Faculty Opinions recommendation of Anesthetics interfere with axon guidance in developing mouse neocortical neurons in vitro via a γ-aminobutyric acid type A receptor mechanism.

2013 ◽  
Author(s):  
Vesna Jevtovic-Todorovic
Keyword(s):  
Axon Guidance ◽  
Type A ◽  
Aminobutyric Acid ◽  
Neocortical Neurons ◽  
Acid Type

scholarly journals Anesthetics Interfere with Axon Guidance in Developing Mouse Neocortical Neurons In Vitro via a γ-Aminobutyric Acid Type A Receptor Mechanism

2013 ◽  
Vol 118 (4) ◽  
pp. 825-833 ◽  
Author(s):  
C. David Mintz ◽  
Kendall M. S. Barrett ◽  
Sarah C. Smith ◽  
Deanna L. Benson ◽  
Neil L. Harrison
Keyword(s):  
Axon Guidance ◽  
Growth Cone ◽  
Type A ◽  
Growth Cones ◽  
Aminobutyric Acid ◽  
Semaphorin 3A ◽  
Axon Targeting ◽  
Growth Cone Collapse ◽  
Neocortical Neurons ◽  
Acid Type

Abstract Background: The finding that exposure to general anesthetics (GAs) in childhood may increase rates of learning disabilities has raised a concern that anesthetics may interfere with brain development. The generation of neuronal circuits, a complex process in which axons follow guidance cues to dendritic targets, is an unexplored potential target for this type of toxicity. Methods: GA exposures were conducted in developing neocortical neurons in culture and in early postnatal neocortical slices overlaid with fluorescently labeled neurons. Axon targeting, growth cone collapse, and axon branching were measured using quantitative fluorescence microscopy. Results: Isoflurane exposure causes errors in Semaphorin-3A–dependent axon targeting (n = 77 axons) and a disruption of the response of axonal growth cones to Semaphorin-3A (n = 2,358 growth cones). This effect occurs at clinically relevant anesthetic doses of numerous GAs with allosteric activity at γ-aminobutyric acid type A receptors, and it was reproduced with a selective agonist. Isoflurane also inhibits growth cone collapse induced by Netrin-1, but does not interfere branch induction by Netrin-1. Insensitivity to guidance cues caused by isoflurane is seen acutely in growth cones in dissociated culture, and errors in axon targeting in brain slice culture occur at the earliest point at which correct targeting is observed in controls. Conclusions: These results demonstrate a generalized inhibitory effect of GAs on repulsive growth cone guidance in the developing neocortex that may occur via a γ-aminobutyric acid type A receptor mechanism. The finding that GAs interfere with axon guidance, and thus potentially with circuit formation, represents a novel form of anesthesia neurotoxicity in brain development.

scholarly journals Propofol at Clinically Relevant Concentrations Increases Neuronal Differentiation But Is Not Toxic to Hippocampal Neural Precursor Cells In Vitro 

2012 ◽  
Vol 117 (5) ◽  
pp. 1080-1090 ◽  
Author(s):  
Jeffrey W. Sall ◽  
Greg Stratmann ◽  
Jason Leong ◽  
Elliott Woodward ◽  
Philip E. Bickler
Keyword(s):  
Cell Death ◽  
Lactate Dehydrogenase ◽  
Neuronal Differentiation ◽  
Cell Function ◽  
Type A ◽  
Receptor Activation ◽  
Aminobutyric Acid ◽  
Neural Precursor ◽  
Acid Type

