451
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Henschel O, Gipson KE, Bordey A. GABAA receptors, anesthetics and anticonvulsants in brain development. CNS & NEUROLOGICAL DISORDERS DRUG TARGETS 2008; 7:211-24. [PMID: 18537647 PMCID: PMC2557552 DOI: 10.2174/187152708784083812] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
GABA, acting via GABA(A) receptors, is well-accepted as the main inhibitory neurotransmitter of the mature brain, where it dampens neuronal excitability. The receptor's properties have been studied extensively, yielding important information about its structure, pharmacology, and regulation that are summarized in this review. Several GABAergic drugs have been commonly used as anesthetics, sedatives, and anticonvulsants for decades. However, findings that GABA has critical functions in brain development, in particular during the late embryonic and neonatal period, raise worthwhile questions regarding the side effects of GABAergic drugs that may lead to long-term cognitive deficits. Here, we will review some of these drugs in parallel with the control of CNS development that GABA exerts via activation of GABA(A) receptors. This review aims to provide a basic science and clinical perspective on the function of GABA and related pharmaceuticals acting at GABA(A) receptors.
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Affiliation(s)
- Oliver Henschel
- Department of Neurosurgery, Yale University, New Haven, CT 06520-8082, USA
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452
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Haines M, Mao LM, Yang L, Arora A, Fibuch EE, Wang JQ. Modulation of AMPA receptor GluR1 subunit phosphorylation in neurons by the intravenous anaesthetic propofol. Br J Anaesth 2008; 100:676-82. [PMID: 18344555 DOI: 10.1093/bja/aen051] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND The ionotropic glutamate receptor is a potential molecular site in the central nervous system that general anaesthetics may interact with to produce some of their biological actions. Protein phosphorylation has been well documented to occur in the intracellular C-terminal domain of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) subtype of glutamate receptors, which represents a pivotal mechanism for the post-translational modulation of AMPA receptor functions. In this study, we investigated a possible influence of an i.v. anaesthetic agent propofol on the phosphorylation of AMPA receptor GluR1 subunits in cultured neurons. METHODS The effect of propofol on phosphorylation of GluR1 subunits at serine 831 and 845 was assayed in cultured rat striatal and cortical neurons by western blot with phospho- and site-specific antibodies. RESULTS Propofol consistently elevated phosphorylation of GluR1 subunits at the C-terminal serine 845 site in both striatal and cortical neurons. The elevation in phosphorylation was concentration-dependent and started at a low concentration (3 microM). This increase in serine 845 phosphorylation was rapid and sustained during the entire course of propofol exposure. In contrast to serine 845, phosphorylation of GluR1 at serine 831 was not altered by propofol in striatal and cortical neurons. Total GluR1 abundance remained unchanged in response to propofol incubation. CONCLUSIONS These data indicate that propofol possesses the ability to upregulate AMPA receptor GluR1 subunit phosphorylation at a specific serine 845 site in neurons and provide evidence supporting the AMPA receptor as a molecular target for general anaesthetics.
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Affiliation(s)
- M Haines
- Department of Anesthesiology, University of Missouri-Kansas City School of Medicine, 2411 Holmes Street, Kansas City, MO 64108, USA
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453
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Mashour GA. Toward a general theory of unconscious processes in psychoanalysis and anesthesiology. J Am Psychoanal Assoc 2008; 56:203-22. [PMID: 18430708 DOI: 10.1177/0003065108315692] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Psychoanalysis and anesthesiology appear radically different in their clinical practice, yet they share a focus of inquiry: unconscious processes. Despite this common domain, there has been no exploration of the relationship between "the unconscious" as conceived by psychoanalysts and "surgical unconsciousness" as conceived by anesthesiologists. This is likely due to the fact that general anesthesia has been assumed to be a state in which the brain is simply "turned off." More recent neuroscientific data invalidate this assumption by demonstrating that the anesthetized brain is both cognitively dynamic and capable of implicit learning. Current perspectives on anesthetic mechanisms suggest that general anesthesia is characterized not simply by the absence of cognitive activity, but by the disintegration of cognitive activity. The cognitive unbinding paradigm of general anesthesia is discussed and its application to Wilfred Bion's theory of thinking, as well as his concept of attacks on linking, is elucidated. Based on the common structure and function of unconscious processes in psychoanalysis and anesthesiology, the foundation of a general theory is established.
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Affiliation(s)
- George A Mashour
- University of Michigan Medical School, 1H247 University Hospital, Ann Arbor, MI 48109-0048, USA.
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454
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Akada S, Fagerlund MJ, Lindahl SG, Sakamoto A, Prabhakar NR, Eriksson LI. Pronounced depression by propofol on carotid body response to CO2 and K+-induced carotid body activation. Respir Physiol Neurobiol 2008; 160:284-8. [DOI: 10.1016/j.resp.2007.10.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2007] [Revised: 10/14/2007] [Accepted: 10/20/2007] [Indexed: 10/22/2022]
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455
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Sonkajärvi E, Puumala P, Erola T, Baer GA, Karvonen E, Suominen K, Jäntti V. Burst suppression during propofol anaesthesia recorded from scalp and subthalamic electrodes: report of three cases. Acta Anaesthesiol Scand 2008; 52:274-9. [PMID: 17995997 DOI: 10.1111/j.1399-6576.2007.01501.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND Measurement of slow EEG activity and burst suppression are the main tasks in monitoring the effects of anaesthestics with EEG, which is often done with commercial univariate indexes such as BIS. The aim of this study was to describe the characteristics of burst suppression EEG during propofol anaesthesia using scalp electrodes and depth electrodes in the subthalamic nucleus. Specifically, we describe the electrical fields of the three EEG patterns we have previously described: the sharp wave, the burst and the spindle. METHODS We recorded the EEG of three Parkinson patients during propofol anaesthesia from the scalp electrodes and the depth electrode implanted in the subthalamic nucleus for treating parkinsonism. RESULTS (1) The slow waves of bursts recorded from all surface electrodes on scalp or neck with depth electrode reference are positive and have the highest amplitude in frontal electrodes, suggesting synchronous generation in the whole cerebral cortex. (2) The sharp wave and spindles have the highest amplitude at vertex. They are opposite in polarity in vertex and depth electrodes when referred to the neck electrode, suggesting generation in the sensorimotor cortex. CONCLUSIONS Recording simultaneously EEG from the depth and scalp electrodes shows that bursts and their slow wave oscillations are synchronous in the whole cortex while spindles and sharp waves are produced by the sensorimotor cortex. The amplitude of slow waves recorded with surface electrodes is equal to the difference of the wave at two electrodes and therefore only a small part of that generated by the cortex.
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Affiliation(s)
- E Sonkajärvi
- Department of Anaesthesiology, Oulu University Hospital, Oulu, Finland
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456
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Bonin RP, Orser BA. GABA(A) receptor subtypes underlying general anesthesia. Pharmacol Biochem Behav 2008; 90:105-12. [PMID: 18201756 DOI: 10.1016/j.pbb.2007.12.011] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Revised: 11/20/2007] [Accepted: 12/03/2007] [Indexed: 02/05/2023]
Abstract
General anesthetics produce a constellation of behavioral responses and widespread neurodepression. Recent studies have implicated the gamma-aminobutyric acid (GABA) subtype A receptor as a primary anesthetic target. During the past decade, considerable progress has been made in dissecting the behavioral effects of anesthetics according to the subunit composition of GABA(A) receptors. In this review, we describe how particular GABA(A) receptor subtypes expressed in different brain regions are critical for the expression of behavioral endpoints, such as amnesia, sedation, and hypnosis.
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Affiliation(s)
- Robert P Bonin
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
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457
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Jäntti V, Sloan TB. EEG and anesthetic effects. INTRAOPERATIVE MONITORING OF NEURAL FUNCTION 2008. [DOI: 10.1016/s1567-4231(07)08004-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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458
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459
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MacCallum JL, Tieleman DP. Chapter 8 Interactions between Small Molecules and Lipid Bilayers. CURRENT TOPICS IN MEMBRANES 2008. [DOI: 10.1016/s1063-5823(08)00008-2] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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460
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McDougall SJ, Bailey TW, Mendelowitz D, Andresen MC. Propofol enhances both tonic and phasic inhibitory currents in second-order neurons of the solitary tract nucleus (NTS). Neuropharmacology 2007; 54:552-63. [PMID: 18082229 DOI: 10.1016/j.neuropharm.2007.11.001] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2007] [Revised: 10/26/2007] [Accepted: 11/04/2007] [Indexed: 02/07/2023]
Abstract
The anesthetic propofol is thought to induce rapid hypnotic sedation by facilitating a GABAergic tonic current in forebrain neurons. The depression of cardiovascular and respiratory regulation often observed during propofol suggests potential additional actions within the brainstem. Here we determined the impacts of propofol on both GABAergic and glutamatergic synaptic mechanisms in a class of solitary tract nucleus (NTS) neurons common to brainstem reflex pathways. In horizontal brainstem slices, we recorded from NTS neurons directly activated by solitary tract (ST) axons. We identified these second-order NTS neurons by time-invariant ("jitter"<200 micros), "all-or-none" glutamatergic excitatory postsynaptic currents (EPSCs) in response to shocks to the ST. In order to assess propofol actions, we measured ST-evoked, spontaneous and miniature EPSCs and inhibitory postsynaptic currents (IPSCs) during propofol exposure. Propofol prolonged miniature IPSC decay time constants by 50% above control at 1.8 microM. Low concentrations of gabazine (SR-95531) blocked phasic GABA currents. At higher concentrations, propofol (30 microM) induced a gabazine-insensitive tonic current that was blocked by picrotoxin or bicuculline. In contrast, total propofol concentrations up to 30 microM had no effect on EPSCs. Thus, propofol enhanced phasic GABA events in NTS at lower concentrations than tonic current induction, opposite to the relative sensitivity observed in forebrain regions. These data suggest that therapeutic levels of propofol facilitate phasic (synaptic) inhibitory transmission in second-order NTS neurons which likely inhibits autonomic reflex pathways during anesthesia.
