NMDA receptor antagonist neurotoxicity and psychotomimetic activity

Non-competitive NMDA receptor antagonists, in spite of their neuroprotective effects against neuronal ischemia, brain trauma, etc., cause neuronal damage in the rodent posterior cingulate and retrosplenial cortices (PC/RS), which are thought to be responsible brain regions for their psychotomimetic activity in humans. A number of anesthetics have not only GABAA receptor activating properties but also NMDA receptor antagonist properties. On the other hand, ketamine and nitrous oxide, both of which are potent non-competitive NMDA receptor antagonists and have little GABAA activating properties, are demonstrated to induce neuronal damage in the rat PC/RS. Furthermore, ketamine potentiates the neuronal damage by nitrous oxide. Although many anesthetics, such as halothane, isoflurane, barbiturates and benzodiazepines, inhibit the neuronal damage in the PC/RS by NMDA receptor antagonists, probably through GABAA receptor activation, we anesthesiologists should be aware of the risk of ketamine or nitrous oxide anesthesia, not to speak of the combined use of them, without using GABAA receptor activating agents.     

Propofol acts at the sigma-1 receptor and inhibits pentazocine-induced c-Fos expression in the mouse posterior cingulate and retrosplenial cortices

BACKGROUND: The sigma-1 receptor is functionally linked with psychotomimetic effects of various drugs. A sigma-1 receptor agonist enhances bradykinin-induced intracellular Ca(2+) concentration ([Ca(2+)]i) increase and induces c-Fos expression in a part of the brain. The aim of this study was to investigate the effects of several intravenous anaesthetics on the sigma-1 receptor. METHODS: First, using Wistar rat brains, (+)[(3)H]SKF-10,047, a selective sigma-1 receptor agonist was displaced by propofol, dexmedetomidine, droperidol, and thiopental. Second, Fura-2 loaded NG-108 cells were incubated with (+)pentazocine, a selective sigma-1 receptor agonist, and propofol and then its fluorescence was observed after stimulation with bradykinin. Third, male ICR mice received Intrafat or propofol intraperitoneally (i.p.), followed by pentazocine i.p. Brain slices were prepared and Fos-like immunoreactivity was detected using an immunohistochemical method. results: Propofol, droperidol, and dexmedetomidine displaced (+)[(3)H]SKF-10,047 binding in a concentration-dependent manner with Ki50s of 10.2 +/- 0.6, 0.17 +/- 0.03, 5.73 +/- 1.2 microM, respectively. Thiopental sodium was practically ineffective. Propofol produced a statistically significant reduction in the maximal binding capacity (Bmax) but did not affect the dissociation constant (K(d)). (+)Pentazocine significantly enhanced bradykinin-induced [Ca(2+)]i increases, but propofol did not affect it. Pentazocine induced marked Fos-LI positive cells in the posterior cingulate and retrosplenial cortices (PC/RS), which was significantly reduced by propofol. CONCLUSIONS: These results suggest that propofol may be a sigma-1 receptor antagonist, and that various effects of propofol on the brain may be mediated, at least partly, by the sigma-1 receptor.     

Evidence for GABA(A) receptor agonistic properties of ketamine: convulsive and anesthetic behavioral models in mice

