异丙酚对大鼠海马神经元NMDA受体通道电流的影响

目的 研究异丙酚对大鼠海马神经元N-甲基-D-天冬氨酸（NMDA）受体通道电流的影响。方法 体外培养新生Wistar大鼠海马神经元8—12d，采用全细胞膜片钳技术和压力喷射给药方式，钳制电压为-80mV，记录3、48μg∥ml异丙酚对100μmol／LNMDA诱发NMDA受体通道电流的影响；然后用7-氨基丁酸（GABA）受体拮抗剂荷包牡丹碱100μmol／L阻断GABA．受体，观察3、48μg／ml异丙酚对NMDA受体通道电流的影响。结果 3、48μg／ml异丙酚抑制自发兴奋性突触后电流并直接激动GABA．受体，使Cl．内流，产生外向超极化的GABA电流，从而间接抑制NMDA受体通道电流。用荷包牡丹碱100μmol／L阻断GABA．受体后，3、48μg∥ml异丙酚仍可抑制100μmol／LNMDA诱发的NMDA受体通道电流（P〈0．05）。结论 异丙酚通过激活GABA．受体影响NMDA受体通道电流，对NMDA受体通道也有直接抑制作用。     

NMDA受体的调控

在中枢神经系统中,广泛存在着NMDA受体,NMDA受体的兴奋与抑制不仅与神经元本身的生长和突触的塑造有关,而且还与大脑的认知功能、大脑的发育以及中枢神经系统损伤时神经细胞的死亡或凋亡有关,研究发现在许多环节上可调控NMDA受体,现对NMDA受体的调控机制作一简要综述。     

脱氢表雄酮硫酸酯与绝经后激素替代治疗

脱氢表雄酮 (DHEA)及其硫酸酯 (DHEAS)是由肾上腺皮质分泌的最丰富的甾体激素 ,DHEA(S)通过与GABA、NMDA等多种受体作用及调节阿片肽分泌等途径发挥缓解抑郁症状、增强体质、调节机体免疫力、改善认知等功能 ,有关DHEA(S)在绝经后妇女的激素替代治疗中潜在应用价值已引起重视     

γ-氨基丁酸受体和神经发生

背景 近年的研究显示γ-氧基丁酸(γ-aminobutyric acid,GABA)-GABAA受体通路与神经发生有密切联系.神经发生不仅存在于胎儿期和新生儿期,同时还存在于成年期.大脑海马区的神经发生状态与认知和学习记忆功能成正比.目的 通过阐述GABAA受体和神经发生的关系,进而探讨与GABAA受体密切相关的全身麻醉药物的临床药理.内容 主要关注GABAA受体、神经发生和认知功能之间的关系及其介导机制.趋向 系统的研究GABAA受体和神经发生关系将为全身麻醉药对认知功能影响的研究提供新的思路.     

异丙酚的镇痛作用及其机制

睡眠剂量和亚睡眠剂量的异丙酚具有镇痛作用。其镇痛作用主要与增强GABA。受体功能、拮抗NMDA受体、增强阿片受体活性和抑制一化氮合成酶（NoS）活性等密切关联。深入研究异丙酚镇痛作用及其机制，对临床更合理地应用异丙酚具有重要的意义。     

NMDA受体的调控

在中枢神经系统中，广泛存在着NMDA受体，NMDA受体的兴奋与抑制不仅与神经元本身的牛长和突触的塑造有关，而且还与大脑的认知功能、大脑的发育以及中枢神经系统损伤时神经细胞的死亡或凋亡有关，研究发现在许多环节上可调控NMDA受体，现对NMDA受体的调控机制作一简要综述。     

