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Immobilizing doses of halothane, isoflurane or propofol, do not preferentially depress noxious heat-evoked responses of rat lumbar dorsal horn neurons with ascending projections. Anesth Analg 2008; 106:985-90, table of contents. [PMID: 18292450 DOI: 10.1213/ane.0b013e318163f8f3] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND The spinal cord is an important site where volatile anesthetics decrease sensation and produce immobility. Beyond this knowledge, our understanding of a site of anesthetic action is limited. Previous evidence suggests that dorsal horn neurons with ascending projections may be more susceptible to depression by general anesthetics than local spinal interneurons. In this study we evaluated the effects of volatile and injectable general anesthetics on lumbar dorsal horn neurons with and without ascending projections. METHODS Thirty-seven adult male rats underwent laminectomies at C1, for placement of a stimulating electrode, and T13/L1, for extracellular recording from the spinal cord dorsal horn. Neuronal responses to heat were evaluated under two doses of halothane, isoflurane, or propofol anesthesia. RESULTS Under both halothane and isoflurane anesthesia, increasing the dose from 0.8 to 1.2 minimum alveolar concentration (MAC) had no significant effect on heat-evoked responses in neurons that had ascending projections identified via antidromic stimulation (AD) or those without ascending projections (nAD). Heat responses in AD neurons 1 min after i.v. administration of 3 and 5 mg/kg of propofol were reduced to 60% +/- 18% (mean +/- SE) and 39% +/- 14% of control respectively. Similarly, in nAD neurons responses were reduced to 56% +/- 14% and 50% +/- 10% of control by 3 and 5 mg/kg propofol respectively. CONCLUSIONS Our findings suggest, at peri-MAC concentrations, these general anesthetics do not preferentially depress lumbar dorsal horn neurons with ascending projections compared to those with no identifiable ascending projections.
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Irifune M, Katayama S, Takarada T, Shimizu Y, Endo C, Takata T, Morita K, Dohi T, Sato T, Kawahara M. MK-801 enhances gabaculine-induced loss of the righting reflex in mice, but not immobility. Can J Anaesth 2008; 54:998-1005. [PMID: 18056209 DOI: 10.1007/bf03016634] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
PURPOSE gamma-Aminobutyric acid (GABA) and N-methyl-D-aspartate (NMDA) receptors are important targets for anesthetic action at the in vitro cellular level. Gabaculine is a GABA-trans-aminase inhibitor that increases endogenous GABA in the brain, and enhances GABA activity. We have recently shown that unconsciousness is associated with the enhanced GABA activity due to gabaculine, but that immobility is not. MK-801 is a selective NMDA channel blocker. In this study, we examined behaviourally whether gabaculine in combination with MK-801 could produce these components of the general anesthetic state. We further compared the effect of MK-801 with ketamine, another NMDA channel blocker. METHODS All drugs were administered intraperitoneally to adult male ddY mice. To assess the general anesthetic components, two endpoints were used. One was loss of the righting reflex (LORR; as a measure of unconsciousness) and the other was loss of movement in response to tail-clamp stimulation (as a measure of immobility). RESULTS Large doses of MK-801 alone (10-50 mg.kg(-1)) induced neither LORR nor immobility in response to noxious stimulation. However, even a small dose (0.2 mgxkg(-1)) significantly enhanced gabaculine-induced LORR (P < 0.05), although gabaculine in combination with MK-801 (0.2-10 mgxkg(-1)) produced no immobility. However, gabaculine plus a subanesthetic dose of ketamine (30 mgxkg(-1)), which acts on NMDA, opioid and nicotinic acetylcholine receptors and neuronal Na(+) channels, suppressed the pain response, but did not achieve a full effect. Ketamine alone dose-dependently produced both LORR and immobility. CONCLUSION These findings suggest that gabaculine-induced LORR is modulated by blocking NMDA receptors, but that immobility is not mediated through GABA or NMDA receptors.
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Affiliation(s)
- Masahiro Irifune
- Department of Dental Anesthesiology, Division of Clinical Medical Science, Programs for Applied Biomedicine, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734- 8553, Japan.
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Kim DI, Kim JR, Kim SY. Propofol-induced Immediate Early Gene Expression in Human Neuroblastoma Cell Lines. Korean J Anesthesiol 2008. [DOI: 10.4097/kjae.2008.54.2.189] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Affiliation(s)
- Dong Il Kim
- Department of Biochemistry and Molecular Biology, College of Medicine, Yeungnam University, Daegu, Korea
- Department of Anesthesiology and Pain Medicine, Masan Bokeum Hospital, Masan, Korea
| | - Jae Ryong Kim
- Department of Biochemistry and Molecular Biology, College of Medicine, Yeungnam University, Daegu, Korea
| | - Seong Yong Kim
- Department of Biochemistry and Molecular Biology, College of Medicine, Yeungnam University, Daegu, Korea
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Jackson SN, Singhal SK, Woods AS, Morales M, Shippenberg T, Zhang L, Oz M. Volatile anesthetics and endogenous cannabinoid anandamide have additive and independent inhibitory effects on alpha(7)-nicotinic acetylcholine receptor-mediated responses in Xenopus oocytes. Eur J Pharmacol 2007; 582:42-51. [PMID: 18242598 DOI: 10.1016/j.ejphar.2007.12.023] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2007] [Revised: 12/12/2007] [Accepted: 12/20/2007] [Indexed: 10/22/2022]
Abstract
In earlier studies, the volatile anesthetics and the endogenous cannabinoid anandamide have been shown to inhibit the function of alpha(7)-nicotinic acetylcholine receptors. In the present study, interactions between the effects of volatile anesthetics and anandamide on the function of alpha(7)-nicotinic acetylcholine receptors expressed in Xenopus oocytes were investigated using the two-electrode voltage-clamp technique. Anandamide and volatile anesthetics isoflurane and halothane inhibited currents evoked with acetylcholine (100 microM) in a reversible and concentration-dependent manner. Coapplication of anandamide and volatile anesthetics caused a significantly greater inhibition of alpha(7)-nicotinic acetylcholine receptor function than anandamide or volatile anesthetics alone. Analyses of oocytes by matrix-assisted laser desorption/ionization mass spectroscopy indicated that volatile anesthetics did not alter the lipid profile of oocytes. Results of studies with chimeric alpha(7)-nicotinic acetylcholine-5-HT(3) receptors comprised of the N-terminal domain of the alpha(7)-nicotinic acetylcholine receptor and the transmembrane and carboxyl-terminal domains of 5-HT(3) receptors suggest that while isoflurane inhibition of the alpha(7)-nicotinic acetylcholine receptor is likely to involve the N-terminal region of the receptor, the site of action for anandamide involves transmembrane and carboxyl-terminal domains of the receptors. These data indicate that endocannabinoids and isoflurane have additive inhibitory effects on alpha(7)-nicotinic acetylcholine receptor function through allosteric binding sites located on the distinct regions of the receptor.
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155
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Seeger HM, Gudmundsson ML, Heimburg T. How anesthetics, neurotransmitters, and antibiotics influence the relaxation processes in lipid membranes. J Phys Chem B 2007; 111:13858-66. [PMID: 18020440 DOI: 10.1021/jp075346b] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We used pressure perturbation calorimetry to investigate the relaxation time scale after a jump into the melting transition regime of artificial lipid membranes. This time is equivalent to the characteristic rate of domain growth. The studies were performed on single-component large unilamellar and multilamellar vesicle systems with and without the addition of small molecules such as general anesthetics, neurotransmitters, and antibiotics. These drugs interact with membranes and affect melting points and profiles. In all systems, we found that heat capacity and relaxation times are linearly related to each other in a simple manner, and we outline the theoretical origin of this finding. Thus, the influence of a drug on the time scale of domain formation processes can be understood on the basis of their influence on the heat capacity profile. This allows estimations of the characteristic relaxation time scales in biological membranes.
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Affiliation(s)
- Heiko M Seeger
- The Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen Ø, Denmark
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156
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Kim J, Yao A, Atherley R, Carstens E, Jinks SL, Antognini JF. Neurons in the ventral spinal cord are more depressed by isoflurane, halothane, and propofol than are neurons in the dorsal spinal cord. Anesth Analg 2007; 105:1020-6, table of contents. [PMID: 17898382 PMCID: PMC2693417 DOI: 10.1213/01.ane.0000280483.17854.56] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND Volatile anesthetics act primarily in the spinal cord to produce immobility but their exact site of action is unclear. Between 0.8 and 1.2 minimum alveolar anesthetic concentration (MAC), isoflurane does not depress neurons in the dorsal horn, suggesting that it acts at a more ventral site within the spinal cord such as in premotor interneurons and motoneurons. We hypothesized that isoflurane, halothane, and propofol would exert a greater depressant effect on nociceptive responses of ventral horn neurons when compared with dorsal horn neurons. METHODS Rats were anesthetized with isoflurane or halothane and responses of dorsal (<1200 microm deep) and ventral (>1200 microm) lumbar neurons to noxious mechanical stimulation of the hindpaw were determined at 0.8 and 1.2 MAC. In a third group anesthetized with isoflurane at 0.8 MAC, we administered 5 mg/kg propofol while recording responses from dorsal horn or ventral horn neurons. RESULTS Dorsal horn neuronal responses were not significantly affected when either isoflurane or halothane was increased from 0.8 to 1.2 MAC; propofol also had no significant effect. On the other hand, with increased isoflurane or halothane concentration, responses of ventral horn neurons were depressed by 60% and 45%, respectively. Propofol profoundly depressed (>90%) ventral horn neurons. CONCLUSIONS These data suggest that, in the peri-MAC range, isoflurane, halothane, and propofol have little or no effect on neuronal responses to noxious mechanical stimulation in the spinal dorsal horn but depress such responses in the ventral horn. Immobility produced in the 0.8-1.2 MAC range by these anesthetics appears to result from a depressant action in the ventral horn.