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Affiliation(s)
- Stuart J McDougall
- Department of Physiology and Pharmacology L334, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland OR 97239-3098, USA.
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461
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Zeller A, Crestani F, Camenisch I, Iwasato T, Itohara S, Fritschy JM, Rudolph U. Cortical glutamatergic neurons mediate the motor sedative action of diazepam. Mol Pharmacol 2007; 73:282-91. [PMID: 17965197 DOI: 10.1124/mol.107.038828] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The neuronal circuits mediating the sedative action of diazepam are unknown. Although the motor-depressant action of diazepam is suppressed in alpha1(H101R) homozygous knockin mice expressing diazepam-insensitive alpha1-GABA(A) receptors, global alpha1-knockout mice show greater motor sedation with diazepam. To clarify this paradox, attributed to compensatory up-regulation of the alpha2 and alpha3 subunits, and to further identify the neuronal circuits supporting diazepam-induced sedation, we generated Emx1-cre-recombinase-mediated conditional mutant mice, selectively lacking the alpha1 subunit (forebrain-specific alpha1(-/-)) or expressing either a single wild-type (H) or a single point-mutated (R) alpha1 allele (forebrain-specific alpha1(-/H) and alpha1(-/R) mice, respectively) in forebrain glutamatergic neurons. In the rest of the brain, alpha1(-/R) mutants are heterozygous alpha1(H101R) mice. Forebrain-specific alpha1(-/-) mice showed enhanced diazepam-induced motor depression and increased expression of the alpha2 and alpha3 subunits in the neocortex and hippocampus, in comparison with their pseudo-wild-type littermates. Forebrain-specific alpha1(-/R) mice were less sensitive than alpha1(-/H) mice to the motor-depressing action of diazepam, but each of these conditional mutants had a similar behavioral response as their corresponding control littermates. Unexpectedly, expression of the alpha1 subunit was reduced in forebrain, notably in alpha1(-/R) mice, and the alpha3 subunit was up-regulated in neocortex, indicating that proper alpha1 subunit expression requires both alleles. In conclusion, conditional manipulation of GABA(A) receptor alpha1 subunit expression can induce compensatory changes in the affected areas. Specifically, alterations in GABA(A) receptor expression restricted to forebrain glutamatergic neurons reproduce the behavioral effects seen after a global alteration, thereby implicating these neurons in the motor-sedative effect of diazepam.
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Affiliation(s)
- A Zeller
- Laboratory of Genetic Neuropharmacology, McLean Hospital, Department of Psychiatry, Harvard Medical School, 115 Mill St., Belmont, MA 02478, USA
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462
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Gervais R, Buonviso N, Martin C, Ravel N. What do electrophysiological studies tell us about processing at the olfactory bulb level? ACTA ACUST UNITED AC 2007; 101:40-5. [PMID: 18054211 DOI: 10.1016/j.jphysparis.2007.10.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Electrophysiological recordings performed in the mammalian olfactory bulb (OB) aimed at deciphering neural rules supporting neural representation of odors. In spite of a fairly large number of available data, no clear picture emerges yet in the mammalian OB. This paper summarizes some important findings and underlines the fact that difference in experimental conditions still represents a major limitation to the emergence of a synthetic view. More specifically, we examine to what extent the absence or the presence of anaesthetic influence OB neuronal responsiveness. In addition, we will see that recordings of either single cell activity or populational activity provide quite different pictures. As a result some experimental approaches provide data underlying sensory properties of OB neurons while others emphasize their capabilities of integrating incoming sensory information with attention, motivation and previous experience.
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Affiliation(s)
- Rémi Gervais
- Laboratoire Neurosciences Sensorielles, Comportement Cognition, UMR 5020 CNRS Université Claude Bernard Lyon 1, Université de Lyon, IFR 19, 50 Avenue T Garnier, 69366, Lyon Cedex 07, France.
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463
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Voss L, Sleigh J. Monitoring consciousness: the current status of EEG-based depth of anaesthesia monitors. Best Pract Res Clin Anaesthesiol 2007; 21:313-25. [PMID: 17900011 DOI: 10.1016/j.bpa.2007.04.003] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Direct and indirect inhibitory effects of anaesthetic agents on cortical activity are reflected in the electroencephalogram (EEG) as: (i) a shift from low-amplitude, high-frequency EEG, to high-amplitude, low-frequency activity (indicative of cortical depowering) and; (ii) the appearance of spindles and K-complexes (indicative of thalamocortical hyperpolarisation and sensory blockade). Existing EEG monitors use cortical activity as a proxy measure for consciousness. However the state of the cortex at any given moment does not accurately predict the state that it will enter in response to a noxious stimulus, and EEG monitors do not differentiate well between different levels of rousability. Also the literature reveals many instances where the EEG pattern is dissociated from conscious state (e.g. an awake-looking EEG, but an unresponsive patient; or a slow-wave EEG in an awake patient). Fortunately, a slow-wave EEG (even in the presence of a responsive patient) usually indicates profound amnesia for explicit memory.
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Affiliation(s)
- Logan Voss
- Department of Anaesthesia, Waikato Clinical School, University of Auckland, Hamilton, New Zealand.
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464
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Culley DJ, Raghavan SV, Waly M, Baxter MG, Yukhananov R, Deth RC, Crosby G. Nitrous oxide decreases cortical methionine synthase transiently but produces lasting memory impairment in aged rats. Anesth Analg 2007; 105:83-8. [PMID: 17578961 DOI: 10.1213/01.ane.0000266491.53318.20] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND Nitrous oxide is a commonly used anesthetic that inhibits the activity of methionine synthase, an enzyme involved in methylation reactions and DNA synthesis and repair. This inhibition triggers vacuole formation and degeneration of neurons in areas of the developing and mature brain that are important for spatial memory, raising the possibility that nitrous oxide might have sustained effects on learning. METHODS To test this possibility, we randomized 18-month-old Fischer 344 rats (n = 13 per group) to 4 h of 70% nitrous oxide + 30% oxygen or 70% nitrogen + 30% oxygen (control) and assessed memory using a 12-arm radial maze for 14 days beginning 2 days after nitrous oxide inhalation. In separate, identically treated groups of rats, we measured methionine synthase activity in the cortex and liver at the end of nitrous oxide exposure and 2 days later (n = 3 rats per group per time point) using a standard assay. RESULTS Liver and cortical methionine synthase was inhibited during nitrous oxide inhalation (6% and 23% of control in liver and cortex, respectively; P < 0.01). Liver enzyme activity remained depressed 2 days later, whereas cortical enzyme activity recovered. There was no difference in error rate between control and nitrous oxide treated rats. However, those exposed to nitrous oxide took more time to complete the maze and made fewer correct choices before first error (P < 0.05). CONCLUSIONS Sedation with 70% nitrous oxide profoundly, but transiently, reduces the activity of cortical methionine synthase but produces lasting impairment in spatial working memory in aged rats.
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Affiliation(s)
- Deborah J Culley
- Department of Anesthesiology Harvard Medical School, Brigham and Women's Hospital, Boston, MA 02115, USA
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465
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Andres-Enguix I, Caley A, Yustos R, Schumacher MA, Spanu PD, Dickinson R, Maze M, Franks NP. Determinants of the Anesthetic Sensitivity of Two-pore Domain Acid-sensitive Potassium Channels. J Biol Chem 2007; 282:20977-90. [PMID: 17548360 DOI: 10.1074/jbc.m610692200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Certain two-pore domain K(+) channels are plausible targets for volatile general anesthetics, yet little is known at the molecular level about how these simple agents cause channel activation. The first anesthetic-activated K(+) current I(K(An)) that was characterized was discovered in the mollusk Lymnaea stagnalis and is remarkable for both its sensitivity to general anesthetics and its stereoselective responses to anesthetic enantiomers (Franks, N. P., and Lieb, W. R. (1988) Nature 333, 662-664 and Franks, N. P., and Lieb, W. R. (1991) Science 254, 427-430). Here we report the molecular cloning of a two-pore domain K(+) channel LyTASK from L. stagnalis and show that, when expressed in HEK-293 cells, it displays the same biophysical characteristics as the anesthetic-activated K(+) current I(K(An)). Sequence analysis and functional properties show it to be a member of the TASK family of channels with approximately 47% identity at the amino acid level when compared with human TASK-1 and TASK-3. By using chimeric channel constructs and site-directed mutagenesis we have identified the specific amino acid 159 to be a critical determinant of anesthetic sensitivity, which, when mutated to alanine, essentially eliminates anesthetic activation in the human channels and greatly reduces activation in LyTASK. The L159A mutation in LyTASK disrupts the stereoselective response to isoflurane while having no effect on the pH sensitivity of the channel, suggesting this critical amino acid may form part of an anesthetic binding site.