We examined the potentiation by ketamine of the gamma-aminobutyric acid(A) (GABA(A)) receptor function using convulsive and anesthetic behavioral models in adult male ddY mice. General anesthetic potencies were evaluated by a rating scale, which provided the data for anesthetic scores, loss of righting reflex, duration, and recovery time. All drugs were administered intraperitoneally. Small subanesthetic doses of ketamine did inhibit tonic seizures induced by a large dose of the GABA(A) receptor antagonist bicuculline (8 mg/kg). The 50% effective dose value was 15 (95% confidence limits 10-22) mg/kg. Even large anesthetic doses (100-150 mg/kg) did not suppress clonic seizures in 50% of the animals. The GABA(A) receptor agonist, muscimol (0.32-1.12 mg/kg), potentiated ketamine-induced anesthesia in a dose-dependent fashion (P < 0.05). Similarly, the benzodiazepine receptor agonist, diazepam (1-3 mg/kg), augmented ketamine anesthesia in a dose-dependent manner (P < 0.05). Bicuculline (2-5 mg/kg) dose-dependently antagonized ketamine-induced anesthesia (P < 0.05). Neither the benzodiazepine receptor antagonist, flumazenil (2-20 mg/kg), nor the GABA synthesis inhibitor, L-allylglycine (200 mg/kg), affected the anesthetic action of ketamine. These results suggest that ketamine has GABA(A) receptor agonistic properties and that ketamine-induced anesthesia is mediated, at least in part, by GABA(A) receptors. Implications: We examined the potentiation by ketamine of the gamma-aminobutyric acid(A) receptor function using convulsive and anesthetic behavioral models in mice. Subanesthetic doses of ketamine-inhibited tonic convulsions induced by the gamma-aminobutyric acid(A) receptor antagonist bicuculline. The gamma-aminobutyric acid(A) receptor agonist, muscimol, potentiated ketamine-induced anesthesia. Bicuculline antagonized ketamine anesthesia, but the benzodiazepine receptor antagonist, flumazenil, and the gamma-aminobutyric acid synthesis inhibitor, L-allyglycine, did not. The effects of ketamine on the gamma-aminobutyric acid(A) receptors appear to correlate with its anesthetic actions.     

Halothane and Diazepam Inhibit Ketamine-induced c-fos Expression in the Rat Cingulate Cortex

Background: Ketamine, a noncompetitive N-methyl-D-aspartate antagonist, has psychotomimetic side effects. Recent studies have shown that noncompetitive N-methyl-D-aspartate antagonists cause morphologic damage to the cingulate and retrosplenial cortices and induce c-fos protein (c-Fos) in the same regions. Although benzodiazepines are effective in preventing these side effects, the neural basis of the drug interactions has not been established.

Methods: The effects of diazepam and halothane on c-Fos expression induced by ketamine were studied. Diazepam (1 and 5 mg/kg) or vehicle were administered subcutaneously, followed 7 min later by 100 mg/kg ketamine given intraperitoneally. Halothane (1.0 and 1.8%), was administered continuously from 10 min before ketamine administration until brain fixation. Two hours after ketamine injection, rats were perfused and their brains fixed and extracted. Brain sections were prepared in a cryostat and c-Fos expression was detected using immunohistochemical methods.

Results: Ketamine induced c-Fos-like immunoreactivity in the cingulate and retrosplenial cortices, thalamus, and neocortex. Diazepam suppressed the ketamine-induced c-Fos-like immunoreactivity in the cingulate and retrosplenial cortices in a dose-dependent manner, leaving the thalamus and neocortex less affected. Halothane suppressed the ketamine-induced c-Fos-like immunoreactivity in the cingulate and retrosplenial cortices and the neocortex in a dose-dependent manner, leaving the thalamus relatively unaffected.     

咪唑安定对氯胺酮诱导的c-fos基因在大鼠后扣带回皮质区表达的影响

目的 观察咪唑安定对氯胺酮诱导的c-fos基因在大鼠后扣带回皮质区表达的影响，探讨咪唑安定预防或减轻氯胺酮所致精神症状及神经损害的机制。方法 雄性Wistar大鼠30只，随机分为生理盐水5ml组、咪唑安定15mg／kg组、氯胺酮100mg／kg组、咪唑安定15mg／kg加氯胺酮100mg／kg组、氯胺酮100mg／kg加咪唑安定15mg／kg组。咪唑安定与氯胺酮两药间隔15min给药，所用药物均由腹腔注射。各组动物于用药后2h开胸经心脏灌流脑固定，用免疫组织化学方法检测后扣带回皮质区c-fos蛋白的表达，用彩色病理图像分析系统测定c-fos阳性细胞的百分率和阳性细胞的密度。结果氯胺酮可明显诱导c-fos蛋白在大鼠后扣带回皮质区的表达；咪唑安定自身不能诱导c-fos的表达；咪唑安定预处理可显著抑制氯胺酮诱导的c-fos在这一区域的表达；先用氯胺酮后给予咪唑安定仅能部分抑制c-fos的表达。结论 咪唑安定预处理可抑制氯胺酮诱导的c-fos基因在大鼠后扣带回皮质区的表达，这可能是其预防或减轻氯胺酮所致精神症状和神经损害的机制之一。     

