Neuroprotective effects depend on the model of focal ischemia following middle cerebral artery occlusion

Neuroprotective effects of oleic acid in rodent models of cerebral ischaemia

Oleic acid (OA) is released from brain phospholipids after cerebral ischaemia; however, its role in ischaemic injury remains unknown. We hypothesised that OA has neuroprotective effects after cerebral ischaemia, which may be exerted through peroxisome proliferator-activated receptor gamma (PPAR-γ) activation, since OA is an endogenous ligand of PPAR-γ. The effects of OA administration were evaluated in rodent models of middle cerebral artery occlusion (MCAO), photothrombosis, and four-vessel occlusion (4-VO). We determined the time window of therapeutic opportunity and examined the ability of the PPAR-γ antagonist GW9662 to reverse OA’s protective effects after MCAO. We found that OA administration decreased the MCAO-induced infarct volume and functional deficits, photothrombosis-induced infarct volume, and 4-VO-induced hippocampal neuronal death. Additionally, OA was highly efficacious when administered up to 3 h after MCAO. Pre-treatment with GW9662 abolished the inhibitory effects of OA on the infarct volume and immunoreactivity of key inflammatory mediators in the ischaemic cortex. Our results indicate that OA has neuroprotective effects against transient and permanent focal cerebral ischaemia, as well as global cerebral ischaemia. It may have therapeutic value for the ischaemic stroke treatment with a clinically feasible therapeutic window. The OA-mediated neuroprotection might be attributable to its anti-inflammatory actions through PPAR-γ activation.

MK-801 attenuates lesion expansion following acute brain injury in rats: a meta-analysis

OBJECTIVE:

To evaluate the efficacy and safety of MK-801 and its effect on lesion volume in rat models of acute brain injury.

DATA SOURCES:

Key terms were “stroke”, “brain diseases”, “brain injuries”, “brain hemorrhage, traumatic”, “acute brain injury”, “dizocilpine maleate”, “dizocilpine”, “MK-801”, “MK801”, “rat”, “rats”, “rattus” and “murine”. PubMed, Cochrane library, EMBASE, the China National Knowledge Infrastructure, WanFang database, the VIP Journal Integration Platform (VJIP) and SinoMed databases were searched from their inception dates to March 2018.

DATA SELECTION:

Studies were selected if they reported the effects of MK-801 in experimental acute brain injury. Two investigators independently conducted literature screening, data extraction, and methodological quality assessments.

OUTCOME MEASURES:

The primary outcomes included lesion volume and brain edema. The secondary outcomes included behavioral assessments with the Bederson neurological grading system and the water maze test 24 hours after brain injury.

RESULTS:

A total of 52 studies with 2530 samples were included in the systematic review. Seventeen of these studies had a high methodological quality. Overall, the lesion volume (34 studies, n = 966, MD = −58.31, 95% CI: −66.55 to −50.07; P < 0.00001) and degree of cerebral edema (5 studies, n = 75, MD = −1.21, 95% CI: −1.50 to −0.91; P < 0.00001) were significantly decreased in the MK-801 group compared with the control group. MK-801 improved spatial cognition assessed with the water maze test (2 studies, n = 60, MD = −10.88, 95% CI: −20.75 to −1.00; P = 0.03) and neurological function 24 hours after brain injury (11 studies, n = 335, MD = −1.04, 95% CI: −1.47 to −0.60; P < 0.00001). Subgroup analysis suggested an association of reduction in lesion volume with various injury models (34 studies, n = 966, MD = −58.31, 95% CI: −66.55 to −50.07; P = 0.004). Further network analysis showed that 0–1 mg/kg MK-801 may be the optimal dose for treatment in the middle cerebral artery occlusion animal model.

CONCLUSION:

MK-801 effectively reduces brain lesion volume and the degree of cerebral edema in rat models of experimental acute brain injury, providing a good neuroprotective effect. Additionally, MK-801 has a good safety profile, and its mechanism of action is well known. Thus, MK-801 may be suitable for future clinical trials and applications.

Ginsenoside Rd for acute ischemic stroke: translating from bench to bedside

Numerous studies have identified pathophysiological mechanisms of acute ischemic stroke and have provided proof-of-principle evidence that strategies designed to impede the ischemic cascade, namely neuroprotection, can protect the ischemic brain. However, the translation of these therapeutic agents to the clinic has not been successful. Ginsenoside Rd, a dammarane-type steroid glycoside extracted from ginseng plants, has exhibited an encouraging neuroprotective efficacy in both laboratory and clinical studies. This article attempts to provide a synopsis of the physiochemical profile, pharmacokinetics, pharmacodynamics, clinical efficacy, safety and putative therapeutic mechanisms of Rd. Finally, the authors discuss the validity of Rd as a neuroprotective agent for acute ischemic stroke.

Cerebroprotective effects of TAK-937, a novel cannabinoid receptor agonist, in permanent and thrombotic focal cerebral ischemia in rats: therapeutic time window, combination with t-PA and efficacy in aged rats

Some occluded arteries of acute ischemic stroke (AIS) patients are not recanalized, even if thrombolytic therapy is performed. Considering such clinical settings, we examined the potential cerebroprotective efficacy of TAK-937, a novel cannabinoid receptor agonist, in young adult and aged rats with a permanent middle cerebral artery occlusion (MCAO) model and conducted a combination study with TAK-937 and tissue type plasminogen activator (t-PA) in a rat thrombotic MCAO model. TAK-937 significantly reduced infarct volume when it was administered 3 and 5h after permanent MCAO in young adult rats. A thrombotic MCAO was induced by photo-irradiation of the middle cerebral artery with Rose Bengal administration and a permanent MCAO was produced by thermoelectric coagulation of occluded arteries. TAK-937 (10, 30 and 100μg/kg/h) was intravenously infused 1, 3, 5, or 8-24h after MCAO. t-PA (3 or 10mg/kg) was intravenously administered 1, 1.5 or 2h after MCAO. Infarct volume was determined using a 2,3,5-triphenyltetrazolium chloride staining method 24 or 48h after MCAO. The combined treatment of TAK-937 with t-PA significantly reduced the cerebral infarction compared with t-PA treatment alone in a rat thrombotic MCAO model. TAK-937 reduced infarct volume of aged rats as well, when it was administered 1h after permanent MCAO. These results suggest that TAK-937 exerts protective effects regardless of age and has a wide therapeutic time window in permanent occlusion. Furthermore, combined treatment of TAK-937 with t-PA would provide more therapeutic efficacy compared to t-PA treatment alone.