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Affiliation(s)
- Isabelle Andres-Enguix
- Biophysics Section, Blackett Laboratory, and Division of Biology, Imperial College, South Kensington, London SW7 2AZ
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466
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Grasshoff C, Jurd R, Rudolph U, Antkowiak B. Modulation of presynaptic beta3-containing GABAA receptors limits the immobilizing actions of GABAergic anesthetics. Mol Pharmacol 2007; 72:780-7. [PMID: 17584992 DOI: 10.1124/mol.107.037648] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Intravenous GABAergic anesthetics are potent hypnotics but are rather ineffective in depressing movements. Immobility is mediated, in part, by the ventral horn of the spinal cord. We hypothesized that the efficacy of these anesthetics in producing immobility is compromised by the activation of GABA(A) receptors located presynaptically, which modulate GABA release onto neurons in the ventral horn. Because anesthetics acting by modulation of GABA(A) receptor function require GABA to be present at its binding site, a decrease in GABA release would abate their efficacy in reducing neuronal excitability. Here we report that in organotypic spinal cord slices, the efficacy of the intravenous anesthetic etomidate to depress network activity of ventral horn neurons is limited to approximately 60% at concentrations greater than 1 microM that produce immobility. Depression of spinal network activity was almost abolished in spinal slices from beta3(N265M) knock-in mice. In the wild type, etomidate prolonged decay times of GABA(A) receptor-mediated inhibitory postsynaptic currents (IPSCs) and concomitantly reduced the frequency of action potential-dependent IPSCs. Etomidate prolonged the decay time of GABA(A) receptors at all tested concentrations. At concentrations greater than 1.0 microM, anesthetic-induced decrease of GABA release via modulation of presynaptic GABA(A) receptors and enhancement of postsynaptic GABA(A) receptor-function compensated for each other. The results suggest that the limited immobilizing efficacy of these agents is probably due to a presynaptic mechanism and that GABAergic agents with a specificity for post-versus presynaptic receptors would probably have much stronger immobilizing actions, pointing out novel avenues for drug development.
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MESH Headings
- Amino Acid Substitution
- Anesthetics, Intravenous/administration & dosage
- Anesthetics, Intravenous/pharmacology
- Animals
- Anterior Horn Cells/drug effects
- Dose-Response Relationship, Drug
- Electrophysiology
- Embryo, Mammalian
- Etomidate/administration & dosage
- Etomidate/pharmacology
- Female
- Homozygote
- Immobility Response, Tonic/drug effects
- Interneurons/drug effects
- Methionine/genetics
- Mice
- Mice, Mutant Strains
- Organ Culture Techniques
- Patch-Clamp Techniques
- Perfusion
- Pregnancy
- Receptors, GABA-A/drug effects
- Receptors, GABA-A/genetics
- Receptors, GABA-A/physiology
- Receptors, Presynaptic/drug effects
- Spinal Cord/drug effects
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Affiliation(s)
- Christian Grasshoff
- Experimental Anesthesiology Section, Department of Anesthesiology and Intensive Care, Eberhard-Karls-University, Tuebingen, Germany.
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467
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Abstract
Fast synaptic inhibition in the brain and spinal cord is mediated largely by ionotropic gamma-aminobutyric acid (GABA) receptors. GABAA receptors play a key role in controlling neuronal activity; thus modulating their function will have important consequences for neuronal excitation. GABAA receptors are important therapeutic targets for a range of sedative, anxiolytic, and hypnotic agents and are involved in a number of CNS diseases, including sleep disturbances, anxiety, premenstrual syndrome, alcoholism, muscle spasms, Alzheimer's disease, chronic pain, schizophrenia, bipolar affective disorders, and epilepsy. This review focuses on the functional and pharmacological properties of GABAA receptors and trafficking as an essential mechanism underlying the dynamic regulation of synaptic strength.
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Affiliation(s)
- Guido Michels
- Department of Neuroscience, University of Pennsylvania, School of Medicine, Philadelphia, PA 19104-6074, USA.
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468
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Ishizawa Y. Mechanisms of anesthetic actions and the brain. J Anesth 2007; 21:187-99. [PMID: 17458649 DOI: 10.1007/s00540-006-0482-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2006] [Accepted: 11/09/2006] [Indexed: 11/25/2022]
Abstract
The neural mechanisms behind anesthetic-induced behavioral changes such as loss of consciousness, amnesia, and analgesia, are insufficiently understood, though general anesthesia has been of tremendous importance for the development of medicine. In this review, I summarize what is currently known about general anesthetic actions at different organizational levels and discuss current and future research, using systems neuroscience approaches such as functional neuroimaging and quantitative electrophysiology to understand anesthesia actions at the integrated brain level.
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Affiliation(s)
- Yumiko Ishizawa
- Department of Anesthesia and Critical Care, Massachusetts General Hospital, 55 Fruit Street, Clinics 3, Boston, MA 02114, USA
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469
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Grasshoff C, Thiermann H, Antkowiak B. Anaesthesia in patients suffering from organophosphorus intoxication—interactions between general anaesthetics and acetylcholine in cortical networks in vitro. Toxicology 2007; 233:214-22. [PMID: 17030394 DOI: 10.1016/j.tox.2006.09.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Revised: 08/31/2006] [Accepted: 09/01/2006] [Indexed: 10/24/2022]
Abstract
In scenarios of mass destruction it is likely that victims are intoxicated by organophosphates and, at the same time, physically injured. Organophosphate compounds produce excessive cholinergic overstimulation in the CNS via blocking acetylcholinesterase activity. The specifics of acute care and anaesthesia in physically traumatized and intoxicated patients are largely unknown. Recent studies in animals and human subjects demonstrated that acetylcholinesterase inhibitors reverse anaesthesia. Two distinct mechanisms are potentially involved. First, acetylcholine produces an excitatory drive onto neurons, thereby counterbalancing the inhibitory actions of anaesthetics. Anaesthesia is reversed because it critically depends on a distinctive depression of several central nervous functions. Second, cholinergic stimulation may affect the mechanisms by which anaesthetics mediate their depressant actions on central neurons. In this case acetylcholine reverses anaesthesia by decreasing the potency of anaesthetic agents. In order to identify potential mechanisms involved in cholinergic reversal of anaesthesia we have investigated interactions between acetylcholine and the volatile anaesthetic sevoflurane in isolated cortical brain slices. Our results provide evidence that cholinergic stimulation counterbalances the effects of general anaesthetics by increasing neuronal excitability, and, in addition, by decreasing anaesthetic potency. These findings imply that in patients suffering from organophosphorus intoxication dose requirements for general anaesthetics are considerably increased.
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Affiliation(s)
- Christian Grasshoff
- Department of Anesthesiology, Experimental Anesthesiology Section, University of Tuebingen, Schaffhausenstr. 113, D-72072 Tuebingen, Germany
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470
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Plourde G. General anaesthetic action: ubiquity, complexity and relevance for neuroscience. J Physiol 2007; 580:5. [PMID: 17331987 PMCID: PMC2075430 DOI: 10.1113/jphysiol.2007.129411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- G Plourde
- Department of Anaesthesia, McGill University and Montreal Neurological Hospital, 3801 University, Montreal, QC, Canada H3A 2B4.
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471
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Möhler H. Molecular regulation of cognitive functions and developmental plasticity: impact of GABAA receptors. J Neurochem 2007; 102:1-12. [PMID: 17394533 DOI: 10.1111/j.1471-4159.2007.04454.x] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
By controlling spike timing and sculpting neuronal rhythms, inhibitory interneurons play a key role in regulating neuronal circuits and behavior. The pronounced diversity of GABAergic (gamma-aminobutyric acid) interneurons is paralleled by an extensive diversity of GABAA receptor subtypes. The region- and domain-specific location of these receptor subtypes offers the opportunity to gain functional insights into the role of defined neuronal circuits. These developments are reviewed with regard to the regulation of sleep, anxiety, memory, sensorimotor processing and post-natal developmental plasticity.
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Affiliation(s)
- Hanns Möhler
- Institute of Pharmacology, University of Zurich, Zurich, Switzerland.
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472
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Bright DP, Adham SD, Lemaire LCJM, Benavides R, Gruss M, Taylor GW, Smith EH, Franks NP. Identification of anesthetic binding sites on human serum albumin using a novel etomidate photolabel. J Biol Chem 2007; 282:12038-47. [PMID: 17311911 DOI: 10.1074/jbc.m700479200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
We have synthesized a novel analog of the general anesthetic etomidate in which the ethoxy group has been replaced by an azide group, and which can be used as a photolabel to identify etomidate binding sites. This acyl azide analog is a potent general anesthetic in both rats and tadpoles and, as with etomidate, is stereoselective in its actions, with the R(+) enantiomer being significantly more potent than the S(-) enantiomer. Its effects on alpha1beta2gamma2s GABA(A) receptors expressed in HEK-293 cells are virtually indistinguishable from the parent compound etomidate, showing stereoselective potentiation of GABA-induced currents, as well as direct mimetic effects at higher concentrations. In addition, a point mutation (beta2 N265M), which is known to attenuate the potentiating actions of etomidate, also blocks the effects of the acyl azide analog. We have investigated the utility of the analog to identify etomidate binding sites by using it to photolabel human serum albumin, a protein that binds approximately 75% of etomidate in human plasma and which is thought to play a major role in its pharmacokinetics. Using HPLC/mass spectrometry we have identified two anesthetic binding sites on HSA. One site is the well-characterized drug binding site I, located in HSA subdomain IIA, and the second site is also an established drug binding site located in subdomain IIIB, which also binds propofol. The acyl azide etomidate may prove to be a useful new photolabel to identify anesthetic binding sites on the GABA(A) receptor or other putative targets.