Xenon inhibits but N(2)O enhances ketamine-induced c-Fos expression in the rat posterior cingulate and retrosplenial cortices

Both nitrous oxide (N(2)O) and xenon are N:-methyl-D-aspartate receptor antagonists that have psychotomimetic effects and cause neuronal injuries in the posterior cingulate and retrosplenial cortices. We investigated the effect of xenon, xenon with ketamine, N(2)O, and N(2)O with ketamine on c-Fos expression in the rat posterior cingulate and retrosplenial cortices, a marker of psychotomimetic effects. Brain sections were prepared, and c-Fos expression was detected with immunohistochemical methods. A loss of microtubule-associated protein 2, a marker of neuronal injury, was also investigated. The number of Fos-like immunoreactivity positive cells by ketamine IV at a dose of 5 mg/kg under 70% N(2)O (128 +/- 12 cells per 0.5 mm(2)) was significantly more than those under 30% (15 +/- 2 cells per 0.5 mm(2)) and 70% xenon (2 +/- 1 cells per 0.5 mm(2)). Despite differences in c-fos immunoreactivity, there was no loss of microtubule-associated protein 2 immunoreactivity in any group examined. Xenon may suppress the adverse neuronal effects of ketamine, and combined use of xenon and ketamine seems to be safe in respect to neuronal adverse effects.     

Midazolam induces expression of c-Fos and EGR-1 by a non-GABAergic mechanism

Gene expression changes induced by general anesthetics have not been extensively examined. In this investigation, we treated rat pheochromocytoma PC12 cells with IV anesthetics, and assessed expression of immediate early gene products, c-Fos and EGR-1, by immunoblot analysis. Thiopental, ketamine, propofol, and diazepam did not significantly change the expression level of c-Fos and EGR-1. In contrast, midazolam dose- and time-dependently induced expression of c-Fos and EGR-1, which was not affected by antagonists of the benzodiazepine receptors, flumazenil and PK11195. The midazolam-induced c-Fos and EGR-1 expression was abolished by PD98059, an inhibitor for mitogen- activated protein kinase/extracellular signal-regulated kinase kinase, suggesting the involvement of extracellular signal-regulated kinases (ERKs). Immunoblot analysis demonstrated that midazolam induces phosphorylation and activation of ERKs. These results indicate that midazolam induces the expression of c-Fos and EGR-1, by activation of ERKs through a mechanism independent from gamma-aminobutyric acid(A) receptors, in PC12 cells, and suggest the possibility that midazolam can induce long-term changes of neural functions by changing gene expression. IMPLICATIONS: Gene expression changes induced by anesthetics in neuronal cells have not been noticed. We demonstrate that a large concentration of midazolam can induce expression of immediate early genes by a non-GABAergic mechanism in PC12 cells, suggesting that the administration of midazolam might lead to long-term changes of neural functions by changing gene expression.     

