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Ketamine promptly normalizes excess norepinephrine and enhances dopamine neuronal activity in Wistar Kyoto rats. Front Pharmacol 2023; 14:1276309. [PMID: 38026921 PMCID: PMC10644068 DOI: 10.3389/fphar.2023.1276309] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2023] [Accepted: 10/06/2023] [Indexed: 12/01/2023] Open
Abstract
Ketamine acts primarily by blocking the N-methyl-D-aspartate (NMDA) receptor at the phencyclidine site. The rapid antidepressant properties of ketamine were demonstrated in the clinic and several behavioral models of depression in rodents. We hypothesized that the normalization of abnormal activity of monoamine neurons in Wistar Kyoto (WKY) rats contributes to the rapid antidepressant effects of ketamine. A single administration of ketamine (10 mg/kg, i. p) or saline was administered to anesthetized WKY rats before in vivo electrophysiological recordings of dorsal raphe nucleus (DRN) serotonin (5-HT), locus coeruleus (LC) norepinephrine (NE) and ventral tegmental area (VTA) dopamine (DA) neuronal activity. Pyramidal neurons from the medial prefrontal cortex (mPFC) were also recorded before and after a ketamine injection. In the VTA, ketamine elicited a significant increase in the population activity of DA neurons. This enhancement was consistent with findings in other depression-like models in which such a decreased population activity was observed. In the LC, ketamine normalized increased NE neuron burst activity found in WKY rats. In the DRN, ketamine did not significantly reverse 5-HT neuronal activity in WKY rats, which is dampened compared to Wistar rats. Ketamine did not significantly alter the neuronal activity of mPFC pyramidal neurons. These findings demonstrate that ketamine normalized NE neuronal activity and enhanced DA neuronal activity in WKY rats, which may contribute to its rapid antidepressant effect.
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Positive Allosteric Modulators of Glycine Receptors and Their Potential Use in Pain Therapies. Pharmacol Rev 2022; 74:933-961. [PMID: 36779343 PMCID: PMC9553105 DOI: 10.1124/pharmrev.122.000583] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2022] [Revised: 04/26/2022] [Accepted: 05/13/2022] [Indexed: 11/22/2022] Open
Abstract
Glycine receptors are ligand-gated ion channels that mediate synaptic inhibition throughout the mammalian spinal cord, brainstem, and higher brain regions. They have recently emerged as promising targets for novel pain therapies due to their ability to produce antinociception by inhibiting nociceptive signals within the dorsal horn of the spinal cord. This has greatly enhanced the interest in developing positive allosteric modulators of glycine receptors. Several pharmaceutical companies and research facilities have attempted to identify new therapeutic leads by conducting large-scale screens of compound libraries, screening new derivatives from natural sources, or synthesizing novel compounds that mimic endogenous compounds with antinociceptive activity. Advances in structural techniques have also led to the publication of multiple high-resolution structures of the receptor, highlighting novel allosteric binding sites and providing additional information for previously identified binding sites. This has greatly enhanced our understanding of the functional properties of glycine receptors and expanded the structure activity relationships of novel pharmacophores. Despite this, glycine receptors are yet to be used as drug targets due to the difficulties in obtaining potent, selective modulators with favorable pharmacokinetic profiles that are devoid of side effects. This review presents a summary of the structural basis for how current compounds cause positive allosteric modulation of glycine receptors and discusses their therapeutic potential as analgesics. SIGNIFICANCE STATEMENT: Chronic pain is a major cause of disability, and in Western societies, this will only increase as the population ages. Despite the high level of prevalence and enormous socioeconomic burden incurred, treatment of chronic pain remains limited as it is often refractory to current analgesics, such as opioids. The National Institute for Drug Abuse has set finding effective, safe, nonaddictive strategies to manage chronic pain as their top priority. Positive allosteric modulators of glycine receptors may provide a therapeutic option.
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Alpha-chloralose poisoning in cats in three Nordic countries - the importance of secondary poisoning. BMC Vet Res 2022; 18:334. [PMID: 36064401 PMCID: PMC9446805 DOI: 10.1186/s12917-022-03370-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2022] [Accepted: 06/27/2022] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Alpha-chloralose (AC) is a compound known to be toxic to various animal species and humans. In 2018 and 2019 an increase in suspected cases of AC poisoning in cats related to the use of AC as a rodenticide was reported to national veterinary and chemical authorities in Finland, Norway and Sweden by veterinarians working in clinical practices in respective country. The aims of this study were to prospectively investigate AC poisoning in cats, including possible secondary poisoning by consuming poisoned mice, and to study metabolism and excretion of AC in cats through analysis of feline urine. METHODS Data on signalment, history and clinical findings were prospectively collected in Finland, Norway and Sweden from July 2020 until March of 2021 using a questionnaire which the attending veterinarian completed and submitted together with a serum sample collected from suspected feline cases of AC-poisoning. The diagnosis was confirmed by quantification of AC in serum samples. Content of AC was studied in four feline urine samples, including screening for AC metabolites by UHPLC-HRMS/MS. Bait intake and amount of AC consumed by mice was observed in wild mice during an extermination of a rodent infestation. RESULTS In total, 59 of 70 collected questionnaires and accompanying serum samples were included, with 127 to 70 100 ng/mL AC detected in the serum. Several tentative AC-metabolites were detected in the analysed feline urine samples, including dechlorinated and oxidated AC, several sulfate conjugates, and one glucuronic acid conjugate of AC. The calculated amount of AC ingested by each mouse was 33 to 106 mg with a mean of 61 mg. CONCLUSIONS Clinical recognition of symptoms of AC poisoning in otherwise healthy cats roaming free outdoors and known to be rodent hunters strongly correlated with confirmation of the diagnosis through toxicological analyses of serum samples. The collected feline exposure data regarding AC show together with the calculation of the intake of bait and subsequent AC concentrations in mice that secondary poisoning from ingestion of mice is possible. The results of the screening for AC metabolites in feline urine confirm that cats excrete AC both unchanged and metabolized through dechlorination, oxidation, glucuronidation and sulfatation pathways.
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A Comparison of Brain-State Dynamics across Common Anesthetic Agents in Male Sprague-Dawley Rats. Int J Mol Sci 2022; 23:ijms23073608. [PMID: 35408973 PMCID: PMC8998244 DOI: 10.3390/ijms23073608] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 03/11/2022] [Accepted: 03/21/2022] [Indexed: 02/04/2023] Open
Abstract
Anesthesia is a powerful tool in neuroscientific research, especially in sleep research where it has the experimental advantage of allowing surgical interventions that are ethically problematic in natural sleep. Yet, while it is well documented that different anesthetic agents produce a variety of brain states, and consequently have differential effects on a multitude of neurophysiological factors, these outcomes vary based on dosages, the animal species used, and the pharmacological mechanisms specific to each anesthetic agent. Thus, our aim was to conduct a controlled comparison of spontaneous electrophysiological dynamics at a surgical plane of anesthesia under six common research anesthetics using a ubiquitous animal model, the Sprague-Dawley rat. From this direct comparison, we also evaluated which anesthetic agents may serve as pharmacological proxies for the electrophysiological features and dynamics of unconscious states such as sleep and coma. We found that at a surgical plane, pentobarbital, isoflurane and propofol all produced a continuous pattern of burst-suppression activity, which is a neurophysiological state characteristically observed during coma. In contrast, ketamine-xylazine produced synchronized, slow-oscillatory activity, similar to that observed during slow-wave sleep. Notably, both urethane and chloral hydrate produced the spontaneous, cyclical alternations between forebrain activation (REM-like) and deactivation (non-REM-like) that are similar to those observed during natural sleep. Thus, choice of anesthesia, in conjunction with continuous brain state monitoring, are critical considerations in order to avoid brain-state confounds when conducting neurophysiological experiments.