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Affiliation(s)
- Damian P Bright
- Biophysics Section, Blackett Laboratory, Imperial College, South Kensington, London SW7 2AZ, United Kingdom
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473
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Rosen A, Bali M, Horenstein J, Akabas MH. Channel opening by anesthetics and GABA induces similar changes in the GABAA receptor M2 segment. Biophys J 2007; 92:3130-9. [PMID: 17293408 PMCID: PMC1852347 DOI: 10.1529/biophysj.106.094490] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
For many general anesthetics, their molecular basis of action involves interactions with GABA(A) receptors. Anesthetics produce concentration-dependent effects on GABA(A) receptors. Low concentrations potentiate submaximal GABA-induced currents. Higher concentrations directly activate the receptors. Functional effects of anesthetics have been characterized, but little is known about the conformational changes they induce. We probed anesthetic-induced conformational changes in the M2 membrane-spanning, channel-lining segment using disulfide trapping between engineered cysteines. Previously, we showed that oxidation by copper phenanthroline in the presence of GABA of the M2 6' cysteine mutants, alpha(1)T261Cbeta(1)T256C and alpha(1)beta(1)T256C resulted in formation of an intersubunit disulfide bond between the adjacent beta-subunits that significantly increased the channels' spontaneous open probability. Oxidation in GABA's absence had no effect. We examined the effect on alpha(1)T261Cbeta(1)T256C and on alpha(1)beta(1)T256C of oxidation by copper phenanthroline in the presence of potentiating and directly activating concentrations of the general anesthetics propofol, pentobarbital, and isoflurane. Oxidation in the presence of potentiating concentration of anesthetics had little effect. Oxidation in the presence of directly activating anesthetic concentrations significantly increased the channels' spontaneous open probability. We infer that activation by anesthetics and GABA induces a similar conformational change at the M2 segment 6' position that is related to channel opening.
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Affiliation(s)
- Ayelet Rosen
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, Yeshiva University, Bronx, New York 10461, USA
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474
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Ikeda Y, Ishiguro K, Fujita SC. Ether stress-induced Alzheimer-like tau phosphorylation in the normal mouse brain. FEBS Lett 2007; 581:891-7. [PMID: 17289030 DOI: 10.1016/j.febslet.2007.01.064] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2006] [Revised: 01/08/2007] [Accepted: 01/23/2007] [Indexed: 10/23/2022]
Abstract
Tau is reversibly hyperphosphorylated in the mouse brain by starvation or cold water swimming. Here, we report tau phosphorylation in the hippocampus of normal mouse after ether anesthesia, known to trigger typical stress reactions. Robust phosphorylation of tau was observed immediately and 10min after ether vapor exposure at Ser202/Thr205 and Thr231/Ser235, sites typically phosphorylated in Alzheimer brains. The phosphorylation levels returned to baseline by 1h. The most conspicuous and consistent change in the protein kinases studied was the inactivating phosphorylation of Ser9 of TPKI/GSK3beta in close correspondence with tau phosphorylation. These findings show that tau phosphorylation is a rapid physiological process integral to stress response system, and suggest involvement therein of TPKI/GSK3beta.
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Affiliation(s)
- Yoshiko Ikeda
- Mitsubishi Kagaku Institute of Life Sciences, 11 Minamiooya, Machida, Tokyo 194-8511, Japan
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475
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Swearengin TA, Fibuch EE, Seidler NW. Sevoflurane modulates the activity of glyceraldehyde 3-phosphate dehydrogenase. J Enzyme Inhib Med Chem 2007; 21:575-9. [PMID: 17194030 DOI: 10.1080/14756360600741925] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
The mechanism of inhalation anesthesia remains to be fully elucidated. While certain neuronal membrane proteins are considered sites of action, cytosolic proteins may also be targets. We hypothesize that inhaled anesthetics may act via glyceraldehyde 3-phosphate dehydrogenase (GAPDH), which has recently been shown to participate in neuronal inhibition. We examined the effects of sevoflurane, a halogenated ether anesthetic, on the catalytic and fluorescence properties of GAPDH. Initial rates of oxidoreductase activity decreased approximately 30% at saturating levels of sevoflurane. NADH-stimulated oxidoreductase activity (25 microM NADH; 0.8mM NAD+) increased with sevoflurane. Sevoflurane quenched tryptophan fluorescence emission and increased polarization. Additionally, sevoflurane increased the susceptibility of GAPDH to thermal denaturation suggesting an effect on conformation. Our findings warrant further research on sevoflurane's effect on GAPDH and indicate that this approach may lead to delineation of a novel contribution to the mechanism of anesthesia.
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Affiliation(s)
- Timothy A Swearengin
- Department of Anesthesiology, University of Missouri, Kansas City School of Medicine, 4401 Wornall Road, Kansas City, MO, USA
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476
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Musizza B, Stefanovska A, McClintock PVE, Palus M, Petrovcic J, Ribaric S, Bajrovic FF. Interactions between cardiac, respiratory and EEG-delta oscillations in rats during anaesthesia. J Physiol 2007; 580:315-26. [PMID: 17234691 PMCID: PMC2075429 DOI: 10.1113/jphysiol.2006.126748] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
We hypothesized that, associated with the state of anaesthesia, characteristic changes exist in both cardio-respiratory and cerebral oscillator parameters and couplings, perhaps varying with depth of anaesthesia. Electrocardiograms (ECGs), respiration and electroencephalograms (EEGs) were recorded from two groups of 10 rats during the entire course of anaesthesia following the administration of a single bolus of ketamine-xylazine (KX group) or pentobarbital (PB group). The phase dynamics approach was then used to extract the instantaneous frequencies of heart beat, respiration and slow delta-waves (within 0.5-3.5 Hz). The amplitudes of delta- and theta-waves were analysed by use of a time-frequency representation of the EEG signal within 0.5-7.5 Hz obtained by wavelet transformation, using the Morlet mother wavelet. For the KX group, where slow delta-waves constituted the dominant spectral component, the Hilbert transform was applied to obtain the instantaneous delta-frequency. The theta-activity was spread over too wide a spectral range for its phase to be meaningfully defined. For both agents, we observed two distinct phases of anaesthesia, with a marked increase in theta-wave activity occurring on passage from a deeper phase of anaesthesia to a shallower one. In other respects, the effects of the two anaesthetics were very different. For KX anaesthesia, the two phases were separated by a marked change in all three instantaneous frequencies: stable, deep, anaesthesia with small frequency variability was followed by a sharp transition to shallow anaesthesia with large frequency variability, lasting until the animal awoke. The transition occurred 16-76 min after injection of the anaesthetic, with simultaneous reduction in the delta-wave amplitude. For PB anaesthesia, the two epochs were separated by the return of a positive response to the pinch test at 53-94 min, following which it took a further period of 45-70 min for the animal to awaken. delta-Waves were not apparent at any stage of PB anaesthesia. We applied non-linear dynamics and information theory to seek evidence of causal relationships between the cardiac, respiratory and slow delta-oscillations. We demonstrate that, for both groups, respiration drives the cardiac oscillator during deep anaesthesia. During shallow KX anaesthesia the direction either reverses, or the cardio-respiratory interaction becomes insignificant; in the deep phase, there is a unidirectional deterministic interaction of respiration with slow delta-oscillations. For PB anaesthesia, the cardio-respiratory interaction weakens during the second phase but, otherwise, there is no observable change in the interactions. We conclude that non-linear dynamics and information theory can be used to identify different stages of anaesthesia and the effects of different anaesthetics.
