• Energy Research

AbstractEthanol (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 memory‐impairing effects of two binge‐like EtOH exposure involve NMDA receptor‐dependent LTD deficits due to a GluN2A/GluN2B imbalance resulting from changes in GluN2B expression induced by HDAC2.

AbstractAs the contribution of cannabinoid (CB1) receptors in the neuroadaptations following chronic alcohol exposure is unknown, we investigated the neuroadaptations induced by chronic alcohol exposure on both NMDA and GABAA receptors in CB1−/− mice. Our results show that basal levels of hippocampal [3H]MK‐801 ((1)‐5‐methyl‐10,11‐dihydro‐5Hdibenzo[a,d]cyclohepten‐5,10‐imine) binding sites were decreased in CB1−/− mice and that these mice were also less sensitive to the locomotor effects of MK‐801. Basal level of both hippocampal and cerebellar [3H]muscimol binding was lower and sensitivity to the hypothermic effects of diazepam and pentobarbital was increased in CB1−/− mice. GABAAα1, β2, and γ2 and NMDA receptor (NR) 1 and 2B subunit mRNA levels were altered in striatum of CB1−/− mice. Our results also showed that [3H]MK‐801 binding sites were increased in cerebral cortex and hippocampus after chronic ethanol ingestion only in wild‐type mice. Chronic ethanol ingestion did not modify the sensitivity to the locomotor effects of MK‐801 in both genotypes. Similarly, chronic ethanol ingestion reduced the number of [3H]muscimol binding sites in cerebral cortex, but not in cerebellum, only in CB1+/+ mice. We conclude that lifelong deletion of CB1 receptors impairs neuroadaptations of both NMDA and GABAA receptors after chronic ethanol exposure and that the endocannabinoid/CB1 receptor system is involved in alcohol dependence.

AbstractBinge drinking during adolescence induces memory impairments, and evidences suggest that females are more vulnerable than males. However, the reason for such a difference is unclear, whereas preclinical studies addressing this question are lacking. Here we tested the hypothesis that endogenous estrogen level (E2) may explain sex differences in the effects of ethanol on hippocampus plasticity, the cellular mechanism of memory. Long‐term depression (LTD) in hippocampus slice of pubertal female rats was recorded 24 h after two ethanol binges (3 g/kg, i.p., 9 h apart). Neither the estrous cycle nor ethanol altered LTD. However, if ethanol was administered during proestrus (i.e., at endogenous E2 peak), LTD was abolished 24 h later, whereas NMDA‐fEPSPs response to a GluN2B antagonist increased. The abolition of LTD was not observed in adult female rats. Exogenous E2 combined with ethanol replicated LTD abolition in pubertal, prepubertal female, and in pubertal male rats without changes in ethanol metabolism. In male rats, a higher dose of ethanol was required to abolish LTD at 24‐h delay. In pubertal female rats, tamoxifen, an antagonist of estrogen receptors, blocked the impairing effects of endogenous and exogenous E2 on LTD, suggesting estrogen interacts with ethanol through changes in gene expression. In addition, tamoxifen prevented LTD abolition at 24 h but not at 48‐h delay. In conclusion, estrogen may explain the increased vulnerability to ethanol‐induced plasticity impairment seen in females compared with males. This increased vulnerability of female rats is likely due to changes in the GluN2B subunit that represent a common target between ethanol and estrogen.

AbstractBehavioral sensitization to repeated ethanol (EtOH) exposure induces an increase in locomotor activity in mice. However, not all animals express such sensitization. Although the literature indicated that the hippocampus may play a role in EtOH sensitization, it is not known whether behavioral sensitization to EtOH is associated with preferential changes in bidirectional synaptic plasticity, i.e., LTP and LTD, two markers of learning capabilities that have also been shown to be involved in addictive behavior. In the present study, we examined whether the vulnerability to develop and express behavioral sensitization to EtOH is associated with altered bidirectional synaptic plasticity in the CA1 area of the dorsal hippocampus. For this purpose, we analyzed both LTP and LTD in resistant and sensitized mice during the expression phase, i.e., 7 days after 10 days of repeated EtOH i.p. administration. We found that resistant mice showed a lack of LTD without changes in LTP. The lack of LTD was associated with an increase in GluN2A protein level and was not due to an altered level of neuronal activity, since no difference was observed between the number of c‐FOS positive neurons in sensitized and resistant mice. Given that both types of synaptic plasticity signals may have distinct roles in specific learning and behaviors, our results suggest that resistant mice could exhibit different phenotypes in terms of learning/memory and addictive behaviors compared to sensitized ones. Synapse 71:e21899, 2017. © 2016 Wiley Periodicals, Inc.

