Publications

2005
H. K. Shin, Dunn, A. K., Jones, P. B., Boas, D. A., Moskowitz, M. A., and Ayata, C., “Vasoconstrictive neurovascular coupling during focal ischemic depolarizations,” Journal of Cerebral Blood Flow & Metabolism, 2005.Abstract
Ischemic depolarizing events, such as repetitive spontaneous periinfarct spreading depolarizations \{(PIDs),\} expand the infarct size after experimental middle cerebral artery \{(MCA)\} occlusion. This worsening may result from increased metabolic demand, exacerbating the mismatch between cerebral blood flow \{(CBF)\} and metabolism. Here, we present data showing that anoxic depolarization \{(AD)\} and \{PIDs\} caused vasoconstriction and abruptly reduced \{CBF\} in the ischemic cortex in a distal \{MCA\} occlusion model in mice. This reduction in \{CBF\} during \{AD\} increased the area of cortex with 20% or less residual \{CBF\} by 140%. With each subsequent \{PID,\} this area expanded by an additional 19%. Drugs that are known to inhibit cortical spreading depression \{(CSD),\} such as \{N-methyl-D-aspartate\} receptor antagonists \{MK-801\} and 7-chlorokynurenic acid, and sigma-1 receptor agonists dextromethorphan and carbetapentane, did not reduce the frequency of \{PIDs,\} but did diminish the severity of episodic hypoperfusions, and prevented the expansion of severely hypoperfused cortex, thus improving \{CBF\} during 90 mins of acute focal ischemia. In contrast, \{AMPA\} receptor antagonist \{NBQX,\} which does not inhibit \{CSD,\} did not impact the deterioration in \{CBF.\} When measured 24 h after distal \{MCA\} occlusion, infarct size was reduced by \{MK-801,\} but not by \{NBQX.\} Our results suggest that \{AD\} and \{PIDs\} expand the \{CBF\} deficit, and by so doing negatively impact lesion development in ischemic mouse brain. Mitigating the vasoconstrictive neurovascular coupling during intense ischemic depolarizations may provide a novel hemodynamic mechanism of neuroprotection by inhibitors of \{CSD.Journal\} of Cerebral Blood Flow &\#38; Metabolism advance online publication, 7 December 2005; doi:10.1038/sj.jcbfm.9600252.
2004
C. Ayata, Shin, H. K., Salomone, S., Ozdemir-Gursoy, Y., Boas, D. A., Dunn, A. K., and Moskowitz, M. A., “Pronounced hypoperfusion during spreading depression in mouse cortex.,” Journal of Cerebral Blood Flow & Metabolism, vol. 24, pp. 1172–82, 2004. Publisher's VersionAbstract
We studied unique cerebral blood flow (CBF) responses to cortical spreading depression in mice using a novel two-dimensional CBF imaging technique, laser speckle flowmetry. Cortical spreading depression caused a triphasic CBF response in both rat and mouse cortex. In rats, mild initial hypoperfusion (approximately 75% of baseline) was followed by a transient hyperemia reaching approximately 220% of baseline. In mice, the initial hypoperfusion was pronounced (40-50% of baseline), and the anticipated hyperemic phase barely reached baseline. The duration of hypoperfusion significantly correlated with the duration of the DC shift. As a possible explanation for the pronounced hypoperfusion, mouse cerebral vessels showed enhanced resistance to relaxation by acetylcholine (3 microM) after K+ -induced preconstriction (20, 40, and 80 mM) but dilated normally in response to acetylcholine after preconstriction with U46619, a synthetic thromboxane A2 analog. By contrast, rat vessels dilated readily to acetylcholine after preconstriction by K+. The transient normalization of CBF after hypoperfusion in the mouse was abolished by L-NA but not 7-NI. In summary, the CBF response to cortical spreading depression in mice contrasts with the rat in that the initial hypoperfusion is pronounced, and the hyperemic phase is markedly diminished. The differences in CBF response between species may be in part caused by an increased sensitivity of mouse cerebral vessels to elevated extracellular K+.
