Cortical blood flow and cerebral perfusion pressure in a new noncraniotomy model of subarachnoid hemorrhage in the rat

The importance of early brain injury after subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a medical emergency that accounts for 5% of all stroke cases. Individuals affected are typically in the prime of their lives (mean age 50 years). Approximately 12% of patients die before receiving medical attention, 33% within 48 h and 50% within 30 days of aSAH. Of the survivors 50% suffer from permanent disability with an estimated lifetime cost more than double that of an ischemic stroke. Traditionally, spasm that develops in large cerebral arteries 3-7 days after aneurysm rupture is considered the most important determinant of brain injury and outcome after aSAH. However, recent studies show that prevention of delayed vasospasm does not improve outcome in aSAH patients. This finding has finally brought in focus the influence of early brain injury on outcome of aSAH. A substantial amount of evidence indicates that brain injury begins at the aneurysm rupture, evolves with time and plays an important role in patients' outcome. In this manuscript we review early brain injury after aSAH. Due to the early nature, most of the information on this injury comes from animals and few only from autopsy of patients who died within days after aSAH. Consequently, we began with a review of animal models of early brain injury, next we review the mechanisms of brain injury according to the sequence of their temporal appearance and finally we discuss the failure of clinical translation of therapies successful in animal models of aSAH.

Impact of anesthesia on pathophysiology and mortality following subarachnoid hemorrhage in rats

BACKGROUND

Anesthesia is indispensable for in vivo research but has the intrinsic potential to alter study results. The aim of the current study was to investigate the impact of three common anesthesia protocols on physiological parameters and outcome following the most common experimental model for subarachnoid hemorrhage (SAH), endovascular perforation.

METHODS

Sprague-Dawley rats (n = 38) were randomly assigned to (1) chloral hydrate, (2) isoflurane or (3) midazolam/medetomidine/fentanyl (MMF) anesthesia. Arterial blood gases, intracranial pressure (ICP), mean arterial blood pressure (MAP), cerebral perfusion pressure (CPP), and regional cerebral blood flow (rCBF) were monitored before and for 3 hours after SAH. Brain water content, mortality and rate of secondary bleeding were also evaluated.

RESULTS

Under baseline conditions isoflurane anesthesia resulted in deterioration of respiratory parameters (arterial pCO2 and pO2) and increased brain water content. After SAH, isoflurane and chloral hydrate were associated with reduced MAP, incomplete recovery of post-hemorrhagic rCBF (23 ± 13% and 87 ± 18% of baseline, respectively) and a high anesthesia-related mortality (17 and 50%, respectively). Anesthesia with MMF provided stable hemodynamics (MAP between 100-110 mmHg), high post-hemorrhagic rCBF values, and a high rate of re-bleedings (> 50%), a phenomenon often observed after SAH in humans.

CONCLUSION

Based on these findings we recommend anesthesia with MMF for the endovascular perforation model of SAH.

A novel intravital method to evaluate cerebral vasospasm in rat models of subarachnoid hemorrhage: a study with synchrotron radiation angiography

Precise in vivo evaluation of cerebral vasospasm caused by subarachnoid hemorrhage has remained a critical but unsolved issue in experimental small animal models. In this study, we used synchrotron radiation angiography to study the vasospasm of anterior circulation arteries in two subarachnoid hemorrhage models in rats. Synchrotron radiation angiography, laser Doppler flowmetry-cerebral blood flow measurement, [¹²⁵I]N-isopropyl-p-iodoamphetamine cerebral blood flow measurement and terminal examinations were applied to evaluate the changes of anterior circulation arteries in two subarachnoid hemorrhage models made by blood injection into cisterna magna and prechiasmatic cistern. Using synchrotron radiation angiography technique, we detected cerebral vasospasm in subarachnoid hemorrhage rats compared to the controls (p<0.05). We also identified two interesting findings: 1) both middle cerebral artery and anterior cerebral artery shrunk the most at day 3 after subarachnoid hemorrhage; 2) the diameter of anterior cerebral artery in the prechiasmatic cistern injection group was smaller than that in the cisterna magna injection group (p<0.05), but not for middle cerebral artery. We concluded that synchrotron radiation angiography provided a novel technique, which could directly evaluate cerebral vasospasm in small animal experimental subarachnoid hemorrhage models. The courses of vasospasm in these two injection models are similar; however, the model produced by prechiasmatic cistern injection is more suitable for study of anterior circulation vasospasm.

Experimental subarachnoid hemorrhage causes early and long-lasting microarterial constriction and microthrombosis: an in-vivo microscopy study

Early brain injury (EBI) after subarachnoid hemorrhage (SAH) is characterized by a severe, cerebral perfusion pressure (CPP)-independent reduction in cerebral blood flow suggesting alterations on the level of cerebral microvessels. Therefore, we aimed to use in-vivo imaging to investigate the cerebral microcirculation after experimental SAH. Subarachnoid hemorrhage was induced in C57/BL6 mice by endovascular perforation. Pial arterioles and venules (10 to 80 μm diameter) were examined using in-vivo fluorescence microscopy, 3, 6, and 72 hours after SAH. Venular diameter or flow was not affected by SAH, while >70% of arterioles constricted by 22% to 33% up to 3 days after hemorrhage (P<0.05 versus sham). The smaller the investigated arterioles, the more pronounced the constriction (r(2)=0.92, P<0.04). Approximately 30% of constricted arterioles were occluded by microthrombi and the frequency of arteriolar microthrombosis correlated with the degree of constriction (r(2)=0.93, P<0.03). The current study demonstrates that SAH induces microarterial constrictions and microthrombosis in vivo. These findings may explain the early CPP-independent decrease in cerebral blood flow after SAH and may therefore serve as novel targets for the treatment of early perfusion deficits after SAH.

The effect of common carotid artery occlusion on delayed brain tissue damage in the rat double subarachnoid hemorrhage model

OBJECTIVE

Delayed ischemic brain tissue damage in the time course of cerebral vasospasm in the rat double-subarachnoid hemorrhage (SAH) model has been described before. However, in order to enhance hemodynamic insufficiency during cerebral vasospasm (CVS), we performed-in a modification to the standard double-hemorrhage model-an additional unilateral common carotid artery occlusion (CCAO), expecting aggravation of brain-tissue damage in areas particularly sensitive to hypoxia.

METHODS

CVS was induced by injection of 0.25 ml autologous blood twice in the cisterna magna of Sprague-Dawley rats with and without unilateral CCAO. The animals were examined on days 2, 3, 4 and 5, and compared with the sham-operated control group without SAH. The functional deficits were graded between 0 and 3. Perfusion weighted imaging (PWI) at 3 Tesla magnetic resonance (MR) tomography was performed to assess cerebral blood flow (CBF). The brains were fixed, stained and evaluated for histological changes.