异丙酚麻醉对新生小鼠海马c-fos表达和caspase-3激活的影响

全麻药可影响中枢神经的发育,导致婴幼儿或幼龄动物发育期后认知功能下降[1-7].异丙酚在小儿和产科麻醉中的应用日益广泛.研究表明,异丙酚麻醉可影响发育期啮齿类动物中枢神经发育[8],还可引起患儿共济失调、幻觉等神经系统损害[9].在中枢神经发育高峰期,阻断NMDA受体或过度激活γ-氨基丁酸A型( GABAA)受体诱发的神经细胞凋亡可影响长期学习记忆功能[10-11].异丙酚可通过激动GABAA受体,直接或间接阻断NMDA受体发挥麻醉效应[12-13],异丙酚对发育期中枢神经功能的影响是否与神经细胞凋亡有关尚有待研究.本研究拟探讨异丙酚麻醉对新生小鼠海马细胞凋亡相关蛋白c-fos表达和caspase-3激活的影响.     

氟马西尼对术后认知功能的影响

术后认知功能障碍的发生可能与围术期某些用药有关.这类药物,尤其是部分麻醉药物可产生遗忘,学习能力、注意力、记忆力、定向力降低等认知功能障碍.苯二氮蔁(benzodiazepine,BDZ)受体拮抗剂氟马西尼不仅可通过影响γ-氨基丁酸(gamma-aminobutyrie acid,GABA)受体促进咪达唑仑、丙泊酚、吸入麻醉药的麻醉后苏醒,还能逆转这些药物所致的认知和精神运动功能的损害,有助于患者术后认知功能的及早恢复.氟马西尼联用5-HT3受体阻断剂恩丹西酮可促进乙酰胆碱的释放,从而推测这种联合用药可拮抗与胆碱能水平减少或功能低下相关的认知功能损害.     

正方：麻醉导致发育期神经细胞凋亡——目前的实验证据

8年前,Ikonomidou等报道谷氨酸受体N-甲基-D-天门冬氨酸（NMDA）亚型阻滞剂可使幼龄大鼠脑发生广泛的神经细胞凋亡。随后的系列研究确认多种药物可致幼龄大鼠或小鼠发生类似的神经变性,这些药物包括：（1）GABAA受体激动剂;（2）拮抗NMDA受体和激动GABA。受体的乙醇;（3）抗癫痫药物,包括能激动GABAA受体和阻滞Na离子通道的药物;     

NMDA受体与躯体内脏的痛觉调制

NMDA受体是兴奋性氨基酸的特异性受体 ,与神经细胞钙离子内流密切相关 ,参与体内各种信号传递和调节神经元的兴奋性。它由不同的亚基组成 ,这些亚基决定着天然NMDA受体的功能特性 ,其中 ,含NR2B亚基的受体对伤害性感受的传递和调制有重要作用。已有大量研究表明 ,NMDA受体在痛觉中枢敏感化的产生、维持中有重要作用 ;NMDA受体也可能同时介导外周敏感化和内脏痛。     

Propofol-induced anesthesia in mice is mediated by gamma-aminobutyric acid-A and excitatory amino acid receptors

To elucidate the role of gamma-aminobutyric acid (GABA)(A) receptor complex and excitatory amino acid receptors (N-methyl-D-aspartate [NMDA] and non-NMDA receptors) in propofol-induced anesthesia, we examined behaviorally the effects of GABAergic and glutamatergic drugs on propofol anesthesia in mice. All drugs were administered intraperitoneally. General anesthetic potencies were evaluated using a righting reflex assay. The GABA(A) receptor agonist muscimol potentiated propofol (140 mg/kg; 50% effective dose for loss of righting reflex) induced anesthesia. Similarly, the benzodiazepine receptor agonist diazepam and the NMDA receptor antagonist MK-801 augmented propofol anesthesia, but the non-NMDA receptor antagonist CNQX did not. In contrast, the GABA(A) receptor antagonist bicuculline antagonized propofol (200 mg/kg; 95% effective dose for loss of righting reflex) induced anesthesia. However, neither the benzodiazepine receptor antagonist flumazenil, the GABA synthesis inhibitor L-allylglycine, nor the NMDA receptor agonist NMDA reversed propofol anesthesia. Conversely, the non-NMDA receptor agonist kainate enhanced propofol anesthesia. These results suggest that propofol-induced anesthesia is mediated, at least in part, by both GABA(A) and excitatory amino acid receptors. IMPLICATIONS: We examined behaviorally the effects of GABAergic and glutamatergic drugs on propofol-induced anesthesia in mice. The results suggest that propofol anesthesia is mediated, at least in part, by both GABA(A) and excitatory amino acid receptors.     

