In Vivo Evaluation of Brain [18F]F-FDG Uptake Pattern Under Different Anaesthesia Protocols

BACKGROUND/AIM

Since the use of anaesthetics has the drawback of altering radiotracer distribution, preclinical positron emission tomography (PET) imaging findings of anaesthetised animals must be carefully handled. This study aimed at assessing the cerebral [18F]F-FDG uptake pattern in healthy Wistar rats under four different anaesthesia protocols using microPET/magnetic resonance imaging (MRI) examinations.

MATERIALS AND METHODS

Post-injection of 15±1.2 MBq of [18F]F-FDG, either while awake or during the isoflurane-induced incubation phase was applied. Prior to microPET/MRI imaging, one group of the rats was subjected to forane-only anaesthesia while the other group was anaesthetised with the co-administration of forane and dexmedetomidine/Dexdor® Results: While as for the whole brain it was the addition of dexmedetomidine/Dexdor® to the anaesthesia protocol that generated the differences between the radiotracer concentrations of the investigated groups, regarding the cortex, the [18F]F-FDG accumulation was rather affected by the way of incubation. To ensure the most consistent and highest uptake, forane-induced anaesthesia coupled with an awake uptake condition seemed to be most suitable method of anaesthetisation for cerebral metabolic assessment. Diminished whole brain and cortical tracer accumulation detected upon dexmedetomidine/Dexdor® administration highlights the significance of the mechanism of action of different anaesthetics on radiotracer pharmacokinetics.

CONCLUSION

Overall, the standardization of PET protocols is of utmost importance to avoid the confounding factors derived from anaesthesia.

A chromosome-level genome assembly of anesthetic drug-producing Anisodus acutangulus provides insights into its evolution and the biosynthesis of tropane alkaloids

Tropane alkaloids (TAs), which are anticholinergic agents, are an essential class of natural compounds, and there is a growing demand for TAs with anesthetic, analgesic, and spasmolytic effects. Anisodus acutangulus (Solanaceae) is a TA-producing plant that was used as an anesthetic in ancient China. In this study, we assembled a high-quality, chromosome-scale genome of A. acutangulus with a contig N50 of 7.4 Mb. A recent whole-genome duplication occurred in A. acutangulus after its divergence from other Solanaceae species, which resulted in the duplication of ADC1 and UGT genes involved in TA biosynthesis. The catalytic activities of H6H enzymes were determined for three Solanaceae plants. On the basis of evolution and co-expressed genes, AaWRKY11 was selected for further analyses, which revealed that its encoded transcription factor promotes TA biosynthesis by activating AaH6H1 expression. These findings provide useful insights into genome evolution related to TA biosynthesis and have potential implications for genetic manipulation of TA-producing plants.

The Biology of General Anesthesia from Paramecium to Primate

General anesthesia serves a critically important function in the clinical care of human patients. However, the anesthetized state has foundational implications for biology because anesthetic drugs are effective in organisms ranging from paramecia, to plants, to primates. Although unconsciousness is typically considered the cardinal feature of general anesthesia, this endpoint is only strictly applicable to a select subset of organisms that are susceptible to being anesthetized. We review the behavioral endpoints of general anesthetics across species and propose the isolation of an organism from its environment - both in terms of the afferent arm of sensation and the efferent arm of action - as a generalizable definition. We also consider the various targets and putative mechanisms of general anesthetics across biology and identify key substrates that are conserved, including cytoskeletal elements, ion channels, mitochondria, and functionally coupled electrical or neural activity. We conclude with a unifying framework related to network function and suggest that general anesthetics - from single cells to complex brains - create inefficiency and enhance modularity, leading to the dissociation of functions both within an organism and between the organism and its surroundings. Collectively, we demonstrate that general anesthesia is not restricted to the domain of modern medicine but has broad biological relevance with wide-ranging implications for a diverse array of species.

A Rationale for Allopregnanolone Treatment of Alcohol Use Disorders: Basic and Clinical Studies

For many years, research from around the world has suggested that the neuroactive steroid (3α,5α)-3-hydroxypregnan-20-one (allopregnanolone or 3α,5α-THP) may have therapeutic potential for treatment of various symptoms of alcohol use disorders (AUDs). In this critical review, we systematically address all the evidence that supports such a suggestion, delineate the etiologies of AUDs that are addressed by treatment with allopregnanolone or its precursor pregnenolone, and the rationale for treatment of various components of the disease based on basic science and clinical evidence. This review presents a theoretical framework for understanding how endogenous steroids that regulate the effects of stress, alcohol, and the innate immune system could play a key role in both the prevention and the treatment of AUDs. We further discuss cautions and limitations of allopregnanolone or pregnenolone therapy with suggestions regarding the management of risk and the potential for helping millions who suffer from AUDs.

(R)-Ketamine exerts antidepressant actions partly via conversion to (2R,6R)-hydroxynorketamine, while causing adverse effects at sub-anaesthetic doses

BACKGROUND AND PURPOSE

(R)-Ketamine (arketamine) may have utility as a rapidly acting antidepressant. While (R)-ketamine has lower potency than (R,S)-ketamine to inhibit NMDA receptors in vitro, the extent to which (R)-ketamine shares the NMDA receptor-mediated adverse effects of (R,S)-ketamine in vivo has not been fully characterised. Furthermore, (R)-ketamine is metabolised to (2R,6R)-hydroxynorketamine (HNK), which may contribute to its antidepressant-relevant actions.

EXPERIMENTAL APPROACH

Using mice, we compared (R)-ketamine with a deuterated form of the drug (6,6-dideutero-(R)-ketamine, (R)-d2 -ketamine), which hinders its metabolism to (2R,6R)-HNK, in behavioural tests predicting antidepressant responses. We also examined the actions of intracerebroventricularly infused (2R,6R)-HNK. Further, we quantified putative NMDA receptor inhibition-mediated adverse effects of (R)-ketamine.

KEY RESULTS

(R)-d2 -Ketamine was identical to (R)-ketamine in binding to and functionally inhibiting NMDA receptors but hindered (R)-ketamine's metabolism to (2R,6R)-HNK. (R)-Ketamine exerted greater potency than (R)-d2 -ketamine in several antidepressant-sensitive behavioural measures, consistent with a role of (2R,6R)-HNK in the actions of (R)-ketamine. There were dose-dependent sustained antidepressant-relevant actions of (2R,6R)-HNK following intracerebroventricular administration. (R)-Ketamine exerted NMDA receptor inhibition-mediated behaviours similar to (R,S)-ketamine, including locomotor stimulation, conditioned-place preference, prepulse inhibition deficits, and motor incoordination, with approximately half the potency of the racemic drug.