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Affiliation(s)
- Bojan Musizza
- Department of Systems and Control, Jozef Stefan Institute, Jamova 39, Ljubljana, Slovenia
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477
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Grasshoff C, Drexler B, Antkowiak B. Effects of cholinergic overstimulation on isoflurane potency and efficacy in cortical and spinal networks. Toxicology 2007; 229:206-13. [PMID: 17141935 DOI: 10.1016/j.tox.2006.10.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2006] [Revised: 10/23/2006] [Accepted: 10/24/2006] [Indexed: 11/19/2022]
Abstract
In scenarios of terrorist attacks with organophosphorus compounds it appears likely that medical aid is required by victims not only suffering from the intoxication but also from physical trauma. These subjects may have to undergo surgical interventions, raising the need for anaesthesia. This prompts the question of how anaesthetic agents work in intoxicated patients. Organophosphates block acetylcholinesterase activity, thereby inducing excessive cholinergic overstimulation in the central nervous system. As the neocortex and spinal cord are important substrates for general anaesthetics, we investigated to what extent cholinergic overstimulation affects the potency and efficacy of the commonly used volatile anaesthetic isoflurane in depressing action potential activity of cortical and spinal neurons. We first quantified the effects of isoflurane in the absence of acetylcholine by performing extracellular voltage recordings in cultured tissue slices. Isoflurane induced a concentration-dependent decrease of neuronal activity in neocortical (EC(50)=0.43+/-0.08 MAC) and spinal slices (EC(50)=0.41+/-0.03 MAC). At concentrations above 1.5 MAC, the anaesthetic almost completely depressed action potential firing in both preparations. Next, we studied the effects of acetylcholine (10microM) in the absence of isoflurane. Acetylcholine approximately doubled spontaneous activity in neocortical and spinal slices. When applying isoflurane together with acetylcholine, different interactions between these agents were observed in neocortical and spinal networks. Acetylcholine significantly reduced both the potency and efficacy of the anaesthetic in neocortical (efficacy 83%; EC(50)=1.16+/-0.02 MAC) but not in spinal (efficacy 100%; EC(50)=0.41+/-0.04 MAC) slices. Our results indicate that cholinergic overstimulation increases the requirement for anaesthetic agents in patients suffering from organophosphorus poisoning via enhancing neuronal background activity of neocortical and spinal neurons and in addition via decreasing drug potency and efficacy in the cortex. Raising anaesthetic concentrations into a high-dose range may not be an appropriate alternative to compensate the increased excitability, since high concentrations of anaesthetics may worsen cardiac abnormalities and hemodynamic instability frequently observed in these patients.
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Affiliation(s)
- Christian Grasshoff
- Department of Anesthesiology, Experimental Anesthesiology Section, Eberhard-Karls-University, Schaffhausenstrasse 113, D-72072 Tuebingen, Germany.
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478
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479
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Abstract
The hypnotic, antinociceptive, and anticonvulsant properties of melatonin endow this neurohormone with the profile of a novel hypnotic-anesthetic agent. Sublingually or orally administered melatonin is an effective premedicant in adults and children. Melatonin premedication like midazolam is associated with sedation and preoperative anxiolysis, however, unlike midazolam these effects are not associated with impaired psychomotor skills or the quality of recovery. Melatonin administration also is associated with a tendency toward faster recovery and a lower incidence of postoperative excitement than midazolam. Oral premedication with 0.2 mg/kg melatonin significantly reduces the propofol and thiopental doses required for loss of responses to verbal commands and eyelash stimulation. In rats, melatonin and the more potent melatonin analogs 2-bromomelatonin and phenylmelatonin have been found to have anesthetic properties similar to those of thiopental and propofol, with the added advantage of providing potent antinociceptive effects. The exact mechanism(s) by which structurally diverse intravenous and volatile anesthetics produce general anesthesia is still largely unknown, but positive modulation of gamma-aminobutyric acid type A (GABAA) receptor function has been recognized as an important and common pathway underlying the depressant effects of many of these agents. Accumulating evidence indicates that there is interplay between the melatonergic and GABAergic systems, and it has been demonstrated that melatonin administration produces significant, dose-dependent increases in GABA concentrations in the central nervous system. Additional in vitro data suggest that melatonin alters GABAergic transmission by modulating GABAA receptor function. Of greater importance, data from in vivo studies suggest that the central anesthetic effects of melatonin are mediated, at least in part, via GABAergic system activation, as they can be blocked or reversed by GABAA receptor antagonists. Further work is needed to better understand the general anesthetic properties of melatonin at the molecular, cellular, and systems levels.
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Affiliation(s)
- Mohamed Naguib
- Department of Anesthesiology and Pain Medicine, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
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480
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Sun Y, Chen J, Pruckmayr G, Baumgardner JE, Eckmann DM, Eckenhoff RG, Kelz MB. High throughput modular chambers for rapid evaluation of anesthetic sensitivity. BMC Anesthesiol 2006; 6:13. [PMID: 17096844 PMCID: PMC1657002 DOI: 10.1186/1471-2253-6-13] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2006] [Accepted: 11/10/2006] [Indexed: 11/10/2022] Open
Abstract
Background Anesthetic sensitivity is determined by the interaction of multiple genes. Hence, a dissection of genetic contributors would be aided by precise and high throughput behavioral screens. Traditionally, anesthetic phenotyping has addressed only induction of anesthesia, evaluated with dose-response curves, while ignoring potentially important data on emergence from anesthesia. Methods We designed and built a controlled environment apparatus to permit rapid phenotyping of twenty-four mice simultaneously. We used the loss of righting reflex to indicate anesthetic-induced unconsciousness. After fitting the data to a sigmoidal dose-response curve with variable slope, we calculated the MACLORR (EC50), the Hill coefficient, and the 95% confidence intervals bracketing these values. Upon termination of the anesthetic, Emergence timeRR was determined and expressed as the mean ± standard error for each inhaled anesthetic. Results In agreement with several previously published reports we find that the MACLORR of halothane, isoflurane, and sevoflurane in 8–12 week old C57BL/6J mice is 0.79% (95% confidence interval = 0.78 – 0.79%), 0.91% (95% confidence interval = 0.90 – 0.93%), and 1.96% (95% confidence interval = 1.94 – 1.97%), respectively. Hill coefficients for halothane, isoflurane, and sevoflurane are 24.7 (95% confidence interval = 19.8 – 29.7%), 19.2 (95% confidence interval = 14.0 – 24.3%), and 33.1 (95% confidence interval = 27.3 – 38.8%), respectively. After roughly 2.5 MACLORR • hr exposures, mice take 16.00 ± 1.07, 6.19 ± 0.32, and 2.15 ± 0.12 minutes to emerge from halothane, isoflurane, and sevoflurane, respectively. Conclusion This system enabled assessment of inhaled anesthetic responsiveness with a higher precision than that previously reported. It is broadly adaptable for delivering an inhaled therapeutic (or toxin) to a population while monitoring its vital signs, motor reflexes, and providing precise control over environmental conditions. This system is also amenable to full automation. Data presented in this manuscript prove the utility of the controlled environment chambers and should allow for subsequent phenotyping of mice with targeted mutations that are expected to alter sensitivity to induction or emergence from anesthesia.
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Affiliation(s)
- Yi Sun
- Department of Anesthesiology and Critical Care, University of Pennsylvania School of Medicine, Philadelphia, USA
| | - Jingqiu Chen
- Department of Anesthesiology and Critical Care, University of Pennsylvania School of Medicine, Philadelphia, USA
| | - Gregory Pruckmayr
- Department of Anesthesiology and Critical Care, University of Pennsylvania School of Medicine, Philadelphia, USA
| | - James E Baumgardner
- Department of Anesthesiology and Critical Care, University of Pennsylvania School of Medicine, Philadelphia, USA
- Oscillogy LLC, Folsom, PA, USA
| | - David M Eckmann
- Department of Anesthesiology and Critical Care, University of Pennsylvania School of Medicine, Philadelphia, USA
- Institute for Medicine and Engineering, University of Pennsylvania School of Medicine, Philadelphia, USA
| | - Roderic G Eckenhoff
- Department of Anesthesiology and Critical Care, University of Pennsylvania School of Medicine, Philadelphia, USA
| | - Max B Kelz
- Department of Anesthesiology and Critical Care, University of Pennsylvania School of Medicine, Philadelphia, USA
- Mahoney Institute for Neurological Science, University of Pennsylvania School of Medicine, Philadelphia, USA
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481
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Abstract
The nature and mechanism of human consciousness is emerging as one of the most important scientific and philosophical questions of the 21st century. Disregarded as a subject of serious inquiry throughout most of the 20th century, it has now regained legitimacy as a scientific endeavor. The investigation of consciousness and the mechanisms of general anesthesia have begun to converge. In the present article I provide an introduction to the study of consciousness, describe the neural correlates of consciousness that may be targets of general anesthetics, and suggest an integrated approach to the science of consciousness and anesthesia.
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Affiliation(s)
- George A Mashour
- Department of Anesthesia, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
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482
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Abstract
General anesthetics abolish behavioral responsiveness in all animals, and in humans this is accompanied by loss of consciousness. Whether similar target mechanisms and behavioral endpoints exist across species remains controversial, although model organisms have been successfully used to study mechanisms of anesthesia. In Drosophila, a number of key mutants have been characterized as hypersensitive or resistant to general anesthetics by behavioral assays. In order to investigate general anesthesia in the Drosophila brain, local field potential (LFP) recordings were made during incremental exposures to isoflurane in wild-type and mutant flies. As in higher animals, general anesthesia in flies was found to involve a succession of distinct endpoints. At low doses, isoflurane uncoupled brain activity from ongoing movement, followed by a sudden attenuation in neural correlates of perception. Average LFP activity in the brain was more gradually attenuated with higher doses, followed by loss of movement behavior. Among mutants, a strong correspondence was found between behavioral and LFP sensitivities, thereby suggesting that LFP phenotypes are proximal to the anesthetic's mechanism of action. Finally, genetic and pharmacological analysis revealed that anesthetic sensitivities in the fly brain are, like other arousal states, influenced by dopaminergic activity. These results suggest that volatile anesthetics such as isoflurane may target the same processes that sustain wakefulness and attention in the brain. LFP correlates of general anesthesia in Drosophila provide a powerful new approach to uncovering the nature of these processes.
