Unilateral blood flow decrease induces bilateral and symmetric responses in the immature brain

Progressive inflammation reduces high-frequency EEG activity and cortical dendritic arborisation in late gestation fetal sheep

BACKGROUND

Antenatal infection/inflammation is associated with disturbances in neuronal connectivity, impaired cortical growth and poor neurodevelopmental outcomes. The pathophysiological substrate that underpins these changes is poorly understood. We tested the hypothesis that progressive inflammation in late gestation fetal sheep would alter cortical neuronal microstructure and neural function assessed using electroencephalogram band power analysis.

METHODS

Fetal sheep (0.85 of gestation) were surgically instrumented for continuous electroencephalogram (EEG) recording and randomly assigned to repeated saline (control; n = 9) or LPS (0 h = 300 ng, 24 h = 600 ng, 48 h = 1200 ng; n = 8) infusions to induce inflammation. Sheep were euthanised 4 days after the first LPS infusion for assessment of inflammatory gene expression, histopathology and neuronal dendritic morphology in the somatosensory cortex.

RESULTS

LPS infusions increased delta power between 8 and 50 h, with reduced beta power from 18 to 96 h (P < 0.05 vs. control). Basal dendritic length, numbers of dendritic terminals, dendritic arborisation and numbers of dendritic spines were reduced in LPS-exposed fetuses (P < 0.05 vs. control) within the somatosensory cortex. Numbers of microglia and interleukin (IL)-1β immunoreactivity were increased in LPS-exposed fetuses compared with controls (P < 0.05). There were no differences in total numbers of cortical NeuN + neurons or cortical area between the groups.

CONCLUSIONS

Exposure to antenatal infection/inflammation was associated with impaired dendritic arborisation, spine number and loss of high-frequency EEG activity, despite normal numbers of neurons, that may contribute to disturbed cortical development and connectivity.

Collateral Supply in Preclinical Cerebral Stroke Models

Enhancing the collateral blood supply during the acute phase of cerebral ischemia may limit both the extension of the core infarct, by rescuing the penumbra area, and the degree of disability. Many imaging techniques have been applied to rodents in preclinical studies, to evaluate the magnitude of collateral blood flow and the time course of responses during the early phase of ischemic stroke. The collateral supply follows several different routes at the base of the brain (the circle of Willis) and its surface (leptomeningeal or pial arteries), corresponding to the proximal and distal collateral pathways, respectively. In this review, we describe and illustrate the cerebral collateral systems and their modifications following pre-Willis or post-Willis occlusion in rodents. We also review the potential pharmaceutical agents for stimulating the collateral blood supply tested to date. The time taken to establish a collateral blood flow supply through the leptomeningeal anastomoses differs between young and adult animals and between different species and genetic backgrounds. Caution is required when transposing preclinical findings to humans, and clinical trials must be performed to check the added value of pharmacological agents for stimulating the collateral blood supply at appropriate time points. However, collateral recruitment appears to be a rapid, beneficial, endogenous mechanism that can be stimulated shortly after artery occlusion. It should be considered a treatment target for use in addition to recanalization strategies.

Poly(ADP-Ribose) Polymerase Inhibitor PJ34 Reduces Brain Damage after Stroke in the Neonatal Mouse Brain

The poly(ADP-ribose) polymerase inhibitor PJ34 has recently been reported to increase cerebral blood flow, via the endothelial NO synthase, in the naive mouse brain throughout life. We addressed here the benefits of PJ34 after neonatal ischemia on hemodynamics and components of the neurovascular unit including the blood-brain barrier (BBB), microglia, and astrocytes. Nine-day-old mice were subjected to permanent MCA occlusion (pMCAo), and treated with either PBS or PJ34 (10 mg/kg). Mean blood-flow velocities (mBFV) were measured in both internal carotid arteries (ICA) and basilar trunk (BT) using Doppler-ultrasonography. BBB opening was assessed through somatostatin-receptor type-2 internalization and immunohistochemistry at 24 and 48 h. Lesion areas were measured 8 days after ischemia. In PBS-treated mice, pMCAo involved a drop in mBFV in the left ICA (p < 0.001 vs. basal), whereas mBFV remained stable in both right ICA and BT. PJ34 prevented this drop in the left ICA (NS vs. basal) and increased mBFV in the right ICA (p = 0.0038 vs. basal). No modification was observed in the BT. In contrast to PBS, BBB disruption extent and astrocyte demise were reduced in PJ34 mice only in the rostral brain at 48 h and 8 days post-pMCAo, respectively. Accordingly, 8 days after pMCAo, affected areas were reduced in the rostral brain (Bregma +0.86 and +0.14 mm), whereas total tissue loss was not reduced after PJ34 (4.0 ± 3.1%) vs. PBS (5.8 ± 3.4%). These results show that PJ34 reduced BBB permeability, astrocyte demise, and tissue loss (particularly in the rostral territories), suggesting that collateral supply mainly proceeds from the anterior ICA’s branches in the ischemic neonatal mouse brain.