Multiparametric assessment of acute and subacute ischemic neuronal damage: a small animal positron emission tomography study with rat photochemically induced thrombosis model

We evaluated sequential changes in rat brain function up to 14 days after focal ischemic insult with a small animal positron emission tomography (PET). Unilateral focal ischemic cerebral damage was induced by left middle cerebral artery occlusion with a photochemically induced thrombosis (PIT) method. PET scans were conducted with [(11)C](R)-PK11195 ([(11)C](R)-PK) for peripheral benzodiazepine receptor (PBR), [(11)C]flumazenil ([(11)C]FMZ) for central benzodiazepine receptor (CBR), and [(18)F]fluoro-2-deoxy-D-glucose ([(18)F]FDG) for glucose metabolism at before (as "Normal") and after PIT. At 1 and 3 days after PIT, [(18)F]FDG indicated lower uptake in the infarct area. Interestingly, unexpectedly high-[(18)F]FDG uptake was observed in the peri-infarct area surrounding the infarct area at day 7. The high-[(18)F]FDG uptake region completely overlapped with the high-[(11)C](R)-PK uptake region at day 7, which resulted in the underestimation of neuronal damage. Immunohistochemical data also suggested that the high-[(18)F]FDG uptake peak at day 7 was caused by inflammation including microglial cell activation. In contrast, imaging with [(11)C]FMZ indicated cortical neuronal damage on days 7 and 14 without any disturbance by microglial formation. These results indicated that [(18)F]FDG might not be a suitable ligand for ischemic neuronal damage detection from acute to subacute phases.

In vivo distribution of liposome-encapsulated hemoglobin determined by positron emission tomography

Positron emission tomography (PET) is a noninvasive imaging technology that enables the determination of biodistribution of positron emitter-labeled compounds. Lipidic nanoparticles are useful for drug delivery system (DDS), including the artificial oxygen carriers. However, there has been no appropriate method to label preformulated DDS drugs by positron emitters. We have developed a rapid and efficient labeling method for lipid nanoparticles and applied it to determine the movement of liposome-encapsulated hemoglobin (LEH). Distribution of LEH in the rat brain under ischemia was examined by a small animal PET with an enhanced resolution. While the blood flow was almost absent in the ischemic region observed by [(15)O]H(2)O imaging, distribution of (18)F-labeled LEH in the region was gradually increased during 60-min dynamic PET scanning. The results suggest that LEH deliver oxygen even into the ischemic brain from the periphery toward the core of ischemia. The real-time observation of flow pattern, deposition, and excretion of LEH in the ischemic rodent brain was possible by the new methods of positron emitter labeling and PET system with a high resolution.

Comparing two methods for assessment of perfusion-diffusion mismatch in a rodent model of ischaemic stroke: a pilot study

This stroke experiment was designed to define the mismatch between perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) in MRI by applying early or instantly acquired PWI. Eight rats were induced with stroke through photothrombotic occlusion of the middle cerebral artery and scanned serially between 1 h and day 3 after induction using DWI and PWI with a 1.5 T MR scanner. The relative lesion volumes (rLV) on MRI and triphenyl tetrazolium chloride-stained specimens were defined as the proportion of lesion volume over brain volume. Discrepancies in the rLV between PWI- and DWI-derived apparent diffusion coefficient (ADC) maps were expressed by subtraction of the ADC from PWI, resulting in three possible patterns: (i) (PWI-ADC > 10% of PWI) denoting a mismatch; (ii) (-(10% of PWI) <or= PWI-ADC <or= 10% of PWI) denoting a match; and (iii) (PWI-ADC < -(10% of PWI)) denoting a reverse mismatch. The differences were compared with the minuend being either early PWI (ePWI) or instant PWI (iPWI) and the subtrahend being instant ADC (iADC). The occurrence and evolution of PWI-ADC patterns were analysed. Over time, PWI-ADC discrepancies evolved from mismatch, through to match, to reversed mismatch. The PWI-ADC mismatch still existed 3 days after MCA occlusion in one to three of the eight cases. The rLVs and mismatch incidences between the ePWI-iADC and iPWI-iADC models were linear correlated. A higher mismatch rate occurred in iPWI-iADC within day 1 and in ePWI-iADC at day 3. Both ePWI and iPWI proved useful to define PWI-ADC patterns within day 1. At day 3, iPWI appeared more adequate.

Pulse radiolysis study on free radical scavenger edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one)

The reactions between edaravone and various one-electron oxidants such as (*)OH, N(3)(*), Br(2)(-), and SO(4)(-), have been studied by pulse radiolysis techniques. The transient species produced by the reaction of edaravone with (*)OH radical shows an absorption band with lambda(max)=320 nm, while the oxidation by N(3)(*), Br(2)(-), SO(4)(-) and CCl(3)OO(*) results in an absorption band with lambda(max)=345 nm. Different from the previous reports, the main transient species by the reaction of edaravone with (*)OH radical in the absence of O(2) is attributed to OH-adducts. At neutral condition (pH 7), the rate constants of edaravone reacting with (*)OH, N(3)(*), SO(4)(-), CCl(3)OO(*), and e(aq)(-) are estimated to be 8.5x10(9), 5.8x10(9), 6x10(8), 5.0x10(8) and 2.4x10(9)dm(3)mol(-1)s(-1), respectively. From the pH dependence on the formation of electron adducts and on the rate constant of edaravone with hydrated electron, the pK(a) of edaravone is estimated to be 6.9+/-0.1.

Quantitative assessments of cerebral vascular damage with a silicon rubber casting method in photochemically-induced thrombotic stroke rat models

Previous studies have described microvascular disturbances downstream of occluded large vessels arising during the acute phase (several hours) following cerebral ischemic insult. Prolonged microvascular disturbances may cause delayed neuronal cell death in ischemic penumbral regions, leading to expanded brain infarctions and poor neurological and functional outcomes. The lack of simple and quantitative methods for investigating this microcirculation failure suggests the need to develop a new method for clarifying the precise distribution and persistence of post-ischemic microvascular disturbances. The present study used a silicone rubber casting method in quantitative analyses of microvascular conditions in photochemically-induced thromboembolic (PIT) stroke rat models. After the casting procedure in rats with PIT stroke, a 6 microm-thick coronal section was obtained, and quantitative analyses of microvascular density and measurements of the infarct area in the serial section were performed. The major findings of the present study are as follows: (1) Silicone rubber casting techniques can be applied to precise quantitative analyses of microvessels in the same individual in whom brain infarct volume was measured; (2) the persistence and spatial distribution of microvascular disturbances assessed at the ischemic core, ischemic penumbra, and non-ischemic regions strongly suggest that microvascular disturbances affect brain infarct expansion; (3) the current method demonstrated the protective effects of MK-801 on microvessels, indicating that the technique may be useful in investigating factors that provide vascular protection. The experimental procedure introduced here would facilitate future evaluations of vascular protective agents.

