Publications (2)7.28 Total impact
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Article: Effects of halothane on GABAergic and glutamatergic transmission in isolated hippocampal nerve-synapse preparations.
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ABSTRACT: We evaluated the effects of halothane on synaptic and extrasynaptic GABA(A) and glutamate receptor responses using mechanically dissociated rat hippocampal CA3 neurons in which the well isolated neurons retain functional native nerve endings (the 'synaptic bouton' preparation). The preparation allows the simultaneous comparison of extrasynaptic GABA(A) and glutamate receptors, activated by bath applied GABA and glutamate, respectively, to the synaptic receptors measured as spontaneous and evoked postsynaptic currents. Paired-pulse synaptic responses evoked by focal electrical stimulation were also measured to evaluate any presynaptic effects. Halothane enhanced the extrasynaptic GABA(A)-receptor mediated postsynaptic responses in a concentration dependent fashion. At clinically relevant concentrations, halothane significantly increased both the amplitude and frequency of spontaneous postsynaptic inhibitory currents (sIPSCs) mediated by synaptic GABA(A) receptors. The relative amplitude of evoked IPSCs (eIPSCs) was also increased, concurrent with a decrease in failure rate and a significantly decreased eIPSC paired-pulse ratio. Halothane concentration dependently decreased the extrasynaptic glutamate-receptor induced postsynaptic responses but had no effects on spontaneous or evoked excitatory postsynaptic currents. These results suggest that halothane acts predominantly at presynaptic sites at GABAergic synapses to enhance inhibitory transmission at CA3 synapses, although it also increases extra-synaptic GABA responses. At excitatory synapses on to CA3 neurons, halothane has no presynaptic action-effecting only extrasynaptic receptors. Our results have clarified the locus of effects of the volatile anesthetic halothane at excitatory and inhibitory synapses, drawing somewhat different conclusions from those deduced from slices and culture systems.Brain research 07/2012; 1473:9-18. · 2.46 Impact Factor -
Article: Volatile anesthetic effects on isolated GABA synapses and extrasynaptic receptors.
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ABSTRACT: The volatile anesthetics enhance GABAergic inhibitory transmission at synaptic and extrasynaptic sites at central neurons. In the present study, we investigated the effects of three volatile anesthetics (isoflurane, enflurane and sevoflurane) on synaptic and extrasynaptic GABA(A) receptor responses using mechanically dissociated rat hippocampal CA1 neurons in which functional native nerve endings (boutons) were retained. The extrasynaptic GABA(A) receptors were activated by exogenous GABA application while synaptic ones were assessed by miniature and evoked inhibitory postsynaptic currents (mIPSCs and eIPSCs, respectively). All volatile anesthetics concentration-dependently enhanced the exogenous GABA-induced postsynaptic responses. The structural isomers, isoflurane and enflurane, increased mIPSC frequency while sevoflurane had no effect. None of these anesthetics altered mIPSC amplitudes at their clinically relevant concentrations. Sevoflurane prolonged event kinetics by increasing decay time of mIPSCs and eIPSCs at clinically relevant concentration. On the other hand, both isoflurane and enflurane only prolonged the kinetics of these events at 1 mM of high concentration. For GABAergic eIPSCs, both isoflurane and enflurane decreased the evoked response amplitude and increased the failure rate (Rf), while sevoflurane decreased the amplitude without affecting Rf. These results suggest that isoflurane and enflurane at the clinically relevant concentrations predominantly act on GABAergic presynaptic nerve endings to decrease action potential dependent GABA release. It was concluded that these anesthetics have heterogeneous effects on mIPSCs and eIPSCs with different modulation of synaptic and extrasynaptic GABA(A) receptors.Neuropharmacology 03/2011; 60(4):701-10. · 4.81 Impact Factor