Potentiation of GABA(A) currents after mechanical injury of cortical neurons

Numerous studies have implicated glutamate receptors, glutamate neurotoxicity, and hyperexcitation in the pathobiology of traumatic brain injury, yet much less is known about the effects of neurotrauma on inhibitory GABA channels of the brain. Using an in vitro cell injury model, we tested whether mild stretch injury altered the GABA(A) currents of cultured rat cortical neurons. The application of 1-100 microM GABA to single pyramidal neurons voltage clamped to -60 mV activated an inward current that reversed near 0 mV in solutions containing symmetrical [Cl-]. This current was inhibited by bicuculline, consistent with mediation by GABA(A) receptor channels. In injured neurons, 50 microM GABA elicited a peak current density of 41.2 +/- 2.6 pA/pF (n = 82), which was significantly larger than in uninjured control neurons, 20.2 +/- 1.7 pA/pF (n = 69, p < 0.01). The GABA(A) currents of injured neurons did not differ from those of control neurons in their sensitivity to GABA or their reversal potentials, suggesting that GABA current potentiation did not result from changes in the agonist affinity or ionic selectivity of the channels. GABA current potentiation was prevented by injuring neurons in the presence of the NMDA antagonist APV, or the CaMKII inhibitor KN93. These results thus suggest that NMDA receptor activation following neuronal injury may potentiate GABA(A) channels through the activation of CaMKII. The increase in GABA(A) receptor function observed following injury could potentially contribute to dysfunctional synaptic function and information processing as well as unconsciousness and coma following human brain trauma.     

The effects of general anesthetics on excitatory and inhibitory synaptic transmission in area CA1 of the rat hippocampus in vitro

It is unclear whether general anesthetics induce enhancement of neural inhibition and/or attenuation of neural excitation. We studied the effects of pentobarbital (5 x 10(-4) mol/L), propofol (5 x 10(-4) mol/L), ketamine (10(-3) mol/L), halothane (1.5 vol%), and isoflurane (2.0 vol%) on both excitatory and inhibitory synaptic transmission in rat hippocampal slices. Excitatory or inhibitory synaptic pathways were isolated using pharmacological antagonists. Extracellular microelectrodes were used to record electrically evoked CA1 neural population spikes (PSs). In the presence of the gamma-aminobutyric acid type A (GABA(A)) receptor antagonist (bicuculline), the inhibitory actions of pentobarbital and propofol were completely antagonized, whereas those of ketamine, halothane, and isoflurane were only partially blocked. To induce the N-methyl-D-aspartate (NMDA) receptor-mediated PS (NMDA PS), the non-NMDA and GABA(A) receptors were blocked in the absence of Mg2+. Ketamine, halothane, and isoflurane decreased the NMDA PS, and pentobarbital and propofol had no effect on the NMDA PS. The non-NMDA receptor-mediated PS (non-NMDA PS) was examined using the antagonists for the NMDA and GABA(A) receptors. Volatile, but not i.v., anesthetics reduced the non-NMDA PS. These findings indicate that pentobarbital and propofol produce inhibitory actions due to enhancement in the GABA(A) receptor; that ketamine reduces NMDA receptor-mediated responses and enhances GABA(A) receptor-mediated responses; and that halothane and isoflurane modulate GABA(A), NMDA, and non-NMDA receptor-mediated synaptic transmission. IMPLICATIONS: Volatile anesthetics modulate both excitatory and inhibitory synaptic transmission of in vitro rat hippocampal pathways, whereas i.v. anesthetics produce more specific actions on inhibitory synaptic events. These results provide further support the idea that general anesthetics produce drug-specific and distinctive effects on different pathways in the central nervous system.     