异丙酚对氯胺酮致老龄大鼠认知功能障碍的影响

目的 探讨异丙酚对氯胺酮致老龄大鼠认知功能障碍的影响.方法 健康雄性SD老龄大鼠32只,月龄18～24月龄,体重380～470 g,随机分为4组(n=8):对照组(C组)、异丙酚组(P组)、氯胺酮组(K组)和异丙酚+氯胺酮组(PK组).P组静脉输注异丙酚30 mg·kg-1·h-1,K组静脉输注氯胺酮40 mg·kg-1·b-1,PK组静脉输注异丙酚30 mg·kg-1·h-1+氯胺酮40 mg·kg-1·h-1,C组给予等容量生理盐水,每天2 h,连续7 d.给药结束后测定大鼠认知功能,记录逃避潜伏期和穿越平台次数.认知功能测试完毕后,处死大鼠,取海马组织,检测CA1区神经元凋亡情况,计算神经元凋亡率;测定CA1区caspase-3的表达水平.结果 与C组比较,P组逃避潜伏期、穿越平台次数、海马CA1区神经元凋亡率和caspase-3表达差异无统计学意义(P＞0.05),K组和PK组逃避潜伏期延长,穿越平台次数减少,海马CA1区神经元凋亡率升高,caspase-3表达上调(P＜0.05);与K组比较,PK组逃避潜伏期缩短,穿越平台次数增加,海马CA1区神经元凋亡率降低,caspase-3表达下调(P＜0.05).结论 异丙酚可减轻氯胺酮致老龄大鼠认知功能障碍,其机制可能与异丙酚可在一定程度上抑制氯胺酮所致caspase-3表达上调,从而抑制氯胺酮诱发的神经元凋亡有关.     

脊髓GABAA受体在异丙酚对内脏痛大鼠镇痛效应中的作用

目的 评价脊髓γ-氨基丁酸A(GABAA)受体在异丙酚对内脏痛大鼠镇痛效应中的作用.方法成年健康雌性SD大鼠,体重190～240 g,进行鞘内置管,并于直肠粘膜下注射10%福尔马林100 μl.取鞘内置管成功的大鼠32只,采用随机数字表法,将其随机分为4组(n=8):二甲基亚砜组(D组)、异丙酚组(P组)、荷包牡丹碱组(B组)和荷包牡丹碱+异丙酚组(BP组).D组、P组和B组分别鞘内注射二甲基亚砜5 μl、异丙酚10 μg、荷包牡丹碱2 μg;BP组先鞘内注射荷包牡丹碱2 μg,10min后鞘内注射异丙酚10 μg.注射福尔马林2 h时,取脊髓L5～S1节段,采用免疫组化法测定FOS蛋白表达水平.结果 与D组和B组比较,P组脊髓FOS蛋白表达下调(P＜0.05);D组和B组脊髓FOS蛋白表达差异无统计学意义(P＞0.05);与P组比较,BP组脊髓FOS蛋白表达上调(P＜0.05).结论 异丙酚可通过脊髓GABAA受体介导,对内脏痛大鼠产生镇痛效应.

Abstract：

Objective To evaluate the role of spinal cord CABAA receptors in the analgesic effect of propofol on visceral pain in rats. Methods Adult female SD rats, weighing 190-240 g, were used in this study.The animals were anesthetized with intraperitoneal ketamine 50-100 mg/kg. Intrathecal (IT) catheters were placed at L5-6 interspace according to the technique described by Storkson et al. Thirty-two animals in which IT catheters were successfully placed were randomly divided into 4 groups ( n = 8 each) : dimethyl sulphoxide (DMSO) group (group D), propofol group (group P), bicuculline group (group B) and bicuculline + propofol group (group B +P). Visceral pain was induced by injecting 10% formalin 100 μl underneath the mucous membrane of rectum.Groups D, P and B received IT DMSO 5 μl, propofol 10 μg and bicuculline 2 μg respectively. Group BP received IT bicuculline 2 μg and then IT propofol 10 μg 10 min later. The L5-S1 segment of the spinal cord was removed 2 h after formalin injection to determine FOS protein expression by hnmuno-histochemistry. Results Compared with groups D and B, FOS protein expression was significantly down-regulated in group P ( P ＜ 0.05 ) . There was no significant difference in FOS protein expression between groups D and B ( P ＞ 0.05) . FOS protein expression was significantly up-regulated in group BP compared with group P ( P ＜ 0.05) . Conclusion Propofol has analgesic effect on visceral pain in rats through spinal cord GABAA receptor action.     

