Pushing for IV Push Medications: Cost-Effectiveness Model of Switching from IV Piggyback to IV Push for Frequently Used Emergency Department Medications.

In considering the potential to reduce the carbon footprint of our emergency department (ED) via decreasing plastic waste, we aimed to evaluate the effects of changing certain common emergency department medications from an intravenous (IV) piggyback administration route to IV push. Our team queried hospital pharmacy data to determine the number of doses of several frequently utilized antibiotics administered over a six-month time period, then calculated the resultant cost savings of a switch to IV push. Based upon our modeling calculations, switching certain medication administration routes to IVP can have significant impacts on cost, with an estimated cost savings of about $47,000 every six months. Maximizing the use of push administration could result in even more dramatic cost savings. In some scenarios, using IVP administration results in less than half the amount of plastic waste generated. Future research including a full life-cycle analysis is needed in order to precisely determine the impact on carbon footprint created by making this change.

Modulation of experimental acute lung injury by exosomal miR-7704 from mesenchymal stromal cells acts through M2 macrophage polarization.

Acute lung injury (ALI) is a life-threatening condition with limited treatment options. The pathogenesis of ALI involves macrophage-mediated disruption and subsequent repair of the alveolar barriers, which ultimately results in lung damage and regeneration, highlighting the pivotal role of macrophage polarization in ALI. Although exosomes derived from mesenchymal stromal cells have been established as influential modulators of macrophage polarization, the specific role of exosomal microRNAs (miRNAs) remains underexplored. This study aimed to elucidate the role of specific exosomal miRNAs in driving macrophage polarization, thereby providing a reference for developing novel therapeutic interventions for ALI. We found that miR-7704 is the most abundant and efficacious miRNA for promoting the switch to the M2 phenotype in macrophages. Mechanistically, we determined that miR-7704 stimulates M2 polarization by inhibiting the MyD88/STAT1 signaling pathway. Notably, intra-tracheal delivery of miR-7704 alone in a lipopolysaccharide-induced murine ALI model significantly drove M2 polarization in lung macrophages and remarkably restored pulmonary function, thus increasing survival. Our findings highlight miR-7704 as a valuable tool for treating ALI by driving the beneficial M2 polarization of macrophages. Our findings pave the way for deeper exploration into the therapeutic potential of exosomal miRNAs in inflammatory lung diseases.

The mitigated carbon emissions of transitioning to virtual medical school and residency interviews: A survey-based study.

PURPOSE: Prior to COVID, thousands of medical school and residency applicants traversed their countries for in-person interviews each year. However, data on the greenhouse gas emissions from in-person interviews is limited. This study estimated greenhouse gas emissions associated with in-person medical school and residency interviews and explored applicant interview structure preferences. METHODS: From March to June 2022, we developed and distributed a nine-question, website-based survey to collect information on applicant virtual interview schedule, demographics and preference for future interview format. We calculated theoretical emissions for all interviews requiring air travel and performed a content analysis of interview preference explanations. RESULTS: We received responses from 258 first-year and 253 fourth-year medical students at 26 allopathic US medical schools who interviewed virtually in 2020-2021 and 2021-2022, respectively. Residency applicants participating in the study were interviewed at a mean of 15.3 programs (SD 5.4) and had mean theoretical emissions of 4.31 tons CO2 eq. Medical school applicants participating in the study were interviewed at a mean of 6.9 programs and had mean theoretical emissions of 2.19 tons CO2 eq. Ninety percent of medical school applicants and 91% of residency applicants participating in the study expressed a preference for hybrid or virtual interviews going forward. CONCLUSION: In-person medical training interviews have significant greenhouse gas emissions. Virtual and hybrid alternatives have a high degree of acceptability among applicants.

Specialties with Few Underrepresented Applicants Lack Diversity Information on Residency Websites.