Halothane depresses glutamatergic neurotransmission to brain stem inspiratory premotor neurons in a decerebrate dog model

BACKGROUND: Inspiratory bulbospinal neurons in the caudal ventral medulla are premotor neurons that drive phrenic motoneurons and ultimately the diaphragm. Excitatory drive to these neurons is mediated by N-methyl-d-aspartate (NMDA) receptors and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors and modulated by an inhibitory gamma-aminobutyric acid(A) (GABA(A))ergic input. The authors investigated the effect of halothane on these synaptic mechanisms in decerebrate dogs. METHODS: Studies were performed in decerebrate, vagotomized, paralyzed, and mechanically ventilated dogs during hypercapnic hyperoxia. The effect of 1 minimum alveolar concentration (MAC) halothane on extracellularly recorded neuronal activity was measured during localized picoejection of the GABA(A) receptor blocker bicuculline and the glutamate agonists AMPA and NMDA. Complete blockade of the GABA(A)ergic mechanism by bicuculline allowed differentiation between the effects of halothane on overall GABA(A)ergic inhibition and on overall glutamatergic excitation. The neuronal responses to exogenous AMPA and NMDA were used to estimate the anesthetic effect on postsynaptic glutamatergic neurotransmission. RESULTS: Halothane, 1 MAC, depressed the spontaneous activity of 21 inspiratory neurons by 20.6 +/- 18.0% (mean +/- SD; P = 0.012). Overall glutamatergic excitation was depressed 15.4 +/- 20.2% (P = 0.001), while overall GABA(A)ergic inhibition did not change. The postsynaptic responses to exogenous AMPA and NMDA were also depressed by 18.6 +/- 35.7% (P = 0.03) and 22.2 +/- 26.2% (P = 0.004), respectively. CONCLUSION: Halothane, 1 MAC, depressed the activity of inspiratory premotor neurons by a reduction of glutamatergic excitation. Overall inhibitory drive did not change. The postsynaptic AMPA and NMDA receptor response was significantly reduced. These findings contrast with studies in expiratory premotor neurons in which overall inhibition was significantly increased by halothane and there was no reduction in the postsynaptic glutamate receptor response.     

Effects of sevoflurane on excitatory neurotransmission to medullary expiratory neurons and on phrenic nerve activity in a decerebrate dog model

BACKGROUND: Sevoflurane is a new volatile anesthetic with a pronounced respiratory depressant effect. Synaptic neurotransmission in canine expiratory bulbospinal neurons is mainly mediated by excitatory N-methyl-D-aspartatic acid (NMDA) receptor input and modulated by inhibitory gamma-aminobutyric acid type A (GABA(A)) receptors. The authors investigated the effect of sevoflurane on these mechanisms in decerebrate dogs. METHODS: Studies were performed in decerebrate, vagotomized, paralyzed and mechanically ventilated dogs during hypercapnic hyperoxia. The effect of 1 minimum alveolar concentration (MAC; 2.4%) sevoflurane on extracellularly recorded neuronal activity was measured during localized picoejection of the glutamate agonist NMDA and the GABA(A) receptor blocker bicuculline in a two-part protocol. First, complete blockade of the GABA(A)ergic mechanism by bicuculline allowed differentiation between the effects of sevoflurane on overall GABA(A)ergic inhibition and on overall glutamatergic excitation. In a second step, the neuronal response to exogenous NMDA was used to estimate sevoflurane's effect on postsynaptic glutamatergic neurotransmission. RESULTS: One minimum alveolar concentration sevoflurane depressed the spontaneous activity of 16 expiratory neurons by 36.7+/-22.4% (mean +/- SD). Overall glutamatergic excitation was depressed 19.5+/-16.2%, and GABA(A)ergic inhibition was enhanced 18.7+/-20.6%. However, the postsynaptic response to exogenous NMDA was not significantly altered. In addition, 1 MAC sevoflurane depressed peak phrenic nerve activity by 61.8+/-17.7%. CONCLUSIONS: In the authors' in vivo expiratory neuronal model, the depressive effect of sevoflurane on synaptic neurotransmission was caused by a reduction of presynaptic glutamatergic excitation and an enhancement of GABA(A)ergic inhibition. The effects on expiratory neuronal activity were similar to halothane, but sevoflurane caused a stronger depression of phrenic nerve activity than halothane.     