RESULTS

On day 5, the neurological state was significantly worse in rats with SAH. The relative CBF/muscle blood ratio was significantly decreased by SAH and lowest in rats with CCAO and SAH (4.5 ± 1.1 vs 2.7 ± 0.6) compared with sham (7.9 ± 1.5; p < 0.001). Basilar artery (BA) diameter was 79 ± 5 μm (SAH) vs 147 ± 4 μm (sham, p < 0.001). Neuronal cell count in the hippocampal areas CA1-CA4 was significantly reduced by SAH on day 5 (p < 0.001) and lowest in rats with SAH and CCAO.

CONCLUSIONS

CCAO leads to an aggravation of CVS-related delayed brain tissue damage in the modified rat double-SAH model.

Inhibition of Rho kinase by hydroxyfasudil attenuates brain edema after subarachnoid hemorrhage in rats

The blood-brain barrier (BBB) disruption and brain edema are important pathophysiologies of early brain injury after subarachnoid hemorrhage (SAH). This study is to evaluate whether Rho kinase (Rock) enhances BBB permeability via disruption of tight junction proteins during early brain injury. Adult male rats were assigned to five groups; Sham-operated, SAH treated with saline, a Rock inhibitor hydroxyfasudil (HF) (10 mg/kg) treatment at 0.5 h after SAH, HF treatment at 0.5 and 6 h (10 mg/kg, each) after SAH, and another Rock inhibitor Y27632 (10 mg/kg) treatment at 0.5 h after SAH. The perforation model of SAH was performed and neurological score and brain water content were evaluated 24 and 72 h after surgery. Evans blue extravasation, Rock activity assay, and western blotting analyses were evaluated 24 h after surgery. Treatment of HF significantly improved neurological scores 24 h after SAH. Single treatment with HF and Y27632, and two treatments with HF reduced brain water content in the ipsilateral hemisphere. HF reduced Evans blue extravasation in the ipsilateral hemisphere after SAH. Rock activity increased 24 h after SAH, and HF reversed the activity. SAH significantly decreased the levels of tight junction proteins, occludin and zonula occludens-1 (ZO-1), and HF preserved the levels of occluding and ZO-1 in ipsilateral hemisphere. In conclusion, HF attenuated BBB permeability after SAH, possibly by protection of tight junction proteins.

Minocycline improves functional outcomes, memory deficits, and histopathology after endovascular perforation-induced subarachnoid hemorrhage in rats

Subarachnoid hemorrhage (SAH) results in significant long-lasting cognitive dysfunction. Therefore, evaluating acute and long-term outcomes after therapeutic intervention is important for clinical translation. The aim of this study was to use minocycline, a known neuroprotectant agent, to evaluate the long-term benefits in terms of neurobehavior and neuropathology after experimental SAH in rats, and to determine which neurobehavioral test would be effective for long-term evaluation. SAH was induced by endovascular perforation in adult male Sprague-Dawley rats (n=118). The animals were treated with intraperitoneal injection of minocycline (45 mg/kg or 135 mg/kg) or vehicle 1 h after SAH induction. In the short-term, animals were euthanized at 24 and 72 h for evaluation of neurobehavior, brain water content, and matrix metalloproteinase (MMP) activity. In the long-term, neurobehavior was evaluated at days 21-28 post-SAH, and histopathological analysis was done at day 28. High-dose but not low-dose minocycline reduced brain water content at 24 h, and therefore only the high-dose regimen was used for further evaluation, which reduced MMP-9 activity at 24 h. Further, high-dose minocycline improved spatial memory and attenuated neuronal loss in the hippocampus and cortex. The rotarod, T-maze, and water maze tests, but not the inclined plane test, detected neurobehavioral deficits in SAH rats at days 21-28. This study demonstrates that minocycline attenuates long-term functional and morphological outcomes after endovascular perforation-induced SAH. Long-term neurobehavioral assessments using the rotarod, T-maze, and water maze tests could be useful to evaluate the efficacy of therapeutic intervention after experimental SAH.

Reduction of neutrophil activity decreases early microvascular injury after subarachnoid haemorrhage

Background

Subarachnoid haemorrhage (SAH) elicits rapid pathological changes in the structure and function of parenchymal vessels (≤ 100 μm). The role of neutrophils in these changes has not been determined. This study investigates the role of neutrophils in early microvascular changes after SAH

Method

Rats were either untreated, treated with vinblastine or anti-polymorphonuclear (PMN) serum, which depletes neutrophils, or treated with pyrrolidine dithiocarbamate (PDTC), which limits neutrophil activity. SAH was induced by endovascular perforation. Neutrophil infiltration and the integrity of vascular endothelium and basement membrane were assessed immunohistochemically. Vascular collagenase activity was assessed by in situ zymography.

Results

Vinblastine and anti-PMN serum reduced post-SAH accumulation of neutrophils in cerebral vessels and in brain parenchyma. PDTC increased the neutrophil accumulation in cerebral vessels and decreased accumulation in brain parenchyma. In addition, each of the three agents decreased vascular collagenase activity and post-SAH loss of vascular endothelial and basement membrane immunostaining.

Conclusions

Our results implicate neutrophils in early microvascular injury after SAH and indicate that treatments which reduce neutrophil activity can be beneficial in limiting microvascular injury and increasing survival after SAH.

Trigeminal ganglion neuron density and regulation of anterior choroid artery vasospasm: In a rabbit model of subarachnoid hemorrhage

Background:

Subarachnoid hemorrhage (SAH) is associated with severe vasospasm caused by a variety of neurochemical mechanisms. The anterior choroid arteries (AChAs) are innervated by vasodilated fibers of the trigeminal ganglion (TGG). The goal of this study was to determine whether there is a relationship between the neuron density of the TGG and the severity of AChAs vasospasm with SAH.

Methods:

Thirty-two rabbits were used for the study; eight served as the baseline control group, seven as a SHAM group, with injections of 1 cc of isotonic saline solution, and 17 rabbits were included in the experimental SAH group, with injection of homologous blood into the cisterna magna. After 10 days, the histopathology of the AChAs and TGGs were examined. The AChAs vasospasm index (VSI) of the external/internal diameter and the neuron density of the ophthalmic root of the TGGs were evaluated stereologically. The AChAs VSI was preferred -- a measure of the degree of vasospasm. As the VSI increased, the degree of arterial vasospasm increased. The results were statistically analyzed.

Results:

The mean AChAs VSI was significantly higher and the mean neuronal density of the ophthalmic root of the TGG was significantly lower in the group with severe vasospasm associated with SAH compared to the controls, SHAM, and the group with mild vasospasm associated with SAH (P< 0.05). The ophthalmic root of the TGG neuron density in the 7 rabbits that developed severe vasospasm was statistically less than that observed in the 10 rabbits with mild vasospasm. There was a linear relationship between the low neuronal density in the ophthalmic root of the TGG and the severity of the AChA vasospasm.