INTRODUCTION: With the advent of virtual interviews and the increasing accessibility of internet resources, students increasingly rely on program websites for residency application decisions. In this cross-sectional study, we evaluated the presence of diversity or inclusion information in the least diverse US specialties' residency program websites, including dermatology, orthopedic surgery, otolaryngology, plastic surgery, and urology residency programs. METHODS: Two authors independently reviewed each Accreditation Council for Graduate Medical Education-accredited non-military US residency program website and ranked the websites' diversity and inclusion information using six pre-determined criteria based on previous studies in the literature. RESULTS: This study reveals that more than half of residency programs of each specialty met zero of the diversity and inclusion information criteria. CONCLUSIONS: Residency program websites in the least diverse specialties are lacking important information for prospective applicants that may help signal programs' commitment to inclusivity and attract a diverse candidate pool.

Bibliometric analysis of the top 100 most-cited articles on video laryngoscope from 2011 to 2022.

BACKGROUND: The popularity of video laryngoscope (VL) has increased rapidly since its introduction in the late 1990s. However, a comprehensive overview of VLs evolution and impact is lacking, which merits further investigation. METHODS: We conducted a bibliometric analysis of the top 100 most-cited articles on VL (Top100VL) published between 2011 and 2022 and retrieved from the PubMed and Web of Science databases. Using social network analysis, we identified the subject terms and subject categories of the Top100VL and compared their citation counts across individual subject terms and categories via one-way analysis of variance (ANOVA). Then, we employed the Medical Query Expert software to assess the practical applications of VL. RESULTS: The Top100VL included 65 subjects across nine subject categories, with "anesthesiology" being the most frequently represented category and "coronavirus infections" with the highest impact factor. The citation counts inferred by subject categories significantly correlated with the actual citation counts (Pearson's R = 0.4; p < 0.01). For enhanced visualization, we employed network visualization and Sankey diagrams to display the article characteristics. We highlighted the clinical advantages of VL, including its usefulness in difficult intubations, wider angle of view, and management of pediatric emergencies, as well as its teaching benefits, such as facilitating training programs and a lower learning curve. CONCLUSION: By using bibliometric analysis and natural language processing methods, we effectively summarized the applications of VL in both clinical and teaching settings, particularly in reducing the risk of cross-infection during the Coronavirus Disease 2019 pandemic.

Nitric oxide synthase and reduced arterial tone contribute to arteriovenous malformation.

Mechanisms underlying arteriovenous malformations (AVMs) are poorly understood. Using mice with endothelial cell (EC) expression of constitutively active Notch4 (Notch4*EC), we show decreased arteriolar tone in vivo during brain AVM initiation. Reduced vascular tone is a primary effect of Notch4*EC, as isolated pial arteries from asymptomatic mice exhibited reduced pressure-induced arterial tone ex vivo. The nitric oxide (NO) synthase (NOS) inhibitor NG-nitro-l-arginine (L-NNA) corrected vascular tone defects in both assays. L-NNA treatment or endothelial NOS (eNOS) gene deletion, either globally or specifically in ECs, attenuated AVM initiation, assessed by decreased AVM diameter and delayed time to moribund. Administering nitroxide antioxidant 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl also attenuated AVM initiation. Increased NOS-dependent production of hydrogen peroxide, but not NO, superoxide, or peroxynitrite was detected in isolated Notch4*EC brain vessels during AVM initiation. Our data suggest that eNOS is involved in Notch4*EC-mediated AVM formation by up-regulating hydrogen peroxide and reducing vascular tone, thereby permitting AVM initiation and progression.

Extracorporeal membrane oxygenation in COVID-19 compared to other etiologies of acute respiratory failure: A single-center experience.

