Putative malignant hyperthermia mutation CaV1.1-R174W is insufficient to trigger a fulminant response to halothane or confer heat stress intolerance

Malignant hyperthermia susceptibility (MHS) is an autosomal dominant pharmacogenetic disorder that manifests as a hypermetabolic state when carriers are exposed to halogenated volatile anesthetics or depolarizing muscle relaxants. In animals, heat stress intolerance is also observed. MHS is linked to over 40 variants in RYR1 that are classified as pathogenic for diagnostic purposes. More recently, a few rare variants linked to the MHS phenotype have been reported in CACNA1S, which encodes the voltage-activated Ca2+ channel CaV1.1 that conformationally couples to RyR1 in skeletal muscle. Here, we describe a knock-in mouse line that expresses one of these putative variants, CaV1.1-R174W. Heterozygous (HET) and homozygous (HOM) CaV1.1-R174W mice survive to adulthood without overt phenotype but fail to trigger with fulminant malignant hyperthermia when exposed to halothane or moderate heat stress. All three genotypes (WT, HET, and HOM) express similar levels of CaV1.1 by quantitative PCR, Western blot, [3H]PN200-110 receptor binding and immobilization-resistant charge movement densities in flexor digitorum brevis fibers. Although HOM fibers have negligible CaV1.1 current amplitudes, HET fibers have similar amplitudes to WT, suggesting a preferential accumulation of the CaV1.1-WT protein at triad junctions in HET animals. Never-the-less both HET and HOM have slightly elevated resting free Ca2+ and Na+ measured with double barreled microelectrode in vastus lateralis that is disproportional to upregulation of transient receptor potential canonical (TRPC) 3 and TRPC6 in skeletal muscle. CaV1.1-R174W and upregulation of TRPC3/6 alone are insufficient to trigger fulminant malignant hyperthermia response to halothane and/or heat stress in HET and HOM mice.

The impact of anesthetic drugs on hemodynamic parameters and neurological outcomes following temporal middle cerebral artery occlusion in rats

The induction of ischemic stroke in the experimental model requires general anesthesia. One of the factors that can be effective in the size of ischemic brain lesions and neurological outcomes is the type of anesthesia. So, the current study was designed to compare the impacts of the most important and widely used anesthetics including halothane, isoflurane, and chloral hydrate on the transient middle cerebral artery occlusion (MCAO) outcomes. Adult Male Sprague-Dawley rats were randomly divided into three groups as follows: (1) MCAO + halothane group, (2) MCAO + isoflurane group, and (3) MCAO + chloral hydrate group. After 24 h, the mortality rate, infarct size, tissue swelling, neurological function, hemodynamic, and arterial blood gas parameters were assessed. Our finding showed that 60 min MCAO rats anesthetized with chloral hydrate significantly increased mortality rate, infarct size, tissue swelling, and neurological deficits compared with halothane and isoflurane anesthetics after 24 h of MCAO. Also, chloral hydrate caused a significant decrease in mean arterial pressure and arterial pO2 compared to halothane and isoflurane anesthetics. On the basis of the current data, we concluded that chloral hydrate increased cerebral infarct volume and neurological outcomes and reduced hemodynamic and metabolic parameters compared with halothane and isoflurane-anesthetized rats temporal MCAO.

Inhibition of mitochondrial respiration by general anesthetic drugs

General anesthetic drugs have been associated with various unwanted effects including an interference with mitochondrial function. We had previously observed increases of lactate formation in the mouse brain during anesthesia with volatile anesthetic agents. In the present work, we used mitochondria that were freshly isolated from mouse brain to test mitochondrial respiration and ATP synthesis in the presence of six common anesthetic drugs. The volatile anesthetics isoflurane, halothane, and (to a lesser extent) sevoflurane caused an inhibition of complex I of the electron transport chain in a dose-dependent manner. Significant effects were seen at concentrations that are reached under clinical conditions (< 0.5 mM). Pentobarbital and propofol also inhibited complex I but at concentrations that were two-fold higher than clinical EC50 values. Only propofol caused an inhibition of complex II. Complex IV respiration was not affected by either agent. Ketamine did not affect mitochondrial respiration. Similarly, all anesthetic agents except ketamine suppressed ATP production at high concentrations. Only halothane increased cytochrome c release indicating damage of the mitochondrial membrane. In summary, volatile general anesthetic agents as well as pentobarbital and propofol dose-dependently inhibit mitochondrial respiration. This action may contribute to depressive actions of the drugs in the brain.

Permeabilised skeletal muscle reveals mitochondrial deficiency in malignant hyperthermia-susceptible individuals

BACKGROUND

Individuals genetically susceptible to malignant hyperthermia (MH) exhibit hypermetabolic reactions when exposed to volatile anaesthetics. Mitochondrial dysfunction has previously been associated with the MH-susceptible (MHS) phenotype in animal models, but evidence of this in human MH is limited.

METHODS

We used high resolution respirometry to compare oxygen consumption rates (oxygen flux) between permeabilised human MHS and MH-negative (MHN) skeletal muscle fibres with or without prior exposure to halothane. A substrate-uncoupler-inhibitor titration protocol was used to measure the following components of the electron transport chain under conditions of oxidative phosphorylation (OXPHOS) or after uncoupling the electron transport system (ETS): complex I (CI), complex II (CII), CI+CII and, as a measure of mitochondrial mass, complex IV (CIV).

RESULTS

Baseline comparisons without halothane exposure showed significantly increased mitochondrial mass (CIV, P=0.021) but lower flux control ratios in CI+CII_(OXPHOS) and CII_(ETS) of MHS mitochondria compared with MHN (P=0.033 and 0.005, respectively) showing that human MHS mitochondria have a functional deficiency. Exposure to halothane triggered a hypermetabolic response in MHS mitochondria, significantly increasing mass-specific oxygen flux in CI_(OXPHOS), CI+CII_(OXPHOS), CI+CII_(ETS), and CII_(ETS) (P=0.001-0.012), while the rates in MHN samples were unaltered by halothane exposure.

CONCLUSIONS

We present evidence of mitochondrial dysfunction in human MHS skeletal muscle both at baseline and after halothane exposure.