In vivo effects of propofol on acetylcholine release from the frontal cortex, hippocampus and striatum studied by intracerebral microdialysis in freely moving rats

Using in vivo microdialysis, we have investigated the effects of propofol on acetylcholine (ACh) release from various regions of the rat brain. Propofol 25 and 50 mg kg-1 i.p. decreased basal ACh release from the frontal cortex by 70% and 85%, respectively. Propofol 25 and 50 mg kg-1 i.p. decreased basal ACh release from the hippocampus by 47% and 72%, respectively. However, in rat striatum, propofol 25 mg kg-1 i.p. did not affect basal ACh release and 50 mg kg-1 i.p. produced slight inhibition of basal ACh release (by 19%) only in the second sample after i.p. injection. In addition, we also examined the pharmacological mechanisms mediating the interaction between propofol and a gamma- aminobutyric acid A (GABAA) receptor complex. In the rat hippocampus, local application of bicuculline 1 mumol litre-1, a GABAA receptor antagonist, significantly antagonized the inhibitory effects of propofol 50 mg kg-1 i.p. on basal ACh release. In the rat frontal cortex, local application of bicuculline 1 mumol litre-1 did not antagonize the inhibitory effects of propofol 50 mg kg-1 i.p. on basal ACh release, while systemic application of bicuculline 1 mg kg-1 i.p. significantly antagonized the inhibitory effects of propofol 50 mg kg-1 i.p. These results suggest that propofol has powerful depressant effects on ACh release from the rat frontal cortex and hippocampus but not from the striatum, indicating that propofol has a "region- selective" anaesthetic action. Further, these results suggest that the inhibitory effects of propofol in the rat hippocampus may involve "intra" hippocampal GABAA receptors while the inhibitory effects in the rat frontal cortex may be mediated by GABAA receptors other than "intra" frontal cortex GABAA receptors.      

GABAergic mechanism of propofol toxicity in immature neurons

Certain anesthetics exhibit neurotoxicity in the brains of immature but not mature animals. Gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the adult brain, is excitatory on immature neurons via its action at the GABAA receptor, due to a reversed transmembrane chloride gradient. GABAA receptor activation in immature neurons is sufficient to open L-type voltage-gated calcium channels. As propofol is a GABAA agonist, we hypothesized that it and more specific GABAA modulators would increase intracellular free calcium ([Ca2+]i), resulting in the death of neonatal rat hippocampal neurons. Neuronal [Ca2+]i was monitored using Fura2-AM fluorescence imaging. Cell death was assessed by double staining with propidium iodide and Hoechst 33258 at 1 hour (acute) and 48 hours (delayed) after 5 hours exposure of neurons to propofol or the GABAA receptor agonist, muscimol, in the presence and absence of the GABA receptor antagonist, bicuculline, or the L-type Ca2+ channel blocker, nifedipine. Fluorescent measurements of caspase-3,-7 activities were performed at 1 hour after exposure. Both muscimol and propofol induced a rapid increase in [Ca2+]i in days in vitro (DIV) 4, but not in DIV 8 neurons, that was inhibited by nifedipine and bicuculline. Caspase-3,-7 activities and cell death increased significantly in DIV 4 but not DIV 8 hippocampal neuronal cultures 1 hour after 5 hours exposure to propofol, but not muscimol, and were inhibited by the presence of bicuculline or nifedipine. We conclude that an increase in [Ca2+]i, due to activation of GABAA receptors and opening of L-type calcium channels, is necessary for propofol-induced death of immature rat hippocampal neurons but that additional mechanisms not elicited by GABAA activation alone also contribute to cell death.     

The effect of ketamine on clinical endpoints of hypnosis and EEG variables during propofol infusion

