Effects of isoflurane and hypothermia on glutamate receptor-mediated calcium influx in brain slices

Are GABAergic drugs beneficial in providing neuroprotection after traumatic brain injuries? A comprehensive literature review of preclinical studies

Traumatic brain injuries (TBI) caused by physical impact to the brain can adversely impact the welfare and well-being of the affected individuals. One of the leading causes of mortality and dysfunction in the world, TBI is a major public health problem facing the human community. Drugs that target GABAergic neurotransmission are commonly used for sedation in clinical TBI yet their potential to cause neuroprotection is unclear. In this paper, I have performed a rigorous literature review of the neuroprotective effects of drugs that increase GABAergic currents based on the results reported in preclinical literature. The drugs covered in this review include the following: propofol, benzodiazepines, barbiturates, isoflurane, and other drugs that are agonists of GABA_A receptors. A careful review of numerous preclinical studies reveals that these drugs fail to produce any neuroprotection after a primary impact to the brain. In numerous circumstances, they could be detrimental to neuroprotection by increasing the size of the contusional brain tissue and by severely interfering with behavioral and functional recovery. Therefore, anesthetic agents that work by enhancing the effect of neurotransmitter GABA should be administered with caution of TBI patients until a clear and concrete picture of their neuroprotective efficacy emerges in the clinical literature.

Nanoparticle-based drug delivery for the treatment of traumatic brain injury

INTRODUCTION

Traumatic brain injuries (TBIs) impact the breadth of society and remain without any approved pharmacological treatments. Despite successful Phase II clinical trials, the failure of many Phase III clinical trials may be explained by insufficient drug targeting and retention, preventing the proper attainment of an observable dosage threshold. To address this challenge, nanoparticles can be functionalized to protect pharmacological payloads, improve targeted drug delivery to sites of injury, and can be combined with supportive scaffolding to improve secondary outcomes.

AREAS COVERED

This review briefly covers the pathophysiology of TBIs and their subtypes, the current pre-clinical and clinical management strategies, explores the common models of focal, diffuse, and mixed traumatic brain injury employed in experimental animals, and surveys the existing literature on nanoparticles developed to treat TBIs.

EXPERT OPINION

Nanoparticles are well suited to improve secondary outcomes as their multifunctionality and customizability enhance their potential for efficient targeted delivery, payload protection, increased brain penetration, low off-target toxicity, and biocompatibility in both acute and chronic timescales.

Comment on " In Vivo [18F]GE-179 Brain Signal Does Not Show NMDA-Specific Modulation with Drug Challenges in Rodents and Nonhuman Primates"

Schoenberger and colleagues ( Schoenberger et al. ( 2018 ) ACS Chem. Neurosci. 9 , 298 - 305 ) recently reported attempts to demonstrate specific binding of the positron emission tomography (PET) radiotracer, [¹⁸F]GE-179, to NMDA receptors in both rats and Rhesus macaques. GE-179 did not work as expected in animal models; however, we disagree with the authors' conclusion that "the [¹⁸F]GE-179 signal seems to be largely nonspecific". It is extremely challenging to demonstrate specific binding for the use-dependent NMDA receptor intrachannel ligands such as [¹⁸F]GE-179 in animals via traditional blocking, due to its low availability of target sites ( B_max^'). Schoenberger and colleagues anesthetized rats and Rhesus monkeys using isoflurane, which has an inhibitory effect on NMDA receptor function and thus would be expected to further reduce the B_max^'. The extent of glutamate release achieved in the provocation experiments is uncertain, as is whether a significant increase in NMDA receptor channel opening can be expected under anesthesia. Prior data suggest that the uptake of disubstituted arylguanidine-based ligands such as GE-179 can be reduced by phencyclidine binding site antagonists, if injection is performed in the absence of ketamine and isoflurane anesthesia, e.g., with GE-179's antecedent, CNS 5161 ( Biegon et al. ( 2007 ) Synapse 61 , 577 - 586 ), and with GMOM ( van der Doef et al. ( 2016 ) J. Cereb. Blood Flow Metab. 36 , 1111 - 1121 ). However, the extent of nonspecific uptake remains uncertain.

Hypothermic preconditioning but not ketamine reduces oxygen and glucose deprivation induced neuronal injury correlated with downregulation of COX-2 expression in mouse hippocampal slices

Hypothermic preconditioning is an effective treatment for limiting ischemic injury, but the mechanism is poorly understood. This study was aimed to explore the effect of hypothermic and ketamine preconditioning on oxygen and glucose deprivation (OGD) induced neuronal injury in mouse hippocampal slices, and to investigate its possible mechanism. The population spike (PS) was recorded in the CA1 region of mouse hippocampal slices using extracellular recordings, Na⁺/K⁺ ATPase activity in slices was determined by spectrophotometer and the expression of Cyclooxygenase-2 (COX-2) was measured by Western blot. Ten min of OGD induced a poor recovery of PS in slices after reoxygenation. Hypothermic (33 °C) preconditioning delayed the appearance of transient recovery (TR) of PS and improved the recovery amplitude of PS after reoxygenation. Hypothermic preconditioning also decreased the expression of COX-2 and increased Na⁺/K⁺ ATPase activity in slices. Pretreatment of ketamine, a non-competitive NMDA receptor antagonist at a subanesthetic dose has no effect on OGD induced neuronal injury. Moreover, the protection of hypothermic preconditioning was not added by ketamine. The downregulation of COX-2 expression and the increase of Na⁺/K⁺ ATPase activity may be associated with the effectiveness of hypothermic preconditioning in increasing tolerance to an OGD insult.

Antibodies That Work Again and Again and Again

In the past few years significant concern has been raised about the quality and reproducibility of antibodies used in numerous scientific publications. In this chapter we discuss some of the biggest contributing factors to the "antibody problem" from both the commercial production side, as well as the end-users side. Specifically we argue that Western blot data should be used to provide a reliable initial indication of antibody quality, as well as a guide to distinguish between multiple offerings for antibodies to the same target. Secondly, we describe a set of best practices for antibody manufacturers to employ that will eliminate most of the variability in polyclonal antibodies. Taken together these proposals provide a way to significantly improve both the quality and the reproducibility of commercial antibodies.

Deep Hypothermia and Circulatory Arrest in Adults

Brain protection during cardiopulmonary bypass has been the subject of intense research. Deep hypothermic circulatory arrest (DHCA) continues to be used for that goal during complex aortic arch and large intracranial aneurysm surgeries. The anesthetic management for adult patients undergoing these types of procedures requires specific knowledge and expertise. Based on our experience and review of the current literature, the authors highlight the key areas of the anesthetic plan, discussing the risk factors associated with adverse neurologic outcome as well as the rationale for decisions regarding specific monitors and medications. In the conclusion an anesthetic protocol for adult patients undergoing DHCA is suggested.