Analysis of Safety Margin of Lithium Carbonate Against Cardiovascular Adverse Events Assessed in the Halothane-Anesthetized Dogs

Lithium is one of the classical drugs that have been widely used for treating bipolar disorder. However, several cardiac side effects including sick sinus syndrome, bundle branch block, ventricular tachycardia/fibrillation, non-specific T-wave abnormalities in addition to Brugada-type electrocardiographic changes have been noticed in patients who were given antidepressant, anticonvulsant, and/or antipsychotic drugs besides lithium. In this study, we assessed cardiohemodynamic and electrophysiological effects of lithium carbonate by itself to begin to analyze onset mechanisms of its cardiovascular side effects. Lithium carbonate in intravenous doses of 0.1, 1, and 10 mg/kg over 10 min was cumulatively administered with an interval of 20 min to the halothane-anesthetized beagle dogs (n = 4), which provided peak plasma Li⁺ concentrations of 0.02, 0.18, and 1.79 mEq/L, respectively, reflecting sub-therapeutic to toxic concentrations. The low and middle doses prolonged the ventricular effective refractory period at 30 min and for 5-30 min, respectively. The high dose decreased the heart rate for 45-60 min, delayed the intraventricular conduction for 15-20 min and the ventricular repolarization at 45 min, and prolonged the effective refractory period for 5-60 min. No significant change was detected in the other cardiovascular variables. Thus, lithium alone may have a wide safety margin against hemodynamic adverse events; however, it would directly and/or indirectly inhibit Na⁺ and K⁺ channels, which may synergistically increase the ventricular refractoriness from the sub-therapeutic concentration and decrease the heart rate at the supra-therapeutic one. These findings may partly explain its clinically observed various types of arrhythmias as well as electrocardiographic changes.

Is there a link between exertional heat stroke and susceptibility to malignant hyperthermia?

Objective

The identification of a predisposition toward malignant hyperthermia (MH) as a risk factor for exertional heat stroke (EHS) remains a matter of debate. Such a predisposition indicates a causal role for MH susceptibility (MHS) after EHS in certain national recommendations and has led to the use of an in vitro contracture test (IVCT) to identify the MHS trait in selected or unselected EHS patients. The aim of this study was to determine whether the MHS trait is associated with EHS.

Methods

EHS subjects in the French Armed Forces were routinely examined for MHS after experiencing an EHS episode. This retrospective study compared the features of IVCT-diagnosed MHS (iMHS) EHS subjects with those of MH-normal EHS patients and MH patients during the 2004–2010 period. MHS status was assessed using the European protocol.

Results

During the study period, 466 subjects (median age 25 years; 31 women) underwent MHS status investigation following an EHS episode. None of the subjects reported previous MH events. An IVCT was performed in 454 cases and was diagnostic of MHS in 45.6% of the study population, of MH susceptibility to halothane in 18.5%, of MH susceptibility to caffeine in 9.9%, and of MH susceptibility to halothane and caffeine in 17.2%. There were no differences in the clinical features, biological features or outcomes of iMHS EHS subjects compared with those of MH-normal or caffeine or halothane MHS subjects without known prior EHS episode. The recurrence rate was 12.7% and was not associated with MH status or any clinical or biological features. iMHS EHS patients exhibited a significantly less informative IVCT response than MH patients.

Conclusions

The unexpected high prevalence of the MHS trait after EHS suggested a latent disturbance of calcium homeostasis that accounted for the positive IVCT results. This study did not determine whether EHS patients have an increased risk of MH, and it could not determine whether MH susceptibility is a risk factor for EHS.

Emulsified halothane produces long-term epidural anesthetic effect: a study in rabbits

Previous studies have demonstrated that volatile anesthetics could produce local anesthesia. Emulsified isoflurane at 8% has been reported to produce epidural anesthetic effect in rabbits. This study was designed to investigate the long-term epidural anesthetic effect of emulsified halothane in rabbits. In this study, 40 healthy adult rabbits (weighting 2.0-2.5 kg) with an epidural catheter were randomly divided into 4 groups (n=10/group), receiving epidural administration of 1% lidocaine (lido group), 8% emulsified isoflurane 1ml (8% E-iso group), 8% emulsified halothane (8% E-Halo group) and 12% emulsified halothane (12% E-Halo group). After administration, sensory and motor functions as well as consciousness state were assessed until 60 minutes after sensory and motor function returned to its baseline or at least for 180 min. After epidural anesthesia, all the rabbits were continuously observed for 7 days and sacrificed for pathological evaluations. As a result, all the four study solutions produced typical epidural anesthesia. Onset times of sensory and motor function blockade were similar among the four groups (P>0.05). Duration of sensory blockade in 12% E-Halo group (83±13 min) was significantly longer than other groups: 51±12 min in 8% E-Halo group (P<0.01), 57±8 min in 8% E-iso group (P<0.01) and 47±9 min in lido group (P<0.01). Duration of sensory blockade in 8% E-iso group is longer than lido group (P<0.05). Duration of motor blockade in 12% E-Halo group (81±12 min) was also significantly longer than other groups: 40±8 min in 8% E-Halo group (P<0.01), 37±3 min in 8% E-iso group (P<0.01), 37±6 min in lido group (P<0.01). Normal consciousness was found in the rabbits from 8% E-Halo, 8% E-iso and lido groups while there were four rabbits in 12% E-Halo group (4/10) showed a light sedation. For all the rabbits, no pathological injury was found. The present study demonstrates that emulsified halothane produces reversible concentration-dependent epidural anesthesia and at 12% (v/v), emulsified halothane could produce long-term anesthesia without pathological injury.

Unwanted intra-operative penile erection during pediatric hypospadiasis repair. Comparison of propofol and halothane

PURPOSE

To compare the erectile effect of propofol and halothane on unwanted intraoperative penile erection (UIOPE) during pediatric hypospadiasis repair.

MATERIALS AND METHODS

One hundred and seventeen boys who were in the age range of 6 months to 6 years and referred for hypospadiasis repair to our referral teaching hospital were included in this randomized clinical trial. Patients were randomly assigned to one of the two study groups before anesthesia induction. Anesthesia was maintained with a continuous intravenous infusion of propofol and inhalational halothane in the propofol (P) and halothane (H) groups, respectively. Data regarding the patients’ age, weight, pre- and intra-operative chordee, UIOPE, anesthesia time, surgery time, hematoma formation, and wound infection were collected. The Chi-Square and Fisher’s exact tests were used for comparison.

RESULTS

No statistically significant differences were noted regarding age, weight, and pre and intra-operative chordee between the two groups. The incidence of UIOPE (10.34% versus 57.63%; P = .000), anesthesia time (174.15 +/- 15.02 versus 181.26 +/- 15.19; P =.012), and surgery time (162.34 +/- 12.99 versus 167.69 +/- 13.90 +/- 13.90; P = .034) were significantly lower in group P compared with group H.

CONCLUSION

The use of propofol during hypospadiasis surgical repair is more safe and effective than halothane in preventing UIOPE and reducing surgery and anesthesia time.

Altered anesthetic sensitivity of mice lacking Ndufs4, a subunit of mitochondrial complex I

Anesthetics are in routine use, yet the mechanisms underlying their function are incompletely understood. Studies in vitro demonstrate that both GABA(A) and NMDA receptors are modulated by anesthetics, but whole animal models have not supported the role of these receptors as sole effectors of general anesthesia. Findings in C. elegans and in children reveal that defects in mitochondrial complex I can cause hypersensitivity to volatile anesthetics. Here, we tested a knockout (KO) mouse with reduced complex I function due to inactivation of the Ndufs4 gene, which encodes one of the subunits of complex I. We tested these KO mice with two volatile and two non-volatile anesthetics. KO and wild-type (WT) mice were anesthetized with isoflurane, halothane, propofol or ketamine at post-natal (PN) days 23 to 27, and tested for loss of response to tail clamp (isoflurane and halothane) or loss of righting reflex (propofol and ketamine). KO mice were 2.5 - to 3-fold more sensitive to isoflurane and halothane than WT mice. KO mice were 2-fold more sensitive to propofol but resistant to ketamine. These changes in anesthetic sensitivity are the largest recorded in a mammal.