Conclusions:

The trigeminal ganglion neuron density may be an important factor in the regulation of AChAs diameter and cerebral blood flow. Low neuron density of the ophthalmic root of the TGG may play a role in the pathogenesis of AChAs vasospasm associated with SAH.

Treatment with Z-ligustilide, a component of Angelica sinensis, reduces brain injury after a subarachnoid hemorrhage in rats

Subarachnoid hemorrhage (SAH) is a devastating stroke subtype accounting for approximately 3 to 7% of cases each year. Despite its rarity among the various stroke types, SAH is still responsible for approximately 25% of all stroke fatalities. Although various preventative and therapeutic interventions have been explored for potential neuroprotection after SAH, a considerable percentage of patients still experience serious neurologic and/or cognitive impairments as a result of the primary hemorrhage and/or secondary brain damage that occurs. Z-ligustilide (LIG), the primary lipophilic component of the Chinese traditional medicine radix Angelica sinensis, has been shown to reduce ischemic brain injury via antiapoptotic pathways. Accordingly, in our study, we investigated the neuroprotective potential of LIG after experimental SAH in rats. Rats with SAH that was induced using the established double hemorrhage model were studied with and without LIG treatment. Mortality, neurobehavioral evaluation, brain water content, blood-brain barrier (BBB) permeability, and vasospasm assessment of the basilar artery were measured on days 3 and 7 after injury. Additional testing was done to evaluate for apoptosis using TdT-mediated dUTP-biotin nick end labeling staining as well as immunohistochemistry and Western blotting to identify key proapoptotic/survival proteins, i.e., p53, Bax, Bcl-2, and cleaved caspase-3. The results showed that LIG treatment reduced mortality, neurobehavioral deficits, brain edema, BBB permeability, and cerebral vasospasm. In addition, treatment reduced the number of apoptotic cells in the surrounding brain injury site, which accompanied a marked down-regulation of proapoptotic proteins, p53, and cleaved caspase-3. Our data suggest that LIG may be an effective therapeutic modality for SAH victims by altering apoptotic mechanisms.

Blood-brain barrier disruption following subarchnoid hemorrhage may be faciliated through PUMA induction of endothelial cell apoptosis from the endoplasmic reticulum

The blood-brain barrier (BBB) plays a vital role as both a physiologic and physical barrier in regulating the movement of water from the vasculature to the brain. During a subarachnoid hemorrhage (SAH), the BBB is disrupted by a variety of mediators, one of which can result in endothelial cell death. As a result, in the present study, we investigated the role of PUMA (p53 upregulated modulator of apoptosis) following SAH injury in rats. Specifically evaluating whether through the endoplasmic reticulum (ER), PUMA could orchestrate the induction of endothelial cell apoptosis and cause a disruption in the blood-brain barrier integrity. One hundred twelve male Sprague-Dawley rats were randomly divided into 4 groups: sham, SAH, SAH+control siRNA, SAH+PUMA siRNA. Outcomes measured include mortality rate, brain edema, BBB disruption, and neurobehavioral testing. We also used Western blotting techniques to measure the expression of key pro-apoptotic proteins such as BAX, BAK, and DRP1. PUMA siRNA treatment significantly reduced the mortality rate, cerebral edema, neurobehavioral deficits, and BBB disruption as measured by Evans blue assay following SAH injury. The T2WI images showed there was an increase in vasogenic edema in the brain following SAH, which could be alleviated by PUMA siRNA. Immunohistochemical staining and Western blot analysis demonstrated an increased expression of PUMA, BAX, BAK, GRP78 and DRP1 in the microvascular endothelial cells of the hippocampus, which was accompanied with endothelium apoptosis. This study showed that PUMA induced endothelial cell apoptosis may in fact play a significant role in BBB disruption following SAH and its mediation may be through the endoplasmic reticulum. By blocking the activity of PUMA using siRNA, we were able to prevent the accumulation of cerebral edema that occurs following BBB disruption. This translated into a preservation of functional integrity and an improvement in mortality.

Characterizing the role of the neuropeptide substance P in experimental subarachnoid hemorrhage

BACKGROUND

Raised intracranial pressure (ICP) following SAH predicts poor outcome and is due to hemorrhage volume and possibly, brain edema, hydrocephalus and increased volume of circulating intracranial blood. Interventions that reduce edema may therefore reduce ICP and improve outcome. The neuropeptide substance P (SP) mediates vasogenic edema formation in animal models of ischemic stroke, intracerebral hemorrhage and brain trauma, and may contribute to development of increased ICP. SP (NK1 tachykinin receptor) blockade using n-acetyl-l-tryptophan (NAT) reduces edema and improves outcome in these models. This study therefore assessed whether SP mediates edema formation in experimental SAH.

METHODS

SAH was induced in rats by either injection of autologous blood into the prechiasmatic cistern (injection SAH) or by arterial puncture of the Circle of Willis (filament SAH). NAT was injected (i.v.) 30min after SAH induction. Subgroups were assessed for brain water content, SP and albumin immunoreactivity, and functional outcome at 5, 24 and 48h or ICP over 5h.

RESULTS

A secondary ICP increase occurred within 2h of SAH. Brain edema followed filament SAH (p<0.001) and correlated with functional deficits (r=0.8, p<0.01). Increased albumin immunoreactivity (p<0.001) indicated vasogenic edema. However, NAT treatment did not improve ICP, edema or outcome.

CONCLUSIONS

Experimental SAH produced secondary ICP elevation, vasogenic brain edema and functional deficits, although it is unclear if edema contributed to ICP. Blockade of SP did not improve any outcome parameters, suggesting that neurogenic inflammation may be less critical than other factors in these models.

Hypoperfusion in the acute phase of subarachnoid hemorrhage

PURPOSE

Acute disruption of cerebral perfusion and metabolism is a well-established hallmark of the immediate phase after subarachnoid hemorrhage (SAH). It is thought to contribute significantly to acute brain injury, but despite its prognostic importance, the exact mechanism and time course is largely unknown and remains to be characterized.

METHODS

We investigated changes in cerebral perfusion after SAH in both an experimental and clinical setting. Using an animal model of massive, experimental SAH (n=91), we employed Laser-Doppler flowmetry (LDF), parenchymal microdialysis (MD; n=61), Diffusion-weighted imaging (DWI) and MR spectroscopy (MRS; n=30) to characterize the first hours after SAH in greater detail. The effect of prophylactic treatment with hypothermia (HT; 32°C) and an endothelin-A (ET-A) receptor antagonist (Clazosentan) was also studied. In a group of patients presenting with acute SAH (n=17) we were able to determine cerebral blood flow (CBF) via Xenon-enhanced computed tomography (XeCT) within 12 h after the ictus.