Multipotential and systemic effects of traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of disability and mortality of people at all ages. Biochemical, cellular and physiological events that occur during primary injury lead to a delayed and long-term secondary damage that can last from hours to years. Secondary brain injury causes tissue damage in the central nervous system and a subsequent strong and rapid inflammatory response that may lead to persistent inflammation. However, this inflammatory response is not limited to the brain. Inflammatory mediators are transferred from damaged brain tissue to the bloodstream and produce a systemic inflammatory response in peripheral organs, including the cardiovascular, pulmonary, gastrointestinal, renal and endocrine systems. Complications of TBI are associated with its multiple and systemic effects that should be considered in the treatment of TBI patients. Therefore, in this review, an attempt was made to examine the systemic effects of TBI in detail. It is hoped that this review will identify the mechanisms of injury and complications of TBI, and open a window for promising treatment in TBI complications.

Proton Magnetic Resonance Spectroscopy Lactate/N-Acetylaspartate Within 48 h Predicts Cell Death Following Varied Neuroprotective Interventions in a Piglet Model of Hypoxia-Ischemia With and Without Inflammation-Sensitization

Despite therapeutic hypothermia, survivors of neonatal encephalopathy have high rates of adverse outcome. Early surrogate outcome measures are needed to speed up the translation of neuroprotection trials. Thalamic lactate (Lac)/N-acetylaspartate (NAA) peak area ratio acquired with proton (1H) magnetic resonance spectroscopy (MRS) accurately predicts 2-year neurodevelopmental outcome. We assessed the relationship between MR biomarkers acquired at 24-48 h following injury with cell death and neuroinflammation in a piglet model following various neuroprotective interventions. Sixty-seven piglets with hypoxia-ischemia, hypoxia alone, or lipopolysaccharide (LPS) sensitization were included, and neuroprotective interventions were therapeutic hypothermia, melatonin, and magnesium. MRS and diffusion-weighted imaging (DWI) were acquired at 24 and 48 h. At 48 h, experiments were terminated, and immunohistochemistry was assessed. There was a correlation between Lac/NAA and overall cell death [terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)] [mean Lac/NAA basal ganglia and thalamus (BGT) voxel r = 0.722, white matter (WM) voxel r = 0.784, p < 0.01] and microglial activation [ionized calcium-binding adapter molecule 1 (Iba1)] (BGT r = -0.786, WM r = -0.632, p < 0.01). Correlation with marker of caspase-dependent apoptosis [cleaved caspase 3 (CC3)] was lower (BGT r = -0.636, WM r = -0.495, p < 0.01). Relation between DWI and TUNEL was less robust (mean diffusivity BGT r = -0.615, fractional anisotropy BGT r = 0.523). Overall, Lac/NAA correlated best with cell death and microglial activation. These data align with clinical studies demonstrating Lac/NAA superiority as an outcome predictor in neonatal encephalopathy (NE) and support its use in preclinical and clinical neuroprotection studies.

High-Dose Melatonin and Ethanol Excipient Combined with Therapeutic Hypothermia in a Newborn Piglet Asphyxia Model

