The sequential change of local cerebral blood flow and local cerebral glucose metabolism after focal cerebral ischaemia and reperfusion in rat and the effect of MK-801 on local cerebral glucose metabolism

Factors affecting bilateral temporal lobe hypometabolism on 18F-FDG PET brain scan in unilateral medial temporal lobe epilepsy

Bilateral temporal lobe hypometabolism (BTH) on (18)F-FDG PET brain scan is frequently seen in unilateral medial temporal lobe epilepsy (mTLE). This study aimed to identify the factors that influence BTH in patients with mTLE in order to minimize the significant factor(s) prior to performing a FDG-PET brain scan. Forty patients with unilateral mTLE who underwent (18)F-FDG PET scan for presurgical epilepsy workup were included. Bilateral temporal lobe hypometabolism of the anterior and medial parts of the temporal lobe was identified by a semiquantitative visual scale. Lateralization of TLE was identified by either intracranial EEG (22/40 cases) and/or improvement of seizure 2 years after temporal lobectomy (37/40 cases). The factors analyzed included basic demographic characteristics (age, sex, occupation, years of education, and handedness), history related to seizure (age at epilepsy onset and epilepsy duration, history of febrile seizure and head injury, frequency of seizure with impaired cognition in the last 3 months, presence of secondarily generalized tonic-clonic seizure, automatism side, presence of postictal confusion, and side of MRI temporal abnormality), information during video-EEG monitoring (clinical lateralization, interictal scalp EEG lateralization (interictal epileptiform discharge), and ictal scalp EEG lateralization), and information during the FDG-PET study (duration from the last seizure (≤2 days or >2 days), last seizure type, and the presence of slow waves or sharp waves during the FDG uptake period). Significant factors related to BTH were analyzed using multivariate analysis. Only the ≤2-day duration from the last seizure to the PET scan shows a significant effect (p=0.021) on BTH finding with 15 times greater incidence compared to a duration >2 days. Bilateral temporal lobe hypometabolism, which causes conflict in lateralizing the epileptogenic zone in temporal lobe epilepsy, can be avoided by performing PET scan more than 2 days after the last seizure.

Does modern ischemic stroke therapy in a large community-based dedicated stroke center improve clinical outcomes? A two-year retrospective study

BACKGROUND

To compare modern endovascular therapies in the acute ischemic stroke patients leading to more comprehensive acute stroke algorithm.

METHODS

A 2-year retrospective nonrandomized study on 76 patients who were placed into 5 different treatment groups for acute ischemic stroke. These groups included: group 1 (no treatment) (n = 24), group 2 (intravenous tissue plasminogen activator [tPA] only) (n = 18), group 3 (intra-arterial [IA] tPA) (n = 9), group 4 (Mechanical Embolus Removal in Cerebral Ischemia [MERCI]; retrieval only) (n = 17), and group 5 (combined IA/MERCI) (n = 8). Age range for all groups was 29-92 years. There were 39 women (51.3%) and 37 men (48.7%). The mean age for all patients was 70.1 years. The pre- and post-National Institutes of Health Stroke Scale (NIHSS) values were obtained for each group on arrival and discharge from the hospital. The results of the 4 treatment cohorts were compared with the no treatment group, providing the relative efficacy of these procedures compared with conservative medical therapy alone.

RESULTS

Group 1 presented with an admission NIHSS value of 11.1 and 8.9 on discharge from the hospital. There was a NIHSS reduction of 2.2 without treatment. Group 2 had an admission NIHSS value of 11.8 and a discharge value of 4.7, resulting in an NIHSS reduction of 7.1. Group 3 had an admission NIHSS value of 16.1 and 7.4 at discharge, resulting in an NIHSS reduction of 8.7. Group 4 had an admission NIHSS value of 15.9 and discharge NIHSS value of 3.1, with an NIHSS reduction of 12.8. Group 5 had an admission NIHSS score of 15.7 and 10.6 at discharge, with an NIHSS reduction of 5.1. Four patients expired during their admission, 2 from group 1 (control group) and 2 from group 5 (combined IA/MERCI group). There was a statistically significant difference for the 5 groups at the P < .05 level in change in NIHSS scores: F (4, 24) = 9.10, P = .000.