RESULTS

The acute phase after SAH is characterized both experimentally and clinically by profound and prolonged hypoperfusion independent from current intracranial pressure (ICP), indicating acute vasospasm. Experimentally, when treated with hypothermia or a ET-A receptor antagonist prophylactically, acute hypoperfusion improved rapidly. DWI showed a generalized, significant decline of the apparent diffusion coefficient (ADC) after SAH, indicating cytotoxic edema which was not present under hypothermia. SAH causes a highly significant reduction in glucose, as well as accumulation of lactate, glutmate and aspartate (MD and MRS). HT significantly ameliorated these metabolic disturbances.

CONCLUSION

Acute vasospasm, cytotoxic edema and a general metabolic stress response occur immediately after experimental SAH. Prophylactic treatment with hypothermia or ET-A antagonists can correct these disturbances in the experimental setting. Clinically, prolonged and ICP-independent hypoperfusion was also confirmed. As the initial phase is of particular importance regarding the neurological outcome and is amenable to beneficial intervention, the acute stage after SAH demands further investigation and warrants the exploration of measures to improve the immediate management of SAH patients.

Apoptotic mechanisms for neuronal cells in early brain injury after subarachnoid hemorrhage

OBJECTS

The major causes of death and disability in subarachnoid hemorrhage (SAH) may be early brain injury (EBI) and cerebral vasospasm. Although cerebral vasospasm has been studied and treated by a lot of drugs, the outcome is not improved even if vasospasm is reversed. Based on these data, EBI is considered a primary target for future research, and apoptosis may be involved in EBI after experimental SAH.

METHODS

We reviewed the published literature about the relationship between SAH induced EBI and apoptosis in PubMed.

RESULT

Most available information can be obtained from the endovascular filament perforation animal model. After onset of SAH, intracranial pressure is increased and then cerebral blood flow is reduced. Many factors are involved in the mechanism of apoptotic cell death in EBI after SAH. In the neuronal cells, both intrinsic and extrinsic pathways of apoptosis can occur. Some antiapoptotic drugs were studied and demonstrated a protective effect against EBI after SAH. However, apoptosis in EBI after SAH has been little studied and further studies will provide us more beneficial findings.

CONCLUSIONS

The study of apoptosis in EBI after experimental SAH may give us new therapies for SAH.

Mechanisms of early brain injury after SAH: matrix metalloproteinase 9

Subarachnoid hemorrhage (SAH) is an important cause of death and disability worldwide. To date, there is not a definitive treatment that completely prevents brain injury after SAH. Recently, early brain injury (EBI) has been pointed out to be the primary cause of mortality in SAH patients. Apoptosis that occurs in neuronal tissues and cerebral vasculature after SAH plays an essential role in EBI. Matrix metalloproteinase 9 (MMP-9) has been found to increase in many cerebral vascular diseases. There have been reports that MMP-9 can mediate apoptosis, which called anoikis in cerebral ischemia models, through cleaving main components of the extracellular matrix (ECM), especially laminin. Therefore, minocycline, which has been found to inhibit MMP-9, may be protective to brain injury after SAH. We based our hypothesis on the fact that SAH possesses some aspects that are similar to those of cerebral ischemia. It is conceivable that MMP-9 may also be involved in the pathological process of EBI after SAH, and minocycline can relieve anoikis and improve EBI after SAH.

Early micro vascular changes after subarachnoid hemorrhage

During the last decade much effort has been invested in understanding the events that occur early after SAH. It is now widely accepted that these early events not only participate in the early ischemic injury but also set the stage for the pathogenesis of delayed vasospasm. That early cerebral ischemia occurs after SAH is documented in both experimental SAH and in human autopsy studies; however, angiographic evidence for vasoconstriction early after SAH is lacking and the source of early ischemic injury is therefore unclear. Recently, the cerebral microvasculature has been identified as an early target of SAH. Changes in the anatomical structure of cerebral microvessels, sufficient to cause functional deficits, are found early after experimental SAH. These changes may explain cerebral ischemia in human in the absence of angiographic evidence of large vessel vasoconstriction. This paper summarizes known alterations in cerebral microvasculature during the first 48 h after SAH.

Advances in experimental subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) remains to be a devastating disease with high mortality and morbidity. Two major areas are becoming the focus of the research interest of SAH: these are cerebral vasospasm (CVS) and early brain injury (EBI). This mini review will provide a broad summary of the major advances in experimental SAH during the last 3 years. Treatments interfering with nitric oxide (NO)- or endothelin-pathways continue to show antispasmotic effects in experimental SAH. HIF 1 may play both a detrimental and beneficial role in the setting of SAH, depending on its activation stage. Inflammation and oxidative stress contribute to the pathophysiology of both CVS and EBI. Apoptosis, a major component of EBI after SAH, also underlie the etiology of CVS. Since we recognize now that CVS and EBI are the two major contributors to the significant mortality and morbidity associated with SAH, ongoing research will continue to elucidate the underlying pathophysiological pathways and treatment strategies targeting both CVS and EBI may be more successful and improve outcome of patients with SAH.

Pharmacologically augmented S-nitrosylated hemoglobin improves recovery from murine subarachnoid hemorrhage

BACKGROUND AND PURPOSE

S-nitrosylated hemoglobin (S-nitrosohemoglobin) has been implicated in the delivery of O(2) to tissues through the regulation of microvascular blood flow. This study tested the hypothesis that enhancement of S-nitrosylated hemoglobin by ethyl nitrite inhalation improves outcome after experimental subarachnoid hemorrhage (SAH).

METHODS

A preliminary dosing study identified 20 ppm ethyl nitrite as a concentration that produced a 4-fold increase in S-nitrosylated hemoglobin concentration with no increase in methemoglobin. Mice were subjected to endovascular perforation of the right anterior cerebral artery and were treated with 20 ppm ethyl nitrite in air, or air alone for 72 hours, after which neurologic function, cerebral vessel diameter, brain water content, cortical tissue Po(2), and parenchymal red blood cell flow velocity were measured.

RESULTS

At 72 hours after hemorrhage, air- and ethyl nitrite-exposed mice had similarly sized blood clots. Ethyl nitrite improved neurologic score and rotarod performance; abated SAH-induced constrictions in the ipsilateral anterior, middle cerebral, and internal carotid arteries; and prevented an increase in ipsilateral brain water content. Ethyl nitrite inhalation increased red blood cell flow velocity and cortical tissue Po(2) in the ipsilateral cortex with no effect on systemic blood pressure.

CONCLUSIONS

Targeted S-nitrosylation of hemoglobin improved outcome parameters, including vessel diameter, tissue blood flow, cortical tissue Po(2), and neurologic function in a murine SAH model. Augmenting endogenous Po(2)-dependent delivery of NO bioactivity to selectively dilate the compromised cerebral vasculature has significant clinical potential in the treatment of SAH.