BACKGROUND: We studied the effect of variable doses of ketamine on the endpoints of hypnosis, e.g., unresponsiveness to verbal commands (UVC), loss of eyelash reflex (LER), and inhibition of body movement response with or without sneezing to nasal membrane stimulation (INBMR), and processed EEG variables, e.g., bispectral index (BIS), 95% spectral edge frequency (SEF) and median frequency (MF) during propofol infusion. METHODS: Forty-eight patients received either propofol infusion, 30 mg.kg-1.h-1 (Group P; n = 12) or ketamine bolus, 0.25, 0.5 or 0.75 mg i.v., followed by propofol infusion, 30 mg.kg-1.h-1 + variable dose ketamine infusion, 0.25, 0.5 or 0.75 mg.kg-1.h-1 (Groups PK0.25, PK0.5 and PK0.75; n = 12 each) until UVC, LER and INBMR. BIS, 95% SEF and MF values were monitored and recorded at the endpoints of hypnosis. Propofol and ketamine concentrations were measured at INBMR. RESULTS: Propofol infusion, 30 mg.kg-1.h-1, induced UVC, LER and INBMR at BIS: 65 +/- 2, 63 +/- 9 and 33 +/- 7; 95% SEF: 17 +/- 3, 17 +/- 4 and 14 +/- 3; and MF values of 5 +/- 2, 5 +/- 3 and 3 +/- 2, respectively. With adjunctive ketamine (Groups PK0.5 and PK0.75), the hypnotic endpoints were achieved at higher BIS and 95% SEF values and lower propofol doses and concentrations as compared to Groups P and PK0.25 (9.9 +/- 5.8 and 9.4 +/- 3.4 vs. 13.4 +/- 4.5 and 14 +/- 5.8 micrograms.ml-1). CONCLUSIONS: Our results suggest additive interaction between propofol and ketamine (Groups PK0.5 and PK0.75) for achieving the hypnotic endpoints; however, ketamine did not depress the EEG variables in proportion to its hypnotic effect. The paradoxically higher BIS and 95% SEF values at the hypnotic endpoints may be due to lower propofol concentrations and/or no effect of ketamine on the EEG variables.     

Different Actions of General Anesthetics on the Firing Patterns of Neocortical Neurons Mediated by the GABAA Receptor

Background: In cultured slice preparations of rat neocortical tissue, clinically relevant concentrations of volatile anesthetics mainly decreased action potential firing of neurons by enhancing [Greek small letter gamma]-aminobutyric acid (GABAA) receptor-mediated synaptic inhibition. The author's aim was to determine if other anesthetic agents are similarly effective in this model system and act via the same molecular mechanism.

Methods: The actions of various general anesthetics on the firing patterns of neocortical neurons were investigated by extracellular single-unit recordings.

Results: Pentobarbital, propofol, ketamine, and ethanol inhibited spontaneous action potential firing in a concentration-dependent manner. The estimated median effective concentration (EC50) values were close to or below the EC50 values for general anesthesia. Bath application of the GABAA antagonist bicuculline (100 [micro sign]M) decreased the effectiveness of propofol, ethanol, halothane, isoflurane, enflurane, and diazepam by more than 90%, indicating that these agents acted predominantly via the GABAA receptor. The depressant effects of pentobarbital and ketamine were not significantly reduced by bicuculline treatment. Drugs acting mainly via the GABAA receptor altered the firing patterns of neocortical cells in different manners. Diazepam reduced the discharge rates by decreasing the number of action potentials per burst, leaving the burst rate unaffected. In contrast, muscimol, GABA, propofol, and volatile anesthetics decreased the burst rate.     

Effects of intravenous anesthetic agents on glutamate release: a role for GABAA receptor-mediated inhibition