Background Propofol in the early postnatal period has been shown to cause brain cell death. One proposed mechanism for cognitive dysfunction after anesthesia is alteration of neural stem cell function and neurogenesis. We examined the effect of propofol on neural precursor or stem cells (NPCs) grown in vitro. Methods Hippocampal-derived NPCs from postnatal day 2 rats were exposed to propofol or Diprivan. NPCs were then analyzed for bromodeoxyuridine incorporation to measure proliferation. Cell death was measured by lactate dehydrogenase release. Immunocytochemistry was used to evaluate the expression of neuronal and glial markers in differentiating NPCs exposed to propofol. Results Propofol dose dependently increases the release of lactate dehydrogenase from NPCs under both proliferating and differentiating conditions at supraclinical concentrations (more than 7.1 µM). Both Diprivan and propofol had the same effect on NPCs. Propofol-mediated release of lactate dehydrogenase is not inhibited by blocking the γ-aminobutyric acid type A receptor or extracellular calcium influx and is not mediated by caspase-3/7. Direct γ-aminobutyric acid type A receptor activation did not have the same effect. In differentiating NPCs, 6 h of propofol at 2.1 µM increased the number neurons but not glial cells 4 days later. Increased neuronal differentiation was not blocked by bicuculline. Conclusions Only supraclinical concentrations of propofol or Diprivan kill NPCs in culture by a non-γ-aminobutyric acid type A, noncaspase-3 mechanism. Clinically relevant doses of propofol increase neuronal fate choice by a non-γ-aminobutyric acid type A mechanism.

Dual Actions of Enflurane on Postsynaptic Currents Abolished by the γ-Aminobutyric Acid Type A Receptor β3(N265M) Point Mutation

2006 ◽  
Vol 105 (2) ◽  
pp. 297-304 ◽  
Author(s):  
Berthold Drexler ◽  
Rachel Jurd ◽  
Uwe Rudolph ◽  
Bernd Antkowiak
Keyword(s):  
Type A ◽  
Mutant Mice ◽  
Aminobutyric Acid ◽  
Gamma Aminobutyric Acid ◽  
Wild Type ◽  
Action Potential Firing ◽  
Postsynaptic Currents ◽  
Neocortical Neurons ◽  
Acid Type ◽  
Beta3 Subunit

Background At concentrations close to 1 minimum alveolar concentration (MAC)-immobility, volatile anesthetics display blocking and prolonging effects on gamma-aminobutyric acid type A receptor-mediated postsynaptic currents. It has been proposed that distinct molecular mechanisms underlie these dual actions. The authors investigated whether the blocking or the prolonging effect of enflurane is altered by a point mutation (N265M) in the beta3 subunit of the gamma-aminobutyric acid type A receptor. Furthermore, the role of the beta3 subunit in producing the depressant actions of enflurane on neocortical neurons was elucidated. Methods Spontaneous inhibitory postsynaptic currents were sampled from neocortical neurons in cultured slices derived from wild-type and beta3(N265M) mutant mice. The effects of 0.3 and 0.6 mm enflurane on decay kinetics, peak amplitude, and charge transfer were quantified. Furthermore, the impact of enflurane-induced changes in spontaneous action potential firing was evaluated by extracellular recordings in slices from wild-type and mutant mice. Results In slices derived from wild-type mice, enflurane prolonged inhibitory postsynaptic current decays and decreased peak amplitudes. Both effects were almost absent in slices from beta3(N265M) mutant mice. At clinically relevant concentrations between MAC-awake and MAC-immobility, the anesthetic was less effective in depressing spontaneous action potential firing in slices from beta3(N265M) mutant mice compared with wild-type mice. Conclusion At concentrations between MAC-awake and MAC-immobility, beta3-containing gamma-aminobutyric acid type A receptors contribute to the depressant actions of enflurane in the neocortex. The beta3(N265M) mutation affects both the prolonging and blocking effects of enflurane on gamma-aminobutyric acid type A receptor-mediated inhibitory postsynaptic currents in neocortical neurons.

scholarly journals Methoxycarbonyl-etomidate

2009 ◽  
Vol 111 (2) ◽  
pp. 240-249 ◽  
Author(s):  
Joseph F. Cotten ◽  
S Shaukat Husain ◽  
Stuart A. Forman ◽  
Keith W. Miller ◽  
Elizabeth W. Kelly ◽  
...  
Keyword(s):  
Half Life ◽  
Human Liver ◽  
Type A ◽  
Aminobutyric Acid ◽  
Gamma Aminobutyric Acid ◽  
Loss Of Righting Reflex ◽  
Acid Type ◽  
Righting Reflex ◽  
S9 Fraction