Orexin-A facilitates emergence of the rat from isoflurane anesthesia via mediation of the basal forebrain

Previous studies have demonstrated that orexinergic neurons involve in promoting emergence from anesthesia of propofol, an intravenous anesthetics, while whether both of orexin-A and orexin-B have promotive action on emergence via mediation of basal forebrain (BF) in isoflurane anesthesia has not been elucidated. In this study, we observed c-Fos expressions in orexinergic neurons following isoflurane inhalation (for 0, 30, 60, and 120min) and at the time when the righting reflex returned after the cessation of anesthesia. The plasma concentrations of orexin-A and -B in anesthesia-arousal process were measured by radioimmunoassay. Orexin-A and -B (30 or 100pmol) or the orexin receptor-1 and -2 antagonist SB-334867A and TCS-OX2-29 (5 or 20μg) were microinjected into the basal forebrain respectively. The effects of them on the induction (loss of the righting reflex) and the emergence time (return of the righting reflex) under isoflurane anesthesia were observed. The results showed that the numbers of c-Fos-immunoreactive orexinergic neurons in the hypothalamus decreased over time with continued isoflurane inhalation, but restored at emergence. Similar alterations were observed in changes of plasma orexin-A concentrations but not in orexin-B during emergence. Administration of orexins had no effect on the induction time, but orexin-A facilitated the emergence of rats from isoflurane anesthesia while orexin-B didn't. Conversely, microinjection of the orexin receptor-1 antagonist SB-334867A delayed emergence from isoflurane anesthesia. The results indicate that orexin-A plays a promotive role in the emergence of isoflurane anesthesia and this effect is mediated by the basal forebrain.

Protective role of isoflurane pretreatment in rats with focal cerebral ischemia and the underlying molecular mechanism

Inflammation and immunity are important in the pathogenesis of cerebral ischemia. Toll-like receptor 4 (TLR4) is involved in the inflammatory responses of injured brain tissues. Emerging studies have focused on the effect of isoflurane (ISO) pretreatment on cerebral ischemia, however, the association between ISO pretreatment and TLR4 during cerebral ischemia remains to be elucidated. In the present study, the protective role of ISO pretreatment in rats with focal cerebral ischemia reperfusion was investigated and the molecular mechanism was discussed. Using a middle cerebral artery occlusion (MCAO) model, triphenyltetrazolium chloride staining was utilized to measure the infarct volume and brain edema and immunofluorescence staining was used to detect the MCAO-induced TLR4 expression and localization. Western blot analyses were conducted to quantify the protein expression levels of TLR4, myeloid differentiation primary response 88 (MyD88) and nuclear factor (NF)-κB in ischemic brain tissue at different time points. The results demonstrated that, following ISO pretreatment, the neurological deficits, brain edema and cerebral infarct size caused by ischemia/reperfusion were attenuated. The astrocyte and microglial activation in the brain tissue was decreased. In addition, the expression levels of TLR4, MyD88 and NF-κB were decreased. The present study indicated that ISO pretreatment may protect the brain from ischemic damage by downregulating the expression levels of TLR4, MyD88 and NF-κB.

Cellular signaling pathways and molecular mechanisms involving inhalational anesthetics-induced organoprotection

Inhalational anesthetics-induced organoprotection has received much research interest and has been consistently demonstrated in different models of organ damage, in particular, ischemia-reperfusion injury, which features prominently in the perioperative period and in cardiovascular events. The cellular mechanisms accountable for effective organoprotection over heart, brain, kidneys, and other vital organs have been elucidated in turn in the past two decades, including receptor stimulations, second-messenger signal relay and amplification, end-effector activation, and transcriptional modification. This review summarizes the signaling pathways and the molecular participants in inhalational anesthetics-mediated organ protection published in the current literature, comparing and contrasting the 'preconditioning' and 'postconditioning' phenomena, and the similarities and differences in mechanisms between organs. The salubrious effects of inhalational anesthetics on vital organs, if reproducible in human subjects in clinical settings, would be of exceptional clinical importance, but clinical studies with better design and execution are prerequisites for valid conclusions to be made. Xenon as the emerging inhalational anesthetic, and its organoprotective efficacy, mechanism, and relative advantages over other anesthetics, are also discussed.

Using anesthetics and analgesics in experimental traumatic brain injury

Valid modeling of traumatic brain injury (TBI) requires accurate replication of both the mechanical forces that cause the primary injury and the conditions that lead to secondary injuries observed in human patients. The use of animals in TBI research is justified by the lack of in vitro or computer models that can sufficiently replicate the complex pathological processes involved. Measures to reduce nociception and distress must be implemented, but the administration of anesthetics and analgesics can influence TBI outcomes, threatening the validity of the research. In this review, the authors present evidence for the interference of anesthetics and analgesics in the natural course of brain injury in animal models of TBI. They suggest that drugs should be selected for or excluded from experimental TBI protocols on the basis of IACUC-approved experimental objectives in order to protect animal welfare and preserve the validity of TBI models.

Effects of intraoperative external head cooling on short-term cognitive function in patients after coronary artery bypass graft surgery

The aim of study was to assess the effects of an intraoperative external head-cooling technique on cognitive dysfunction in the early postoperative period (at the 10th day) in patients after coronary artery bypass graft (CABG) surgery. Patients in Group H (n=25) were cooled with CPB and the intraoperative, external head-cooling technique, patients in Group C (n=25) were cooled only with cardiopulmonary bypass (CPB) to achieve mild hypothermia (33 - 34 °C). Cognitive function was analyzed before the operation and after the surgery using the Mini Mental State Examination (MMSE), the Modified Visual Reproduction Test from the Wechsler Memory Scale, Trail Making (A/B), WAIS--Digit Span (WDS) and WAIS Digit Symbol Substitution Test (WDSST). The incidence of cognitive impairment at the 10th day after the surgery was 36% (n=9) in Group H and 64% (n=16) in Group C (p=0.048). The temperature during the aortic cross-clamp period was associated with a lower rate of cognitive dysfunction (p=0.05, r(2)=0.09). The intraoperative, external head-cooling technique during the aortic cross-clamp period has a neuroprotective effect and leads to less short-term cognitive function impairment after CABG surgery.

Anesthetic protection of neurons injured by hypothermia and rewarming: roles of intracellular Ca2+ and excitotoxicity

BACKGROUND

Mild hypothermia is neuroprotective after cerebral ischemia but surgery involving profound hypothermia (PH, temperature less than 18°C) is associated with neurologic complications. Rewarming (RW) from PH injures hippocampal neurons by glutamate excitotoxicity, N-methyl-D-aspartate receptors, and intracellular calcium. Because neurons are protected from hypoxia-ischemia by anesthetic agents that inhibit N-methyl-D-aspartic acid receptors, we tested whether anesthetics protect neurons from damage caused by PH/RW.

METHODS

Organotypic cultures of rat hippocampus were used to model PH/RW injury, with hypothermia at 4°C followed by RW to 37°C and assessment of cell death 1 or 24 h later. Cell death and intracellular Ca were assessed with fluorescent dye imaging and histology. Anesthetic agents were present in the culture media during PH and RW or only RW.

RESULTS

Injury to hippocampal CA1, CA3, and dentate neurons after PH and RW involved cell swelling, cell rupture, and adenosine triphosphate (ATP) loss; this injury was similar for 4 through 10 h of PH. Isoflurane (1% and 2%), sevoflurane (3%) and xenon (60%) reduced cell loss but propofol (3 μM) and pentobarbital (100 μM) did not. Isoflurane protection involved reduction in N-methyl-D-aspartate receptor-mediated Ca influx during RW but did not involve γ-amino butyric acid receptors or KATP channels. However, cell death increased over the next day.