BACKGROUND: The COVID-19 pandemic has led to a boom in the use of V-V ECMO for ARDS secondary to COVID. Comparisons of outcomes of ECMO for COVID to ECMO for influenza have emerged. Very few comparisons of ECMO for COVID to ECMO for ARDS of all etiologies are available. OBJECTIVES: To compare clinically important outcome measures in recipients of ECMO for COVID to those observed in recipients of ECMO for ARDS of other etiologies. METHODS: V-V ECMO recipients between March 2020 and March 2022 consisted exclusively of COVID patients and formed the COVID ECMO group. All patients who underwent V-V ECMO for ARDS between January 2014 and March 2020 were eligible for analysis as the non-COVID ECMO comparator group. The primary outcome was survival to hospital discharge. Secondary outcomes included ECMO decannulation, ECMO duration >30 days, and serious complications. RESULTS: Thirty-six patients comprised the COVID ECMO group and were compared to 18 non-COVID ECMO patients. Survival to hospital discharge was not significantly different between the two groups (33% in COVID vs. 50% in non-COVID; p = 0.255) nor was there a significant difference in the rate of non-palliative ECMO decannulation. The proportion of patients connected to ECMO for >30 days was significantly higher in the COVID ECMO group: 69% vs. 17%; p = 0.001. There was no significant difference in serious complications. CONCLUSION: This study could not identify a statistically significant difference in hospital survival and rate of successful ECMO decannulation between COVID ECMO and non-COVID ECMO patients. Prolonged ECMO may be more common in COVID. Complications were not significantly different.

Constructing, validating, and updating machine learning models to predict survival in children with Ebola Virus Disease.

BACKGROUND: Ebola Virus Disease (EVD) causes high case fatality rates (CFRs) in young children, yet there are limited data focusing on predicting mortality in pediatric patients. Here we present machine learning-derived prognostic models to predict clinical outcomes in children infected with Ebola virus. METHODS: Using retrospective data from the Ebola Data Platform, we investigated children with EVD from the West African EVD outbreak in 2014-2016. Elastic net regularization was used to create a prognostic model for EVD mortality. In addition to external validation with data from the 2018-2020 EVD epidemic in the Democratic Republic of the Congo (DRC), we updated the model using selected serum biomarkers. FINDINGS: Pediatric EVD mortality was significantly associated with younger age, lower PCR cycle threshold (Ct) values, unexplained bleeding, respiratory distress, bone/muscle pain, anorexia, dysphagia, and diarrhea. These variables were combined to develop the newly described EVD Prognosis in Children (EPiC) predictive model. The area under the receiver operating characteristic curve (AUC) for EPiC was 0.77 (95% CI: 0.74-0.81) in the West Africa derivation dataset and 0.76 (95% CI: 0.64-0.88) in the DRC validation dataset. Updating the model with peak aspartate aminotransferase (AST) or creatinine kinase (CK) measured within the first 48 hours after admission increased the AUC to 0.90 (0.77-1.00) and 0.87 (0.74-1.00), respectively. CONCLUSION: The novel EPiC prognostic model that incorporates clinical information and commonly used biochemical tests, such as AST and CK, can be used to predict mortality in children with EVD.

Risk Prediction Score for Pediatric Patients with Suspected Ebola Virus Disease.

Rapid diagnostic tools for children with Ebola virus disease (EVD) are needed to expedite isolation and treatment. To evaluate a predictive diagnostic tool, we examined retrospective data (2014-2015) from the International Medical Corps Ebola Treatment Centers in West Africa. We incorporated statistically derived candidate predictors into a 7-point Pediatric Ebola Risk Score. Evidence of bleeding or having known or no known Ebola contacts was positively associated with an EVD diagnosis, whereas abdominal pain was negatively associated. Model discrimination using area under the curve (AUC) was 0.87, which outperforms the World Health Organization criteria (AUC 0.56). External validation, performed by using data from International Medical Corps Ebola Treatment Centers in the Democratic Republic of the Congo during 2018-2019, showed an AUC of 0.70. External validation showed that discrimination achieved by using World Health Organization criteria was similar; however, the Pediatric Ebola Risk Score is simpler to use.