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Affiliation(s)
- JongBun Kim
- Department of Anesthesiology and Pain Medicine, University of California, Davis, California
- Department of Anesthesia and Pain Medicine, Catholic University of Korea, Seoul, Korea
| | - Aubrey Yao
- Department of Anesthesiology and Pain Medicine, University of California, Davis, California
| | - Richard Atherley
- Department of Anesthesiology and Pain Medicine, University of California, Davis, California
| | - Earl Carstens
- Section of Neurobiology, Physiology and Behavior, University of California, Davis, California
| | - Steven L. Jinks
- Department of Anesthesiology and Pain Medicine, University of California, Davis, California
| | - Joseph F. Antognini
- Department of Anesthesiology and Pain Medicine, University of California, Davis, California
- Section of Neurobiology, Physiology and Behavior, University of California, Davis, California
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Roussin A, Montastruc JL, Lapeyre-Mestre M. Pharmacological and clinical evidences on the potential for abuse and dependence of propofol: a review of the literature. Fundam Clin Pharmacol 2007; 21:459-66. [PMID: 17868199 DOI: 10.1111/j.1472-8206.2007.00497.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Propofol (2,6-diisopropylphenol) is an intravenous short-acting anaesthetic widely used for inducing and maintaining anaesthesia. Propofol is also being increasingly used for sedation. Beside medical use, propofol is abused for recreational purpose, mostly in medical professionals who are not informed of the risk of dependence to this compound. The aim of this review was to provide an overview of molecular, animal and clinical pharmacological data of the literature evidencing the potential for abuse and dependence of propofol.
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Affiliation(s)
- Anne Roussin
- Service de Pharmacologie Clinique, Centre d'Evaluation et d'Information sur la Pharmacodépendance de Toulouse, EA 3696, Université Paul Sabatier, Faculté de Médecine, 31000 Toulouse, France.
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Goetz T, Arslan A, Wisden W, Wulff P. GABA(A) receptors: structure and function in the basal ganglia. PROGRESS IN BRAIN RESEARCH 2007; 160:21-41. [PMID: 17499107 PMCID: PMC2648504 DOI: 10.1016/s0079-6123(06)60003-4] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
gamma-Aminobutyric acid type A (GABA(A)) receptors, the major inhibitory neurotransmitter receptors responsible for fast inhibition in the basal ganglia, belong to the superfamily of "cys-cys loop" ligand-gated ion channels. GABA(A) receptors form as pentameric assemblies of subunits, with a central Cl(-) permeable pore. On binding of two GABA molecules to the extracellular receptor domain, a conformational change is induced in the oligomer and Cl(-), in most adult neurons, moves into the cell leading to an inhibitory hyperpolarization. Nineteen mammalian subunit genes have been identified, each showing distinct regional and cell-type-specific expression. The combinatorial assembly of the subunits generates considerable functional diversity. Here we place the focus on GABA(A) receptor expression in the basal ganglia: striatum, globus pallidus, substantia nigra and subthalamic nucleus, where, in addition to the standard alpha1beta2/3gamma2 receptor subtype, significant levels of other subunits (alpha2, alpha3, alpha4, gamma1, gamma3 and delta) are expressed in some nuclei.
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Affiliation(s)
- T. Goetz
- Department of Clinical Neurobiology, University of Heidelberg, Im Neuenheimer Feld 364, 69120 Heidelberg, Germany
| | - A. Arslan
- Department of Clinical Neurobiology, University of Heidelberg, Im Neuenheimer Feld 364, 69120 Heidelberg, Germany
| | - W. Wisden
- Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK
| | - P. Wulff
- Department of Clinical Neurobiology, University of Heidelberg, Im Neuenheimer Feld 364, 69120 Heidelberg, Germany
- Corresponding author. Tel.: +0044-1224-551941; Fax: +0044-1224-555719; E-mail:
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Milutinovic PS, Yang L, Cantor RS, Eger EI, Sonner JM. Anesthetic-like modulation of a gamma-aminobutyric acid type A, strychnine-sensitive glycine, and N-methyl-d-aspartate receptors by coreleased neurotransmitters. Anesth Analg 2007; 105:386-92. [PMID: 17646495 DOI: 10.1213/01.ane.0000267258.17197.7d] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
INTRODUCTION A mechanism of anesthesia has recently been proposed which predicts that coreleased neurotransmitters may modulate neurotransmitter receptors for which they are not the native agonist in a manner similar to anesthetics. METHODS We tested this prediction by applying acetylcholine to a NR1/NR2A N-methyl-d-aspartate receptor, glycine to a wild-type alpha(1)beta(2) and anesthetic-resistant alpha(1)(S270I)beta(2) gamma-amino-butyric acid (GABA) type A receptor, and GABA to a homomeric alpha(1) wild type and anesthetic-resistant alpha(1) S267I glycine receptor. Receptors were expressed in Xenopus laevis oocytes and studied using two-electrode voltage clamping. RESULTS We found inhibition of N-methyl-d-aspartate receptor function by acetylcholine, enhancement of glycine receptor function by GABA, and enhancement of GABA type A receptor function by glycine. As expected of compounds with anesthetic activity, GABA showed far less potentiation (enhancement) of the function of the anesthetic-resistant S267I glycine receptor than that of the wild-type receptor. Glycine potentiated the function of wild-type GABA type A receptors but inhibited the function of the anesthetic-resistant S270I GABA type A receptor. CONCLUSIONS These results show that neurotransmitters that are coreleased onto anesthetic-sensitive receptors may modulate the function of receptors for which they are not the native agonist via an anesthetic-like mechanism. These findings lend support to a recent theory of anesthetic action.
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160
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Abstract
A number of oxygenated compounds (oxygenates) are available for use in gasoline to reduce vehicle exhaust emissions, reduce the aromatic compound content, and avoid the use of organo-lead compounds, while maintaining high octane numbers. Ethyl tertiary-butyl ether (ETBE) is one such compound. The current use of ETBE in gasoline or petrol is modest but increasing, with consequently similar trends in the potential for human exposure. Inhalation is the most likely mode of exposure, with about 30% of inhaled ETBE being retained by the lungs and distributed around the body. Following cessation of exposure, the blood concentration of ETBE falls rapidly, largely as a result of its metabolism to tertiary-butyl alcohol (TBA) and acetaldehyde. TBA may be further metabolized, first to 2-methyl-1,2-propanediol and then to 2-hydroxyisobutyrate, the two dominant metabolites found in urine of volunteers and rats. The rapid oxidation of acetaldehyde suggests that its blood concentration is unlikely to rise above normal as a result of human exposure to sources of ETBE. Single-dose toxicity tests show that ETBE has low toxicity and is essentially nonirritant to eyes and skin; it did not cause sensitization in a maximization test in guinea pigs. Neurological effects have been observed only at very high exposure concentrations. There is evidence for an effect of ETBE on the kidney of rats. Increases in kidney weight were seen in both sexes, but protein droplet accumulation (with alpha(2u)-globulin involvement) and sustained increases in cell proliferation occurred only in males. In liver, centrilobular necrosis was induced in mice, but not rats, after exposure by inhalation, although this lesion was reported in some rats exposed to very high oral doses of ETBE. The proportion of liver cells engaged in S-phase DNA synthesis was increased in mice of both sexes exposed by inhalation. ETBE has no specific effects on reproduction, development, or genetic material. Carcinogenicity studies have been conducted with ETBE, TBA, and ethanol (included in this review as an endogenous precursor of acetaldehyde in the absence of TBA). A single experiment with ETBE in rats and several experiments with ethanol in rats and mice were not considered adequate for an evaluation of ETBE carcinogenicity. In male rats only, TBA induced alpha(2u)-globulin nephropathy-related renal tubule adenomas. These are generally considered to have no human relevance. In addition, increases in thyroid follicular cell adenoma incidence were associated with TBA treatment in female mice. This result lacks independent confirmation and is not supported by experiments in which similar or higher internal doses of TBA were delivered.
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Affiliation(s)
- Douglas McGregor
- Toxicity Evaluation Consultants. Aberdour, Scotland. United Kingdom.
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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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162
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Rüsch D, Braun HA, Wulf H, Schuster A, Raines DE. Inhibition of human 5-HT(3A) and 5-HT(3AB) receptors by etomidate, propofol and pentobarbital. Eur J Pharmacol 2007; 573:60-4. [PMID: 17669396 PMCID: PMC2276611 DOI: 10.1016/j.ejphar.2007.07.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2007] [Revised: 06/28/2007] [Accepted: 07/04/2007] [Indexed: 11/26/2022]
Abstract
The actions of intravenous anaesthetics on 5-HT(3AB) receptors have not been studied. Using oocyte electrophysiology, the effects of etomidate, propofol, and pentobarbital on human 5-HT(3A) and 5-HT(3AB) receptors were studied and compared. Inhibition of peak currents by all three compounds in both receptor subtypes was anaesthetic concentration-dependant and non-competitive. Because the half-maximal inhibitory concentrations for etomidate, propofol and pentobarbital in 5-HT(3A) and 5-HT(3AB) receptors were all above their respective anaesthetic concentrations, the results of our study suggest that neither 5-HT(3) receptor subtype contributes to the anaesthetic actions of etomidate, propofol or pentobarbital.
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Affiliation(s)
- Dirk Rüsch
- Department of Anaesthesia and Critical Care, University Hospital Giessen-Marburg GmbH, Marburg Campus, Baldingerstrasse, 35033 Marburg, Germany.
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163
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Uribe-Escamilla R, Mota-Rojas D, Sánchez-Aparicio P, Alonso-Spilsbury M, González-Piña R, Alfaro-Rodríguez A. Effect of pentobarbital on pH and electrolyte levels after induced seizure in rats. Seizure 2007; 16:397-401. [PMID: 17395499 DOI: 10.1016/j.seizure.2007.02.010] [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: 11/29/2006] [Revised: 01/25/2007] [Accepted: 02/20/2007] [Indexed: 11/30/2022] Open
Abstract
We studied the effects of high doses of pentobarbital (PB) and carbamazepine (CBZ) on electrolyte levels and pH in an epileptic animal model. Pentobarbital decreased Ca2+ and Na+ levels without pentylenetetrazole (PTZ). After this, Ca2+ and Na+ levels continued to decrease except when CBZ was used, which preserved the Ca2+ levels PTZ may have opposed effects on PB. Our results suggest that PB causes changes in electrolyte levels and pH, but these changes are diminished by CBZ.
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Affiliation(s)
- R Uribe-Escamilla
- Laboratory of Neurochemistry, National Institute of Rehabilitation, SSA, México City, Mexico
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164
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Abstract
PURPOSE OF REVIEW Anesthetics influence a wide variety of transmitter- and voltage-gated ion channels in the mammalian central nervous system. At the molecular level, the gamma-aminobutyric acid (GABA) subtype A receptor has emerged as a primary therapeutic target. This review highlights recent advances in our understanding of how anesthetics modify GABA(A) receptor function. RECENT FINDINGS Anesthetics bind to discrete selective binding sites on GABA(A) receptors--a discovery that challenges lipid-based theories of anesthesia. Not all GABA(A) receptors are equally sensitive to anesthetics because positive allosteric modulation is critically dependent on receptor subunit composition. Moreover, GABA(A) receptors located in extrasynaptic regions of hippocampal neurons display a greater sensitivity to propofol and benzodiazepines than do receptors located in subsynaptic regions. Enhancement in GABAergic inhibition may not account for all of the behavioral end-points associated with the anesthetic state. In particular, the immobilizing properties of anesthetics may not be solely mediated by GABA(A) receptors. Finally, synthetic neurosteroids are being developed as improved general anesthetics. SUMMARY Detailed insights into anesthetic-GABA(A) receptor interactions have resulted in intense efforts to develop safer drugs that selectively target subtypes of GABA(A) receptors.