Background Etomidate is a rapidly acting sedative-hypnotic that provides hemodynamic stability. It causes prolonged suppression of adrenocortical steroid synthesis; therefore, its clinical utility and safety are limited. The authors describe the results of studies to define the pharmacology of (R)-3-methoxy-3-oxopropyl1-(1-phenylethyl)-1H-imidazole-5-carboxylate (MOC-etomidate), the first etomidate analogue designed to be susceptible to ultra-rapid metabolism. Methods The gamma-aminobutyric acid type A receptor activities of MOC-etomidate and etomidate were compared by using electrophysiological techniques in human alpha1beta2gamma2l receptors. MOC-etomidate's hypnotic concentration was determined in tadpoles by using a loss of righting reflex assay. Its in vitro metabolic half-life was measured in human liver S9 fraction, and the resulting metabolite was provisionally identified by using high-performance liquid chromatography/mass spectrometry techniques. The hypnotic and hemodynamic actions of MOC-etomidate, etomidate, and propofol were defined in rats. The abilities of MOC-etomidate and etomidate to inhibit corticosterone production were assessed in rats. Results MOC-etomidate potently enhanced gamma-aminobutyric acid type A receptor function and produced loss of righting reflex in tadpoles. Metabolism in human liver S9 fraction was first-order, with an in vitro half-life of 4.4 min versus more than 40 min for etomidate. MOC-etomidate's only detectable metabolite was a carboxylic acid. In rats, MOC-etomidate produced rapid loss of righting reflex that was extremely brief and caused minimal hemodynamic changes. Unlike etomidate, MOC-etomidate produced no adrenocortical suppression 30 min after administration. Conclusions MOC-etomidate is an etomidate analogue that retains etomidate's important favorable pharmacological properties. However, it is rapidly metabolized, ultra-short-acting, and does not produce prolonged adrenocortical suppression after bolus administration.

scholarly journals Analogues of Etomidate

2014 ◽  
Vol 121 (2) ◽  
pp. 290-301 ◽  
Author(s):  
Ervin Pejo ◽  
Peter Santer ◽  
Spencer Jeffrey ◽  
Hilary Gallin ◽  
S. Shaukat Husain ◽  
...  
Keyword(s):  
Adrenocorticotropic Hormone ◽  
Type A ◽  
Chiral Center ◽  
Aminobutyric Acid ◽  
Adrenocortical Function ◽  
Receptor Subtypes ◽  
Structure Activity ◽  
Acid Type ◽  
Righting Reflex

Abstract Background: R-etomidate possesses unique desirable properties but potently suppresses adrenocortical function. Consequently, efforts are being made to define structure–activity relationships with the goal of designing analogues with reduced adrenocortical toxicity. The authors explored the pharmacological impact of modifying etomidate’s chiral center using R-etomidate, S-etomidate, and two achiral etomidate analogues (cyclopropyl etomidate and dihydrogen etomidate). Methods: The γ-aminobutyric acid type A receptor modulatory potencies of drugs were assessed in oocyte-expressed α1(L264T)β3γ2L and α1(L264T)β1γ2L γ-aminobutyric acid type A receptors (for each drug, n = 6 oocytes per subtype). In rats, hypnotic potencies and durations of action were measured using a righting reflex assay (n = 26 to 30 doses per drug), and adrenocortical potencies were quantified by using an adrenocorticotropic hormone stimulation test (n = 20 experiments per drug). Results: All four drugs activated both γ-aminobutyric acid type A receptor subtypes in vitro and produced hypnosis and suppressed adrenocortical function in rats. However, drug potencies in each model ranged by 1 to 2 orders of magnitude. R-etomidate had the highest γ-aminobutyric acid type A receptor modulatory, hypnotic, and adrenocortical inhibitory potencies. Respectively, R-etomidate, S-etomidate, and cyclopropyl etomidate were 27.4-, 18.9-, and 23.5-fold more potent activators of receptors containing β3 subunits than β1 subunits; however, dihydrogen etomidate’s subunit selectivity was only 2.48-fold and similar to that of propofol (2.08-fold). S-etomidate was 1/23rd as potent an adrenocortical inhibitor as R-etomidate. Conclusion: The linkage between the structure of etomidate’s chiral center and its pharmacology suggests that altering etomidate’s chiral center may be used as part of a strategy to design analogues with more desirable adrenocortical activities and/or subunit selectivities.