CONCLUSIONS AND IMPLICATIONS

Metabolism of (R)-ketamine to (2R,6R)-HNK increases the potency of (R)-ketamine to exert antidepressant-relevant actions in mice. Adverse effects of (R)-ketamine require higher doses than those necessary for antidepressant-sensitive behavioural changes in mice. However, our data revealing that (R)-ketamine's adverse effects are elicited at sub-anaesthetic doses indicate a potential risk for sensory dissociation and abuse liability.

[Determination of 5 kinds of fish anesthetics residues in fish by ultra-high performance liquid chromatography-tandem mass spectrometry]

OBJECTIVE

A method for the simultaneous determination of 5 kinds of fish anesthetics residues in fish has been developed by ultra-high performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS). Eugenol, methyl-eugenol, methyl-isoeugenol, acetyl-isoeugenol and tricaine methanesulfonate(MS-222) were concerned.

METHODS

After homogenization fish samples were extracted by acetonitrile-water(80↿0, V/V), purified by Oasis PRiME HLB solid-phase extraction column. Then after centrifuged and concentrated, the samples were separated by Waters ACQUITY UPLC BEH Phenyl column(2. 1 mm×100 mm, 1. 7 μm). The detection was confirmed and quantified by mass spectrum of triple quadrupole in the multiple reaction monitoring(MRM) mode.

RESULTS

The calibration curves showed good linearity in each range with correlation coefficients greater than 0. 995. Three levels spiked recovery experiments were carried out using blank fish mud extraction as substrate, the recoveries ranged from 72. 6% to 106. 0%, the relative standard deviations(RSDs) ranged from 2. 2% to 20. 1%(n=6). The qualitative limits of detections(S/N>3) were 0. 14-0. 30 μg/kg and the quantitative limits(S/N>10) were 0. 5-1. 0 μg/kg.

CONSLUSION

The method is simple and easy to operate, with less organic reagent, high sensitivity and good stability. The isomers of methyl eugenol and methyl isoeugenol were successfully separated. It is suitable for the detection of 5 kinds of fish anesthetics in fish.

Noninvasive Ultrasonic Drug Uncaging Maps Whole-Brain Functional Networks

Being able to noninvasively modulate brain activity, where and when an experimenter desires, with an immediate path toward human translation is a long-standing goal for neuroscience. To enable robust perturbation of brain activity while leveraging the ability of focused ultrasound to deliver energy to any point of the brain noninvasively, we have developed biocompatible and clinically translatable nanoparticles that allow ultrasound-induced uncaging of neuromodulatory drugs. Utilizing the anesthetic propofol, together with electrophysiological and imaging assays, we show that the neuromodulatory effect of ultrasonic drug uncaging is limited spatially and temporally by the size of the ultrasound focus, the sonication timing, and the pharmacokinetics of the uncaged drug. Moreover, we see secondary effects in brain regions anatomically distinct from and functionally connected to the sonicated region, indicating that ultrasonic drug uncaging could noninvasively map the changes in functional network connectivity associated with pharmacologic action at a particular brain target.

Transepidermal water loss and skin conductance as barrier integrity tests

In vitro skin permeation studies are commonly used in the risk assessment of toxic compound skin exposure. The present study examined the utility of transepidermal water loss (TEWL) and electrical conductance as barrier integrity tests before skin permeation studies in vitro using a large number of skin samples and fentanyl. TEWL and conductance of the skin samples were measured before the permeation experiments in Franz diffusion cells in vitro with a vapometer and low voltage application, respectively. The data were analyzed based on the in vitro permeation results and in vivo skin absorption information from the transdermal fentanyl product labels. The results showed poor correlations between TEWL and electrical conductance for the skin samples. Weak correlations between fentanyl delivery rate (flux x area) and TEWL and skin conductance were observed. For comparison, TEWL and conductance were also examined after skin perturbation with a syringe needle, and both TEWL and conductance values of the skin samples increased after the perturbation. The data suggest that either TEWL of 10 g/m²/h or skin conductance of 0.07 mS/cm² can be used as exclusion criteria in skin integrity testing to remove skin samples with high permeabilities under the in vitro conditions studied.

Facile fabrication of polyanhydride/anesthetic nanoparticles with tunable release kinetics

This work illustrates a two-step strategy for the fabrication of polymer/drug nanoparticles. Utilizing solvent/non-solvent precipitation and gaseous basification, composite nanoparticles with 0-100% drug loadings are fabricated. Drug release kinetics are dictated by nanoparticle composition allowing future tuning for therapeutic applications.

NMR structures of the human α7 nAChR transmembrane domain and associated anesthetic binding sites

The α7 nicotinic acetylcholine receptor (nAChR), assembled as homomeric pentameric ligand-gated ion channels, is one of the most abundant nAChR subtypes in the brain. Despite its importance in memory, learning and cognition, no structure has been determined for the α7 nAChR TM domain, a target for allosteric modulators. Using solution state NMR, we determined the structure of the human α7 nAChR TM domain (PDB ID: 2MAW) and demonstrated that the α7 TM domain formed functional channels in Xenopus oocytes. We identified the associated binding sites for the anesthetics halothane and ketamine; the former cannot sensitively inhibit α7 function, but the latter can. The α7 TM domain folds into the expected four-helical bundle motif, but the intra-subunit cavity at the extracellular end of the α7 TM domain is smaller than the equivalent cavity in the α4β2 nAChRs (PDB IDs: 2LLY; 2LM2). Neither drug binds to the extracellular end of the α7 TM domain, but two halothane molecules or one ketamine molecule binds to the intracellular end of the α7 TM domain. Halothane and ketamine binding sites are partially overlapped. Ketamine, but not halothane, perturbed the α7 channel-gate residue L9'. Furthermore, halothane did not induce profound dynamics changes in the α7 channel as observed in α4β2. The study offers a novel high-resolution structure for the human α7 nAChR TM domain that is invaluable for developing α7-specific therapeutics. It also provides evidence to support the hypothesis: only when anesthetic binding perturbs the channel pore or alters the channel motion, can binding generate functional consequences.

