logo

Limitations of collateral flow after occlusion of a single cortical penetrating arteriole

Nozomi Nishimura*, Nathanael L Rosidi*, Costantino Iadecola and Chris B Schaffer

Journal of Cerebral Blood Flow & Metabolism (2010)

 View Abstract

Occlusions of penetrating arterioles, which plunge into cortex and feed capillary beds, cause severe decreases in blood flow and are potential causes of ischemic microlesions. However, surrounding arterioles and capillary beds remain flowing and might provide collateral flow around the occlusion. We used femtosecond laser ablation to trigger clotting in single penetrating arterioles in rat cortex and two-photon microscopy to measure changes in microvessel diameter and red blood cell speed after the clot. We found that after occlusion of a single penetrating arteriole, nearby penetrating and surface arterioles did not dilate, suggesting that alternate blood flow routes are not actively recruited. In contrast, capillaries showed two types of reactions. Capillaries directly downstream from the occluded arteriole dilated after the clot, but other capillaries in the same vicinity did not dilate. This heterogeneity in capillary response suggests that signals for vasodilation are vascular rather than parenchymal in origin. Although both neighboring arterioles and capillaries dilated in response to topically applied acetylcholine after the occlusion, the flow in the territory of the occluded arteriole did not improve. Collateral flow from neighboring penetrating arterioles is neither actively recruited nor effective in improving blood flow after the occlusion of a single penetrating arteriole.

 Get it!
 Supplement 1
 Supplement 2
 Supplement 3

Two-photon microscopy-guided femtosecond-laser photoablation of avian cardiogenesis: noninvasive creation of localized heart defects

Huseyin C. Yalcin, Akshay Shekhar, Nozomi Nishimura, Ajinkya A. Rane, Chris B. Schaffer, and Jonathan T. Butcher

Am J Physiol Heart Circ Physiol (2010)

 View Abstract

Embryonic heart formation is driven by complex feedback between genetic and hemodynamic stimuli. Clinical congenital heart defects (CHD), however, often manifest as localized microtissue malformations with no underlying genetic mutation, suggesting that altered hemodynamics during embryonic development may play a role. An investigation of this relationship has been impaired by a lack of experimental tools that can create locally targeted cardiac perturbations. Here we have developed noninvasive optical techniques that can modulate avian cardiogenesis to dissect relationships between alterations in mechanical signaling and CHD. We used two-photon excited fluorescence microscopy to monitor cushion and ventricular dynamics and femtosecond pulsed laser photoablation to target micrometer-sized volumes inside the beating chick hearts. We selectively photoablated a small (100 m radius) region of the superior atrioventricular (AV) cushion in Hamburger- Hamilton 24 chick embryos. We quantified via ultrasound that the disruption causes AV regurgitation, which resulted in a venous pooling of blood and severe arterial constriction. At 48 h postablation, quantitative X-ray microcomputed tomography imaging demonstrated stunted ventricular growth and pronounced left atrial dilation. A histological analysis demonstrated that the laser ablation produced defects localized to the superior AV cushion: a small quasispherical region of cushion tissue was completely obliterated, and the area adjacent to the myocardial wall was less cellularized. Both cushions and myocardium were significantly smaller than sham-operated controls. Our results highlight that two-photon excited fluorescence coupled with femtosecond pulsed laser photoablation should be considered a powerful tool for studying hemodynamic signaling in cardiac morphogenesis through the creation of localized microscale defects that may mimic clinical CHD

 Get it!

Deep tissue multiphoton microscopy using longer wavelength excitation

Demirhan Kobat, Michael E. Durst, Nozomi Nishimura, Angela W. Wong, Chris B. Schaffer, and Chris Xu

Optics Express (2009)

 View Abstract

We compare the maximal two-photon fluorescence microscopy (TPM) imaging depth achieved with 775-nm excitation to that achieved with 1280-nm excitation through in vivo and ex vivo TPM of fluorescently-labeled blood vessels in mouse brain. We achieved high contrast imaging of blood vessels at approximately twice the depth with 1280-nm excitation as with 775-nm excitation. An imaging depth of 1 mm can be achieved in in vivo imaging of adult mouse brains at 1280 nm with approximately 1-nJ pulse energy at the sample surface. Blood flow speed measurements at a depth of 900 µm are performed.

 Get it!

Flexible microfluidic devices supported by biodegradable insertion scaffolds for convection-enhanced neural drug delivery

Conor P. Foley, Nozomi Nishimura, Keith B. Neeves, Chris B. Schaffer, and William L. Olbricht

Biomed Microdevices (2009)

 View Abstract

Convection enhanced delivery (CED) can improve the spatial distribution of drugs delivered directly to the brain. In CED, drugs are infused locally into tissue through a needle or catheter inserted into brain parenchyma. Transport of the infused material is dominated by convection, which enhances drug penetration into tissue compared with diffusion mediated delivery. We have fabricated and characterized an implantable microfluidic device for chronic convection enhanced delivery protocols. The device consists of a flexible parylene-C microfluidic channel that is supported during its insertion into tissue by a biodegradable poly(DL-lactide-co-glycolide) scaffold. The scaffold is designed to enable tissue penetration and then erode over time, leaving only the flexible channel implanted in the tissue. The device was able to reproducibly inject fluid into neural tissue in acute experiments with final infusate distributions that closely approximate delivery from an ideal point source. This system shows promise as a tool for chronic CED protocols.