Halothane changes the domain structure of a binary lipid membrane

X-ray and neutron diffraction studies of a binary lipid membrane demonstrate that halothane at physiological concentrations produces a pronounced redistribution of lipids between domains of different lipid types identified by different lamellar d-spacings and isotope composition. In contrast, dichlorohexafluorocyclobutane (F6), a halogenated nonanesthetic, does not produce such significant effects. These findings demonstrate a specific effect of inhalational anesthetics on mixing phase equilibria of a lipid mixture.

A minimal stress model for the assessment of electroacupuncture analgesia in rats under halothane

The use of anesthetics in acupuncture analgesia is controversial. We evaluate a steady-state light anesthesia model to test whether minimal stress manipulation and reliable measurement of analgesia could be simultaneously achieved during electroacupuncture (EA) in animals. A series of experiments were performed. Firstly, EA compliance and tail-flick latencies (TFL) were compared in rats under 0.1%, 0.3%, 0.5%, 0.7%, or 1.1% halothane for 120min. Under 0.5% halothane, TFL were then measured in groups receiving EA at intensity of 3, 10 or 20 volt (V), 1 or 2mg/kg morphine, 20V EA plus naloxone, or control. Subsequently, the effect of EA on formalin-induced hyperalgesia was tested and c-fos expression in the spinal dorsal horn was analyzed. Rats exhibited profound irritable behaviors and highly variable TFL under 0.1% or 0.3% halothane, as well as a time-dependent increase of TFL under 0.7% or 1.1% halothane. TFL remained constant at 0.5% halothane, and needle insertion and electrical stimulation were well tolerated. Under 0.5% halothane, EA increased TFL and suppressed formalin-induced hyperalgesia in an intensity-dependent and naloxone-reversible manner. EA of 20V prolonged TFL by 74%, suppressed formalin-induced hyperalgesia by 32.6% and decreased c-fos expression by 29.7% at the superficial and deep dorsal horn with statistically significant difference. In conclusion, 0.5% halothane provides a steady-state anesthetic level which enables the humane application of EA stimulus with the least interference on analgesic assessment. This condition serves as a minimal stress EA model in animals devoid of stress-induced analgesia while maintaining physiological and biochemical response in the experiment.

Molecular dynamics and brownian dynamics investigation of ion permeation and anesthetic halothane effects on a proton-gated ion channel

Bacterial Gloeobacter violaceus pentameric ligand-gated ion channel (GLIC) is activated to cation permeation upon lowering the solution pH. Its function can be modulated by anesthetic halothane. In the present work, we integrate molecular dynamics (MD) and Brownian dynamics (BD) simulations to elucidate the ion conduction, charge selectivity, and halothane modulation mechanisms in GLIC, based on recently resolved X-ray crystal structures of the open-channel GLIC. MD calculations of the potential of mean force (PMF) for a Na(+) revealed two energy barriers in the extracellular domain (R109 and K38) and at the hydrophobic gate of transmembrane domain (I233), respectively. An energy well for Na(+) was near the intracellular entrance: the depth of this energy well was modulated strongly by the protonation state of E222. The energy barrier for Cl(-) was found to be 3-4 times higher than that for Na(+). Ion permeation characteristics were determined through BD simulations using a hybrid MD/continuum electrostatics approach to evaluate the energy profiles governing the ion movement. The resultant channel conductance and a near-zero permeability ratio (P(Cl)/P(Na)) were comparable to experimental data. On the basis of these calculations, we suggest that a ring of five E222 residues may act as an electrostatic gate. In addition, the hydrophobic gate region may play a role in charge selectivity due to a higher dehydration energy barrier for Cl(-) ions. The effect of halothane on the Na(+) PMF was also evaluated. Halothane was found to perturb salt bridges in GLIC that may be crucial for channel gating and open-channel stability, but had no significant impact on the single ion PMF profiles.

Anesthetic binding in a pentameric ligand-gated ion channel: GLIC

Cys-loop receptors are molecular targets of general anesthetics, but the knowledge of anesthetic binding to these proteins remains limited. Here we investigate anesthetic binding to the bacterial Gloeobacter violaceus pentameric ligand-gated ion channel (GLIC), a structural homolog of cys-loop receptors, using an experimental and computational hybrid approach. Tryptophan fluorescence quenching experiments showed halothane and thiopental binding at three tryptophan-associated sites in the extracellular (EC) domain, transmembrane (TM) domain, and EC-TM interface of GLIC. An additional binding site at the EC-TM interface was predicted by docking analysis and validated by quenching experiments on the N200W GLIC mutant. The binding affinities (K(D)) of 2.3 ± 0.1 mM and 0.10 ± 0.01 mM were derived from the fluorescence quenching data of halothane and thiopental, respectively. Docking these anesthetics to the original GLIC crystal structure and the structures relaxed by molecular dynamics simulations revealed intrasubunit sites for most halothane binding and intersubunit sites for thiopental binding. Tryptophans were within reach of both intra- and intersubunit binding sites. Multiple molecular dynamics simulations on GLIC in the presence of halothane at different sites suggested that anesthetic binding at the EC-TM interface disrupted the critical interactions for channel gating, altered motion of the TM23 linker, and destabilized the open-channel conformation that can lead to inhibition of GLIC channel current. The study has not only provided insights into anesthetic binding in GLIC, but also demonstrated a successful fusion of experiments and computations for understanding anesthetic actions in complex proteins.

The role of structured water in mediating general anesthetic action on alpha4beta2 nAChR

Water is an essential component for many biological processes. Pauling proposed that water might play a critical role in general anesthesia by forming water clathrates around anesthetic molecules. To examine potential involvement of water in general anesthesia, we analyzed water within alpha4beta2 nAChR, a putative protein target hypersensitive to volatile anesthetics. Experimental structure-derived closed- and open-channel nAChR systems in a fully hydrated lipid bilayer were examined using all-atom molecular dynamics simulations. At the majority of binding sites in alpha4beta2 nAChR, halothane replaced the slow-exchanging water molecules and caused a regional water population decrease. Only two binding sites had an increased quantity of water in the presence of halothane, where water arrangements resemble clathrate-like structures. The small number of such clathrate-like water clusters suggests that the formation of water clathrates is unlikely to be a primary cause for anesthesia. Despite the decrease in water population at most of the halothane binding sites, the number of sites that can be occupied transiently by water is actually increased in the presence of halothane. Many of these water sites were located between two subunits or in regions containing agonist binding sites or critical structural elements for transducing agonist binding to channel gating. Changes in water sites in the presence of halothane affected water-mediated protein-protein interactions and the protein dynamics, which can have direct impact on protein function. Collectively, water contributes to the action of anesthetics in proteins by mediating interactions between protein subunits and altering protein dynamics, instead of forming water clathrates around anesthetics.