Insights into distinct modulation of α7 and α7β2 nicotinic acetylcholine receptors by the volatile anesthetic isoflurane

Nicotinic acetylcholine receptors (nAChRs) are targets of general anesthetics, but functional sensitivity to anesthetic inhibition varies dramatically among different subtypes of nAChRs. Potential causes underlying different functional responses to anesthetics remain elusive. Here we show that in contrast to the α7 nAChR, the α7β2 nAChR is highly susceptible to inhibition by the volatile anesthetic isoflurane in electrophysiology measurements. Isoflurane-binding sites in β2 and α7 were found at the extracellular and intracellular end of their respective transmembrane domains using NMR. Functional relevance of the identified β2 site was validated via point mutations and subsequent functional measurements. Consistent with their functional responses to isoflurane, β2 but not α7 showed pronounced dynamics changes, particularly for the channel gate residue Leu-249(9'). These results suggest that anesthetic binding alone is not sufficient to generate functional impact; only those sites that can modulate channel dynamics upon anesthetic binding will produce functional effects.

Ketamine pharmacology: an update (pharmacodynamics and molecular aspects, recent findings)

For more than 50 years, ketamine has proven to be a safe anesthetic drug with potent analgesic properties. The active enantiomer is S(+)-ketamine. Ketamine is mostly metabolized in norketamine, an active metabolite. During "dissociative anesthesia", sensory inputs may reach cortical receiving areas, but fail to be perceived in some association areas. Ketamine also enhances the descending inhibiting serotoninergic pathway and exerts antidepressive effects. Analgesic effects persist for plasma concentrations ten times lower than hypnotic concentrations. Activation of the (N-Methyl-D-Aspartate [NMDA]) receptor plays a fundamental role in long-term potentiation but also in hyperalgesia and opioid-induced hyperalgesia. The antagonism of NMDA receptor is responsible for ketamine's more specific properties. Ketamine decreases the "wind up" phenomenon, and the antagonism is more important if the NMDA channel has been previously opened by the glutamate binding ("use dependence"). Experimentally, ketamine may promote neuronal apoptotic lesions but, in usual clinical practice, it does not induce neurotoxicity. The consequences of high doses, repeatedly administered, are not known. Cognitive disturbances are frequent in chronic users of ketamine, as well as frontal white matter abnormalities. Animal studies suggest that neurodegeneration is a potential long-term risk of anesthetics in neonatal and young pediatric patients.

3-Hydroxybutyric acid interacts with lipid monolayers at concentrations that impair consciousness

3-Hydroxybutyric acid (also referred to as β-hydroxybutyric acid or BHB), a small molecule metabolite whose concentration is elevated in type I diabetes and diabetic coma, was found to modulate the properties of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayers when added to the subphase at clinical concentrations. This is a key piece of evidence supporting the hypothesis that the anesthetic actions of BHB are due to the metabolite's abilities to alter physical properties of cell membranes, leading to indirect effects on membrane protein function. Pressure-area isotherms show that BHB changes the compressibility of the monolayer and decrease the size of the two-phase coexistence region. Epi-fluorescent microscopy further reveals that the reduction of the coexistence region is due to the significant reduction in morphology of the liquid condensed domains in the two-phase coexistence region. These changes in monolayer morphology are associated with the diminished interfacial viscosity of the monolayers (measured using an interfacial stress rheometer), which gives insight as to how changes in phase and structure may contribute to membrane function.

Evaluation of tetrahydrobiopterin pathway in operating room workers: changes in biopterin status and tryptophan metabolism

The aim of the study was to evaluate the effect of anesthetics as operating room contaminants on tetrahydrobiopterin pathway in 40 operating room personnel and 30 healthy controls by measuring biopterin, dihydrobiopterin reductase, tryptophan, kynurenine and serotonin. Biopterin concentrations were 124 ± 12.3 µmol/mol creatinine in workers and 88 ± 5.7 µmol/mol creatinine in controls whereas kynurenine concentrations were 1.75 ± 0.09 µM and 1.95 ± 0.06 µM, respectively (both, p < 0.05). It can be claimed that enhanced biopterin and diminished kynurenine levels may play a triggering role in disruption of metabolic events in operating room personnel.

Impact of respiratory pattern on lung mechanics and interstitial proteoglycans in spontaneously breathing anaesthetized healthy rats

AIM

The aim of this study was to investigate the effect of different pattern of spontaneous breathing on the respiratory mechanics and on the integrity of the pulmonary extracellular matrix.

METHODS

Experiments were performed on adult healthy rats in which different spontaneously breathing pattern was elicited through administration of two commonly used anaesthetic mixtures: pentobarbital/urethane (P/U) and ketamine/medetomidine (K/M). The animals (five per group) were randomized and left to spontaneously breath for 10 min (P/U-sham; K/M-sham) or for 4h (P/U-4h; K/M-4h), targeting the anaesthesia level to obtain a tidal volume of about 8 mL kg(-1) body wt. At the end of the experiment, lung matrix integrity was assessed through determination of the glycosaminoglycans (GAGs) content in the lung parenchyma.

RESULTS

Compared with K/M, anaesthesia with P/U cocktail induced: (1) a higher respiratory rate and minute ventilation attained with lower P(a) CO(2) ; (2) a higher pressure-time-product and work of breathing per minute; (3) a lower static lung compliance; (4) an increased activation of lung tissue metalloproteases; and (5) greater extraction of pulmonary interstitial GAGs.

CONCLUSIONS

This study suggests that the breathing pattern induced by the different anaesthetic regimen may damage the pulmonary interstitium even during spontaneous breathing at physiological tidal volumes.

The use of Eugenol and electro-narcosis as anaesthetics: transcriptional impacts on the European eel (Anguilla anguilla L.)

Ecotoxicological studies aim to assess the potential environmental risks of various products. This implies the use of various biological models and tests on live animals. In case of handling fish and mammals, ethical rules have to be respected. The use of anaesthesia is considered to be the best way to ensure animal welfare. Eugenol and electro-narcosis are among the most popular chemical and physical anaesthetics used in fisheries and by field biologists. In this study, the genetic and endocrine impacts of these anaesthetics were assessed in order to establish whether the use of such methods could skew the results of ecotoxicological studies. Twenty yellow European eels (Anguilla anguilla) were submitted to Eugenol (50mg/L) and electro-narcosis until they reached a level of deep anaesthesia, while 20 other eels were kept aware. Five anaesthetized and five unanaesthetized eels were sacrificed and analysed directly after treatment and after 1, 7 and 21 days of recovery. At the brain level, Eugenol triggered an increase in the transcription level of genes encoding proteins involved in oxidative stress responses (catalase expression 2.5-fold, mitochondrial superoxide dismutase expression 3-fold), probably due to a hypoxic event during anaesthesia. Later impacts were detected in muscles 21 days after anaesthesia (ATP synthase subunit 6 3-fold, NADH deshydrogenase subunit 5 4-fold and mitochondrial superoxide dismutase 3-fold increased) revealing oxidative stress from an accrued mitochondrial respiratory metabolism. Hormone dosages showed that the use of Eugenol reduced the release of plasma cortisol during anaesthesia. However, this impact seemed to be reversible within one day. In case of electro-narcosis, no significant variation in transcriptional levels could be detected between anaesthetized and unanaesthetized eels. Our results suggest that the use of Eugenol as an aesthetic in ecotoxicological studies measuring gene expression or plasma cortisol concentration is not appropriate, while electro-narcosis does not seem to have any impact, at least on the parameters taken into consideration in this study.