scholarly journals Effects of γ-Aminobutyric Acid Type A Receptor Modulation by Flumazenil on Emergence from General Anesthesia

2016 ◽  
Vol 125 (1) ◽  
pp. 147-158 ◽  
Author(s):  
Seyed A. Safavynia ◽  
Glenda Keating ◽  
Iris Speigel ◽  
Jonathan A. Fidler ◽  
Matthias Kreuzer ◽  
...  
Keyword(s):  
General Anesthesia ◽  
Expression System ◽  
Type A ◽  
Aminobutyric Acid ◽  
Clinical Effects ◽  
General Anesthetics ◽  
Isoflurane Anesthesia ◽  
Receptor Modulation ◽  
Acid Type

Abstract Background Transitions into conscious states are partially mediated by inactivation of sleep networks and activation of arousal networks. Pharmacologic hastening of emergence from general anesthesia has largely focused on activating subcortical monoaminergic networks, with little attention on antagonizing the γ-aminobutyric acid type A receptor (GABAAR). As the GABAAR mediates the clinical effects of many common general anesthetics, the authors hypothesized that negative GABAAR modulators would hasten emergence, possibly via cortical networks involved in sleep. Methods The authors investigated the capacity of the benzodiazepine rescue agent, flumazenil, which had been recently shown to promote wakefulness in hypersomnia patients, to alter emergence. Using an in vivo rodent model and an in vitro GABAAR heterologous expression system, they measured flumazenil’s effects on behavioral, neurophysiologic, and electrophysiologic correlates of emergence from isoflurane anesthesia. Results Animals administered intravenous flumazenil (0.4 mg/kg, n = 8) exhibited hastened emergence compared to saline-treated animals (n = 8) at cessation of isoflurane anesthesia. Wake-like electroencephalographic patterns occurred sooner and exhibited more high-frequency electroencephalography power after flumazenil administration (median latency ± median absolute deviation: 290 ± 34 s) compared to saline administration (473 ± 186 s; P = 0.042). Moreover, in flumazenil-treated animals, there was a decreased impact on postanesthesia sleep. In vitro experiments in human embryonic kidney-293T cells demonstrated that flumazenil inhibited isoflurane-mediated GABA current enhancement (n = 34 cells, 88.7 ± 2.42% potentiation at 3 μM). Moreover, flumazenil exhibited weak agonist activity on the GABAAR (n = 10 cells, 10.3 ± 3.96% peak GABA EC20 current at 1 μM). Conclusions Flumazenil can modulate emergence from isoflurane anesthesia. The authors highlight the complex role GABAARs play in mediating consciousness and provide mechanistic links between emergence from anesthesia and arousal.

scholarly journals Carboetomidate

2010 ◽  
Vol 112 (3) ◽  
pp. 637-644 ◽  
Author(s):  
Joseph F. Cotten ◽  
Stuart A. Forman ◽  
Joydev K. Laha ◽  
Gregory D. Cuny ◽  
S. Shaukat Husain ◽  
...  
Keyword(s):  
Critically Ill ◽  
Critically Ill Patients ◽  
Type A ◽  
Aminobutyric Acid ◽  
Adrenocortical Function ◽  
Gamma Aminobutyric Acid ◽  
Wild Type ◽  
High Affinity ◽  
Acid Type

