The emergence of the calvarial hematopoietic niche in health and disease.

The diploë region of skull has recently been discovered to act as a myeloid cell reservoir to the underlying meninges. The presence of ossified vascular channels traversing the inner skull of cortex provides a passageway for the cells to traffic from the niche, and CNS-derived antigens traveling through cerebrospinal fluid in a perivascular manner reaches the niche to signal myeloid cell egress. This review will highlight the recent findings establishing this burgeoning field along with the known role this niche plays in CNS aging and disease. It will further highlight the anatomical routes and physiological properties of the vascular structures these cells use for trafficking, spanning from skull to brain parenchyma.

Astrocyte plasticity in mice ensures continued endfoot coverage of cerebral blood vessels following injury and declines with age.

Astrocytes extend endfeet that enwrap the vasculature, and disruptions to this association which may occur in disease coincide with breaches in blood-brain barrier (BBB) integrity. Here we investigate if focal ablation of astrocytes is sufficient to disrupt the BBB in mice. Targeted two-photon chemical apoptotic ablation of astrocytes induced a plasticity response whereby surrounding astrocytes extended processes to cover vascular vacancies. In young animals, replacement processes occur in advance of endfoot retraction, but this is delayed in aged animals. Stimulation of replacement astrocytes results in constriction of pre-capillary arterioles, suggesting that replacement astrocytes are functional. Pharmacological inhibition of pSTAT3, as well as astrocyte specific deletion of pSTAT3, reduces astrocyte replacement post-ablation, without perturbations to BBB integrity. Similar endfoot replacement occurs following astrocyte cell death due to reperfusion in a stroke model. Together, these studies uncover the ability of astrocytes to maintain cerebrovascular coverage via substitution from nearby cells.

Capillary-associated microglia regulate vascular structure and function through PANX1-P2RY12 coupling in mice.

Microglia are brain-resident immune cells with a repertoire of functions in the brain. However, the extent of their interactions with the vasculature and potential regulation of vascular physiology has been insufficiently explored. Here, we document interactions between ramified CX3CR1 + myeloid cell somata and brain capillaries. We confirm that these cells are bona fide microglia by molecular, morphological and ultrastructural approaches. Then, we give a detailed spatio-temporal characterization of these capillary-associated microglia (CAMs) comparing them with parenchymal microglia (PCMs) in their morphological activities including during microglial depletion and repopulation. Molecularly, we identify P2RY12 receptors as a regulator of CAM interactions under the control of released purines from pannexin 1 (PANX1) channels. Furthermore, microglial elimination triggered capillary dilation, blood flow increase, and impaired vasodilation that were recapitulated in P2RY12-/- and PANX1-/- mice suggesting purines released through PANX1 channels play important roles in activating microglial P2RY12 receptors to regulate neurovascular structure and function.

Using Zebrafish to Elucidate Glial-Vascular Interactions During CNS Development.

An emerging area of interest in Neuroscience is the cellular relationship between glia and blood vessels, as many of the presumptive support roles of glia require an association with the vasculature. These interactions are best studied in vivo and great strides have been made using mice to longitudinally image glial-vascular interactions. However, these methods are cumbersome for developmental studies, which could benefit from a more accessible system. Zebrafish (Danio rerio) are genetically tractable vertebrates, and given their translucency, are readily amenable for daily live imaging studies. We set out to examine whether zebrafish glia have conserved traits with mammalian glia regarding their ability to interact with and maintain the developing brain vasculature. We utilized transgenic zebrafish strains in which oligodendrocyte transcription factor 2 (olig2) and glial fibrillary acidic protein (gfap) identify different glial populations in the zebrafish brain and document their corresponding relationship with brain blood vessels. Our results demonstrate that olig2+ and gfap+ zebrafish glia have distinct lineages and each interact with brain vessels as previously observed in mouse brain. Additionally, we manipulated these relationships through pharmacological and genetic approaches to distinguish the roles of these cell types during blood vessel development. olig2+ glia use blood vessels as a pathway during their migration and Wnt signaling inhibition decreases their single-cell vessel co-option. By contrast, the ablation of gfap+ glia at the beginning of CNS angiogenesis impairs vessel development through a reduction in Vascular endothelial growth factor (Vegf), supporting a role for gfap+ glia during new brain vessel formation in zebrafish. This data suggests that zebrafish glia, akin to mammalian glia, have different lineages that show diverse interactions with blood vessels, and are a suitable model for elucidating glial-vascular relationships during vertebrate brain development.

The Implementation of a Collaborative Pediatric Telesimulation Intervention in Rural Critical Access Hospitals.

