental disorders. We also identify pitfalls in current literature and highlight promising vascular biomarkers. Better understanding of how these adaptations can contribute to mental health status is essential not only in the context of MDD, BD and SZ but also cardiovascular diseases and stroke which are associated with higher prevalence of these conditions.

Inhibition of Exosome Release Alleviates Cognitive Impairment After Repetitive Mild Traumatic Brain Injury

Background

Repetitive mild traumatic brain injury (rmTBI) is closely associated with chronic traumatic encephalopathy (CTE). Neuroinflammation and neuropathological protein accumulation are key links to CTE progression. Exosomes play important roles in neuroinflammation and neuropathological protein accumulation and spread. Here, we explored the role of brain-derived exosomes (BDEs) in mice with rmTBI and how the inhibition of BDE release contributes to neuroprotection.

Methods

GW4869 was used to inhibit exosome release, and behavioural tests, PET/CT and western blotting were conducted to explore the impact of this inhibition from different perspectives. We further evaluated cytokine expression by Luminex and microglial activation by immunofluorescence in mice with rmTBI after exosome release inhibition.

Results

Inhibition of BDE release reversed cognitive impairment in mice with rmTBI, enhanced glucose uptake and decreased neuropathological protein expression. Inhibition of BDE release also changed cytokine production trends and enhanced microglial proliferation.

Conclusion

In this study, we found that BDEs are key factor in cognitive impairment in mice with rmTBI and that microglia are the main target of BDEs. Thus, inhibition of exosome release may be a new strategy for improving CTE prognoses.

Systemic infection exacerbates cerebrovascular dysfunction in Alzheimer's disease

We studied the effects of systemic infection on brain cytokine level and cerebral vascular function in Alzheimer's disease and vascular dementia, in superior temporal cortex (Brodmann area 22) from Alzheimer's disease patients (n = 75), vascular dementia patients (n = 22) and age-matched control subjects (n = 46), stratified according to the presence or absence of terminal systemic infection. Brain cytokine levels were measured using Mesoscale Discovery Multiplex Assays and markers of cerebrovascular function were assessed by ELISA. Multiple brain cytokines were elevated in Alzheimer's disease and vascular dementia: IL-15 and IL-17A were maximally elevated in end-stage Alzheimer's disease (Braak tangle stage V-VI) whereas IL-2, IL-5, IL12p40 and IL-16 were highest in intermediate Braak tangle stage III-IV disease. Several cytokines (IL-1β, IL-6, TNF-α, IL-8 and IL-15) were further raised in Alzheimer's disease with systemic infection. Cerebral hypoperfusion-indicated by decreased MAG:PLP1 and increased vascular endothelial growth factor-A (VEGF)-and blood-brain barrier leakiness, indicated by raised levels of fibrinogen, were exacerbated in Alzheimer's disease and vascular dementia patients, and also in non-dementia controls, with systemic infection. Amyloid-β42 level did not vary with infection or in association with brain cytokine levels. In controls, cortical perfusion declined with increasing IFN-γ, IL-2, IL-4, IL-6, IL-10, IL-12p70, IL-13 and tumour necrosis factor-α (TNF-α) but these relationships were lost with progression of Alzheimer's disease, and with infection (even in Braak stage 0-II brains). Cortical platelet-derived growth factor receptor-β (PDGFRβ), a pericyte marker, was reduced, and endothelin-1 (EDN1) level was increased in Alzheimer's disease; these were related to amyloid-β level and disease progression and only modestly affected by systemic infection. Our findings indicate that systemic infection alters brain cytokine levels and exacerbates cerebral hypoperfusion and blood-brain barrier leakiness associated with Alzheimer's disease and vascular dementia, independently of the level of insoluble amyloid-β, and highlight systemic infection as an important contributor to dementia, requiring early identification and treatment in the elderly population.