With the current practice of therapeutic hypothermia for neonatal encephalopathy, disability rates and the severity spectrum of cerebral palsy are reduced. Nevertheless, safe and effective adjunct therapies are needed to optimize outcomes. This study's objective was to assess if 18 mg/kg melatonin given rapidly over 2 h at 1 h after hypoxia-ischemia with cooling from 1-13 h was safe, achieved therapeutic levels within 3 h and augmented hypothermic neuroprotection. Following hypoxia-ischemia, 20 newborn piglets were randomized to: (i) Cooling 1-13 h (HT; n = 6); (ii) HT+ 2.5% ethanol vehicle (HT+V; n = 7); (iii) HT + Melatonin (HT+M; n = 7). Intensive care was maintained for 48 h; aEEG was acquired throughout, brain MRS acquired at 24 and 48 h and cell death (TUNEL) evaluated at 48 h. There were no differences for insult severity. Core temperature was higher in HT group for first hour after HI. Comparing HT+M to HT, aEEG scores recovered more quickly by 19 h (p < 0.05); comparing HT+V to HT, aEEG recovered from 31 h (p < 0.05). Brain phosphocreatine/inorganic phosphate and NTP/exchangeable phosphate were higher at 48 h in HT+M versus HT (p = 0.036, p = 0.049 respectively). Including both 24 h and 48 h measurements, the rise in Lactate/N-acetyl aspartate was reduced in white (p = 0.030) and grey matter (p = 0.038) after HI. Reduced overall TUNEL positive cells were observed in HT+M (47.1 cells/mm²) compared to HT (123.8 cells/mm²) (p = 0.0003) and HT+V (97.5 cells/mm²) compared to HT (p = 0.012). Localized protection was seen in white matter for HT+M versus HT (p = 0.036) and internal capsule for HT+M compared to HT (p = 0.001) and HT+V versus HT (p = 0.006). Therapeutic melatonin levels (15-30mg/l) were achieved at 2 h and were neuroprotective following HI, but ethanol vehicle was partially protective.

Acute LPS sensitization and continuous infusion exacerbates hypoxic brain injury in a piglet model of neonatal encephalopathy

Co-existing infection/inflammation and birth asphyxia potentiate the risk of developing neonatal encephalopathy (NE) and adverse outcome. In a newborn piglet model we assessed the effect of E. coli lipopolysaccharide (LPS) infusion started 4 h prior to and continued for 48 h after hypoxia on brain cell death and systemic haematological changes compared to LPS and hypoxia alone. LPS sensitized hypoxia resulted in an increase in mortality and in brain cell death (TUNEL positive cells) throughout the whole brain, and in the internal capsule, periventricular white matter and sensorimotor cortex. LPS alone did not increase brain cell death at 48 h, despite evidence of neuroinflammation, including the greatest increases in microglial proliferation, reactive astrocytosis and cleavage of caspase-3. LPS exposure caused splenic hypertrophy and platelet count suppression. The combination of LPS and hypoxia resulted in the highest and most sustained systemic white cell count increase. These findings highlight the significant contribution of acute inflammation sensitization prior to an asphyxial insult on NE illness severity.

A Model of Perinatal Ischemic Stroke in the Rat: 20 Years Already and What Lessons?

Neonatal hypoxia-ischemia (HI) and ischemia are a common cause of neonatal brain injury resulting in cerebral palsy with subsequent learning disabilities and epilepsy. Recent data suggest a higher incidence of focal ischemia-reperfusion located in the middle cerebral artery (MCA) territory in near-term and newborn babies. Pre-clinical studies in the field of cerebral palsy research used, and still today, the classical HI model in the P7 rat originally described by Rice et al. (1). At the end of the 90s, we designed a new model of focal ischemia in the P7 rat to explore the short and long-term pathophysiology of neonatal arterial ischemic stroke, particularly the phenomenon of reperfusion injury and its sequelae (reported in 1998). Cerebral blood-flow and cell death/damage correlates have been fully characterized. Pharmacologic manipulations have been applied to the model to test therapeutic targets. The model has proven useful for the study of seizure occurrence, a clinical hallmark for neonatal ischemia in babies. Main pre-clinical findings obtained within these 20 last years are discussed associated to clinical pattern of neonatal brain damage.

Protective Effect of Ischemic Preconditioning on Myocardium Against Remote Tissue Injury Following Transient Focal Cerebral Ischemia in Diabetic Rats

Background

Remote ischemic preconditioning (IPreC) could provide tissue-protective effect at a remote site by anti-inflammatory, neuronal, and humoral signaling pathways.

Objectives

The aim of the study was to investigate the possible protective effects of remote IPreC on myocardium after transient middle cerebral artery occlusion (MCAo) in streptozotocin- induced diabetic (STZ) and non-diabetic rats.

Methods

48 male Spraque Dawley rats were divided into eight groups: Sham, STZ, IPreC, MCAo, IPreC+MCAo, STZ+IPreC, STZ+MCAo and STZ+IPreC+MCAo groups. We induced transient MCAo seven days after STZ-induced diabetes, and performed IPreC 72 hours before transient MCAo. Remote myocardial injury was investigated histopathologically. Bax, Bcl2 and caspase-3 protein levels were measured by Western blot analysis. Total antioxidant status (TAS), total oxidant status (TOS) of myocardial tissue were measured by colorimetric assay. Oxidative stress index(OSI) was calculated as TOS-to-TAS ratio. For all statistical analysis, p values < 0.05 were considered significant.