[How far has our understanding of mechanisms of general anesthesia advanced?: preface and comments]

Although the great advance has been made in clinical anesthesia practice, the fundamental mechanisms of anesthetic action still remain to be an unsolved mystery. The early lipid membrane theory based on Meyer and Overton's law was taken over by the proteo-centric view of mechanism. Studies at the molecular and cellular level have shown that anesthetics act on a wide rage of functional proteins, including ligand-gated ion channels (GABA, glycine, NMDA receptors), two pore domain K channels and other ion channels. The effects on the individual channels, however, differ among various types of anesthetics. Elucidating how anesthetics work on the neuronal pathways is important to find the link between the molecular studies and in vivo action of anesthetics. Anesthesia disrupts the linkages between cortical and thalamic neurons and those among the cortical neurons, as well as depression and activation of the arousal and sleep nuclei, respectively. Functional brain imaging has revealed the global effects of general anesthetics on the human brain. Taken together, the disruption of thalamocortical connectivity and the integrative properties of the cerebral cortex might be an essential common feature of anesthetic action.

A review of recent neurochemical data on inert gas narcosis

Nitrogen narcosis occurs in humans at around 0.4 MPa (4 ATA). Hydrogen narcosis occurs between 2.6 and 3.0 MPa. In rats, nitrogen disturbances occur from 1 MPa and a loss of righting reflex around 4 MPa. Neurochemical studies in striatum of rats with nitrogen at 3 MPa (75% of anesthesia threshold) with differential pulse voltammetry have demonstrated a decrease in dopamine (DA) release by neurons originated from the substantia nigra pars compacta (SNc). Such a decrease is found also with compressed argon, which is more narcotic than nitrogen and with the anesthetic gas nitrous oxide. Inversely, compressed helium with its very low narcotic potency induces DA increase. Microdialysis studies in the striatum have indicated that nitrogen also induces a decrease of glutamate concentration. Nitrogen pressure did not modify NMDA glutamate receptor activities in SNc or striatum but enhanced GABAA receptors activities in SNc. Repetitive exposures to nitrogen narcosis suppressed the DA decrease and induced an increase. This fact and the lack of improvement of motor disturbances did not support the hypothesis of a physiological adaptation. The desensitization of the GABAA receptors on DA cells during recurrent exposures and the parallel long-lasting decrease of glutamate coupled to the increase in NMDA receptor sensitivity suggest a nitrogen neurotoxicity or addiction induced by recurrent exposures. The differential changes produced by inert gases indifferent neurotransmitter receptors would support the binding protein theory.

[Pharmacogenetical aspects of clinical anaesthesiology]

This survey of literature highlights the issues of pharmacogenetics and pharmacogenomics, the nomenclature of polymorphisms and the major clinically significant polymorphisms for the classes of medications which are most widespread in clinical anaesthesia. 53 data sources has been analyzed, including the polymorphism data base of National Center for Biotechnological Information (USA). Nowadays, choosing a medication do not provide for a individual genetic variability. It is possible that some of the drugs are potent to cause severe adverse effects or ineffective in certain subclasses of population due to unfavourable effectiveness/toxicity ratio. As the technology is developing, it is possible in future to treat every genetic subpopulation with a specific medication in order to obtain a target effect. Perhaps, it is too early to expect some immediate results of pharmacogenetics for a daily practice in anaesthesia. Nevertheless, it is possible that progress in genomics will enable a better understanding of those single nucleotide polymorphisms (SNPs) and haplotypes which alter the response to a medication. Those future discoveries will enable the targeting of the anaesthesia medications and personalization of the anaesthesia strategy aimed at improving the surgery outcomes as well as treating the acute and chronic pain according to a genetic profile of the patient.

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.

Interaction of lipids and ligands with nicotinic acetylcholine receptor vesicles assessed by electron paramagnetic resonance spectroscopy

Electron paramagnetic resonance (EPR) spectroscopy is a powerful technique that permits the study of membrane-embedded proteins in its lipid environment by assessing the interaction of spin labels with the protein in its natural environment (i.e., native membranes) or in reconstituted systems prepared with exogenous lipid species. Nicotinic acetylcholine receptors (AChRs) contain a large surface in intimate contact with the lipid membrane. AChRs, members of the Cys-loop receptor superfamily, have essential functional roles in the nervous system and its malfunctioning has been considered as the origin of several neurological diseases including Alzheimer's disease, drug addiction, depression, and schizophrenia. In this regard, these receptors have been extensively studied as therapeutic targets for the action of several drugs. The majority of the marketed medications bind to the neurotransmitter sites, the so-called agonists. However, several drugs, some of them still in clinical trials, interact with non-competitive antagonist (NCA) binding sites. A potential location for these binding sites is the proper ion channel, blocking ion flux and thus, inhibiting membrane depolarization. However, several NCAs also bind to the lipid-protein interface, modulating the AChR functional properties. The best known examples of these NCAs are local and general anesthetics. Several endogenous molecules such as free fatty acids and neurosteroids also bind to the lipid-protein interface, probably mediating important physiological functions. Phospholipids, natural components of lipid membranes interacting with the AChR, are also essential to maintain the structural and functional properties of the AChR. EPR studies showed that local anesthetics bind to the lipid-protein interface by essentially the same dynamic mechanisms found in lipids, and that local and general anesthetics preferably decrease the phospholipid but not the fatty acid interactions with the AChR. This is consistent with the existence of annular and non-annular lipid domains on the AChR.

Preoperative risk assessment for patients with liver disease

Patients with underlying liver disease often present for non-liver-related surgery and are at risk for postoperative decompensation. Several predictive models exist to determine the risk of morbidity and mortality after surgery in such patients, but the risk depends on the severity of liver disease and also the type and urgency of the surgery. Clinicians should be cognizant of the various risk assessment tools and incorporate them into their practice when encountering patients with liver disease undergoing surgery.