Preliminary Report: Localized Cerebral Blood Flow Mediates the Relationship between Progesterone and Perceived Stress Symptoms among Female Collegiate Club Athletes after Mild Traumatic Brain Injury

Female athletes are under-studied in the field of concussion research, despite evidence of higher injury prevalence and longer recovery time. Hormonal fluctuations caused by the natural menstrual cycle (MC) or hormonal contraceptive (HC) use impact both post-injury symptoms and neuroimaging findings, but the relationships among hormone, symptoms, and brain-based measures have not been jointly considered in concussion studies. In this preliminary study, we compared cerebral blood flow (CBF) measured with arterial spin labeling between concussed female club athletes 3-10 days after mild traumatic brain injury (mTBI) and demographic, HC/MC matched controls (CON). We tested whether CBF statistically mediates the relationship between progesterone serum levels and post-injury symptoms, which may support a hypothesis for progesterone's role in neuroprotection. We found a significant three-way relationship among progesterone, CBF, and perceived stress score (PSS) in the left middle temporal gyrus for the mTBI group. Higher progesterone was associated with lower (more normative) PSS, as well as higher (more normative) CBF. CBF mediates 100% of the relationship between progesterone and PSS (Sobel p value = 0.017). These findings support a hypothesis for progesterone having a neuroprotective role after concussion and highlight the importance of controlling for the effects of sex hormones in future concussion studies.

A Proposed Hypothesis on Dementia: Inflammation, Small Vessel Disease, and Hypoperfusion Is the Sequence That Links All Harmful Lifestyles to Cognitive Impairment

There is growing consensus that certain lifestyles can contribute to cognitive impairment and dementia, but the physiological steps that link a harmful lifestyle to its negative impact are not always evident. It is also unclear whether all lifestyles that contribute to dementia do so through the same intermediary steps. This article will focus on three lifestyles known to be risk factors for dementia, namely obesity, sedentary behavior, and insufficient sleep, and offer a unifying hypothesis proposing that lifestyles that negatively impact cognition do so through the same sequence of events: inflammation, small vessel disease, decline in cerebral perfusion, and brain atrophy. The hypothesis will then be tested in a recently identified risk factor for dementia, namely hearing deficit. If further studies confirm this sequence of events leading to dementia, a significant change in our approach to this debilitating and costly condition may be necessary, possible, and beneficial.

Brain Perfusion Bridges Virtual-Reality Spatial Behavior to TPH2 Genotype for Head Acceleration Events

Neuroimaging demonstrates that athletes of collision sports can suffer significant changes to their brain in the absence of concussion, attributable to head acceleration event (HAE) exposure. In a sample of 24 male Division I collegiate football players, we examine the relationships between tryptophan hydroxylase 2 (TPH2), a gene involved in neurovascular function, regional cerebral blood flow (rCBF) measured by arterial spin labeling, and virtual reality (VR) motor performance, both pre-season and across a single football season. For the pre-season, TPH2 T-carriers showed lower rCBF in two left hemisphere foci (fusiform gyrus/thalamus/hippocampus and cerebellum) in association with higher (better performance) VR Reaction Time, a dynamic measure of sensory-motor reactivity and efficiency of visual-spatial processing. For TPH2 CC homozygotes, higher pre-season rCBF in these foci was associated with better performance on VR Reaction Time. A similar relationship was observed across the season, where TPH2 T-carriers showed improved VR Reaction Time associated with decreases in rCBF in the right hippocampus/amygdala, left middle temporal lobe, and left insula/putamen/pallidum. In contrast, TPH2 CC homozygotes showed improved VR Reaction Time associated with increases in rCBF in the same three clusters. These findings show that TPH2 T-carriers have an abnormal relationship between rCBF and the efficiency of visual-spatial processing that is exacerbated after a season of high-impact sports in the absence of diagnosable concussion. Such gene-environment interactions associated with behavioral changes after exposure to repetitive HAEs have been unrecognized with current clinical analytical tools and warrant further investigation. Our results demonstrate the importance of considering neurovascular factors along with traumatic axonal injury to study long-term effects of repetitive HAEs.

The Immune System's Role in the Consequences of Mild Traumatic Brain Injury (Concussion)

Mild traumatic brain injury (mild TBI), often referred to as concussion, is the most common form of TBI and affects millions of people each year. A history of mild TBI increases the risk of developing emotional and neurocognitive disorders later in life that can impact on day to day living. These include anxiety and depression, as well as neurodegenerative conditions such as chronic traumatic encephalopathy (CTE) and Alzheimer's disease (AD). Actions of brain resident or peripherally recruited immune cells are proposed to be key regulators across these diseases and mood disorders. Here, we will assess the impact of mild TBI on brain and patient health, and evaluate the recent evidence for immune cell involvement in its pathogenesis.