CONCLUSIONS

Modern endovascular therapies for acute ischemic stroke do improve clinical outcomes when implemented in the setting of a dedicated comprehensive stroke team.

Functional Recovery after Scutellarin Treatment in Transient Cerebral Ischemic Rats: A Pilot Study with (18) F-Fluorodeoxyglucose MicroPET

Objective. To investigate neuroprotective effects of scutellarin (Scu) in a rat model of cerebral ischemia with use of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) micro positron emission tomography (microPET). Method. Middle cerebral artery occlusion was used to establish cerebral ischemia. Rats were divided into 5 groups: sham operation, cerebral ischemia-reperfusion untreated (CIRU) group, Scu-25 group (Scu 25 mg/kg/d), Scu-50 group (Scu 50 mg/kg/d), and nimodipine (10 mg/Kg/d). The treatment groups were given for 2 weeks. The therapeutic effects in terms of cerebral infarct volume, neurological deficit scores, and cerebral glucose metabolism were evaluated. Levels of vascular density factor (vWF), glial marker (GFAP), and mature neuronal marker (NeuN) were assessed by immunohistochemistry. Results. The neurological deficit scores were significantly decreased in the Scu-50 group compared to the CIRU group (P < 0.001). ¹⁸F-FDG accumulation in the ipsilateral cerebral infarction increased steadily over time in Scu-50 group compared with CIRU group (P < 0.01) and Scu-25 group (P < 0.01). Immunohistochemical analysis demonstrated Scu-50 enhanced neuronal maturation. Conclusion. ¹⁸F-FDG microPET imaging demonstrated metabolic recovery after Scu-50 treatment in the rat model of cerebral ischemia. The neuroprotective effects of Scu on cerebral ischemic injury might be associated with increased regional glucose activity and neuronal maturation.

Sensitive reduction in 14C-acetate uptake in a short-term ischemic rat brain

14C-acetate is preferentially taken up by astrocytes, and is a useful tool for measurement of glial metabolism. The aim of this study was to determine the effects of short-term ischemia on 14C-acetate uptake in the rat brain. The middle cerebral artery was occluded for 3, 10, or 30 minutes. Five minutes after reperfusion, rats were injected with 14C-acetate and decapitated 5 minutes later. Radioactivity concentrations in striatum and cerebral cortex were determined by autoradiography. Cerebral blood flow was also measured using 14C-iodoamphetamine. Neuronal cell death was measured by Nissl staining, and expression of monocarboxylate transporter-1 was examined by immunohistochemical staining. A significant reduction of 14C-acetate uptake was observed in striatum by 3 minutes of occlusion. The degree of reduction of 14C-acetate uptake and reduction area were increased with occlusion period. In contrast, within the same region the regional blood flow was increased by 10 minutes of occlusion, suggesting that uptake of 14C-acetate was independent of blood flow. No neural cell death was detected, and no significant alteration of monocarboxylate transporter-1 expression was observed by 30 minutes of occlusion. These results indicate that 14C-acetate uptake is a sensitive marker for glial metabolism in the ischemic rat brain.

Vasoconstrictive neurovascular coupling during focal ischemic depolarizations

Ischemic depolarizing events, such as repetitive spontaneous periinfarct spreading depolarizations (PIDs), expand the infarct size after experimental middle cerebral artery (MCA) occlusion. This worsening may result from increased metabolic demand, exacerbating the mismatch between cerebral blood flow (CBF) and metabolism. Here, we present data showing that anoxic depolarization (AD) and PIDs caused vasoconstriction and abruptly reduced CBF in the ischemic cortex in a distal MCA occlusion model in mice. This reduction in CBF during AD increased the area of cortex with 20% or less residual CBF by 140%. With each subsequent PID, this area expanded by an additional 19%. Drugs that are known to inhibit cortical spreading depression (CSD), such as N-methyl-D-aspartate receptor antagonists MK-801 and 7-chlorokynurenic acid, and sigma-1 receptor agonists dextromethorphan and carbetapentane, did not reduce the frequency of PIDs, but did diminish the severity of episodic hypoperfusions, and prevented the expansion of severely hypoperfused cortex, thus improving CBF during 90 mins of acute focal ischemia. In contrast, AMPA receptor antagonist NBQX, which does not inhibit CSD, did not impact the deterioration in CBF. When measured 24 h after distal MCA occlusion, infarct size was reduced by MK-801, but not by NBQX. Our results suggest that AD and PIDs expand the CBF deficit, and by so doing negatively impact lesion development in ischemic mouse brain. Mitigating the vasoconstrictive neurovascular coupling during intense ischemic depolarizations may provide a novel hemodynamic mechanism of neuroprotection by inhibitors of CSD.