BACKGROUND: Over 5.8 million pediatric visits to rural emergency department (EDs) occur each year in the United States. Most rural EDs care for less than five pediatric patients per day and are not well prepared for pediatrics. Simulation has been associated with improvements in pediatric preparedness. The implementation of pediatric simulation in rural settings is challenging due to limited access to equipment and pediatric specialists. Telesimulation involves a remote facilitator interacting with onsite learners. This article aims to describe the implementation experiences and participant feedback of a 1-year remotely facilitated pediatric emergency telesimulation program in three critical-access hospitals. METHODS: Three hospitals were recruited to participate with a nurse manager serving as the on-site lead. The managers worked with a study investigator to set up the simulation technology during an in-person pilot testing visit with the off-site facilitators. A curriculum consisting of eight pediatric telesimulations and debriefings was conducted over a 12-month period. Participant feedback was collected via a paper survey after each simulation. Implementation metrics were collected after each session including technical and logistic issues. RESULTS: Of 147 participant feedback surveys 90% reported that pediatric simulations should be conducted on a regular basis and overall feedback was positive. Forty-seven of 48 simulations were completed on the first attempt with few major technologic issues. The most common issue encountered related to the simulator not working correctly locally and involved the facilitator running the session without the heart and lung sounds. All debriefings occurred without any issues. CONCLUSIONS: This replicable telesimulation program can be used in the small, rural hospital setting, overcoming time and distance barriers and lending pediatric emergency medicine expertise to the education of critical-access hospital providers.

Nano-optoelectrodes Integrated with Flexible Multifunctional Fiber Probes by High-Throughput Scalable Fabrication.

Metallic nano-optoelectrode arrays can simultaneously serve as nanoelectrodes to increase the electrochemical surface-to-volume ratio for high-performance electrical recording and optical nanoantennas to achieve nanoscale light concentrations for ultrasensitive optical sensing. However, it remains a challenge to integrate nano-optoelectrodes with a miniaturized multifunctional probing system for combined electrical recording and optical biosensing in vivo. Here, we report that flexible nano-optoelectrode-integrated multifunctional fiber probes can have hybrid optical-electrical sensing multimodalities, including optical refractive index sensing, surface-enhanced Raman spectroscopy, and electrophysiological recording. By physical vapor deposition of thin metal films through free-standing masks of nanohole arrays, we exploit a scalable nanofabrication process to create nano-optoelectrode arrays on the tips of flexible multifunctional fiber probes. We envision that the development of flexible nano-optoelectrode-integrated multifunctional fiber probes can open significant opportunities by allowing for multimodal monitoring of brain activities with combined capabilities for simultaneous electrical neural recording and optical biochemical sensing at the single-cell level.

Spatially expandable fiber-based probes as a multifunctional deep brain interface.

Understanding the cytoarchitecture and wiring of the brain requires improved methods to record and stimulate large groups of neurons with cellular specificity. This requires miniaturized neural interfaces that integrate into brain tissue without altering its properties. Existing neural interface technologies have been shown to provide high-resolution electrophysiological recording with high signal-to-noise ratio. However, with single implantation, the physical properties of these devices limit their access to one, small brain region. To overcome this limitation, we developed a platform that provides three-dimensional coverage of brain tissue through multisite multifunctional fiber-based neural probes guided in a helical scaffold. Chronic recordings from the spatially expandable fiber probes demonstrate the ability of these fiber probes capturing brain activities with a single-unit resolution for long observation times. Furthermore, using Thy1-ChR2-YFP mice we demonstrate the application of our probes in simultaneous recording and optical/chemical modulation of brain activities across distant regions. Similarly, varying electrographic brain activities from different brain regions were detected by our customizable probes in a mouse model of epilepsy, suggesting the potential of using these probes for the investigation of brain disorders such as epilepsy. Ultimately, this technique enables three-dimensional manipulation and mapping of brain activities across distant regions in the deep brain with minimal tissue damage, which can bring new insights for deciphering complex brain functions and dynamics in the near future.

The Decline in Community Preceptor Teaching Activity: Exploring the Perspectives of Pediatricians Who No Longer Teach Medical Students.