Background Etomidate is a sedative hypnotic that is often used in critically ill patients because it provides superior hemodynamic stability. However, it also binds with high affinity to 11beta-hydroxylase, potently suppressing the synthesis of steroids by the adrenal gland that are necessary for survival. The authors report the results of studies to define the pharmacology of (R)-ethyl 1-(1-phenylethyl)-1H-pyrrole-2-carboxylate (carboetomidate), a pyrrole analog of etomidate specifically designed not to bind with high affinity to 11beta-hydroxylase. Methods The hypnotic potency of carboetomidate was defined in tadpoles and rats using loss of righting reflex assays. Its ability to enhance wild-type alpha1beta2gamma2l and etomidate-insensitive mutant alpha1beta2M286Wgamma2l human gamma-aminobutyric acid type A receptor activities was assessed using electrophysiologic techniques. Its potency for inhibiting in vitro cortisol synthesis was defined using a human adrenocortical cell assay. Its effects on in vivo hemodynamic and adrenocortical function were defined in rats. Results Carboetomidate was a potent hypnotic in tadpoles and rats. It increased currents mediated by wild-type but not etomidate-insensitive mutant gamma-aminobutyric acid type A receptors. Carboetomidate was a three orders of magnitude less-potent inhibitor of in vitro cortisol synthesis by adrenocortical cells than was etomidate. In rats, carboetomidate caused minimal hemodynamic changes and did not suppress adrenocortical function at hypnotic doses. Conclusions Carboetomidate is an etomidate analog that retains many beneficial properties of etomidate, but it is dramatically less potent as an inhibitor of adrenocortical steroid synthesis. Carboetomidate is a promising new sedative hypnotic for potential use in critically ill patients in whom adrenocortical suppression is undesirable.

Preparation of Barbiturate Optical Isomers and Their Effects on GABA (A) Receptors

1999 ◽  
Vol 90 (6) ◽  
pp. 1714-1722. ◽  
Author(s):  
Sarah L. Tomlin ◽  
Andrew Jenkins ◽  
William R. Lieb ◽  
Nicholas P. Franks
Keyword(s):  
Rank Order ◽  
Type A ◽  
Mouse Fibroblast ◽  
Aminobutyric Acid ◽  
Optical Isomers ◽  
Gamma Aminobutyric Acid ◽  
Patch Clamp Technique ◽  
Acid Type ◽  
Induced Currents

Background Barbiturate anesthetics are optically active and usually exist in two mirror-image enantiomeric forms. Their stereoselective effects in mammals are well known, but remarkably few data are available concerning their effects on anesthetic targets in vitro. This is in part because of the lack of availability of pure barbiturate enantiomers. Such in vitro data could be used to test the relevance of putative molecular targets. Methods A high-performance liquid chromatography technique using a permethylated beta-cyclodextrin column was used to separate the optical isomers of three barbiturates in preparative quantities. The effects of the isomers on GABA-induced currents in stably transfected mouse fibroblast cells were investigated using the whole-cell patch-clamp technique. Results Highly purified optical isomers of hexobarbital, pentobarbital, and thiopental were prepared, and their effects were studied on a gamma-aminobutyric acid type A receptor of defined subunit composition. For each of the three barbiturates, both enantiomers potentiated gamma-aminobutyric acid-induced currents at pharmacologically relevant concentrations, with the S-enantiomer being more potent than the R-enantiomer by a factor of between 1.7 and 3.5. The degree of stereoselectivity did not vary greatly with anesthetic concentration. Conclusions The rank order and degree of stereoselectivity that we have observed for the enantiomers of hexobarbital, pentobarbital, and thiopental acting on the gamma-aminobutyric acid type A receptor are entirely consistent with this receptor playing a central role in the anesthetic actions of barbiturates.

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