Serum S100B is a useful surrogate marker for long-term outcomes in photochemically-induced thrombotic stroke rat models

In recent years, serum S100B has been used as a secondary endpoint in some clinical trials, in which serum S100B has successfully indicated the benefits or harm done by the tested agents. Compared to clinical stroke studies, few experimental stroke studies report using serum S100B as a surrogate marker for estimating the long-term effects of neuroprotectants. This study sought to observe serum S100B kinetics in PIT stroke models and to clarify the association between serum S100B and both final infarct volumes and long-term neurological outcomes. Furthermore, to demonstrate that early elevations in serum S100B reflect successful neuroprotective treatment, a pharmacological study was performed with a non-competitive NMDA glutamate receptor antagonist, MK-801. Serum S100B levels were significantly elevated after PIT stroke, reaching peak values 48 h after the onset and declining thereafter. Single measurements of serum S100B as early as 48 h after PIT stroke correlated significantly with final infarct volumes and long-term neurological outcomes. Elevated serum S100B was significantly attenuated by MK-801, correlating significantly with long-term beneficial effects of MK-801 on infarct volumes and neurological outcomes. Our results showed that single measurements of serum S100B 48 h after PIT stroke would serve as an early and simple surrogate marker for long-term evaluation of histological and neurological outcomes in PIT stroke rat models.

Microplasmin and tissue plasminogen activator: comparison of therapeutic effects in rat stroke model at multiparametric MR imaging

PURPOSE

To prospectively compare therapeutic and hemorrhagic effects of microplasmin and tissue plasminogen activator (tPA) in stroke therapy by using multiparametric magnetic resonance (MR) imaging in a photothrombotic rat stroke model.

MATERIALS AND METHODS

The animal experiment complied with institutional regulations for laboratory animals. Stroke was induced in rats with photothrombotic occlusion of middle cerebral artery (MCA). T2-weighted, perfusion-weighted (PW), and diffusion-weighted (DW) MR imaging was performed 1 hour and 24 hours after occlusion. On the basis of PW and DW images at 1 hour, 49 rats with cortex and subcortex involvement and with perfusion-diffusion mismatch were randomly assigned into one of four groups: control group, group treated with 7.5 mg microplasmin, group treated with 10 mg/kg microplasmin, or group treated with 10 mg/kg tPA. Agents were intravenously injected 1.5 hours after occlusion. Infarct size and hemorrhagic transformation were assessed with MR imaging and histomorphologic findings. Neurologic deficit was scored. Measurements were statistically analyzed.

RESULTS

There were 13 rats in the control group, 13 in the 7.5 mg/kg microplasmin group, nine in the 10 mg/kg microplasmin group, and 14 in the 10 mg/kg tPA group. Despite similar baseline perfusion-diffusion mismatch, histochemically defined total infarct volume was reduced from 25% +/- 5 (standard deviation) in control group to 21% +/- 2, 20% +/- 4, and 20% +/- 5 in 7.5 mg/kg microplasmin, 10 mg/kg microplasmin, and tPA groups, respectively, as similarly shown on T2-weighted, DW, and PW images at 24 hours (P < .05). Cerebral hemorrhage rate at 24 hours was higher in tPA group than in the other three groups. Bederson score of neurologic deficits was significantly reduced in treated groups compared with that in control group.

CONCLUSION

Perfusion-diffusion mismatch appeared useful in selecting candidates for thrombolytic therapy. Multiparametric MR imaging allowed noninvasive assessment of effects of microplasmin and tPA in rats; microplasmin had a significantly lower hemorrhagic rate.

Liposome-encapsulated hemoglobin reduces the size of cerebral infarction in the rat: evaluation with photochemically induced thrombosis of the middle cerebral artery

BACKGROUND AND PURPOSE

Liposome-encapsulated hemoglobin (LEH; TRM-645) is a novel oxygen (O(2)) carrier with a lower O(2) affinity (P(50)O(2)=40 mm Hg) than red blood cells. In contrast to cell-free hemoglobin, encapsulation prevents hemoglobin extravasation, whereas its subcellular size (230 nm) may improve O(2) delivery and limit the severity of cerebral infarction.

METHODS

The extent of cerebral infarction was determined 24 hours after photochemically induced thrombosis of the middle cerebral artery from the integrated area of infarction detected by triphenyltetrazolium chloride staining in rats receiving no treatment, 10 mL/kg of LEH, homologous blood, empty liposomes, or saline. To develop a dose-response relationship, LEH dose was reduced from 10 mL/kg to 2 mL/kg, 0.4 mL/kg, and 0.08 mL/kg.

RESULTS

Infarction extent was significantly suppressed in rats receiving LEH as compared with animals receiving no infusion, saline, empty liposome, or transfusion in the cortex but not in the basal ganglia, where all had similar degrees of damage. The dose-response relationship revealed that as little as 2 mL/kg of LEH was protective, whereas the total blood O(2) content, hemoglobin level, and transfusion and/or infusion of empty liposomes or saline were not effective.

CONCLUSIONS

Our results suggest that LEH significantly reduces the area of infarction in the cortex but not in basal ganglia after photochemically induced thrombosis of the middle cerebral artery in the rat.

Rodent stroke induced by photochemical occlusion of proximal middle cerebral artery: evolution monitored with MR imaging and histopathology

PURPOSE

To longitudinally investigate stroke in rats after photothrombotic occlusion of proximal middle cerebral artery (MCA) with magnetic resonance imaging (MRI) in correlation with histopathology.