Is isoflurane safer than halothane in equine anaesthesia? Results from a prospective multicentre randomised controlled trial

REASONS FOR PERFORMING STUDY

Approximately 1 in 100 horses suffer unexpectedly from anaesthetic-related death. Identification and use of the safest anaesthetic drugs should support this aim. Experimental evidence has suggested that isoflurane should be a safer maintenance agent in equine anaesthesia than halothane.

HYPOTHESIS

The death rate would be reduced in horses being maintained with isoflurane compared to halothane.

METHODS

A multicentre randomised controlled trial was undertaken to compare the effects of isoflurane and halothane for maintenance of equine anaesthesia for all types of operation. Data were analysed from 8242 horses in which anaesthesia was maintained with either halothane or isoflurane using mixed effects logistic regression models.

RESULTS

No overall benefit of either drug was detected. However, although not part of the primary hypothesis, data showed that the overall death rate was significantly reduced in horses age 2-5 years with isoflurane and that death from cardiac arrest was also reduced with isoflurane, particularly in high risk cases.

CONCLUSIONS AND POTENTIAL RELEVANCE

Halothane remains an acceptable anaesthetic for maintenance of anaesthesia in horses, but isoflurane may be safer in the young horse and in high risk cases.

Mechanism of interaction between the general anesthetic halothane and a model ion channel protein, III: Molecular dynamics simulation incorporating a cyanophenylalanine spectroscopic probe

A nitrile-derived amino acid, Phe(CN), has been used as an internal spectroscopic probe to study the binding of an inhalational anesthetic to a model membrane protein. The infrared spectra from experiment showed a blue-shift of the nitrile vibrational frequency in the presence of the anesthetic halothane. To interpret the infrared results and explore the nature of the interaction between halothane and the model protein, all-atom molecular dynamics (MD) simulations have been used to probe the structural and dynamic properties of the protein in the presence and absence of one halothane molecule. The frequency shift analyzed from MD simulations agrees well with the experimental infrared results. Decomposition of the forces acting on the nitrile probes demonstrates an indirect impact on the probes from halothane, namely a change of the protein's electrostatic local environment around the probes induced by halothane. Although the halothane remains localized within the designed hydrophobic binding cavity, it undergoes a significant amount of translational and rotational motion, modulated by the interaction of the trifluorine end of halothane with backbone hydrogens of the residues forming the cavity. This dominant interaction between halothane and backbone hydrogens outweighs the direct interaction between halothane and the nitrile groups, making it a good "spectator" probe of the halothane-protein interaction. These MD simulations provide insight into action of anesthetic molecules on the model membrane protein, and also support the further development of nitrile-labeled amino acids as spectroscopic probes within the designed binding cavity.

Genetic variation in RYR1 and malignant hyperthermia phenotypes

BACKGROUND

Malignant hyperthermia (MH) is associated, in the majority of cases, with mutations in RYR1, the gene encoding the skeletal muscle ryanodine receptor. Our primary aim was to assess whether different RYR1 variants are associated with quantitative differences in MH phenotype.

METHODS

The degree of in vitro pharmacological muscle contracture response and the baseline serum creatine kinase (CK) concentration were used to generate a series of quantitative phenotypes for MH. We then undertook the most extensive RYR1 genotype-phenotype correlation in MH to date using 504 individuals from 204 MH families and 23 RYR1 variants. We also determined the association between a clinical phenotype and both the laboratory phenotype and RYR1 genotype.

RESULTS

We report a novel correlation between the degree of in vitro pharmacological muscle contracture responses and the onset time of the clinical MH response in index cases (P<0.05). There was also a significant correlation between baseline CK concentration and clinical onset time (P=0.039). The specific RYR1 variant was a significant determinant of the severity of each laboratory phenotype (P<0.0001).

CONCLUSIONS

The MH phenotype differs significantly with different RYR1 variants. Variants leading to more severe MH phenotype are distributed throughout the gene and tend to lie at relatively conserved sites in the protein. Differences in phenotype severity between RYR1 variants may explain the variability in clinical penetrance of MH during anaesthesia and why some variants have been associated with exercise-induced rhabdomyolysis and heat stroke. They may also inform a mutation screening strategy in cases of idiopathic hyperCKaemia.

Porcine malignant hyperthermia carrier detection and chromosomal assignment using a linked probe

In pigs, the gene for glucosephosphate isomerase (GPI) is linked to the halothane (HAL) gene which is responsible for malignant hyperthermia (MH). A single copy DNA probe, designated GPI8R, has been isolated from a pig genomic library using a porcine GPI cDNA probe. This probe detects, as was the case for the cDNA probe, a five allele polymorphism in SacI and PvuII digested pig DNA. Family studies show that this polymorphism is linked to the HAL locus and hence can be used in carrier detection. In situ hybridization with GPI8R assigned the GPI locus to bands p12-q22 of chromosome 6. We conclude that the HAL linkage group resides on chromosome 6.

Linkage studies between the halothane (Hal), phosphohexose isomerase (Phi) and the S(A-O) and H red blood cell loci of Pietrain/Hampshire and Landrace pigs

Frequency of blood group factors at the A-O and H loci were markedly altered within halothane positive (HP) and halothane negative (HN) composite synthetic Pietrain/Hampshire lines (PTH) over four generations of selection. Linkage studies on the litters from 45 double backcross and 20 mixed and intercross matings, involving the S(A-O), H, Phi and Hal loci, were made in the PTH line and halothane positive and negative selected British Landrace lines. Crossing-over frequencies of 0.05 +/- 0.04, 0.05 +/- 0.03 and 0.1 +/- 0.03 were established between Phi and Hal, H and Hal, and Phi and H respectively. An unequal crossing-over frequency between Phi and H was found when the alleles Ha and Hcd were compared. The difference in recombination frequency between the Ha and Hcd alleles amounted to 0.04 to 0.06. No cross-overs were observed between the S(A-O) and Phi, H or Hal loci in 15 families studied. The position of the S locus in relation to the other loci could not be established, but statistical evidence of association favours a haplotype sequence of Phi-Hal-S-H.

Blood group association with severity and speed of the halothane reaction

The second generation (n = 227) of British Landrace pigs from selected halothane-positive parents (36 litters) were blood-typed for the S(A-O), H and Phi loci and subjected to four 5-minute halothane tests at 21, 35, 49 and 63 days of age. Cumulative scores based on severity and speed of reaction were analysed in relation to single-locus blood group genotypes and linkage group sequences at two and three loci. A highly significant negative correlation (r = -0.79) was found between severity and speed of reaction. Significant differences occurred between blood group genotypes and linkage groups in both severity and speed of reaction. Genotypes S s/s, H a/a or H a/- and Phi B/B and linkage groups involving these three types had the highest cumulative reaction score and the fastest reaction time, whereas genotypes Phi A/B, S S/S or S S/s and H a/cd and linkage groups with these types had the lowest and slowest reaction scores. Some differences between genotypes and linkage groups were attributed to phenotypically halothane-positive parents and offspring being genotypically Hal N/n. These effects could result from linkage with heterozygous types such as H a/cd and S S/s. The possible role of the H cd allele acting as a genetic marker for a suppressor gene to the halothane reaction is discussed.