[Anaesthetics and breast feeding]

Many women undergo anaesthetic procedures related to childbirth or during the period of lactation. Most anaesthetic drugs are lipophilic and are thus excreted into breast milk. This article summarises available knowledge regarding anaesthetics, their excretion into breast milk and possible effects on the suckling infant. The consequences of such an exposure are discussed in terms of whether breast-feeding should be allowed or not after anaesthetic procedures.

Anesthetic properties of the ketone bodies beta-hydroxybutyric acid and acetone

BACKGROUND

We tested the hypothesis that two metabolites that are elevated in ketosis (beta-hydroxybutyric acid, and acetone) modulate ion channels in a manner similar to anesthetics and produce anesthesia in animals.

METHODS

alpha1beta2gamma2sgamma-aminobutyric acid type A (GABA(A)), alpha1 glycine, NR1/NR2A N-methyl-d-aspartate, and two pore domain TRESK channels were expressed in Xenopus laevis oocytes and studied using two-electrode voltage clamping. The effect of beta hydroxybutyric acid and acetone on channel function was measured. The anesthetic effects of these drugs were measured in X. laevis tadpoles.

RESULTS

Both beta hydroxybutyric acid and acetone enhanced glycine receptor function in the concentration range that is obtained in ketoacidosis in humans. Beta hydroxybutyric acid also enhanced GABA(A) receptor function at these concentrations. Both acetone and beta-hydroxybutyric acid anesthetized tadpoles, with an EC50 for acetone of 264 +/- 2 mM (mean +/- se) and for beta-hydroxybutyric acid of 151 +/- 11 mM at pH 7.0. Acetone enhanced GABA(A) receptors at concentrations of 50 mM and above. Inhibition of TRESK channel function was seen with 100 mM acetone or larger concentration. N-methyl-D-aspartate receptor function was inhibited at concentrations of acetone of 200 mM and larger.

CONCLUSIONS

Beta hydroxybutyric acid and acetone are anesthetics. Both ketone bodies enhance inhibitory glycine receptors at concentrations observed clinically in ketoacidosis. In addition, beta-hydroxybutyric acid enhances GABA(A) receptor function at these concentrations. Subanesthetic concentrations of these drugs may contribute to the lethargy and impairment of consciousness seen in ketoacidosis.

Effects of hypothermia on drug disposition, metabolism, and response: A focus of hypothermia-mediated alterations on the cytochrome P450 enzyme system

OBJECTIVES

Therapeutic hypothermia has been shown to decrease neurologic damage in patients experiencing out-of-hospital cardiac arrest. In addition to being treated with hypothermia, critically ill patients are treated with an extensive pharmacotherapeutic regimen. The effects of hypothermia on drug disposition increase the probability for unanticipated toxicity, which could limit its putative benefit. This review examines the effects of therapeutic hypothermia on the disposition, metabolism, and response of drugs commonly used in the intensive care unit, with a focus on the cytochrome P450 enzyme system.

DATA SOURCES AND STUDY SELECTION

A MEDLINE/PubMed search from 1965 to June 2006 was conducted using the search terms hypothermia, drug metabolism, P450, critical care, cardiac arrest, traumatic brain injury, and pharmacokinetics.

DATA EXTRACTION AND SYNTHESIS

Twenty-one studies were included in this review. The effects of therapeutic hypothermia on drug disposition include both the effects during cooling and the effects after rewarming on drug metabolism and response. The studies cited in this review demonstrate that the addition of mild to moderate hypothermia decreases the systemic clearance of cytochrome P450 metabolized drugs between approximately 7% and 22% per degree Celsius below 37degreesC during cooling. The addition of hypothermia decreases the potency and efficacy of certain drugs.

CONCLUSIONS

This review provides evidence that the therapeutic index of drugs is narrowed during hypothermia. The magnitude of these alterations indicates that intensivists must be aware of these alterations in order to maximize the therapeutic efficacy of this modality. In addition to increased clinical attention, future research efforts are essential to delineate precise dosing guidelines and mechanisms of the effect of hypothermia on drug disposition and response.

[Effects of brain stem and spinal cord by isoflurane inhibiting nociceptive reflex]

OBJECTIVE

To explore the effect positions of the volatile anesthetic inhibiting the nociceptive reflex in the central nervous system.

METHODS

Thirty adult SD rats were randomly and equally divided into two groups that the lip and hind paw of rats were held by clamp. The minimum alveolar concentration (MAC) was determined by clamping two places: one was to clamp the hind paw of rats, of which the nervous reflex is controlled via the spinal cord; the another group was to clamp the lip of rats, of which the nervous reflex is controlled through the brain stem.

RESULTS

The isoflurane MAC was 1.44% +/- 0.09% in clamping the hind paw group, while 1.29% +/- 0.11% for clamping the lip group (P < 0.05).

CONCLUSION

Both brain stem and spinal cord are the effect positions of volatile anesthetics (especially isoflurane).

The Common Chemical Motifs Within Anesthetic Binding Sites

BACKGROUND

It is not yet possible to obtain crystal structures of anesthetic molecules bound to proteins that are plausible neuronal targets; for example, ligand-gated ion channels. However, there are x-ray crystal structures in which anesthetics are complexed with proteins that are not directly related to anesthetic action. Much useful information about anesthetic-protein interactions can be derived from the x-ray crystal structures of halothane-cholesterol oxidase, bromoform-luciferase, halothane-albumin, and dichloroethane-dehalogenase. These structures show anesthetic-protein interactions at the atomic level.

METHODS

We obtained the known coordinate files for bromoform-luciferase, halothane- albumin, dichloroethane-dehalogenase, and halothane-cholesterol oxidase. These were then modified by adding hydrogens, edited into subsets, and underwent a series of restrained molecular mechanics optimizations. Final analysis of anesthetic polarization within the anesthetic binding site occurred via combined molecular mechanics-quantum mechanics calculations.

RESULTS

The anesthetic binding sites within these well-characterized anesthetic-protein complexes possess a set of common characteristics that we refer to as "binding motifs." The common features of these motifs are polar and nonpolar interactions within an amphiphilic binding cavity, including the presence of weak hydrogen bond interactions with amino acids and water molecules. Calculations also demonstrated the polarizing effect of the amphipathic binding sites on what are otherwise considered quite hydrophobic anesthetics. This polarization appears energetically favorable.

CONCLUSIONS

Anesthetic binding to proteins involves amphipathic interactions.