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Towards Quantum-Chemical Modeling of the Activity of Anesthetic Compounds. Int J Mol Sci 2021; 22:ijms22179272. [PMID: 34502179 PMCID: PMC8431746 DOI: 10.3390/ijms22179272] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Revised: 08/16/2021] [Accepted: 08/17/2021] [Indexed: 12/16/2022] Open
Abstract
The modeling of the activity of anesthetics is a real challenge because of their unique electronic and structural characteristics. Microscopic approaches relevant to the typical features of these systems have been developed based on the advancements in the theory of intermolecular interactions. By stressing the quantum chemical point of view, here, we review the advances in the field highlighting differences and similarities among the chemicals within this group. The binding of the anesthetics to their partners has been analyzed by Symmetry-Adapted Perturbation Theory to provide insight into the nature of the interaction and the modeling of the adducts/complexes allows us to rationalize their anesthetic properties. A new approach in the frame of microtubule concept and the importance of lipid rafts and channels in membranes is also discussed.
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Development and Validation of a Quantitative UHPLC-MS/MS Method for the Determination of Alpha-Chloralose in Feline Blood and Application on Blood Samples Collected From Cats With Symptoms of Alpha-Chloralose Poisoning. J Anal Toxicol 2021; 46:651-657. [PMID: 34313718 PMCID: PMC9282274 DOI: 10.1093/jat/bkab087] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Revised: 07/23/2021] [Accepted: 07/27/2021] [Indexed: 12/03/2022] Open
Abstract
Alpha-chloralose (AC) is used as a rodenticide as well as an anesthetic agent in laboratory animals. It was previously also used as an avicide. Detection of AC in blood samples or in body tissues collected postmortem is key for the diagnosis of clinical cases and a requirement for surveillance of secondary toxicosis, including potential cases in wild animals. Reports on poisoning of humans and non-laboratory animals confirmed by the detection of AC or its metabolites are available, however poisoning of domestic animals are rarely available. Furthermore, reports on clinical cases in domestic animals rarely report quantifications of AC in blood or body tissues. The present study describes the validation of a quantitative ultra high performance liquid chromatography--tandem mass spectrometry (UHPLC--MS-MS) method that can be used in cases of suspected AC poisoning in cats. The validation study showed the method to be fit for purpose. In serum, the limit of quantification was 100 ng/mL and the limit of detection was 30 ng/mL. The new analytical method was applied on blood samples collected from 20 individual cats with a preliminary clinical diagnosis of acute AC poisoning. AC was confirmed in all 20 feline blood samples, and the concentration range of AC was 538–17,500 ng/mL. The quantitative method developed in this study was found to be a fast and selective method for confirmation of AC poisoning using blood samples from cats.
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Mesoscopic Mapping of Ictal Neurovascular Coupling in Awake Behaving Mice Using Optical Spectroscopy and Genetically Encoded Calcium Indicators. Front Neurosci 2021; 15:704834. [PMID: 34366781 PMCID: PMC8343016 DOI: 10.3389/fnins.2021.704834] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Accepted: 06/30/2021] [Indexed: 11/13/2022] Open
Abstract
Unambiguously identifying an epileptic focus with high spatial resolution is a challenge, especially when no anatomic abnormality can be detected. Neurovascular coupling (NVC)-based brain mapping techniques are often applied in the clinic despite a poor understanding of ictal NVC mechanisms, derived primarily from recordings in anesthetized animals with limited spatial sampling of the ictal core. In this study, we used simultaneous wide-field mesoscopic imaging of GCamp6f and intrinsic optical signals (IOS) to record the neuronal and hemodynamic changes during acute ictal events in awake, behaving mice. Similar signals in isoflurane-anesthetized mice were compared to highlight the unique characteristics of the awake condition. In awake animals, seizures were more focal at the onset but more likely to propagate to the contralateral hemisphere. The HbT signal, derived from an increase in cerebral blood volume (CBV), was more intense in awake mice. As a result, the “epileptic dip” in hemoglobin oxygenation became inconsistent and unreliable as a mapping signal. Our data indicate that CBV-based imaging techniques should be more accurate than blood oxygen level dependent (BOLD)-based imaging techniques for seizure mapping in awake behaving animals.
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Volatile Anesthetics Regulate Anti-Cancer Relevant Signaling. Front Oncol 2021; 11:610514. [PMID: 33718164 PMCID: PMC7952859 DOI: 10.3389/fonc.2021.610514] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2020] [Accepted: 01/22/2021] [Indexed: 11/27/2022] Open
Abstract
Volatile anesthetics are widely used inhalation anesthetics in clinical anesthesia. In recent years, the regulation of anti-cancer relevant signaling of volatile anesthetics has drawn the attention of investigators. However, their underlying mechanism remains unclear. This review summarizes the research progress on the regulation of anti-cancer relevant signaling of volatile anesthetics, including sevoflurane, desflurane, xenon, isoflurane, and halothane in vitro, in vivo, and clinical studies. The present review article aims to provide a general overview of regulation of anti-cancer relevant signaling and explore potential underlying molecular mechanisms of volatile anesthetics. It may promote promising insights of guiding clinical anesthesia procedure and instructing enhance recovery after surgery (ERAS) with latent benefits.
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Isoflurane Potentiation of GABA A Receptors Is Reduced but Not Eliminated by the β3(N265M) Mutation. Int J Mol Sci 2020; 21:ijms21249534. [PMID: 33333797 PMCID: PMC7765171 DOI: 10.3390/ijms21249534] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2020] [Revised: 12/10/2020] [Accepted: 12/11/2020] [Indexed: 12/16/2022] Open
Abstract
Background: Mice carrying the GABAA receptor β3(N265M) point mutation, which renders receptors incorporating β3-subunits insensitive to many general anesthetics, have been used experimentally to link modulation of different receptor subtypes to distinct behavioral endpoints. Remarkably, however, the effect of the mutation on the susceptibility to modulation by isoflurane (a standard reference agent for inhalational vapors) has never been tested directly. Therefore, we compared the modulation by isoflurane of expressed α5β3(N265M)γ2L receptors with their wild type counterparts. Methods: Using whole-cell electrophysiological recording and rapid solution exchange techniques, we tested the effects of isoflurane at concentrations ranging from 80 μM to 320 μM on currents activated by 1 μM GABA. We measured drug modulation of wild-type α5β3γ2L GABAA receptors and their counterparts harboring the β3(N265M) mutation. Results: Currents elicited by GABA were enhanced two- to four-fold by isoflurane, in a concentration-dependent manner. Under the same conditions, receptors incorporating the β3(N265M) mutation were enhanced by approximately 1.5- to two-fold; i.e., modulation by isoflurane was attenuated by approximately one-half. Direct activation by isoflurane was also present in mutant receptors but also attenuated. Conclusions: In contrast to the complete insensitivity of β3(N265M) mutant receptors to etomidate and propofol, the mutation has only a partial effect on receptor modulation by isoflurane. Therefore, the persistence of isoflurane effects in mutant mice does not exclude a possible contribution of β3-GABAA receptors.
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Quantitative Analysis of Retinal Structure and Function in Two Chromosomally Altered Mouse Models of Down Syndrome. Invest Ophthalmol Vis Sci 2020; 61:25. [PMID: 32416604 PMCID: PMC7405684 DOI: 10.1167/iovs.61.5.25] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Purpose Ophthalmic disorders are among the most prevalent Down syndrome (DS) comorbidities. Therefore, when studying mouse models of DS, ignoring how vision is affected can lead to misinterpretation of results from assessments dependent on the integrity of the visual system. Here, we used imaging and electroretinography (ERG) to study eye structure and function in two important mouse models of DS: Ts65Dn and Dp(16)1Yey/+. Methods Cornea and anterior segment were examined with a slit-lamp. Thickness of retinal layers was quantified by optical coherence tomography (OCT). Eye and lens dimensions were measured by magnetic resonance imaging (MRI). Retinal vasculature parameters were assessed by bright field and fluorescent imaging, and by retinal flat-mount preparations. Ganzfeld ERG responses to flash stimuli were used to assess retinal function in adult mice. Results Total retinal thickness is significantly increased in Ts65Dn and Dp(16)1Yey/+ compared with control mice, because of increased thickness of inner retinal layers, including the inner nuclear layer (INL). Increased retinal vessel caliber was found in both chromosomally altered mice when compared with controls. ERG responses in Ts65Dn and Dp(16)1Yey/+ mice showed subtle alterations compared with controls. These, however, seemed to be unrelated to the thickness of the INL, but instead dependent on the anesthetic agent used (ketamine, tribromoethanol, or urethane). Conclusions We provide evidence of retinal alterations in Ts65Dn and Dp(16)1Yey/+ mice that are similar to those reported in persons with DS. Our ERG results are also a reminder that consideration should be given to the choice of anesthetic agents in such experiments.