Development of three Drosophila melanogaster strains with different sensitivity to volatile anesthetics

BACKGROUND

The mechanisms of action for volatile anesthetics remain unknown for centuries partly owing to the insufficient or ineffective research models. We designed this study to develop three strains derived from a wild-type Drosophila melanogaster with different sensitivities to volatile anesthetics, which may ultimately facilitate molecular and genetic studies of the mechanism involved.

METHODS

Median effective doses (ED(50)) of sevoflurane in seven-day-old virgin female and male wild-type Drosophila melanogaster were determined. The sensitive males and females of percentile 6 - 10 were cultured for breeding sensitive offspring (S(1)). So did median ones of percentile 48 - 52 for breeding median offspring (M(1)), resistant ones of percentile 91 - 95 for breeding resistant offspring (R(1)). Process was repeated through 31 generations, in the 37th generation, S(37), M(37) and R(37) were used to determine ED(50) for enflurane, isoflurane, sevoflurane, desflurane, halothane, methoxyflurane, chloroform and trichloroethylene, then ED(50) values were correlated with minimum alveolar concentration (MAC) values in human.

RESULTS

From a wild-type Drosophila melanogaster we were able to breed three strains with high, median and low sevoflurane requirements. The ratio of sevoflurane requirements of three strains were 1.20:1.00:0.53 for females and 1.22:1.00:0.72 for males. Strains sensitive, median and resistant to sevoflurane were also sensitive, median and resistant to other volatile anesthetics. For eight anesthetics, ED(50) values in three strains correlated directly with MAC values in human.

CONCLUSIONS

Three Drosophila melanogaster strains with high, median and low sensitivity to volatile anesthetics, but with same hereditary background were developed. The ED(50) are directly correlated with MAC in human for eight volatile anesthetics.

Comparison of the effect of sevoflurane and halothane anesthesia on the fall in heart rate as a predictor of successful single shot caudal epidural in children

OBJECTIVE

To investigate the effect of sevoflurane anesthesia on heart rate HR fall with the injection of the initial drug in caudal space to confirm the correct needle placement.

METHODS

After the ethical approval was obtained from the hospital's ethics committee, a prospective, randomized, clinical study was designed in Yeditepe University Hospital, in 2007. Children aged 1-12 years, scheduled for infraumbilical surgery under general anesthesia, and caudal block were included in the study. Anesthesia was induced, and maintained by sevoflurane in group S (n=85), and by halothane in group H (n=82). Baseline HR was recorded before the caudal block was performed. The HR changes during the initial dose, and total drug injection were recorded followed by 2 more HR recordings taken 5, and 10 minutes after caudal injection. The success of the block was recorded by a blind observer.

RESULTS

There were 167 children included in the study. Caudal block success was 96.5% in group S, and 97.6% in group H. Basal HR was 110.9 +/- 10.9 in group S, and 105.9 +/- 10.1 in group H. Following the initial drug injection, mean HR was 109.8 +/- 10.9 in group S, and 102.9 +/- 9.9 in group H. It was significantly lower than the baseline in group H. The only significant decrease in the HR of the patients in group S was at the tenth minute following caudal injection.

CONCLUSION

The decrease in HR with drug injection has no value to predict the success of caudal block under sevoflurane anesthesia.

Use of calcium imaging for analysis of neuronal gap junction coupling

We recently used Western blots for connexin 36 and neuronal dye coupling with neurobiotin to measure developmental decrease in neuronal gap junction coupling in cell cultures. To ask whether Ca2+ imaging also can be used to measure changes in the amount of neuronal gap junction coupling, we defined a Ca2+ coupling coefficient as the percentage of neurons with bicuculline-induced increases in intracellular Ca2+ that are suppressed by blocking gap junctions. We demonstrate in rat and mouse hypothalamic neuronal cultures that the Ca2+ coupling coefficient decreases during culture development, this decrease is prevented by manipulations that also prevent developmental decrease in neuronal gap junction coupling, and the coefficient is low in cultures lacking connexin 36. The results indicate that Ca2+ imaging is a useful tool to quantify the amount of neuronal gap junction coupling in cultures.

Effects of halothane, isoflurane, and sevoflurane on lipid peroxidation following experimental closed head trauma in rats

BACKGROUND

In a rat closed head trauma model we examined both the time course of lipid peroxidation and the effects of halothane, isoflurane, and sevoflurane on it by analysis of malondialdehyde (MDA) formation.

METHODS

Animals were divided randomly into five groups: sham-operated (SO), n=18; control-closed head trauma to left frontal pole, n=18; closed head trauma model+halothane, n=18; closed head trauma model+isoflurane, n=18; and closed head trauma model+sevoflurane, n=18. Halothane, isoflurane, or sevoflurane were applied 15 min after trauma for 30 min. Rats were euthanized 1,3, and 5 h after the inhalation agents. Brain tissue samples were taken 5 mm from the left and right frontal poles. MDA was considered to reflect the degree of lipid peroxidation.

RESULTS

MDA concentrations were greater in the control, halothane, sevoflurane, and isoflurane groups than in SO animals (P<0.001). No statistical difference between the hemispheres was found between the halothane, isoflurane, or sevoflurane groups, but MDA levels were lower with isoflurane than in the halothane, sevoflurane, and control groups at 1, 3, and 5 h (P<0.001). MDA levels were higher as compared with the halothane and sevoflurane groups at 1 h but not at 3 or 5 h (P<0.001).

CONCLUSION

MDA levels with the isoflurane group were lower than in the other trauma groups, which suggest that isoflurane, given after closed head trauma, might be protective against lipid peroxidation of cerebral injury.

Volatile anesthetics affect the morphology of rat glioma C6 cells via RhoA, ERK, and Akt activation

Treatment of rat glioma C6 cells with the beta-receptor agonist isoproterenol induces a massive increase in cAMP. Concomitantly the cells change their morphology from a fibroblast-type to an astrocyte-like (stellated) cell shape. The stellated morphology can be completely reverted by thrombin and sphingosine-1-phosphate (S-1-P) but also to a certain extent by clinical concentrations of volatile anesthetics. The anesthetic-induced reversion of the stellated cell shape seems to be mediated by a number of cellular alterations. Central to the effect is most likely a RhoA/Rho-kinase activation, but also the MAPKK/MEK and the Akt/protein kinase B pathway are activated by the anesthetics. With the use of specific inhibitors we were able to show that activation of the MAPKK/MEK pathway inhibits, whereas activation of the Akt/protein kinase B pathway stimulates the reversal of the stellated cell shape by the anesthetics. In summary, volatile anesthetics affect the morphology of rat glioma C6 cells by activation of the RhoA/Rho kinase, the MAPKK/MEK, and the Akt/protein kinase B signaling pathways.