CONCLUSION

Anesthetic protection of neurons rewarmed from 4°C involves suppression of N-methyl-D-aspartate receptor-mediated Ca overload in neurons undergoing ATP loss and excitotoxicity. Unlike during hypoxia/ischemia, anesthetic agents acting predominantly on γ-aminobutyric acid receptors do not protect against PH/RW. The durability of anesthetic protection against cold injury may be limited.

Comparison Between Local and General Anesthesia for Carotid Endarterectomy: Early and Late Results

Background: The aim of this retrospective study was to compare the results between general and local anesthesia (LA) for carotid endarterectomy (CEA). Methods: Three hundred and twenty-nine patients in whom 365 CEA procedures were performed between January 1990 and September 2001, were included in this study. Results: Operation time, shunt usage rates, hospitalization time ( P < .0001), and permanent stroke rates ( P < .05) were significantly lower in group with LA. For long-term period (121.3 ± 37.45 vs 98.6 ± 28.98 months), no significant difference was observed in these 2 group with respect to restenosis rates, neurological events, and deaths. Conclusions: Despite the lack of significant difference between LA and general anesthesia in terms of restenosis, neurological events, and death in the long-term period; LA is more preferable due its associated advantages including availability of testing the consciousness of the patients by direct contact, reduced use of shunts, shorter hospitalization periods, and less prevalence of permanent stroke in the short-term period.

Isoflurane does not cause neuroapoptosis but reduces astroglial processes in young adult mice

BACKGROUND

Isoflurane, a volatile anesthetic widely used clinically, has been implicated to be both neuroprotective and neurotoxic. The claim about isoflurane causing neural apoptosis remains controversial. In this study, we investigated the effects of isoflurane exposures on apoptotic and anti-apoptotic signals, cell proliferation and neurogenesis, and astroglial processes in young adult mouse brains.

METHODS

Sixty 6-week-old mice were randomly assigned to four anesthetic concentration groups (0 as control and 0.6%, 1.3%, and 2%) with four recovery times (2 h and 1, 6, and 14 d) after 2-h isoflurane exposure. Immunohistochemistry measurements of activated caspase-3 and Bcl-xl for apoptotic and anti-apoptotic signals, respectively, glial fibrillary acidic protein (GFAP) and vimentin for reactive astrocytosis, doublecortin (Dcx) for neurogenesis, and BrdU for cell proliferation were performed.

RESULTS

Contrary to the previous conclusion derived from studies with neonatal rodents, we found no evidence of isoflurane-induced apoptosis in the adult mouse brain. Neurogenesis in the subgranule zone of the dentate gyrus was not affected by isoflurane. However, there is a tendency of reduced cell proliferation after 2% isoflurane exposure. VIM and GFAP staining showed that isoflurane exposure caused a delayed reduction of astroglial processes in the hippocampus and dentate gyrus.

CONCLUSION

Two-hour exposure to isoflurane did not cause neuroapoptosis in adult brains. The delayed reduction in astroglial processes after isoflurane exposure may explain why some volatile anesthetics can confer neuroprotection after experimental stroke because reduced glial scarring facilitates better long-term neuronal recoveries.

Deep hypothermic circulatory arrest: Alternative strategies for cerebral perfusion. A review article

Deep hypothermic circulatory arrest is an essential tool in the surgeon’s armamentarium. There are essentially three strategies to address cerebral ischemia during arrest periods. Early surgical case series pioneered the option of complete anoxia with deep hypothermia. Subsequent innovators introduced the concept of retrograde perfusion of the cerebral vessels through the venous system, and others have advocated the use of selective and non-selective antegrade perfusion of the cerebral arteries. Clinical studies assessing outcomes of the three approaches are compromised by small patient numbers, retrospective design and surgeon bias.

In this review, the authors will briefly discuss the conceptual basis of these strategies and the literature comparing these approaches in terms of key neurologic outcomes. The importance of this topic will emphasize the key role the perfusion community plays in establishing guidelines for best practice in circulatory arrest to go forward with education and research in this area.

Influence of a brief episode of anesthesia during the induction of experimental brain trauma on secondary brain damage and inflammation

It is unclear whether a single, brief, 15-minute episode of background anesthesia already modulates delayed secondary processes after experimental brain injury. Therefore, this study was designed to characterize three anesthesia protocols for their effect on molecular and histological study endpoints. Mice were randomly separated into groups that received sevoflurane (sevo), isoflurane (iso) or an intraperitoneal anesthetic combination (midazolam, fentanyl and medetomidine; comb) prior to traumatic brain injury (controlled cortical impact, CCI; 8 m/s, 1 mm impact depth, 3 mm diameter). Twenty-four hours after insult, histological brain damage, neurological function (via neurological severity score), cerebral inflammation (via real-time RT-PCR for IL6, COX-2, iNOS) and microglia (via immunohistochemical staining for Iba1) were determined. Fifteen minutes after CCI, the brain contusion volume did not differ between the anesthetic regimens (sevo = 17.9±5.5 mm³; iso = 20.5±3.7 mm³; comb = 19.5±4.6 mm³). Within 24 hours after injury, lesion size increased in all groups (sevo = 45.3±9.0 mm³; iso = 31.5±4.0 mm³; comb = 44.2±6.2 mm³). Sevo and comb anesthesia resulted in a significantly larger contusion compared to iso, which was in line with the significantly better neurological function with iso (sevo = 4.6±1.3 pts.; iso = 3.9±0.8 pts.; comb = 5.1±1.6 pts.). The expression of inflammatory marker genes was not significantly different at 15 minutes and 24 hours after CCI. In contrast, significantly more Iba1-positive cells were present in the pericontusional region after sevo compared to comb anesthesia (sevo = 181±48/mm³; iso = 150±36/mm³; comb = 113±40/mm³). A brief episode of anesthesia, which is sufficient for surgical preparations of mice for procedures such as delivering traumatic brain injury, already has a significant impact on the extent of secondary brain damage.

Avoiding stroke during cardiac surgery

The life saving benefits of cardiac surgery are frequently accompanied by negative side effects such as stroke, that occurs with an incidence of 2%-13% dependent to type of surgery. The etiology is most likely multifactorial with embolic events considered as main contributor. Although stroke presents a common complication, no guidelines for any routine use of pharmacological substances or non-pharmacological strategies exist to date. Non-pharmacological strategies include monitoring of brain oxygenation and perfusion with devices such as near infrared spectroscopy and Transcranial Doppler help. Epiaortic and transesophageal echocardiography visualize aorta pathology, enabling the surgeon to sidestep atheromatous segments. Additionally can the use of specially designed aortic cannulae and filters help to reduce embolization. Brain perfusion can be improved by using antero- or retrograde cerebral perfusion during deep hypothermic circulatory arrest, by tightly monitoring mean arterial blood pressure and hemodilution. Controlling perioperative temperature and glucose levels may additionally help to ameliorate secondary damage. Many pharmacological compounds have been shown to be neuroprotective in preclinical models, but clinical studies failed to confirm these results so far. Remacemide, an NMDA-receptor-antagonist showed a significant drug-based neuroprotection during cardiac surgery. Other substances currently assessed in clinical trials whose results are still pending are acadesine, an adenosine-regulating substance, the free radical scavenger edaravone and the local anesthetic lidocaine. Stroke remains as significant complication after cardiac surgery. Non-pharmacological strategies allow perioperative caregivers to detect injurious events and to ameliorate stroke and its sequelae. Considering the multi-factorial etiology though, stroke prevention will likely have to be addressed with an individualistic combination of different strategies and substances.