MATERIALS AND METHODS

Forty-two rats were subjected to photochemical MCA occlusion and MRI at 1.5T, and sacrificed in seven groups (n=6 each) at the following time points: 1, 3, 6 and 12h, and at day 1, 3 and 9. T2-weighted (T2WI) and diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) map was performed in all rats. Contrast-enhanced T1-weighted imaging (CE-T1WI) was compared to intravital staining with Evans blue in one group for assessing blood-brain barrier (BBB) integrity. The brain was stained histochemically with triphenyl tetrazolium chloride (TTC) and processed for pathological assessment. The evolutional changes of relative lesion volume, signal intensity (SI), and the BBB integrity on MRI with corresponding histopathology were evaluated.

RESULTS

The ischemic lesion volume reached a maximum around 12h to day 1 as visualized successively by DWI, ADC map and T2WI, implicating the evolving pathology from cytotoxic edema through vasogenic edema to tissue death. The ADC of brain infarction underwent a significant reversion after 12h, reflecting the colliquative necrosis. On CE-T1WI, BBB leakage peaked at 6h and at day 3 with a transitional partial recovery around 24h. The infarct volume on T2WI, DWI and ADC map matched well with that on TTC staining at 12h and at day 1 (p>0.05).

CONCLUSION

The evolution of the present photothrombotic stroke model in rats could be characterized by MRI. The obtained information may help longitudinal studies of cerebral ischemia and anti-stroke agents using the same model.

Characterization of a thromboembolic photochemical model of repeated stroke in mice

Many stroke research groups utilize the model of middle cerebral artery occlusion induced by insertion of an intraluminal thread, owing to its pragmatism and reliability of cerebral infarct generation. However, 75% of stroke cases result from a thromboembolic event and 10% from occlusive atherothrombosis in situ. Here, we characterize a mouse model of repeated thromboembolic stroke, which closely mimics the intravascular pathophysiology of arterial thrombus generation from an atherosclerotic plaque, and subsequent release of a thrombus into the cerebral circulation as an embolus. Common carotid artery thrombosis (CCAT) was induced photochemically leading to non-occlusive platelet aggregation in C57/BL6 male mice (n=35), and was followed by mechanical assistance to facilitate release of the thrombus (MRT) and thus promote embolism. Six experimental groups, differing by changes in the surgical protocol, were used for the purpose of determining which such procedure yielded the most reliable and consistent brain infarct volumes with the lowest mortality at 3 days after surgery. The group which best satisfied these conditions was a double insult group which consisted of animals that underwent CCAT for 2 min by means of argon laser irradiation (514.5 nm) at an intensity of ca. 130 W/cm(2), with concomitant injection of erythrosin B (EB) (35 mg/kg infused over those same 2 min), followed by MRT 1 min later; the entire procedure was repeated 24h later. This group showed a percent of brain lesion volume of 15+/-4% (mean+/-S.D.) with no associated 3-day mortality. Compared to a single insult group which sustained a percent brain lesion volume of 7+/-3%, there was a statistically significant (p<0.05) increase in the volume of infarction in the double-insult group.

Delayed perfusion phenomenon in a rat stroke model at 1.5T MR: An imaging sign parallel to spontaneous reperfusion and ischemic penumbra?

INTRODUCTION

Delayed perfusion (DP) sign at MR imaging was reported in stroke patients. We sought to experimentally elucidate its relation to spontaneous reperfusion and ischemic penumbra.

METHODS

Stroke was induced by photothrombotic occlusion of middle cerebral artery in eight rats and studied up to 72 h using a 1.5 T MR scanner with T2 weighted imaging (T2WI), diffusion weighted imaging (DWI), and dynamic susceptibility contrast-enhanced perfusion weighted imaging (DSC-PWI). Relative signal intensity (rSI), relative lesion volume (rLV), relative cerebral blood flow (rCBF), PWI(rLV)-DWI(rLV) mismatch (penumbra) and DP(rLV) were quantified and correlated with neurological deficit score (NDS), triphenyl tetrazolium chloride (TTC) staining, microangiography (MA) and histopathology.

RESULTS

The rSI and rLV characterized this stroke model on different MRI sequences and time points. DSC-PWI reproduced cortical DP in all rats, where rCBF evolved from 88.9% at 1 h through 64.9% at 6 h to 136.3% at 72 h. The PWI(rLV)-DWI(rLV) mismatch reached 10+/-5.4% at 1 h, remained positive through 12 h and decreased to -3.3+/-4.5% at 72 h. The incidence and rLV of the DP were well correlated with those of the penumbra (p<0.01, r(2)=0.85 and p<0.0001, r(2)=0.96, respectively). Shorter DP durations and more collateral arterioles occurred in rats without (n=4) than with (n=4) cortex involvement (p<0.05). Rats without cortex involvement tended to earlier reperfusion and a lower NDS. Microscopy confirmed MRI, MA and TTC findings.

CONCLUSIONS

In this rat stroke model, we reproduced clinically observed DP on DSC-PWI, confirmed spontaneous reperfusion, and identified the penumbra extending to 12h post-ischemia, which appeared interrelated.

Injury to axons and oligodendrocytes following endothelin-1-induced middle cerebral artery occlusion in conscious rats

Injury to axons and oligodendrocytes has been poorly characterized in most animal models of stroke, and hence has been difficult to target therapeutically. It is therefore necessary to characterize axonal and oligodendroglial injury in these models, in order to rationally design putative protective compounds that minimize this injury. This study aims to characterize injury to axons and oligodendrocytes in the endothelin-1 (ET-1) model of middle cerebral artery occlusion (MCAO) in conscious rats. Transient forebrain ischemia was induced in conscious adult male Long Evans rats by the perivascular microinjection of ET-1. Quantitative histopathology was performed on forebrain sections at 6, 24, 48 and 72 h after ET-1 administration, using ballistic light analyses and immunohistochemistry for amyloid precursor protein (APP), SMI32, and Tau-1. Ballistic light analyses of cortical and striatal lesions revealed that the infarct volume was maximal in these regions by 6 h. APP and SMI32 immunohistochemistry demonstrated that axonal injury was maximal by 6 h in this model; however, some injured axons appeared to maintain good structural integrity up to 72 h after insult. Density measurements for Tau-1-immunopositive oligodendrocytes were significantly elevated within the corpus callosum from 48 h, but reductions in total oligodendrocyte numbers were not apparent up 72 h after ET-1 injection. These results indicate that axonal and oligodendroglial injury should be investigated as potential targets for delayed therapeutic intervention after MCAO.