Serum S-100b protein as a biomarker for the assessment of neuroprotectants

The study of biomarkers associated with stroke has proved to be of considerable utility. The astroglial protein S-100b is a candidate marker for cerebral tissue damage. We used a rat embolic model produced by injection of microspheres to demonstrate that serum S-100b is a useful biochemical marker for ischemic brain injury. Serum S-100b levels were significantly increased following microsphere injection, which was closely correlated with the development of brain edema. We found that structurally and mechanistically independent neuroprotective agents, such as 3-[2-[4-(3-chloro-2-methylphenylmethyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate (DY-9760e), a novel calmodulin antagonist, and the N-methyl-d-aspartate (NMDA) receptor antagonist MK-801, are capable of attenuating increased serum S-100b levels and brain edema. In contrast, the hyperosmolar agent glycerol, which has no direct neuroprotective action, had little effect on serum S-100b levels, despite a significant decrease in brain water content. These results suggest that lowering of serum S-100b is mediated by neuroprotection against ischemic brain injury. Thus, serum S-100b reflects the extent of brain damage following cerebral ischemia and serves as a useful biomarker for the assessment of neuroprotectants.

Widespread and long-lasting alterations in GABA(A)-receptor subtypes after focal cortical infarcts in rats: mediation by NMDA-dependent processes

Impairment of inhibitory neurotransmission has been reported to occur in widespread, structurally intact brain regions after focal ischemic stroke. These long-lasting alterations contribute to the functional deficit and influence long-term recovery. Inhibitory neurotransmission is primarily mediated by gamma-aminobutyric acid (GABA)A receptors assembled of five subunits that allow a variety of adaptive changes. In this study, the regional distribution of five major GABA(A)-receptor subunits (alpha1, alpha2, alpha3, alpha5, and gamma2) was analyzed immunohistochemically 1, 7, and 30 days after photochemically induced cortical infarcts. When compared with sham-operated controls, a general and regionally differential reduction in immunostaining was found within the cortex, hippocampus, and thalamus of both hemispheres for almost all subunits. Within ipsilateral and contralateral neocortical areas, a specific pattern of changes with a differential decrease of subunits alpha1, alpha2, alpha5, and gamma2 and a significant upregulation of subunit alpha3 was observed in the contralateral cortex homotopic to the infarct. This dysregulation was most prominent at day 7 and still present at day 30. Interestingly, a single application of the noncompetitive N-methyl-D-aspartate-receptor antagonist MK-801 during lesion induction completely blocked these bihemispheric alterations. Cortical spreading depressions induced by topical application of KCl do not change GABA(A)-receptor subunit expression. As alterations in subtype distribution crucially influence inhibitory function, ischemia-induced modifications in GABA(A)-receptor subtype expression may be of relevance for functional recovery after stroke.

Repeated, short-term ischemia augments bradykinin-mediated opening of the blood-tumor barrier in rats with RG2 glioma