Metamorphosis of subarachnoid hemorrhage research: from delayed vasospasm to early brain injury

Delayed vasospasm that develops 3–7 days after aneurysmal subarachnoid hemorrhage (SAH) has traditionally been considered the most important determinant of delayed ischemic injury and poor outcome. Consequently, most therapies against delayed ischemic injury are directed towards reducing the incidence of vasospasm. The clinical trials based on this strategy, however, have so far claimed limited success; the incidence of vasospasm is reduced without reduction in delayed ischemic injury or improvement in the long-term outcome. This fact has shifted research interest to the early brain injury (first 72 h) evoked by SAH. In recent years, several pathological mechanisms that activate within minutes after the initial bleed and lead to early brain injury are identified. In addition, it is found that many of these mechanisms evolve with time and participate in the pathogenesis of delayed ischemic injury and poor outcome. Therefore, a therapy or therapies focused on these early mechanisms may not only prevent the early brain injury but may also help reduce the intensity of later developing neurological complications. This manuscript reviews the pathological mechanisms of early brain injury after SAH and summarizes the status of current therapies.

Adenosine A(2A) receptors in early ischemic vascular injury after subarachnoid hemorrhage. Laboratory investigation

OBJECT

The role of adenosine A(2A) receptors in the early vascular response after subarachnoid hemorrhage (SAH) is unknown. In other forms of cerebral ischemia both activation and inhibition of A(2A) receptors is reported to be beneficial. However, these studies mainly used pharmacological receptor modulation, and most of the agents available exhibit low specificity. The authors used adenosine A(2A) receptor knockout mice to study the role of A(2A) receptors in the early vascular response to SAH.

METHODS

Subarachnoid hemorrhage was induced in wild-type mice (C57BL/6) and A(2A) receptor knockout mice by endovascular puncture. Cerebral blood flow, intracranial pressure, and blood pressure were recorded, and cerebral perfusion pressure was deduced. Animals were sacrificed at 1, 3, or 6 hours after SAH or sham surgery. Coronal brain sections were immunostained for Type IV collagen, the major protein of the basal lamina. The internal diameter of major cerebral arteries and the area fraction of Type IV collagen-positive microvessels (< 100 μm) were determined.

RESULTS

The initial increase in intracranial pressure and decrease in cerebral perfusion pressure at SAH induction was similar in both types of mice, but cerebral blood flow decline was significantly smaller in A(2A) receptor knockout mice as compared with wild-type cohorts. The internal diameter of major cerebral vessels decreased progressively after SAH. The extent of diameter reduction was significantly less in A(2A) receptor knockout mice than in wild-type mice. Type IV collagen immunostaining decreased progressively after SAH. This decrease was significantly less in A(2A) receptor knockout mice than in wild-type mice.

CONCLUSIONS

These results demonstrate that global inactivation of A(2A) receptors decreases the intensity of the early vascular response to SAH. Early inhibition of A(2A) receptors after SAH might reduce cerebral injury.

Effect of vardenafil on cerebral vasospasm following experimental subarachnoid hemorrhage in rats

We examined the effects of the phosphodiesterase 5 (PDE-5) inhibitor vardenafil on cerebral vasospasm in an experimental rat subarachnoid hemorrhage (SAH) model. Thirty-two albino Wistar rats were divided into five groups: G1, no experimental intervention; G2, administered subarachnoid physiological saline after sham surgery; G3, subjected to SAH; G4, subjected to SAH and administered low-dose (0.5 mg/kg) vardenafil treatment; and G5, subjected to SAH and administered high-dose (5 mg/kg) vardenafil treatment. For animals in G3, G4 and G5, SAH was induced by an injection of autologous non-heparinized blood into the cisterna magna. Immediately after SAH, for animals in G4 and G5, vardenafil was administered by gavage at intervals of 8 hours for 2 days. The rats were then decapitated, and basilar arteries and blood samples were taken for biochemical and histopathological examination. Malonyldialdehyde values in G2 (p = 0.004) and G3 (p = 0.002) were significantly higher than those in G1. G4 and G5 had significantly lower values than G2 and G3 (p = 0.014, G4 v. G2; p = 0.005, G4 v. G3; p = 0.005, G5 v. G2; p = 0.002, G5 v. G3). Total antioxidant capacity (TAC) values in G3 were significantly lower than those in G1 (p = 0.041). TAC values in G4 and G5 were significantly higher than those in G3 (p = 0.043). Mean luminal diameter in G3 was significantly smaller compared with G1 and G2 (p = 0.002), but larger in G4 (p = 0.002) and G5 (p = 0.001) compared with G3. Mean luminal diameter was also significantly larger in G5 than in G2 (p = 0.008) and G4 (p = 0.038). Mean wall thickness in G2 (p = 0.015) and G3 (p = 0.002) was significantly thicker compared with G1. Wall thickness was significantly thinner in G4 and G5 compared with G2 and G3 (p = 0.008, G4 v. G2; p = 0.001, G4 v. G3; p = 0.005, G5 v. G2; p = 0.001, G5 v. G3). Our results confirm that vardenafil may induce vasodilatation and provide potential benefits in SAH therapy by preventing vasospasm.

Luminal platelet aggregates in functional deficits in parenchymal vessels after subarachnoid hemorrhage

The pathophysiology of early ischemic injury after aneurysmal subarachnoid hemorrhage (SAH) is not understood. This study examined the acute effect of endovascular puncture-induced SAH on parenchymal vessel function in rat, using intravascular fluorescent tracers to assess flow and vascular permeability and immunostaining to assess structural integrity and to visualize platelet aggregates. In sham-operated animals, vessels were well filled with tracer administered 10s before sacrifice, and parenchymal escape of tracer was rare. At ten minutes and three hours after hemorrhage, patches of poor vascular filling were distributed throughout the forebrain. Close examination of these regions revealed short segments of narrowed diameter along many profiles. Most vascular profiles with reduced perfusion contained platelet aggregates and in addition showed focal loss of collagen IV, a principal component of basal lamina. In contrast, vessels were well filled at 24h post-hemorrhage, indicating that vascular perfusion had recovered. Parenchymal escape of intravascular tracer was detected at 10 min post-hemorrhage and later as plumes of fluorescence emanating into parenchyma from restricted microvascular foci. These data demonstrate that parenchymal microvessels are compromised in function by 10 min after SAH and identify focal microvascular constriction and local accumulation of luminal platelet aggregates as potential initiators of that compromise.

Brain interstitial fluid TNF-alpha after subarachnoid hemorrhage

OBJECTIVE

TNF-alpha is an inflammatory cytokine that plays a central role in promoting the cascade of events leading to an inflammatory response. Recent studies have suggested that TNF-alpha may play a key role in the formation and rupture of cerebral aneurysms, and that the underlying cerebral inflammatory response is a major determinate of outcome following subrarachnoid hemorrhage (SAH).

METHODS

We studied 14 comatose SAH patients who underwent multimodality neuromonitoring with intracranial pressure (ICP) and cerebral microdialysis as part of their clinical care. Continuous physiological variables were time-locked every 8h and recorded at the same point that brain interstitial fluid TNF-alpha was measured in brain microdialysis samples. Significant associations were determined using generalized estimation equations.