Neuroprotective effects of KCL-440, a new poly(ADP-ribose) polymerase inhibitor, in the rat middle cerebral artery occlusion model

It is reported that ischemic brain injury is mediated by the activation of poly(ADP-ribose) polymerase (PARP). In this study, we examined the pharmacological profile of KCL-440, a new PARP inhibitor, and its neuroprotective effects in the rat acute cerebral infarction model induced by photothrombotic middle cerebral artery (MCA) occlusion. In an in vitro study, KCL-440 exhibited potency with regard to inhibition of PARP activity, with an IC50 value of 68 nM. An in vivo pharmacokinetic study showed that the brain concentration of KCL-440 was sufficient to inhibit PARP activity during the intravenous infusion of KCL-440 at the rate of 1 mg/kg/h. KCL-440 at various doses or saline was administered for 24 h immediately after the MCA occlusion. Administration of KCL-440 led to a dose-dependent reduction in the infarct size at 24 h after MCA occlusion. Infarct sizes were 44.8% +/- 3.0% (n = 8), 40.5% +/- 1.1% (n = 8), 38.2% +/- 1.4% (n = 8), 35.1% +/- 2.1% (n = 8), 34.2% +/- 2.3% (n = 7), 32.6% +/- 1.9% (n = 8), and 31.0% +/- 2.1% (n = 5) at doses of 0, 0.01, 0.03, 0.1, 0.3, 1.0, and 3.0 mg/kg/h. When compared to the control group, a statistically significant difference was observed in the doses that were higher than 0.03 mg/kg/h. When the infusion of KCL-440 (1 mg/kg/h, n = 8) was started at 1 h after the MCA occlusion, a significant reduction in infarct size was observed; this was not observed when KCL-440 infusion was started 2 or 3 h after the MCA occlusion. Furthermore, increased poly(ADP-ribose) immunostaining was confirmed at the ischemic border zone 2 h after the MCA occlusion, and it was reduced by KCL-440 treatment. These results suggest that KCL-440 is a possible neuroprotective agent with high blood-brain barrier permeability and high PARP inhibitory activity.

Systematic review and metaanalysis of the efficacy of FK506 in experimental stroke

FK506 is a candidate drug for acute stroke. For such drugs, any decision to proceed to clinical trial should be based on a full and unbiased assessment of the animal data, and consideration should be given to the limitations of those data. Such an assessment should include not only the efficacy of a drug but also the in vivo characteristics and limits to that efficacy. Here we use systematic review and meta-analysis to assess the evidence for a protective effect of FK506 in animal models of stroke. In all, 29 studies were identified describing procedures involving 1759 animals. The point estimate for the effect of FK506 was a 31.3% (95% confidence interval 27.2% to 35.4%) improvement in outcome. Efficacy was higher with ketamine anaesthesia and temporary ischaemia and was lower in rats, in animals with comorbidities, and where outcome was measured as infarct size alone. Reported study quality was modest by clinical trial standards, and efficacy was lower in high-quality studies. These findings show a substantial efficacy for FK506 in experimental stroke, but raise concerns that our estimate of effect size might be too high because of factors such as study quality and possible publication bias.

Neuroprotective effects of the free radical scavenger Edaravone (MCI-186) in mice permanent focal brain ischemia

The present study was aimed to evaluate the effect of the free radical scavenger Edaravone on infarct volume due to permanent MCA occlusion in mice and, if so, to elucidate the mechanism of its neuroprotective effects. Male Balb/c mice were subjected to permanent middle cerebral artery occlusion and were treated with 3.0 mg/kg of Edaravone or vehicle 30 min before ischemia. Infarct volume was assessed by 2,3,5-triphenyltetrazolium chloride (TTC) method after 24 h. Furthermore, in situ detection of superoxide in the ipsilateral neocortex was carried out using the superoxide-sensitive dye dihydroethidium (DHE) staining technique. Pretreatment with 3.0 mg/kg of Edaravone ameliorated the tissue damage in the infarct rim and significantly reduced infarct volume to about 77% of the control (p<0.05). Semi-quantitative measurement of red fluorescence emitted from DHE revealed that the superoxide increased in the ischemic core at 1 h after the onset of ischemia and extended towards the infarct rim at 3 and 6 h, and that pretreatment with 3.0 mg/kg of Edaravone significantly inhibited the increase of superoxide in the infarct rim at 3 and 6 h (p<0.01). Double staining with DHE and monoclonal antibody against NeuN showed that the majority of the nuclei positive for DHE were also positive for NeuN. These findings suggest that Edaravone salvages the boundary zone of infarct by scavenging reactive oxygen species especially in the neurons during permanent focal cerebral ischemia.

Rat cerebral ischemia induced with photochemical occlusion of proximal middle cerebral artery: a stroke model for MR imaging research

A stroke model in rats with photochemically induced thrombosis (PIT) of proximal cerebral middle artery (MCA) is introduced for magnetic resonance imaging (MRI) study. Thirty-seven rats subjected to surgical and optical procedures for inducing the PIT models were scanned using a 1.5-T scanner with T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), diffusion-weighted imaging (DWI), and contrast-enhanced perfusion-weighted imaging (PWI) at 1 h and 24 h after MCA occlusion. The penumbra evolution and PWI-derived parameters including relative cerebral blood volume (rCBV) and relative cerebral blood flow (rCBF) were monitored; and the relative lesion size (RLS) was compared with the final RLS on the gold standard triphenyl tetrazolium chloride (TTC) staining at 24 h. The results showed that the focal cerebral ischemic lesions were detectable in all rats with different MR approaches. The lesion on PWI at 1 h and on all MR images at 24 h was matched well with that seen on TTC staining; the peri-infarct area decreased from 6.2 +/- 7.2% of the brain volume at 1 h to 0.3 +/- 5.6% at 24 h. Compared to that in the contralateral hemisphere, rCBV in ischemic region was 52.6 +/- 21.4 and 40.0 +/- 15.8% (p > 0.05), and rCBF was 64.6 +/- 11.2 and 47.3 +/- 11.1% (p < 0.05) at 1 h and 24 h respectively. The present PIT model in rats has been successfully adopted for MRI research, which might be feasible for certain stroke studies and should be beneficial for the evaluation on effects of potential diagnostic and therapeutic approaches.