The objective of this study was to investigate the effects of repeated, short-term ischemia on bradykinin-mediated permeability of the blood-brain barrier (BBB) and the blood-tumor barrier (BTB). The mechanism by which bradykinin transiently opens the BTB, involves B2 receptors, Ca2+ flux, nitric oxide (NO) and cyclic GMP (cGMP). Since global and focal cerebral ischemia are known to increase levels of brain nitric oxide synthase (bNOS) and endothelial nitric oxide synthase (eNOS) we tested the hypothesis that bradykinin may increase the BTB permeability to a greater extent under ischemic rather than nonischemic conditions. The vertebral arteries in female Wistar rats were coagulated immediately after intracerebral implantation of RG2 glioma. Short-term ischemia was produced in some rats by a modification of the four-vessel occlusion procedure for incomplete forebrain ischemia, in which the common carotid arteries were clamped daily for 15 min on days 7, 8 and 9 after tumor implantation, after which reperfusion was allowed. On day 10 after tumor implantation, bradykinin (10 microg kg(-1) min(-1)) or phosphate-buffered saline (PBS) was infused for 15 min into the right carotid artery of anesthetized, sham-operated (nonischemic controls) and ischemic rats, followed by an intravenous bolus (100 microCi kg(-1)) each of [14C]-iodo-antipyrine (IAP), [14C]-dextran or [14C]-aminoisobutyric acid (AIB) to measure regional cerebral blood flow (rCBF), blood volume, or unidirectional transfer constant Ki, respectively, by quantitative autoradiography. A single 15-min ischemic episode significantly decreased rCBF in the tumor center (158.9 +/- 17.33 in control vs. 58.78 +/- 24.45 ml 100 g(-1) min(-1) in ischemic group; p < 0.01) and in the tumor periphery (106.82 +/- 7.34 in control vs. 70.55 +/- 26.66 ml 100 g(-1) min(-1) in ischemic group; p < 0.05). Respective mean blood volume in tumors (11.7 +/- 13.3, 12.7 +/- 14.0, and 13.3 +/- 14.5 microl g(-1)) from ischemic-PBS, nonischemic-bradykinin, and ischemic-bradykinin groups, respectively, was not significantly different; mean blood volume in normal brain (3.7, 3.1 and 3.8 microl g(-1)) was not significantly different among these groups either. Intracarotid infusion of bradykinin following repeated ischemia significantly increased mean Ki, as compared to bradykinin infusion in nonischemic controls, in both the tumor center (36.60 +/- 8.4 vs. 22.90 +/- 4.61 microl g(-1) min(-1), p < 0.05) and in tumor periphery (17.70 +/- 5.93 vs. 8.50 +/- 4.42 microl g(-1) min(-1), p < 0.05). Mean Ki values for tumor center and tumor periphery of ischemic rats receiving intracarotid bradykinin were 3-fold greater than those of nonischemic rats infused with PBS. Immunohistochemical and Western blot analyses showed that repeated, short-term ischemia significantly increased the levels of bNOS in tumor cells and eNOS in tumor capillaries, but neither induced iNOS nor affected B2 receptor levels in tumor cells in vivo, as compared with nonischemic controls. Taken together, these results demonstrate for the first time that repeated, short-term ischemia augments bradykinin-mediated opening of the BTB. We conclude that the elevated intratumoral levels of bNOS and eNOS may 'prime' the NO generating capacity of tumor cells. Consequently, increased de novo synthesis and a correspondingly elevated concentration of NO within the tumor, therefore, may be one mechanistic explanation for the significantly increased, bradykinin-mediated BTB opening under ischemic conditions, reported here.

Brain energetics of cardiopulmonary cerebral resuscitation

Recovery of normal brain energetic conditions during and after resuscitation from cardiac arrest is critical for survival and good neurologic outcome. This review emphasizes the glucose-driven metabolic processes during and after ischemia and on the post-resuscitation development of secondary energy derangements. It also explores some potential therapeutic interventions designed to attenuate these energy derangements. The article summarizes some bench research and is not intended to provide treatment strategies for clinical application.

Angiotensin II AT(1) blockade normalizes cerebrovascular autoregulation and reduces cerebral ischemia in spontaneously hypertensive rats

BACKGROUND AND PURPOSE

Angiotensin II, through stimulation of AT(1) receptors, not only controls blood pressure but also modulates cerebrovascular flow. We sought to determine whether selective AT(1) antagonists could be therapeutically advantageous in brain ischemia during chronic hypertension.

METHODS

We pretreated spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto controls with the AT(1) antagonist candesartan (CV-11974), 0.5 mg/kg per day, for 3 to 14 days, via subcutaneously implanted osmotic minipumps. We analyzed cerebral blood flow by laser-Doppler flowmetry, cerebral stroke in SHR after occlusion of the middle cerebral artery with reperfusion, and brain AT(1) receptors by quantitative autoradiography.