Chirality in anesthesia II: stereoselective modulation of ion channel function by secondary alcohol enantiomers

Chirality has been proposed as a means for distinguishing relevant from irrelevant molecular targets of action, but the sensitivity and specificity of this test is unknown for volatile anesthetics. We applied enantiomers of two chiral anesthetic alcohols (2-butanol and 2-pentanol) that are enantioselective for the minimum alveolar concentration (MAC) preventing movement in 50% of animals and one (2-hexanol) that was not to frog oocytes. Each oocyte expressed one of three anesthetic-sensitive ion channels: a Twik-related-spinal cord K+ (TRESK) channel, a gamma-amino butyric acid type A (GABA(A)) receptor and an N-methyl-d-aspartate (NMDA) receptor. Using voltage-clamp techniques, we found that 2-butanol was not enantioselective for any channel (e.g., 16 mM 2-butanol R(-) and S(-) enantiomers decreased current through an NMDA receptors by 44% +/- 3% [mean +/- se] and 37% +/- 4%, respectively); 2-pentanol was enantioselective for one channel (the GABA(A) receptor, the enantiomers increasing current by 277% +/- 20% and 141% +/- 30%); 2-hexanol was enantioselective for both GABA(A) and NMDA receptors (e.g., decreasing current through the NMDA receptor by 19% +/- 3% and 43% +/- 5%). We calculated the sensitivity and specificity of chirality as a test of anesthetic relevance under two scenarios: 1) all three channels were relevant mediators of MAC and 2) no channel was a mediator of MAC. These sensitivities and specificities were poor because there is no consistent correspondence between receptor and whole animal results. We recommend that enantioselectivity not be used as a test of relevance for inhaled anesthetic targets.     

Additive effects of sevoflurane and propofol on gamma-aminobutyric acid receptor function

BACKGROUND: Previous studies have shown that propofol and sevoflurane enhance the function of gamma-aminobutyric acid type A (GABAA) receptors. However, it is not known whether these two drugs modulate the same molecular pathways. In addition, little is known about receptor function in the presence of both propofol and sevoflurane. The aim of this study was to better understand the interactions of propofol and sevoflurane with the GABAA receptor. METHODS: Wild-type alpha1, beta(2), gamma(2s) GABA(A) receptor subunit complementary DNAs were transfected into human embryonic kidney cells grown on glass coverslips using a calcium phosphate transfection method. After transfection (36-72 h), cells were whole cell patch clamped and exposed to combinations of the following: 0.3-1,000 microm gamma-aminobutyric acid (GABA), 0-10 microm propofol, and 0-1,650 microm sevoflurane. Chemicals were delivered to the cells using two 10-channel infusion pumps and a rapid solution exchanger. RESULTS: Both propofol and sevoflurane alone enhanced the amplitude of GABA(A) receptor responses to submaximal concentrations of GABA in a dose-dependent manner. The enhancement was underpinned by an increase in the apparent affinity of the receptor for GABA. Coapplication of both anesthetics further enhanced the apparent affinity of the receptor for GABA. CONCLUSIONS: Response surface modeling of the potentiation of GABA responses (0.3-1,000 microm) by sevoflurane and propofol revealed that the two anesthetics modulated receptor function in an additive manner. These results are consistent with recent mutagenesis studies, suggesting that these two drugs have separate binding sites and converging pathways of action on the GABAA receptor.     

