Tejapratap Bollu, Nathan R Cornelius, John Sunwoo, Nozomi Nishimura, Chris B Schaffer and Peter C Doerschuk
Journal of Cerebral Blood Flow & Metabolism (2017)
Computations are described which estimate flows in all branches of the cortical surface arteriole network from two-photon excited fluorescence (2PEF) microscopy images which provide the network topology and, in selected branches red blood cell (RBC) speeds and lumen diameters. Validation is done by comparing the flow predicted by the model with experimentally measured flows and by comparing the predicted flow redistribution in the network due to single-vessel strokes with experimental observations. The model predicts that tissue is protected from RBC flow decreases caused by multiple occlusions of surface arterioles but not penetrating arterioles. The model can also be used to study flow rerouting due to vessel dilations and constrictions.
M. Koyama, F. Minale, J. Shum, N. Nishimura, C. B. Schaffer, and J. R. Fetcho
Animals collect sensory information from the world and make adaptive choices about how to respond to it. Here, we reveal a network motif in the brain for one of the most fundamental behavioral choices made by bilaterally symmetric animals: whether to respond to a sensory stimulus by moving to the left or to the right. We define network connectivity in the hindbrain important for the lateralized escape behavior of zebrafish and then test the role of neurons by using laser ablations and behavioral studies. Key inhibitory neurons in the circuit lie in a column of morphologically similar cells that is one of a series of such columns that form a developmental and functional ground plan for building hindbrain networks. Repetition within the columns of the network motif we defined may therefore lie at the foundation of other lateralized behavioral choices.
M. J. Farrar, J. D. Rubin, D. M. Diago, and C. B. Schaffer
Journal of Cerebral Blood flow and Metabolism (2015)
The availability of transgenic strains has made the laboratory mouse a popular model for the study of healthy and diseased state spinal cord (SC). Essential to identifying physiologic and pathologic events is an understanding of the microvascular network and flow patterns of the SC. Using 2-photon excited fluorescence (2PEF) microscopy we performed in vivo measurements of blood flow in the lower thoracic portion of the mouse dorsal spinal vein (dSV) and in the first upstream branches supplying it, denoted as dorsal ascending venules (dAVs). We found that the dSV had large radiculomedullary veins (RMVs) exiting the SC, and that flow in the dSV between pairs of RMVs was bidirectional. Volumetric flow increased in each direction away from the point of bifurcation. Flow in the upstream dAVs varied with diameter in a manner consistent with a constant distal pressure source. By performing ex vivo 2PEF microscopy of fluorescent-gel perfused tissue, we created a 3-D map of the dorsal spinal vasculature. From these data, we constructed a simple model that predicted changes in the flow of upstream branches after occlusion of the dSV in different locations. Using an atraumatic model of dSV occlusion, we confirmed the predictions of this model in vivo.
Lindsey SE, Menon PG, Kowalski WJ, Shekhar A, Yalcin HC, Nishimura N, Schaffer CB, Butcher JT, Pekkan K.
Biomech Model Mechanobiol (2015)
The majority of severe clinically significant forms of congenital heart disease (CHD) are associated with great artery lesions, including hypoplastic, double, right or interrupted aortic arch morphologies. While fetal and neonatal interventions are advancing, their potential ability to restore cardiac function, optimal timing, location, and intensity required for intervention remain largely unknown. Here, we combine computational fluid dynamics (CFD) simulations with in vivo experiments to test how individual pharyngeal arch artery hemodynamics alter as a result of local interventions obstructing individual arch artery flow. Simulated isolated occlusions within each pharyngeal arch artery were created with image-derived three-dimensional (3D) reconstructions of normal chick pharyngeal arch anatomy at Hamburger-Hamilton (HH) developmental stages HH18 and HH24. Acute flow redistributions were then computed using in vivo measured subject-specific aortic sinus inflow velocity profiles. A kinematic vascular growth-rendering algorithm was then developed and implemented to test the role of changing local wall shear stress patterns in downstream 3D morphogenesis of arch arteries. CFD simulations predicted that altered pressure gradients and flow redistributions were most sensitive to occlusion of the IVth arches. To evaluate these simulations experimentally, a novel in vivo experimental model of pharyngeal arch occlusion was developed and implemented using two-photon microscopy-guided femtosecond laser-based photodisruption surgery. The right IVth arch was occluded at HH18, and resulting diameter changes were followed for up to 24 h. Pharyngeal arch diameter responses to acute hemodynamic changes were predicted qualitatively but poorly quantitatively. Chronic growth and adaptation to hemodynamic changes, however, were predicted in a subset of arches. Our findings suggest that this complex biodynamic process is governed through more complex forms of mechanobiological vascular growth rules. Other factors in addition to wall shear stress or more complex WSS rules are likely important in the long-term arterial growth and patterning. Combination in silico/experimental platforms are essential for accelerating our understanding and prediction of consequences from embryonic/fetal cardiovascular occlusions and lay the foundation for noninvasive methods to guide CHD diagnosis and fetal intervention.