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483
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Möhler H. GABA(A) receptor diversity and pharmacology. Cell Tissue Res 2006; 326:505-16. [PMID: 16937111 DOI: 10.1007/s00441-006-0284-3] [Citation(s) in RCA: 262] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2006] [Accepted: 06/13/2006] [Indexed: 12/22/2022]
Abstract
Because of its control of spike-timing and oscillatory network activity, gamma-aminobutyric acid (GABA)-ergic inhibition is a key element in the central regulation of somatic and mental functions. The recognition of GABA(A) receptor diversity has provided molecular tags for the analysis of distinct neuronal networks in the control of specific pharmacological and physiological brain functions. Neurons expressing alpha(1)GABA(A) receptors have been found to mediate sedation, whereas those expressing alpha(2)GABA(A) receptors mediate anxiolysis. Furthermore, associative temporal and spatial memory can be regulated by modulating the activity of hippocampal pyramidal cells via extrasynaptic alpha(5)GABA(A) receptors. In addition, neurons expressing alpha(3)GABA(A) receptors are instrumental in the processing of sensory motor information related to a schizophrenia endophenotype. Finally, during the postnatal development of the brain, the maturation of GABAergic interneurons seems to provide the trigger for the experience-dependent plasticity of neurons in the visual cortex, with alpha(1)GABA(A) receptors setting the time of onset of a critical period of plasticity. Thus, particular neuronal networks defined by respective GABA(A) receptor subtypes can now be linked to the regulation of various clearly defined behavioural patterns. These achievements are of obvious relevance for the pharmacotherapy of certain brain disorders, in particular sleep dysfunctions, anxiety disorders, schizophrenia and diseases associated with memory deficits.
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Affiliation(s)
- H Möhler
- Institute of Pharmacology and Department of Chemistry and Applied Biosciences, University and ETH Zurich, Winterthurerstrasse 190, Zürich, CH-8057, Switzerland.
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484
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Gozzi A, Schwarz A, Reese T, Bertani S, Crestan V, Bifone A. Region-specific effects of nicotine on brain activity: a pharmacological MRI study in the drug-naïve rat. Neuropsychopharmacology 2006; 31:1690-703. [PMID: 16292320 DOI: 10.1038/sj.npp.1300955] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We have applied pharmacological magnetic resonance imaging (phMRI) methods to map the functional response to nicotine in drug-naïve rats. Nicotine (0.35 mg/kg intravenous (i.v.)) increased relative cerebral blood volume (rCBV) in cortical (including medial prefrontal, cingulate orbitofrontal, insular) and subcortical (including amygdala and dorsomedial hippocampus) structures. The pharmacological specificity of the effect was demonstrated by acute pretreatment with the nicotinic acetylcholine receptor (nAChR) ion-channel-blocking agent mecamylamine, which suppressed the rCBV response to nicotine. Control experiments with norepinephrine, a potent non-brain-penetrant vasopressor, at a dose that mimics the cardiovascular response induced by nicotine were performed to assess the potential confounding effects of peripheral blood pressure changes induced by nicotine. In an attempt to highlight the relative contribution of different nAChR subtypes to the observed activation pattern of nicotine, we also investigated the central phMRI response to an acute challenge with (R)-N-(1-azabicyclo[2.2.2]oct-3-yl)(5-(2-pyridyl)thiophene-2-carboxamide) (cpdA, at 5, 10, 20, and 30 mg/kg i.v.) and 5-iodo-A-85380 (5IA, 5 mg/kg i.v.). CpdA is a selective agonist at homomeric alpha7 nAChRs, while 5IA features high in vivo affinity for the alpha4beta2* and other less-abundant beta2-containing nicotinic receptors. CpdA did not produce significant rCBV changes at any of the doses tested, whereas 5IA induced a pattern of activation very similar to that induced by nicotine. The lack of phMRI response to cpdA together with the high spatial overlap between the activation profile of nicotine and 5IA, suggest that the acute functional response to nicotine in drug-naïve rats is mediated by beta2-containing nAChR isoforms, presumably belonging to the alpha4beta2* subtype.
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Affiliation(s)
- Alessandro Gozzi
- Department of Neuroimaging, Centre of Excellence for Drug Discovery, Psychiatry, GlaxoSmithKline Medicines Research Centre, Verona, Italy.
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485
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Johansson JS. Central nervous system electrical synapses as likely targets for intravenous general anesthetics. Anesth Analg 2006; 102:1689-91. [PMID: 16717310 DOI: 10.1213/01.ane.0000220014.93126.b4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Jonas S Johansson
- Department of Anesthesiology and Critical Care and the Johnson Research Foundation, University of Pennsylvania, Philadelphia, PA 19104, USA.
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486
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Abstract
Since 1997, bispectral index (BIS; Aspect Medical Systems Inc., Natick, MA) has been in clinical practice and a wealth of experimental research has accumulated on its use. Originally, the device was approved only for monitoring hypnosis and has now received an indication for reducing the incidence of intraoperative awareness during anesthesia. Numerous studies have documented the ability of BIS to reduce intermediate outcomes such as hypnotic drug administration, extubation time, postoperative nausea and shortened recovery room discharge. Two recent large-scale outcome studies using BIS (one randomized controlled trial and one prospective, nonrandomized historical cohort study) identified an approximately 80% reduction in the incidence of recall after anesthesia. BIS provides clinicians with unique information that can be used to tailor hypnotic drug doses to individual patient requirements. BIS does not predict movement or hemodynamic response to stimulation, nor will it predict the exact moment consciousness returns. This review will also discuss other BIS applications including use in pediatrics, intensive care and for procedural sedation. Some limitations exist to the use of BIS and it is not useful for some individual hypnotic agents (ketamine, dexmedetomidine, nitrous oxide, xenon, opioids). BIS technology is moving out of the operating room and into diverse environments where conscious and deep sedation are provided. Anesthesiologists need to be actively involved in promoting patient safety and helping transition this technology into broader use.
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Affiliation(s)
- Jay W Johansen
- Emory University School of Medicine, Department of Anesthesiology, Grady Health System, 49 Jesse Hill Jr. Drive, SE, Atlanta, Georgia 30303, USA.
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487
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Statler KD, Alexander H, Vagni V, Dixon CE, Clark RSB, Jenkins L, Kochanek PM. Comparison of seven anesthetic agents on outcome after experimental traumatic brain injury in adult, male rats. J Neurotrauma 2006; 23:97-108. [PMID: 16430376 DOI: 10.1089/neu.2006.23.97] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
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.
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Affiliation(s)
- Kimberly D Statler
- Department of Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
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488
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Laudenbach V. Mécanismes d'action des anesthésiques généraux. Arch Pediatr 2006; 13:775-7. [PMID: 16697562 DOI: 10.1016/j.arcped.2006.03.070] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Affiliation(s)
- V Laudenbach
- Unité de réanimation pédiatrique, UPRES EA 2122, service de pédiatrie néonatale et réanimation, CHU Charles-Nicolle, 1, rue de Germont, 76031 Rouen cedex, France.
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489
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McDaniel WW, Sahota AK, Vyas BV, Laguerta N, Hategan L, Oswald J. Ketamine appears associated with better word recall than etomidate after a course of 6 electroconvulsive therapies. J ECT 2006; 22:103-6. [PMID: 16801824 DOI: 10.1097/00124509-200606000-00005] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Ten patients treated with electroconvulsive therapy (ECT) for depressive illness received anesthesia with either etomidate or ketamine. Three patients received both etomidate and ketamine anesthesia for ECT during separate episodes of depression. Patients anesthetized with ketamine for ECT had significantly less impairment of short-term memory function than did patients who received ECT with etomidate anesthesia. All patients who received both anesthetics for ECT during 2 different episodes had less memory loss during ECT with ketamine than with etomidate. These results show the importance of studying the effects of all anesthetic agents used during ECT on cognitive functions. The results imply that the effect of ECT on memory may be largely caused by effects mediated by glutamate at N-methyl-d-aspartate receptors and suggest that N-methyl-d-aspartate antagonists may offer protection from memory dysfunction during ECT.
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Affiliation(s)
- William W McDaniel
- Department of Psychiatry and Behavioral Science, Eastern Virginia Medical School, 825 Fairfax Avenue, Norfolk, VA 23507, USA.