An Overview and Therapeutic Promise of Nutraceuticals against Sports-Related Brain Injury

Sports-related traumatic brain injury (TBI) is one of the common neurological maladies experienced by athletes. Earlier the term 'punch drunk syndrome' was used in the case TBI of boxers and now this term is replaced by chronic traumatic encephalopathy (CTE). Sports-related brain injury can either be short term or long term. A common instance of brain injury encompasses subdural hematoma, concussion, cognitive dysfunction, amnesia, headache, vision issue, axonopathy, or even death if remain undiagnosed or untreated. Further, chronic TBI may lead to pathogenesis of neuroinflammation and neurodegeneration via tauopathy, formation of neurofibrillary tangles, and damage to the blood-brain barrier, microglial, and astrocyte activation. Thus, altered pathological, neurochemical, and neurometabolic attributes lead to the modulation of multiple signaling pathways and cause neurological dysfunction. Available pharmaceutical interventions are based on one drug one target hypothesis and thereby unable to cover altered multiple signaling pathways. However, in recent time's pharmacological intervention of nutrients and nutraceuticals have been explored as they exert a multifactorial mode of action and maintain over homeostasis of the body. There are various reports available showing the positive therapeutic effect of nutraceuticals in sport-related brain injury. Therefore, in the current article we have discussed the pathology, neurological consequence, sequelae, and perpetuation of sports-related brain injury. Further, we have discussed various nutraceutical supplements as well as available animal models to explore the neuroprotective effect/ upshots of these nutraceuticals in sports-related brain injury.

Electroacupuncture effects on the P2X4R pathway in microglia regulating the excitability of neurons in the substantia gelatinosa region of rats with spinal nerve ligation

Electroacupuncture (EA) has been used to treat neuropathic pain induced by peripheral nerve injury (PNI) by applying an electrical current to acupoints with acupuncture needles. However, the mechanisms by which EA treats pain remain indistinct. High P2X4 receptor (P2X4R) expression levels demonstrate a notable increase in hyperactive microglia in the ipsilateral spinal dorsal horn following PNI. In order to demonstrate the possibility that EA analgesia is mediated in part by P2X4R in hyperactive microglia, the present study performed mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) tests in male Sprague-Dawley rats that had undergone spinal nerve ligation (SNL). The expression levels of spinal P2X4R were determined using reverse transcription-quantitative PCR, western blotting analysis and immunofluorescence staining. Furthermore, spontaneous excitatory postsynaptic currents (sEPSCs) were recorded using whole-cell patch clamp to demonstrate the effect of EA on synaptic transmission in rat spinal substantia gelatinosa (SG) neurons. The results of the present study demonstrated that EA increased the MWT and TWL and decreased overexpression of P2X4R in hyperactive microglia in SNL rats. Moreover, EA attenuated the frequency of sEPSCs in SG neurons in SNL rats. The results of the present study indicate that EA may mediate P2X4R in hyperactive spinal microglia to inhibit nociceptive transmission of SG neurons, thus relieving pain in SNL rats.

Cerebrovascular reactivity measured in awake mice using diffuse correlation spectroscopy