A.Y. Shih, C. Ruhlmann, P. Blinder, A. Devor, P. J. Drew, B. Friedman, P. M. Knutsen, P. D. Lyden, C. Mateo, L. Mellander, N. Nishimura, C. B. Schaffer, P. S. Tsai, and D. Kleinfeld
We review the organizational principles of the cortical vasculature and the underlying patterns of blood flow under normal conditions and in response to occlusion of single vessels. The cortex is sourced by a two-dimensional network of pial arterioles that feeds a three-dimensional network of subsurface microvessels in close proximity to neurons and glia. Blood flow within the surface and subsurface networks is largely insensitive to occlusion of a single vessel within either network. However, the penetrating arterioles that connect the pial network to the subsurface network are bottlenecks to flow; occlusion of even a single penetrating arteriole results in the death of a 500 μm diameter cylinder of cortical tissue despite the potential for collateral flow through microvessels. This pattern of flow is consistent with that calculated from a full reconstruction of the angioarchitecture. Conceptually, collateral flow is insufficient to compensate for the occlusion of a penetrating arteriole because penetrating venules act as shunts of blood that flows through collaterals. Future directions that stem from the analysis of the angioarchitecture concern cellular-level issues, in particular the regulation of blood flow within the subsurface microvascular network, and system-level issues, in particular the role of penetrating arteriole occlusions in human cognitive impairment.
R. Cohen, J. P. Lata, Y. Lee, J. C. Cruz-Hernandez, N. Nishimura, C. B. Schaffer, C. Mukai, J. L. Nelson, S. A. Brangman, Y. Agrawal, and A. J. Travis
Public Library of Science (2015)
Background Rapid diagnosis for time-sensitive illnesses such as stroke, cardiac arrest, and septic shock is essential for successful treatment. Much attention has therefore focused on new strategies for rapid and objective diagnosis, such as Point-of-Care Tests (PoCT) for blood biomarkers. Here we use a biomimicry-based approach to demonstrate a new diagnostic platform, based on enzymes tethered to nanoparticles (NPs). As proof of principle, we use oriented immobilization of pyruvate kinase (PK) and luciferase (Luc) on silica NPs to achieve rapid and sensitive detection of neuron-specific enolase (NSE), a clinically relevant biomarker for multiple diseases ranging from acute brain injuries to lung cancer. We hypothesize that an approach capitalizing on the speed and catalytic nature of enzymatic reactions would enable fast and sensitive biomarker detection, suitable for PoCT devices. Methods and findings We performed in-vitro, animal model, and human subject studies. First, the efficiency of coupled enzyme activities when tethered to NPs versus when in solution was tested, demonstrating a highly sensitive and rapid detection of physiological and pathological concentrations of NSE. Next, in rat stroke models the enzyme-based assay was able in minutes to show a statistically significant increase in NSE levels in samples taken 1 hour before and 0, 1, 3 and 6 hours after occlusion of the distal middle cerebral artery. Finally, using the tethered enzyme assay for detection of NSE in samples from 20 geriatric human patients, we show that our data match well (r = 0.815) with the current gold standard for biomarker detection, ELISA—with a major difference being that we achieve detection in 10 minutes as opposed to the several hours required for traditional ELISA. Conclusions Oriented enzyme immobilization conferred more efficient coupled activity, and thus higher assay sensitivity, than non-tethered enzymes. Together, our findings provide proof of concept for using oriented immobilization of active enzymes on NPs as the basis for a highly rapid and sensitive biomarker detection platform. This addresses a key challenge in developing a PoCT platform for time sensitive and difficult to diagnose pathologies.