E. M. Hillman, Boas, D. A., and Dunn, A. K., “Laminar optical tomography: demonstration of millimeter-scale depth-resolved imaging in turbid media,” Optics Letters, vol. 29, pp. 1650–1652, 2004.Abstract
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C. Ayata, Dunn, A. K., Gursoy, O. Z. Y., Huang, Z., Boas, D. A., and Moskowitz, M. A., “Laser speckle flowmetry for the study of cerebrovascular physiology in normal and ischemic mouse cortex,” Journal of Cerebral Blood Flow & Metabolism, vol. 24, pp. 744–755, 2004.Abstract
Laser speckle flowmetry \{(LSF)\} is useful to assess noninvasively two-dimensional cerebral blood flow \{(CBF)\} with high temporal and spatial resolution. The authors show that \{LSF\} can image the spatiotemporal dynamics of \{CBF\} changes in mice through an intact skull. When measured by \{LSF,\} peak \{CBF\} increases during whisker stimulation closely correlated with simultaneous \{laser-Doppler\} flowmetry \{(LDF)\} measurements, and were greater within the branches of the middle cerebral artery supplying barrel cortex than within barrel cortex capillary bed itself. When \{LSF\} was used to study the response to inhaled \{CO2\} (5%), the flow increase was similar to the response reported using \{LDF.\} For the upper and lower limits of autoregulation, mean arterial pressure values were 110 and 40 mm Hg, respectively. They also show a linear relationship between absolute resting \{CBF,\} as determined by \{[C]iodoamphetamine\} technique, and 1/tau(c) values obtained using \{LSF,\} and used 1/tau(c) values to compare resting \{CBF\} between different animals. Finally, the authors studied \{CBF\} changes after distal middle cerebral artery ligation, and developed a model to investigate the spatial distribution and hemodynamics of moderate to severely ischemic cortex. In summary, \{LSF\} has distinct advantages over \{LDF\} for \{CBF\} monitoring because of high spatial resolution.
Mouse model of microembolic stroke and reperfusion,” Stroke, vol. 35, pp. 2177–2182, 2004.Abstract
\{BACKGROUND\} \{AND\} \{PURPOSE:\} To test the role of fibrinolysis in stroke, we used a mouse model in which preformed 2.5- to 3-microm-diameter fibrin microemboli are injected into the cerebral circulation. The microemboli lodge in the downstream precapillary vasculature and are susceptible to fibrinolysis. \{METHODS:\} We injected various doses of microemboli into the internal carotid artery in mice and characterized their distribution, effects on cerebral blood flow, neurological deficit, infarct area, and spontaneous dissolution. By comparing wild-type and tissue plasminogen activator \{(tPA)\} knockout \{(tPA-/-)\} mice, we analyzed the role of endogenous \{tPA\} in acute thrombotic stroke. \{RESULTS:\} Microemboli cause dose-dependent brain injury. Although moderate doses of microemboli are followed by spontaneous reperfusion, they result in reproducible injury. Gene knockout of \{tPA\} markedly delays dissolution of cerebral emboli and restoration of blood flow and aggravates ischemic thrombotic infarction in the brain. \{CONCLUSIONS:\} We describe a microembolic model of stroke, in which degree of injury can be controlled by the dose of microemboli injected. Unlike vessel occlusion models, this model can be modulated to allow spontaneous fibrinolysis. Application to \{tPA-/-\} mice supports a key role of endogenous \{tPA\} in restoring cerebral blood flow and limiting infarct size after thrombosis.
J. L. Hollmann, Dunn, A. K., and Dimarzio, C. A., “Computational microscopy in embryo imaging,” Optics Letters, vol. 29, pp. 2267–2269, 2004.Abstract
The growth of computing power has greatly improved our ability to extract quantitative information about complicated three-dimensional structures from microscope images. New hardware techniques are also being developed to provide suitable images for these tasks. However, a need exists for synthetic data to test these new developments. The work reported here was motivated by studies of embryo health, but similar needs exist across the field of microscopy. We report a rigorous computer model, based on Maxwell’s equations, that can produce the required synthetic images for bright-field, differential interference contrast, interferometric imaging, and polarimetric imaging. After a description of the algorithm, sample results are presented, followed by a discussion of future plans and applications.