Results

We observed serious damage including necrosis, congestion and mononuclear cell infiltration in myocardial tissue of the diabetic and ischemic groups. In these groups TOS and OSI levels were significantly higher; TAS levels were lower than those of IPreC related groups (p < 0.05). IPreC had markedly improved histopathological alterations and increased TAS levels in IPreC+MCAo and STZ+IPreC+MCAo compared to MCAo and STZ+MCAo groups (p < 0.05). In non-diabetic rats, MCAo activated apoptotic cell death via increasing Bax/Bcl2 ratio and caspase-3 levels. IPreC reduced apoptotic cell death by suppressing pro-apoptotic proteins. Diabetes markedly increased apoptotic protein levels and the effect did not reversed by IPreC.

Conclusions

We could suggest that IPreC attenuates myocardial injury via ameliorating histological findings, activating antioxidant mechanisms, and inducing antiapoptotic activity in diabetic rats.

Different response to antiepileptic drugs according to the type of epileptic events in a neonatal ischemia-reperfusion model

Perinatal arterial stroke is the most frequent form of cerebral infarction in children. Neonatal seizures are the most frequent symptom during the neonatal period. The current management of perinatal stroke is based on supportive care. It is currently unknown if treatment of the seizures modifies the outcome, and no clinical studies have focused on seizures during neonatal stroke. We studied the effect of phenobarbital and levetiracetam on an ischemic-reperfusion stroke model in P7 rats using prolonged electroencephalographic recordings and a histologic analysis of the brain (24h after injury). The following two types of epileptic events were observed: 1) bursts of high amplitude spikes during ischemia and the first hours of reperfusion and 2) organized seizures consisting in discharges of a 1-2Hz spike-and-wave. Both phenobarbital and levetiracetam decreased the total duration of the bursts of high amplitude spikes. Phenobarbital also delayed the start of seizures without changing the total duration of epileptic discharges. The markedly limited efficacy of the antiepileptic drugs studied in our neonatal stroke rat model is frequently observed in human neonatal seizures. Both drugs did not modify the stroke volume, which suggests that the modification of the quantity of bursts of high amplitude spikes does not influence the infarct size. In the absence of a reduction in seizure burden by the antiepileptic drugs, we increased the seizure burden and stroke volume by combining our neonatal stroke model with a lithium-pilocarpine-induced status epilepticus. Our data suggest that the reduction of burst of spikes did not influence the stroke volume. The presence of organized seizure with a pattern close to what is observed in human newborns seems related to the presence of the infarct. Further research is required to determine the relationship between seizure burden and infarct volume.

Neuroprotective effect of ischemic preconditioning via modulating the expression of cerebral miRNAs against transient cerebral ischemia in diabetic rats

OBJECTIVES

In this study, we aimed to evaluate the effect of the Ischemic preconditioning (IPreC) on the expression profile of cerebral miRNAs against stroke by induced transient middle cerebral artery occlusion (MCAo) in diabetic rats.

METHODS

Eighty male Spraque Dawley rats were allocated to eight groups. In order to evaluate the expression profile of miRNAs, we induced transient MCAo seven days after STZ-induced diabetes (DM). Also we performed IPreC 72 h before transient MCAo to assess whether IPreC could have a neuroprotective effect against ischemia-reperfusion injury.

RESULTS

The general characteristics of STZ-treated rats included reduced body weight and elevated blood glucose levels compared to non-diabetic ones. We demonstrated that miRNA expression profiles, which are determined for biological functions such as aquaporin 4 formation (miR-29b-2, miR-124a-3p, miR-130a, miR-223 and miR-320a), glutamate toxicity (miR107, miR-145, miR-223), salvageable ischemic area (miR-9a, miR-19b, miR-29b-2, miR-341, miR-339-5p, miR-15-5p, miR-99b-5p), and neoangiogenesis (let-7f-5p, miR-126a and miR-322-3p), were regulated following IPreC. Ischemic preconditioning before cerebral ischemia significantly reduced infarction size compared with the other groups [IPreC + MCAo (27 ± 11 mm³) vs. MCAo (109 ± 15 mm³) p < 0.001; DM + IPreC + MCAo (38 ± 9 mm³) vs. DM + MCAo (165 ± 41 mm³) p < 0.001, respectively].

DISCUSSION

The study results revealed the neuroprotective effects of ischemic preconditioning, supported with the upregulated pro-survival miRNAs in MCA infarcts.

