The Effect And Mechanism Of Sevoflurane On GABAergic Neurons In Basal Forebrain In Mice

Objective: The mechanism underlying general anesthetics is still unclear.Emerging studies show that the generation of general anesthesia is based on the activation of inhibitory ?-aminobutyric acid(GABA)neurons,the reinforcement of the inhibitory effect mediated by GABAA receptors and the inhibition of wake-active neurons in mammalian central nervous system.Recently researches showed that activation of the cortically projecting basal forebrain(BF)GABAergic neurons in mice increased the amount of wakefulness in mice.Therefore,these wake-active neurons which are GABAergic may be inhibited rather than activated by general anesthetics.Here,whole-cell patch-clamp recording were used to study the effect of inhaled anesthetic,sevoflurane on cortically projecting BF GABAergic neurons,glutamatergic and GABAergic signs which is highly correlated with general anesthesia in vitro,for the purpose of providing fondermental scientific evidence for uncovering the mechanism of general anesthetics in vivo.Methods: Preparation of acute brain slices containing the basal forebrain region by using GAD67-GFP mice.By using patch clamp technique,this research investigated the effect of sevoflurane on two subgroups of basal forebrain GABAergic neurons(BF GABAergic neurons with a small Ih and GABAergic neurons with a large Ih)in whole-cell current-clamp mode and studied the effect of sevoflurane on inhibitory inputs and excitatory inputs to BF GABAergic neurons with a small Ih and a large Ih in whole-cell voltage clamp-mode.Results:(1)Infusion of sevoflurane at 150 ?M in 5 min didn't affect the spontaneous firing frequency of BF GABAergic neurons with a small Ih or a large Ih.Infusion of sevoflurane at 500 ?M in 5 min significantly decreased the firing frequency of BF GABAergic neurons with a small Ih and a large Ih.Infusion of sevoflurane at 1.5 mM in 5 min completely inhibited the firing of BF GABAergic neurons with a small Ih and a large Ih.(2)Infusion of sevoflurane at 500 ?M in 5 min didn't affect the membrane potential of BF GABAergic neurons with a small Ih or a large Ih in the presence of tetrodotoxin(TTX).(3)Infusion of sevoflurane at 500 ?M in 3 min increased the frequency and amplitude of spontaneous inhibitory postsynapatic currents(sIPSCs)and miniature inhibitory postsynapatic currents(mIPSCs)recorded in BF GABAergic neurons with a small Ih,but only increased the amplitude of s IPSCs and mIPSCs of BF GABAergic neurons with a large Ih.(4)Infusion of sevoflurane at 500 ?M in 3 min decreased the frequency and amplitude of spontaneous excitatory postsynapatic currents(s EPSCs)of BF GABAergic neurons with a small Ih,but increased the frequency of sEPSCs of BF GABAergic neurons with a large Ih.And sevoflurane didn't affect miniature excitatory postsynapatic currents(mIPSCs)of both the two types of neurons.Conclusion: The inhibition of BF GABAergic neurons with a small Ih induced by sevoflurane is though the enhancement of inhibitory inputs due to an effect on presynaptic GABA release probability and postsynaptic GABAA receptors and the decline of excitatory inputs caused by an effect on the action potential-dependent neurotransmiter release of local glutamatergic neurons.But the inhibition of BF GABAergic neurons with a large Ih induced by sevoflurane is though the enhancement of inhibitory inputs due to an effect on postsynaptic GABAA receptors.So,we infer that one of the mechanism underlying general anesthesia induced by inhaled anesthetic,sevoflurane may is through the inhibition of BF GABAergic neurons with a small Ih and a large Ih which are wake-acitve.