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490
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Belelli D, Peden DR, Rosahl TW, Wafford KA, Lambert JJ. Extrasynaptic GABAA receptors of thalamocortical neurons: a molecular target for hypnotics. J Neurosci 2006; 25:11513-20. [PMID: 16354909 PMCID: PMC6726038 DOI: 10.1523/jneurosci.2679-05.2005] [Citation(s) in RCA: 211] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Among hypnotic agents that enhance GABAA receptor function, etomidate is unusual because it is selective for beta2/beta3 compared with beta1 subunit-containing GABAA receptors. Mice incorporating an etomidate-insensitive beta2 subunit (beta(2N265S)) revealed that beta2 subunit-containing receptors mediate the enhancement of slow-wave activity (SWA) by etomidate, are required for the sedative, and contribute to the hypnotic actions of this anesthetic. Although the anatomical location of the beta2-containing receptors that mediate these actions is unknown, the thalamus is implicated. We have characterized GABAA receptor-mediated neurotransmission in thalamic nucleus reticularis (nRT) and ventrobasalis complex (VB) neurons of wild-type, beta2(-/-), and beta(2N265S) mice. VB but not nRT neurons exhibit a large GABA-mediated tonic conductance that contributes approximately 80% of the total GABAA receptor-mediated transmission. Consequently, although etomidate enhances inhibition in both neuronal types, the effect of this anesthetic on the tonic conductance of VB neurons is dominant. The GABA-enhancing actions of etomidate in VB but not nRT neurons are greatly suppressed by the beta(2N265S) mutation. The hypnotic THIP (Gaboxadol) induces SWA and at low, clinically relevant concentrations (30 nM to 3 microM) increases the tonic conductance of VB neurons, with no effect on VB or nRT miniature IPSCs (mIPSCs) or on the holding current of nRT neurons. Zolpidem, which has no effect on SWA, prolongs VB mIPSCs but is ineffective on the phasic and tonic conductance of nRT and VB neurons, respectively. Collectively, these findings suggest that enhancement of extrasynaptic inhibition in the thalamus may contribute to the distinct sleep EEG profiles of etomidate and THIP compared with zolpidem.
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Affiliation(s)
- Delia Belelli
- Neurosciences Institute, Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, United Kingdom.
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491
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Solt K, Johansson JS, Raines DE. Kinetics of anesthetic-induced conformational transitions in a four-alpha-helix bundle protein. Biochemistry 2006; 45:1435-41. [PMID: 16445285 PMCID: PMC2581500 DOI: 10.1021/bi052206o] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Inhaled anesthetics are thought to alter the conformational states of Cys-loop ligand-gated ion channels (LGICs) by binding within discrete cavities that are lined by portions of four alpha-helical transmembrane domains. Because Cys-loop LGICs are complex molecules that are notoriously difficult to express and purify, scaled-down models have been used to better understand the basic molecular mechanisms of anesthetic action. In this study, stopped-flow fluorescence spectroscopy was used to define the kinetics with which inhaled anesthetics interact with (Aalpha(2)-L1M/L38M)(2), a four-alpha-helix bundle protein that was designed to model anesthetic binding sites on Cys-loop LGICs. Stopped-flow fluorescence traces obtained upon mixing (Aalpha(2)-L1M/L38M)(2) with halothane revealed immediate, fast, and slow components of quenching. The immediate component, which occurred within the mixing time of the spectrofluorimeter, was attributed to direct quenching of tryptophan fluorescence upon halothane binding to (Aalpha(2)-L1M/L38M)(2). This was followed by a biexponential fluorescence decay containing fast and slow components, reflecting anesthetic-induced conformational transitions. Fluorescence traces obtained in studies using sevoflurane, isoflurane, and desflurane, which poorly quench tryptophan fluorescence, did not contain the immediate component. However, these anesthetics did produce the fast and slow components, indicating that they also alter the conformation of (Aalpha(2)-L1M/L38M)(2). Cyclopropane, an anesthetic that acts with unusually low potency on Cys-loop LGICs, acted with low apparent potency on (Aalpha(2)-L1M/L38M)(2). These results suggest that four-alpha-helix bundle proteins may be useful models of in vivo sites of action that allow the use of a wide range of techniques to better understand how anesthetic binding leads to changes in protein structure and function.
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Affiliation(s)
| | | | - Douglas E. Raines
- Corresponding author. Address: Department of Anesthesia and Critical Care, Massachusetts General Hospital, 55 Fruit Street, Clinics Building 3, Boston MA 02114. Telephone: (617) 724−0343. Fax: (617) 724−8644. E-mail:
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492
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Cheng VY, Martin LJ, Elliott EM, Kim JH, Mount HTJ, Taverna FA, Roder JC, MacDonald JF, Bhambri A, Collinson N, Wafford KA, Orser BA. Alpha5GABAA receptors mediate the amnestic but not sedative-hypnotic effects of the general anesthetic etomidate. J Neurosci 2006; 26:3713-20. [PMID: 16597725 PMCID: PMC6674127 DOI: 10.1523/jneurosci.5024-05.2006] [Citation(s) in RCA: 175] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A fundamental objective of anesthesia research is to identify the receptors and brain regions that mediate the various behavioral components of the anesthetic state, including amnesia, immobility, and unconsciousness. Using complementary in vivo and in vitro approaches, we found that GABAA receptors that contain the alpha5 subunit (alpha5GABAARs) play a critical role in amnesia caused by the prototypic intravenous anesthetic etomidate. Whole-cell recordings from hippocampal pyramidal neurons showed that etomidate markedly increased a tonic inhibitory conductance generated by alpha5GABAARs, whereas synaptic transmission was only slightly enhanced. Long-term potentiation (LTP) of field EPSPs recorded in CA1 stratum radiatum was reduced by etomidate in wild-type (WT) but not alpha5 null mutant (alpha5-/-) mice. In addition, etomidate impaired memory performance of WT but not alpha5-/- mice for spatial and nonspatial hippocampal-dependent learning tasks. The brain concentration of etomidate associated with memory impairment in vivo was comparable with that which increased the tonic inhibitory conductance and blocked LTP in vitro. The alpha5-/- mice did not exhibit a generalized resistance to etomidate, in that the sedative-hypnotic effects measured with the rotarod, loss of righting reflex, and spontaneous motor activity were similar in WT and alpha5-/- mice. Deletion of the alpha5 subunit of the GABAARs reduced the amnestic but not the sedative-hypnotic properties of etomidate. Thus, the amnestic and sedative-hypnotic properties of etomidate can be dissociated on the basis of GABAAR subtype pharmacology.
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493
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Atkins JH, Johansson JS. Technologies to shape the future: proteomics applications in anesthesiology and critical care medicine. Anesth Analg 2006; 102:1207-16. [PMID: 16551925 DOI: 10.1213/01.ane.0000198673.23026.b3] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Broadly speaking, proteomics is concerned with the simultaneous characterization of the features (for example, the concentration or activity) of the many different proteins that are typically found in biological or clinical specimens. The field is being driven forward both by innovative biotechnology companies and by academicians who are introducing the technology required for the parallel identification of individual proteins. The technology currently relies heavily on two-dimensional gel electrophoresis combined with mass spectrometry, but protein microarray chips are rapidly becoming a reality. Protein biomarkers are increasingly being recognized as crucially important for the study of disease processes, both from diagnostic and prognostic points of view. Proteome level studies will therefore be used increasingly both to identify and follow the course of various pathological conditions. In the specialty of anesthesiology, this technology will allow an improved understanding of the mechanisms of action of many of the drugs that are routinely administered in the operating room and also the effects of these therapeutic drugs on protein expression. In addition, proteomic studies will increasingly be used for both diagnostic and prognostic purposes in the intensive care unit and the chronic pain clinic.
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Affiliation(s)
- Joshua H Atkins
- Department of Anesthesiology and Critical Care, University of Pennsylvania, Philadelphia 19104, USA
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494
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Yang CX, Xu TL. Thiopental inhibits glycine receptor function in acutely dissociated rat spinal dorsal horn neurons. Neurosci Lett 2006; 397:196-200. [PMID: 16406669 DOI: 10.1016/j.neulet.2005.12.020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2005] [Revised: 11/18/2005] [Accepted: 12/07/2005] [Indexed: 10/25/2022]
Abstract
Whole-cell patch-clamp was used to assess the modulatory effect of thiopental (Thio) on glycine (Gly) receptor in mechanically dissociated rat spinal dorsal horn neurons. It was found that Thio inhibited the amplitude, accelerated the desensitization and prolonged the deactivation of Gly-induced currents (IGly) in a concentration-dependent manner. In addition, a rebound current occurred after washout of the co-application of Gly and Thio in most neurons tested. Moreover, the inhibitory effect of Thio was not the result of cross-inhibition between Gly and GABAA receptors. Furthermore, taurine-induced currents, a low-affinity agonist for Gly receptors, were also markedly inhibited by Thio in a similar way to IGly. These results indicate that Thio suppresses Gly receptor function and suggest that Thio anesthetic actions might not be mediated by Gly receptors. We speculate that the weak muscle relaxation and the limited analgesic effects observed during Thio anesthesia may attribute to its inhibitory effects on Gly receptors.