Hepatic expression of serum amyloid A1 is induced by traumatic brain injury and modulated by telmisartan

Traumatic brain injury affects the whole body in addition to the direct impact on the brain. The systemic response to trauma is associated with the hepatic acute-phase response. To further characterize this response, we performed controlled cortical impact injury on male mice and determined the expression of serum amyloid A1 (SAA1), an apolipoprotein, induced at the early stages of the acute-phase response in liver and plasma. After cortical impact injury, induction of SAA1 was detectable in plasma at 6 hours post-injury and in liver at 1 day post-injury, followed by gradual diminution over time. In the liver, cortical impact injury increased neutrophil and macrophage infiltration, apoptosis, and expression of mRNA encoding the chemokines CXCL1 and CXCL10. An increase in angiotensin II AT1 receptor mRNA at 3 days post-injury was also observed. Administration of the AT1 receptor antagonist telmisartan 1 hour post-injury significantly decreased liver SAA1 levels and CXCL10 mRNA expression, but did not affect CXCL1 expression or the number of apoptotic cells or infiltrating leukocytes. To our knowledge, this is the first study to demonstrate that SAA1 is induced in the liver after traumatic brain injury and that telmisartan prevents this response. Elucidating the molecular pathogenesis of the liver after brain injury will assist in understanding the efficacy of therapeutic approaches to brain injury.

Neuroprotective effect of ischemic preconditioning via modulating the expression of adropin and oxidative markers against transient cerebral ischemia in diabetic rats

INTRODUCTION

Ischemic preconditioning (IPreC) can render the brain more tolerant to a subsequent potential lethal ischemic injury. Hyperglycemia has been shown to increase the size of ischemic stroke and worsen the clinical outcome following a stroke, thus exacerbating oxidative stress. Adropin has a significant association with cardiovascular disease, especially with diabetes. In this study, we aimed to evaluate the role of the IPreC due to modulating the expression of adropin and oxidative damage markers against stroke by induced transient middle cerebral artery occlusion (MCAo) in streptozotocin (STZ)-induced diabetic rats.

MATERIAL-METHOD

72 male Spraque Dawley rats were allocated to 8 groups. In order to evaluate alterations of anti/oxidative status and adropin level, we induced transient MCAo seven days after STZ-induced diabetes. Also we performed IPreC 72h before transient MCAo to assess whether IPreC could have a neuroprotective effect against ischemia-reperfusion injury.

RESULTS

The general characteristics of STZ-treated rats (STZ) included reduced body weight and elevated blood glucose levels compared to non-diabetic ones. Ischemic preconditioning before cerebral ischemia significantly reduced infarction size compared with the other groups [IPreC+MCAo (27±11mm(3)) vs. MCAo (109±17mm(3)) p<0.001; STZ+IPreC+MCAo (38±10mm(3)) vs. STZ+MCAo (165±45mm(3)) p<0.001, respectively]. The mean total antioxidant status level in IPreC groups was higher than other groups (p≤0.05). Moreover, IPreC considerably decreased mean adropin levels compared with other groups (p≤0.05).

CONCLUSION

The study results supported the neuroprotective effects of ischemic preconditioning in MCA infarcts correlated with the level of oxidative damage markers and adropin.

Neurorestoration after traumatic brain injury through angiotensin II receptor blockage

See Moon (doi:10.1093/awv239) for a scientific commentary on this article.Traumatic brain injury frequently leads to long-term cognitive problems and physical disability yet remains without effective therapeutics. Traumatic brain injury results in neuronal injury and death, acute and prolonged inflammation and decreased blood flow. Drugs that block angiotensin II type 1 receptors (AT1R, encoded by AGTR1) (ARBs or sartans) are strongly neuroprotective, neurorestorative and anti-inflammatory. To test whether these drugs may be effective in treating traumatic brain injury, we selected two sartans, candesartan and telmisartan, of proven therapeutic efficacy in animal models of brain inflammation, neurodegenerative disorders and stroke. Using a validated mouse model of controlled cortical impact injury, we determined effective doses for candesartan and telmisartan, their therapeutic window, mechanisms of action and effect on cognition and motor performance. Both candesartan and telmisartan ameliorated controlled cortical impact-induced injury with a therapeutic window up to 6 h at doses that did not affect blood pressure. Both drugs decreased lesion volume, neuronal injury and apoptosis, astrogliosis, microglial activation, pro-inflammatory signalling, and protected cerebral blood flow, when determined 1 to 3 days post-injury. Controlled cortical impact-induced cognitive impairment was ameliorated 30 days after injury only by candesartan. The neurorestorative effects of candesartan and telmisartan were reduced by concomitant administration of the peroxisome proliferator-activated receptor gamma (PPARγ, encoded by PPARG) antagonist T0070907, showing the importance of PPARγ activation for the neurorestorative effect of these sartans. AT1R knockout mice were less vulnerable to controlled cortical impact-induced injury suggesting that the sartan's blockade of the AT1R also contributes to their efficacy. This study strongly suggests that sartans with dual AT1R blocking and PPARγ activating properties have therapeutic potential for traumatic brain injury.