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Affiliation(s)
- Beverley A Orser
- Department of Anesthesia, University of Toronto, Toronto, Ontario, Canada.
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165
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Crawford DK, Trudell JR, Bertaccini EJ, Li K, Davies DL, Alkana RL. Evidence that ethanol acts on a target in Loop 2 of the extracellular domain of alpha1 glycine receptors. J Neurochem 2007; 102:2097-2109. [PMID: 17561937 DOI: 10.1111/j.1471-4159.2007.04680.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Considerable evidence indicates that ethanol acts on specific residues in the transmembrane domains of glycine receptors (GlyRs). In this study, we tested the hypothesis that the extracellular domain is also a target for ethanol action by investigating the effect of cysteine substitutions at positions 52 (extracellular domain) and 267 (transmembrane domain) on responses to n-alcohols and propyl methanethiosulfonate (PMTS) in alpha1GlyRs expressed in Xenopus oocytes. In support of the hypothesis: (i) The A52C mutation changed ethanol sensitivity compared to WT GlyRs; (ii) PMTS produced irreversible alcohol-like potentiation in A52C GlyRs; and (iii) PMTS binding reduced the n-chain alcohol cutoff in A52C GlyRs. Further studies used PMTS binding to cysteines at positions 52 or 267 to block ethanol action at one site in order to determine its effect at other site(s). In these situations, ethanol caused negative modulation when acting at position 52 and positive modulation when acting at position 267. Collectively, these findings parallel the evidence that established the TM domain as a target for ethanol, suggest that positions 52 and 267 are part of the same alcohol pocket and indicate that the net effect of ethanol on GlyR function reflects the summation of its positive and negative modulatory effects on different targets.
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Affiliation(s)
- Daniel K Crawford
- Alcohol and Brain Research Laboratory, Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California, USANeuroscience Graduate Program, University of Southern California, Los Angeles, California, USADepartment of Anesthesia and Beckman Program for Molecular and Genetic Medicine, Stanford School of Medicine, Stanford, California, USADepartment of Anesthesia, Palo Alto Veterans Affairs Health Care System, Palo Alto, California, USA
| | - James R Trudell
- Alcohol and Brain Research Laboratory, Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California, USANeuroscience Graduate Program, University of Southern California, Los Angeles, California, USADepartment of Anesthesia and Beckman Program for Molecular and Genetic Medicine, Stanford School of Medicine, Stanford, California, USADepartment of Anesthesia, Palo Alto Veterans Affairs Health Care System, Palo Alto, California, USA
| | - Edward J Bertaccini
- Alcohol and Brain Research Laboratory, Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California, USANeuroscience Graduate Program, University of Southern California, Los Angeles, California, USADepartment of Anesthesia and Beckman Program for Molecular and Genetic Medicine, Stanford School of Medicine, Stanford, California, USADepartment of Anesthesia, Palo Alto Veterans Affairs Health Care System, Palo Alto, California, USA
| | - Kaixun Li
- Alcohol and Brain Research Laboratory, Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California, USANeuroscience Graduate Program, University of Southern California, Los Angeles, California, USADepartment of Anesthesia and Beckman Program for Molecular and Genetic Medicine, Stanford School of Medicine, Stanford, California, USADepartment of Anesthesia, Palo Alto Veterans Affairs Health Care System, Palo Alto, California, USA
| | - Daryl L Davies
- Alcohol and Brain Research Laboratory, Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California, USANeuroscience Graduate Program, University of Southern California, Los Angeles, California, USADepartment of Anesthesia and Beckman Program for Molecular and Genetic Medicine, Stanford School of Medicine, Stanford, California, USADepartment of Anesthesia, Palo Alto Veterans Affairs Health Care System, Palo Alto, California, USA
| | - Ronald L Alkana
- Alcohol and Brain Research Laboratory, Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California, USANeuroscience Graduate Program, University of Southern California, Los Angeles, California, USADepartment of Anesthesia and Beckman Program for Molecular and Genetic Medicine, Stanford School of Medicine, Stanford, California, USADepartment of Anesthesia, Palo Alto Veterans Affairs Health Care System, Palo Alto, California, USA
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166
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Emmanouil DE, Quock RM. Advances in understanding the actions of nitrous oxide. Anesth Prog 2007; 54:9-18. [PMID: 17352529 PMCID: PMC1821130 DOI: 10.2344/0003-3006(2007)54[9:aiutao]2.0.co;2] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2006] [Accepted: 09/09/2006] [Indexed: 02/07/2023] Open
Abstract
Nitrous oxide (N(2)O) has been used for well over 150 years in clinical dentistry for its analgesic and anxiolytic properties. This small and simple inorganic chemical molecule has indisputable effects of analgesia, anxiolysis, and anesthesia that are of great clinical interest. Recent studies have helped to clarify the analgesic mechanisms of N(2)O, but the mechanisms involved in its anxiolytic and anesthetic actions remain less clear. Findings to date indicate that the analgesic effect of N(2)O is opioid in nature, and, like morphine, may involve a myriad of neuromodulators in the spinal cord. The anxiolytic effect of N(2)O, on the other hand, resembles that of benzodiazepines and may be initiated at selected subunits of the gamma-aminobutyric acid type A (GABA(A)) receptor. Similarly, the anesthetic effect of N(2)O may involve actions at GABA(A) receptors and possibly at N-methyl-D-aspartate receptors as well. This article reviews the latest information on the proposed modes of action for these clinical effects of N(2)O.
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Affiliation(s)
- Dimitris E Emmanouil
- Department of Pediatric Dentistry, School of Dentistry, Athens University, Athens, Greece.
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167
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Katayama S, Irifune M, Kikuchi N, Takarada T, Shimizu Y, Endo C, Takata T, Dohi T, Sato T, Kawahara M. Increased γ-Aminobutyric Acid Levels in Mouse Brain Induce Loss of Righting Reflex, but Not Immobility, in Response to Noxious Stimulation. Anesth Analg 2007; 104:1422-9, table of contents. [PMID: 17513635 DOI: 10.1213/01.ane.0000261519.04083.3e] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND The general anesthetic state comprises behavioral and perceptual components, including amnesia, unconsciousness, and immobility. gamma-Aminobutyric acidergic (GABAergic) inhibitory neurotransmission is an important target for anesthetic action at the in vitro cellular level. In vivo, however, the functional relevance of enhancing GABAergic neurotransmission in mediating essential components of the general anesthetic state is unknown. Gabaculine is a GABA-transaminase inhibitor that inhibits degradation of released GABA, and consequently increases endogenous GABA in the central nervous system. Here, we examined, behaviorally, the ability of increased GABA levels to produce components of the general anesthetic state. METHODS All drugs were administered systemically in adult male ddY mice. To assess the general anesthetic components, two end-points were used. One was loss of righting reflex (LORR; as a measure of unconsciousness); the other was loss of movement in response to tail-clamp stimulation (as a measure of immobility). RESULTS Gabaculine induced LORR in a dose-dependent fashion with a 50% effective dose of 100 (75-134; 95% confidence limits) mg/kg. The behavioral and microdialysis studies revealed that the endogenous GABA-induced LORR occurred in a brain concentration-dependent manner. However, even larger doses of gabaculine (285-400 mg/kg) produced no loss of tail-clamp response. In contrast, all the tested volatile anesthetics concentration-dependently abolished both righting and tail-clamp response, supporting the evidence that volatile anesthetics act on a variety of molecular targets. CONCLUSIONS These findings indicate that LORR is associated with enhanced GABAergic neurotransmission, but that immobility in response to noxious stimulation is not, suggesting that LORR and immobility are mediated through different neuronal pathways and/or regions in the central nervous system.
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Affiliation(s)
- Sohtaro Katayama
- Department of Dental Anesthesiology, Division of Clinical Medical Science, Programs for Applied Biomedicine, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan
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168
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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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169
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Johansson JS, Solt K, Reddy KS. Binding of the General Anesthetics Chloroform and 2,2,2-Trichloroethanol to the Hydrophobic Core of a Four-α-Helix Bundle Protein¶. Photochem Photobiol 2007. [DOI: 10.1562/0031-8655(2003)0770089botgac2.0.co2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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170
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Kim J, Atherley R, Werner DF, Homanics GE, Carstens E, Antognini JF. Isoflurane depression of spinal nociceptive processing and minimum alveolar anesthetic concentration are not attenuated in mice expressing isoflurane resistant gamma-aminobutyric acid type-A receptors. Neurosci Lett 2007; 420:209-12. [PMID: 17543455 PMCID: PMC3045261 DOI: 10.1016/j.neulet.2007.04.057] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2007] [Revised: 04/24/2007] [Accepted: 04/24/2007] [Indexed: 01/04/2023]
Abstract
Anesthetics produce immobility and depress spinal nociceptive processing, but the exact sites and mechanisms of anesthetic action are unknown. The gamma-aminobutyric acid type-A (GABAA) receptor is thought to be important to anesthetic action. We studied knock-in mice that had mutations in the alpha1 subunit of the GABAA receptor that imparts resistance to isoflurane in in vitro systems. We determined the isoflurane minimum alveolar concentration (MAC) that produces immobility in 50% of subjects and responses of lumbar neurons (single-unit recordings) to noxious stimulation (5 s pinch) of the hindpaw. Isoflurane MAC did not differ between wild-type (1.1+/-0.1%) and knock-in (1.1+/-0.1%) mice. Isoflurane depressed neuronal responses to noxious stimulation (60 s period during and after pinch) similarly in both wild-type and knock-in mice (555+/-133 and 636+/-106 impulses/min, respectively, at 0.8 MAC and 374+/-81 and 409+/-85 impulses/min at 1.2 MAC). We conclude that isoflurane enhancement of alpha1-containing GABAA receptors is not required to produce immobility or depress spinal nociceptive processing.