[Anesthesia in malignant hyperthermia]

Malignant hyperthermia is a condition for which the anesthesiologist must be prepared to take specific measures. Associated mortality is high despite correct diagnosis and, occasionally, the right treatment. Malignant hyperthermia is rare in Spain, however, and perhaps for this reason the Spanish public health authorities have not made an effort to respond to persistent calls for a national reference center for study and diagnosis, such as can be found in other European countries. The problem of malignant hyperthermia may become worse in the near future due to changes in the population brought about by immigration. It is therefore necessary to establish appropriately revised protocols and action plans to cope with this possibility. A reference center cannot be created by individuals, but we can become more aware of the need to establish up-to-date protocols in our departments in order to be prepared for this situation.

Effects of ryanodine on skeletal muscle lactate and pyruvate in malignant hyperthermia-susceptible and normal swine as assessed by microdialysis

BACKGROUND

The caffeine/halothane contracture test in North America and the in vitro contracture test in Europe are currently the only validated bioassays for diagnosing malignant hyperthermia susceptibility and phenotyping families. Both tests are invasive requiring surgical muscle biopsy. Here, we report first use of the selective ryanodine receptor type I agonist ryanodine in a percutaneous microdialysis protocol designed to test whether microdialysis-induced local metabolic responses of skeletal muscle due to ryanodine receptor activation can differentiate between malignant hyperthermia-sensitive and normal pigs.

METHODS

Six microdialysis catheters were implanted percutaneously into the adductor muscles of the right and left thighs of malignant hyperthermia-susceptible (n = 9) and normal (n = 8) anaesthetized (ketamine/propofol) and mechanically ventilated swine. Systemic blood gases, haemodynamic parameters and creatine kinase levels were measured before, during and after microdialysis perfusion of ryanodine. After a post-implantation equilibration period of 30 min, one catheter perfused (2 micro min-1) with 0.9% NaCl (control) and was compared with the remaining five catheters perfused with increasing concentrations of ryanodine (0.2-100 micromol). Lactate and pyruvate levels were measured enzymatically.

RESULTS

Continuous perfusion with ryanodine revealed dose-dependent sigmoidal increases in the dialysate lactate and lactate-pyruvate ratio parameters; these effects were greatly augmented in malignant hyperthermia-susceptible pigs compared to normal pigs (two- to threefold): estimated EC50 greatly decreased (>19-fold) while the maximum effect increased (>twofold) in the malignant hyperthermia-susceptible group.

CONCLUSION

The in vivo percutaneous microdialysis protocol for skeletal muscle, using ryanodine as the ryanodine receptor type I agonist and dialysed lactate-pyruvate parameters as metabolic index, can reproducibly differentiate between malignant hyperthermia-susceptible and normal swine.

[Responses of hemodynamics and splanchnic organ blood flow to esmolol during inhalation of volatile anesthetics in dogs]

BACKGROUND

Because the hemodynamic alterations due to sympathetic suppression by the interaction of esmolol with volatile anesthetics may alter the blood flow to the splanchnic organs, this study was designed to investigate whether esmolol might modify the hemodynamics and splanchnic organ blood flow in anesthetized dogs.

METHODS

Anesthesia was maintained with 0.9% halothane, 1.3% isoflurane or 2.4% sevoflurane (1MAC, n=8, each) in oxygen. Esmolol was infused at a constant rate of 400 microg * kg(-1) x min(-1) during a 60 min-infusion period. The renal, hepatic, and pancreatic blood flows (RBF, HBF, and PBF) were measured by using the hydrogen clearance method.

RESULTS

Mean arterial pressure in all three groups decreased without any changes in heart rate or systemic vascular resistance. Cardiac index in all three groups decreased with reductions in cardiac contractility. The RBF, HBF, and PBF in all three groups were reduced during the esmolol infusion.

CONCLUSIONS

The splanchnic organ blood flow reductions caused by esmolol may be due to cardiac depression, whereas there appears to be no differences in there change regarding the kind of the volatile anesthetics. These findings suggest that hypotension induced by esmolol may impair the maintenance of splanchnic organ blood flow during anesthesia by volatile agents.

S100B levels in the cerebrospinal fluid of rats are sex and anaesthetic dependent

1. S100B is a calcium-binding protein that acts as a neurotrophic cytokine and is expressed in the central nervous system, predominantly by astrocytes. At nanomolar concentrations, S100B stimulates neurite outgrowth and glial glutamate uptake, as well as protecting neurons against glutamate excitoxicity. 2. Peripheral S100B concentrations, particularly in the serum and cerebrospinal fluid (CSF), have been used as a parameter of glial activation or death in several physiological and pathological conditions. 3. In the present study, we investigated the effect of anaesthetics (thiopental, ketamine and halothane) on CSF concentrations of S100B, as well as a possible sex dependence, because several studies have suggested astrocytes as putative targets for oestrogen. 4. Higher levels of CSF S100B were found when rats were anaesthetized with thiopental; these levels, independently of anaesthetic, were sex dependent. Conversely, no effect of anaesthetic or sex was observed on serum concentrations of S100B. 5. The increase in CSF concentrations of S100B induced by thiopental was confirmed in non-anaesthetized neonatal rats and cortical astrocyte cultures. 6. Assuming CSF S100B as a marker of development, glial activation or even brain damage, investigations regarding the sex dependence of its concentration may be useful in gaining an understanding of sex variations in the behaviour and the pathological course of, as well as susceptibility to, many brain disorders. The findings of the present study reinforce the sex effect on synaptic plasticity and suggest a sex dependence of neural communication mediated by extracellular S100B without restricting the influence of astrocytes on the developmental phase.

Effects of propofol and halothane on long-term potentiation in the rat hippocampus after transient cerebral ischaemia

BACKGROUND

Propofol is reported to have protective effects on cerebral ischaemia-induced neuronal death. The aim of this study was to explore whether propofol and halothane can protect hippocampal neuronal function from ischaemic injury during general anaesthesia in rats.

METHODS

Rats were divided into 2-vessel occlusion (incomplete cerebral ischaemia) and 4-vessel occlusion (complete cerebral ischaemia) groups consisting of three subgroups each (sham-operated, propofol and halothane groups). One hour after starting propofol 1 mg kg(-1) min(-1) with 30% O2 and N2 or halothane 0.8% in 30% O2 and N2 rats with or without bilateral vertebral artery occlusion had bilateral common carotid arteries occluded by vessel clips for 10 min. Anaesthesia was maintained for another 1 h. Seven days after ischaemia-reperfusion, hippocampal long-term potentiation in the perforant path-dentate gyrus synapse was determined as an index of cerebral outcome.

RESULTS

In the propofol groups, the formation of long-term potentiation was significantly impaired in the 2-vessel and 4-vessel occlusion groups compared to the respective sham-operated groups (P < 0.01 and P < 0.05, respectively). Impaired formation of long-term potentiation in propofol groups was comparable to that in halothane groups. The formation of long-team potentiation in the propofol and halothane 2-vessel group was not significantly different from that in the awake 2-vessel group.