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Anaesthesia with diethyl ether impairs jasmonate signalling in the carnivorous plant Venus flytrap (Dionaea muscipula). ANNALS OF BOTANY 2020; 125:173-183. [PMID: 31677265 PMCID: PMC6948209 DOI: 10.1093/aob/mcz177] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 08/06/2019] [Accepted: 10/25/2019] [Indexed: 05/18/2023]
Abstract
BACKGROUND AND AIMS General anaesthetics are compounds that induce loss of responsiveness to environmental stimuli in animals and humans. The primary site of action of general anaesthetics is the nervous system, where anaesthetics inhibit neuronal transmission. Although plants do not have neurons, they generate electrical signals in response to biotic and abiotic stresses. Here, we investigated the effect of the general volatile anaesthetic diethyl ether on the ability to sense potential prey or herbivore attacks in the carnivorous plant Venus flytrap (Dionaea muscipula). METHODS We monitored trap movement, electrical signalling, phytohormone accumulation and gene expression in response to the mechanical stimulation of trigger hairs and wounding under diethyl ether treatment. KEY RESULTS Diethyl ether completely inhibited the generation of action potentials and trap closing reactions, which were easily and rapidly restored when the anaesthetic was removed. Diethyl ether also inhibited the later response: jasmonic acid (JA) accumulation and expression of JA-responsive genes (cysteine protease dionain and type I chitinase). However, external application of JA bypassed the inhibited action potentials and restored gene expression under diethyl ether anaesthesia, indicating that downstream reactions from JA are not inhibited. CONCLUSIONS The Venus flytrap cannot sense prey or a herbivore attack under diethyl ether treatment caused by inhibited action potentials, and the JA signalling pathway as a consequence.
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Gut microbiome: An intermediary to neurotoxicity. Neurotoxicology 2019; 75:41-69. [PMID: 31454513 DOI: 10.1016/j.neuro.2019.08.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2019] [Revised: 08/04/2019] [Accepted: 08/16/2019] [Indexed: 12/12/2022]
Abstract
There is growing recognition that the gut microbiome is an important regulator for neurological functions. This review provides a summary on the role of gut microbiota in various neurological disorders including neurotoxicity induced by environmental stressors such as drugs, environmental contaminants, and dietary factors. We propose that the gut microbiome remotely senses and regulates CNS signaling through the following mechanisms: 1) intestinal bacteria-mediated biotransformation of neurotoxicants that alters the neuro-reactivity of the parent compounds; 2) altered production of neuro-reactive microbial metabolites following exposure to certain environmental stressors; 3) bi-directional communication within the gut-brain axis to alter the intestinal barrier integrity; and 4) regulation of mucosal immune function. Distinct microbial metabolites may enter systemic circulation and epigenetically reprogram the expression of host genes in the CNS, regulating neuroinflammation, cell survival, or cell death. We will also review the current tools for the study of the gut-brain axis and provide some suggestions to move this field forward in the future.
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New evidence for refinement of anesthetic choice in procedures preceding the forced swimming test and the elevated plus-maze. Behav Brain Res 2019; 368:111897. [PMID: 30978407 DOI: 10.1016/j.bbr.2019.04.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 04/07/2019] [Accepted: 04/08/2019] [Indexed: 01/04/2023]
Abstract
Previous studies indicated that some general anesthetics induce long-term antidepressant and/or anxiolytic-like effects. This raises the concern about the use of anesthesia in surgeries that precede psychopharmacological tests, since it may be a potential bias on results depending on the experimental design used. Thus, we evaluated whether general anesthetics used in surgeries preceding psychopharmacological tests would affect rats behavior in tests predictive of antidepressant or anxiolytic-like effects. We tested if a single exposure to sub-anesthetic or anesthetic doses of tribromoethanol, chloral hydrate, thiopental or isoflurane would change rats behavior in the forced swimming test (FST) or in the elevated plus-maze (EPM) test, at 2 h or 7 days after their administration. We also evaluated whether prior anesthesia would interfere in the detection of the antidepressant-like effect of imipramine or the anxiolytic-like effect of diazepam. Previous anesthesia with the aforementioned anesthetics did not change rats behaviors in FST per se nor it changed the antidepressant-like effect induced by imipramine treatment. Rats previously anesthetized with tribromoethanol or chloral hydrate exhibited, respectively, anxiogenic-like and anxiolytic-like behaviors in the EPM. Prior anesthesia with thiopental or isoflurane did not produce any per se effect in rats behaviors in the EPM nor disturbed the anxiolytic-like effect of diazepam. Our results suggest that, in our experimental conditions, tribromoethanol and chloral hydrate are improper anesthetics for surgeries that precede behavioral analysis in the EPM. Isoflurane or thiopental may be suitable for anesthesia before evaluation in the EPM or in the FST.
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Abstract
Inhalants are a loosely organized category of abused compounds defined entirely by their common route of administration. Inhalants include volatile solvents, fuels, volatile anesthetics, gasses, and liquefied refrigerants, among others. They are ubiquitous in modern society as ingredients in a wide variety of household, commercial, and medical products. Persons of all ages abuse inhalants but the highest prevalence of abuse is in younger adolescents. Although inhalants have been shown to act upon a host of neurotransmitter receptors, the stimulus effects of the few inhalants which have been trained or tested in drug discrimination procedures suggest that their discriminative stimulus properties are mediated by a few key neurotransmitter receptor systems. Abused volatile solvent inhalants have stimulus effects that are similar to a select group of GABAA positive modulators comprised of benzodiazepines and barbiturates. In contrast the stimulus effects of nitrous oxide gas appear to be at least partially mediated by uncompetitive antagonism of NMDA receptors. Finally, volatile anesthetic inhalants have stimulus effects in common with both GABAA positive modulators as well as competitive NMDA antagonists. In addition to a review of the pharmacology underlying the stimulus effects of inhalants, the chapter also discusses the scientific value of utilizing drug discrimination as a means of functionally grouping inhalants according to their abuse-related pharmacological properties.
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Increased glymphatic influx is correlated with high EEG delta power and low heart rate in mice under anesthesia. SCIENCE ADVANCES 2019; 5:eaav5447. [PMID: 30820460 PMCID: PMC6392807 DOI: 10.1126/sciadv.aav5447] [Citation(s) in RCA: 242] [Impact Index Per Article: 48.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Accepted: 01/14/2019] [Indexed: 05/15/2023]
Abstract
The glymphatic system is responsible for brain-wide delivery of nutrients and clearance of waste via influx of cerebrospinal fluid (CSF) alongside perivascular spaces and through the brain. Glymphatic system activity increases during sleep or ketamine/xylazine (K/X) anesthesia, yet the mechanism(s) facilitating CSF influx are poorly understood. Here, we correlated influx of a CSF tracer into the brain with electroencephalogram (EEG) power, heart rate, blood pressure, and respiratory rate in wild-type mice under six different anesthesia regimens. We found that glymphatic CSF tracer influx was highest under K/X followed by isoflurane (ISO) supplemented with dexmedetomidine and pentobarbital. Mice anesthetized with α-chloralose, Avertin, or ISO exhibited low CSF tracer influx. This is the first study to show that glymphatic influx correlates positively with cortical delta power in EEG recordings and negatively with beta power and heart rate.