Relationship between simultaneously recorded spiking activity and fluorescence signal in GCaMP6 transgenic mice.

Fluorescent calcium indicators are often used to investigate neural dynamics, but the relationship between fluorescence and action potentials (APs) remains unclear. Most APs can be detected when the soma almost fills the microscope's field of view, but calcium indicators are used to image populations of neurons, necessitating a large field of view, generating fewer photons per neuron, and compromising AP detection. Here, we characterized the AP-fluorescence transfer function in vivo for 48 layer 2/3 pyramidal neurons in primary visual cortex, with simultaneous calcium imaging and cell-attached recordings from transgenic mice expressing GCaMP6s or GCaMP6f. While most APs were detected under optimal conditions, under conditions typical of population imaging studies, only a minority of 1 AP and 2 AP events were detected (often <10% and ~20-30%, respectively), emphasizing the limits of AP detection under more realistic imaging conditions.

Neurons, the cells that make up the nervous system, transmit information using electrical signals known as action potentials or spikes. Studying the spiking patterns of neurons in the brain is essential to understand perception, memory, thought, and behaviour. One way to do that is by recording electrical activity with microelectrodes. Another way to study neuronal activity is by using molecules that change how they interact with light when calcium binds to them, since changes in calcium concentration can be indicative of neuronal spiking. That change can be observed with specialized microscopes know as two-photon fluorescence microscopes. Using calcium indicators, it is possible to simultaneously record hundreds or even thousands of neurons. However, calcium fluorescence and spikes do not translate one-to-one. In order to interpret fluorescence data, it is important to understand the relationship between the fluorescence signals and the spikes associated with individual neurons. The only way to directly measure this relationship is by using calcium imaging and electrical recording simultaneously to record activity from the same neuron. However, this is extremely challenging experimentally, so this type of data is rare. To shed some light on this, Huang, Ledochowitsch et al. used mice that had been genetically modified to produce a calcium indicator in neurons of the visual cortex and simultaneously obtained both fluorescence measurements and electrical recordings from these neurons. These experiments revealed that, while the majority of time periods containing multi-spike neural activity could be identified using calcium imaging microscopy, on average, less than 10% of isolated single spikes were detectable. This is an important caveat that researchers need to take into consideration when interpreting calcium imaging results. These findings are intended to serve as a guide for interpreting calcium imaging studies that look at neurons in the mammalian brain at the population level. In addition, the data provided will be useful as a reference for the development of activity sensors, and to benchmark and improve computational approaches for detecting and predicting spikes.

A large-scale standardized physiological survey reveals functional organization of the mouse visual cortex.

To understand how the brain processes sensory information to guide behavior, we must know how stimulus representations are transformed throughout the visual cortex. Here we report an open, large-scale physiological survey of activity in the awake mouse visual cortex: the Allen Brain Observatory Visual Coding dataset. This publicly available dataset includes the cortical activity of nearly 60,000 neurons from six visual areas, four layers, and 12 transgenic mouse lines in a total of 243 adult mice, in response to a systematic set of visual stimuli. We classify neurons on the basis of joint reliabilities to multiple stimuli and validate this functional classification with models of visual responses. While most classes are characterized by responses to specific subsets of the stimuli, the largest class is not reliably responsive to any of the stimuli and becomes progressively larger in higher visual areas. These classes reveal a functional organization wherein putative dorsal areas show specialization for visual motion signals.

Neuronal cell-subtype specificity of neural synchronization in mouse primary visual cortex.