CONCLUSIONS

Propofol and halothane administered during ischaemia do not possess protective effects against hippocampal neuronal dysfunction induced by cerebral ischaemia-reperfusion as evaluated by our transient ischaemic rat models.

Neurons in the ventral spinal cord are more depressed by isoflurane, halothane, and propofol than are neurons in the dorsal spinal cord

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.

Inhaled anesthetic modulation of amyloid beta(1-40) assembly and growth

Anesthesia and surgery have been reported to produce long-term cognitive problems, and to accelerate neurodegenerative disorders in the elderly. In previous work, we found that inhaled anesthetics enhance fibril formation and cytotoxicity of amyloid beta peptide. In this work we show that the inhaled anesthetics halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) and isoflurane (1-chloro-2,2,2-trifluoroethyl difluoromethyl ether) also favor intermediate oligomers of amyloid beta(1-40), and reduce solubility of amyloid beta(1-40) monomer. Size-exclusion chromatography, analytical ultracentrifugation and photo-induced cross-linking experiments indicate halothane enhancement of oligomeric species having molecular weight approximately 44-100 kDa. Bis-ANS fluorescence experiments revealed that halothane stabilizes a population of diffusible oligomers relative to the monomer or the mature fibril. These data show that inhaled anesthetics lower the amyloid beta(1-40) concentration necessary to initiate oligomer formation, probably by preferential binding to intermediate oligomers en route to fibril formation.

Reduced inhibition of cortical glutamate and GABA release by halothane in mice lacking the K+ channel, TREK-1

BACKGROUND AND PURPOSE

Deletion of TREK-1, a two-pore domain K(+) channel (K(2P)) activated by volatile anaesthetics, reduces volatile anaesthetic potency in mice, consistent with a role for TREK-1 as an anaesthetic target. We used TREK-1 knockout mice to examine the presynaptic function of TREK-1 in transmitter release and its role in the selective inhibition of glutamate vs GABA release by volatile anaesthetics.

EXPERIMENTAL APPROACH

The effects of halothane on 4-aminopyridine-evoked and basal [(3)H]glutamate and [(14)C]GABA release from cerebrocortical nerve terminals isolated from TREK-1 knockout (KO) and littermate wild-type (WT) mice were compared. TREK-1 was quantified by immunoblotting of nerve terminal preparations.

KEY RESULTS

Deletion of TREK-1 significantly reduced the potency of halothane inhibition of 4-aminopyridine-evoked release of both glutamate and GABA without affecting control evoked release or the selective inhibition of glutamate vs GABA release. TREK-1 deletion also reduced halothane inhibition of basal glutamate release, but did not affect basal GABA release.

CONCLUSIONS AND IMPLICATIONS

The reduced sensitivity of glutamate and GABA release to inhibition by halothane in TREK-1 KO nerve terminals correlates with the reduced anaesthetic potency of halothane in TREK-1 KO mice observed in vivo. A presynaptic role for TREK-1 was supported by the enrichment of TREK-1 in isolated nerve terminals determined by immunoblotting. This study represents the first evidence for a link between an anaesthetic-sensitive 2-pore domain K(+) channel and presynaptic function, and provides further support for presynaptic mechanisms in determining volatile anaesthetic action.

Differential effects of volatile and intravenous anesthetics on the activity of human TASK-1

Volatile anesthetics have been shown to activate various two-pore (2P) domain K(+) (K(2P)) channels such as TASK-1 and TREK-1 (TWIK-related acid-sensitive K(+) channel), and mice deficient in these channels are resistant to halothane-induced anesthesia. Here, we investigated whether K(2P) channels were also potentially important targets of intravenous anesthetics. Whole cell patch-clamp techniques were used to determine the effects of the commonly used intravenous anesthetics etomidate and propofol on the acid-sensitive K(+) current in rat ventricular myocytes (which strongly express TASK-1) and selected human K(2P) channels expressed in Xenopus laevis oocytes. In myocytes, etomidate decreased both inward rectifier K(+) (K(ir)) current (I(K1)) and acid-sensitive outward K(+) current at positive potentials, suggesting that this drug may inhibit TASK channels. Indeed, in addition to inhibiting guinea pig Kir2.1 expressed in oocytes, etomidate inhibited human TASK-1 (and TASK-3) in a concentration-dependent fashion. Propofol had no effect on human TASK-1 (or TASK-3) expressed in oocytes. Moreover, we showed that, similar to the known effect of halothane, sevoflurane and the purified R-(-)- and S-(+)-enantiomers of isoflurane, without stereoselectivity, activated human TASK-1. We conclude that intravenous and volatile anesthetics have dissimilar effects on K(2P) channels. Human TASK-1 (and TASK-3) are insensitive to propofol but are inhibited by supraclinical concentrations of etomidate. In contrast, stimulatory effects of sevoflurane and enantiomeric isoflurane on human TASK-1 can be observed at clinically relevant concentrations.

Halothane Increases Non-vesicular [3H]dopamine Release from Brain Cortical Slices

Experimental data suggest that halothane anesthesia is associated with significant changes in dopamine (DA) concentration in some brain regions but the mechanism of this effect is not well known. Rat brain cortical slices were labeled with [(3)H]DA to further characterize the effects of halothane on the release of this neurotransmitter from the central nervous system. Halothane induced an increase on the release of [(3)H]DA that was dependent on incubation time and anesthetic concentration (0.012, 0.024, 0.048, 0.072 and 0.096 mM). This effect was independent of extracellular or intracellular calcium. In addition, [(3)H]DA release evoked by halothane was not affected by TTX (blocker of voltage-dependent Na(+) channels) or reserpine (a blocker of vesicular monoamine transporter). These data suggest that [(3)H]DA release induced by halothane is non-vesicular and would be mediated by the dopamine transporter (DAT) and norepinephrine transporter (NET). GBR 12909 and nomifensine, inhibitors of DAT, decreased the release of [(3)H]DA evoked by halothane. Nisoxetine, a blocker of NET, reduced the release of [(3)H]DA induced by halothane. In addition, GBR 12909, nisoxetine and, halothane decrease the uptake of [(3)H]DA into rat brain cortical slices. A decrease on halothane-induced release of [(3)H]DA was also observed when the brain cortical slices were incubated at low temperature and low extracellular sodium, which are known to interfere with the carrier-mediated release of the neurotransmitter. Ouabain, a Na(+)/K(+) ATPase pump inhibitor, which induces DA release through reverse transport, decreased [(3)H]DA release induced by halothane. It is suggested that halothane increases [(3)H]DA release in brain cortical slices that is mediated by DAT and NET present in the plasma membrane.

Genetic variability of induction and emergence times for inhalational anaesthetics

BACKGROUND AND OBJECTIVES

Anaesthetic requirements differ among inbred mouse strains. We tested the genetic influence on induction and arousal times to inhalational anaesthetics in two of these strains.

