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(Stroke. 1996;27:1381-1385.)
© 1996 American Heart Association, Inc.

Articles

Temporal Correlation Mapping Analysis of the Hemodynamic Penumbra in Mutant Mice Deficient in Endothelial Nitric Oxide Synthase Gene Expression

Eng H. Lo, PhD; Hideaki Hara, PhD; Jadwiga Rogowska, PhD; Marek Trocha, DVM; Allen R. Pierce, BA; Paul L. Huang, MD, PhD; Mark C. Fishman, MD; Gerald L. Wolf, MD, PhD Michael A. Moskowitz, MD

the Center for Imaging and Pharmaceutical Research and Department of Radiology (E.H.L., J.R., M.T., A.R.P., G.L.W.), the Stroke and Neurovascular Regulation Laboratory and Department of Neurology (H.H., M.A.M.), and the Cardiovascular Research Center and Department of Medicine (P.L.H., M.C.F.), Massachusetts General Hospital, Harvard Medical School, Boston, Mass.

Correspondence to Eng H. Lo, PhD, Center for Imaging and Pharmaceutical Research, Harvard Medical School, MGH East Bldg 149, Charlestown, MA 02129. E-mail eng@cipr.mgh.harvard.edu.

	Abstract

Top Abstract Introduction Materials and Methods Results Discussion References Introduction  References

 
Background and Purpose Mice containing deletions in the genes encoding nitric oxide (NO) synthase have been useful to dissect the role of NO in cerebral ischemia. We recently reported that mice lacking expression of the endothelial isoform of NO synthase (eNOS) develop larger infarcts after middle cerebral artery occlusion. Because NO or a related product of NO synthase activity is important for relaxation of cerebral blood vessels, we examined for possible hemodynamic differences in the peri-ischemic zone of eNOS-deficient and wild-type mice after middle cerebral artery occlusion using functional CT scanning techniques.

Methods Wild-type SV129 mice (n=10) and mice deficient in eNOS gene expression (n=10) were subjected to middle cerebral artery occlusion under halothane anesthesia. Thirty minutes after ischemia, functional CT scanning was performed with dynamic scanning protocols to measure the cerebral transit profiles of injected contrast agents. A temporal correlation mapping technique was used to analyze the pattern of hemodynamic perturbations based on alterations in the shape of the cerebral transit profiles. Statistical thresholds defined the hemodynamic core and penumbra.

Results Hemodynamic deficits were more severe in the mutant than wild-type mouse. When expressed as a percentage of the total insult, core areas were significantly increased in mutant mice (39.8±3.7%) compared with wild types (28.8±3.4%). Conversely, areas of the hemodynamic penumbra were significantly smaller in mice deficient in eNOS activity (60.2±3.7%) than in wild-type mice (71.2±3.4%). Furthermore, the calculated relative perfusion index within the hemodynamic penumbra was significantly lower in the group with eNOS gene deletion (35.6±1.5% in mutants versus 43.0±2.4% in wild types).

Conclusions These data indicate that mice lacking eNOS expression show a greater degree of hemodynamic compromise after middle cerebral artery occlusion and suggest that a product of eNOS activity (eg, NO) may protect brain after focal cerebral ischemia, possibly by improving blood flow within the penumbral zone.

Key Words: cerebral ischemia, focal • hemodynamics • nitric oxide synthase • tomography • mice

	Introduction

Top Abstract Introduction Materials and Methods Results Discussion References Introduction  References

 
The role of NO in stroke pathophysiology is complex and multifactorial.^{1 2 3 4 5} During ischemia, NO levels increase dramatically and can positively and negatively affect stroke outcome. NO derived from nNOS is detrimental to cellular survival, possibly by enhancing ADP ribosylation, peroxynitrite formation, and/or binding to iron-sulfur complexes.^{1 2 3} Accordingly, smaller infarcts develop in rats after nNOS inhibition by 7-nitroindazole or in mutant mice deficient in nNOS gene expression.^{6 7 8 9} Alternatively, endothelium-derived NO appears to improve ischemic hemodynamics by promoting vasodilation and collateral blood supply and by augmenting blood flow within the penumbral zone. Enhancing NO synthesis in blood vessels with L-arginine infusion or NO donors improves penumbral perfusion, secondarily increases functional tissue recovery, and decreases infarct size.^{10 11 12} Consistent with these findings, larger infarcts develop after middle cerebral artery occlusion in eNOS-deficient mice and when eNOS is inhibited in nNOS-deficient mice by nitro-L-arginine.^{7 8 13}

In the present study we used a novel image analysis technique in combination with high-resolution functional CT scanning^{14 15 16 17 18} to visualize hemodynamic changes within the margins of a focal ischemic insult in wild-type mice and mutant mice deficient in eNOS gene expression. Based on the importance of NO as a potent vasodilator, we hypothesized that the hemodynamic core would be larger and the hemodynamic penumbra smaller in mutant mice with eNOS gene deletion.