Spatiotemporally synchronised neuronal activity is central to sensation, motion and cognition. Brain circuits consist of dynamically interconnected neuronal cell-types, thus elucidating how neuron types synergise within the network is key to understand the neuronal orchestra. Here we show that in neocortex neuron-network coupling is neuronal cell-subtype specific. Employing in vivo two-photon (2-p) Calcium (Ca) imaging and 2-p targeted whole-cell recordings, we cell-type specifically investigated the coupling profiles of genetically defined neuron populations in superficial layers (L) of mouse primary visual cortex (V1). Our data reveal novel subtlety of neuron-network coupling in inhibitory interneurons (INs). Parvalbumin (PV)- and Vasoactive intestinal peptide (VIP)-expressing INs exhibit skewed distributions towards strong network-coupling; in Somatostatin (SST)-expressing INs, however, two physiological subpopulations are identified with distinct neuron-network coupling profiles, providing direct evidence for subtype specificity. Our results thus add novel functional granularity to neuronal cell-typing, and provided insights critical to simplifying/understanding neural dynamics.

SCID/NOD mice model for 5-FU induced intestinal mucositis: Safety and effects of probiotics as therapy.

BACKGROUND: For chemotherapy patients, intestinal mucositis is a frequent complication. Previously, we evaluated the beneficial effect of oral probiotics in 5-Fluorouracil (5-FU) induced mucositis in BALB/c mice. Here, we used SCID/NOD mice instead to simulate the immunodeficiency of chemotherapy patients: first, to evaluate the safety of probiotic supplementation and second, to determine the probiotic effect in response to 5-FU intestinal mucositis. METHODS: Thirty-six SCID/NOD mice were injected with saline (three control groups) or 5-FU (three experimental groups) intraperitoneally daily for five days. Mice were given either oral saline daily, probiotic suspension of Lactobacillus casei variety rhamnosus (Lcr35, Antibiophilus™, France) or Lactobacillus acidophilus and Bifidobacterium bifidum (LaBi, Infloran™, Italy). Blood, liver, spleen, and lymph node tissue samples were evaluated for probiotic translocation via culture and Q-PCR. Weight change, diarrhea score, jejunal villus height (VH) and crypt depth (CD), and serum cytokine levels of TNF-α, IFNγ, IL-1ß, IL-6, IL-4, IL-10, IL-13, and IL-17 were also assessed. RESULTS: No weight loss was found in the SCID control group. Mean weight loss of 10.63 ± 0.87% was noted by day five in 5-FU group without probiotics but it was only 6.2 ± 0.43% if mice were given Lcr35 (p < 0.01) and 7.1 ± 1.80% (p < 0.01) if they were given LaBi. Diarrhea score of 5-FU group without probiotics was 2.0 ± 0.0 by day five, which dropped to 1.33 ± 0.17 (p < 0.05) and 1.42 ± 0.24 (p < 0.05) with Lcr35 and LaBi, respectively. Average VH significantly decreased and CD significantly increased in SCID mice given 5-FU. With probiotics, average CD improved (p < 0.05) while VH lengthened as well. Besides IL-13, all cytokine levels increased in 5-FU SCID mice. Both Lcr35 and LaBi significantly inhibited serum cytokines (p < 0.05). No probiotic strains were detected in blood cultures of any mice. CONCLUSION: Using SCID/NOD mice as a novel model for 5-FU induced intestinal mucositis, we find that probiotics Lcr35 and LaBi do not lead to bacteremia, can improve diarrhea and body weight, can restore jejunal crypt depth, and significantly inhibit cytokines TNF-α, IL-1ß, IFNγ, IL-6, IL-4, IL-10, and IL-17.

A Suite of Transgenic Driver and Reporter Mouse Lines with Enhanced Brain-Cell-Type Targeting and Functionality.

Modern genetic approaches are powerful in providing access to diverse cell types in the brain and facilitating the study of their function. Here, we report a large set of driver and reporter transgenic mouse lines, including 23 new driver lines targeting a variety of cortical and subcortical cell populations and 26 new reporter lines expressing an array of molecular tools. In particular, we describe the TIGRE2.0 transgenic platform and introduce Cre-dependent reporter lines that enable optical physiology, optogenetics, and sparse labeling of genetically defined cell populations. TIGRE2.0 reporters broke the barrier in transgene expression level of single-copy targeted-insertion transgenesis in a wide range of neuronal types, along with additional advantage of a simplified breeding strategy compared to our first-generation TIGRE lines. These novel transgenic lines greatly expand the repertoire of high-precision genetic tools available to effectively identify, monitor, and manipulate distinct cell types in the mouse brain.

