Memory and plasticity impairment after binge drinking in adolescent rat hippocampus: GluN2A/GluN2B NMDA receptor subunits imbalance through HDAC2

Abstract

Ethanol (EtOH) induces cognitive impairment through modulation of synaptic plasticity notably in the hippocampus. The cellular mechanism(s) of these EtOH effects may range from synaptic signaling modulation to alterations of the epigenome. Previously, we reported that two binge-like exposures to EtOH (3 g/kg, ip, 9 h apart) in adolescent rats abolished long-term synaptic depression (LTD) in hippocampus slices, induced learning deficits, and increased N-methyl-D-aspartate (NMDA) receptor signaling through its GluN2B subunit after 48 hours. Here, we tested the hypothesis of EtOH-induced epigenetic alterations leading to modulation of GluN2B and GluN2A NMDA receptor subunits. Forty-two days old rats were treated with EtOH or the histone deacetylase inhibitor (HDACi) sodium butyrate (NaB, 600 mg/kg, ip) injected alone or 30 minutes before EtOH. After 48 hours, learning was tested with novel object recognition while synaptic plasticity and the role of GluN2A and GluN2B subunits in NMDA-fEPSP were measured in CA1 field of hippocampus slices. LTD and memory were impaired 48 hours after EtOH and NMDA-fEPSP analysis unraveled changes in the GluN2A/GluN2B balance. These results were associated with an increase in histone deacetylase (HDAC) activity and HDAC2 mRNA and protein while Ac-H4K12 labelling was decreased. EtOH increases expression of HDAC2 and mRNA level for GluN2B subunit (but not GluN2A), while HDAC2 modulates the promoter of the gene encoding GluN2B. Interestingly, NaB pretreatment prevented all the cellular and memory-impairing effects of EtOH. In conclusion, the memoryimpairing effects of two binge-like EtOH exposure involve NMDA receptordependent LTD deficits due to a GluN2A/GluN2B imbalance resulting from changes in GluN2B expression induced by HDAC2. KEYWORDS epigenetic, ethanol, long-term depression Catherine Vilpoux and Olivier Pierrefiche are co-last authors. I.D., C.D., and R.A. performed and analyzed electrophysiology and behavior experiments; G.F., I.M., and V.D. performed and analyzed cellular biology; P.G., H.S., and C.V. performed and analyzed immunohistochemistry; S.P., M.N., C.V., and O.P. wrote and edited the manuscript. /journal/adb 1 of 15 2 | MATERIAL AND METHODS Experiments were performed following the European Community guiding principles for the care and use of animals (2010/63/UE, CE Off.

Patch‐Clamp Recording of Low Frequency Stimulation‐induced Long‐Term Synaptic Depression in Rat Hippocampus Slices During Early and Late Neurodevelopment

“…Control pLFS200‐900 LTD reached 54% ± 3% ( p < 0.001; n = 4) of baseline values, whereas 48 hours after the EtOH intoxications, LTD was 88% ± 7% ( p < 0.05 compared to control; n = 5). This first series of experiments replicate our previous results obtained with field recordings (Drissi et al, 2020; Silvestre de Ferron et al, 2015) and extends it to 3‐week‐old rats. However, we could not replicate those results using patch‐clamp recordings above 3 weeks of age, revealing that the analysis of specific transmembrane currents targeted by EtOH with this method is not possible during the late‐adolescent period, that is in 7‐week‐old animals.…”

“…EtOH (from VWR, Fontenay‐sous‐Bois, France) injections were performed as previously described in our laboratory (Drissi et al, 2020; Silvestre de Ferron et al, 2015). Briefly, animals received 2 i.p.…”

“…Furthermore, the cellular mechanisms underlying the effects of EtOH on cognitive processes are not yet fully understood. In this context, our laboratory developed a model in the adolescent rat hippocampus slice to better understand the cognitive impairing effects of only 2 high EtOH intoxication episodes, to model those observed in the young adult human population (Drissi et al, 2020; Silvestre de Ferron et al, 2015). With this model, we measured a selective vulnerability to low‐frequency stimulation (LFS)‐induced LTD that is abolished and that accompanied memory impairment long after EtOH has been eliminated from the animal.…”

Murine Models for the Study of Fetal Alcohol Spectrum Disorders: An Overview

“…Several proteins used as biomarkers participate in neural plasticity processes. Histone deacetylase 2 alters the GluN2A/GluN2B balance [the major subunits of functional N-methyl-D-aspartate (NMDA) receptors] through changes in GluN2B expression, which leads to memory-impairing effects (152). The neurotrophin family of proteins includes NGF, BDNF, NT-3, NT-4/5, and NT-6.…”

Effect of Alcohol on Hippocampal-Dependent Plasticity and Behavior: Role of Glutamatergic Synaptic Transmission

“…The effect of only two episodes of alcohol intoxication has been studied, and two injections of alcohol at toxic concentrations abolished the LTD at 48 h after the protocol ended. A possible mechanism is a change in the composition of the NMDAR subunits, indicating a shift toward increased GluN2B subunit expression (Silvestre de Ferron et al, 2016;Drissi et al, 2019).…”