	Materials and Methods

Top Abstract Introduction Materials and Methods Results Discussion References Introduction  References

 
Mouse Focal Ischemia Model
Adult male wild-type (SV129) mice (n=10; weight, 23.5±0.5 g) and adult male mutant mice (n=10; weight, 24.0±1.1 g) were induced with 1.5% and maintained with 0.5% to 1.0% halothane under spontaneous respiration. Polyethylene tubing (PE-10) was placed into the femoral vein for contrast injections. In addition, five mice from each group were also implanted with femoral arterial catheters for monitoring blood pressure and sampling arterial blood gases and pH. Surgical cutdowns were performed in the ventral neck region, and silicon-coated 8-0 nylon monofilament sutures (Ethicon) were inserted into the left internal carotid artery as described previously.⁶ The sutures were inserted until the tips were approximately 10 mm from the bifurcation of the common carotid artery. Based on our previous studies, this distance was optimal for consistent occlusion of the middle cerebral artery circulation.⁶ Successful placement of the occluding monofilament was confirmed in all animals by the absence of flow in the internal carotid artery on the ipsilateral hemisphere, as described below.

Functional CT Scanning
Thirty minutes after arterial occlusion, mice were placed in a Toshiba TCT-900S/X spiral CT scanner (Toshiba Medical Systems). Scanning at 120 kV and 150 mA was performed under continued 0.5% to 1.0% halothane anesthesia. After scout images were obtained to localize the brain, axial images were then collected with a 60-mm field of view and a 512x512 matrix size, resulting in 0.1x0.1-mm pixel sizes. The thickness of each image slice was 2 mm. A single axial slice was chosen as representative of middle cerebral artery territory. A dynamic scanning protocol that has been previously described was used.^{14 15 16 18} Briefly, dynamic scans were collected at a rate of one image every second. A 1.5-mL/kg bolus of iohexol (Omnipaque-350, Sterling-Winthrop) was injected via the femoral vein after 5 seconds of scanning, and images were collected for a total of 35 seconds. For each mouse, a selected precontrast image was subtracted from a postcontrast image to show large blood vessels at the base of the brain. Successful occlusion was then confirmed in all mice by ensuring that the internal carotid artery at the middle cerebral artery junction supplying the ipsilateral hemisphere was completely obliterated.

TCM Analysis
The functional CT data sets describe the cerebral transit profile of the injected iodinated contrast agent, which remains restricted to the intravascular compartment during the acute phase of ischemia.^{11 12 13 15} Changes in signal intensity with time therefore reflect the intravascular cerebral transit profile. For each pixel, data can be plotted as signal intensity versus time. The plot is flat before injection. Signal intensity increases when the contrast agent bolus arrives in that pixel and decreases again as the contrast agent is cleared. Alterations in cerebral hemodynamics change the shape of the transit profile curve.^{14 15 16 18}

A TCM analysis was used to quantitatively compare the shape of the cerebral transit profiles from each pixel within the brain with a reference profile selected from any brain region such as that from the contralateral hemisphere in focal ischemia. For each pixel in the brain, an NCOR was calculated:

where S(t) is the transit profile from each pixel, R(t) is the reference transit profile from the contralateral cortex, and µ_S and µ_R are the mean values of S(t) and R(t), respectively. Each pixel in the resulting TCM image thus has an NCOR value that quantifies how similar the shape of the transit profile is compared with normal transit profiles in unaffected brain.

Statistical analyses distinguish normal from abnormal hemodynamics, as previously described and validated.¹³ Briefly, a simple cutoff was arbitrarily set based on the distribution of "normal" NCOR values obtained from the contralateral hemisphere; any pixel in the ipsilateral hemisphere less than 2 SDs below this contralateral mean was deemed abnormal and thus part of the ischemic distribution. Based on this definition, hemodynamically compromised areas were calculated as a percentage of the ipsilateral hemisphere. To differentiate core and hemodynamic penumbra, a second threshold was used based on one-tailed t distributions. Each dynamic study in a mouse generated 35 images, resulting in 33 df. Therefore, P<.01 corresponded to NCOR greater than 0.4. Thus, regions on the TCM image with NCOR values below this threshold have signal intensity time curves that are significantly different from normal transit profiles; these regions were defined as core. The hemodynamic penumbra was defined as those regions below the 2 SD cutoff that represents the normal distribution in the contralateral hemisphere but with abnormal NCOR values that lie above the threshold of 0.4.