BACKGROUND: Many anesthetic agents are known to enhance the alpha1beta2gamma2S gamma-aminobutyric acid type A (GABAA) chloride current; however, they also depress excitatory neurotransmission. The authors evaluated two hypotheses: intravenous anesthetic agents inhibit glutamate release and any observed inhibition may be secondary to GABAA receptor activation. METHODS: Cerebrocortical slices were prepared from Wistar rats. After perfusion in oxygenated Krebs buffer for 60 min at 37 degrees C, samples for glutamate assay were obtained at 2-nmin intervals. After 6 min, a 2-min pulse of 46 mM K+ was applied to the slices (S1); this was repeated after 30 min (S2). Bicuculline (1-100 microM) was applied when the S1 response returned to basal level, and 10 min later, thiopental (1-300 micro/M), propofol (10 microM), or ketamine (30 microM) were also applied until the end of S2. Perfusate glutamate concentrations were measured fluorometrically, and the area under the glutamate release curves was expressed as a ratio (S2/S1). RESULTS: Potassium (46 mM) evoked a monophasic release of glutamate during S1 and S2, with a mean control S2/S1 ratio of 1.07 +/- 0.33 (mean +/- SD, n = 96). Ketamine and thiopental produced a concentration-dependent inhibition of K+-evoked glutamate release with half-maximum inhibition of release values of 18.2 and 10.9 /microM, respectively. Release was also inhibited by propofol. Bicuculline produced a concentration dependent reversal of thiopental inhibition of glutamate release with a half-maximum reversal of the agonist effect of 10.3 microM. Bicuculline also reversed the effects of propofol but not those of ketamine. CONCLUSIONS: The authors' data indicate that thiopental, propofol, and ketamine inhibit K+-evoked glutamate release from rat cerebrocortical slices. The inhibition produced by thiopental and propofol is mediated by activation of GABAA receptors, revealing a subtle interplay between GABA-releasing (GABAergic) and glutamatergic transmission in anesthetic action.     

Neuroprotective properties of propofol and midazolam, but not pentobarbital, on neuronal damage induced by forebrain ischemia, based on the GABAA receptors

BACKGROUND: The mechanism of the neuroprotective effects of propofol was compared to two other types of intravenous (i.v.) anesthetics (i.e., benzodiazepine; midazolam and barbiturate; pentobarbital) using Mongolian gerbils focusing on GABA receptor subtypes. METHODS: Neuronal injury was induced by a 4-min occlusion of the common carotid arteries followed by reperfusion. One week after occlusion, animals were transcardially perfused for histochemistry. Neuronal death in four brain regions was evaluated by direct visual counting of acidophilic neurons. RESULTS: Seven days after this ischemic episode, severe neuronal injury was measured in the hippocampal CA1 area (> 98% of total cells damaged) and parietal cortex (> 35%). Also lateral thalamus and caudate putamen were damaged but to a lesser extent (about 10%). The neuronal injury in these areas was significantly attenuated by propofol, midazolam and the GABAA agonist, muscimol, intraperitoneally administered 15 min prior to ischemia. This neuroprotective property, however, was lacking with pentobarbital and GABAB agonist baclofen. Concomitant pretreatment with subthreshold doses of propofol and muscimol significantly reduced the amount of cell death induced by brain ischemia. On the other hand, pretreatment with the GABAA antagonist bicuculline significantly inhibited the neuroprotective effects of propofol. However, a GABAB antagonist, phaclofen, was without effect on neuronal damage and on neuronal protection of propofol. CONCLUSION: These results indicate that activation of GABAA receptors, which include the specific binding subunits for propofol and midazolam, but not pentobarbital, plays a role in the inhibition of neuronal death induced by brain ischemia.     

Preliminary report: the effect of flumazenil on the hypnotic dose of propofol in ddY mice

The present investigation dealt with the effect of simultaneous administration of flumazenil on the hypnotic activity of propofol using a behavioral model of ddY mice. The mixed solution of propofol and flumazenil was administered intravenously into the mice tail vein and the achievement of hypnosis was defined as the loss of the righting reflex. Flumazenil 0.2 mg.kg-1 significantly decreased the required dose of propofol for hypnosis (8.43 +/- 0.46 mg.kg-1) compared to the control group (10.55 +/- 0.55 mg.kg-1). The mixture with a pH-3.9 acetate buffer solution did not change the hypnotic dose of propofol (10.88 +/- 0.62 mg.kg-1). The results suggest that flumazenil might potentiate the hypnotic activity of propofol in ddY mice.     