RESULTS

Each patient had a mean of 9 brain tissue TNF-alpha measurements obtained over an average of 72h of monitoring. TNF-alpha levels rose progressively over time. Predictors of elevated brain interstitial TNF-alpha included higher brain interstitial fluid glucose levels (beta=0.066, p<0.02), intraventricular hemorrhage (beta=0.085, p<0.021), and aneurysm size >6mm (beta=0.14, p<0.001). There was no relationship between TNF-alpha levels and the burden of cisternal SAH; concurrent measurements of serum glucose, or lactate-pyruvate ratio.

INTERPRETATION

Brain interstitial TNF-alpha levels are elevated after SAH, and are associated with large aneurysm size, the burden of intraventricular blood, and elevation brain interstitial glucose levels.

Role of matrix metalloproteinase-9 in apoptosis of hippocampal neurons in rats during early brain injury after subarachnoid hemorrhage

This study investigated the possible involvement of matrix metalloproteinase 9 (MMP-9) in early brain injury (EBI) of subarachnoid hemorrhage (SAH) in rats. MMP-9 activities in hippocampus were examined at 6, 12, 24, 48 and 72 h after SAH. Laminin was detected by immunohistochemistry. Apoptosis of neurons in hippocampus was observed by TUNEL. Brain water content was also examined. MMP-9 activity and the number of apoptotic neurons increased from 12 to 72 h with a peak at 24 h. Laminin was found to decrease at 12 h, reached minimum at 24 h and began to increase from 48 h, which had a negative correlation with apoptotic neurons. The changes of brain water content were found to be coincidence with that of neuronal apoptosis. Our findings suggest that MMP-9 is probably involved in the pathophysiological events of EBI after SAH, through degrading laminin which leads to neuronal anoikis of hippocampus.

Gamma-secretase inhibitor (GSI1) attenuates morphological cerebral vasospasm in 24h after experimental subarachnoid hemorrhage in rats

Notch signaling plays an important role in the arteriogenesis. We hypothesized that the Notch inhibitor--gamma-secretase inhibitor (GSI1) exerted its effects on the vasospasm via regulation of NF-kappaB and MMP-9. In this study, 160 male Sprague-Dawley (SD) rats were randomly assigned into four groups: Sham, subarachnoid hemorrhage (SAH), SAH treated with dimethyl sulfoxide (DMSO) and SAH treated with GSI1. After 24h SAH, the mortality, neurological scores, blood-brain barrier permeability and brain water content were examined. The mRNA and protein level of Notch1, the expression and activity of NF-kappaB and MMP-9 were evaluated. Severe morphological vasospasm in the basilar artery was observed in SAH and DMSO treated rats. GSI1 significantly effected on neurological deficits, but not on mortality; significantly reduced morphological vasospasm, blood-brain barrier permeability, brain water content; significantly decreased the protein level of Notch1, NF-kappaB p50 and MMP-9, as well as the DNA-binding activity of NF-kappaB (EMSA) and the activity of MMP-9 (Zymography). These findings suggest that GSI1 plays a critical role in the attenuation of acute cerebral vasospasm, which may provide a novel therapeutic target for cerebral vasospasm after SAH insult.

Role of gap junctions in early brain injury following subarachnoid hemorrhage

Gap junction inhibition has been demonstrated to reverse the vascular contraction that follows experimental subarachnoid hemorrhage. This study hypothesizes that the use of established gap junction inhibitors: octonal and carbenoxolone, to interrupt cell to cell communication will provide neuroprotection against early brain injury after SAH. The filament perforation model of SAH was performed in male Sprague-Dawley rats weighing between 300 and 380 g. Octanol (260.46 mg or 781.38 mg/kg), carbenoxolone (100 mg/kg), or vehicles were given via intraperitoneal injection 1 h after SAH. Neurologic deficits and cerebral apoptosis were assessed 24 and 72 h after SAH. In addition, Western blot analysis was performed to confirm the in vivo inhibition of CNS gap junctions. The administration of octanol and carbenoxolone both failed to attenuate the neurological deficits induced by SAH, and they did not reduce neuronal apoptosis. Additionally, carbenoloxone increased post SAH mortality and exacerbated SAH-induced apoptosis. Despite previous studies that show gap junction inhibitors reverse vasospasm following experimental SAH, they failed to improve clinical outcomes or provide neuroprotection in this study.

Brain edema formation and neurological impairment after subarachnoid hemorrhage in rats

Object

Global cerebral edema is an independent risk factor for early death and poor outcome after subarachnoid hemorrhage (SAH). In the present study, the time course of brain edema formation, neurological deficits, and neuronal cell loss were investigated in the rat filament SAH model.

Methods

Brain water content and neurological deficits were determined in rats randomized to sham (1-, 24-, or 48-hour survival), SAH by endovascular perforation (1-, 24-, or 48-hour survival), or no surgery (control). The neuronal cell count (CA1–3) was quantified in a separate set of SAH (6-, 24-, 48-, or 72-hour survival) and shamoperated animals.

Results

Brain water content increased significantly 24 (80.2 ± 0.4% [SAH] vs 79.2 ± 0.1% [sham]) and 48 hours (79.8 ± 0.2% [SAH] vs 79.3 ± 0.1% [sham]) after SAH. The neuroscore was significantly worse after SAH (33 ± 15 [24 hours after SAH] vs 0 ± 0 points [sham]) and correlated with the extent of brain edema formation (r = 0.96, p < 0.001). No hippocampal damage was present up to 72 hours after SAH.

Conclusions

Brain water content and neurological dysfunction reached a maximum at 24 hours after SAH. This time point, therefore, seems to be optimal to test the effects of therapeutic interventions on brain edema formation. Neuronal cell loss was not present in CA1–3 up to 72 hours of SAH. Therefore, morphological damage needs to be evaluated at later time points.

Comparison of experimental rat models of early brain injury after subarachnoid hemorrhage

OBJECTIVE

To investigate acute pathophysiological changes after subarachnoid hemorrhage (SAH) in rats and compare endovascular perforation and double blood injection models for studies of early brain injury after SAH.

METHODS

Rat SAH was induced by endovascular perforation of the internal carotid artery (n = 41) or double injection of autologous blood into the cisterna magna (n = 23). Effects of SAH on arterial blood pressure, intracranial pressure, cerebral artery dimensions, and cerebral blood flow were measured. Neuronal death was assessed 24 hours after SAH.

RESULTS

SAH was more severe in the endovascular perforation model (4-fold greater hemoglobin content on the basal brain surface), and mortality was greater (47%) than in the blood injection model (0%). Intracranial pressure increases were faster and greater in the perforation model. Correspondingly, cerebral blood flow reductions were greater after perforation than in the blood injection model, particularly in middle cerebral artery-supplied regions (32 +/- 16 versus 65 +/- 18 mL/100 g/min, P < 0.01). Diffuse neuronal death occurred in all rats in the perforation model but more seldom after blood injection. Anterior cerebral artery diameter and cross sectional area were significantly decreased on day 1 after SAH induction (52 +/- 21% and 22 +/- 16% of control values; P < 0.001) in the perforation model but not after blood injection.