Color look-up tables were constructed to display the TCM images, as previously described.¹⁶ Within the normal NCOR range, various gradations of green were used. The mean minus 2 SD threshold was identified as a green-to-red boundary. All other NCOR values below this threshold were assigned to a sliding color scale from red to black. As a result, normal brain should appear green, the core black, and the hemodynamic penumbra as an intermediate reddish zone that surrounds the core.

Relative `Perfusion' Index
For bolus injections coupled with rapid scanning rates, cerebral transit profiles represent the first-pass transit of tracer. It is well known that when pure first-pass transits are not contaminated by multiple passes and/or recirculation, standard indicator dilution kinetics can be applied to calculate discrete perfusion parameters.¹⁹ For example, relative blood volumes can be derived as the area under the first-pass transit plot. Blood flow velocities may also be calculated based on the mean transit times of the bolus profile. In this study, pure first-pass transits were not obtained. Because of limitations in the size of the catheter that can be safely inserted into mouse femoral veins, the contrast agent bolus was actually injected over a 2- to 3-second interval. Since the cardiac output of a mouse is approximately 0.1 mL/s and the combined cerebral and pulmonary blood volume is approximately 0.13 mL, each pass through the brain would take approximately 1.3 seconds. Therefore, it is likely that the cerebral transit profiles measured in the present study extended over several passes through the brain. In this case, standard indicator dilution kinetics cannot be used to calculate discrete perfusion parameters. For the purposes of this study, the relative peak height of transit profiles was used to compare, on a first-order basis, the "perfusion" in peri-ischemic zones from wild-type and mutant mice. This index has been widely used to estimate perfusion and will include both blood flow and blood volume influences.^{19 20 21 22 23}

	Results

Top Abstract Introduction Materials and Methods Results Discussion References Introduction  References

 
Systemic parameters for both wild-type and mutant mice were within the normal range (Table). Mean arterial blood pressure was significantly higher in the anesthetized mutant mice, consistent with our previous report.²⁴

View this table: [in this window] [in a new window]   Table 1. Systemic Parameters for Wild-Type and Mutant Mice

TCM analysis showed high and stable NCOR values in the contralateral hemisphere, where hemodynamics would be normal, as expected. There were no differences between wild-type (0.918±0.01) and mutant (0.908±0.01) mice. On the TCM images, focal ischemia was evident in the occluded hemisphere, with the distribution of hemodynamic deficits typically involving the basal ganglia and overlying cortex (Fig 1). Areas with perturbed hemodynamics constituted 71.4±8.8% and 66.4±9.7% of the ipsilateral hemisphere in wild-type and mutant mice, respectively.

View larger version (42K): [in this window] [in a new window]   Figure 1. A, TCM image shows the distribution of hemodynamic deficits after focal cerebral ischemia in the wild-type mouse. Hemodynamic status is proportional to the NCOR value (ranging from 0 to 1) in each pixel of the image. Normal hemodynamic status (high NCOR values) is shown as gradations of green. Regions with abnormal hemodynamics (reduced NCOR values that fall below the 2 SD threshold) are represented with a red-to-black sliding color scale. Therefore, the core appears black, and the hemodynamic penumbra is the reddish rim surrounding the core (see "Materials and Methods" for details on statistics). Note that 30 minutes after focal ischemia, an extensive hemodynamic penumbra in wild-type mice still exists. B, TCM image shows the distribution of hemodynamic deficits in the mutant eNOS-deficient mouse after focal ischemia. Note that the hemodynamic deficit appears to be more severe. The core appears larger, and the surrounding rim of hemodynamic penumbra is more restricted than that of the wild-type mouse.