Temporal dynamics of cerebral blood flow, cortical damage, apoptosis, astrocyte-vasculature interaction and astrogliosis in the pericontusional region after traumatic brain injury

Traumatic brain injury (TBI) results in a loss of brain tissue at the moment of impact in the cerebral cortex. Subsequent secondary injury involves the release of molecular signals with dramatic consequences for the integrity of damaged tissue, leading to the evolution of a pericontusional-damaged area minutes to days after in the initial injury. The mechanisms behind the progression of tissue loss remain under investigation. In this study, we analyzed the spatial–temporal profile of blood flow, apoptotic, and astrocytic–vascular events in the cortical regions around the impact site at time points ranging from 5 h to 2 months after TBI. We performed a mild–moderate controlled cortical impact injury in young adult mice and analyzed the glial and vascular response to injury. We observed a dramatic decrease in perilesional cerebral blood flow (CBF) immediately following the cortical impact that lasted until days later. CBF finally returned to baseline levels by 30 days post-injury (dpi). The initial impact also resulted in an immediate loss of tissue and cavity formation that gradually increased in size until 3 dpi. An increase in dying cells localized in the pericontusional region and a robust astrogliosis were also observed at 3 dpi. A strong vasculature interaction with astrocytes was established at 7 dpi. Glial scar formation began at 7 dpi and seemed to be compact by 60 dpi. Altogether, these results suggest that TBI results in a progression from acute neurodegeneration that precedes astrocytic activation, reformation of the neurovascular unit to glial scar formation. Understanding the multiple processes occurring after TBI is critical to the ability to develop neuroprotective therapeutics to ameliorate the short and long-term consequences of brain injury.

Dynamic spatio-temporal imaging of early reflow in a neonatal rat stroke model

The aim of the study was to better understand blood-flow changes in large arteries and microvessels during the first 15 minutes of reflow in a P7 rat model of arterial occlusion. Blood-flow changes were monitored by using ultrasound imaging with sequential Doppler recordings in internal carotid arteries (ICAs) and basilar trunk. Relative cerebral blood flow (rCBF) changes were obtained by using laser speckle Doppler monitoring. Tissue perfusion was measured with [(14)C]-iodoantipyrine autoradiography. Cerebral energy metabolism was evaluated by mitochondrial oxygen consumption. Gradual increase in mean blood-flow velocities illustrated a gradual perfusion during early reflow in both ICAs. On ischemia, the middle cerebral artery (MCA) territory presented a residual perfusion, whereas the caudal territory remained normally perfused. On reflow, speckle images showed a caudorostral propagation of reperfusion through anastomotic connections, and a reduced perfusion in the MCA territory. Autoradiography highlighted the caudorostral gradient, and persistent perfusion in ventral and medial regions. These blood-flow changes were accompanied by mitochondrial respiration impairment in the ipsilateral cortex. Collectively, these data indicate the presence of a primary collateral pathway through the circle of Willis, providing an immediate diversion of blood flow toward ischemic regions, and secondary efficient cortical anastomoses in the immature rat brain.

Neuroprotection targeting ischemic penumbra and beyond for the treatment of ischemic stroke

Neuroprotection to attenuate or block the ischemic cascade and salvage neuronal damage has been extensively explored for the treatment of ischemic stroke. In the last two decades, neuroprotective strategy has been evolving from targeting a signal pathway in neurons to protecting all neurovascular components and improving cell-cell and cell-extracellular matrix interaction that ultimately benefits the brain recovery after ischemic stroke. The progression from potentially reversible to irreversible injury in the ischemic penumbra has provided the opportunity to develop therapies to attenuate the ischemic stroke damage. Thus, the ischemic penumbra has been the main target for the current neuroprotective intervention. However, despite our increasing knowledge of the physiologic, mechanistic, and imaging characterizations of the ischemic penumbra, no effective neuroprotective therapy has been found so far for the treatment of ischemic stroke. The current acute neuroprotective approach focusing on the damaging mechanisms at the ischemic penumbra is greatly limited by the rapid evolution of the deleterious cascades in the ischemic penumbra. Neuroprotective intervention attempts to promote endogenous repairing in the transition zone of the penumbra for the therapeutic purposes may overcome the unrealistic therapeutic windows under the current neuroprotective strategy. In addition, increasing evidence has indicated ischemic stroke could induce long-lasing cellular and hemodynamic changes beyond the ischemic territory. It is unclear whether and how the global responses induced by the ischemic cascade contribute to the progression of cognitive impairment after ischemic stroke. The prolonged pathophysiological cascades induced by ischemic stroke beyond the ischemic penumbra might provide novel therapeutic opportunities for the neuroprotective intervention, which could prevent or slow down the progression of vascular dementia after ischemic stroke.