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Identification of eugenol as the major determinant of GABAA-receptor activation by aqueous Syzygium aromaticum L. (clove buds) extract. J Funct Foods 2017. [DOI: 10.1016/j.jff.2017.08.033] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Methoxyflurane inhalation vapour in trauma pain: a profile of its use in the EU. DRUGS & THERAPY PERSPECTIVES 2017. [DOI: 10.1007/s40267-017-0433-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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GABAergic effect on resting-state functional connectivity: Dynamics under pharmacological antagonism. Neuroimage 2017; 149:53-62. [DOI: 10.1016/j.neuroimage.2017.01.040] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Revised: 12/06/2016] [Accepted: 01/17/2017] [Indexed: 11/19/2022] Open
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Halogenated Ether, Alcohol, and Alkane Anesthetics Activate TASK-3 Tandem Pore Potassium Channels Likely through a Common Mechanism. Mol Pharmacol 2017; 91:620-629. [PMID: 28325748 DOI: 10.1124/mol.117.108290] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2017] [Accepted: 03/20/2017] [Indexed: 01/10/2023] Open
Abstract
The TWIK-related acid-sensitive potassium channel 3 (TASK-3; KCNK9) tandem pore potassium channel function is activated by halogenated anesthetics through binding at a putative anesthetic-binding cavity. To understand the pharmacologic requirements for TASK-3 activation, we studied the concentration-response of TASK-3 to several anesthetics (isoflurane, desflurane, sevoflurane, halothane, α-chloralose, 2,2,2-trichloroethanol [TCE], and chloral hydrate), to ethanol, and to a panel of halogenated methanes and alcohols. We used mutagenesis to probe the anesthetic-binding cavity as observed in a TASK-3 homology model. TASK-3 activation was quantified by Ussing chamber voltage clamp analysis. We mutagenized the residue Val-136, which lines the anesthetic-binding cavity, its flanking residues (132 to 140), and Leu-122, a pore-gating residue. The 2-halogenated ethanols activate wild-type TASK-3 with the following rank order efficacy (normalized current [95% confidence interval]): 2,2,2-tribromo-(267% [240-294]) > 2,2,2-trichloro-(215% [196-234]) > chloral hydrate (165% [161-176]) > 2,2-dichloro- > 2-chloro ≈ 2,2,2-trifluoroethanol > ethanol. Similarly, carbon tetrabromide (296% [245-346]), carbon tetrachloride (180% [163-196]), and 1,1,1,3,3,3-hexafluoropropanol (200% [194-206]) activate TASK-3, whereas the larger carbon tetraiodide and α-chloralose inhibit. Clinical agents activate TASK-3 with the following rank order efficacy: halothane (207% [202-212]) > isoflurane (169% [161-176]) > sevoflurane (164% [150-177]) > desflurane (119% [109-129]). Mutations at and near residue-136 modify TCE activation of TASK-3, and interestingly M159W, V136E, and L122D were resistant to both isoflurane and TCE activation. TASK-3 function is activated by a multiple agents and requires a halogenated substituent between ∼30 and 232 cm3/mol volume with potency increased by halogen polarizeability. Val-136 and adjacent residues may mediate anesthetic binding and stabilize an open state regulated by pore residue Leu-122. Isoflurane and TCE likely share commonalities in their mechanism of TASK-3 activation.
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Abstract
Methoxyflurane (Penthrox®) is a halogenated ether first used clinically as a volatile inhalational anaesthetic. It has been used as an analgesic in Australia and New Zealand for the past 30 years. In the UK and Europe, methoxyflurane has been approved for the emergency relief of moderate to severe trauma pain in conscious adult patients. Methoxyflurane is self-administered using a hand-held inhaler. This article reviews the pharmacological properties of methoxyflurane and its clinical efficacy and tolerability in these patients. In the phase III STOP! trial, methoxyflurane was effective and generally well tolerated for the management of acute pain due to minor trauma, with a rapid onset of analgesia. In a prospective study, methoxyflurane was more effective than intramuscular tramadol when administered for the treatment of acute musculoskeletal pain in the pre-hospital setting (i.e. by paramedics). Methoxyflurane had a more rapid onset of action than tramadol when administered for the treatment of pain related to ankle injuries in the emergency department. Although methoxyflurane is known to be potentially nephrotoxic at anaesthetic doses, the much lower doses used for pain relief were not associated with nephrotoxicity or an increased risk of renal disease. Inhaled methoxyflurane may offer advantages over other analgesics administered via the intravenous, intramuscular or intranasal routes in terms of its non-invasive self-administration, ease of use and/or rapid onset of action. As such, it is a useful additional treatment option for the management of trauma pain in the pre-hospital or emergency department setting.
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Three-Step Test System for the Identification of Novel GABA A Receptor Modulating Food Plants. PLANT FOODS FOR HUMAN NUTRITION (DORDRECHT, NETHERLANDS) 2016; 71:355-360. [PMID: 27392961 DOI: 10.1007/s11130-016-0566-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Potentiation of γ-amino butyric acid (GABA)-induced GABAA receptor (GABAAR) activation is a common pathway to achieve sedative, sleep-enhancing, anxiolytic, and antidepressant effects. Presently, a three-component test system was established for the identification of novel GABAAR modulating food plants. In the first step, potentiation of GABA-induced response of the GABAAR was analysed by two-electrode voltage clamp (TEVC) for activity on human α1β2-GABAAR expressed in Xenopus laevis oocytes. Positively tested food plants were then subjected to quantification of GABA content by high-performance liquid chromatography with fluorescence detection (HPLC-FLD) to exclude test foods, which evoke a TEVC-response by endogenous GABA. In the third step, specificity of GABAA-modulating activity was assessed by TEVC analysis of Xenopus laevis oocytes expressing the homologous glycine receptor (GlyR). The three-component test was then applied to screen 10 aqueous extracts of food plants for their GABAAR activity. Thus, hop cones (Humulus lupulus) and Sideritis sipylea were identified as the most potent specific GABAAR modulators eliciting significant potentiation of the current by 182 ± 27 and 172 ± 19 %, respectively, at the lowest concentration of 0.5 μg/mL. The extracts can now be further evaluated by in vivo studies and by structural evaluation of the active components.
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Exploring the Effects on Lipid Bilayer Induced by Noble Gases via Molecular Dynamics Simulations. Sci Rep 2015; 5:17235. [PMID: 26601882 PMCID: PMC4658558 DOI: 10.1038/srep17235] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2015] [Accepted: 10/27/2015] [Indexed: 12/30/2022] Open
Abstract
Noble gases seem to have no significant effect on the anesthetic targets due to their simple, spherical shape. However, xenon has strong narcotic efficacy and can be used clinically, while other noble gases cannot. The mechanism remains unclear. Here, we performed molecular dynamics simulations on phospholipid bilayers with four kinds of noble gases to elucidate the difference of their effects on the membrane. Our results showed that the sequence of effects on membrane exerted by noble gases from weak to strong was Ne, Ar, Kr and Xe, the same order as their relative narcotic potencies as well as their lipid/water partition percentages. Compared with the other three kinds of noble gases, more xenon molecules were distributed between the lipid tails and headgroups, resulting in membrane’s lateral expansion and lipid tail disorder. It may contribute to xenon’s strong anesthetic potency. The results are well consistent with the membrane mediated mechanism of general anesthesia.
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Isoflurane does not aggregate inside POPC bilayers at high pressure: Implications for pressure reversal of general anaesthesia. Chem Phys Lett 2015. [DOI: 10.1016/j.cplett.2015.07.065] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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Dominant Alcohol-Protein Interaction via Hydration-Enabled Enthalpy-Driven Binding Mechanism. J Phys Chem B 2015; 119:5367-75. [PMID: 25856773 DOI: 10.1021/acs.jpcb.5b00378] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Water plays an important role in weak associations of small drug molecules with proteins. Intense focus has been on binding-induced structural changes in the water network surrounding protein binding sites, especially their contributions to binding thermodynamics. However, water is also tightly coupled to protein conformations and dynamics, and so far little is known about the influence of water-protein interactions on ligand binding. Alcohols are a type of low-affinity drugs, and it remains unclear how water affects alcohol-protein interactions. Here, we present alcohol adsorption isotherms under controlled protein hydration using in situ NMR detection. As functions of hydration level, Gibbs free energy, enthalpy, and entropy of binding were determined from the temperature dependence of isotherms. Two types of alcohol binding were found. The dominant type is low-affinity nonspecific binding, which is strongly dependent on temperature and the level of hydration. At low hydration levels, this nonspecific binding only occurs above a threshold of alcohol vapor pressure. An increased hydration level reduces this threshold, with it finally disappearing at a hydration level of h ≈ 0.2 (g water/g protein), gradually shifting alcohol binding from an entropy-driven to an enthalpy-driven process. Water at charged and polar groups on the protein surface was found to be particularly important in enabling this binding. Although further increase in hydration has smaller effects on the changes of binding enthalpy and entropy, it results in a significant negative change in Gibbs free energy due to unmatched enthalpy-entropy compensation. These results show the crucial role of water-protein interplay in alcohol binding.