Within the ischemic hemisphere, gradations of NCOR values ranged from almost zero in the core to intermediate values toward the periphery of the insult. In general, hemodynamic deficits appeared to be more severe in the mutant mice than in the wild-type mice (Fig 1). To normalize for differences in the sizes of hemodynamic deficits between individual mice, areas of the hemodynamic core and penumbra were expressed as a percentage of the total insult size. The results showed that core areas were significantly (P=.03) larger in mutant mice lacking eNOS (39.8±3.7%) than in wild-type mice (28.8±3.4%). Conversely, the hemodynamic penumbra was significantly narrower in the mutant mice (60.2±3.7%) than in wild-type mice (71.2±3.4%) (Fig 2). Within the hemodynamic core, no perfusion (ie, no detectable contrast transit profile) was discernible in either group. Within the hemodynamic penumbral zones, the relative perfusion index was significantly (P=.01) reduced in the mutant mice (35.6±1.5%) compared with wild-type mice (43.0±2.4%), consistent with the increased severity of ischemia after genetic deletion of eNOS (Fig 3).

View larger version (29K): [in this window] [in a new window]   Figure 2. Hemodynamic penumbra and core areas are represented as percentages of the total deficit (mean±SEM). Core areas are significantly larger and hemodynamic penumbral areas are significantly reduced in eNOS-deficient mutant mice compared with wild-type SV129 mice. *P=.03.

View larger version (33K): [in this window] [in a new window]   Figure 3. The relative "perfusion" index is calculated as the peak of the cerebral transit profile within the hemodynamic penumbra compared with the peak of cerebral transit profiles from the normal contralateral cortex. Penumbral perfusion is significantly decreased in the eNOS-deficient mutant mice compared with SV129 mice. **P=.01.

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion References Introduction  References

 
We compared perturbations in cerebrovascular hemodynamics during focal cerebral ischemia in wild-type and mutant mice deficient in eNOS gene expression using a novel image analysis technique. Differences were sought based on comparisons of cerebral transit profiles measured with TCM analysis in concert with functional CT scanning. We previously showed that this technique can measure hemodynamic gradients in ischemic brain after middle cerebral artery occlusion and thus can be used to visualize the hemodynamic core and penumbra with high spatial resolution.^{14 15 16 18} Other groups have also noted the functional significance of perturbations in cerebral transit profiles after contrast injection during focal ischemia.^{22 25 26}

Consistent with the predicted role for NO as a major blood vessel relaxant, genetic deletion of eNOS led to more severe hemodynamic deficits after focal ischemia. This was primarily identified as a proportionally smaller hemodynamic penumbral rim surrounding a core area. Within the hemodynamic penumbra itself, estimates of cerebral perfusion were also reduced, again reflecting the increased severity of the ischemic insult. Whether systemic arterial hypertension contributed to the size of the hemodynamic core and penumbra was not determined at this time. However, treatment of eNOS mutants with hydralazine to lower blood pressure did not decrease infarct volumes 24 hours after permanent middle cerebral artery occlusion.¹³

We and others have previously shown that the penumbra undergoes significant evolution over the first few hours after ischemia^{14 15 16 18 22 27} and therefore did not attempt to compare imaging data at 30 minutes with infarct size obtained 24 hours after middle cerebral artery occlusion. However, it is interesting to note that within an axial brain slice centered at the caudate putamen, ischemic infarct areas typically encompass 60% to 70% of the ipsilateral hemisphere after focal ischemia.^{7 8 13} This corresponds to the range of areas exhibiting hemodynamic deficits (including both core and penumbra) found in the present study.

Assessing cerebrovascular hemodynamics with TCM analysis in concert with functional CT scanning compares favorably with more traditional methods such as microsphere injections or tracer autoradiography. The spatial resolution with functional CT is high (0.1x0.1-mm pixels), and hemodynamic changes can potentially be assessed over time. Autoradiography is technically challenging in mice, and microspheres do not provide sufficient spatial resolution for the small mouse brain. Therefore, the image analysis technique offers a powerful alternative approach, despite the fact that it does not provide absolute measurements of blood flow per se. Furthermore, measuring changes in the shape of cerebral transit profiles (ie, hemodynamic alterations) may provide data that are complementary to measurements of volumetric flow rates within the ischemic periphery.¹⁶

In conclusion, dynamic CT scanning demonstrates significant differences in the hemodynamic core and penumbra after middle cerebral artery occlusion in eNOS mutants and wild-type mice. This suggests that NO derived from endothelial sources may mediate compensatory mechanisms of vasodilation and collateral recruitment that can temporarily sustain the hemodynamic penumbral zone after focal ischemia. Further examination of the hemodynamic penumbra with the described imaging technique may offer additional insights into the complex role of NO in stroke evolution.