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Affiliation(s)
- Chuan-Xiu Yang
- Institute of Neuroscience and Key Laboratory of Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-yang Road, Shanghai 200031, China
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495
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Araki T, Uesono Y, Oguchi T, Toh-E A. LAS24/KOG1, a component of the TOR complex 1 (TORC1), is needed for resistance to local anesthetic tetracaine and normal distribution of actin cytoskeleton in yeast. Genes Genet Syst 2006; 80:325-43. [PMID: 16394584 DOI: 10.1266/ggs.80.325] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
It is known that some local anesthetics inhibit the growth of budding yeast cells. To investigate the pathway of local anesthetics' action, we isolated and characterized mutants that were hyper-sensitive to tetracaine, and at the same time, temperature-sensitive for growth. They were collectively called las (local anesthetic sensitive) mutants. One of the LAS genes, LAS24, was found to be identical to KOG1, which had been independently discovered as a member of the TOR complex 1 (TORC1). Las24p/Kog1p is a widely conserved TOR binding protein containing the NRC domain, HEAT repeats and WD-40 repeats, but its function remains unknown. Like the tor mutants, the las24 mutants were found to have a defect in cell wall integrity and to show sensitivity to rapamycin. Furthermore, Las24p is required not only in TORC1-mediated (rapamycin-sensitive) pathways such as translation initiation control and phosphorylation of Npr1p and Gln3p, but also for the normal distribution of the actin cytoskeleton, which has been regarded as a TORC2-mediated event. Intriguingly, the temperature-sensitivity of the las24 mutant was suppressed by either activation of Tap42/PPase or by down-regulation of the RAS/cAMP pathway. Suppressors of the temperature-sensitivity of the las24-1 mutant were found not to be effective for suppression of the tetracaine-sensitivity of the same mutant. These observations along with the facts that tetracaine and high temperature differentially affected the las24-1 mutant suggest that Las24p/Kog1p is not a target of tetracaine and that the tetracaine-sensitive step may be one of downstream branches of the TORC1 pathway. Consistent with the broad cellular functions exerted by the TOR pathway, we found that Las24p was associated with membranes and was localized at vacuoles, the plasma membrane and small vesicles.
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Affiliation(s)
- Tomoyuki Araki
- Department of Biological Science, Graduate School of Science, University of Tokyo, Hongo, Japan
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496
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Urban BW, Bleckwenn M, Barann M. Interactions of anesthetics with their targets: non-specific, specific or both? Pharmacol Ther 2006; 111:729-70. [PMID: 16483665 DOI: 10.1016/j.pharmthera.2005.12.005] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2005] [Accepted: 12/23/2005] [Indexed: 01/11/2023]
Abstract
What makes a general anesthetic a general anesthetic? We shall review first what general anesthesia is all about and which drugs are being used as anesthetics. There is neither a unique definition of general anesthesia nor any consensus on how to measure it. Diverse drugs and combinations of drugs generate general anesthetic states of sometimes very different clinical quality. Yet the principal drugs are still considered to belong to the same class of 'general anesthetics'. Effective concentrations of inhalation anesthetics are in the high micromolar range and above, and even for intravenous anesthetics they do not go below the micromolar range. At these concentrations, many molecular and higher level targets are affected by inhalation anesthetics, fewer probably by intravenous anesthetics. The only physicochemical characteristic shared by anesthetics is the correlation of their anesthetic potencies with hydrophobicity. These correlations depend on the group of general anesthetics considered. In this review, anesthetic potencies for many different targets are plotted against octanol/water partition coefficients as measure of hydrophobicity. Qualitatively, similar correlations result, suggesting several but weak interactions with proteins as being characteristic of anesthetic actions. The polar interactions involved are weak, being roughly equal in magnitude to hydrophobic interactions. Generally, intravenous anesthetics are noticeably more potent than inhalation anesthetics. They differ considerably more between each other in their interactions with various targets than inhalation anesthetics do, making it difficult to come to a decision which of these should be used in future studies as representative 'prototypical general anesthetics'.
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Affiliation(s)
- Bernd W Urban
- Klinik für Anästhesiologie und Operative Intensivmedizin, Universitätsklinikum Bonn, Sigmund-Freud-Strasse 25, D-53127 Bonn, Germany.
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497
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Abstract
BACKGROUND Coma is a medical emergency and may constitute a diagnostic and therapeutic challenge for the intensivist. OBJECTIVE To review currently available data on the etiology, diagnosis, and outcome of coma. To propose an evidence-based approach for the clinical management of the comatose patient. DATA SOURCE Search of Medline and Cochrane databases; manual review of bibliographies from selected articles and monographs. DATA SYNTHESIS AND CONCLUSIONS Coma and other states of impaired consciousness are signs of extensive dysfunction or injury involving the brainstem, diencephalon, or cerebral cortex and are associated with a substantial risk of death and disability. Management of impaired consciousness includes prompt stabilization of vital physiologic functions to prevent secondary neurologic injury, etiological diagnosis, and the institution of brain-directed therapeutic or preventive measures. Neurologic prognosis is determined by the underlying etiology and may be predicted by the combination of clinical signs and electrophysiological tests.
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Affiliation(s)
- Robert D Stevens
- Division of Neurosciences Critical Care, Department of Anesthesiology/Critical Care Medicine, Neurology and Neurosurgery, The Johns Hopkins University School of Medicine, Baltimore, MD, USA
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498
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Linden AM, Aller MI, Leppä E, Vekovischeva O, Aitta-Aho T, Veale EL, Mathie A, Rosenberg P, Wisden W, Korpi ER. The in vivo contributions of TASK-1-containing channels to the actions of inhalation anesthetics, the alpha(2) adrenergic sedative dexmedetomidine, and cannabinoid agonists. J Pharmacol Exp Ther 2006; 317:615-26. [PMID: 16397088 DOI: 10.1124/jpet.105.098525] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Inhalation anesthetics activate and cannabinoid agonists inhibit TWIK-related acid-sensitive K(+) channels (TASK)-1 two-pore domain leak K(+) channels in vitro. Many neuromodulators, such as noradrenaline, might also manifest some of their actions by modifying TASK channel activity. Here, we have characterized the basal behavioral phenotype of TASK-1 knockout mice and tested their sensitivity to the inhalation anesthetics halothane and isoflurane, the alpha(2) adrenoreceptor agonist dexmedetomidine, and the cannabinoid agonist WIN55212-2 mesylate [R-(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3,-de]-1,4-benzoxazinyl]-(1-naphtalenyl)methanone mesylate)]. TASK-1 knockout mice had a largely normal behavioral phenotype. Male, but not female, knockout mice displayed an enhanced acoustic startle response. The knockout mice showed increased sensitivity to thermal nociception in a hot-plate test but not in a tail-flick test. The analgesic, sedative, and hypothermic effects of WIN55212-2 (2-6 mg/kg s.c.) were reduced in TASK-1 knockout mice. These results implicate TASK-1-containing channels in supraspinal pain pathways, in particular those modulated by endogenous cannabinoids. TASK-1 knockout mice were less sensitive to the anesthetic effects of halothane and isoflurane than wild-type littermates, requiring higher anesthetic concentrations to induce immobility as reflected by loss of the tail-withdrawal reflex. Our results support the idea that the activation of multiple background K(+) channels is crucial for the high potency of inhalation anesthetics. Furthermore, TASK-1 knockout mice were less sensitive to the sedative effects of dexmedetomidine (0.03 mg/kg s.c.), suggesting a role for the TASK-1 channels in the modulation of function of the adrenergic locus coeruleus nuclei and/or other neuronal systems.
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Affiliation(s)
- Anni-Maija Linden
- Institute of Biomedicine, Pharmacology, University of Helsinki, P.O. Box 63 (Haartmaninkatu 8), 00014 University of Helsinki, Finland
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499
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Sieghart W. Structure, pharmacology, and function of GABAA receptor subtypes. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2006; 54:231-63. [PMID: 17175817 DOI: 10.1016/s1054-3589(06)54010-4] [Citation(s) in RCA: 228] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Werner Sieghart
- Division of Biochemistry and Molecular Biology, Center for Brain Research, and Section of Biochemical Psychiatry, University Clinic for Psychiatry, Medical University Vienna, Austria
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500
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Sendowski I, Raffin F, Clarençon D. Spectrum of neural electrical activity in guinea pig cochlea: Effects of anaesthesia regimen, body temperature and ambient noise. Hear Res 2006; 211:63-73. [PMID: 16310327 DOI: 10.1016/j.heares.2005.10.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2005] [Accepted: 08/29/2005] [Indexed: 11/23/2022]
Abstract
Spectral analysis of electric noise recorded from the round window of the cochlea is thought to represent the summed spontaneous activity of the auditory nerve. It has been postulated that it could provide a possible tinnitus index. Because experimental conditions could change this neural activity, the effect of anaesthesia regimen, body temperature and ambient noise on the spectrum of spontaneous neural noise (SNN) were investigated in guinea pig cochlea. SNN was studied in awake guinea pigs and after anaesthesia with pentobarbital (P), xylazine/ketamine (XK) or xylazine/tiletamine-zolazepam (XTZ). Body temperature varied gradually from 33 to 41 degrees C under XK regimen. In awake animals, broadband noise was generated with intensity varying from 0 to 50 dB. The SNN consisted in a broad peak at approximately 900 Hz. With ambient broadband noise, it increased exponentially with the sound level with no shift in frequency. Soon after anaesthetic induction, the lowest frequencies were constantly decreased, and gradually the 900 Hz peak either increased moderately (P) or dropped steeply (XTZ) or remained unchanged (XK). Peak frequency increased linearly with body temperature whereas the amplitude reached a maximum at around 39.5 degrees C. In conclusion, these data indicate that experimental conditions such as anaesthesia regimen, body temperature and ambient noise modify the spontaneous neural outflow of the cochlea and must be taken into account when studying SNN.
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Affiliation(s)
- I Sendowski
- Centre de recherches du service de santé des Armées (CRSSA), Département de radiobiologie, 24 avenue des Maquis du Grésivaudan BP 87, 38702, La Tronche Cedex, France.
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