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Affiliation(s)
- JongBun Kim
- Department of Anesthesiology, The Catholic University of Korea, Seoul, Korea
| | - Richard Atherley
- Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, California 95616 United States
| | - David F. Werner
- Department of Anesthesiology, University of Pittsburgh, Pittsburgh, PA 15260, United States
| | - Gregg E. Homanics
- Department of Anesthesiology, University of Pittsburgh, Pittsburgh, PA 15260, United States
| | - Earl Carstens
- Section of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, California 95616 United States
| | - Joseph F. Antognini
- Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, California 95616 United States
- Section of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, California 95616 United States
- Correspondence to: Joseph F. Antognini, M.D., Department of Anesthesiology and Pain Medicine, University of California, Davis, TB-170, Davis, California 95616, FAX 530-752-7807,
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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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172
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Campagna-Slater V, Weaver DF. Anaesthetic binding sites for etomidate and propofol on a GABAA receptor model. Neurosci Lett 2007; 418:28-33. [PMID: 17412502 DOI: 10.1016/j.neulet.2007.02.091] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2006] [Revised: 02/19/2007] [Accepted: 02/26/2007] [Indexed: 11/17/2022]
Abstract
Investigating the molecular basis of general anaesthetic activity at the GABA(A) ligand-gated ion channel is challenging due to the wide structural diversity among known general anaesthetics, and the lack of an experimental structure for the GABA(A) protein. In this molecular modelling study, two distinct binding cavities were identified within the beta(2) subunit of the transmembrane domain in a molecular model of the GABA(A) protein. The first, located near the centre of the alpha-helical bundle, contains Asn265 (TM2), which is essential for modulation by etomidate. The second, located near the TM1, TM3 and TM4 segments close to the membrane-extracellular interface, is capped by Met286 (TM3), a residue thought to be involved in the propofol binding site. Potential interactions of etomidate and propofol with other side-chains were also identified.
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Lallemand MA, Lentschener C, Roche K, Grabar S, Bonnichon P, Ozier Y. [Hydroxyzine premedication does not alter bispectral index changes following etomidate induction of general anaesthesia]. ANNALES FRANCAISES D'ANESTHESIE ET DE REANIMATION 2007; 26:202-6. [PMID: 17258423 DOI: 10.1016/j.annfar.2006.09.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2006] [Accepted: 09/19/2006] [Indexed: 05/13/2023]
Abstract
OBJECTIVE Various drugs including hydroxyzine are preoperatively administered to facilitate the induction of general anaesthesia. We investigated the effect of hydroxyzine premedication on BIS-based etomidate induction of general anaesthesia. PATIENTS AND METHODS Sixty-seven ASA I-II consecutive patients were randomly allocated to receive oral hydroxyzine 1.5 mg/kg or placebo, 90 min prior to inducing general anaesthesia using intravenous etomidate alone 0.3 mg/kg. BIS values were continuously recorded. The times for the BIS to decrease to 50 and to loss of eyelid reflex; the evolution of arterial pressure and heart rate; and myoclonia rate and grade were investigated and compared. RESULTS The results for the hydroxyzine and placebo groups were similar with respect to: a) time [median (range) (seconds)] to a BIS decrease to 50 [100 (21-266) versus 113 (30-510), P=0.1] and to loss of eyelid reflex [83 (21-210) versus 97 (30-300), P=0.1]; b) myoclonia frequency (yes/no) (9/26 versus 4/28, P=0.2) and grade (P=0.3); the evolution of mean arterial pressure and heart rate (P=0.3). CONCLUSION Oral weight-related hydroxyzine premedication does not alter BIS-based etomidate induction of GA.
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Affiliation(s)
- M-A Lallemand
- Service d'anesthésie-réanimation, faculté de médecine, université Paris-V-René-Descartes, hôpital Cochin, EA 3623, Assistance publique-Hôpitaux de Paris, 27, rue du Faubourg Saint-Jacques, 75679 Paris cedex 14, France
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Abstract
PURPOSE To further understand a common veterinary anesthetic, propofol (2,6- di-isopropylphenol) and effects of infusion rates on the retinal neurons in Beagle dogs. METHODS Standard full-field blue xenon-flash stimulation elicited responses of dark-adapted eyes, which were recorded from dogs before and after a propofol infusion rate increase. RESULTS Electroretinogram b-waves increased significantly after the infusion rate increase and decreased with decline (P < 0.0001). Also, a weak significance (P = 0.041) for a-wave peak amplitude increase was found after infusion rate increase. The initial part (first 18 ms) of the leading edge of the a-wave remained unchanged. No significant differences in times to a- and b-wave peaks were found. CONCLUSION Enhanced b-wave response and decline is due to sensitivity of postreceptoral cells, possibly interplexiform and amacrine cells, to propofol concentration.
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Affiliation(s)
- Bertel Kommonen
- Section of Surgery, Department of Clinical Veterinary Medicine, University of Helsinki, Finland.
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175
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Abstract
BACKGROUND Some drugs used for sedation and anesthesia produce histopathologic central nervous system changes in juvenile animal models. These observations have raised concerns regarding the use of these drugs in pediatric patients. We summarized the findings in developing animals and describe the steps that the Food and Drug Administration (FDA) and others are taking to assess potential risks in pediatric patients. The FDA views this communication as opening a dialog with the anesthesia community to address this issue. METHODS We reviewed the available animal studies literature examining the potential neurotoxic effects of commonly used anesthetic drugs on the developing brain. The search strategy involved crossing the keywords neurotoxic and neuroapoptosis with the following general and specific terms: anesthetic, N-methyl-d-aspartate (NMDA), ketamine, midazolam, lorazepam, fentanyl, methadone, morphine, meperidine, isoflurane, nitrous oxide, sevoflurane, halothane, enflurane, desflurane, propofol, etomidate, barbiturate, methoxyflurane, and chloral hydrate. We summarized several studies sponsored by the FDA in rats and monkeys, initially examining the potential for ketamine, as a prototypical agent, to induce neurodegeneration in the developing brain. RESULTS Numerous animal studies in rodents indicate that NMDA receptor antagonists, including ketamine, induce neurodegeneration in the developing brain. The effects of ketamine are dose dependent. The data suggest that limiting exposure limits the potential for neurodegeneration. There is also evidence that other general anesthetics, such as isoflurane, can induce neurodegeneration in rodent models, which may be exacerbated by concurrent administration of midazolam or nitrous oxide. There are very few studies that have examined the potential functional consequences of the neurodegeneration noted in the animal models. However, the studies that have been reported suggest subtle, but prolonged, behavioral changes in rodents. Although the doses and durations of ketamine exposure that resulted in neurodegeneration were slightly larger than those used in the clinical setting, those associated with isoflurane were not. There are insufficient human data to either support or refute the clinical applicability of these findings. CONCLUSIONS Animal studies suggest that neurodegeneration, with possible cognitive sequelae, is a potential long-term risk of anesthetics in neonatal and young pediatric patients. The existing nonclinical data implicate not only NMDA-receptor antagonists, but also drugs that potentiate gamma-aminobutyric acid signal transduction, as potentially neurotoxic to the developing brain. The potential for the combination of drugs that have activity at both receptor systems or that can induce more or less neurotoxicity is not clear; however, recent nonclinical data suggest that some combinations may be more neurotoxic than the individual components. The lack of information to date precludes the ability to designate any one anesthetic agent or regimen as safer than any other. Ongoing studies in juvenile animals should provide additional information regarding the risks. The FDA anticipates working with the anesthesia community and pharmaceutical industry to develop strategies for further assessing the safety of anesthetics in neonates and young children, and for providing data to guide clinicians in making the most informed decisions possible when choosing anesthetic regimens for their pediatric patients.
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Affiliation(s)
- R Daniel Mellon
- Division of Anesthesia, Analgesia, and Rheumatology Products, Office of Drug Evaluation II, Center for Drug Evaluation and Research, Food and Drug Administration, Department of Health and Human Services, Silver Spring, Maryland 20993, USA
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Zeller A, Arras M, Jurd R, Rudolph U. Mapping the contribution of beta3-containing GABAA receptors to volatile and intravenous general anesthetic actions. BMC Pharmacol 2007; 7:2. [PMID: 17319964 PMCID: PMC1810244 DOI: 10.1186/1471-2210-7-2] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2006] [Accepted: 02/24/2007] [Indexed: 02/06/2023] Open
Abstract
Background Agents belonging to diverse chemical classes are used clinically as general anesthetics. The molecular targets mediating their actions are however still only poorly defined. Both chemical diversity and substantial differences in the clinical actions of general anesthetics suggest that general anesthetic agents may have distinct pharmacological targets. It was demonstrated previously that the immobilizing action of etomidate and propofol is completely, and the immobilizing action of isoflurane partly mediated, by β3-containing GABAA receptors. This was determined by using the β3(N265M) mice, which carry a point mutation known to decrease the actions of general anesthetics at recombinant GABAA receptors. In this communication, we analyzed the contribution of β3-containing GABAA receptors to the pharmacological actions of isoflurane, etomidate and propofol by means of β3(N265M) mice. Results Isoflurane decreased core body temperature and heart rate to a smaller degree in β3(N265M) mice than in wild type mice, indicating a minor but significant role of β3-containing GABAA receptors in these actions. Prolonged time intervals in the ECG and increased heart rate variability were indistinguishable between genotypes, suggesting no involvement of β3-containing GABAA receptors. The anterograde amnesic action of propofol was indistinguishable in β3(N265M) and wild type mice, suggesting that it is independent of β3-containing GABAA receptors. The increase of heart rate variability and prolongation of ECG intervals by etomidate and propofol were also less pronounced in β3(N265M) mice than in wild type mice, pointing to a limited involvement of β3-containing GABAA receptors in these actions. The lack of etomidate- and propofol-induced immobilization in β3(N265M) mice was also observed in congenic 129X1/SvJ and C57BL/6J backgrounds, indicating that this phenotype is stable across different backgrounds. Conclusion Our results provide evidence for a defined role of β3-containing GABAA receptors in mediating some, but not all, of the actions of general anesthetics, and confirm the multisite model of general anesthetic action. This pharmacological separation of anesthetic endpoints also suggests that subtype-selective substances with an improved side-effect profile may be developed.