Significance: Cerebrovascular reactivity (CVR), defined as the ability of the cerebral vasculature to dilate or constrict in response to a vasoactive stimulus, is an important indicator of the brain's vascular health. However, mechanisms of cerebrovascular dysregulation are poorly understood, and no effective treatment strategies for impaired CVR exist. Preclinical murine models provide an excellent platform for interrogating mechanisms underlying CVR dysregulation and determining novel therapeutics that restore impaired CVR. However, quantification of CVR in mice is challenging. Aim: We present means of assessing CVR in awake mice using intraperitoneal injection of acetazolamide (ACZ) combined with continuous monitoring of cerebral blood flow. Approach: Measurements of cerebral blood flow were made with a minimally invasive diffuse correlation spectroscopy sensor that was secured to an optical window glued to the intact skull. Two source-detector separations (3 and 4.5 mm) per hemisphere were used to probe different depths. CVR was quantified as the relative increase in blood flow due to ACZ. CVR was assessed once daily for 5 days in 5 mice. Results: We found that CVR and the response half-time were remarkably similar across hemispheres and across 3- versus 4.5-mm separations, suggesting a homogenous, whole brain response to ACZ. Mean(std) intra- and intermouse coefficients of variations were 15(9)% and 19(10)%, respectively, for global CVR and 24(15)% and 27(11)%, respectively, for global response half-time. Conclusion: In sum, we report a repeatable method of measuring CVR in free-behaving mice which can be used to screen for impairments with disease and to track changes in CVR with therapeutic interventions.

Microglia dynamics in adolescent traumatic brain injury

Repetitive, mild traumatic brain injuries (RmTBIs) are increasingly common in adolescents and encompass one of the largest neurological health concerns in the world. Adolescence is a critical period for brain development where RmTBIs can substantially impact neurodevelopmental trajectories and life-long neurological health. Our current understanding of RmTBI pathophysiology suggests key roles for neuroinflammation in negatively regulating neural health and function. Microglia, the brain’s resident immune population, play important roles in brain development by regulating neuronal number, and synapse formation and elimination. In response to injury, microglia activate to inflammatory phenotypes that may detract from these normal homeostatic, physiological, and developmental roles. To date, however, little is known regarding the impact of RmTBIs on microglia function during adolescent brain development. This review details key concepts surrounding RmTBI pathophysiology, adolescent brain development, and microglia dynamics in the developing brain and in response to injury, in an effort to formulate a hypothesis on how the intersection of these processes may modify long-term trajectories.

Brain Perfusion Mediates the Relationship Between miRNA Levels and Postural Control

Transcriptomics, regional cerebral blood flow (rCBF), and a virtual reality-based spatial motor task were integrated using mediation analysis in a novel demonstration of “imaging omics.” Data collected in National Collegiate Athletic Association (NCAA) Division I football athletes cleared for play before in-season training showed significant relationships in 1) elevated levels of miR-30d and miR-92a to elevated putamen rCBF, 2) elevated putamen rCBF to compromised Balance scores, and 3) compromised Balance scores to elevated microRNA (miRNA) levels. rCBF acted as a consistent mediator variable (Sobel’s test P < 0.05) between abnormal miRNA levels and compromised Balance scores. Given the involvement of these miRNAs in inflammation and immune function and that vascular perfusion is a component of the inflammatory response, these findings support a chronic inflammatory model in these athletes with 11 years of average football exposure. rCBF, a systems biology measure, was necessary for miRNA to affect behavior.

Cerebral Perfusion Effects of Cognitive Training and Transcranial Direct Current Stimulation in Mild-Moderate TBI

Background: Persistent post-traumatic symptoms (PPS) after traumatic brain injury (TBI) can lead to significant chronic functional impairment. Pseudocontinuous arterial spin labeling (pCASL) has been used in multiple studies to explore changes in cerebral blood flow (CBF) that may result in acute and chronic TBI, and is a promising neuroimaging modality for assessing response to therapies. Methods: Twenty-four subjects with chronic mild-moderate TBI (mmTBI) were enrolled in a pilot study of 10 days of computerized executive function training combined with active or sham anodal transcranial direct current stimulation (tDCS) for treatment of cognitive PPS. Behavioral surveys, neuropsychological testing, and magnetic resonance imaging (MRI) with pCASL sequences to assess global and regional CBF were obtained before and after the training protocol. Results: Robust improvements in depression, anxiety, complex attention, and executive function were seen in both active and sham groups between the baseline and post-treatment visits. Global CBF decreased over time, with differences in regional CBF noted in the right inferior frontal gyrus (IFG). Active stimulation was associated with static or increased CBF in the right IFG, whereas sham was associated with reduced CBF. Neuropsychological performance and behavioral symptoms were not associated with changes in CBF. Discussion: The current study suggests a complex picture between mmTBI, cerebral perfusion, and recovery. Changes in CBF may result from physiologic effect of the intervention, compensatory neural mechanisms, or confounding factors. Limitations include a small sample size and heterogenous injury sample, but these findings suggest promising directions for future studies of cognitive training paradigms in mmTBI.