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Manipulations of extracellular Loop 2 in α1 GlyR ultra-sensitive ethanol receptors (USERs) enhance receptor sensitivity to isoflurane, ethanol, and lidocaine, but not propofol. Neuroscience 2015; 297:68-77. [PMID: 25827497 DOI: 10.1016/j.neuroscience.2015.03.034] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2015] [Revised: 03/16/2015] [Accepted: 03/17/2015] [Indexed: 11/18/2022]
Abstract
We recently developed ultra-sensitive ethanol receptors (USERs) as a novel tool for investigation of single receptor subunit populations sensitized to extremely low ethanol concentrations that do not affect other receptors in the nervous system. To this end, we found that mutations within the extracellular Loop 2 region of glycine receptors (GlyRs) and γ-aminobutyric acid type A receptors (GABAARs) can significantly increase receptor sensitivity to micro-molar concentrations of ethanol resulting in up to a 100-fold increase in ethanol sensitivity relative to wild-type (WT) receptors. The current study investigated: (1) Whether structural manipulations of Loop 2 in α1 GlyRs could similarly increase receptor sensitivity to other anesthetics; and (2) If mutations exclusive to the C-terminal end of Loop 2 are sufficient to impart these changes. We expressed α1 GlyR USERs in Xenopus oocytes and tested the effects of three classes of anesthetics, isoflurane (volatile), propofol (intravenous), and lidocaine (local), known to enhance glycine-induced chloride currents using two-electrode voltage clamp electrophysiology. Loop 2 mutations produced a significant 10-fold increase in isoflurane and lidocaine sensitivity, but no increase in propofol sensitivity compared to WT α1 GlyRs. Interestingly, we also found that structural manipulations in the C-terminal end of Loop 2 were sufficient and selective for α1 GlyR modulation by ethanol, isoflurane, and lidocaine. These studies are the first to report the extracellular region of α1 GlyRs as a site of lidocaine action. Overall, the findings suggest that Loop 2 of α1 GlyRs is a key region that mediates isoflurane and lidocaine modulation. Moreover, the results identify important amino acids in Loop 2 that regulate isoflurane, lidocaine, and ethanol action. Collectively, these data indicate the commonality of the sites for isoflurane, lidocaine, and ethanol action, and the structural requirements for allosteric modulation on α1 GlyRs within the extracellular Loop 2 region.
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Ionic Fragmentation Mechanisms of 2,2,2-Trifluoroethanol Following Excitation with Synchrotron Radiation. Chemphyschem 2014; 16:322-30. [DOI: 10.1002/cphc.201402669] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Indexed: 11/07/2022]
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Hydrocarbon molar water solubility predicts NMDA vs. GABAA receptor modulation. BMC Pharmacol Toxicol 2014; 15:62. [PMID: 25410726 PMCID: PMC4247779 DOI: 10.1186/2050-6511-15-62] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Accepted: 11/13/2014] [Indexed: 12/02/2022] Open
Abstract
Background Many anesthetics modulate 3-transmembrane (such as NMDA) and 4-transmembrane (such as GABAA) receptors. Clinical and experimental anesthetics exhibiting receptor family specificity often have low water solubility. We hypothesized that the molar water solubility of a hydrocarbon could be used to predict receptor modulation in vitro. Methods GABAA (α1β2γ2s) or NMDA (NR1/NR2A) receptors were expressed in oocytes and studied using standard two-electrode voltage clamp techniques. Hydrocarbons from 14 different organic functional groups were studied at saturated concentrations, and compounds within each group differed only by the carbon number at the ω-position or within a saturated ring. An effect on GABAA or NMDA receptors was defined as a 10% or greater reversible current change from baseline that was statistically different from zero. Results Hydrocarbon moieties potentiated GABAA and inhibited NMDA receptor currents with at least some members from each functional group modulating both receptor types. A water solubility cut-off for NMDA receptors occurred at 1.1 mM with a 95% CI = 0.45 to 2.8 mM. NMDA receptor cut-off effects were not well correlated with hydrocarbon chain length or molecular volume. No cut-off was observed for GABAA receptors within the solubility range of hydrocarbons studied. Conclusions Hydrocarbon modulation of NMDA receptor function exhibits a molar water solubility cut-off. Differences between unrelated receptor cut-off values suggest that the number, affinity, or efficacy of protein-hydrocarbon interactions at these sites likely differ.
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Butanol isomers exert distinct effects on voltage-gated calcium channel currents and thus catecholamine secretion in adrenal chromaffin cells. PLoS One 2014; 9:e109203. [PMID: 25275439 PMCID: PMC4183593 DOI: 10.1371/journal.pone.0109203] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2014] [Accepted: 09/08/2014] [Indexed: 12/20/2022] Open
Abstract
Butanol (C4H10OH) has been used both to dissect the molecular targets of alcohols/general anesthetics and to implicate phospholipase D (PLD) signaling in a variety of cellular functions including neurotransmitter and hormone exocytosis. Like other primary alcohols, 1-butanol is a substrate for PLD and thereby disrupts formation of the intracellular signaling lipid phosphatidic acid. Because secondary and tertiary butanols do not undergo this transphosphatidylation, they have been used as controls for 1-butanol to implicate PLD signaling. Recently, selective pharmacological inhibitors of PLD have been developed and, in some cases, fail to block cellular functions previously ascribed to PLD using primary alcohols. For example, exocytosis of insulin and degranulation of mast cells are blocked by primary alcohols, but not by the PLD inhibitor FIPI. In this study we show that 1-butanol reduces catecholamine secretion from adrenal chromaffin cells to a much greater extent than tert-butanol, and that the PLD inhibitor VU0155056 has no effect. Using fluorescent imaging we show the effect of these drugs on depolarization-evoked calcium entry parallel those on secretion. Patch-clamp electrophysiology confirmed the peak amplitude of voltage-gated calcium channel currents (ICa) is inhibited by 1-butanol, with little or no block by secondary or tert-butanol. Detailed comparison shows for the first time that the different butanol isomers exert distinct, and sometimes opposing, effects on the voltage-dependence and gating kinetics of ICa. We discuss these data with regard to PLD signaling in cellular physiology and the molecular targets of general anesthetics.
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Which agonist properties are important for the activation of 5-HT3A receptors? BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:2564-73. [PMID: 23792067 DOI: 10.1016/j.bbamem.2013.06.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Revised: 06/04/2013] [Accepted: 06/11/2013] [Indexed: 11/21/2022]
Abstract
PURPOSE Why do anesthetics not activate excitatory ligand-gated ion channels such as 5-HT3 receptors in contrast to inhibitory ligand-gated ion channels? This study examines the actions of structural closely-related 5-HT derivatives and 5-HT constituent parts on 5-HT3A receptors with the aim of finding simpler if not minimal agonists and thus determining requirements for successful agonist action. EXPERIMENTAL APPROACH Responses to 5-HT derivatives of human 5-HT3A receptors stably expressed in HEK 293 cells have been examined with the patch-clamp technique in the outside-out configuration combined with a fast solution exchange system. RESULTS Phenol, pyrrole and alkyl amines, constituents of 5-HT, even at high concentrations, cannot activate 5-HT3A receptors but they can inhibit them. To date, tyramines are the smallest known agonists. However, an aromatic ring is not required for activation as acetylcholine is also an agonist of similar strength. CONCLUSION Simultaneous interactions of adequate strength at two separate subsites within the 5-HT binding domain appear to be essential for successful agonist function. Anesthetics either fail to achieve this or the activation they produce is so weak that it is masked by a comparatively very strong inhibition.
