Studies on Cellular Mechanisms Underlying General Anesthesia Using Cultured Molluscan Neurons (original) (raw)
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Differential effects of general anaesthetics on identified molluscan neurones in situ and in culture
General Pharmacology: The Vascular System, 1992
The only umfymg pnnclple of general anaesthesm ~s that general anaestheucs interact with membrane components and no single cellular mechamsm appears to explain their w~despread effects m the central nervous system 2 The gastropod mollusc, Lymnaea stagnahs, prowdes an excellent model system for studies on general anaesthettcs because it has large, umquely ldenUfiable nerve cells Several of these cells are mterneurones w~th identified neurotransmltters and monosynapt~c connectmns to other cells 3 Recent work on Lymnaea neurones suggests that calcium currents are depressed by volatile general anaesthetics apphed in the chmcal range, whist ewdence from other preparations m&cates that there ~s a rise m mtracellular calcmm concentratmn follovang apphcatmn of these substances 4 Identified Lymnaea neurones have &fferent responses to apphed anaesthetics, ~rrespectwe of the anaesthetic used Following apphcatmn of halothane, barbiturates and several other anaesthettc agents, some cells gradually become qmescent after a short period, whdst m others a series of paroxysmal depolanmng shifts occur pnor to qmescence 5 Cultured neurones of Lymnaea, Hehsoma and related species retain their characteristic action potentml types and neurotransmttter ~dentlty Their responses to anaesthetics are s~mllar to those m the intact brain They may also form synapses m culture Thus, they are a useful tool for studymg the cellular and subcellular actmns of general anaesthetics
Mechanisms of Anesthetic Action and Neurotoxicity: Lessons from Molluscs
Frontiers in physiology, 2017
Anesthesia is a prerequisite for most surgical procedures in both animals and humans. Significant strides have been made in search of effective and safer compounds that elicit rapid induction and recovery from anesthesia. However, recent studies have highlighted possible negative effects of several anesthetic agents on the developing brain. The precise nature of this cytotoxicity remains to be determined mainly due to the complexity and the intricacies of the mammalian brain. Various invertebrates have contributed significantly toward our understanding of how both local and general anesthetics affect intrinsic membrane and synaptic properties. Moreover, the ability to reconstructsynapses between individually identifiable pre- and postsynaptic neurons is a unique characteristic of molluscan neurons allowing us to ask fundamental questions vis-à-vis the long-term effects of anesthetics on neuronal viability and synaptic connectivity. Here, we highlight some of the salient aspects of v...
British Journal of Pharmacology, 1998
1 K + currents activated by volatile general anaesthetics (I K(An)) and by the neuropeptide FMRFamide (I K(FMRFa)) were studied under voltage clamp in isolated identi®ed neurones from the pond snail Lymnaea stagnalis. 2 I K(An) was activated by all the volatile anaesthetics studied. The maximal responses varied from agent to agent, with halothane&sevo¯urane4iso¯urane4en¯urane&chloroform. 3 I K(An) was inhibited rather than activated by the n-alcohols from hexanol to dodecanol and by the 6and 8-carbon cycloalcohols. The n-alcohols exhibited a cuto eect, with dodecanol being unable to half-inhibit I K(An). 4 Unlike I K(An) which did not desensitize at reasonable halothane concentrations, I K(FMRFa) desensitized at most FMRFamide concentrations studied. This desensitization could be substantially removed by halothane. Nonetheless, both I K(An) and I K(FMRFa) had similar sensitivities to the potassium channel blockers tetraethylammonium and 4-aminopyridine, consistent with both currents¯owing through the same channels. Responses to low concentrations of halothane and FMRFamide showed synergy. 5 The phospholipase A 2 inhibitor aristolochic acid inhibited I K(An) , consistent with a role for arachidonic acid (AA). The lipoxygenase and cyclooxygenase inhibitor nordihydroguaiaretic acid blocked I K(FMRFa) but did not aect I K(An). I K(An) and I K(FMRFa) were little aected by the cyclooxygenase inhibitor indomethacin. These ®ndings suggest that neither lipoxygenase nor cyclooxygenase pathways of AA metabolism are involved in the anaesthetic activation of I K(An). 6 Inhibitors of a third, cytochrome P450-mediated, pathway of AA metabolism (clotrimazole and econazole) potently blocked I K(An) , suggesting possible roles for certain cytochrome P450 isoforms in the activation of I K(An) .