METHODS

Five male C57BL/6J (B6) and five male C3H/HeJ (C3) mice were each exposed to five different concentrations of nitrous oxide (N2O) at five different levels of halothane. Time to sleep and arousal were assessed. Data were analysed by repeated measures of analysis of variance.

RESULTS

Halothane, N2O and genetic strain, all were significant independent factors on the time to sleep, while only N2O was a significant independent factor on the time to arousal (P = 0.004). B6 mice took significantly longer to fall asleep compared to the C3 mice controlling for halothane and N2O concentrations (F-ratio = 36, P < 0.0001). The effect of N2O on time to arousal was only significant for the B6 strain (F-ratio = 10, P = 0.005), and not for the C3 strain (F-ratio = 0.8, P = 0.38).

CONCLUSIONS

Genetics influences the time to sleep for anaesthetic agents in mice.

Quantitative Evaluation of the Neuroprotective Effects of Thiopental Sodium, Propofol, and Halothane on Brain Ischemia in the Gerbil: Effects of the Anesthetics on Ischemic Depolarization and Extracellular Glutamate Concentration

Although propofol and thiopental are commonly used as neuroprotective agents, it has not been determined which is more neuroprotective. This study was designed to quantitatively evaluate the neuroprotective effects of thiopental, propofol, and halothane on brain ischemia by determining P50, ischemic time necessary for causing 50% neuronal damage. Gerbils were anesthetized with thiopental, propofol, or halothane and underwent 2-vessel occlusion (0, 3, 5 or 10 min). Direct current potentials were measured in bilateral CA1 regions, in which histologic evaluation was performed 5 days later. In some animals, extracellular glutamate concentrations (microdialysis) were measured during 7.5 minutes of ischemia. P50 in the thiopental, propofol, and halothane groups were estimated to be 8.4, 6.5 (P<0.05, vs. thiopental), and 5.1 (P<0.05) minutes, respectively. Durations of ischemic depolarization were equally reduced in the thiopental and propofol groups compared with that in the halothane group. Severity of neuronal damage with identical duration of ischemic depolarization was attenuated by thiopental compared with the effect of propofol. Maximum glutamate concentrations in the thiopental and propofol group were significantly reduced compared with that in the halothane groups but were comparable. By using P50, we found that the neuroprotective effect of thiopental was greater than that of propofol. Although duration of ischemic depolarization was equally reduced in thiopental and propofol groups, thiopental has a greater suppressive effect on neuronal injury during identical duration of ischemic depolarization than propofol does. Glutamate concentration during brain ischemia tended to be attenuated more by thiopental than by propofol, but it was not statistically significant.

Functional MRI of the cervical spinal cord during noxious and innocuous thermal stimulation in the alpha-chloralose- and halothane-anesthetized rat

Patterns of neuronal activity in the spinal cord using functional magnetic resonance imaging during noxious (48 degrees C) and innocuous (40 degrees C) thermal stimulation of the rat forepaw were examined. The patterns of functional activity elicited by thermal stimuli were compared in alpha-chloralose- and halothane-anesthetized rats. Although the locations of active pixels were similar during both types of stimulation, the mean percentage signal change was higher during noxious stimulation in both anesthetic groups. Ipsilateral dorsal horn activity was evident during both noxious and innocuous stimulation in all animals. The greatest consistency of ipsilateral dorsal horn activity occurred at the C3 to C5 spinal cord segments in all groups. Consistent contralateral dorsal horn activity appeared in segments C6 to C8 in all groups. C-fos immunohistochemical staining confirmed the presence of neural activity in the spinal cords of all animals.

Transgenic upregulation of IK1 in the mouse heart is proarrhythmic

The role of the cardiac current Ik1 in arrhythmogenesis remains highly controversal. To gain further insights into the mechanisms of IK1 involvement in cardiac excitability, we studied the susceptibility of transgenic mice with altered IK1 to arrhythmia during various pharmacological and physiological challenges. Arrhythmogenesis was studied in transgenic mice expressing either dominant negative Kir2.1-AAA or wild type Kir2.1 subunits in the heart, models of IK1 suppression (AAA-TG) and up-regulation (WT-TG), respectively. Under normal conditions, both anesthetized wild type (WT) and AAA-TG mice did not display any spontaneous arrhythmias. In contrast,WT-TG mice displayed numerous arrhythmias of various types. In isolated hearts, the threshold concentration for halothane-induced ventricular tachycardias (VT) was increased to 167% [corrected] in the AAA-TG and decreased to 54% [corrected] in WT-TG hearts when compared to WT hearts. The number of PVCs induced by AV node ablation combined with hypokalemia was reduced in AAA-TG hearts and increased in WT-TG mice. After AV node ablation AAA-TG hearts were more tolerant, and WT-TG less tolerant to isoproterenol- induced arrhythmias than WT hearts. Analysis of monophasic action potentials in isolated hearts shows a significant reduction in the dispersion of action potential repolarization in mice with suppressed IK1. The data strongly support the hypothesis that in the mouse heart upregulation of IK1 is proarrhythmic, and that under certain conditions IK1 blockade in cardiac myocytes may be a potentially useful antiarrhythmic strategy.

Cardiac rhythm and left ventricular function of infants at 1 MAC sevoflurane and halothane

BACKGROUND

The implementation of sevoflurane in pediatric anesthesia practice led to a decrease in the incidence of cardiac arrest previously reported with halothane. Nevertheless, the effects of sevoflurane on cardiac rhythm and function have not been systematically investigated in infants. Thus, we compared cardiac rhythm and left ventricular function at 1 MAC sevoflurane and halothane anesthesia and investigated the potential benefit effect of atropine.

METHODS

Twenty infants ASA physical status I or II were randomly assigned to have anesthesia induced with either sevoflurane (up to 5%) or halothane (up to 1.5%). After insertion of an i.v. line, anesthesia was maintained at 1 MAC sevoflurane (group S) or 1 MAC halothane (group H) with infants breathing spontaneously in 100% oxygen. Cardiac output and contractility were measured by transthoracic echocardiography. Three sets of hemodynamic parameters were averaged prior to and after administration of 20 microg x kg(-1) of i.v. atropine.

RESULTS

Infants breathing spontaneously 1 MAC halothane or 1 MAC sevoflurane were found to have comparable hemodynamic parameters. After atropine administration, heart rate and cardiac index (CI) increased significantly in both groups (19.6 +/- 7.6% in group H and 21.3 +/- 13.1% in group S, 18.6 +/- 8.8% in group H and 17.7 +/- 12% in group S respectively). Moreover, atropine induced an increase in left ventricular shortening fraction with no difference between groups. In contrast, only infants in group S presented a significant increase in ejection fraction.

CONCLUSIONS

Indices of left ventricular function were comparable between groups with no clinically significant change following atropine administration. The present study confirms the favorable hemodynamic profile of sevoflurane in infants breathing spontaneously at 1 MAC concentration.