PURPOSE: Difficulty in recruiting and retaining community preceptors for medical student education has been described in the literature. Yet little, if any, information is known about community outpatient preceptors who have stopped or decreased teaching time with students. This study aimed to examine these preceptors' perspectives about this phenomenon. METHOD: Using a phenomenology framework, this multi-institutional qualitative study used semistructured interviews with community pediatric preceptors who had stopped or reduced teaching time with medical students. Interviews were conducted between October 2017 and January 2018 and transcribed verbatim. Interviews explored factors for engaging in teaching, or decreasing or ceasing teaching, that would enable future teaching. An initial code book was developed and refined as data were analyzed to generate themes. RESULTS: Twenty-seven community pediatricians affiliated with 10 institutions participated. Thirty-seven codes resulted in 4 organizing themes: evolution of health care, personal barriers, educational system, and ideal situations to recruit and retain preceptors, each with subthemes. CONCLUSIONS: From the viewpoints of physicians who had decreased or stopped teaching students, this study more deeply explores previously described reasons contributing to the decline of community preceptors, adds newly described barriers, and offers strategies to help counter this phenomenon based on preceptors' perceptions. These findings appear to be manifestations of deeper issues including the professional identify of clinical educators. Understanding the barriers and strategies and how they relate to preceptors themselves should better inform education leaders to more effectively halt the decline of community precepting and enhance the clinical precepting environment for medical students.

EphA4/Tie2 crosstalk regulates leptomeningeal collateral remodeling following ischemic stroke.

Leptomeningeal anastomoses or pial collateral vessels play a critical role in cerebral blood flow (CBF) restoration following ischemic stroke. The magnitude of this adaptive response is postulated to be controlled by the endothelium, although the underlying molecular mechanisms remain under investigation. Here we demonstrated that endothelial genetic deletion, using EphA4fl/fl/Tie2-Cre and EphA4fl/fl/VeCahderin-CreERT2 mice and vessel painting strategies, implicated EphA4 receptor tyrosine kinase as a major suppressor of pial collateral remodeling, CBF, and functional recovery following permanent middle cerebral artery occlusion. Pial collateral remodeling is limited by the crosstalk between EphA4-Tie2 signaling in vascular endothelial cells, which is mediated through p-Akt regulation. Furthermore, peptide inhibition of EphA4 resulted in acceleration of the pial arteriogenic response. Our findings demonstrate that EphA4 is a negative regulator of Tie2 receptor signaling, which limits pial collateral arteriogenesis following cerebrovascular occlusion. Therapeutic targeting of EphA4 and/or Tie2 represents an attractive new strategy for improving collateral function, neural tissue health, and functional recovery following ischemic stroke.

Potassium and glutamate transport is impaired in scar-forming tumor-associated astrocytes.

Unprovoked recurrent seizures are a serious comorbidity affecting most patients who suffer from glioma, a primary brain tumor composed of malignant glial cells. Cellular mechanisms contributing to the development of recurrent spontaneous seizures include the release of the excitatory neurotransmitter glutamate from glioma into extracellular space. Under physiological conditions, astrocytes express two high affinity glutamate transporters, Glt-1 and Glast, which are responsible for the removal of excess extracellular glutamate. In the context of neurological disease or brain injury, astrocytes become reactive which can negatively affect neuronal function, causing hyperexcitability and/or death. Using electrophysiology, immunohistochemistry, fluorescent in situ hybridization, and Western blot analysis in different orthotopic xenograft and allograft models of human and mouse gliomas, we find that peritumoral astrocytes exhibit astrocyte scar formation characterized by proliferation, cellular hypertrophy, process elongation, and increased GFAP and pSTAT3. Overall, peritumoral reactive astrocytes show a significant reduction in glutamate and potassium uptake, as well as decreased glutamine synthetase activity. A subset of peritumoral astrocytes displayed a depolarized resting membrane potential, further contributing to reduced potassium and glutamate homeostasis. These changes may contribute to the propagation of peritumoral neuronal hyperexcitability and excitotoxic death.

LRRTM1 underlies synaptic convergence in visual thalamus.

It has long been thought that the mammalian visual system is organized into parallel pathways, with incoming visual signals being parsed in the retina based on feature (e.g. color, contrast and motion) and then transmitted to the brain in unmixed, feature-specific channels. To faithfully convey feature-specific information from retina to cortex, thalamic relay cells must receive inputs from only a small number of functionally similar retinal ganglion cells. However, recent studies challenged this by revealing substantial levels of retinal convergence onto relay cells. Here, we sought to identify mechanisms responsible for the assembly of such convergence. Using an unbiased transcriptomics approach and targeted mutant mice, we discovered a critical role for the synaptic adhesion molecule Leucine Rich Repeat Transmembrane Neuronal 1 (LRRTM1) in the emergence of retinothalamic convergence. Importantly, LRRTM1 mutant mice display impairment in visual behaviors, suggesting a functional role of retinothalamic convergence in vision.

Improving Pediatric Preparedness in Critical Access Hospital Emergency Departments: Impact of a Longitudinal In Situ Simulation Program.