Effect of mild and moderate hypothermia on hypoxic injury in nearly pure neuronal culture

PURPOSE

The effects of mild and moderate hypothermic therapy on cerebral injury are still controversial. Our hypothesis is that mild and moderate hypothermia should have some effects on neurons themselves if they really have protective effects. By using a nearly pure neuronal culture, we evaluated the effects and mechanism of hypothermia against hypoxic insult.

METHODS

A nearly pure neuronal culture from cortices of 18-day-old Wister rats was used. The neurons were exposed to below 1% oxygen at 3 different temperatures (30, 33 and 37°C). First, cell viability was measured by assessing viable neurons with trypan blue. Second, to evaluate the mechanism, the extracellular glutamate concentration was measured by high-performance liquid chromatography after hypoxia; cell viability after exposure to extrinsic glutamate was also evaluated. Next, mitochondrial membrane potential was estimated, by monitoring aggregation of MitoCapture™, and the percentage of apoptotic cells was evaluated by staining with Hoechst 33342 and propidium iodide.

RESULTS

After 24-h hypoxic insult, cell viability at 30 and 33°C was significantly higher than at 37°C. There was no significant difference between extracellular concentrations of glutamate after hypoxia or cell viability after glutamate exposure among the 3 temperature groups. In moderate hypothermia, the number of neurons with mitochondrial injury and the percentage of apoptotic cells were significantly reduced.

CONCLUSION

Mild and moderate hypothermia inhibited hypoxic neuronal cell death. The mechanism of this effect may be related to protection of mitochondrial function, presumably followed by inhibition of apoptosis, at least in moderate hypothermia.

Neuroprotective effects of a combination of dexmedetomidine and hypothermia after incomplete cerebral ischemia in rats

BACKGROUND

Dexmedetomidine and hypothermia are known to reduce neuronal injury following cerebral ischemia. We examined whether a combination of dexmedetomidine and hypothermia reduces brain injury after transient forebrain ischemia in rats to a greater extent than either treatment alone.

METHODS

Thirty-eight male Sprague-Dawley rats were anesthetized with fentanyl and nitrous oxide in oxygen. Four groups were tested: group C (saline 1 ml/kg, temporal muscle temperature 37.5 degrees C); group H (saline 1 ml/kg, 35.0 degrees C); group D (dexmedetomidine 100 microg/kg, 37.5 degrees C); and group DH (dexmedetomidine 100 microg/kg, 35.0 degrees C). Dexmedetomidine or saline was administered intraperitoneally 30 min before ischemia. Cerebral ischemia was produced by right carotid artery ligation with hemorrhagic hypotension (mean arterial pressure 40 mmHg) for 20 min. Neurologic outcome was evaluated at 24, 48, and 72 h after ischemia. Histopathology was evaluated in the caudate and hippocampus at 72 h after ischemia.

RESULTS

Neurologic outcome was significantly better in the group DH than the group C (P<0.05), whereas it was similar between the group DH and the groups D or H. Survival rate of the hippocampal CA1 neurons was significantly greater in groups D, H, and DH than group C (P<0.05). Histopathologic injury in the caudate section was significantly less in groups H and DH than group C (P<0.05).

CONCLUSION

The combination of dexmedetomidine and hypothermia improved short-term neurologic outcome compared with the control group, whereas the combination therapy provided comparable neuroprotection with either of the two therapies alone.

Isoflurane attenuates dynorphin-induced cytotoxicity and downregulation of Bcl-2 expression in differentiated neuroblastoma SH-SY5Y cells

BACKGROUND

It has been proposed that the volatile anesthetic isoflurane induces neuroprotection and that the endogenous opioid peptide dynorphin induces neurocytotoxicity in cells. The levels of dynorphin are often significantly elevated in neuropathophysiological conditions, and dynorphin can directly induce toxicity. However, the neuroprotective effects of isoflurane on dynorphin-induced cytotoxicity are still unclear.

METHODS

In order to determine the effect of isoflurane on dynorphin-induced cytotoxicity in neuronal cells, we have designed a device wherein cultured human neuroblastoma SH-SY5Y cells can be exposed to isoflurane. Fully differentiated SH-SY5Y cells were obtained by treating the cells with retinoic acid for 6 days. We examined SH-SY5Y cell survival, apoptosis, and antiapoptotic protein expression by cell viability, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling stain, and Western blot analysis, respectively.

RESULTS

After 16 h of dynorphin (10 microM) treatment, the SH-SY5Y cells showed significant cytotoxicity, apoptosis, and downregulation of the antiapoptotic Bcl-2 protein expression. These effects of dynorphin were significantly inhibited by isoflurane exposure for 32 h [pretreatment for 16 h and posttreatment (after dynorphin treatment) for 16 h].

CONCLUSION

Thus, our results suggest that isoflurane exerts neuroprotective effects in the case of dynorphin-induced pathophysiological disruption.

Neuroprotection during cardiac surgery

Cardiac surgery continues to be associated with significant adverse cerebral outcomes, ranging from stroke to cognitive decline. The underlying mechanism of the associated cerebral injury is incompletely understood but is believed to be primarily caused by cerebral embolism and hypoperfusion, exacerbated by ischemia/reperfusion injury. Extensive research has been undertaken in an attempt to minimize the incidence of perioperative cerebral injury, and both pharmacological and nonpharmacological strategies have been investigated. Although many agents demonstrated promise in preclinical studies, there is currently insufficient evidence from clinical trials to recommend the routine administration of any pharmacological agents for neuroprotection during cardiac surgery. The nonpharmacological strategies that can be recommended on the basis of evidence include transesophageal echocardiography and epiaortic ultrasound-guided assessment of the atheromatous ascending aorta with appropriate modification of cannulation, clamping or anastomotic technique and optimal temperature management. Large-scale randomized controlled trials are still required to address further the issues of optimal pH management, glycemic control, blood pressure management and hematocrit during cardiopulmonary bypass. Past, present and future directions in the field of neuroprotection in cardiac surgery will be discussed.

Effects of halothane, isoflurane, and sevoflurane on lipid peroxidation following experimental closed head trauma in rats

BACKGROUND

In a rat closed head trauma model we examined both the time course of lipid peroxidation and the effects of halothane, isoflurane, and sevoflurane on it by analysis of malondialdehyde (MDA) formation.

METHODS

Animals were divided randomly into five groups: sham-operated (SO), n=18; control-closed head trauma to left frontal pole, n=18; closed head trauma model+halothane, n=18; closed head trauma model+isoflurane, n=18; and closed head trauma model+sevoflurane, n=18. Halothane, isoflurane, or sevoflurane were applied 15 min after trauma for 30 min. Rats were euthanized 1,3, and 5 h after the inhalation agents. Brain tissue samples were taken 5 mm from the left and right frontal poles. MDA was considered to reflect the degree of lipid peroxidation.

RESULTS

MDA concentrations were greater in the control, halothane, sevoflurane, and isoflurane groups than in SO animals (P<0.001). No statistical difference between the hemispheres was found between the halothane, isoflurane, or sevoflurane groups, but MDA levels were lower with isoflurane than in the halothane, sevoflurane, and control groups at 1, 3, and 5 h (P<0.001). MDA levels were higher as compared with the halothane and sevoflurane groups at 1 h but not at 3 or 5 h (P<0.001).