Neuroprotective and neurotoxic properties of the 'inert' gas,xenon

Background. Antagonists of the N-methyl-D-aspartate (NMDA) subtypeof glutamate receptors have been shown not only to have neuroprotectiveeffects but also to exhibit neurotoxic properties. In this study,we used c-Fos, a protein product of an immediate early gene,as a marker of neuronal injury to compare the neuroprotectiveeffects of xenon and the neurotoxic properties of xenon, nitrousoxide, and ketamine, three anaesthetics with NMDA receptor antagonistproperties. Methods. We used an in vivo rat model of brain injury in whichN-methyl-DL-aspartic acid (NMA) is injected subcutaneously (s.c.)and c-Fos expression in the arcuate nucleus is used as a measureof injury. To examine the neurotoxic potential of each of thethree anaesthetics with NMDA receptor antagonist properties,c-Fos expression in the posterior cingulate and retrosplenial(PC/RS) cortices was measured. Results. Xenon dose-dependently suppressed NMA-induced c-Fosexpression in the arcuate nucleus with an IC₅₀ of 47 (2)% atm.At the highest concentration tested (75% atm) NMA-induced neuronalinjury was decreased by as much as that observed with the prototypicalNMDA antagonist MK801 (0.5 mg kg^–1 s.c.). Both nitrousoxide and ketamine dose-dependently increased c-Fos expressionin PC/RS cortices; in contrast, xenon produced no significanteffect. If the dopamine receptor antagonist haloperidol wasgiven before either nitrous oxide or ketamine, their neurotoxiceffects were eliminated. Conclusions. Uniquely amongst anaesthetics with known NMDA receptorantagonist action, xenon exhibits neuroprotective propertieswithout co-existing neurotoxicity. The reason why ketamine andnitrous oxide, but not xenon, produce neurotoxicity may involvetheir actions on dopaminergic pathways. Br J Anaesth 2002; 89: 739–46     

The changes of bispectral index induced by administration of midazolam during propofol anesthesia

The effect of the additional administration of midazolam or flumazenil on bispectral index (BIS) during propofol anesthesia was investigated in 22 scheduled surgical patients. Midazolam 10 or 30 micrograms.kg-1, or flumazenil 6 or 12 micrograms.kg-1 was injected to the patients to evaluate their effect on BIS after achieving steady state of hypnosis more than 1 hr of propofol anesthesia with 5 mg.kg-1.hr-1. The only midazolam 30 micrograms.kg-1 significantly reduced BIS value from 47.8 +/- 8.6 to 36.8 +/- 6.5. The synergistic interaction between midazolam and propofol assessed by BIS might be less clear than that assessed by hypnotic dose of propofol using psychopharmacological investigation.     

The involvement of the mu-opioid receptor in ketamine-induced respiratory depression and antinociception.

N-methyl-D-aspartate receptor antagonism probably accounts for most of ketamine's anesthetic effects; its analgesic properties are mediated partly via N-methyl-D-aspartate and partly via opioid receptors. We assessed the involvement of the mu-opioid receptor in S(+) ketamine-induced respiratory depression and antinociception by performing dose-response curves in exon 2 mu-opioid receptor knockout mice (MOR(-/-)) and their wild-type littermates (WT). The ventilatory response to increases in inspired CO(2) was measured with whole body plethysmography. Two antinociceptive assays were used: the tail-immersion test and the hotplate test. S(+) ketamine (0, 10, 100, and 200 mg/kg intraperitoneally) caused a dose-dependent respiratory depression in both genotypes, with greater depression observed in WT relative to MOR(-/-) mice. At 200 mg/kg, S(+) ketamine reduced the slope of the hypercapnic ventilatory response by 93% +/- 15% and 49% +/- 6% in WT and MOR(-/-) mice, respectively (P < 0.001). In both genotypes, S(+) ketamine produced a dose-dependent increase in latencies in the hotplate test, with latencies in MOR(-/-) mice smaller compared with those in WT animals (P < 0.05). In contrast to WT mice, MOR(-/-) mice displayed no ketamine-induced antinociception in the tail-immersion test. These results indicate that at supraspinal sites S(+) ketamine interacts with the mu-opioid system. This interaction contributes significantly to S(+) ketamine-induced respiratory depression and supraspinal antinociception. IMPLICATIONS: The involvement of the mu-opioid receptor system in S(+) ketamine-induced respiratory depression and spinal and supraspinal analgesia was demonstrated by performing experiments in mice lacking the mu-opioid receptor and in mice with intact mu-opioid receptors.