J. Skoch, Dunn, A. K., Hyman, B. T., and Bacskai, B. J., “Development of an optical approach for non-invasive imaging of Alzheimer’s disease pathology,” Journal of Biomedical Optics, 2004.Abstract
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2003
A. Devor, Dunn, A. K., Andermann, M. L., Ulbert, I., Boas, D. A., and Dale, A. M., “Coupling of total hemoglobin concentration, oxygenation, and neural activity in rat somatosensory cortex,” Neuron, vol. 39, pp. 353–359, 2003.Abstract
Recent advances in brain imaging techniques, including functional magnetic resonance imaging \{(fMRI),\} offer great promise for noninvasive mapping of brain function. However, the indirect nature of the imaging signals to the underlying neural activity limits the interpretation of the resulting maps. The present report represents the first systematic study with sufficient statistical power to quantitatively characterize the relationship between changes in blood oxygen content and the neural spiking and synaptic activity. Using two-dimensional optical measurements of hemodynamic signals, simultaneous recordings of neural activity, and an event-related stimulus paradigm, we demonstrate that (1) there is a strongly nonlinear relationship between electrophysiological measures of neuronal activity and the hemodynamic response, (2) the hemodynamic response continues to grow beyond the saturation of electrical activity, and (3) the initial increase in deoxyhemoglobin that precedes an increase in blood volume is counterbalanced by an equal initial decrease in oxyhemoglobin.
A. K. Dunn, Devor, A., Bolay, H., Andermann, M. L., Moskowitz, M. A., Dale, A. M., and Boas, D. A., “Simultaneous imaging of total cerebral hemoglobin concentration, oxygenation, and blood flow during functional activation,” Optics Letters, vol. 28, pp. 28–30, 2003.Abstract
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2002
H. Bolay, Reuter, U., Dunn, A. K., Huang, Z., Boas, D. A., and Moskowitz, M. A., “Intrinsic brain activity triggers trigeminal meningeal afferents in a migraine model,” Nature Medicine, vol. 8, pp. 136–42, 2002.Abstract
Although the trigeminal nerve innervates the meninges and participates in the genesis of migraine headaches, triggering mechanisms remain controversial and poorly understood. Here we establish a link between migraine aura and headache by demonstrating that cortical spreading depression, implicated in migraine visual aura, activates trigeminovascular afferents and evokes a series of cortical meningeal and brainstem events consistent with the development of headache. Cortical spreading depression caused long-lasting blood-flow enhancement selectively within the middle meningeal artery dependent upon trigeminal and parasympathetic activation, and plasma protein leakage within the dura mater in part by a neurokinin-1-receptor mechanism. Our findings provide a neural mechanism by which extracerebral cephalic blood flow couples to brain events; this mechanism explains vasodilation during headache and links intense neurometabolic brain activity with the transmission of headache pain by the trigeminal nerve.