Visualization of stroke with clinical MR imagers in rats: a feasibility study

This experiment was conducted in compliance with the guidelines of the International Committee on Thrombosis and Hemostasis and the current institutional regulations for use and care of laboratory animals. The purpose of the present study was to report the feasibility of using clinical magnetic resonance (MR) imaging devices for depiction of stroke in a rat model. Twenty-four rats with photochemically induced thrombosis of the middle cerebral artery were examined at superacute (1 hour, n = 24), acute (12 hours, n = 12), and subacute (24 hours, n = 12) phases with 1.5-T MR imaging weighted for T1, T2, diffusion, and gadopentetate dimeglumine-enhanced perfusion. With reasonable signal-to-noise ratio and imaging times, ischemic lesions were well distinguished on MR images as validated qualitatively and quantitatively with postmortem standard-of-reference techniques, including volume-rendered computed tomography, microangiography, and histochemistry. In the superacute phase, the perfusion defect at perfusion-weighted MR imaging was well matched with microangiographic and pathologic findings (P > .05). There was no difference in lesion size at perfusion-weighted MR imaging between superacute and subacute phases (P > .05). Performance of certain stroke-related research in rats is feasible with clinical MR imagers.

Effect of ifenprodil, a polyamine site NMDA receptor antagonist, on brain edema formation following asphyxial cardiac arrest in rats

OBJECTIVE

Brain edema occurs in experimental and clinical cardiac arrest (CA) and is predictive of a poor neurological outcome. N-Methyl--aspartate (NMDA) receptors contribute to brain edema elicited by focal cerebral ischemia/reperfusion (I/R). Ifenprodil, a NMDA receptor antagonist, attenuates brain edema and injury size in rats after focal cerebral I/R. We assessed the hypothesis that ifenprodil reduces CA-elicited brain edema.

METHODS

Eighteen male Sprague-Dawley rats were assigned to group 1 (normal control, n=6), group 2 (placebo-treated CA, n=6), or group 3 (ifenprodil-treated CA, n=6). CA was induced by 8 min of asphyxiation and the animals were resuscitated with cardiopulmonary resuscitation (CPR), ventilation, epinephrine (adrenaline), and sodium bicarbonate (NaHCO3). Ifenprodil of 10 mg/kg or a placebo vehicle was given intraperitoneally 5 min before CA. Brain edema was determined by brain wet-to-dry weight ratio at 1 h after resuscitation.

RESULTS

There were no differences between groups 2 and 3 in all physiological variables at baseline. Time from asphyxiation to CA was 201.5 +/- 7.5 s in group 2 and 160.7 +/- 10.4 s in group 3 (P<0.001). Resuscitation time was 68.2 +/- 13.3 s in group 2 and 92.8 +/- 18.2 s in group 3 (P<0.05). Ifenprodil decreased mean arterial pressure (MAP) before asphyxiation, from 128 +/- 7 in group 2 to 82 +/- 15 mmHg in group 3 (P<0.001), and negated immediate post-resuscitation hypertension. Brain wet-to-dry weight ratio was 5.64 +/- 0.44 in group 1, 7.34 +/- 0.95 in group 2 (P<0.01 versus group 1), and 5.93 +/- 0.40 in group 3 (P<0.05 versus group 2).

CONCLUSIONS

Ifenprodil reduces CA-elicited brain edema. In addition, we observed significant hemodynamic changes caused by ifenprodil.

Protective effects of a selective L-type voltage-sensitive calcium channel blocker, S-312-d, on neuronal cell death

Amyloid beta protein (Abeta)- and human group IIA secretory phospholipase A(2) (sPLA(2)-IIA)-induced neuronal cell death have been established as in vitro models for Alzheimer's disease (AD) and stroke. Both sPLA(2)-IIA and Abeta causes neuronal apoptosis by increasing the influx of Ca(2+) through L-type voltage-sensitive Ca(2+) channel (L-VSCC). In the present study, we evaluated effects of a selective L-VSCC blocker, S-(+)-methyl 4,7-dihydro-3-isobutyl-6-methyl-4-(3-nitro-phenyl)thieno[2,3-b]pyridine-5-carboxylate (S-312-d), on Abeta- and sPLA(2)-IIA-induced neuronal apoptosis in primary cultures of rat cortical neurons. S-312-d significantly rescued cortical neurons from Abeta- and sPLA(2)-IIA-induced cell death. Both cell death stimuli caused the appearance of apoptotic features such as plasma membrane blebs, chromatin condensation, and DNA fragmentation. S-312-d completely suppressed these apoptotic features. Before apoptosis, the two death ligands markedly enhanced an influx of Ca(2+) into neurons. S-312-d significantly prevented neurons from sPLA(2)-IIA- and Abeta-induced Ca(2+) influx. Furthermore, the neuroprotective effect of S-312-d was more potent than that of another L-VSCC blocker, nimodipine. On the other hand, blockers of other VSCCs such as the N-type and P/Q-type calcium channels had no effect on the neuronal cell death, apoptotic features and Ca(2+) influx. In conclusion, we demonstrated that S-312-d rescues cortical neurons from Abeta- and sPLA(2)-IIA-induced apoptosis.

A Novel Potent Radical Scavenger, 8-(4-Fluorophenyl)-2-((2E)-3-phenyl-2-propenoyl)-1,2,3,4-tetrahydropyrazolo[5,1-c] [1,2,4]triazine (FR210575), Prevents Neuronal Cell Death in Cultured Primary Neurons and Attenuates Brain Injury after Focal Ischemia in Rats

Reactive oxygen species (ROS) play a vital role in brain damage after cerebral ischemia-reperfusion injury, and ROS scavengers have been shown to exert neuroprotective effects against ischemic brain injury. We have recently identified 8-(4-fluorophenyl)-2-((2E)-3-phenyl-2-propenoyl)-1,2,3,4-tetrahydropyrazolo[5,1-c][1,2,4]triazine (FR210575) as a novel, powerful free-radical scavenger. In the present study, the neuroprotective efficacy of FR210575 was evaluated in two neuronal death models in vitro as well as rat focal cerebral ischemia models in vivo. In the first model, primary cortical cultures were exposed to a high oxygen atmosphere (50% O2) for 48 h to induce cell death with apoptotic features. Treatment with FR210575 (10-7-10-5 M) significantly inhibited neuronal death. The second model used a growth-factor withdrawal paradigm. Withdrawal of TIP (transferrin, insulin, putrescine and progesterone)-supplemented medium induced apoptotic cell death after 2 days, but treatment with FR210575 exhibited dramatic protection against neuronal death. In two models of cerebral ischemia [photothrombotic occlusion of middle cerebral artery (MCA) for transient model and by permanent MCA occlusion for permanent model], rats received 3-h intravenous infusion (1-10 mg/kg/3 h) of FR210575, with brain damage determined 24 h later. FR210575 (3.2 mg/kg/3 h) significantly reduced the volume of focal damage in the cortex by 36% in the transient model and also reduced the size of ischemic brain damage in the permanent model. These findings indicate that the powerful radical scavenger FR210575 has potent neuroprotective activity and that FR210575 could be an attractive candidate for the treatment of stroke or other neurodegenerative disorders.