	Selected Abbreviations and Acronyms

 

eNOS = endothelial nitric oxide synthase NCOR = normalized correlation coefficient nNOS = neuronal nitric oxide synthase NO = nitric oxide TCM = temporal correlation mapping

	Acknowledgments

 
This study was funded in part by National Institute of Neurological Disorders and Stroke grant R29 NS-32806 (Dr Lo), an American Heart Association Grant-in-Aid (Dr Lo), a Biomedical Engineering Research Grant from the Whitaker Foundation (Dr Rogowska), and Interdepartmental Stroke Program Project grant NS-10828 (Dr Moskowitz). The authors thank Mary Theresa Shore for expert assistance with the functional CT scanning procedures and Dr Elkan Halpern for advice on the choice of statistical thresholds.

Received March 6, 1996; revision received April 15, 1996; accepted April 19, 1996.

	References

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1. Dalkara T, Moskowitz MA. The complex role of nitric oxide in the pathophysiology of focal cerebral ischemia. Brain Pathol. 1994;4:49-57.[Medline] [Order article via Infotrieve]

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6. Hara H, Huang PL, Panahian N, Fishman MC, Moskowitz MA. Reduced brain edema and infarction volume in mice lacking neuronal isoform of nitric oxide synthase after transient MCA occlusion. J Cereb Blood Flow Metab. 1996;16:605-611.[Medline] [Order article via Infotrieve]

7. Huang Z, Huang PL, Panahian N, Dalkara T, Fishman MC, Moskowitz MA. Effects of cerebral ischemia in mice deficient in neuronal nitric oxide synthase. Science. 1994;265:1883-1885.[Abstract/Free Full Text]

8. Huang Z, Huang PL, Fishman MC, Moskowitz MA. Focal cerebral ischemia in mice deficient in either endothelial (eNOS) or neuronal nitric oxide (nNOS) synthase. Stroke. 1996;27:173. Abstract.

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13. Huang Z, Huang PL, Ma J, Meng W, Ayata C, Fishman MC, Moskowitz MA. Enlarged infarcts in endothelial nitric oxide synthase knockout mice are attenuated by nitro-L-arginine. J Cereb Blood Flow Metab. In press.

14. Lo EH, Rogowska J, Bogorodzki P, Trocha M, Matsumoto K, Saffran BN, Wolf GL. Temporal correlation analysis of penumbral dynamics in focal cerebral ischemia. J Cereb Blood Flow Metab. 1995;16:60-68.

15. Lo EH, Rogowska J, Bogorodzki P, Trocha M, Matsumoto K, Saffran BN, Wolf GL. A new method for imaging the penumbra in focal ischemia: temporal evolution and correlation with histologic outcomes. J Cereb Blood Flow Metab. 1995;15(suppl 1):s324. Abstract.

16. Lo EH, Rogowska J, Batchelder K, Wolf GL. Hemodynamic alterations in focal cerebral ischemia: temporal correlation analysis for functional imaging. Neurol Res. 1996;18:150-156.[Medline] [Order article via Infotrieve]

17. Rogowska J, Preston K, Hunter GJ, Hamberg LM, Kwong KK, Salonen O, Wolf GL. Applications of similarity mapping in dynamic MRI. IEEE Trans Med Imaging. 1995;14:480-486.[Medline] [Order article via Infotrieve]

18. Rogowska J, Lo EH, Bogorodzki P, Trocha M, Wolf GL. New temporal correlation techniques for imaging the penumbra in stroke. Pharm Res. 1995;12:s102. Abstract.

19. Zierler KL. Theoretical basis for indicator dilution methods for measuring flow and volume. Circ Res. 1962;10:393-407.[Free Full Text]

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Editorial Comment

Pak H. Chan, PhD, Guest Editor

Department of Neurosurgery and Neurology, University of California, School of Medicine, San Francisco, Calif

	Introduction

Top Abstract Introduction Materials and Methods Results Discussion References Introduction  References

 
Despite intensive research efforts, the role of NO in the pathogenesis of ischemic brain injury still remains unclear and is at times controversial. NO has been proposed as either neurotoxic to or neuroprotective of the central nervous system.^{1R 2R 3R} The cellular specificity and functional diversity of the three existing isozyme forms of NO synthases (ie, neuronal, endothelial, and inducible) and their complex responses to pharmacological agents and inhibitors may account for this uncertainty.