CONCLUSION

MDA levels with the isoflurane group were lower than in the other trauma groups, which suggest that isoflurane, given after closed head trauma, might be protective against lipid peroxidation of cerebral injury.

Mitochondrial ATP-sensitive K+ channels regulate NMDAR activity in the cortex of the anoxic western painted turtle

Hypoxic mammalian neurons undergo excitotoxic cell death, whereas painted turtle neurons survive prolonged anoxia without apparent injury. Anoxic survival is possibly mediated by a decrease in N-methyl-d-aspartate receptor (NMDAR) activity and maintenance of cellular calcium concentrations ([Ca(2+)](c)) within a narrow range during anoxia. In mammalian ischaemic models, activation of mitochondrial ATP-sensitive K(+) (mK(ATP)) channels partially uncouples mitochondria resulting in a moderate increase in [Ca(2+)](c) and neuroprotection. The aim of this study was to determine the role of mK(ATP) channels in anoxic turtle NMDAR regulation and if mitochondrial uncoupling and [Ca(2+)](c) changes underlie this regulation. In isolated mitochondria, the K(ATP) channel activators diazoxide and levcromakalim increased mitochondrial respiration and decreased ATP production rates, indicating mitochondria were 'mildly' uncoupled by 10-20%. These changes were blocked by the mK(ATP) antagonist 5-hydroxydecanoic acid (5HD). During anoxia, [Ca(2+)](c) increased 9.3 +/- 0.3% and NMDAR currents decreased 48.9 +/- 4.1%. These changes were abolished by K(ATP) channel blockade with 5HD or glibenclamide, Ca(2+)(c) chelation with 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) or by activation of the mitochondrial Ca(2+) uniporter with spermine. Similar to anoxia, diazoxide or levcromakalim increased [Ca(2+)](c) 8.9 +/- 0.7% and 3.8 +/- 0.3%, while decreasing normoxic whole-cell NMDAR currents by 41.1 +/- 6.7% and 55.4 +/- 10.2%, respectively. These changes were also blocked by 5HD or glibenclamide, BAPTA, or spermine. Blockade of mitochondrial Ca(2+)-uptake decreased normoxic NMDAR currents 47.0 +/- 3.1% and this change was blocked by BAPTA but not by 5HD. Taken together, these data suggest mK(ATP) channel activation in the anoxic turtle cortex uncouples mitochondria and reduces mitochondrial Ca(2+) uptake via the uniporter, subsequently increasing [Ca(2+)](c) and decreasing NMDAR activity.

Neuroprotection during cardiac surgery

Cerebral injury following cardiac surgery continues to be a significant source of morbidity and mortality after cardiac surgery. A spectrum of injuries ranging from subtle neurocognitive dysfunction to fatal strokes are caused by a complex series of multifactorial mechanisms. Protecting the brain from these injuries has focused on intervening on each of the various etiologic factors. Although numerous studies have focused on a pharmacologic solution, more success has been found with nonpharmacologic strategies, including optimal temperature management and reducing emboli generation.

Inhalational anesthetics as neuroprotectants or chemical preconditioning agents in ischemic brain

This review will focus on inhalational anesthetic neuroprotection during cerebral ischemia and inhalational anesthetic preconditioning before ischemic brain injury. The limitations and challenges of past and current research in this area will be addressed before reviewing experimental and clinical studies evaluating the effects of inhalational anesthetics before and during cerebral ischemia. Mechanisms underlying volatile anesthetic neuroprotection and preconditioning will also be examined. Lastly, future directions for inhalational anesthetics and ischemic brain injury will be briefly discussed.

Anesthetic-mediated protection/preconditioning during cerebral ischemia

Cerebral ischemia is a multi-faceted neurodegenerative pathology that causes cellular injury to neurons within the central nervous system. In light of the underlying mechanisms being elucidated, clinical trials to find possible neuroprotectants to date have failed, thus highlighting the need for new putative targets to offer protection. Recent evidence has clearly shown that anesthetics can confer significant protection and or induce a preconditioning effect against cerebral ischemia-induced injury. This review will focus on the putative protection/preconditioning that is afforded by anesthetics, their possible interaction with GABA(A) and glutamate receptors and two-pore potassium channels. In addition, the interaction with inflammatory, apoptotic and underlying molecular (particularly immediately early genes and inducible nitric oxide synthase etc) pathways, the activation of K(ATP) channels and the ability to provide lasting protection will also be addressed.

Hypothermia Protects Cultured Human Retinal Pigment Epithelial Cells against Indocyanine Green Toxicity

PURPOSE

The aim of this study was to determine whether indocyanine green (ICG) is toxic to cultured human retinal pigment epithelial (ARPE-19) cells, and whether hypothermia can protect the ARPE-19 cells against the ICG toxicity.

METHODS

Cultured ARPE-19 cells were exposed to 0.25, 0.5, 1, 2.5, and 5 mg/mL of ICG dye at 37 and 4 degrees C for 30 min. The percentage of ARPE-19 cells that survived was determined by resazurin 1 day after the exposure.

RESULTS

Exposure of the RPE cells to a hypotonic saline solution with an osmolarity equal to 5 mg/mL of ICG did not induce a statistically significant decrease in the percentage of RPE cells that survived. Exposure of the ARPE-19 cells to ICG induced a significant decrease in the percentage of cell survival at all concentrations of ICG (P<0.05), except in 0.25 mg/mL at 37 degrees C. At 4 degrees C, on the other hand, ICG induced a statistically significant decrease in the percentage of RPE cell survival only at 5 mg/mL of ICG (P<0.05).

CONCLUSIONS

These results indicate that ICG is toxic to human RPE cells in culture, and that cell death cannot be attributed to the low osmolarity. Hypothermia of 4 degrees C has a protective effect against ICG toxicity.

Comparison of seven anesthetic agents on outcome after experimental traumatic brain injury in adult, male rats

Isoflurane is commonly used in experimental traumatic brain injury (TBI), both before and early after injury, yet it is rarely used clinically. Narcotics and benzodiazepines are frequently used after injury in clinical TBI. We compared seven anesthetic/sedative agents applied after injury in the controlled cortical impact model: diazepam, fentanyl, isoflurane, ketamine, morphine, pentobarbital, and propofol. Our objective was to provide insight into the relative degrees of neuroprotection provided by these agents in a standard model of TBI. We hypothesized that the choice of anesthetic/sedative early after experimental TBI critically impacts outcome and that the agents most commonly used clinically may be less neuroprotective than isoflurane. Rats treated with isoflurane had the best cognitive recovery (p < 0.05) and hippocampal neuronal survival (p < 0.05). Conversely, rats treated with ketamine had the most hippocampal neuronal death (p < 0.05). Morphine or propofol, two agents commonly used clinically, were associated with the poorest motor function on post-trauma day 1-5 (p < 0.05). Our data support beneficial effects of isoflurane early after experimental TBI. Our data suggest that the early post-TBI use of isoflurane, despite practical logistical issues, could potentially provide clinical benefits in TBI--versus other commonly used sedatives or analgesics. Furthermore, the choice of post-injury sedation and analgesia could have important implications on attempts to translate novel therapies from bench to field or bedside.