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Anesthetics interfere with axon guidance in developing mouse neocortical neurons in vitro via a γ-aminobutyric acid type A receptor mechanism. Anesthesiology 2013; 118:825-33. [PMID: 23364597 DOI: 10.1097/aln.0b013e318287b850] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
BACKGROUND The finding that exposure to general anesthetics (GAs) in childhood may increase rates of learning disabilities has raised a concern that anesthetics may interfere with brain development. The generation of neuronal circuits, a complex process in which axons follow guidance cues to dendritic targets, is an unexplored potential target for this type of toxicity. METHODS GA exposures were conducted in developing neocortical neurons in culture and in early postnatal neocortical slices overlaid with fluorescently labeled neurons. Axon targeting, growth cone collapse, and axon branching were measured using quantitative fluorescence microscopy. RESULTS Isoflurane exposure causes errors in Semaphorin-3A-dependent axon targeting (n = 77 axons) and a disruption of the response of axonal growth cones to Semaphorin-3A (n = 2,358 growth cones). This effect occurs at clinically relevant anesthetic doses of numerous GAs with allosteric activity at γ-aminobutyric acid type A receptors, and it was reproduced with a selective agonist. Isoflurane also inhibits growth cone collapse induced by Netrin-1, but does not interfere branch induction by Netrin-1. Insensitivity to guidance cues caused by isoflurane is seen acutely in growth cones in dissociated culture, and errors in axon targeting in brain slice culture occur at the earliest point at which correct targeting is observed in controls. CONCLUSIONS These results demonstrate a generalized inhibitory effect of GAs on repulsive growth cone guidance in the developing neocortex that may occur via a γ-aminobutyric acid type A receptor mechanism. The finding that GAs interfere with axon guidance, and thus potentially with circuit formation, represents a novel form of anesthesia neurotoxicity in brain development.
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4-Chloropropofol enhances chloride currents in human hyperekplexic and artificial mutated glycine receptors. BMC Neurol 2012; 12:104. [PMID: 23006332 PMCID: PMC3517478 DOI: 10.1186/1471-2377-12-104] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2011] [Accepted: 09/19/2012] [Indexed: 01/23/2023] Open
Abstract
BACKGROUND The mammalian neurological disorder hereditary hyperekplexia can be attributed to various mutations of strychnine sensitive glycine receptors. The clinical symptoms of "startle disease" predominantly occur in the newborn leading to convulsive hypertonia and an exaggerated startle response to unexpected mild stimuli. Amongst others, point mutations R271Q and R271L in the α1-subunit of strychnine sensitive glycine receptors show reduced glycine sensitivity and cause the clinical symptoms of hyperekplexia.Halogenation has been shown to be a crucial structural determinant for the potency of a phenolic compound to positively modulate glycine receptor function.The aim of this in vitro study was to characterize the effects of 4-chloropropofol (4-chloro-2,6-dimethylphenol) at four glycine receptor mutations. METHODS Glycine receptor subunits were expressed in HEK 293 cells and experiments were performed using the whole-cell patch-clamp technique. RESULTS 4-chloropropofol exerted a positive allosteric modulatory effect in a low sub-nanomolar concentration range at the wild type receptor (EC50 value of 0.08 ± 0.02 nM) and in a micromolar concentration range at the mutations (1.3 ± 0.6 μM, 0.1 ± 0.2 μM, 6.0 ± 2.3 μM and 55 ± 28 μM for R271Q, L, K and S267I, respectively). CONCLUSIONS 4-chloropropofol might be an effective compound for the activation of mutated glycine receptors in experimental models of startle disease.
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Ligand-gated ion channels: new insights into neurological disorders and ligand recognition. Chem Rev 2012; 112:6285-318. [PMID: 22988962 DOI: 10.1021/cr3000829] [Citation(s) in RCA: 114] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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A possible molecular mechanism for the pressure reversal of general anaesthetics: Aggregation of halothane in POPC bilayers at high pressure. Chem Phys Lett 2012. [DOI: 10.1016/j.cplett.2012.06.044] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Bursting as a source of non-linear determinism in the firing patterns of nigral dopamine neurons. Eur J Neurosci 2012; 36:3214-23. [PMID: 22831464 DOI: 10.1111/j.1460-9568.2012.08238.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Nigral dopamine (DA) neurons in vivo exhibit complex firing patterns consisting of tonic single-spikes and phasic bursts that encode information for certain types of reward-related learning and behavior. Non-linear dynamical analysis has previously demonstrated the presence of a non-linear deterministic structure in complex firing patterns of DA neurons, yet the origin of this non-linear determinism remains unknown. In this study, we hypothesized that bursting activity is the primary source of non-linear determinism in the firing patterns of DA neurons. To test this hypothesis, we investigated the dimension complexity of inter-spike interval data recorded in vivo from bursting and non-bursting DA neurons in the chloral hydrate-anesthetized rat substantia nigra. We found that bursting DA neurons exhibited non-linear determinism in their firing patterns, whereas non-bursting DA neurons showed truly stochastic firing patterns. Determinism was also detected in the isolated burst and inter-burst interval data extracted from firing patterns of bursting neurons. Moreover, less bursting DA neurons in halothane-anesthetized rats exhibited higher dimensional spiking dynamics than do more bursting DA neurons in chloral hydrate-anesthetized rats. These results strongly indicate that bursting activity is the main source of low-dimensional, non-linear determinism in the firing patterns of DA neurons. This finding furthermore suggests that bursts are the likely carriers of meaningful information in the firing activities of DA neurons.
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Diffusive nature of xenon anesthetic changes properties of a lipid bilayer: molecular dynamics simulations. J Phys Chem B 2012; 116:8989-95. [PMID: 22715916 DOI: 10.1021/jp303330c] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Effects of general anesthesia can be controllable by the ambient pressure. We perform molecular dynamics simulations for a 1-palmitoyl-2-oleoyl phosphatidylethanolamine lipid bilayer with or without xenon molecules by changing the pressure to elucidate the mechanism of the pressure reversal of general anesthesia. According to the diffusive nature of xenon molecules in the lipid bilayer, a decrease in the orientational order of the lipid tails, an increase in the area and volume per lipid molecule, and an increase in the diffusivity of lipid molecules are observed. We show that the properties of the lipid bilayer with xenon molecules at high pressure come close to those without xenon molecules at 0.1 MPa. Furthermore, we find that xenon molecules are concentrated in the middle of the lipid bilayer at high pressures by the pushing effect and that the diffusivity of xenon molecules is suppressed. These results suggest that the pressure reversal originates from a jamming and suppression of the diffusivity of xenon molecules in lipid bilayers.
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Increased NMDA receptor inhibition at an increased Sevoflurane MAC. BMC Anesthesiol 2012; 12:9. [PMID: 22672766 PMCID: PMC3439310 DOI: 10.1186/1471-2253-12-9] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2011] [Accepted: 06/06/2012] [Indexed: 11/10/2022] Open
Abstract
Background Sevoflurane potently enhances glycine receptor currents and more modestly decreases NMDA receptor currents, each of which may contribute to immobility. This modest NMDA receptor antagonism by sevoflurane at a minimum alveolar concentration (MAC) could be reciprocally related to large potentiation of other inhibitory ion channels. If so, then reduced glycine receptor potency should increase NMDA receptor antagonism by sevoflurane at MAC. Methods Indwelling lumbar subarachnoid catheters were surgically placed in 14 anesthetized rats. Rats were anesthetized with sevoflurane the next day, and a pre-infusion sevoflurane MAC was measured in duplicate using a tail clamp method. Artificial CSF (aCSF) containing either 0 or 4 mg/mL strychnine was then infused intrathecally at 4 μL/min, and the post-infusion baseline sevoflurane MAC was measured. Finally, aCSF containing strychnine (either 0 or 4 mg/mL) plus 0.4 mg/mL dizocilpine (MK-801) was administered intrathecally at 4 μL/min, and the post-dizocilpine sevoflurane MAC was measured. Results Pre-infusion sevoflurane MAC was 2.26%. Intrathecal aCSF alone did not affect MAC, but intrathecal strychnine significantly increased sevoflurane requirement. Addition of dizocilpine significantly decreased MAC in all rats, but this decrease was two times larger in rats without intrathecal strychnine compared to rats with intrathecal strychnine, a statistically significant (P < 0.005) difference that is consistent with increased NMDA receptor antagonism by sevoflurane in rats receiving strychnine. Conclusions Glycine receptor antagonism increases NMDA receptor antagonism by sevoflurane at MAC. The magnitude of anesthetic effects on a given ion channel may therefore depend on the magnitude of its effects on other receptors that modulate neuronal excitability.