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Affiliation(s)
- Anja Zeller
- Institute of Pharmacology and Toxicology, University of Zürich, Winterthurerstr. 190, CH-8057 Switzerland
| | - Margarete Arras
- Institute of Laboratory Animal Science, University of Zürich, Winterthurerstr. 190, CH-8057 Switzerland
| | - Rachel Jurd
- Institute of Pharmacology and Toxicology, University of Zürich, Winterthurerstr. 190, CH-8057 Switzerland
- Ernest Gallo Clinic and Research Center, University of California, San Francisco, 5858 Horton Street, Suite 200, Emeryville, CA 94608, USA
| | - Uwe Rudolph
- Institute of Pharmacology and Toxicology, University of Zürich, Winterthurerstr. 190, CH-8057 Switzerland
- Laboratory of Genetic Neuropharmacology, McLean Hospital, Harvard Medical School, Belmont, MA 02478, USA
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177
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Hara K, Sata T. Inhibitory effect of gabapentin on N-methyl-D-aspartate receptors expressed in Xenopus oocytes. Acta Anaesthesiol Scand 2007; 51:122-8. [PMID: 17073851 DOI: 10.1111/j.1399-6576.2006.01183.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
BACKGROUND Gabapentin (GBP) is a prescription drug used for the treatment of neuropathic and post-operative pain. However, the mechanism by which it exerts its analgesic action is not well understood. Because intrathecal administration of GBP has been shown to exert antinociceptive effects in animal studies, we hypothesized that the spinal cord may be a plausible action site. METHODS We examined the effects of GBP on neurotransmitter-gated ion channels and G protein-coupled inwardly rectifying potassium (GIRK) channels distributed in the spinal cord and involved in pain modulation. Recombinant human NR1/NR2A N-methyl-D-aspartate (NMDA), alpha(1)beta(2)gamma(2S)gamma-aminobutyric acid type A (GABA(A)) or alpha(1) glycine receptors, or GIRK1/GIRK2 channels were expressed in Xenopus laevis oocytes and the effects of GBP (0.1-1000 microM) on them were assessed using a two-electrode, voltage-clamp system. RESULTS GABA(A) and glycine receptors and GIRK channels were not affected by GBP, even at the highest concentrations. Conversely, NMDA receptors were inhibited by GBP in a concentration-dependent manner, with significant inhibition observed at 10 microM. At 30 microM, GBP inhibited the glutamate-concentration response curve without changing the half-maximal effective concentration or the Hill coefficient, indicating a non-competitive inhibition. Glycine decreased the inhibitory effect in a concentration-dependent manner. CONCLUSIONS These findings suggest that the inhibitory effect of GBP on NMDA receptors may play an important role in the antinociceptive property of GBP; however, it does not appear that GABA(A) and glycine receptors or GIRK channels contribute to the pharmacological properties of GBP.
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Affiliation(s)
- K Hara
- Department of Anesthesiology, University of Occupational and Environmental Health, School of Medicine, Kitakyushu, Japan.
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178
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Zeller A, Arras M, Jurd R, Rudolph U. Identification of a Molecular Target Mediating the General Anesthetic Actions of Pentobarbital. Mol Pharmacol 2006; 71:852-9. [PMID: 17164405 DOI: 10.1124/mol.106.030049] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Barbiturates were introduced into medical practice in 1934. They are widely used today as general anesthetics. Although in vitro studies revealed that the activity of a variety of ligand-gated channels is modulated by barbiturates, the target(s) mediating the anesthetic actions of barbiturates in vivo are unknown. Studying pentobarbital action in beta3(N265M) mice harboring beta3-containing GABAA receptors insensitive to a variety of general anesthetic agents, we found that the immobilizing action of pentobarbital is mediated fully, and the hypnotic action is mediated in part by this receptor subtype. It was surprising that the respiratory depressant action of pentobarbital is indistinguishable between beta3(N265M) and wild-type mice and thus is mediated by other as-yet-unidentified targets. Whereas the target for the immobilizing and hypnotic actions of pentobarbital seems to be the same as for etomidate and propofol, these latter agents' respiratory depressant actions are mediated by beta3-containing GABAA receptors. Thus, in contrast to etomidate and propofol, pentobarbital can elicit respiratory depression by a beta3-independent pathway. Pentobarbital reduced heart rate and body temperature to a slightly smaller extent in beta3(N265M) mice compared with wild-type mice, indicating that these actions are largely mediated by other targets. Pentobarbital-induced increase of heart rate variability and prolongation of ECG intervals are seen in both beta3(N265M) mice and wild-type mice, suggesting that they are not dependent on beta3-containing GABAA receptors. In summary, we show a clear pharmacological dissociation of the immobilizing/hypnotic and respiratory/cardiovascular actions of pentobarbital.
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Affiliation(s)
- Anja Zeller
- Institute of Pharmacology and Toxicology, University of Zürich, Switzerland
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179
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Ng KP, Antognini JF. Isoflurane and Propofol Have Similar Effects on Spinal Neuronal Windup at Concentrations that Block Movement. Anesth Analg 2006; 103:1453-8. [PMID: 17122222 DOI: 10.1213/01.ane.0000247732.33602.f5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND We investigated the actions of isoflurane and propofol on neuronal windup in the spinal cord of intact rats. We hypothesized that propofol would depress windup more than isoflurane. METHODS In a cross-over design, rats received 0.8 and 1.2 minimum alveolar concentration (MAC) isoflurane and 0.8 and 1.2 ED50 (effective dose(50%)) of propofol, as recordings were made from single units in the lumbar cord (n = 13). Electrical stimuli were applied (20 stimuli at 0.1, 1, and 3 Hz). Neuronal responses were analyzed for those occurring in the C-fiber range (100-400 ms after each stimulus), combined C-fiber and afterdischarge range (100-1000 ms) and the 100-333 ms range for the 3 Hz stimuli. Absolute windup was also calculated (the sum of action potentials for 20 stimuli - 20 x response to the first stimulus). RESULTS At 1 Hz, total action potentials (mean, standard error) summed across the 20 stimuli (100-1000 ms range) were 571 +/- 106 and 742 +/- 214 for isoflurane (at 0.8 and 1.2 MAC) and 586 +/- 148 and 641 +/- 143 for propofol (at 0.8 and 1.2 ED50), respectively (P = NS); corresponding values for the 0.1 Hz stimuli were 345 +/- 104, 370 +/- 108, 430 +/- 86, and 403 +/- 106 (P = NS), and for the 3 Hz stimuli (100-333 ms range) were 266 +/- 66, 333 +/- 76, 343 +/- 85, and 252 +/- 72 (P = NS). Absolute windup in the 100-1000 ms range was greater for 1.2 MAC isoflurane at 1 Hz (445 +/- 82, P < 0.01), when compared with absolute windup at 0.8 MAC isoflurane and 0.8 and 1.2 ED50 propofol (232 +/- 31, 88 +/- 65, and 210 +/- 41, respectively). CONCLUSIONS These data suggest that isoflurane and propofol have similar effects on neuronal windup in the spinal cord, although there was enhanced absolute windup at 1.2 MAC isoflurane for the 1 Hz stimulus.
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Affiliation(s)
- Kevin P Ng
- Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, California 95616, USA
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180
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Menezes RCA, Fontes MAP. Cardiovascular effects produced by activation of GABA receptors in the rostral ventrolateral medulla of conscious rats. Neuroscience 2006; 144:336-43. [PMID: 17049168 DOI: 10.1016/j.neuroscience.2006.08.062] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2006] [Revised: 08/25/2006] [Accepted: 08/29/2006] [Indexed: 10/23/2022]
Abstract
The rostral ventrolateral medulla (RVLM) has been proposed as a region playing a major role in the tonic and reflex control of sympathetic vasomotor activity and blood pressure. Pharmacological activation of GABA(A) receptors with muscimol in the RVLM of anesthetized rats results in a large fall in mean arterial pressure (MAP), heart rate (HR) and sympathetic activity. In this study we evaluated the effects of activation of GABA receptors in the RVLM of conscious, freely moving rats. Bilateral microinjections of muscimol into the RVLM of conscious rats produced a large fall in MAP (-38+/-4 mm Hg, n=7) when compared with saline injections (NaCl 0.9%, 7+/-1 mm Hg, n=4). The decrease in MAP evoked by muscimol was accompanied by a significant increase in HR (muscimol 69+/-13 bpm vs. vehicle -33+/-12 bpm, P<0.05), an effect that was completely abolished by beta1 adrenergic receptor blockade. Conversely, bilateral microinjections of GABA(B) agonist, baclofen, evoked a pressor response, but in this case, the increase was not significantly different from that evoked by vehicle injections. These results 1) indicate that GABA(A) receptors have a powerful influence on the resting activity of RVLM neurons in conscious rats; 2) indicate that a compensatory sympathetic-mediated tachycardia is present after inhibition of RVLM neurons in conscious rats; 3) confirm and extend previous findings showing that RVLM neurons are critical for blood pressure maintenance even in normal non-anesthetized conditions.
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Affiliation(s)
- R C A Menezes
- Hypertension Laboratory, Department of Physiology, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG 31270 901, Brazil
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181
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Antognini JF, Atherley RJ, Laster MJ, Carstens E, Dutton RC, Eger EI. A method for recording single unit activity in lumbar spinal cord in rats anesthetized with nitrous oxide in a hyperbaric chamber. J Neurosci Methods 2006; 160:215-22. [PMID: 17045342 PMCID: PMC2693129 DOI: 10.1016/j.jneumeth.2006.09.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2006] [Revised: 08/31/2006] [Accepted: 09/05/2006] [Indexed: 11/24/2022]
Abstract
The limited potency of nitrous oxide mandates the use of a hyperbaric chamber to produce anesthesia. Use of a hyperbaric chamber complicates anesthetic delivery, ventilation, and electrophysiological recording. We constructed a hyperbaric acrylic-aluminum chamber allowing recording of single unit activity in spinal cord of rats anesthetized only with N(2)O. Large aluminum plates secured to each other by rods that span the length of the chamber close each end of the chamber. The 122 cm long, 33 cm wide chamber housed ventilator, intravenous infusion pumps, recording headstage, including hydraulic microdrive and stepper motors (controlled by external computers). Electrical pass-throughs in the plates permitted electrical current or signals to enter or leave the chamber. In rats anesthetized only with N(2)O we recorded extracellular action potentials with a high signal-to-noise ratio. We also recorded electroencephalographic activity. This technique is well-suited to study actions of weak anesthetics such as N(2)O and Xe at working pressures of 4-5 atm or greater. The safety of such pressures depends on the wall thickness and chamber diameter.
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Affiliation(s)
- Joseph F Antognini
- Department of Anesthesiology and Pain Medicine, University of California, Davis, TB-170, Davis, CA 95616, USA.