The combination of isoflurane and caspase 8 inhibition results in sustained neuroprotection in rats subject to focal cerebral ischemia

Although isoflurane can reduce ischemic neuronal injury after short postischemic recovery intervals, data from our laboratory have demonstrated that this neuroprotection is not sustained and that delayed apoptotic neuronal death, mediated in part by activation of caspases, contributes to the gradual increase in the size of the infarction. We tested the hypothesis that the neuroprotective efficacy of isoflurane can be prolonged with the administration of z-IETD-fmk, a specific inhibitor of caspase 8. Fasted Wister rats were anesthetized with isoflurane and randomly allocated to awake-vehicle, isoflurane-vehicle, awake-IETD, or isoflurane-IETD groups (n = 25 per group). Animals were subjected to 60 min focal ischemia by filament occlusion of the middle cerebral artery (MCAO). Daily intracerebroventricular injections of z-IETD-fmk or vehicle were administered via an implanted cannula starting before ischemia and continuing until 14 days post-MCAO. Neurological assessment was performed 14 days after ischemia after which the volume of cerebral infarction and number of intact neurons in the peri-infarct cortex were determined. Total infarction volume was less in the isoflurane-IETD group than in awake-vehicle, isoflurane-vehicle, and awake-IETD groups. Infarction volume was also less in the awake-IETD group versus the awake-vehicle group. The number of intact neurons within the peri-infarct cortex was significantly less in the awake-vehicle group in comparison with the other three experimental groups. The isoflurane-IETD group had better neurologic outcomes than both vehicle-treated groups at 14 days post-MCAO. These results suggest that a combination of isoflurane and a caspase 8 inhibitor can produce neuroprotection that is evident even after a recovery period of 14 days. This combination demonstrated greater efficacy than the administration of either isoflurane or z-IETD-fmk alone. These results are consistent with the premise that continuing apoptosis contributes to the enlargement of cerebral infarction during the recovery period and that its inhibition can provide sustained neuroprotection.

Isoflurane exerts neuroprotective actions at or near the time of severe traumatic brain injury

Isoflurane improves outcome vs. fentanyl anesthesia, in experimental traumatic brain injury (TBI). We assessed the temporal profile of isoflurane neuroprotection and tested whether isoflurane confers benefit at the time of TBI. Adult, male rats were randomized to isoflurane (1%) or fentanyl (10 mcg/kg iv bolus then 50 mcg/kg/h) for 30 min pre-TBI. Anesthesia was discontinued, rats recovered to tail pinch, and TBI was delivered by controlled cortical impact. Immediately post-TBI, rats were randomized to 1 h of isoflurane, fentanyl, or no additional anesthesia, creating 6 anesthetic groups (isoflurane:isoflurane, isoflurane:fentanyl, isoflurane:none, fentanyl:isoflurane, fentanyl:fentanyl, fentanyl:none). Beam balance, beam walking, and Morris water maze (MWM) performances were assessed over post-trauma d1-20. Contusion volume and hippocampal survival were assessed on d21. Rats receiving isoflurane pre- and post-TBI exhibited better beam walking and MWM performances than rats treated with fentanyl pre- and any treatment post-TBI. All rats pretreated with isoflurane had better CA3 neuronal survival than rats receiving fentanyl pre- and post-TBI. In rats pretreated with fentanyl, post-traumatic isoflurane failed to affect function but improved CA3 neuronal survival vs. rats given fentanyl pre- and post-TBI. Post-traumatic isoflurane did not alter histopathological outcomes in rats pretreated with isoflurane. Rats receiving fentanyl pre- and post-TBI had the worst CA1 neuronal survival of all groups. Our data support isoflurane neuroprotection, even when used at the lowest feasible level before TBI (i.e., when discontinued with recovery to tail pinch immediately before injury). Investigators using isoflurane must consider its beneficial effects in the design and interpretation of experimental TBI research.

Isoflurane anesthesia induces biphasic effect on dopamine release in the rat striatum

The effect of isoflurane anesthesia on changes in the extracellular concentrations of dopamine (DA) and its metabolites (3-methoxytyramine (3-MT), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA)) modulated by pargyline, monoamine oxidase inhibitor, was studied using in vivo microdialysis techniques. A microdialysis probe was implanted into the right striatum of male SD rats. Each rat (n=5-6) was given saline or the same volume of 30 or 75 mg kg(-1) pargyline intraperitoneally with or without 1 h isoflurane anesthesia (1 or 3%). Isoflurane anesthesia increased the extracellular concentration of DA in high dose (3%) and increased the metabolite concentrations in a dose-dependent manner. Pargyline administration increased the extracellular concentration of DA and 3-MT, and decreased that of other metabolites. After 30 mg kg(-1) pargyline treatment, 1% isoflurane-induced DA release and increasing of 3-MT were preserved, whereas high dose isoflurane (3%) decreased the concentration of metabolites (DOPAC and HVA), despite of the increase by low dose isoflurane (DOPAC). When 75 mg kg(-1) pargyline was administered, isoflurane anesthesia decreased the concentration of DA and DOPAC. The isoflurane-induced 3-MT increase was preserved in all experiments. Our results suggest that isoflurane anesthesia induced biphasic effect on DA regulation probably by the potentiation of DA release and the inhibition of DA synthesis. Isoflurane might modulate DA homeostasis presynaptically.

Experimental models of traumatic brain injury: do we really need to build a better mousetrap?

Approximately 4000 human beings experience a traumatic brain injury each day in the United States ranging in severity from mild to fatal. Improvements in initial management, surgical treatment, and neurointensive care have resulted in a better prognosis for traumatic brain injury patients but, to date, there is no available pharmaceutical treatment with proven efficacy, and prevention is the major protective strategy. Many patients are left with disabling changes in cognition, motor function, and personality. Over the past two decades, a number of experimental laboratories have attempted to develop novel and innovative ways to replicate, in animal models, the different aspects of this heterogenous clinical paradigm to better understand and treat patients after traumatic brain injury. Although several clinically-relevant but different experimental models have been developed to reproduce specific characteristics of human traumatic brain injury, its heterogeneity does not allow one single model to reproduce the entire spectrum of events that may occur. The use of these models has resulted in an increased understanding of the pathophysiology of traumatic brain injury, including changes in molecular and cellular pathways and neurobehavioral outcomes. This review provides an up-to-date and critical analysis of the existing models of traumatic brain injury with a view toward guiding and improving future research endeavors.

Clampage vasculaire temporaire

In many situations, temporary artery occlusion is an integral component of aneurysm surgery. The use of temporary clip may allow safer and easier aneurysmal dissection and clipping. Several points, concerning the duration and overall risks of temporary occlusion and the method of choice for cerebral function monitoring have to be discussed.

MATERIAL AND METHODS

Non exhaustive review of neurosurgical literature.

DISCUSSION

Temporary clip application decreases the risk of intraoperative aneurysmal rupture. The analysis of data published in the literature showed that several questions remain open concerning the optimal method of neuroprotection and cerebral function monitoring, as well as the limit of occlusion duration. Other clinical trials are needed to assess the efficacy and safety of this technique.