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Effects of general anaesthetics on 5-HT neuronal activity in the dorsal raphe nucleus. Neuropharmacology 2011; 62:1787-96. [PMID: 22197516 DOI: 10.1016/j.neuropharm.2011.12.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Revised: 11/04/2011] [Accepted: 12/02/2011] [Indexed: 11/22/2022]
Abstract
The ascending 5-HT system has been and continues to be the subject of much research. The majority of in vivo electrophysiological and neurochemical studies of 5-HT function in rodents have been conducted in animals under anaesthesia - usually chloral hydrate or urethane. However, the effects of anaesthetics, on 5-HT function have not been systematically investigated. Here we used in vitro electrophysiology in dorsal raphe slices, to determine the effects of anaesthetically relevant concentrations of chloral hydrate (100 μM and 1 mM), urethane (10 and 30 mM), pentobarbitone (10 and 100 μM) and ketamine (10, 100 and 300 μM) on regulators of 5-HT firing activity. We examined i) basal firing (driven by α(1) adrenoceptors), ii) the excitatory response to N-methyl-d-aspartate (NMDA), iii) the 5-HT(1A) autoreceptor-mediated inhibitory response to 5-HT and iv) the GABA(A) receptor-mediated inhibitory response to 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridinyl-3-ol (THIP, gaboxadol). Pentobarbitone selectively enhanced the response to THIP. Ketamine decreased basal firing, attenuated the response to NMDA, and enhanced responses to both 5-HT and THIP. Chloral hydrate had marginal effects on basal firing, slightly attenuated the NMDA response, and enhanced both the 5-HT and THIP responses. Urethane increased basal firing, decreased the NMDA response, increased the response to THIP, but had no effect on the 5-HT response. Our data indicate that all anaesthetics tested significantly affect the regulators of 5-HT neuronal function. These findings will aid in the interpretation of previous reports of in vivo studies of the 5-HT system and will allow researchers to make a rational selection of anaesthetic for future studies.
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Dynamic loss of surface-expressed AMPA receptors in mouse cortical and striatal neurons during anesthesia. J Neurosci Res 2011; 90:315-23. [PMID: 21932367 DOI: 10.1002/jnr.22749] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2011] [Revised: 05/11/2011] [Accepted: 06/27/2011] [Indexed: 11/08/2022]
Abstract
Ionotropic glutamate receptors, especially the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor subtype, undergo dynamic trafficking between the surface membrane and intracellular organelles. This trafficking activity determines the efficacy and strength of excitatory synapses and is subject to modulation by changing synaptic inputs. Given the possibility that glutamate receptors in the central nervous system might be a sensitive target of anesthetic agents, this study investigated the possible impact of anesthesia on trafficking and subcellular expression of AMPA receptors in adult mouse brain neurons in vivo. We found that anesthesia induced by a systemic injection of pentobarbital did not alter total protein levels of three AMPA receptor subunits (GluR1-3) in cortical neurons. However, an anesthetic dose of pentobarbital reduced GluR1 and GluR3 proteins in the surface pool and elevated these proteins in the intracellular pool of cortical neurons. The similar redistribution of GluR1/3 was observed in mouse striatal neurons. Pentobarbital did not significantly alter GluR2 expression in the two pools. Chloral hydrate at an anesthetic dose also reduced surface GluR1/3 expression and increased intracellular levels of these proteins. The effect of pentobarbital on subcellular distribution of AMPA receptors was reversible. Altered subcellular distribution of GluR1/3 returned to normal levels after the anesthesia subsided. These data indicate that anesthesia induced by pentobarbital and chloral hydrate can alter AMPA receptor trafficking in both cortical and striatal neurons. This alteration is characterized by the concurrent loss and addition of GluR1/3 subunits in the respective surface and intracellular pools.
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A review of potential neurotoxic mechanisms among three chlorinated organic solvents. Toxicol Appl Pharmacol 2011; 255:113-26. [DOI: 10.1016/j.taap.2011.05.008] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2011] [Revised: 05/06/2011] [Accepted: 05/08/2011] [Indexed: 12/17/2022]
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Pentobarbital anesthesia alters neural responses in the precedence effect. Neurosci Lett 2011; 498:72-7. [DOI: 10.1016/j.neulet.2011.04.066] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2011] [Revised: 04/21/2011] [Accepted: 04/26/2011] [Indexed: 11/26/2022]
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On the use of α-chloralose for repeated BOLD fMRI measurements in rats. J Neurosci Methods 2011; 195:236-40. [DOI: 10.1016/j.jneumeth.2010.12.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2010] [Revised: 11/30/2010] [Accepted: 12/02/2010] [Indexed: 11/26/2022]
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Abstract
Tert-Butanol is an important intermediate in industrial chemical synthesis, particularly of fuel oxygenates. Human exposure to tert-butanol may occur following fuel oxygenate metabolism or biodegradation. It is poorly absorbed through skin, but is rapidly absorbed upon inhalation or ingestion and distributed to tissues throughout the body. Elimination from blood is slower and the half-life increases with dose. It is largely metabolised by oxidation via 2-methyl-1,2-propanediol to 2-hydroxyisobutyrate, the dominant urinary metabolites. Conjugations also occur and acetone may be found in urine at high doses. The single-dose systemic toxicity of tert-butanol is low, but it is irritant to skin and eyes; high oral doses produce ataxia and hypoactivity and repeated exposure can induce dependence. Tert-Butanol is not definable as a genotoxin and has no effects specific for reproduction or development; developmental delay occurred only with marked maternal toxicity. Target organs for toxicity clearly identified are kidney in male rats and urinary bladder, particularly in males, of both rats and mice. Increased tumour incidences observed were renal tubule cell adenomas in male rats and thyroid follicular cell adenomas in female mice and, non-significantly, at an intermediate dose in male mice. The renal adenomas were associated with alpha(2u)-globulin nephropathy and, to a lesser extent, exacerbation of chronic progressive nephropathy. Neither of these modes of action can function in humans. The thyroid tumour response could be strain-specific. No thyroid toxicity was observed and a study of hepatic gene expression and enzyme induction and thyroid hormone status has suggested a possible mode of action.
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45
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New insights into the molecular mechanisms of general anaesthetics. Br J Pharmacol 2010; 161:288-307. [PMID: 20735416 PMCID: PMC2989583 DOI: 10.1111/j.1476-5381.2010.00891.x] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2010] [Revised: 04/27/2010] [Accepted: 04/30/2010] [Indexed: 01/22/2023] Open
Abstract
This paper provides new insights of how general anaesthetic research should be carried out in the future by an analysis of what we know, what we do not know and what we would like to know. I describe previous hypotheses on the mechanism of action of general anaesthetics (GAs) involving membranes and protein receptors. I provide the reasons why the GABA type A receptor, the NMDA receptor and the glycine receptor are strong candidates for the sites of action of GAs. I follow with a review on attempts to provide a mechanism of action, and how future research should be conducted with the help of physical and chemical methods.