CONCLUSION

The perforation model produced more severe pathophysiological changes than the double blood injection, and it mimics human SAH in having an injured blood vessel and direct hemorrhagic brain lesion under arterial blood pressure. Therefore, endovascular perforation seems more suitable for study of acute SAH sequelae. However, further model refinement is required to reduce the high mortality rate.

Mild hypothermia (33 degrees C) reduces intracranial hypertension and improves functional outcome after subarachnoid hemorrhage in rats

OBJECTIVE

After a subarachnoid hemorrhage (SAH), the primary cause of mortality is secondary brain injury occurring within the first 48 hours after the initial bleeding. Because of the unknown pathophysiology of these early events, therapeutic approaches are scarce. Because mild hypothermia (33 degrees C) is among the strongest neuroprotectants known so far, the aim of this study was to investigate acute and delayed effects of hypothermia if applied after SAH.

METHODS

Male Sprague-Dawley rats were subjected to SAH and randomly assigned to the following groups: 1) SAH under normothermia, 2) SAH followed by 2 hours of hypothermia starting 1 hour after the bleeding, and 3) SAH followed by 2 hours of hypothermia starting 3 hours after the bleeding. Cerebral blood flow and intracranial pressure were continuously measured up to 6 hours after SAH. Mortality, neurological deficits, and body weight were assessed from postoperative day 1 to day 7. Brain water content and morphological brain damage were quantified 24 hours and 7 days after SAH, respectively.

RESULTS

Mild hypothermia reduced intracranial pressure (P < 0.001) and posthemorrhagic neurological deficits (P < 0.05) and improved postoperative weight gain significantly (P < 0.05). Mortality, cerebral blood flow, and the formation of cerebral edema were not significantly influenced by mild hypothermia.

CONCLUSION

The current results show that mild hypothermia (33 degrees C) exhibits sustained neuroprotection if applied up to 3 hours after SAH. Overall, mild hypothermia seems to be an effective neuroprotective strategy after SAH and should therefore be evaluated as a treatment option for SAH in patients.

Escape of intraluminal platelets into brain parenchyma after subarachnoid hemorrhage

Platelet aggregates are present in parenchymal vessels as early as 10 min after experimental subarachnoid hemorrhage (SAH). Structural injury to parenchymal vessel walls and depletion of collagen-IV (the major protein of basal lamina) occur in a similar time frame. Since platelets upon activation release enzymes which can digest collagen-IV, we investigated the topographic relationship between platelet aggregates, endothelium, and basal lamina after SAH produced by endovascular perforation, using triple immunofluorescence and confocal microscopy with deconvolution. The location of platelet aggregates in relation to zymography-detected active collagenase was also examined. As reported previously, most cerebral vessels profiles contained platelets aggregates at 10 min after SAH. High-resolution three-dimensional image analysis placed many platelets at the ab-luminal (basal) side of endothelium at 10 min, and others either within the vascular basal lamina or in nearby parenchyma. By 24 h post hemorrhage, large numbers of platelets had entered the brain parenchyma. The vascular sites of platelet movement were devoid of endothelium and collagen-IV. Collagenase activity colocalized with vascular platelet aggregates. Our data demonstrate that parenchymal entry of platelets into brain parenchyma begins within minutes after hemorrhage. Three-dimensional analysis suggests that platelet aggregates initiate or stimulate local disruption of endothelium and destruction of adjacent basal lamina after SAH.

Neurological and neurobehavioral assessment of experimental subarachnoid hemorrhage

About 50% of humans with aneurysmal subarachnoid hemorrhage (SAH) die and many survivors have neurological and neurobehavioral dysfunction. Animal studies usually focused on cerebral vasospasm and sometimes neuronal injury. The difference in endpoints may contribute to lack of translation of treatments effective in animals to humans. We reviewed prior animal studies of SAH to determine what neurological and neurobehavioral endpoints had been used, whether they differentiated between appropriate controls and animals with SAH, whether treatment effects were reported and whether they correlated with vasospasm. Only a few studies in rats examined learning and memory. It is concluded that more studies are needed to fully characterize neurobehavioral performance in animals with SAH and assess effects of treatment.

Anterior circulation mouse model of subarachnoid hemorrhage

A model of subarachnoid hemorrhage (SAH) first described in rats where blood is injected into the prechiasmatic cistern was adapted to mice. The hypothesis was that such an anterior circulation SAH model would produce vasospasm of greater severity and longer duration than other mouse models. The goal was to create a mouse model that could then be used in transgenic and knockout animals in order to further knowledge of SAH and vasospasm. A needle was inserted stereotactically into the prechiasmatic cistern and 100 microl autologous arterial blood injected over seconds (n=10). Effects were compared to injection of saline (n=10) or to sham operation (n=7). Monitoring of cerebral blood flow by laser Doppler showed a statistically similar decrease during injection in both groups. 7 days after SAH there was vasospasm of the middle and anterior cerebral arteries (51% reduction in MCA radius in SAH compared to saline-injected group, P<0.009, Student's t-test). In order to determine if SAH in this model was associated with neuronal injury, brains were examined for TUNEL and fluoro-jade-positive cells. 60% of SAH but not saline-injected mice exhibited TUNEL-positive cells in the cerebral cortex and 30% of the SAH but no saline-injected mice had fluoro-jade positive cells in the cortex, hippocampus and dentate gyrus. The model is simple to perform and may be useful for investigating the pathophysiology of SAH.

Use of prolonged hypothermia to treat ischemic and hemorrhagic stroke

Therapeutic (induced) hypothermia (TH) has been extensively studied as a means to reduce brain injury following global and focal cerebral ischemia, intracerebral hemorrhage (ICH), and subarachnoid hemorrhage (SAH). Here, we briefly review the clinical and experimental evidence supporting the use of TH in each condition. We emphasize the importance of systematically evaluating treatment parameters, especially the duration of cooling, in each condition. We contend that TH provides considerable protection after global and focal cerebral ischemia, especially when cooling is prolonged (e.g., >24 h). However, there is presently insufficient evidence to support the clinical use of TH for ICH and SAH. In any case, further animal work is needed to develop optimized protocols for treating cardiac arrest (global ischemia), and to maximize the likelihood of successful clinical translation in focal cerebral ischemia.

Acute vasoconstriction: decrease and recovery of cerebral blood flow after various intensities of experimental subarachnoid hemorrhage in rats

OBJECT

Immediate vasoconstriction after subarachnoid hemorrhage (SAH) has been observed in a number of experimental studies. However, it has not yet been examined which pattern this acute-type vascular reaction follows and whether it correlates with the intensity of SAH. It was the purpose of the present study to vary the extent of SAH using the endovascular filament model of SAH with increasing filament sizes and to compare the course of intracranial pressure (ICP), cerebral perfusion pressure (CPP), and regional cerebral blood flow (rCBF).