OBJECTIVES: Critical access hospitals (CAH) see few pediatric patients. Many of these hospitals do not have access to physicians with pediatric training. We sought to evaluate the impact of an in situ pediatric simulation program in the CAH emergency department setting on care team performance during resuscitation scenarios. METHODS: Five CAHs conducted 6 high-fidelity pediatric simulations over a 12-month period. Team performance was evaluated using a validated 35-item checklist representing commonly expected resuscitation team interventions. Checklists were scored by assigning zero point for "yes" and 1 point for "no". A lower final score meant more items on the list had been completed. The Kruskal-Wallis rank test was used to assess for differences in average scores among institutions. A linear mixed effects model with a random institution intercept was used to examine trends in average scores over time. P < 0.05 was considered significant. RESULTS: The Kruskal-Wallis rank test showed no difference in average scores among institutions. (P = 0.90). Checklist scores showed a significant downward trend over time, with a scenario-to-scenario decrease of 0.022 (P < 0.01). One hundred percent of providers surveyed in the last month stated they would benefit from ongoing scenarios. CONCLUSIONS: Regularly scheduled pediatric simulations in the CAH emergency department setting improved team performance over time on expected resuscitation tasks. The program was accepted by providers. Implementation of simulation-based training programs can help address concerns regarding pediatric preparedness in the CAH setting. A future project will look at the impact of the program on patient care and safety.

Recruiting and Retaining Community-Based Preceptors: A Multicenter Qualitative Action Study of Pediatric Preceptors.

PURPOSE: The recruitment and retention of community preceptors to teach medical students is difficult. The authors sought to characterize the underlying motivational factors for becoming a preceptor and to identify strategies for recruiting and retaining community-based pediatric preceptors. METHOD: This multicenter qualitative action study included semistructured interviews with community-based pediatric preceptors affiliated with 12 institutions from August to December 2015. Only active preceptors were included, and participating institutions were diverse with respect to geographic location and class size. Interviews were conducted over the telephone and transcribed verbatim. Six investigators used deidentified transcripts to develop a codebook. Through a constant comparative method, codes were revised as data were analyzed and disagreements were resolved through discussion. All investigators organized the themes into dimensions. RESULTS: Fifty-one preceptors were interviewed. Forty-one themes coalesced into four dimensions: (1) least liked aspects of teaching, (2) preparation to teach, (3) inspiration to teach, and (4) ways to improve recruitment and retention. Time constraints and patient care demands were the most commonly cited deterrents to teaching. Successful preceptors balanced their clinical demands with their desire to teach using creative scheduling. External rewards (e.g., recognition, continuing medical education credit) served as incentives. Internal motivation inspired participants to share their enthusiasm for pediatrics and to develop longitudinal relationships with their learners. CONCLUSIONS: Changes in health care delivery have imposed more time constraints on community-based preceptors. However, this study identified underlying factors motivating physicians to volunteer as preceptors. Strategies to recruit new and retain current preceptors must be collaborative.

Project CAPE: a high-fidelity, in situ simulation program to increase Critical Access Hospital Emergency Department provider comfort with seriously ill pediatric patients.

OBJECTIVES: Variation exists between the qualities of emergency department (ED) care provided to urban versus rural pediatric patients. We implemented a pediatric simulation program in the Critical Access Hospital (CAH) ED setting and evaluated whether this training would increase provider comfort with seriously ill children. METHODS: Five CAH hospitals conducted 6 scenarios for 12 months. Baseline surveys assessed ED staff exposure to and comfort with children. Surveys were repeated after 6 and 12 months. Respondents' answers were matched longitudinally. Changes in responses over time were analyzed using paired t tests for continuous variables. Changes in frequencies and percentages of categorical variables over time were analyzed using χ test. Scenario participants completed an additional survey at the end of each simulation. RESULTS: The baseline survey was completed by 104 of 150 eligible participants, giving a 71% response rate. Fifty-eight percent completed at least 1 additional survey. On survey 1, mean provider comfort score for procedures was 69 (0-100 point scale). Scores increased 6 points from surveys 1 to 2 and a total of 6.5 points from surveys 1 to 3 (P < 0.05).One hundred fifty postscenario surveys were completed. Of the providers, 83.7% believed that scenario participation increased their comfort with children. One hundred percent of the providers in month 12 felt that they would benefit from additional scenarios. CONCLUSIONS: An in situ pediatric simulation program can be implemented effectively in CAH EDs and results in increased comfort with pediatric patients. Such a program could be used as the core feature of a CAH education program aimed at improving the quality of pediatric emergency services provided at these safety net institutions.