Mild hypothermia, but not propofol, is neuroprotective in organotypic hippocampal cultures

The neuroprotective potency of anesthetics such as propofol compared to mild hypothermia remains undefined. Therefore, we determined whether propofol at two clinically relevant concentrations is as effective as mild hypothermia in preventing delayed neuron death in hippocampal slice cultures (HSC). Survival of neurons was assessed 2 and 3 days after 1 h oxygen and glucose deprivation (OGD) either at 37 degrees C (with or without 10 or 100 microM propofol) or at an average temperature of 35 degrees C during OGD (mild hypothermia). Cell death in CA1, CA3, and dentate neurons in each slice was measured with propidium iodide fluorescence. Mild hypothermia eliminated death in CA1, CA3, and dentate neurons but propofol protected dentate neurons only at a concentration of 10 microM; the more ischemia vulnerable CA1 and CA3 neurons were not protected by either 10 microM or 100 microM propofol. In slice cultures, the toxicity of 100 muM N-methyl-D-aspartate (NMDA), 500 microM glutamate, and 20 microM alpha-amino-5-methyl-4-isoxazole propionic acid (AMPA) was not reduced by 100 microM propofol. Because propofol neuroprotection may involve gamma-aminobutyric acid (GABA)-mediated indirect inhibition of glutamate receptors (GluRs), the effects of propofol on GluR activity (calcium influx induced by GluR agonists) were studied in CA1 neurons in HSC, in isolated CA1 neurons, and in cortical brain slices. Propofol (100 and 200 microM, approximate burst suppression concentrations) decreased glutamate-mediated [Ca2+]i increases (Delta[Ca2+]i) responses by 25%-35% in isolated CA1 neurons and reduced glutamate and NMDA Delta[Ca2+]i in acute and cultured hippocampal slices by 35%-50%. In both CA1 neurons and cortical slices, blocking GABAA receptors with picrotoxin reduced the inhibition of GluRs substantially. We conclude that mild hypothermia, but not propofol, protects CA1 and CA3 neurons in hippocampal slice cultures subjected to oxygen and glucose deprivation. Propofol was not neuroprotective at concentrations that reduce glutamate and NMDA receptor responses in cortical and hippocampal neurons.

Apoptosis is not enhanced in primary mixed neuronal/glial cultures protected by isoflurane against N-methyl-D-aspartate excitotoxicity

Volatile anesthetics reduce acute excitotoxic cell death in primary neuronal/glial cultures. We hypothesized that cells protected by isoflurane against N-methyl-d-aspartate (NMDA)-induced necrosis would instead become apoptotic. Primary mixed neuronal/glial cultures prepared from fetal rat brain were exposed to dissolved isoflurane (0 mM, 0.4 mM [1.8 minimum alveolar anesthetic concentration], or 1.6 mM [7 minimum alveolar anesthetic concentration]) and NMDA (0 or 100 microM) at 37 degrees C for 30 min. Dizocilpine (10 microM) plus 100 microM NMDA served as a positive control. Necrosis and apoptosis were assessed at 24 and/or 48 h after exposure by using Hoechst/propidium iodide staining, terminal-deoxynucleotidyl transferase end-nick labeling, DNA fragmentation enzyme-linked immunoabsorbence, and caspase-3 activity assays. NMDA increased the number of necrotic cells. Isoflurane (1.6 mM) and dizocilpine partially reduced cellular necrosis but did not increase the number of morphologically apoptotic or apoptotic-like cells resulting from exposure to 100 microM NMDA at 24 h. At 48 h, no evidence was found to indicate that cells protected by isoflurane had become apoptotic or apoptotic-like. However, cells protected by dizocilpine against necrosis showed evidence of caspase-3-mediated apoptosis. These in vitro data do not support the hypothesis that isoflurane protection against acute excitotoxic necrosis results in apoptosis.

Impaired Acquisition of Spatial Memory 2 Weeks After Isoflurane and Isoflurane-Nitrous Oxide Anesthesia in Aged Rats

Aged rats are impaired on a spatial memory task for at least 24-48 h after isoflurane-nitrous oxide anesthesia. In this study, we tested how long the impairment lasts and investigated the role of nitrous oxide. Eighteen-month-old rats were randomized to anesthesia for 2 h with 1.2% isoflurane with or without 70% nitrous oxide or a control group (30% oxygen). Two weeks later, rats were tested daily for 14 days on a 12-arm radial maze. The number of correct choices to first error, total errors, and time to complete the maze were recorded. Rats anesthetized with 1.2% isoflurane with 70% nitrous oxide made fewer correct choices before first error (P < or = 0.05). Trends toward similar results were noted for error rate and time to complete the maze, but these did not achieve statistical significance. Post hoc analysis comparing all anesthetized rats to controls demonstrated that anesthetized rats made fewer correct choices to first error (P < or = 0.05) and took longer to complete the maze (P <or = 0.05). There were no differences in total number of errors (P < or = 0.06). Thus, spatial memory is impaired for 2 wk after general anesthesia in aged rats independent of whether nitrous oxide is used.

Effect of isoflurane on neuronal apoptosis in rats subjected to focal cerebral ischemia

Although isoflurane can reduce ischemic neuronal injury after short postischemic recovery intervals, this neuroprotective efficacy is not sustained. Neuronal apoptosis can contribute to the gradual increase in infarct size after ischemia. This suggests that isoflurane, although capable of reducing early neuronal death, may not inhibit ischemia-induced apoptosis. We investigated the effects of isoflurane on markers of apoptosis in rats subjected to focal ischemia. Fasted Wistar-Kyoto rats were anesthetized with isoflurane and randomly allocated to awake (n = 40) or isoflurane (n = 40) groups. Animals in both groups were subjected to focal ischemia by filament occlusion of the middle cerebral artery for 70 min. Pericranial temperature was servo-controlled at 37 degrees C +/- 0.2 degrees C throughout the experiment. In the awake group, isoflurane was discontinued and the animals were allowed to awaken. In the isoflurane group, isoflurane anesthesia was maintained at 1.5 MAC (minimum alveolar anesthetic concentration). Animals were killed 7 h, 1 day, 4 days, or 7 days after reperfusion (n = 10/group/time point). The area of cerebral infarction was measured by image analysis in a hematoxylin and eosin stained section. In three adjacent sections, apoptotic neurons were identified by TUNEL staining and immunostaining for active caspase-9 and caspase-3. Infarct size was smaller in the isoflurane group than the awake group 7 h, 1 day, and 4 days after reperfusion (P < 0.05). However, this difference was absent 7 days after reperfusion. The number of apoptotic (TUNEL, caspase-3, and caspase-9 positive) cells 1 day after ischemia was significantly more in the awake versus isoflurane group. After a recovery period of 4 or 7 days, the number of apoptotic cells in the isoflurane group was more than in the awake group. After 7 days, the number of caspase-3 and -9 positive neurons was more in the isoflurane group (P < 0.05). The data indicate that isoflurane delays but does not prevent the development of cerebral infarction caused by ischemia. Isoflurane reduced the development of apoptosis early after ischemia but did not prevent it at later stages of postischemic recovery.

IMPLICATIONS

The effect of isoflurane on neuronal apoptosis was investigated in rats subjected to focal cerebral ischemia. In isoflurane-anesthetized animals, ischemia-induced apoptosis occurred during the later stages of postischemic recovery. Isoflurane did not inhibit postischemic neuronal apoptosis.