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182
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Colloc'h N, Sopkova-de Oliveira Santos J, Retailleau P, Vivarès D, Bonneté F, Langlois d'Estainto B, Gallois B, Brisson A, Risso JJ, Lemaire M, Prangé T, Abraini JH. Protein crystallography under xenon and nitrous oxide pressure: comparison with in vivo pharmacology studies and implications for the mechanism of inhaled anesthetic action. Biophys J 2006; 92:217-24. [PMID: 17028130 PMCID: PMC1697869 DOI: 10.1529/biophysj.106.093807] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In contrast with most inhalational anesthetics, the anesthetic gases xenon (Xe) and nitrous oxide (N(2)O) act by blocking the N-methyl-d-aspartate (NMDA) receptor. Using x-ray crystallography, we examined the binding characteristics of these two gases on two soluble proteins as structural models: urate oxidase, which is a prototype of a variety of intracellular globular proteins, and annexin V, which has structural and functional characteristics that allow it to be considered as a prototype for the NMDA receptor. The structure of these proteins complexed with Xe and N(2)O were determined. One N(2)O molecule or one Xe atom binds to the same main site in both proteins. A second subsite is observed for N(2)O in each case. The gas-binding sites are always hydrophobic flexible cavities buried within the monomer. Comparison of the effects of Xe and N(2)O on urate oxidase and annexin V reveals an interesting relationship with the in vivo pharmacological effects of these gases, the ratio of the gas-binding sites' volume expansion and the ratio of the narcotic potency being similar. Given these data, we propose that alterations of cytosolic globular protein functions by general anesthetics would be responsible for the early stages of anesthesia such as amnesia and hypnosis and that additional alterations of ion-channel membrane receptor functions are required for deeper effects that progress to "surgical" anesthesia.
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Affiliation(s)
- Nathalie Colloc'h
- Centre CYCERON, UMR 6185, Université de Caen--CNRS, 14074 Caen cedex, France
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183
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Xie Z, Herring BE, Fox AP. Excitatory and inhibitory actions of isoflurane in bovine chromaffin cells. J Neurophysiol 2006; 96:3042-50. [PMID: 16956992 DOI: 10.1152/jn.00571.2006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Isoflurane, a halogenated volatile anesthetic, is thought to produce anesthesia by depressing CNS function. Many anesthetics, including isoflurane, are thought to modulate and/or directly activate GABA(A) receptors. Chromaffin cells are known to express functional GABA(A) receptors. We previously showed that activation of the GABA(A) receptors, with specific agonists, leads to cellular excitation resulting from the depolarized anion equilibrium potential. In this study, our goal was to determine whether isoflurane mimicked this response and to explore the functional consequences of this activation. Furthermore, we sought to study the actions of isoflurane on nicotinic acetylcholine receptors (nAChRs) as they mediate the "sympathetic drive" in these cells. For these studies the Ca(2+)-indicator dye fura-2 was used to assay [Ca(2+)](i). Amperometric measurements were used to assay catecholamine release. We show that bovine adrenal chromaffin cells were excited by isoflurane at clinically relevant concentrations. Isoflurane directly activated GABA(A) receptors found in chromaffin cells, which depolarized the cells and elevated [Ca(2+)](i). Application of isoflurane directly to the chromaffin cells elicited catecholamine secretion from these cells. At the same time, isoflurane suppressed activation of nAChRs, which presumably blocks "sympathetic drive" to the chromaffin cells. These latter results may help explain why isoflurane produces the hypotension observed clinically.
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Affiliation(s)
- Z Xie
- The University of Chicago, Dept. of Anesthesia and Critical Care, 5841 S. Maryland, MC 4028, Chicago, IL 60637, USA.
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184
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Wegner FV, Both M, Fink RHA, Friedrich O. Elementary Ca2+ release events in mammalian skeletal muscle: effects of the anaesthetic drug thiopental. J Muscle Res Cell Motil 2006; 27:315-26. [PMID: 16897573 DOI: 10.1007/s10974-006-9092-3] [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: 05/09/2006] [Accepted: 07/13/2006] [Indexed: 02/04/2023]
Abstract
We examined the effect of clinically relevant doses of thiopental (10-100 microM) on Ca2+ release from the sarcoplasmic reticulum of chemically skinned skeletal muscle fibres of the mouse. Elementary Ca2+ release events (ECRE) were recorded with confocal microscopy and were detected and analysed by an automated algorithm. Thiopental at 25 microM evoked a marked increase in ECRE frequency (events/100 microm/s) from 0.64 +/- 0.32 to 1.56 +/- 0.38 (P < 0.001). Incubation with 5 microM ryanodine significantly reduced spontaneous and evoked ECRE frequencies to 0.08 +/- 0.08 (P < 0.001) and 0.39 +/- 0.25 (25 microM thiopental, P < 0.001) respectively. Thiopental-evoked ECRE show different morphological characteristics compared to spontaneous events. Maximum relative amplitudes (DeltaF/F0)max and spatial width (full width at half maximum) of the events were substantially increased. Full duration at half maximum was increased and some very long events (200 ms compared to approximately 30 ms standard) were produced. The rise times as an indicator of the channel open time were slightly increased. Furthermore, the occurrence of repetitive ECRE was observed. These events, in contrast to previous observations in amphibian skeletal muscle fibres, displayed a multitude of different release patterns. In particular, a repetitive ECRE mode with successively decaying amplitudes was identified and the inter-event intervals were analysed. Estimation of the underlying Ca2+ release current suggests that during repetitive events with a decaying amplitude a decreasing amount of Ca2+ was released within the individual release event. Possible underlying mechanisms are discussed. In summary, thiopental seems to be a potent RyR1 agonist and substantially alters the gating mechanisms of RyR Ca2+ release channel clusters already in clinically relevant doses, i.e. doses administered during general anaesthesia.
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Affiliation(s)
- F v Wegner
- Medical Biophysics, Institute for Physiology and Pathophysiology, University of Heidelberg, INF 326, D-69120, Heidelberg, Germany
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185
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Vemparala S, Saiz L, Eckenhoff RG, Klein ML. Partitioning of anesthetics into a lipid bilayer and their interaction with membrane-bound peptide bundles. Biophys J 2006; 91:2815-25. [PMID: 16877515 PMCID: PMC1578482 DOI: 10.1529/biophysj.106.085324] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Molecular dynamics simulations have been performed to investigate the partitioning of the volatile anesthetic halothane from an aqueous phase into a coexisting hydrated bilayer, composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipids, with embedded alpha-helical peptide bundles based on the membrane-bound portions of the alpha- and delta-subunits, respectively, of nicotinic acetylcholine receptor. In the molecular dynamics simulations halothane molecules spontaneously partitioned into the DOPC bilayer and then preferentially occupied regions close to lipid headgroups. A single halothane molecule was observed to bind to tyrosine (Tyr-277) residue in the alpha-subunit, an experimentally identified specific binding site. The binding of halothane attenuated the local loop dynamics of alpha-subunit and significantly influenced global concerted motions suggesting anesthetic action in modulating protein function. Steered molecular dynamics calculations on a single halothane molecule partitioned into a DOPC lipid bilayer were performed to probe the free energy profile of halothane across the lipid-water interface and rationalize the observed spontaneous partitioning. Partitioned halothane molecules affect the hydrocarbon chains of the DOPC lipid, by lowering of the hydrocarbon tilt angles. The anesthetic molecules also caused a decrease in the number of peptide-lipid contacts. The observed local and global effects of anesthetic binding on protein motions demonstrated in this study may underlie the mechanism of action of anesthetics at a molecular level.
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Affiliation(s)
- Satyavani Vemparala
- Department of Chemistry and Center for Molecular Modeling, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
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186
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Vahle-Hinz C, Detsch O, Siemers M, Kochs E. Contributions of GABAergic and glutamatergic mechanisms to isoflurane-induced suppression of thalamic somatosensory information transfer. Exp Brain Res 2006; 176:159-72. [PMID: 16847609 DOI: 10.1007/s00221-006-0604-6] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2005] [Accepted: 06/14/2006] [Indexed: 12/01/2022]
Abstract
Indications for a pivotal role of the thalamocortical network in producing the state of anesthesia have come from in vivo animal studies as well as imaging studies in humans. We studied possible synaptic mechanisms of anesthesia-induced suppression of touch perception in the rat's thalamus. Thalamocortical relay neurons (TCNs) receive ascending and descending glutamatergic excitatory inputs via NMDA and non-NMDA receptors (AMPAR) and are subjected to GABA(A)ergic inhibitory input which shapes the sensory information conveyed to the cortex. The involvement of these synaptic receptors in the suppressive effects of the prototypic volatile anesthetic isoflurane was assessed by local iontophoretic administration of receptor agonists/antagonists during extracellular recordings of TCNs of the ventral posteromedial nucleus responding to whisker vibration in rats anesthetized with isoflurane concentrations of approximately 0.9 vol.% (baseline) and approximately 1.9 vol.% (ISO high). ISO high induced a profound suppression of response activity reflected by a conversion of the sustained vibratory responses to ON responses. Administration of NMDA, AMPA, or GABA(A)R antagonists caused a reversal to sustained responses in 88, 94 and 88% of the neurons, respectively, with a recovery to baseline levels of response activity. The data show that the block of thalamocortical transfer of tactile information under ISO high may result from an enhancement of GABA(A)ergic inhibition and/or a reduction of glutamatergic excitation. Furthermore, they show that the ascending vibratory signals still reach the thalamic neurons under the high isoflurane concentration, indicating that this input is resistant to isoflurane while the attenuation of excitation may be brought about at the corticothalamic glutamatergic facilitatory input.
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Affiliation(s)
- Christiane Vahle-Hinz
- Institut für Neurophysiologie und Pathophysiologie, Zentrum für Experimentelle Medizin, Universitätsklinikum Hamburg-Eppendorf, Martinistr. 52, 20246, Hamburg, Germany.
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187
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Sinner B, Friedrich O, Zink W, Fink RHA, Graf BM. GABAmimetic intravenous anaesthetics inhibit spontaneous Ca2+ -oscillations in cultured hippocampal neurons. Acta Anaesthesiol Scand 2006; 50:742-8. [PMID: 16987371 DOI: 10.1111/j.1399-6576.2006.01031.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
BACKGROUND Spontaneous Ca2+ -oscillations are a possible mechanism of Ca2+ -mediated signal transduction in neurons. They develop by a periodical interplay of Ca2+, which enters the neuron from the extracellular medium and triggers Ca2+ release from the endoplasmic reticulum (ER). Ca2+ -oscillations are terminated by reuptake into the ER or plasmalemmal extrusion. Spontaneous Ca2+ -oscillations are glutamate dependent and appear to be responsible for neuronal plasticity and integration of information. Here, we examined the role of the gamma-aminobutyric acid (GABAA) receptor on spontaneous Ca2+ -oscillations and studied the effects of the anaesthetics midazolam, thiopental and the non-anesthetic barbituric acid on spontaneous Ca2+ -oscillations. METHODS Hippocampal neuronal cell cultures of 19-day-old embryonic Wistar rats 17-18 days in culture were loaded with the Ca2+ -sensitive dye Fura-2AM. Experiments were performed using dual wave-length excitation fluorescence microscopy and calibration constants were obtained from in situ calibration. RESULTS Spontaneous Ca2+ -oscillations are influenced by the GABAA receptor. The intravenous anaesthetics midazolam and thiopental suppressed the amplitude and frequency reversibly in a dose-dependent manner with EC50 in clinically relevant concentrations. This effect was mediated via the GABAA receptor as it could be reversed by the GABAA receptor antagonist bicuculline. In contrast, the application of barbituric acid had no effects on the spontaneous Ca2+ -oscillations. CONCLUSION Spontaneous Ca2+ -oscillations are influenced by the GABAA receptor. Spontaneous Ca2+ -oscillations might represent an interesting model system to study anaesthetic mechanisms on neuronal information processing.