Clinical Applications of Extracellular Vesicles in the Diagnosis and Treatment of Traumatic Brain Injury

Extracellular vesicles (EVs) have emerged as key mediators of cell-cell communication during homeostasis and in pathology. Central nervous system (CNS)-derived EVs contain cell type-specific surface markers and intralumenal protein, RNA, DNA, and metabolite cargo that can be used to assess the biochemical and molecular state of neurons and glia during neurological injury and disease. The development of EV isolation strategies coupled with analysis of multi-plexed biomarker and clinical data have the potential to improve our ability to classify and treat traumatic brain injury (TBI) and resulting sequelae. Additionally, their ability to cross the blood-brain barrier (BBB) has implications for both EV-based diagnostic strategies and for potential EV-based therapeutics. In the present review, we discuss encouraging data for EV-based diagnostic, prognostic, and therapeutic strategies in the context of TBI monitoring and management.

Systemic Inflammation Persists the First Year after Mild Traumatic Brain Injury: Results from the Prospective Trondheim Mild Traumatic Brain Injury Study

Innate immune activation has been attributed a key role in traumatic brain injury (TBI) and successive morbidity. In mild TBI (mTBI), however, the extent and persistence of innate immune activation are unknown. We determined plasma cytokine level changes over 12 months after an mTBI in hospitalized and non-hospitalized patients compared with community controls; and examined their associations to injury-related and demographic variables at admission. Prospectively, 207 patients presenting to the emergency department (ED) or general practitioner with clinically confirmed mTBI and 82 matched community controls were included. Plasma samples were obtained at admission, after 2 weeks, 3 months, and 12 months. Cytokine levels were analysed with a 27-plex beads-based immunoassay. Brain magnetic resonance imaging (MRI) was performed on all participants. Twelve cytokines were reliably detected. Plasma levels of interferon gamma (IFN-γ), interleukin 8 (IL-8), eotaxin, macrophage inflammatory protein-1-beta (MIP-1β), monocyte chemoattractant protein 1 (MCP-1), IL-17A, IL-9, tumor necrosis factor (TNF), and basic fibroblast growth factor (FGF-basic) were significantly increased at all time-points in patients compared with controls, whereas IFN-γ-inducing protein 10 (IP-10), platelet-derived growth factor (PDGF), and IL-1ra were not. IL-17A and FGF-basic showed significant increases in patients from admission to follow-up at 3 months, and remained increased at 12 months compared with admission. Interestingly, MRI findings were negatively associated with four cytokines: eotaxin, MIP-1β, IL-9, and IP-10, whereas age was positively associated with nine cytokines: IL-8, eotaxin, MIP-1β, MCP-1, IL-17A, IL-9, TNF, FGF-basic, and IL-1ra. TNF was also increased in those with presence of other injuries. In conclusion, mTBI activated the innate immune system consistently and this is the first study to show that several inflammatory cytokines remain increased for up to 1 year post-injury.

Amyloid beta and diabetic pathology cooperatively stimulate cytokine expression in an Alzheimer's mouse model

BACKGROUND

Diabetes is a risk factor for developing Alzheimer's disease (AD); however, the mechanism by which diabetes can promote AD pathology remains unknown. Diabetes results in diverse molecular changes in the brain, including dysregulation of glucose metabolism and loss of cerebrovascular homeostasis. Although these changes have been associated with increased Aβ pathology and increased expression of glial activation markers in APPswe/PS1dE9 (APP/PS1) mice, there has been limited characterization, to date, of the neuroinflammatory changes associated with diabetic conditions.

METHODS

To more fully elucidate neuroinflammatory changes associated with diabetes that may drive AD pathology, we combined the APP/PS1 mouse model with either high-fat diet (HFD, a model of pre-diabetes), the genetic db/db model of type 2 diabetes, or the streptozotocin (STZ) model of type 1 diabetes. We then used a multiplexed immunoassay to quantify cortical changes in cytokine proteins.