Tacrolimus, a potential neuroprotective agent, ameliorates ischemic brain damage and neurologic deficits after focal cerebral ischemia in nonhuman primates

Tacrolimus (FK506), an immunosuppressive drug, is known to have potent neuroprotective activity and attenuate cerebral infarction in experimental models of stroke. Here we assess the neuroprotective efficacy of tacrolimus in a nonhuman primate model of stroke, photochemically induced thrombotic occlusion of the middle cerebral artery (MCA) in cynomolgus monkeys. In the first experiment, tacrolimus (0.01, 0.032, or 0.1 mg/kg) was intravenously administered immediately after MCA occlusion, and neurologic deficits and cerebral infarction volumes were assessed 24 hours after the ischemic insult. Tacrolimus dose-dependently reduced neurologic deficits and infarction volume in the cerebral cortex, with statistically significant amelioration of neurologic deficits at 0.032 and 0.1 mg/kg and significant reduction of infarction at 0.1 mg/kg. In the second experiment, the long-term efficacy of tacrolimus on neurologic deficits and cerebral infarction was assessed. Vehicle-treated monkeys exhibited persistent and severe deficits in motor and sensory function for up to 28 days. A single intravenous bolus injection of tacrolimus (0.1 or 0.2 mg/kg) produced long-lasting amelioration of neurologic deficits and significant reduction of infarction volume. In conclusion, we have provided compelling evidence that a single dose of tacrolimus not only reduces brain infarction but also ameliorates long-term neurologic deficits in a nonhuman primate model of stroke, strengthening the view that tacrolimus might be beneficial in treating stroke patients.

Neuroprotective action of tacrolimus (FK506) in focal and global cerebral ischemia in rodents: dose dependency, therapeutic time window and long-term efficacy

Tacrolimus (FK506), a potent immunosuppressive drug, is effective in attenuating brain infarction after cerebral ischemia. However, there has been no report characterizing the neuroprotective action and therapeutic time window of tacrolimus systematically using different types of stroke models and extended observation periods. Therefore, we evaluated the neuroprotective effect of tacrolimus in three different animal models of cerebral ischemia: transient and permanent focal ischemia in rats and transient global ischemia in gerbils. Tacrolimus at doses higher than 0.1 mg/kg (i.v.) produced a statistically significant reduction in ischemic brain damage following permanent and transient focal ischemia in rats when administered immediately after the onset of ischemia. Tacrolimus (1 mg/kg, i.v.) demonstrated similar neuroprotective activity even after delayed administration (2 h after permanent or 1 h after transient focal ischemia). The neuroprotective effect of tacrolimus was still present 2 weeks after transient focal ischemia and 1 week after permanent focal ischemia. After transient global ischemia in gerbils, tacrolimus (1 mg/kg, i.v.) given immediately after reperfusion also produced long-lasting neuroprotective effects with a protective time-window of 1-2 h. Taken together, the results clearly indicate that tacrolimus exerts potent, long-term neuroprotective effects with a favorable therapeutic time-window, regardless of the model of cerebral ischemia. These results strengthen the notion that tacrolimus might be of clinical value for the treatment of acute stroke.

Ability of NMDA and non-NMDA receptor antagonists to inhibit cerebral ischemic damage in aged rats

Although stroke is a major cause of death and disability in the elderly, the inhibitory effects of neuroprotectants in acute stroke have been investigated using experimental cerebral ischemic models of young animals. Recent clinical trials have found that few neuroprotectants are effective. These observations indicate that effects in the clinical setting do not always reflect data from young animals. Thus, we compared the effects of the NMDA receptor antagonist MK-801 and of the AMPA receptor antagonist NBQX [2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinixaline] on ischemic cerebral damage in the photothrombosis model of aged and young rats. MK-801 administered immediately after MCA occlusion significantly (P<0.05) reduced the extent of cerebral damage in young, but not in aged, rats and the effects of NBQX were similar. In separate experiments, we evaluated brain damage after microinjecting NMDA or kainic acid into the cortex using a stereotaxic apparatus. We found no significant differences in focal cerebral damage caused by NMDA between young and aged rats. On the other hand, kainic acid caused all of the aged rats tested to die, but none of the young rats. Our observations indicate that NMDA and AMPA receptor antagonists are less effective in aged, than in young, rats and that cerebral damage by receptor agonists depends on the type of receptor, such as NMDA and AMPA.

A combined treatment with tacrolimus (FK506) and recombinant tissue plasminogen activator for thrombotic focal cerebral ischemia in rats: increased neuroprotective efficacy and extended therapeutic time window

The authors evaluated the therapeutic efficacy of tacrolimus (FK506), administered alone or in combination with recombinant tissue plasminogen activator (t-PA), on brain infarction following thrombotic middle cerebral artery (MCA) occlusion. Thrombotic occlusion of the MCA was induced by a photochemical reaction between rose bengal and green light in Sprague-Dawley rats, and the volume of ischemic brain damage was determined 24 hours later. Intravenous administration of tacrolimus or t-PA dose-dependently reduced the volume of ischemic brain infarction, whether administered immediately or 1 hour after MCA occlusion. When tacrolimus or t-PA was administered 2 hours after MCA occlusion, each drug showed a tendency to reduce ischemic brain damage. However, combined treatment with both drugs resulted in a significant reduction in ischemic brain damage. On administration 3 hours after MCA occlusion, tacrolimus alone showed no effect, and t-PA tended to worsen ischemic brain damage. However, the combined treatment with both drugs not only ameliorated the worsening trend seen with t-PA alone, but also tended to reduce ischemic brain damage. In conclusion, tacrolimus, used in combination with t-PA, augmented therapeutic efficacy on brain damage associated with focal ischemia and extended the therapeutic time window compared to single-drug treatments.