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Affiliation(s)
- B Sinner
- Zentrum Anaesthesiologie, Rettungs- und Intensivmedizin Universität Göttingen, Göttingen, Germany
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188
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David HN, Ansseau M, Lemaire M, Abraini JH. Nitrous oxide and xenon prevent amphetamine-induced carrier-mediated dopamine release in a memantine-like fashion and protect against behavioral sensitization. Biol Psychiatry 2006; 60:49-57. [PMID: 16427030 DOI: 10.1016/j.biopsych.2005.10.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/27/2005] [Revised: 09/27/2005] [Accepted: 10/12/2005] [Indexed: 10/25/2022]
Abstract
BACKGROUND Amphetamine administration induces stimulation-independent dopamine release in the nucleus accumbens (NAcc) through reverse dopamine transport, a critical neurochemical event involved in its psychostimulant action, and furthermore decreases stimulation-dependent vesicular dopamine release. These effects may involve possible indirect glutamatergic mechanisms. METHODS We investigated the effects of nitrous oxide and xenon, which possess antagonistic action at the N-methyl-D-aspartate (NMDA) receptor, on brain slices ex vivo on amphetamine-induced changes in carrier-mediated and KCl-evoked dopamine release in the NAcc, and in vivo on amphetamine-induced locomotor sensitization. RESULTS Like the low-affinity NMDA receptor antagonist memantine, but not the prototypical compound MK-801, nitrous oxide and xenon at appropriate concentrations blocked both the increase in carrier-mediated dopamine release and locomotor sensitization produced by amphetamine. CONCLUSIONS In contrast to what has generally been found using prototypical NMDA receptor antagonists, these data regarding the effect of memantine, nitrous oxide, and xenon support the hypothesis that activation of certain NMDA receptors (possibly those containing the NR1a/NR2D subunit) in the NAcc is involved in the amphetamine-induced increase in carrier-mediated dopamine release and the development of behavioral sensitization to amphetamine. Nitrous oxide, xenon, and memantine may be of therapeutic interest for treating drug dependence.
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189
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Campagna-Slater V, Weaver DF. Molecular modelling of the GABAA ion channel protein. J Mol Graph Model 2006; 25:721-30. [PMID: 16877018 DOI: 10.1016/j.jmgm.2006.06.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2006] [Revised: 06/08/2006] [Accepted: 06/12/2006] [Indexed: 10/24/2022]
Abstract
The GABAA ion channel protein is central to the mechanism of action of general anaesthetics and thus to the phenomenon of human consciousness. A molecular model of the alpha1beta2gamma2 gamma-aminobutyric acid type-A (GABAA) ligand-gated ion channel protein has been constructed. The cryo-electron microscopy structure of the nicotinic acetylcholine receptor (nAChR) from Torpedo marmorata and the X-ray crystal structure of the acetylcholine binding protein (AChBP) from Lymnaea stagnalis were used as starting templates for comparative modelling. Features of the modelling approach used in the development of this GABAA model include: (1) multiple sequence alignment of members of the Cys-loop superfamily; (2) the design and implementation of a quasi-ab initio loop modelling algorithm; (3) expansion of the transmembrane domain (TMD) ion pore to model the open-state of the GABAA channel; (4) hydrophobicity analysis of the TMD to refine the structure in regions involved in general anaesthetic binding. The final model of the alpha1beta2gamma2 GABAA protein agrees with available experimental data concerning general anaesthetics.
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190
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Weir CJ. The molecular mechanisms of general anaesthesia: dissecting the GABA A receptor. ACTA ACUST UNITED AC 2006. [DOI: 10.1093/bjaceaccp/mki068] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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191
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Elsen FP, Liljelund P, Werner DF, Olsen RW, Homanics GE, Harrison NL. GABAA-R α1 subunit knockin mutation leads to abnormal EEG and anesthetic-induced seizure-like activity in mice. Brain Res 2006; 1078:60-70. [PMID: 16490182 DOI: 10.1016/j.brainres.2006.01.036] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2005] [Revised: 01/11/2006] [Accepted: 01/16/2006] [Indexed: 11/19/2022]
Abstract
Gamma-aminobutyric acid-type A receptors (GABA(A)-Rs) have been proposed as a target for many general anesthetics. We recently created knockin (KI) mice harboring a point mutation (serine 270 to histidine) in the GABA(A)-R alpha1 subunit. This mutation abolishes sensitivity of recombinant GABA(A)-Rs to isoflurane while maintaining normal sensitivity to halothane and increasing the potency of GABA. KI mice showed abnormalities in the EEG baseline, including occasional spike-wave activity and spindle-like bursts. When anesthetized with isoflurane, the KI mice but not the control mice revealed repetitive 4-5 Hz slow wave discharges in the cortical EEG. KI mice did not differ from controls in response to isoflurane or halothane in the standard tail clamp/withdrawal and loss of righting reflex assays. We recorded miniature inhibitory postsynaptic currents (mIPSCs) from hippocampal interneurons and pyramidal cells in brain slices. mIPSCs in neurons from KI mice were of normal amplitude, but decayed more slowly than controls. Hippocampal mIPSCs in control mice were significantly prolonged by 0.4 and 0.9 MAC isoflurane, and by 0.5 MAC halothane. In KI mice, the effect of isoflurane on mIPSC decay was dramatically reduced, while halothane prolonged mIPSCs as for controls. We conclude that the kinetic and pharmacological properties of hippocampal GABA(A)-Rs in the KI mouse recapitulate many features of mutant alpha1beta2gamma2 GABA(A)-Rs observed in vitro. GABA(A)-Rs containing alpha1 subunits do not appear to contribute to the actions of isoflurane in the spinal cord, but both EEG and synaptic recordings provide evidence for effects of isoflurane on these GABA(A)-R isoforms in cortical structures.
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Affiliation(s)
- Frank P Elsen
- Department of Anesthesiology, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10021, USA
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192
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Chen X, Sirois JE, Lei Q, Talley EM, Lynch C, Bayliss DA. HCN subunit-specific and cAMP-modulated effects of anesthetics on neuronal pacemaker currents. J Neurosci 2006; 25:5803-14. [PMID: 15958747 PMCID: PMC6724885 DOI: 10.1523/jneurosci.1153-05.2005] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
General anesthetics have been a mainstay of surgical practice for more than 150 years, but the mechanisms by which they mediate their important clinical actions remain unclear. Ion channels represent important anesthetic targets, and, although GABA(A) receptors have emerged as major contributors to sedative, immobilizing, and hypnotic effects of intravenous anesthetics, a role for those receptors is less certain in the case of inhalational anesthetics. The neuronal hyperpolarization-activated pacemaker current (Ih) is essential for oscillatory and integrative properties in numerous cell types. Here, we show that clinically relevant concentrations of inhalational anesthetics modulate neuronal Ih and the corresponding HCN channels in a subunit-specific and cAMP-dependent manner. Anesthetic inhibition of Ih involves a hyperpolarizing shift in voltage dependence of activation and a decrease in maximal current amplitude; these effects can be ascribed to HCN1 and HCN2 subunits, respectively, and both actions are recapitulated in heteromeric HCN1-HCN2 channels. Mutagenesis and simulations suggest that apparently distinct actions of anesthetics on V(1/2) and amplitude represent different manifestations of a single underlying mechanism (i.e., stabilization of channel closed state), with the predominant action determined by basal inhibition imposed by individual subunit C-terminal domains and relieved by cAMP. These data reveal a molecular basis for multiple actions of anesthetics on neuronal HCN channels, highlight the importance of proximal C terminus in modulation of HCN channel gating by diverse agents, and advance neuronal pacemaker channels as potentially relevant targets for clinical actions of inhaled anesthetics.
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Affiliation(s)
- Xiangdong Chen
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908, USA
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193
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194
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Arias HR, Bhumireddy P, Bouzat C. Molecular mechanisms and binding site locations for noncompetitive antagonists of nicotinic acetylcholine receptors. Int J Biochem Cell Biol 2006; 38:1254-76. [PMID: 16520081 DOI: 10.1016/j.biocel.2006.01.006] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2005] [Revised: 01/03/2006] [Accepted: 01/12/2006] [Indexed: 01/16/2023]
Abstract
Nicotinic acetylcholine receptors are pentameric proteins that belong to the Cys-loop receptor superfamily. Their essential mechanism of functioning is to couple neurotransmitter binding, which occurs at the extracellular domain, to the opening of the membrane-spanning cation channel. The function of these receptors can be modulated by structurally different compounds called noncompetitive antagonists. Noncompetitive antagonists may act at least by two different mechanisms: a steric and/or an allosteric mechanism. The simplest idea representing a steric mechanism is that the antagonist molecule physically blocks the ion channel. On the other hand, there exist distinct allosteric mechanisms. For example, noncompetitive antagonists may bind to the receptor and stabilize a nonconducting conformational state (e.g., resting or desensitized state), and/or increase the receptor desensitization rate. Barbiturates, dissociative anesthetics, antidepressants, and neurosteroids have been shown to inhibit nicotinic receptors by allosteric mechanisms and/or by open- and closed-channel blockade. Receptor modulation has proved to be highly complex for most noncompetitive antagonists. Noncompetitive antagonists may act by more than one mechanism and at distinct sites in the same receptor subtype. The binding site location for one particular molecule depends on the conformational state of the receptor. The mechanisms of action and binding affinities of noncompetitive antagonists differ among nicotinic receptor subtypes. Knowledge of the structure of the nicotinic acetylcholine receptor, the location of its noncompetitive antagonist binding sites, and the mechanisms of inhibition will aid the design of new and more efficacious drugs for treatment of neurological diseases.
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Affiliation(s)
- Hugo R Arias
- Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, 309 E. Second Street, Pomona, CA 91766-1854, USA.