RESULTS

Candesartan treatment normalized blood pressure and the shift toward higher blood pressures at both the upper and lower limits of cerebrovascular autoregulation in SHR. Candesartan pretreatment of SHR for 14 days partially prevented the decrease in blood flow in the marginal zone of ischemia and significantly reduced the volume of total and cortical infarcts after either 1 or 2 hours of middle cerebral artery occlusion with reperfusion, relative to untreated SHR, respectively. This treatment also significantly reduced brain edema after 2 hours of middle cerebral artery occlusion with reperfusion. In SHR, candesartan markedly decreased AT(1) binding in areas inside (nucleus of the solitary tract) and outside (area postrema) the blood-brain barrier and in the middle cerebral artery.

CONCLUSIONS

Pretreatment with an AT(1) antagonist protected hypertensive rats from brain ischemia by normalizing the cerebral blood flow response, probably through AT(1) receptor blockade in cerebral vessels and in brain areas controlling cerebrovascular flow during stroke.

Imaging developing brain infarction

Continued advances in neuroimaging technology have made it practical to image multiple aspects of evolving brain infarction during the potential window period of therapeutic opportunity in stroke. Recent methodologic developments include computed tomography angiography and perfusion, and the description of quantitative parameters for magnetic resonance blood oxygen level-dependent perfusion imaging. In pathophysiologic studies, metabolism and function in the ischemic focus and the peri-infarct tissue have been further characterized. Clinical studies have focused on the applications of computed tomography and magnetic resonance imaging for prethrombolysis patient selection. These methods have an important role in the evaluation and development of new pharmaceutical agents and will be increasingly used in clinical practice as new therapies become available.

Issues in measuring glucose metabolism of rat brain using PET: the effect of harderian glands on the frontal lobe

We estimated the effect of the Harderian gland (an orbital gland of land vertebrates) on the measurement of cerebral metabolic rate of glucose (CMRGIc) of the rat brain using positron emission tomography (PET) for animal use. The Harderian gland had the high accumulation of 18-F labeled deoxyglucose (FDG) after intravenous injection. By placing the large regions of interest (ROI) (twice the full width at half maximum in diameter), the CMRGIc in the frontal region was slightly higher compared with the CMRGIc after Harderian gland resection, but the parietal and occipital regions and the cerebellum had the similar level of CMRGIc before and after Harderian gland resection. Therefore the Harderian gland has a slight effect on the frontal lobe CMRGIc, but such overestimation can be within the permissible range for PET study of rat brains.

Core and Penumbral Nitric Oxide Synthase Activity During Cerebral Ischemia and Reperfusion

Background and Purpose —The present studies examined the hypothesis that the distribution of cerebral injury after a focal ischemic insult is associated with the regional distribution of nitric oxide synthase (NOS) activity.

Methods —Based on previous studies that certain anatomically well-defined areas are prone to become either core or penumbra after middle cerebral artery occlusion (MCAO), we measured NOS activity in these areas from the right and left hemispheres in a spontaneously hypertensive rat filament model. Four groups were studied: (1) controls (immediate decapitation); (2) 1.5 hours of MCAO with no reperfusion (R0); (3) 1.5 hours of MCAO with 0.5 hour of reperfusion (R0.5); and (4) 1.5 hours of MCAO with 24 hours of reperfusion (R24). Three groups of corresponding isoflurane sham controls were also included: 1.5 (S1.5) or 2 (S2.0) hours of anesthesia and 1.5 hours of anesthesia+24 hours of observation (S24).

Results —Control core NOS activity for combined right and left hemispheres was 129% greater than penumbral NOS activity ( P <0.05). Combined core NOS activity was also greater ( P <0.05) in the three sham groups: 208%, 122%, and 161%, respectively. In the three MCAO groups, ischemic and nonischemic core NOS remained higher than penumbral regions ( P <0.05). However, NOS activity was lower in the ischemic than in the nonischemic core in all three groups: R0 (29% lower), R0.5 (48%), and R24 (86%) ( P <0.05). Addition of cofactors (10 μmol/L tetrahydrobiopterin, 3 μmol/L flavin adenine dinucleotide, and 3 μmol/L flavin mononucleotide) increased NOS activity in all groups and lessened the decrease in ischemic core and penumbral NOS.

Conclusions —Greater NOS activity in core regions could explain in part the increased vulnerability of that region to ischemia and could theoretically contribute to the progression of the infarct over time. The data also suggest that NOS activity during ischemia and reperfusion could be influenced by the availability of cofactors.