Photoactive analogues of the haloether anesthetics provide high-resolution features from low-affinity interactions

The difficulty in obtaining binding target and site information for low-affinity drugs, like the inhaled anesthetics, has limited identification of their molecular effectors. Because such information can be provided by photoactive analogues, we designed, synthesized, and characterized a novel diazirnyl haloether that closely mimics isoflurane, the most widely used clinical general anesthetic. This compound, H-diaziflurane, is a nontoxic, potent anesthetic that potentiates GABA-gated ion channels in primary cultures of hippocampal neurons. Calorimetric and structural characterizations show that H-diaziflurane binds a model anesthetic host protein with similar energetics as isoflurane and forms photoadducts with residues lining the isoflurane binding site. H-diaziflurane will be immediately useful for identifying targets and sites important for the molecular pharmacology of the inhaled haloether anesthetics.

Recent neurochemical basis of inert gas narcosis and pressure effects

Compressed air or a nitrogen-oxygen mixture produces from 0.3 MPa nitrogen narcosis. The traditional view was that anaesthesia or narcosis occurs when the volume of a hydrophobic site is caused to expand beyond a critical amount by the absorption of molecules of a narcotic gas. The observation of the pressure reversal effect on general anaesthesia has for a long time supported the lipid theory. However, recently, protein theories are in increasing consideration since results have been interpreted as evidence for a direct anaesthetic-protein interaction. The question is to know whether inert gases act by binding processes on proteins of neurotransmitter receptors. Compression with breathing mixtures where nitrogen is replaced by helium which has a low narcotic potency induces from 1 MPa, the high pressure nervous syndrome which is related to neurochemical disturbances including changes of the amino-acid and monoamine neurotransmissions. The use of narcotic gas (nitrogen or hydrogen) added to a helium-oxygen mixture, reduced some symptoms of the HPNS but also had some effects due to an additional effect of the narcotic potency of the gas. The researches performed at the level of basal ganglia of the rat brain and particularly the nigro-striatal pathway involved in the control of the motor, locomotor and cognitive functions, disrupted by narcosis or pressure, have indicated that GABAergic neurotransmission is implicated via GABAa receptors.

Concentrations of extracellular free zinc (pZn)e in the central nervous system during simple anesthetization, ischemia and reperfusion

"Free Zn2+" (rapidly exchangeable Zn2+) is stored along with glutamate in the presynaptic terminals of specific specialized (gluzinergic) cerebrocortical neurons. This synaptically releasable Zn2+ has been recognized as a potent modulator of glutamatergic transmission and as a key toxin in excitotoxic neuronal injury. Surprisingly (despite abundant work on bound zinc), neither the baseline concentration of free Zn2+ in the brain nor the presumed co-release of free Zn2+ and glutamate has ever been directly observed in the intact brain in vivo. Here, we show for the first time in dialysates of rat and rabbit brain and human CSF samples from lumbar punctures that: (i) the resting or "tonic" level of free Zn2+ signal in the extracellular fluid of the rat, rabbit and human being is approximately 19 nM (95% range: 5-25 nM). This concentration is 15,000-fold lower than the "300 microM" concentration which is often used as the "physiological" concentration of free zinc for stimulating neural tissue. (ii) During ischemia and reperfusion in the rabbit, free zinc and glutamate are (as has often been presumed) released together into the extracellular fluid. (iii) Unexpectedly, Zn2+ is also released alone (without glutamate) at a variable concentration for several hours during the reperfusion aftermath following ischemia. The source(s) of this latter prolonged release of Zn2+ is/are presumed to be non-synaptic and is/are now under investigation. We conclude that both Zn2+ and glutamate signaling occur in excitotoxicity, perhaps by two (or more) different release mechanisms.

Monolayers of a model anesthetic-binding membrane protein: formation, characterization, and halothane-binding affinity

hbAP0 is a model membrane protein designed to possess an anesthetic-binding cavity in its hydrophilic domain and a cation channel in its hydrophobic domain. Grazing incidence x-ray diffraction shows that hbAP0 forms four-helix bundles that are vectorially oriented within Langmuir monolayers at the air-water interface. Single monolayers of hbAP0 on alkylated solid substrates would provide an optimal system for detailed structural and dynamical studies of anesthetic-peptide interaction via x-ray and neutron scattering and polarized spectroscopic techniques. Langmuir-Blodgett and Langmuir-Schaeffer deposition and self-assembly techniques were used to form single monolayer films of the vectorially oriented peptide hbAP0 via both chemisorption and physisorption onto suitably alkylated solid substrates. The films were characterized by ultraviolet absorption, ellipsometry, circular dichroism, and polarized Fourier transform infrared spectroscopy. The alpha-helical secondary structure of the peptide was retained in the films. Under certain conditions, the average orientation of the helical axis was inclined relative to the plane of the substrate, approaching perpendicular in some cases. The halothane-binding affinity of the vectorially oriented hbAP0 peptide in the single monolayers, with the volatile anesthetic introduced into the moist vapor environment of the monolayer, was found to be similar to that for the detergent-solubilized peptide.

SELECTIVE PATHWAYS FOR THE METABOLISM OF PHENCYCLIDINE BY CYTOCHROME P450 2B ENZYMES: IDENTIFICATION OF ELECTROPHILIC METABOLITES, GLUTATHIONE, AND N-ACETYL CYSTEINE ADDUCTS

The metabolism of phencyclidine (PCP) has been studied previously in cytochrome P450 (P450)-containing microsomal systems. However, the reactive intermediate(s) that covalently binds to the P450 and leads to inactivation or leaves the active site to modify other proteins has not been identified. In this study two electrophilic intermediates of PCP were identified by mass spectrometry and by trapping with reduced glutathione (GSH) or N-acetyl cysteine (NAC). The tentative structures of these electrophilic intermediates were determined using mass spectrometry. P450s 2B1 and 2B4 formed a metabolite that exhibited an m/z of 240 corresponding to the mass of the 2,3-dihydropyridinium species of PCP or its conjugate base, the 1,2-dihydropyridine. Chemical reduction of the incubation mixture using NaBH4 resulted in the disappearance of the signal at m/z 240, consistent with reduction of a 2,3-dihydropyridinium species. Furthermore, the reactive metabolite trapped by GSH resulted in an adduct exhibiting an m/z of 547, consistent with the mass of the 2,3-dihydropyridinium species of PCP (m/z 240), that has reacted with a molecule of GSH (m/z 308). However, P450 2B6 formed a different reactive intermediate of PCP that was isolated as a GSH adduct exhibiting an m/z of 581 and an NAC adduct with an m/z of 437. Liquid chromatography-tandem mass spectrometry analysis of these adducts suggested that a di-oxygenated iminium metabolite of PCP could be the reactive intermediate formed by P450 2B6 but not by the other 2B isoforms. These data suggest that P450 2B6 favors oxidation pathways for PCP metabolism that are different from those of P450s 2B1 and 2B4.