D. A. Boas, Culver, J. P., Stott, J. J., and Dunn, A. K., “Three dimensional Monte Carlo code for photon migration through complex heterogeneous media including the adult human head,” Optics Express, vol. 10, pp. 159–170, 2002.Abstract
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2001
A. K. Dunn, Bolay, H., Moskowitz, M. A., and Boas, D. A., “Dynamic imaging of cerebral blood flow using laser speckle,” Journal of Cerebral Blood Flow & Metabolism, vol. 21, pp. 195–201, 2001.Abstract
A method for dynamic, high-resolution cerebral blood flow \{(CBF)\} imaging is presented in this article. By illuminating the cortex with laser light and imaging the resulting speckle pattern, relative \{CBF\} images with tens of microns spatial and millisecond temporal resolution are obtained. The regional \{CBF\} changes measured with the speckle technique are validated through direct comparison with conventional \{laser-Doppler\} measurements. Using this method, dynamic images of the relative \{CBF\} changes during focal cerebral ischemia and cortical spreading depression were obtained along with electrophysiologic recordings. Upon middle cerebral artery \{(MCA)\} occlusion, the speckle technique yielded high-resolution images of the residual \{CBF\} gradient encompassing the ischemic core, penumbra, oligemic, and normally perfused tissues over a 6 x 4 mm cortical area. Successive speckle images demonstrated a further decrease in residual \{CBF\} indicating an expansion of the ischemic zone with finely delineated borders. Dynamic \{CBF\} images during cortical spreading depression revealed a 2 to 3 mm area of increased \{CBF\} (160% to 250%) that propagated with a velocity of 2 to 3 mm/min. This technique is easy to implement and can be used to monitor the spatial and temporal evolution of \{CBF\} changes with high resolution in studies of cerebral pathophysiology.
C. K. Hayakawa, Spanier, J., Bevilacqua, F., Dunn, A. K., Yoo, J. S., Tromberg, B. J., and Venugopalan, V., “Perturbation Monte Carlo methods to solve inverse photon migration problems in heterogeneous tissues,” Optics Letters, vol. 26, pp. 1335–1337, 2001.Abstract
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A. Dunn and Boas, D., “Transport Based Image Reconstruction in Turbid Media with Small Source-Detector Separations,” Optics Letters, vol. 25, pp. 1777–1779, 2001.Abstract
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2000
M. W. Berns, Wang, Z., Dunn, A., Wallace, V., and Venugopalan, V., “Gene inactivation by multiphoton-targeted photochemistry.,” Proceedings of the National Academy of Sciences of the United States of America, vol. 97, pp. 9504–7, 2000. Publisher's VersionAbstract
Multiphoton-targeted photochemistry was used to selectively inactivate the expression of genes in vertebrate cells. A membrane permeable DNA-associating vital dye, ethidium bromide monoacetate (visible wavelength single photon absorption peak at 530 nm) was used to photosensitize chromosomes in dividing cells. A 100-ps infrared laser beam operating at 1.06 microns was focused onto a selected region of a mitotic chromosome corresponding to the sites of the nucleolar (ribosomal) genes. Individual cells followed through mitosis demonstrated a reduction in the number of nucleoli formed in daughter cells that corresponded to the number of nucleolar genes sites irradiated. These results demonstrate the ability to selectively manipulate genes by using the focal point specificity characteristic of multiphoton microscopy. This technique should have wide biotechnology applications both in vitro and in vivo.
A. K. Dunn, Wallace, V. P., Coleno, M., Berns, M. W., and Tromberg, B. J., “Influence of optical properties on two-photon fluorescence imaging in turbid samples,” Applied Optics, vol. 39, pp. 1194–1201, 2000.Abstract
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R. Drezek, Dunn, A., and Richards-Kortum, R., “A pulsed finite-difference time-domain (FDTD) method for calculating light scattering from biological cells over broad wavelength ranges,” Optics Express, vol. 6, pp. 147–157, 2000.Abstract
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1999
R. Drezek, Dunn, A. K., and Richards-Kortum, R., “Light scattering from cells: finite-difference time-domain simulations and goniometric measurements,” Applied Optics, vol. 38, pp. 3651–3661, 1999.Abstract
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1998
C. Smithpeter, Dunn, A., Drezek, R., Collier, T., and Richards-Kortum, R., “Near Real Time Confocal Microscopy of Cultured Amelanotic Cells: Sources of Signal, Contrast Agents and Limits of Contrast,” Journal of Biomedical Optics, vol. 3, pp. 429–436, 1998.Abstract
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B. Nemati, Dunn, A., Welch, A. J., and Rylander, H. G., “Optical model for light distribution during transscleral cyclophotocoagulation,” Applied Optics, vol. 37, pp. 764–771, 1998.Abstract
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