Dual action of NO synthases on blood flow and infarct volume consecutive to neonatal focal cerebral ischemia

Research into neonatal ischemic brain damage is impeded by the lack of a complete understanding of the initial hemodynamic mechanisms resulting in a lesion, particularly that of NO-mediated vascular mechanisms. In a neonatal stroke rat model, we recently show that collateral recruitment contributes to infarct size variability. Non-specific and selective NO synthase (NOS) inhibition was evaluated on cerebral blood-flow changes and outcome in a P7 rat model of arterial occlusion (left middle cerebral artery electrocoagulation with 50 min occlusion of both common carotid arteries). Blood-flow changes were measured by using ultrasound imaging with sequential Doppler recordings in both internal carotid arteries and basilar trunk. Cortical perfusion was measured by using laser Doppler flowmetry. We showed that global NOS inhibition significantly reduced collateral support and cortical perfusion (collateral failure), and worsened the ischemic injury in both gender. Conversely, endothelial NOS inhibition increased blood-flows and aggravated volume lesion in males, whereas in females blood-flows did not change and infarct lesion was significantly reduced. These changes were associated with decreased phosphorylation of neuronal NOS at Ser(847) in males and increased phosphorylation in females at 24h, respectively. Neuronal NOS inhibition also increased blood-flows in males but not in females, and did not significantly change infarct volumes compared to their respective PBS-treated controls. In conclusion, both nNOS and eNOS appear to play a key role in modulating arterial blood flow during ischemia mainly in male pups with subsequent modifications in infarct lesion.

Intracortical injection of endothelin-1 induces cortical infarcts in mice: effect of neuronal expression of an adenosine transporter

Background

Activation of adenosine A₁ receptors has neuroprotective effects in animal stroke models. Adenosine levels are regulated by nucleoside transporters. In vitro studies showed that neuron-specific expression of human equilibrative nucleoside transporter 1 (hENT1) decreases extracellular adenosine levels and adenosine A₁ receptor activity. In this study, we tested the effect of hENT1 expression on cortical infarct size following intracerebral injection of the vasoconstrictor endothelin-1 (ET-1) or saline.

Methods

Mice underwent stereotaxic intracortical injection of ET-1 (1 μl; 400 pmol) or saline (1 μl). Some mice received the adenosine receptor antagonist caffeine (25 mg/kg, intraperitoneal) 30 minutes prior to ET-1. Perfusion and T₂-weighted magnetic resonance imaging (MRI) were used to measure cerebral blood flow (CBF) and subsequent infarct size, respectively.

Results

ET-1 reduced CBF at the injection site to 7.3 ± 1.3% (n = 12) in hENT1 transgenic (Tg) and 12.5 ± 2.0% (n = 13) in wild type (Wt) mice. At 48 hours following ET-1 injection, CBF was partially restored to 35.8 ± 4.5% in Tg and to 45.2 ± 6.3% in Wt mice; infarct sizes were significantly greater in Tg (9 ± 1.1 mm³) than Wt (5.4 ± 0.8 mm³) mice. Saline-treated Tg and Wt mice had modest decreases in CBF and infarcts were less than 1 mm³. For mice treated with caffeine, CBF values and infarct sizes were not significantly different between Tg and Wt mice.

Conclusions

ET-1 produced greater ischemic injury in hENT1 Tg than in Wt mice. This genotype difference was not observed in mice that had received caffeine. These data indicate that hENT1 Tg mice have reduced ischemia-evoked increases in adenosine receptor activity compared to Wt mice.