An alcohol withdrawal test battery measuring multiple behavioral symptoms in mice.

Despite acceptance that risk for alcohol-use disorder (AUD) has a large genetic component, the identification of genes underlying various components of risk for AUD has been hampered in humans, in part by the heterogeneity of expression of the phenotype. One aspect of AUD is physical dependence. Alcohol withdrawal is a serious consequence of alcohol dependence with multiple symptoms, many of which are seen in multiple species, and can be experienced over a wide-ranging time course. In the present three studies, we developed a battery of withdrawal tests in mice, examining behavioral symptoms from multiple domains that could be measured over time. To permit eventual use of the battery in different strains of mice, we used male and female mice of a genetically heterogeneous stock developed from intercrossing eight inbred strains. Withdrawal symptoms were assessed using commonly used tests after administration of ethanol in vapor for 72 continuous hours. We found significant effects of ethanol withdrawal versus air-breathing controls on nearly all symptoms, spanning 4 days following ethanol vapor inhalation. Withdrawal produced hypothermia, greater neurohyperexcitability (seizures and tremor), anxiety-like behaviors using an apparatus (such as reduced transitions between light and dark compartments), anhedonia (reduced sucrose preference), Straub tail, backward walking, and reductions in activity; however, there were no changes in thermal pain sensitivity, hyper-reactivity to handling, or anxiety-like emergence behaviors in other apparatus. Using these data, we constructed a refined battery of withdrawal tests. Individual differences in severity of withdrawal among different tests were weakly correlated at best. This battery should be useful for identifying genetic influences on particular withdrawal behaviors, which should reflect the influences of different constellations of genes.

Abnormal arterial-venous fusions and fate specification in mouse embryos lacking blood flow.

The functions of blood flow in the morphogenesis of mammalian arteries and veins are not well understood. We examined the development of the dorsal aorta (DA) and the cardinal vein (CV) in Ncx1 -/- mutants, which lack blood flow due to a deficiency in a sodium calcium ion exchanger expressed specifically in the heart. The mutant DA and CV were abnormally connected. The endothelium of the Ncx1 -/- mutant DA lacked normal expression of the arterial markers ephrin-B2 and Connexin-40. Notch1 activation, known to promote arterial specification, was decreased in mutant DA endothelial cells (ECs), which ectopically expressed the venous marker Coup-TFII. These findings suggest that flow has essential functions in the DA by promoting arterial and suppressing venous marker expression. In contrast, flow plays a lesser role in the CV, because expression of arterial-venous markers in CV ECs was not as dramatically affected in Ncx1 -/- mutants. We propose a molecular mechanism by which blood flow mediates DA and CV morphogenesis, by regulating arterial-venous specification of DA ECs to ensure proper separation of the developing DA and CV.

High Drinking in the Dark (HDID) mice are sensitive to the effects of some clinically relevant drugs to reduce binge-like drinking.