Effect of TTC-909 in a middle cerebral artery thrombosis model in stroke-prone spontaneously hypertensive rats

We investigated the effect of TTC-909, a preparation of the stable prostaglandin I(2) analogue clinprost (isocarbacyclin methylester; methyl 5-[(1S,5S,6R,7R)-7-hydroxy-6-[(E)-(S)-3-hydroxy-1-octenyl] bicyclo[3.3.0]oct-2-en-3-yl] pentanoate) incorporated into lipid microspheres, on infarct volume 24 h after photochemically induced thrombotic occlusion of the middle cerebral artery in stroke-prone spontaneously hypertensive rats (SHR). Under anesthesia, the photosensitizing dye rose bengal (20 mg/kg) was administered intravenously and photoirradiation with green light (wavelength 540 nm) on the middle cerebral artery above the rhinal fissure was achieved using a xenon lamp for 10 min. Infarct volume 24 h after the photochemically induced thrombotic occlusion of the middle cerebral artery was significantly larger in stroke-prone SHR than in Wistar rats. When TTC-909 in doses of 100, 300 and 900 ng/kg/h was intravenously infused for 3 h, starting immediately after the end of the 10-min photoirradiation, the infarct volume was dose-dependently reduced and was statistically significant at a dose of 900 ng/kg/h (p < 0.05). Ozagrel, a thromboxane A(2) synthetase inhibitor, significantly reduced the infarct volume. The model of photochemically induced thrombotic occlusion of the middle cerebral artery in stroke-prone SHR is very useful, because the cerebral infarction is large enough and reproducible. TTC-909 may be effective for the treatment of acute ischemic stroke.

Specific ligand for a central type prostacyclin receptor attenuates neuronal damage in a rat model of focal cerebral ischemia

The neuroprotective effect of a central type prostacyclin receptor ligand was examined in a rat model of focal cerebral ischemia. Under halothane anesthesia, male Sprague-Dawley rats were subjected to left middle cerebral artery occlusion. A selective central type prostacyclin receptor ligand, 15-deoxy-(16-m-tolyl)-17,18,19,20-tetranorisocarbacyclin methylester, or a peripheral type prostacyclin receptor ligand, iloprost methylester, were administered intravenously immediately after ischemia. Twenty-four hours after ischemia, brain damage was evaluated. In separate experiments, concentrations of 15-deoxy-(16-m-tolyl)-17,18,19,20-tetranorisocarbacyclin in ischemic brain tissue were measured by injection of a tritium labeled compound. Treatment with 15-deoxy-(16-m-tolyl)-17,18,19,20-tetranorisocarbacyclin methylester (0.03 mg/kg) significantly (P<0.05) reduced the volume of brain damage by 35%. With this treatment, the concentration of this compound in the brain was more than 10 nM. Treatment with iloprost methylester did not show a neuroprotective effect. These results indicated that activation of a central type prostacyclin receptor attenuates ischemic brain damage. The present study demonstrated that the intravenous application of a central type prostacyclin receptor ligand could be a novel therapeutic agent for acute stroke.

Generation of a constitutively active fragment of PKN in microglia/macrophages after middle cerebral artery occlusion in rats

PKN is a fatty acid- and Rho-activated serine/threonine kinase, which has a catalytic domain highly homologous to that of protein kinase C (PKC). Recent studies have demonstrated that PKN is proteolytically cleaved after apoptotic stimulation and then a constitutively active 55-kDa fragment is generated. However, the role of the 55-kDa fragment are poorly understood. Adult Sprague-Dawley (SD) rats underwent middle cerebral artery occlusion (MCAO), and the temporal and spatial changes in the fragmentation of PKN and of PKC delta were examined by immunoblotting. No proteolytic fragment of PKC delta (about 40 kDa) was detected. The 55-kDa fragment of PKN appeared transiently from 3 days after MCAO at the ipsilateral normal cortex. At the boundary zone of infarction, the 55-kDa fragment was markedly induced from day 5 then peaked on day 21 and persisted until day 28. Analysis of anti-phosphoserine immunoprecipitates with an anti-PKN antibody revealed phosphorylation of the 55-kDa band. Double staining for PKN and Ox42 was used to examine the source of the 55-kDa fragment. PKN immunoreactivity was significantly increased in Ox42-positive cells (microglia/hematogenous macrophages). No DNA laddering and only a few terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive cells were observed on day 14 in despite of the high level appearance of the 55-kDa band. These results suggest that the constitutively active 55-kDa fragment of PKN does not contribute to apoptosis, but may contribute to a function of microglia/macrophages.

Effect of FK-506 on inflammation and behavioral outcome following intracerebral hemorrhage in rat

Beginning 15 min after induction of intracerebral hemorrhage (ICH) by intrastriatal administration of collagenase, rats were treated intramuscularly with FK-506 (3 mg/kg) or with vehicle. Treatment was repeated daily for 7 days. MR imaging 1, 7, and 28 days post-ICH showed that treatment did not affect hematoma size or its subsequent resolution. Two days post-ICH, neutrophil infiltration around the hematoma was decreased in the FK-506-treated rats, as was the number of TUNEL-positive cells at the edge of the hematoma and in the peripheral region. The decreased inflammatory response was accompanied by functional improvement in the treated rats. The neurological deficit induced by the ICH (beam walking ability, postural reflex, spontaneous circling) was significantly decreased from 3 to 21 days post-ICH by treatment with FK-506. Skilled use of the forelimb ipsilateral to the ICH was improved and sensory neglect of the same limb was decreased 8-9 weeks post-ICH in rats treated with FK-506. However, neuronal loss assessed 9 weeks post-ICH was not different in the treated and untreated rats.

Changes in local cerebral blood flow in photochemically induced thrombotic occlusion model in rats

We demonstrated earlier that in a photochemically induced thrombotic occlusion model, a reperfusion-like phenomenon may be involved in the progress of brain damage. Therefore, we now investigated changes in local cerebral blood flow in a photochemical model compared with changes in a thermocoagulated occlusion model, using autoradiography. At 5 min, and 3, 6 and 24 h after middle cerebral artery occlusion, local cerebral blood flow was measured by intravenous injection of 4-iodo[N-methyl-14C]antipyrine (20 mu Ci). In the ischemic core zone, the reduction in blood flow was similar in the two models. However, blood flow in the ischemic border zone in the photochemical model decreased transiently in the third hour after ischemia and then increased again, while the blood flow in a thermocoagulated model continued to decrease. Time courses of brain damage formation in both models were no different up to 24 h. These findings suggest that the transient reduction in cerebral blood flow in the third hour following ischemia may contribute to a reperfusion-like phenomenon in a photochemical model.