Transient focal cerebral ischemia induces long-term cerebral vasculature dysfunction in a rodent experimental stroke model

Constriction and dilation of large arteries of brain regulates cerebral vascular resistance and cerebral microvascular pressure, which play key roles in regulation of cerebral circulation. We investigated the effect of ischemic stroke on vascular reactivity of middle cerebral artery (MCA) using a rat transient focal cerebral ischemia model. Focal cerebral ischemia was induced by 1 hour MCA occlusion followed by reperfusion. MCAs were dissected from ischemic or contralateral hemisphere at 2 days or 2 weeks post reperfusion and mounted on 2 glass micropipettes for assessment of vascular reactivity. MCAs from brains of sham surgeries were used as control. At 2 days post reperfusion, a significant alteration of myogenic reactivity was found in MCAs dissected from both ischemic and non-ischemic hemispheres, which could still be identified at 2 weeks after reperfusion. Phenylephrine (PE) induced remarkable vasoconstriction in MCAs from animals that underwent sham surgery. No significant alteration of vasoconstrictive response to PE was found in MCAs isolated from either ischemic or contralateral hemisphere at 2 days or 2 weeks after ischemic stroke, as compared with MCAs from sham animals. Acetylcholine (ACh) induced mild dilation in normal MCAs, which was reversed in MCAs from both ischemic and non-ischemic hemispheres at 2 weeks after ischemic stroke. Sodium nitroprusside (SNP) induced vasodilation in MCAs from animals with sham operation, which was diminished in MCAs from both ischemic and non-ischemic hemisphere at 2 days and 2 weeks after ischemic stroke. These results demonstrated that focal cerebral ischemia could induce long-term global cerebral vasculature dysfunction.

Targeting neonatal ischemic brain injury with a pentapeptide-based irreversible caspase inhibitor

Brain protection of the newborn remains a challenging priority and represents a totally unmet medical need. Pharmacological inhibition of caspases appears as a promising strategy for neuroprotection. In a translational perspective, we have developed a pentapeptide-based group II caspase inhibitor, TRP601/ORPHA133563, which reaches the brain, and inhibits caspases activation, mitochondrial release of cytochrome c, and apoptosis in vivo. Single administration of TRP601 protects newborn rodent brain against excitotoxicity, hypoxia-ischemia, and perinatal arterial stroke with a 6-h therapeutic time window, and has no adverse effects on physiological parameters. Safety pharmacology investigations, and toxicology studies in rodent and canine neonates, suggest that TRP601 is a lead compound for further drug development to treat ischemic brain damage in human newborns.

Blockade of Caspase-2 Activity Inhibits Ischemia/Reperfusion-Induced Mitochondrial Reactive Oxygen Burst and Cell Death in Cardiomyocytes

We previously showed that initiator caspases-2 and −8 are prominently activated in ischemia/reperfusion (I/R)-induced injury in cardiomyocytes, but while blockade of caspase-2 activity enhanced cell survival, blockade of caspase-8 activity did not protect cardiomyocytes. Because apoptotic death in these cells is characterized by a burst of reactive oxygen species (ROS) at reperfusion and their survival by inhibition of this burst, we examined the effects of blocking caspase-2 and caspase-8 activities on ROS production. Caspase-2 inhibition blocked the reperfusion-induced ROS burst, while inhibition of caspase-8 did not. We also examined effects of caspase inhibition on mitochondrial membrane potential (ΔΨm) and mitochondrial function and found that blocking caspase-2, but not caspase-8, allowed recovery of ΔΨm and mitochondrial functionality. Furthermore, knockdown of caspase-2 by small-interfering (si)RNA confirmed caspase-2 participation in cytochrome c release, which correlates with loss of ΔΨm and cell death in these cardiomyocytes.

Melatonin promotes myelination by decreasing white matter inflammation after neonatal stroke

Melatonin demonstrates neuroprotective properties in adult models of cerebral ischemia, acting as a potent antioxidant and anti-inflammatory agent. We investigated the effect of melatonin in a 7-d-old rat model of ischemia-reperfusion, leading to both cortical infarct and injury in the underlying white matter observed using MRI and immunohistochemistry. Melatonin was given i.p. as either a single dose before ischemia or a double-dose regimen, combining one before ischemia and one 24 h after reperfusion. At 48 h after injury, neither a significant reduction in cortical infarct volume nor a variation in the number of TUNEL- and nitrotyrosine-positive cells within the ipsilateral lesion was observed in melatonin-treated animals compared with controls. However, a decrease in the density of tomato lectin-positive cells after melatonin treatment was found in the white matter underlying cortical lesion. Furthermore, we showed a marked increase in the myelin basic protein-immunoreactivity in the cingulum and in the density of mature oligodendrocytes (APC-immunoreactive) in both the ipsilateral cingulum and external capsule. These results suggest that melatonin is not able to reduce cortical infarct volume in a neonatal stroke model but strongly reduces inflammation and promotes subsequent myelination in the white matter.