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MESH Headings
- Anesthetics, General/adverse effects
- Anesthetics, General/chemistry
- Anesthetics, General/pharmacology
- Animals
- Biomedical Research/methods
- Biomedical Research/trends
- Brain/drug effects
- Brain/metabolism
- Humans
- Models, Molecular
- Molecular Structure
- Point Mutation
- Protein Binding
- Receptors, GABA-A/chemistry
- Receptors, GABA-A/genetics
- Receptors, GABA-A/metabolism
- Receptors, N-Methyl-D-Aspartate/chemistry
- Receptors, N-Methyl-D-Aspartate/genetics
- Receptors, N-Methyl-D-Aspartate/metabolism
- Stereoisomerism
- Structure-Activity Relationship
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Inhaled anesthetic responses of recombinant receptors and knockin mice harboring α2(S270H/L277A) GABA(A) receptor subunits that are resistant to isoflurane. J Pharmacol Exp Ther 2010; 336:134-44. [PMID: 20807777 DOI: 10.1124/jpet.110.170431] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The mechanism by which the inhaled anesthetic isoflurane produces amnesia and immobility is not understood. Isoflurane modulates GABA(A) receptors (GABA(A)-Rs) in a manner that makes them plausible targets. We asked whether GABA(A)-R α2 subunits contribute to a site of anesthetic action in vivo. Previous studies demonstrated that Ser270 in the second transmembrane domain is involved in the modulation of GABA(A)-Rs by volatile anesthetics and alcohol, either as a binding site or a critical allosteric residue. We engineered GABA(A)-Rs with two mutations in the α2 subunit, changing Ser270 to His and Leu277 to Ala. Recombinant receptors with these mutations demonstrated normal affinity for GABA, but substantially reduced responses to isoflurane. We then produced mutant (knockin) mice in which this mutated subunit replaced the wild-type α2 subunit. The adult mutant mice were overtly normal, although there was evidence of enhanced neonatal mortality and fear conditioning. Electrophysiological recordings from dentate granule neurons in brain slices confirmed the decreased actions of isoflurane on mutant receptors contributing to inhibitory synaptic currents. The loss of righting reflex EC(50) for isoflurane did not differ between genotypes, but time to regain the righting reflex was increased in N(2) generation knockins. This effect was not observed at the N(4) generation. Isoflurane produced immobility (as measured by tail clamp) and amnesia (as measured by fear conditioning) in both wild-type and mutant mice, and potencies (EC(50)) did not differ between the strains for these actions of isoflurane. Thus, immobility or amnesia does not require isoflurane potentiation of the α2 subunit.
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47
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Presynaptic inhibition of primary afferents by depolarization: observations supporting nontraditional mechanisms. Ann N Y Acad Sci 2010; 1198:140-52. [PMID: 20536928 DOI: 10.1111/j.1749-6632.2010.05436.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Primary afferent neurotransmission is the fundamental first step in the central processing of sensory stimuli and is controlled by pre- and postsynaptic inhibitory mechanisms. Presynaptic inhibition (PSI) is probably the more powerful form of inhibitory control in all primary afferent fibers. A major mechanism producing afferent PSI is via a channel-mediated depolarization of their intraspinal terminals, which can be recorded extracellularly as a dorsal root potential (DRP). Based on measures of DRP latency it has been inferred that this primary afferent depolarization (PAD) of low-threshold afferents is mediated by minimally trisynaptic pathways with pharmacologically identified GABAergic interneurons forming last-order axo-axonic synapses onto afferent terminals. There is still no "squeaky clean" evidence of this organization. This paper describes recent and historical work that supports the existence of PAD occurring by more direct pathways and with a complex pharmacology that questions the proprietary role of GABA and GABA(A) receptors in this process. Cholinergic transmission in particular may contribute significantly to PAD, including via direct release from primary afferents.
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Identification of novel specific allosteric modulators of the glycine receptor using phage display. J Biol Chem 2010; 285:22840-5. [PMID: 20501662 DOI: 10.1074/jbc.m110.130815] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The glycine receptor (GlyR) is a member of the Cys-loop superfamily of ligand-gated ion channels and the major mediator of inhibitory neurotransmission in the spinal cord and brainstem. Many allosteric modulators affect the functioning of members of this superfamily, with some such as benzodiazepines showing great specificity and others such as zinc, alcohols, and volatile anesthetics acting on multiple members. To date, no potent and efficacious allosteric modulator acting specifically at the GlyR has been identified, hindering both experimental characterization of the receptor and development of GlyR-related therapeutics. We used phage display to identify novel peptides that specifically modulate GlyR function. Peptide D12-116 markedly enhanced GlyR currents at low micromolar concentrations but had no effects on the closely related gamma-aminobutyric acid type A receptors. This approach can readily be adapted for use with other channels that currently lack specific allosteric modulators.
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The current functional state of local neuronal circuits controls the magnitude of a BOLD response to incoming stimuli. Neuroimage 2010; 50:1364-75. [PMID: 20114080 DOI: 10.1016/j.neuroimage.2010.01.070] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2009] [Revised: 01/19/2010] [Accepted: 01/21/2010] [Indexed: 02/07/2023] Open
Abstract
The purpose of this study was to determine how the history-dependent activation state of neuronal networks controls fMRI signals to incoming stimuli. Simultaneous electrophysiological and blood oxygen level-dependent (BOLD) responses were monitored during stimulation of the perforant pathway with low, high, and again low intensity but, otherwise identical pulse trains. Under three different anesthetics (alpha-chloralose, medetomidine, isoflurane) consecutive low intensity stimulation trains, set just below the threshold for population spike generation to single pulses, yielded a stable BOLD response, although at different magnitudes. The first high intensity train increased the BOLD response under all anesthetics and generated population spikes, with varying amplitudes and latencies (alpha-chloralose, metedomidine) or in a regular pattern (isoflurane). Concurrent to the second high intensity train, the BOLD response became minimal, then slowly increasing with subsequent trains (alpha-chloralose, metedomidine), or immediately rising to a stable level (isoflurane). Second train population spikes became regularized, but at low amplitudes and long latencies that were slowly reversed across trains (alpha-chloralose, medetomidine); while under isoflurane, amplitude and latencies became stabilized with the second train. In comparison to initial stimulation, the final low intensity stimulation trains failed to produce BOLD responses (alpha-chloralose, medetomidine), or left the response unchanged (isoflurane), only reaching stable potentiation of population spikes when under isoflurane. Therefore, the fate of BOLD responses depends on whether a new stable functional state of the intrinsic network can be reached after high intensity stimulation.
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Nitrous oxide plus isoflurane induces apoptosis and increases beta-amyloid protein levels. Anesthesiology 2010; 111:741-52. [PMID: 19741497 DOI: 10.1097/aln.0b013e3181b27fd4] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
BACKGROUND Some anesthetics have been suggested to induce neurotoxicity, including promotion of Alzheimer's disease neuropathogenesis. Nitrous oxide and isoflurane are common anesthetics. The authors set out to assess the effects of nitrous oxide and/or isoflurane on apoptosis and beta-amyloid (Abeta) levels in H4 human neuroglioma cells and primary neurons from naïve mice. METHODS The cells or neurons were exposed to 70% nitrous oxide and/or 1% isoflurane for 6 h. The cells or neurons and conditioned media were harvested at the end of the treatment. Caspase-3 activation, apoptosis, processing of amyloid precursor protein, and Abeta levels were determined. RESULTS Treatment with a combination of 70% nitrous oxide and 1% isoflurane for 6 h induced caspase-3 activation and apoptosis in H4 naïve cells and primary neurons from naïve mice. The 70% nitrous oxide plus 1% isoflurane, but neither alone, for 6 h induced caspase-3 activation and apoptosis, and increased levels of beta-site amyloid precursor protein-cleaving enzyme and Abeta in H4-amyloid precursor protein cells. In addition, the nitrous oxide plus isoflurane-induced Abeta generation was reduced by a broad caspase inhibitor, Z-VAD. Finally, the nitrous oxide plus isoflurane-induced caspase-3 activation was attenuated by gamma-secretase inhibitor L-685,458, but potentiated by exogenously added Abeta. CONCLUSION These results suggest that the common anesthetics nitrous oxide plus isoflurane may promote neurotoxicity by inducing apoptosis and increasing Abeta levels. The generated Abeta may further potentiate apoptosis to form another round of apoptosis and Abeta generation. More studies, especially the in vivo confirmation of these in vitro findings, are needed.
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