Synaptic effects of ethanol on the agranular insunlar cortex
Creators: name: Shillinglaw, Joel E.
name: 0000-0002-7983-1514
Publisher: name: The University of Texas at Austin
Year: 2019
Subjects: Insular cortex
Alcohol
Electrophysiology

description: The purpose of this study was to provide the first examination of whether the agranular insular cortex (AIC) is a target for the actions of ethanol. Initially, we wished to determine whether basic excitatory and inhibitory synaptic transmission in the AIC are sensitive to acute ethanol. Therefore, we collected brain slices from ethanol-naïve adult male mice, obtained whole-cell recording configuration in layer 2/3 AIC pyramidal neurons, and bath-applied ethanol at pharmacologically relevant concentrations during electrophysiological assays of glutamatergic and γ-amino-butyric acid (GABA)ergic synaptic transmission and plasticity. We found that ethanol inhibited electrically evoked N-methyl-D-aspartate receptor (NMDAR)-mediated excitatory postsynaptic currents (EPSCs) in a concentration-related fashion, and had little effect on other electrophysiological parameters of glutamatergic and (GABA)ergic synaptic transmission. Synaptic conditioning (low-frequency stimulation for 15 min at 1 Hz) induced a form of long-term depression (LTD) that was inhibited by a nonselective NMDAR antagonist (DL-2-amino-5-phosphonovaleric acid), and also by acute, intoxicating concentrations of ethanol. We then wished to determine whether NMDAR-dependent LTD in the AIC is sensitive to chronic ethanol. We utilized the Becker-Lopez chronic intermittent ethanol (CIE) exposure model to model chronic ethanol experience, and found that CIE vapor exposure disrupted the ability to induce NMDAR-dependent LTD in the AIC. Then, we wished to determine whether NMDAR-dependent LTD and other glutamatergic synaptic properties in the AIC are differentially modulated by conditions that promote aspects of alcohol use disorder (AUD) relative to conditions that do not. Therefore, groups of ethanol-drinking mice underwent either extended CIE (Drinking + CIE) or air (Drinking + Air) to generate AUD-like and non AUD-like phenotypes, respectively, before undergoing electrophysiological recordings testing for LTD and other glutamatergic synaptic properties. Drinking + CIE and Drinking + Air groups no longer displayed NMDAR-dependent LTD, but Drinking + CIE groups displayed a reduced NMDA/AMPA ratio relative to Drinking + Air groups. To verify the reduction in NMDA/AMPA ratio between Drinking + CIE and Drinking + Air groups, as well as determine whether modest amounts of ethanol drinking alter NMDA/AMPA ratio, we replicated the experiment with an additional ethanol-naïve handling control group. We found that ethanol drinking alone reduces NMDA/AMPA ratio relative to ethanol naïve animals. Finally, to verify whether AIC NMDAR-dependent LTD was not an age-dependent phenomenon, we tested for the presence of LTD in an additional ethanol-naïve group age-matched to the Drinking + CIE and Drinking + Air groups (≥14 weeks). We no longer observed the presence of LTD. These data indicate that glutamatergic transmission is sensitive to acute and chronic ethanol in AIC 2/3 pyramidal neurons, and that even moderate, non AUD-like ethanol drinking may alter age-dependent glutamatergic synaptic plasticity mechanisms.