RESULTS

Our analysis revealed that pathology associated with either db/db, HFD, or STZ models yielded upregulation of a broad profile of cytokines, including chemokines (e.g., MIP-1α, MIP-1β, and MCP-1) and pro-inflammatory cytokines, including IL-1α, IFN-γ, and IL-3. Moreover, multivariate partial least squares regression analysis showed that combined diabetic-APP/PS1 models yielded cooperatively enhanced expression of the cytokine profile associated with each diabetic model alone. Finally, in APP/PS1xdb/db mice, we found that circulating levels of Aβ1-40, Aβ1-42, glucose, and insulin all correlated with cytokine expression in the brain, suggesting a strong relationship between peripheral changes and brain pathology.

CONCLUSIONS

Altogether, our multiplexed analysis of cytokines shows that Alzheimer's and diabetic pathologies cooperate to enhance profiles of cytokines reported to be involved in both diseases. Moreover, since many of the identified cytokines promote neuronal injury, Aβ and tau pathology, and breakdown of the blood-brain barrier, our data suggest that neuroinflammation may mediate the effects of diabetes on AD pathogenesis. Therefore, strategies targeting neuroinflammatory signaling, as well as metabolic control, may provide a promising strategy for intervening in the development of diabetes-associated AD.

Mapping brain recovery after concussion: From acute injury to 1 year after medical clearance

OBJECTIVE

To test the hypothesis that concussion-related brain alterations seen at symptomatic injury and medical clearance to return to play (RTP) will have dissipated by 1 year after RTP.

METHODS

For this observational study, 24 athletes with concussion were scanned longitudinally within 1 week after injury, at RTP, and 1 year after RTP. A large control cohort of 122 athletes were also scanned before the season. Each imaging session assessed global functional connectivity (Gconn) and cerebral blood flow (CBF), along with white matter fractional anisotropy (FA) and mean diffusivity (MD). The main effects of concussion on MRI parameters were evaluated at each postinjury time point. In addition, covariation was assessed between MRI parameters and clinical measures of acute symptom severity and time to RTP.

RESULTS

Different aspects of brain physiology showed different patterns of recovery over time. Both Gconn and FA displayed no significant effects at 1 year after RTP, whereas CBF and MD exhibited persistent long-term effects. The effects of concussion on MRI parameters were also dependent on acute symptom severity and time to RTP for all postinjury time points.

CONCLUSION

This study provides the first longitudinal evaluation of concussion focused on time of RTP and 1 year after medical clearance, using multiple different MRI measures to assess brain structure and function. These findings significantly enhance our understanding of the natural course of brain recovery after a concussion.

Apparent Correlations Between AMPK Expression and Brain Inflammatory Response and Neurological Function Factors in Rats with Chronic Renal Failure

To explore the correlations between AMP-activated protein kinase (AMPK) expression and brain inflammatory response and neurological function factors in rats with chronic renal failure. Chronic renal failure models in rats were established, and the healthy control group (normal group) was set. Chronic renal failure model rats were divided into model group (without any treatment), control group (intraperitoneal injection of normal saline), A-769662 group (intraperitoneal injection of AMPK specific activator), and compound C group (intraperitoneal injection of AMPK specific inhibitor). The results of HE staining showed renal tissue enlargement, and significant pathological changes. Compared with the normal group, AMPK level in peripheral blood and AMPK mRNA and protein expressions in brain tissue were significantly reduced, and AMPK pathway activation was significantly inhibited in other groups. Compared with the model group, rats in the A-769662 group had significantly decreased serum creatinine (Scr) and blood urea nitrogen (BUN) levels and γ-aminobutyric acid (γ-GABA) content, significantly increased brain-derived neurotrophic factor (BDNF) positive expressions and 5-hydroxytryptamine (5-HT) content, and decreased interleukin-1 (IL-1), tumor necrosis factor-α (TNF-α), and intercellular adhesion molecule 1 (ICAM-1) expressions (all P < 0.05), while it was just the opposite in compound C group (all P < 0.05). There is an apparent correlation between AMPK expression and brain inflammatory response in chronic renal failure rats. AMPK is expected to be an important pathway in the treatment of uremic encephalopathy.