Hyperglycolysis is exacerbated after traumatic brain injury with fentanyl vs. isoflurane anesthesia in rats

Despite common use of narcotics in the clinical management of severe traumatic brain injury (TBI), in experimental models rats treated with fentanyl have exhibited worse functional outcome and more CA1 hippocampal death than rats treated with standard isoflurane anesthesia. We hypothesized that greater post-traumatic excitotoxicity, reflected by cerebral glucose utilization (CMRglu), may account for detrimental effects of fentanyl vs. isoflurane. Rats were anesthetized with either isoflurane (1% by inhalation) or fentanyl (10 mcg/kg iv bolus then 50 mcg/kg/h infusion). 14C-deoxyglucose autoradiography was performed 45 min after controlled cortical impact (CCI) to left parietal cortex (n=4 per anesthetic group) or in uninjured rats after 45 min of anesthesia (n=3 per anesthetic group). Uninjured rats treated with fentanyl vs. isoflurane showed 35-45% higher CMRglu in all brain structures (p<0.05) except CA3. After TBI in rats treated with isoflurane, CMRglu increased significantly only in ipsilateral CA1 and ipsilateral parietal cortex (p<0.05 vs. isoflurane uninjured). Conversely, after TBI in rats treated with fentanyl, CMRglu increased markedly and bilaterally in CA1 and CA3 (p<0.05 vs. fentanyl uninjured), but not ipsilateral parietal cortex. In contralateral CA1, CMRglu was nearly two times greater after TBI in fentanyl vs. isoflurane treated rats (p<0.05). Hyperglycolysis was exacerbated in CA1 and CA3 hippocampus after TBI in rats treated with fentanyl vs. isoflurane anesthesia. This post-traumatic hyperglycolysis suggests greater excitotoxicity and concurs with reports of worse functional outcome and more CA1 hippocampal death after TBI with fentanyl vs. isoflurane anesthesia.

Nasopharyngeal cooling selectively and rapidly decreases brain temperature and attenuates neuronal damage, even if initiated at the onset of cardiopulmonary resuscitation in rats

OBJECTIVE

To determine the effectiveness of nasopharyngeal cooling for selective brain cooling and neuroprotection from ischemia.

DESIGN

Prospective animal study.

SETTING

Experimental laboratory in a university hospital.

SUBJECTS

Male Wistar rats (n = 28).

INTERVENTIONS

In study 1, hippocampal temperature was decreased to 31 degrees C under spontaneous circulation. In the nasopharyngeal cooling group, physiologic saline (5 degrees C) was infused to the bilateral nasal cavities at the rate of 100 mL.min-1.kg weight-1. In the whole body cooling group, a fan and a water blanket (5 degrees C) were used. In study 2, ischemia and resuscitation were performed in normothermic and nasopharyngeal cooling (initiated with resuscitation after 5 mins of ischemia and continued for 20 mins) groups.

MEASUREMENTS AND MAIN RESULTS

The hippocampal temperature was decreased to 31 degrees C in 7 +/- 2 mins without any change in the rectal temperature in the nasopharyngeal cooling group, whereas a decrease in hippocampal temperature to 31 degrees C took 33 +/- 1 mins in the whole body cooling group. Although skull base region was cooled by nasopharyngeal cooling, the epidural temperature of the parietal region was lower than the hippocampal temperature, indicating that brain temperature was hematogenously lowered. There was no difference between changes in cerebral blood flow or between the ratios of oxygen extraction from arterial blood in the head region in the nasopharyngeal cooling and whole body cooling groups. In the second study, all animals were successfully resuscitated, and the times required for recovery of mean arterial blood pressure (60 mm Hg) after resuscitation in the nasopharyngeal cooling and normothermic groups were the same. The histologic damage was significantly attenuated in the nasopharyngeal cooling group (33 +/- 21% cell death in the hippocampus) compared with that in the normothermic group (73 +/- 11%).

CONCLUSIONS

Nasopharyngeal cooling enables rapid and selective reductions in cortical and subcortical temperatures without disturbing the recovery of systemic circulation after resuscitation.

Desflurane affords greater protection than halothane against focal cerebral ischaemia in the rat

BACKGROUND

We studied the potential neuroprotective effects of halothane and desflurane, compared with the awake state, on infarct size following 2 h of intraluminal middle cerebral artery occlusion (MCAo) and 22 h of reperfusion.

METHODS

Male Sprague-Dawley rats were anaesthetized with desflurane or halothane, intubated, and mechanically ventilated. Mean arterial pressure (MAP), blood gases, and pH were controlled. Body temperature was maintained at 37.5-38 degrees C. Animals were assigned to one of four groups according to the anaesthetic type (halothane or desflurane) and the duration of anaesthesia: "short-duration", during the preparation only; "long-duration", during both preparation and ischaemia. Twenty-four hours after MCAo, infarcts were visualized by staining with 2,3,5-triphenyltetrazolium chloride. Two additional groups of rats were subjected to the same protocol as that of long-duration halothane and long-duration desflurane with additional pericranial temperature measurements made.

RESULTS

Physiological parameters were comparable between the groups but MAP was higher (P<0.0001) in the short-duration groups. In the short-duration groups, cerebral infarct volumes were not significantly different between anaesthetics (short-duration halothane: 288 (61) mm(3), mean (SD); short-duration desflurane: 269 (71) mm(3), P>0.56). Compared with the awake state (short-duration groups), halothane and desflurane significantly reduced infarct volumes (long-duration halothane: 199 (54) mm(3), P<0.0047 vs short-duration halothane; long-duration desflurane: 121 (55) mm(3), P<0.0001 vs short-duration desflurane). The mean infarct volume in the long-duration desflurane group was significantly lower than that in the long-duration halothane group (P<0.0053). Pericranial temperatures were similar in the desflurane and halothane long-duration groups (P>0.17).

CONCLUSIONS

In rats, desflurane-induced neuroprotection against focal cerebral ischaemia was greater than that conferred by halothane.

Acute etomidate treatment reduces cognitive deficits and histopathology in rats with traumatic brain injury

OBJECTIVE

To test the hypothesis that etomidate treatment improves functional, cognitive, and histologic outcome after experimental traumatic brain injury.

DESIGN

Controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Traumatic brain injury was produced by controlled cortical impact injury (4 m/sec, 2.6 mm of tissue deformation). Etomidate (2 mg/kg) was administered intravenously immediately before injury (n = 13) or 5 mins after injury (n = 12). Additional rats received saline treatment 5 mins after injury (n = 12) or served as sham controls (n = 10).

MEASUREMENTS AND MAIN RESULTS

Rats were evaluated on beam balance and beam walk tasks on postoperative days 1-5 and then trained in the Morris water maze on postoperative days 14-18. On day 28, the rats were killed, and hippocampal CA1 and CA3 neuron counts and cortical lesion volume were measured in histologic brain sections. Preinjury etomidate attenuated beam balance deficits, water maze deficits, hippocampal CA3 neuronal loss, and cortical tissue loss but did not attenuate beam walk deficits or hippocampal CA1 neuronal loss. Postinjury etomidate attenuated water maze deficits, but it did not affect any other outcome measure.

CONCLUSIONS

Administration of etomidate both before and after injury attenuates secondary injury resulting from traumatic brain injury, but the effect is more pronounced with pretreatment. The ineffectiveness of postinjury etomidate on motor and histologic tasks suggests a brief therapeutic treatment window in rats. However, the treatment window in humans is unknown. Lastly, postinjury etomidate did not exacerbate neurologic or histologic outcome.