BACKGROUND: There is a serious public health need for better understanding of alcohol use disorder disease mechanisms and for improved treatments. At this writing, only three drugs are approved by the Food and Drug Administration as medications to treat alcohol use disorders - disulfiram, naltrexone, and acamprosate. Binge drinking is a form of abusive alcohol drinking defined by the NIAAA as a drinking to blood alcohol levels (BALs)>0.08% during a period of approximately 2h. To model genetic risk for binge-like drinking, we have used selective breeding to create a unique animal model, High Drinking in the Dark (HDID) mice. Behavioral characterization of HDID mice has revealed that HDID mice exhibit behavioral impairment after drinking, withdrawal after a single binge-drinking session, and escalate their intake in response to induction of successive cycles of dependence. Notably, HDID mice do not exhibit altered tastant preference or alcohol clearance rates. We therefore asked whether drugs of known clinical relevance could modulate binge-like ethanol drinking in HDID mice, reasoning that this characterization of HDID responses should inform future use of this genetic animal model for screening and development of novel potential therapeutics. METHODS: We tested the efficacy of acamprosate and naltrexone to reduce binge-like drinking in HDID mice. Additionally, we tested the GABAB receptor agonist, baclofen, based on recent pre-clinical and clinical studies demonstrating that it reduces alcohol drinking. We elected not to include disulfiram due to its more limited clinical usage. Mice were tested after acute doses of drugs in the limited-access Drinking in the Dark (DID) paradigm. RESULTS: HDID mice were sensitive to the effects of acamprosate and baclofen, but not naltrexone. Both drugs reduced binge-like drinking. However, naltrexone failed to reduce drinking in HDID mice. Thus, HDID mice may represent a useful model for screening novel compounds.

Polarized actin structural dynamics in response to cyclic uniaxial stretch.

Endothelial cell (EC) alignment to directional flow or stretch supports anti-inflammatory functions, but mechanisms controlling polarized structural adaptation in response to physical cues remain unclear. This study aimed to determine whether factors associated with early actin edge ruffling implicated in cell polarization are prerequisite for stress fiber (SF) reorientation in response to cyclic uniaxial stretch. Time-lapse analysis of EGFP-actin in confluent ECs showed that onset of either cyclic uniaxial or equibiaxial stretch caused a non-directional increase in edge ruffling. Edge activity was concentrated in a direction perpendicular to the stretch axis after 60 min, consistent with the direction of SF alignment. Rho-kinase inhibition caused reorientation of both stretch-induced edge ruffling and SF alignment parallel to the stretch axis. Arp2/3 inhibition attenuated stretch-induced cell elongation and disrupted polarized edge dynamics and microtubule organizing center reorientation, but it had no effect on the extent of SF reorientation. Disrupting localization of p21-activated kinase (PAK) did not prevent stretch-induced SF reorientation, suggesting that this Rac effector is not critical in regulating stretch-induced cytoskeletal remodeling. Overall, these results suggest that directional edge ruffling is not a primary mechanism that guides SF reorientation in response to stretch; the two events are coincident but not causal.

Constitutively active Notch4 receptor elicits brain arteriovenous malformations through enlargement of capillary-like vessels.

Arteriovenous (AV) malformation (AVM) is a devastating condition characterized by focal lesions of enlarged, tangled vessels that shunt blood from arteries directly to veins. AVMs can form anywhere in the body and can cause debilitating ischemia and life-threatening hemorrhagic stroke. The mechanisms that underlie AVM formation remain poorly understood. Here, we examined the cellular and hemodynamic changes at the earliest stages of brain AVM formation by time-lapse two-photon imaging through cranial windows of mice expressing constitutively active Notch4 (Notch4*). AVMs arose from enlargement of preexisting microvessels with capillary diameter and blood flow and no smooth muscle cell coverage. AV shunting began promptly after Notch4* expression in endothelial cells (ECs), accompanied by increased individual EC areas, rather than increased EC number or proliferation. Alterations in Notch signaling in ECs of all vessels, but not arteries alone, affected AVM formation, suggesting that Notch functions in the microvasculature and/or veins to induce AVM. Increased Notch signaling interfered with the normal biological control of hemodynamics, permitting a positive feedback loop of increasing blood flow and vessel diameter and driving focal AVM growth from AV connections with higher blood velocity at the expense of adjacent AV connections with lower velocity. Endothelial expression of constitutively active Notch1 also led to brain AVMs in mice. Our data shed light on cellular and hemodynamic mechanisms underlying AVM pathogenesis elicited by increased Notch signaling in the endothelium.