Emerging molecular mechanisms of general anesthetic action

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.

Flotillins and the PHB Domain Protein Family: Rafts, Worms and Anaesthetics

While our understanding of lipid microdomains has advanced in recent years, many aspects of their formation and dynamics are still unclear. In particular, the molecular determinants that facilitate the partitioning of integral membrane proteins into lipid raft domains are yet to be clarified. This review focuses on a family of raft-associated integral membrane proteins, termed flotillins, which belongs to a larger class of integral membrane proteins that carry an evolutionarily conserved domain called the prohibitin homology (PHB) domain. A number of studies now suggest that eucaryotic proteins carrying this domain have affinity for lipid raft domains. The PHB domain is carried by a diverse array of proteins including stomatin, podocin, the archetypal PHB protein, prohibitin, lower eucaryotic proteins such as the Dictyostelium discoideum proteins vacuolin A and vacuolin B and the Caenorhabditis elegans proteins unc-1, unc-24 and mec-2. The presence of this domain in some procaryotic proteins suggests that the PHB domain may constitute a primordial lipid recognition motif. Recent work has provided new insights into the trafficking and targeting of flotillin and other PHB domain proteins. While the function of this large family of proteins remains unclear, studies of the C. elegans PHB proteins suggest possible links to a class of volatile anaesthetics raising the possibility that these lipophilic agents could influence lipid raft domains. This review will discuss recent insights into the cell biology of flotillins and the large family of evolutionarily conserved PHB domain proteins.

Formation and toxicity of anesthetic degradation products

Toxic degradation products are formed from a range of old and modern anesthetic agents. The common element in the formation of degradation products is the reaction of the anesthetic agent with the bases in the carbon dioxide absorbents in the anesthesia circuit. This reaction results in the conversion of trichloroethylene to dichloroacetylene, halothane to 2-bromo-2-chloro-1,1-difluoroethylene, sevoflurane to 2-(fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (Compound A), and desflurane, isoflurane, and enflurane to carbon monoxide. Dichloroacetylene, 2-bromo-2-chloro-1,1-difluoroethylene, and Compound A form glutathione S-conjugates that undergo hydrolysis to cysteine S-conjugates and bioactivation of the cysteine S-conjugates by renal cysteine conjugate beta-lyase to give nephrotoxic metabolites. The elucidation of the mechanisms of formation and bioactivation of degradation products has allowed for the safe use of anesthetics that may undergo degradation in the anesthesia circuit.

The lipid/protein interface as xenobiotic target site

High-resolution X-ray diffraction structures of integral membrane proteins have revealed various binding modes of lipids, but current spectroscopic studies still use uniform macroscopic binding constants to describe lipid binding. The Adair approach employing microscopic lipid-binding constants has previously been taken to explain the enhancement of agonist binding to the nicotinic acetylcholine receptor by general anaesthetics in terms of the competitive displacement of essential lipid activator molecules [Walcher S, Altschuh J & Sandermann H (2001) J. Biol. Chem.276, 42191-42195]. This approach was extended to tadpole narcosis induced by alcohols. A single class, or two different classes of lipid activator binding sites, are considered. Microscopic lipid and inhibitor binding constants are derived and allow a close fit to dose-response curves of tadpole narcosis on the basis of a preferential displacement of more loosely bound essential lipid activator molecules. This study illustrates the potential of the Adair approach to resolve protein-bound lipid populations.

Pharmacogenetics of Anesthetic and Analgesic Agents

Predicting a patient's response to a particular drug has long been a goal of clinicians. Rapid advances in molecular biology have enabled researchers to identify associations between an individual's genetic profile and drug response. Pharmacogenetics is the study of the molecular mechanisms that underlie individual differences in drug metabolism, efficacy, and side effects. The pharmacogenetics of commonly used anesthetic and analgesic agents are reviewed.

Homology Modeling of a Human Glycine Alpha 1 Receptor Reveals a Plausible Anesthetic Binding Site

The superfamily of ligand-gated ion channels (LGICs) has been implicated in anesthetic and alcohol responses. Mutations within glycine and GABA receptors have demonstrated that possible sites of anesthetic action exist within the transmembrane subunits of these receptors. The exact molecular arrangement of this transmembrane region remains at intermediate resolution with current experimental techniques. Homology modeling methods were therefore combined with experimental data to produce a more exact model of this region. A consensus from multiple bioinformatics techniques predicted the topology within the transmembrane domain of a glycine alpha one receptor (GlyRa1) to be alpha helical. This fold information was combined with sequence information using the SeqFold algorithm to search for modeling templates. Independently, the FoldMiner algorithm was used to search for templates that had structural folds similar to published coordinates of the homologous nAChR (1OED). Both SeqFold and Foldminer identified the same modeling template. The GlyRa1 sequence was aligned with this template using multiple scoring criteria. Refinement of the alignment closed gaps to produce agreement with labeling studies carried out on the homologous receptors of the superfamily. Structural assignment and refinement was achieved using Modeler. The final structure demonstrated a cavity within the core of a four-helix bundle. Residues known to be involved in modulating anesthetic potency converge on and line this cavity. This suggests that the binding sites for volatile anesthetics in the LGICs are the cavities formed within the core of transmembrane four-helix bundles.

Cytochrome P450 in neurological disease

Advances in a multitude of disciplines support an emerging role for cytochrome P450 enzymes and their metabolic substrates and end-products in the pathogenesis and treatment of central nervous system disorders, including acute cerebrovascular injury, such as stroke, chronic neurodegenerative disease, such as Alzheimer's and Parkinson's disease, as well as epilepsy, multiple sclerosis and psychiatric disorders, including anxiety and depression. The neural tissue contains its own unique set of P450 genes that are regulated in a manner that is distinct from their molecular regulation in peripheral tissue. Furthermore, brain P450s catalyze the formation of important brain signaling molecules, such as neurosteroids and eicosanoids, and metabolize substrates as diverse as vitamins A and D, cholesterol, bile acids, as well as centrally acting drugs, anesthetics and environmental neurotoxins. These unique characteristics allow this family of proteins and their metabolites to perform such vital functions in brain as neurotrophic support, neuroprotection, control of cerebral blood flow, temperature control, neuropeptide release, maintenance of brain cholesterol homoeostasis, elimination of retinoids from CNS, regulation of neurotransmitter levels and other functions important in brain physiology, development and disease.