Frontiers in physiology, 2018
Recent progress in animal welfare legislation stresses the need to treat cephalopod molluscs, such as , humanely, to have regard for their wellbeing and to reduce their pain and suffering resulting from experimental procedures. Thus, appropriate measures for their sedation and analgesia are being introduced. Clinical anesthetics are renowned for their ability to produce unconsciousness in vertebrate species, but their exact mechanisms of action still elude investigators. In vertebrates it can prove difficult to specify the differences of response of particular neuron types given the multiplicity of neurons in the CNS. However, gastropod molluscs such as , , or , with their large uniquely identifiable nerve cells, make studies on the cellular, subcellular, network and behavioral actions of anesthetics much more feasible, particularly as identified cells may also be studied in culture, isolated from the rest of the nervous system. To date, the sorts of study outlined above have never ...
Effects of general anaesthetics on neuronal sodium and potassium channels
General pharmacology, 1992
1. The effects of clinical inhalation anaesthetics, such as halothane and methoxyflurane, and "model" anaesthetics, such as hydrocarbons and n-alkanols, on neuronal sodium and potassium channels are reviewed. 2. Lipid-based mechanisms for the actions of anaesthetics on the gating parameters of squid axon sodium and delayed rectifier potassium currents are considered in conjunction with evidence of more specific effects in other preparations, notably a fast inactivating potassium current in Helix neurones and a voltage-gated sodium current in rat dorsal root ganglion neurones. 3. The proconvulsant actions of some inhalation anaesthetics are discussed in relation to the induction of spontaneous firing of action potentials in the squid giant axon.
European Journal of Pharmacology, 1987
The actions of ethanol, halothane and pentobarbital on the membrane electrical properties and synaptic transmission of isolated crayfish stretch receptor neurons were studied to determine possible sites of action contributing to differential effects previously described on physiological discharge activity. The three agents depressed GABA-mediated transmission and altered postsynaptic membrane electrical properties. Both pre-and postsynaptic sites of action appeared to contribute to the anesthetic-induced alteration of neuronal function. The agents studied produced different, concentration-dependent, membrane effects which included biphasic actions on membrane resistance and spike threshold. The results suggest that multiple-sites of action are involved and different anesthetics may not act via the same mechanism(s) at these sites.
Membrane-Mediated Activity of Local Anesthetics
Molecular Pharmacology
The activity of local anesthetics (LAs) has been attributed to the inhibition of ion channels, causing anesthesia. However, there is a growing body of research showing that LAs act on a wide range of receptors and channel proteins, far beyond simple analgesia. The current concept of ligand recognition may no longer explain the multitude of protein targets influenced by LAs. We hypothesize that LAs can cause anesthesia without directly binding to the receptor proteins, just by changing the physical properties of the lipid bilayer surrounding these proteins and ion channels, based on LAs' amphiphilicity. It is possible that LAs act in one of the following ways: they (a) dissolve raft-like membrane micro-domains, (b) impede nerve impulse propagation by lowering the lipid phase transition temperature, or (c) modulate the lateral pressure profile of the lipid bilayer. This could also explain the numerous additional effects of LA besides anesthesia. Furthermore, the concepts of membrane-mediated activity and binding to ion channels do not have to exclude each other. If we were to consider LA as the middle part of a continuum, between unspecific membrane mediated activity on one end, and highly specific ligand binding on the other end, we could describe LA as the link between the unspecific action of general anesthetics, and toxins with their highly specific receptor binding. This comprehensive membrane-mediated model offers a fresh perspective to clinical and pharmaceutical research and therapeutic applications of local anesthetics.
2020
The crayfish stretch receptor organ (SRO) preparation represents a robust experimental model for undergraduate laboratory experiences. For example, this preparation may be included as part of a course-based undergraduate research experience (CURE), where students work independently to plan and carry out their own experiments. In the current paper, we provide an example of how local anesthetics may be used to manipulate the SRO preparation and to perform quantitative analyses of SRO action potential firing rates. Local anesthetics provide interesting tools for manipulating physiological responses within the nervous system. A variety of inexpensive anesthetics are available for student use and each of these is expected to inhibit neurophysiological responses. While specific anesthetics exhibit subtle differences in chemical organization, they are generally understood to block voltage gated sodium channels. In the current study, we investigated the effects of two local anesthetics, MS-...