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195
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Imas OA, Ropella KM, Ward BD, Wood JD, Hudetz AG. Volatile anesthetics disrupt frontal-posterior recurrent information transfer at gamma frequencies in rat. Neurosci Lett 2005; 387:145-50. [PMID: 16019145 DOI: 10.1016/j.neulet.2005.06.018] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2005] [Revised: 05/13/2005] [Accepted: 06/08/2005] [Indexed: 01/13/2023]
Abstract
We seek to understand neural correlates of anesthetic-induced unconsciousness. We hypothesize that cortical integration of sensory information may underlie conscious perception and may be disrupted by anesthetics. A critical role in frontal-posterior interactions has been proposed, and gamma (20-60 Hz) oscillations have also been assigned an essential role in consciousness. Here we investigated whether general anesthetics may interfere with the exchange of information encoded in gamma oscillations between frontal and posterior cortices. Bipolar electrodes for recording of event-related potentials (ERP) were chronically implanted in the primary visual cortex, parietal association and frontal association cortices of six rats. Sixty light flashes were presented every 5s, and ERPs were recorded at increasing concentrations of halothane or isoflurane (0-2%). Information exchange was estimated by transfer entropy, a novel measure of directional information transfer. Transfer entropy was calculated from 1-s wavelet-transformed ERPs. We found that (1) feedforward transfer entropy (FF-TE) and feedback transfer entropy (FB-TE) were balanced in conscious-sedated state; (2) anesthetics at concentrations producing unconsciousness augmented both FF-TE and FB-TE at 30 Hz but reduced them at 50 Hz; (3) reduction at 50 Hz was more pronounced for FB-TE, especially between frontal and posterior regions; (4) at high concentrations, both FF-TE and FB-TE at all frequencies were at or below conscious-sedated baseline. Our findings suggest that inhalational anesthetics preferentially impair frontal-posterior FB information transfer at high gamma frequencies consistent with the postulated role of frontal-posterior interactions in consciousness.
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Affiliation(s)
- Olga A Imas
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, 8701 Watertown Plank Rd., Milwaukee, WI 53226, USA
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Hara K, Yamakura T, Sata T, Harris RA. The effects of anesthetics and ethanol on alpha2 adrenoceptor subtypes expressed with G protein-coupled inwardly rectifying potassium channels in Xenopus oocytes. Anesth Analg 2005; 101:1381-1388. [PMID: 16243998 DOI: 10.1213/01.ane.0000180190.05238.d5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
A wide range of physiological effects are mediated by alpha2-adrenoceptors (ARs) through their association with G protein-coupled inwardly rectifying potassium (GIRK) channels. Although alpha2-ARs are divided into three subtypes (alpha2A-C), a pharmacological distinction among the subtypes is difficult to establish because of the lack of a selective agonist and antagonist; therefore, little is known about the effects of anesthetics on the alpha2-AR subtypes. We expressed each subtype together with GIRK1/GIRK2 subunits in Xenopus oocytes and observed alpha2-AR-mediated GIRK1/GIRK2 currents to test the effects of ethanol, halothane, and several IV anesthetics at clinical concentrations. UK 14,304, a selective alpha2-AR agonist, evoked GIRK1/GIRK2 currents in every subtype. None of the IV anesthetics, which included pentobarbital, propofol, ketamine, and alphaxalone, influenced UK 14,304-evoked potassium currents in any of the receptor subtypes. Ethanol enhanced the UK 14,304-evoked potassium currents, whereas halothane inhibited the currents. However, these effects were not significantly different from those on the baseline-GIRK1/GIRK2 current, suggesting that neither ethanol nor halothane acts directly on the alpha2-AR subtypes. Although none of the drugs examined had any effect on the alpha2-ARs, the physiological actions of the alpha2-ARs mediated by the GIRK1/GIRK2 channels may be affected by ethanol and halothane.
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Affiliation(s)
- Koji Hara
- *Waggoner Center for Alcohol and Addiction Research and Institute for Cellular and Molecular Biology, University of Texas at Austin; †Department of Anesthesiology, University of Occupational and Environmental Health, School of Medicine, Kitakyushu; and ‡Division of Anesthesiology, Niigata University Graduate School of Medical and Dental Sciences, Japan
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Liefaard LC, Ploeger BA, Molthoff CFM, Boellaard R, Lammertsma AA, Danhof M, Voskuyl RA. Population Pharmacokinetic Analysis for Simultaneous Determination of B max and K D In Vivo by Positron Emission Tomography. Mol Imaging Biol 2005; 7:411-21. [PMID: 16328648 DOI: 10.1007/s11307-005-0022-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
PURPOSE Changes in GABA(A)-receptor density and affinity play an important role in many forms of epilepsy. A novel approach, using positron emission tomography (PET) and [C-11]flumazenil ([C-11]FMZ), was developed for simultaneous estimation of GABA(A)-receptor properties, characterized by B (max) and K (D). PROCEDURES Following an injection of [C-11]FMZ (dose range: 1-2,000 mug) to 21 rats, concentration time curves of FMZ in brain (using PET) and blood (using HPLC-UV) were analyzed simultaneously using a population pharmacokinetic (PK) model, containing expressions to describe the time course of the plasma concentration (including distribution to the body), the brain distribution, and the specific binding within the brain. RESULTS Application of this method in control rats resulted in estimates of B (max) and K (D) (14.5 +/- 3.7 ng/ml and 4.68 +/- 1.5 ng/ml, respectively). CONCLUSIONS The proposed population PK model allowed for simultaneous estimation of B (max) and K (D) for a group of animals using single injection PET experiments per animal.
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Affiliation(s)
- Lia C Liefaard
- Division of Pharmacology, LACDR, Leiden University, P.O. Box 9502, 2300 RA, Leiden, The Netherlands
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Mashour GA, Forman SA, Campagna JA. Mechanisms of general anesthesia: from molecules to mind. Best Pract Res Clin Anaesthesiol 2005; 19:349-64. [PMID: 16013686 DOI: 10.1016/j.bpa.2005.01.004] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Despite the widespread presence of clinical anesthesiology in medical practice, the mechanism by which diverse inhalational agents result in the state of general anesthesia remains unknown. Over recent decades, our understanding of general anesthetic mechanisms has evolved dramatically from early unitary hypotheses, largely due to the development and influence of a myriad of scientific disciplines ranging from molecular biology to cognitive neuroscience. These discoveries have led to a renaissance of investigation into the mechanisms of general anesthetics and have generated both novel answers and questions. In this chapter, we review the major hypotheses of general anesthetic mechanisms of action and present an expanded overview of current investigation into those mechanisms. We also present a framework to aid in thinking about the actions of these agents, highlighting the relationship between putative targets at the molecular level and the more integrated functional changes in behavior and consciousness.
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Affiliation(s)
- George A Mashour
- Harvard Medical School, and Massachusetts General Hospital, Boston, MA 02114, USA.
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199
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Orth M, Barter L, Dominguez C, Atherley R, Carstens E, Antognini JF. Halothane and propofol differentially affect electroencephalographic responses to noxious stimulation. Br J Anaesth 2005; 95:477-84. [PMID: 16051650 DOI: 10.1093/bja/aei208] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND Anaesthetics blunt neuronal responses to noxious stimulation, including effects on electroencephalographic (EEG) responses. It is unclear how anaesthetics differ in their ability to modulate noxious stimulation-evoked EEG activation. We investigated the actions of propofol and halothane on EEG responses to noxious stimuli, including repetitive electrical C-fibre stimulation, which normally evokes neuronal wind-up. METHODS Rats were anaesthetized with halothane (n=8) or propofol (n=8), at 0.8x or 1.2x the amount required to produce immobility in response to tail clamping [minimum alveolar concentration (MAC) for halothane and median effective dose (ED(50)) for propofol]. We recorded EEG responses to repetitive electrical stimulus trains (delivered to the tail at 0.1, 1 and 3 Hz) as well as supramaximal noxious tail stimulation (clamp; 50 Hz electrical stimulus, each for 30 s). RESULTS Under halothane anaesthesia, noxious stimuli evoked an EEG activation response manifested by increased spectral edge frequency (SEF) and median edge frequency (MEF). At 0.8 MAC halothane, the tail clamp increased the MEF from approximately 6 to approximately 8.5 Hz, and the SEF from approximately 25.5 to approximately 27 Hz. At both 0.8 and 1.2 MAC halothane, similar patterns of EEG activation were observed with the 1 Hz, 3 Hz and tetanic stimulus trains, but not with 0.1 Hz stimulation, which does not evoke wind-up. Under propofol anaesthesia, noxious stimuli were generally ineffective in causing EEG activation. At 0.8 ED(50) propofol, only the tail clamp and 1 Hz stimuli increased MEF ( approximately 8 to approximately 10-10.5 Hz). At the higher propofol infusion rate (1.2 ED(50)) the repetitive electrical stimuli did not evoke an EEG response, but the tetanic stimulus and the tail clamp paradoxically decreased SEF (from approximately 23 to approximately 21.5 Hz). CONCLUSIONS Propofol has a more significant blunting effect on EEG responses to noxious stimulation compared with halothane.
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Affiliation(s)
- M Orth
- Department of Anesthesiology and Pain Medicine, University of California, Davis, 95616, USA
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Hemmings HC, Akabas MH, Goldstein PA, Trudell JR, Orser BA, Harrison NL. Emerging molecular mechanisms of general anesthetic action. Trends Pharmacol Sci 2005; 26:503-10. [PMID: 16126282 DOI: 10.1016/j.tips.2005.08.006] [Citation(s) in RCA: 372] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2005] [Revised: 07/18/2005] [Accepted: 08/12/2005] [Indexed: 10/25/2022]
Abstract
General anesthetics are essential to modern medicine, and yet a detailed understanding of their mechanisms of action is lacking. General anesthetics were once believed to be "drugs without receptors" but this view has been largely abandoned. During the past decade significant progress in our understanding of the mechanisms of general anesthetic action at the molecular, cellular and neural systems levels has been made. Different molecular targets in various regions of the nervous system are involved in the multiple components of anesthetic action, and these targets can vary between specific anesthetics. Neurotransmitter-gated ion channels, particularly receptors for GABA and glutamate, are modulated by most anesthetics, at both synaptic and extrasynaptic sites, and additional ion channels and receptors are also being recognized as important targets for general anesthetics. In this article, these developments, which have important implications for the development of more-selective anesthetics, are reviewed in the context of recent advances in ion channel structure and function.
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Affiliation(s)
- Hugh C Hemmings
- Departments of Anesthesiology and Pharmacology, Weill Cornell Medical College, 1300 York Avenue, Box 50, New York, NY 10021, USA.
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