Acute neurosteroid modulation and subunit isolation of the gamma-aminobutyric acidA receptor in the bullfrog, Rana catesbeiana

The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) has multiple receptors. In mammals, the GABA(A) receptor subtype is modulated by neurosteroids. However, whether steroid interaction with the GABA(A) receptor is unique to mammals or a conserved feature in vertebrates is unknown. Thus, neurosteroid modulation of the GABA(A) receptor was investigated in the brain of the bullfrog (Rana catesbeiana) using the mammalian GABA(A) receptor agonist [(3)H]muscimol. Two neurosteroids, allopregnanolone and pregnenolone sulfate, affected [(3)H]muscimol specific binding in bullfrog brain membrane preparations. Allopregnanolone significantly increased [(3)H]muscimol specific binding in a dose- and time-dependent manner. The pattern of allopregnanolone modulation supports the hypothesis that the bullfrog brain possesses both high-affinity and low-affinity [(3)H]muscimol binding sites. Unlike allopregnanolone, pregnenolone sulfate showed biphasic modulation with increased [(3)H]muscimol specific binding at low nanomolar concentrations and decreased specific binding at micromolar concentrations. Additionally, three cDNA fragments with significant homology to mammalian GABA(A) receptor subunits were isolated from the bullfrog brain. These fragments belong to the alpha1, beta1, and gamma2 subunit families. In mammals, GABA(A) receptors composed of these specific subunit isoforms are effectively modulated by neurosteroids, including allopregnanolone. Neurosteroid modulation of the amphibian brain GABA(A) receptor is therefore supported by both [(3)H]muscimol binding studies and subunit sequences. Allopregnanolone and pregnenolone sulfate modulation of this receptor may thus represent a significant mechanism for steroid influence on amphibian brain and behavior.

Evaluation of the induction and recovery characteristics of anesthesia with desflurane in cats

OBJECTIVE

To qualitatively and quantitatively evaluate the characteristics of desflurane with regard to the induction of and recovery from anesthesia in cats.

ANIMALS

6 cats.

PROCEDURE

Anesthesia was induced and maintained with desflurane in oxygen. Individual minimum alveolar concentration (MAC) values were determined; anesthesia was maintained at 1.25 x MAC for a total anesthesia time (including MAC determination) of 5 hours. Cats were allowed to recover from anesthesia. Induction and recovery periods were video recorded and later scored by use of a grading scale from 0 to 100 (100 being the best outcome). Timing of events was recorded.

RESULTS

The MAC of desflurane was 10.27 +/- 1.06%, and mean dose was 5.6 +/- 0.2 MAC-hours. Times to loss of coordination, recumbency, and endotracheal intubation were 1.3 +/- 0.4, 2.3 +/- 0.3, and 6.4 +/- 1.1 minutes, respectively. Median score for quality of anesthetic induction was 93 (range, 91 to 94). Times to first movement, extubation, standing, and ability to jump and land with coordination were 2.8 +/- 1.0, 3.8 +/- 0.5, 14.3 +/- 3.9, and 26.4 +/- 5.1 minutes, respectively. Alveolar washout of desflurane was rapid. Median score for quality of anesthetic recovery was 94 (range, 86 to 96).

CONCLUSIONS AND CLINICAL RELEVANCE

Desflurane was associated with rapid induction of and recovery from anesthesia in cats; assessors rated the overall quality of induction and recovery as excellent. Results appear to support the use of desflurane for induction and maintenance of anesthesia in healthy cats.

Receptor desensitization by neurotransmitters in membranes: are neurotransmitters the endogenous anesthetics?

A mechanism of anesthesia is proposed that addresses one of the most troubling peculiarities of general anesthesia: the remarkably small variability of sensitivity within the human population and across a broad range of animal phyla. It is hypothesized that in addition to the rapid, saturable binding of a neurotransmitter to its receptor that results in activation, the neurotransmitter also acts indirectly on the receptor by diffusing into the postsynaptic membrane and changing its physical properties, causing a shift in receptor conformational equilibrium (desensitization). Unlike binding, this slower indirect mechanism is nonspecific: each neurotransmitter will, in principle, affect all receptors in the membrane. For proteins modeled as having only resting and active conformational states, time-dependent ion currents are predicted that exhibit many characteristics of desensitization for both inhibitory and excitatory channels. If receptors have been engineered to regulate the time course of ion currents by this mechanism, then (a) mutations that significantly alter receptor sensitivity to this effect would be lethal and (b) by design, excitatory receptors would be inhibited, but inhibitory receptors activated, so that their effects are not counterproductive. The wide range of exogenous molecules that affect the physical properties of membranes as do neurotransmitters, but that do not bind to receptors, would thus inhibit excitatory channels and activate inhibitory channels, i.e., they would act as anesthesics. The endogenous anesthetics would thus be the neurotransmitters, the survival advantage conferred by their proper membrane-mediated desensitization of receptors explaining the selection pressure for anesthesic sensitivity.

[Surgery patients' intake of herbal preparations and dietary supplements]

INTRODUCTION

Herbal medicine is being frequently used by patients around the world. Several products may interact with ordinary medicine, so it is important for doctors to know what kind of herbal medicines their patients take.

MATERIAL AND METHODS

A questionnaire was given to presurgery patients during a two-month period.

RESULTS

A total of 115 consecutive patients responded, 69 women (60%) and 46 men (40%). 50.4% had taken or still took herbal medicine, with the following distribution of gender: women 69.8%, men 30.2%. The age group was 18-82 years. The frequently used herbal medicines were fish oil, ginkgo, Echinacea, Co-Q10, garlic, and hip. Twenty-five patients took nutritional supplements with the following spread of gender: 84% women and 16% men. The frequently used nutritional supplements were Gerimax, LongoVital, and Melbrosia. Not all patients would inform their doctor about their use of herbal medicine. 28.6% retained information because of the doctor and 64.3%, did not perceive herbal medicine as "real medicine".

DISCUSSION

It is important for anaesthesiologists to know what specific kind of herbal medicines patients are using before they anaesthetize them as interactions between herbal medicine and anaesthesia are prevalent. Anaesthesiologists have to ask specific questions to receive full information regarding herbal medicines during the preoperative period.