To address this issue, alternative strategies have successfully used molecular genetic approaches to create transgenic and knockout mutants that target these three NO synthase genes.^{4R 5R 6R}

In a series of elegant studies in which both neuronal and endothelial mutant mice were used, Moskowitz and colleagues demonstrated that NO produced by nNOS contributes to ischemic neuronal damage after focal and global ischemia, whereas the NO produced by eNOS protects neurons from focal stroke.^{7R 8R}

In the accompanying article, Lo and colleagues further extend these studies into the early hemodynamic changes in eNOS (-/-) mutants after 30 minutes of focal cerebral ischemia, measured by cerebral transit profiles of a contrast agent with the use of functional CT scanning. They found that hemodynamic deficits are significantly increased in mutant mice deficient in eNOS activity compared with wild-type mice. Thus, the present study confirms and extends the concept that NO produced by eNOS is beneficial to neurons after a focal stroke. In addition, this unique physiological study in which knockout mutant mice were used affirms the concept that transgenic and knockout mutants are useful tools to study the physiological and pathological roles of a particular gene and its gene product in cerebrovascular diseases.^9R

	Selected Abbreviations and Acronyms

 

eNOS = endothelial nitric oxide synthase NCOR = normalized correlation coefficient nNOS = neuronal nitric oxide synthase NO = nitric oxide TCM = temporal correlation mapping

MABP indicates mean arterial blood pressure. Values are mean±SEM.

*P<.05, difference between wild-type and eNOS mutants.

	References

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1R. Choi DW. Nitric oxide: foe or friend to the injured brain? Proc Natl Acad Sci U S A.. 1993;90:9741-9743.[Free Full Text]

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3R. Iadecola C, Pelligrino DA, Moskowitz MA, Lassen NA. Nitric oxide synthase inhibition and cerebrovascular regulation. J Cereb Blood Flow Metab.. 1994;14:175-192.

4R. Huang PL, Dawson PM, Bredt DS, Snyder SH, Fishman ME. Targeted disruption of the neuronal nitric oxide synthase gene. Cell.. 1993;75:1273-1286.[Medline] [Order article via Infotrieve]

5R. Huang PL, Huang Z, Mashimo H, Bloch KD, Moskowitz MA, Bevan JA, Fishman MC. Hypertension in mice lacking the gene for endothelial nitric oxide synthase. Nature.. 1995;377:239-242.

6R. MacMicking JD, Nathan C, Hom G, Chartrain N, Fletcher DS, Trumbauer M, Stevens K, Xie Q-W, Sokol K, Hutchinson N, Chen H, Mudgett JS. Altered responses to bacterial infection and endotoxic shock in mice lacking inducible nitric oxide synthase. Cell.. 1995;81:641-650.[Medline] [Order article via Infotrieve]

7R. Huang Z, Huang PL, Panahian N, Dalkara T, Fishman M, Moskowitz MA. Effects of cerebral ischemia in mice deficient in neuronal nitric oxide synthase. Science.. 1994;265:1883-1885.

8R. Huang Z, Huang PL, Fishman MC, Moskowitz MA. Focal cerebral ischemia in mice deficient in either endothelial (eNOS) or neuronal nitric oxide (nNOS) synthase. Stroke.. 1996;27:173. Abstract.

9R. Chan PH. Role of oxidants in ischemic brain damage. Stroke.. 1996;27:1124-1129.[Abstract/Free Full Text]

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				J. Hatazawa, E. Shimosegawa, H. Toyoshima, B. A. Ardekani, A. Suzuki, T. Okudera, and Y. Miura Cerebral Blood Volume in Acute Brain Infarction : A Combined Study With Dynamic Susceptibility Contrast MRI and 99mTc-HMPAO-SPECT Stroke, April 1, 1999; 30(4): 800 - 806. [Abstract] [Full Text] [PDF]

				M. Shimizu-Sasamata, P. Bosque-Hamilton, P. L. Huang, M. A. Moskowitz, and E. H. Lo Attenuated Neurotransmitter Release and Spreading Depression-Like Depolarizations after Focal Ischemia in Mutant Mice with Disrupted Type I Nitric Oxide Synthase Gene J. Neurosci., November 15, 1998; 18(22): 9564 - 9571. [Abstract] [Full Text] [PDF]

				M. Shimizu-Sasamata, T. Kano, J. Rogowska, G. L. Wolf, M. A. Moskowitz, E. H. Lo, and C. Iadecola YM872, a Highly Water-Soluble AMPA Receptor Antagonist, Preserves the Hemodynamic Penumbra and Reduces Brain Injury After Permanent Focal Ischemia in Rats • Editorial Comment Stroke, October 1, 1998; 29(10): 2141 - 2148. [Abstract] [Full Text] [PDF]

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