Spontaneous synaptic activity of subplate neurons in neonatal rat somatosensory cortex

Subplate neurons play an important role in early cortical development. To investigate whether these transient neurons receive synaptic inputs, we performed whole-cell recordings from visually identified and biocytin-labeled subplate cells in somatosensory cortical slices from postnatal day 0-3 rats. Subplate neurons had an average resting membrane potential of -55 mV and input resistance of approximately 1.1 G ohms. Suprathreshold current injection elicited in 67% of the cells repetitive action potentials at 4-13 Hz and the remaining 33% showed only one spike. Three classes of spontaneous postsynaptic currents (sPSCs) could be identified: (i) Fast sPSCs, with an average amplitude of 14 pA and a decay time of 6.3 ms, which showed a 95% decrease in their frequency during (+/-)-gamma-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA)/kainate receptor blockade. Cyclothiazide caused a 3.5-fold increase in the decay time, indicating that fast sPSCs were mediated by AMPA receptors. (ii) Slow sPSCs, with 18 pA amplitude and 51.2 ms decay time were blocked by the N-methyl-D-aspartate (NMDA) receptor antagonist CPP. (iii) Chloride-driven sPSCs, with 34.4 pA amplitude and 123 ms decay time that were blocked by the gamma-amino-butyric acid A (GABA(A)) receptor antagonist gabazine. While tetrodotoxin citrate (TTX) blocked completely NMDA-mediated slow sPSCs, the frequency of AMPA- and GABA(A)-mediated sPSCs was reduced in TTX by 55 and 90%, respectively. These results indicate that subplate neurons receive functional synaptic inputs mediated by AMPA, NMDA and GABA(A) receptors.     

Small-dose pentobarbital enhances synaptic transmission in rat hippocampus.

We investigated the contribution of bicarbonate ion, gamma-aminobutyric acid-A (GABA(A)) receptors, and N-methyl-D-aspartate (NMDA) receptors to pentobarbital-induced enhancement of excitatory synaptic transmission in the hippocampal slice. Transverse hippocampal slices (400 microm thick) were prepared from 20- to 30-day-old Sprague-Dawley rats and maintained in an interface chamber perfused with warmed (35 degrees C) oxygenated artificial cerebrospinal fluid. Extracellular field potentials, evoked by orthodromic paired-pulse stimulation of the Schaffer collateral CA1 pathway, were analyzed for the population spike (PS) amplitude. Pentobarbital had a concentration-dependent, biphasic effect on PS amplitudes, which were increased approximately twofold (P < 0.001) when the slice was exposed to pentobarbital concentrations of 1 and 5 microM and depressed at drug concentrations larger than 10 microM. Pentobarbital (5 microM) did not increase the PS amplitude when stimulation was stopped during exposure to the drug. The enhancement of PS amplitude was suppressed in the presence of 10 microM acetazolamide, a nonselective carbonic anhydrase inhibitor, and when the slice was bathed in CO(2)/HCO(3)(-)-free artificial cerebrospinal fluid. Pretreatment with 1 microM picrotoxin, a GABA(A) receptor antagonist, or 5 microM 2-amino-5-phosphopentanoic acid, a specific NMDA receptor antagonist, also suppressed enhancement of PS amplitude by 5 microM pentobarbital. The results suggest that small concentrations of pentobarbital (1 and 5 microM) enhance synaptic transmission through mechanisms involving GABA(A) and NMDA receptors and the HCO(3)(-) ion. IMPLICATIONS: Enhanced hippocampal synaptic transmission after exposure to subanesthetic concentrations of pentobarbital persists during drug washout. This finding may help to explain why some patients experience excitation and enhanced pain during emergence from anesthesia.