 Get it!

Light and Matter Interactions: Going with the Grain

Chris B. Schaffer

Nature Photonics (2008)

 View Abstract

Non-reciprocal optical phenomena — effects that depend on the direction of light propagation —are rare. Researchers have now observed non-reciprocal material modification when moving a beam of ultrashort light pulses through a lithium niobate crystal.

 Get it!

Large two-photon absorptivity of hemoglobin in the infrared range of 780-880 nm

G. Omar Clay, Chris B. Schaffer, and David Kleinfeld

Journal of Chemical Physics (2007)

 View Abstract

Porphyrin molecules have a highly conjugated cyclic structure and are theorized to have unusually large two-photon absorptivities (σTPA), i.e., σTPA ~ 10^2 GM. The authors tested this claim. Ultrafast two-photon absorption (TPA) spectroscopy was performed on solutions of hemoglobin, which contains a naturally occurring metaloporphyrin. They used a pump-probe technique to directly detect the change in transmission induced by TPA over the wavelength range of λ0=780–880 nm. As controls, they measured the TPA of the dyes rhodamine 6G and B; their measurements both verify and extend previously reported values. In new results, hemoglobin was found to have a peak two-photon absorptivity of σTPA~150 GM at λ0=825 nm, near a resonance of the Soret band. This value supports theoretical expectations. They also found a significant difference in the TPA of carboxyhemoglobin versus oxyhemoglobin, e.g., σTPA=61 GM versus σTPA=18 GM, respectively, at λ0=850 nm, which shows that the ligand affects the electronic states involved in TPA.

 Get it!

Penetrating arterioles are a bottleneck in the perfusion of neocortex

Nozomi Nishimura, Chris B. Schaffer, Beth Friedman, Patrick D. Lyden, and David Kleinfeld

Proceedings of the National Academy of Sciences (2007)

 View Abstract

Penetrating arterioles bridge the mesh of communicating arterioles on the surface of cortex with the subsurface microvascular bed that feeds the underlying neural tissue. We tested the conjecture that penetrating arterioles, which are positioned to regulate the delivery of blood, are loci of severe ischemia in the event of occlusion. Focal photothrombosis was used to occlude single penetrating arterioles in rat parietal cortex, and the resultant changes in flow of red blood cells were measured with two-photon laser-scanning microscopy in individual subsurface microvessels that surround the occlusion. We observed that the average flow of red blood cells nearly stalls adjacent to the occlusion and remains within 30% of its baseline value in vessels as far as 10 branch points downstream from the occlusion. Preservation of average flow emerges 350 µm away; this length scale is consistent with the spatial distribution of penetrating arterioles. We conclude that penetrating arterioles are a bottleneck in the supply of blood to neocortex, at least to superficial layers.

 Get it!
 Supplement 1

Photonic band-gap fiber gas cell fabricated using femtosecond micromachining

Christopher J. Hensley , Daniel H. Broaddus, Chris B. Schaffer, and Alexander L. Gaeta

Optics Express (2007)

 View Abstract

Femtosecond laser drilling is used to produce a variable-pressure fiber gas cell. Tightly focused laser pulses are used to produce micrometer-diameter radial channels in a hollow-core photonic band-gap fiber (HC-PBGF), and through these microchannels the core of the fiber is filled with a gas. The fiber cell is formed by fusion splicing and sealing the ends of the HC-PBGF to standard step-index fiber. As a demonstration, acetylene is introduced into an evacuated fiber at multiple backing pressures and spectra are measured.

 Get it!

Suppressed neuronal activity and concurrent arteriolar vasoconstriction may explain negative blood oxygenation level-dependent signal

28. Devor A, Tian P, Nishimura N, Teng IC, Hillman EM, Narayanan SN, Ulbert I, Boas DA, Kleinfeld D, Dale AM.

Journal of Neuroscience (2007)

 View Abstract

Synaptic transmission initiates a cascade of signal transduction events that couple neuronal activity to local changes in blood flow and oxygenation. Although a number of vasoactive molecules and specific cell types have been implicated, the transformation of stimulus-induced activation of neuronal circuits to hemodynamic changes is still unclear. We use somatosensory stimulation and a suite of in vivo imaging tools to study neurovascular coupling in rat primary somatosensory cortex. Our stimulus evoked a central region of net neuronal depolarization surrounded by net hyperpolarization. Hemodynamic measurements revealed that predominant depolarization corresponded to an increase in oxygenation, whereas predominant hyperpolarization corresponded to a decrease in oxygenation. On the microscopic level of single surface arterioles, the response was composed of a combination of dilatory and constrictive phases. Critically, the relative strength of vasoconstriction covaried with the relative strength of oxygenation decrease and neuronal hyperpolarization. These results suggest that a neuronal inhibition and concurrent arteriolar vasoconstriction correspond to a decrease in blood oxygenation, which would be consistent with a negative blood oxygenation level-dependent functional magnetic resonance imaging signal.

 Get it!

Laser photoablation: a new biomedical tool

Nozomi Nishimura, Chris Schaffer, Beth Friedman, Philbert Tsai, Patrick Lyden, and David Kleinfeld

SPIE Newsroom (2006)

 View Abstract

Ultrashort laser pulses can be used to produce lesions in single blood vessels located in the cortex of live rats, thus enabling the study of microstrokes.

 Get it!
First    Previous Next    Last

Sort by Archive Year

Sort by Principal Investigators