M. J. Farrar and C. B. Schaffer
Journal of Visualized Experiments (2014)
Studies in the mammalian neocortex have enabled unprecedented resolution of cortical structure, activity, and response to neurodegenerative insults by repeated, time-lapse in vivo imaging in live rodents. These studies were made possible by straightforward surgical procedures, which enabled optical access for a prolonged period of time without repeat surgical procedures. In contrast, analogous studies of the spinal cord have been previously limited to only a few imaging sessions, each of which required an invasive surgery. As previously described, we have developed a spinal chamber that enables continuous optical access for upwards of 8 weeks, preserves mechanical stability of the spinal column, is easily stabilized externally during imaging, and requires only a single surgery. Here, the design of the spinal chamber with its associated surgical implements is reviewed and the surgical procedure is demonstrated in detail. Briefly, this video will demonstrate the preparation of the surgical area and mouse for surgery, exposure of the spinal vertebra and appropriate tissue debridement, the delivery of the implant and vertebral clamping, the completion of the chamber, the removal of the delivery system, sealing of the skin, and finally, post-operative care. The procedure for chronic in vivo imaging using nonlinear microscopy will also be demonstrated. Finally, outcomes, limitations, typical variability, and a guide for troubleshooting are discussed.
Santisakultarm TP, Paduano CQ, Stokol T, Southard TL, Nishimura N, Skoda RC, Olbricht WL, Schafer AI, Silver RT, Schaffer CB.
J Thromb Haemost. (2014)
Background Essential thrombocythemia (ET) and polycythemia vera (PV) are myeloproliferative neoplasms (MPNs) that share the JAK2V617F mutation in hematopoietic stem cells, leading to excessive production of predominantly platelets in ET, and predominantly red blood cells (RBCs) in PV. The major cause of morbidity and mortality in PV and ET is thrombosis, including cerebrovascular occlusive disease. Objectives To identify the effect of excessive blood cells on cerebral microcirculation in ET and PV. Methods We used two-photon excited fluorescence microscopy to examine cerebral blood flow in transgenic mouse models that mimic MPNs. Results and conclusions We found that flow was ‘stalled’ in an elevated fraction of brain capillaries in ET (18%), PV (27%), mixed MPN (14%) and secondary (non-MPN) erythrocytosis (27%) mice, as compared with controls (3%). The fraction of capillaries with stalled flow increased when the hematocrit value exceeded 55% in PV mice, and the majority of stalled vessels contained only stationary RBCs. In contrast, the majority of stalls in ET mice were caused by platelet aggregates. Stalls had a median persistence time of 0.5 and 1 h in ET and PV mice, respectively. Our findings shed new light on potential mechanisms of neurological problems in patients with MPNs.
Nozomi Nishimura and Chris B. Schaffer
Stroke 44, S90 (2013)
Improvement in clinical imaging technologies has made it possible to resolve small, previously invisible lesions in the brains of elderly humans. Initially, these lesions were called silent strokes because they do not present with dramatic acute symptoms like major stroke. It was later shown that these small lesions have cognitive consequences and are a contributing factor to age-related mental decline and dementia.
Shih AY, Nishimura N, Nguyen J, Friedman B, Lyden PD, Schaffer CB, Kleinfeld D.
Cold Spring Harbor (2013)
The ability to form targeted vascular occlusions in small vessels of the brain is an important technique for studying the microscopic basis of cerebral ischemia. We describe two complementary methods that enable targeted occlusion of any single blood vessel within the upper 500 µm of adult rodent neocortex. Our goal is to generate highly localized regions of ischemia by blocking penetrating arterioles and ascending venules, which are bottlenecks of flow in the cortical angioarchitecture. One method, termed photothrombosis, makes use of linear optical absorption by a photosensitizer, transiently circulated in the blood stream, to induce a clot in a surface or near-surface segment of a vessel. The second method, termed plasma-mediated ablation, makes use of nonlinear optical interactions, without the need to introduce an exogenous absorber, to induce clots in subsurface segments of penetrating vessels, as well as subsurface microvessels and capillaries. The choice of the method for occlusion of individual vessels depends on the location of the vessels being studied and the objectives of the study. Here we describe concurrent high resolution in vivo imaging and auxiliary laser setups, occlusion protocols, and post hoc histological procedures.