METHODS

Male Sprague-Dawley rats were subjected to SAH using the endovascular filament model. Subarachnoid hemorrhage was induced using a 3-0, 4-0, or 5-0 Prolene monofilament (8 rats in each group). Eight animals served as controls. Bilateral rCBF (laser Doppler flowmetry), mean arterial blood pressure, and ICP were continuously monitored. Thereafter, the rats were allowed to wake up. Twenty-four hours later, the animals were killed, their brains were removed, and the extent of SAH was determined.

RESULTS

After induction of SAH, ICP steeply increased while CPP and rCBF rapidly declined in all groups. With increasing size of the filament, the increase of ICP and the decrease of CPP were more pronounced. However, the decline of rCBF exceeded the decline of CPP in all SAH groups. In a number of animals with minor SAH, an oscillating pattern of rCBF was observed during induction of SAH and during early recovery.

CONCLUSIONS

The disparity between the decline and recovery of CPP and rCBF suggests that acute vasoconstriction occurs even in SAH of a minor extent. Acute vasoconstriction may contribute significantly to a perfusion deficit in the acute stage after SAH. The oscillating pattern of rCBF in the period of early recovery after SAH resembles the pattern of synchronized vasomotion, which has been thoroughly examined for other vascular territories and may yield therapeutic potential.

Simvastatin attenuates cerebral vasospasm and improves outcomes by upregulation of PI3K/Akt pathway in a rat model of subarachnoid hemorrhage

BACKGROUND

Cerebral vasospasm is a common sequelae of subarachonoid hemorrhage (SAH), however, the mechanism of cerebral vasospasm is still unclear. Recently, statins have been shown to have efficacy in ameliorating cerebral vasospasm. The present study investigates whether simvastatin attenuates cerebral vasospasm after subarachnoid hemorrhage (SAH) via upregulation of the PI3K/Akt pathway.

METHODS

47 adult male Sprague-Dawley rats were divided into 6 groups: sham-operated, SAH treated with vehicle, SAH treated with low dose simvastatin (1 mg/kg), high dose simvastatin (20 mg/kg), SAH treated with simvastatin plus the PI3K inhibitor (wortmannin), and sham-operated plus wortmannin. Simvastatin was administered intraperitoneally 30 minutes after SAH created by the standard endovascular perforation model. Histological parameters of the ipsilateral internal carotid artery (ICA-diameter, perimeter, and wall thickness) and neurological score were assessed at 24 hours.

FINDINGS

Mortality was reduced to zero in both the treated groups as compared to 20% in the vehicle-treated and 36% in the simvastatin plus wortmannin-treated groups. The decrease in ICA diameter and perimeter observed in vehicle-treated group (203.2 +/- 10.3 microm, 652.7 +/- 29.0 microm) as compared to sham (259.7 +/- 10.6, 865.4 +/- 39.5) were significantly attenuated by high-dose simvastatin (267.4 +/- 8.0, 882.4 +/- 30.0). The increase in wall thickness (vehicle 29.50 +/- 2.42 microm v/s sham 9.52 +/- 0.56 microm) was significantly attenuated by both high and low dose simvastatin (11.87 +/- 1.56, 19.75 +/- 1.40). These effects of simvastatin were blocked with the addition of wortmannin (162.7 +/- 20.6, 528.9 +/- 65.9, 29.19 +/- 1.97). High dose simvastatin improved the neurological deficits after SAH, but this was also blocked by wortmannin.

CONCLUSIONS

The beneficial effects of high dose simvastatin in ameliorating cerebral vasospasm are likely mediated by upregulation of the PI3K/Akt pathway.

Melatonin reduces experimental subarachnoid hemorrhage-induced oxidative brain damage and neurological symptoms

Oxidative stress has detrimental effects in several models of neurodegenerative diseases, including subarachnoid hemorrhage (SAH). This study investigated the putative neuroprotective effect of melatonin, a powerful antioxidant, in a rat model of SAH. Male Wistar albino rats were divided as control, vehicle-treated SAH, and melatonin-treated (10 mg/kg, i.p.) SAH groups. To induce SAH, 0.3 mL blood was injected into cisterna magna of rats. Forty-eight hours after SAH induction, neurological examination scores were measured and the rats were decapitated. Brain tissue samples were taken for blood-brain barrier (BBB) permeability, brain water content, histological examination, or determination of malondialdehyde (MDA) and glutathione (GSH) levels, myeloperoxidase (MPO), and Na+-K+-ATPase activities. Formation of reactive oxygen species in brain tissue samples was monitored by using a chemiluminescence (CL) technique. The neurological examination scores were increased in SAH groups on the second day of SAH induction and SAH caused a significant decrease in brain GSH content and Na+-K+-ATPase activity, which was accompanied with significant increases in CL, MDA levels, and MPO activity. On the other hand, melatonin treatment reversed all these biochemical indices as well as SAH-induced histopathological alterations, while increased brain water content and impaired BBB were also reversed by melatonin treatment. This study suggests that melatonin, which can easily cross BBB, alleviates SAH-induced oxidative stress and exerts neuroprotection by preserving BBB permeability and by reducing brain edema.

Time-course of cerebral perfusion and tissue oxygenation in the first 6 h after experimental subarachnoid hemorrhage in rats

Present knowledge about hemodynamic and metabolic changes after subarachnoid hemorrhage (SAH) originates from neuromonitoring usually starting with aneurysm surgery and animal studies that have been focusing on the first 1 to 3 h after SAH. Most patients, however, are referred to treatment several hours after the insult. We examined the course of hemodynamic parameters, cerebral blood flow, and tissue oxygenation (ptiO2) in the first 6 h after experimental SAH. Sixteen Sprague-Dawley rats were subjected to SAH using the endovascular filament model or served as controls (n=8). Bilateral local cortical blood flow, intracranial pressure, cerebral perfusion pressure, and ptiO2 were followed for 6 h after SAH. After induction of SAH, local cortical blood flow rapidly declined to 22% of baseline and returned to 80% after 6 h. The decline of local cortical blood flow markedly exceeded the decline of cerebral perfusion pressure. ptiO2 declined to 57%, recovered after 2 h, and reached > or =140% of baseline after 6 h. Acute vasoconstriction after SAH is indicated by the marked discrepancy of cerebral perfusion pressure and local cortical blood flow. The excess tissue oxygenation several hours after SAH suggests disturbed oxygen utilization and cerebral metabolic depression. Aside from the sudden increase of intracranial pressure at the time of hemorrhage and delayed cerebral vasospasm, the occurrence of acute vasoconstriction and disturbed oxygen utilization may be additional factors contributing to secondary brain damage after SAH.