Binge drinking during adolescence impairs learning and memory on the long term, and many studies suggest a role of neuroinflammation. However, whether neuroinflammation occurs after the very first exposures to alcohol remains unclear, while initial alcohol exposure impairs learning for several days in male rats.To investigate the role of neuroinflammation in the effects of only two binge-like episodes on learning and on neuronal plasticity in adolescent male rat hippocampus.Animals received two ethanol i.p. injections (3 g/kg) 9 h apart. Forty-eight hours later, we recorded long-term depression (LTD) and potentiation (LTP) in CA1 area of hippocampus slices. In isolated CA1, we measured immunolabelings for microglial activation and Toll-like receptor 4 (TLR4) and mRNA levels for several cytokines.Forty-eight hours after the two binges, rats performed worse than control rats in novel object recognition, LTD was reduced, LTP was increased, and excitatory neurotransmission was more sensitive to an antagonist of the GluN2B subunit of the NMDA receptor. Exposure to ethanol with minocycline or indomethacin, two anti-inflammatory drugs, or with a TLR4 antagonist, prevented all effects of ethanol. Immunolabelings at 48 h showed a reduction of neuronal TLR4 that was prevented by minocycline pretreatment, while microglial reactivity was undetected and inflammatory cytokines mRNA levels were unchanged.Two binge-like ethanol exposures during adolescence in rat involved neuroinflammation leading to changes in TLR4 expression and in GluN2B functioning inducing disturbances in synaptic plasticity and cognitive deficits. Anti-inflammatory drugs are good candidates to prevent brain function and memory deficits induced by few binge-drinking episodes.

Binge drinking (BD) in young adults/adolescents can lead to cognitive deficits in the adult probably through neuroinflammation and epigenetic. However, the mode of action of alcohol during the initial exposure is less known while it may be the origin of the deficits seen in adults. Recent studies in adolescent rat hippocampus revealed that loss of memory occurred since the very first exposure to BD with similar mechanisms than those highlighted for longer alcohol exposure. Thus, initiation to BD in the young is responsible for cognitive deficits that will be probably entertained by repeated BD behavior. These kind of data may serve to reinforce the prevention campaigns towards the young population who practice BD.

AbstractLow to moderate perinatal ethanol exposure (PEE) may have disastrous consequences for the central nervous system resulting notably in permanent cognitive deficits. Learning and memory are mediated in the hippocampus by long‐term potentiation (LTP) and long term depression (LTD), two forms of synaptic plasticity. PEE decreases LTP but also abnormally facilitates LTD (Kervern et al. ) through a presently unknown mechanism. We studied in rat hippocampus slice, the involvement of the chloride co‐transporters NKCC1 and KCC2, in the role of GABAA inhibitions in facilitated LTD after moderate PEE. After PEE and in contrast to control slices, facilitated LTD in CA1 field was reduced by the GABAA receptor antagonist bicuculline with no changes in sensitivity to bicuculline and in GABA and benzodiazepine binding sites. Also, sensitivity to diazepam was unaltered, whereas aberrant LTD was blocked. Immunohistochemistry and protein analysis demonstrated an increase in KCC2 protein level at cell membrane in CA1 after PEE with no change in NKCC1 expression. Specifically, both monomeric and dimeric forms of KCC2 were increased in CA1. Bumetanide (10–100 μM), a dose‐dependent blocker of NKCC1 and KCC2, or VU0240551 (10 μM) a specific antagonist of KCC2, corrected the enhanced LTD and interestingly bumetanide also restored the lower LTP after PEE. These results demonstrate for the first time an upregulation of the KCC2 co‐transporter expression after moderate PEE associated with disturbances in GABAergic neurotransmission modulating bidirectional synaptic plasticity in the hippocampus. Importantly, bumetanide compensated deficits in both LTP and LTD, revealing its potential therapeutic properties.

Alcohol (ethanol) disturbs cognitive functions including learning and memory in humans, non-human primates, and laboratory animals such as rodents. As studied in animals, cellular mechanisms for learning and memory include bidirectional synaptic plasticity, long-term potentiation (LTP), and long-term depression (LTD), primarily in the hippocampus. Most of the research in the field of alcohol has analyzed the effects of ethanol on LTP; however, with recent advances in the understanding of the physiological role of LTD in learning and memory, some authors have examined the effects of ethanol exposure on this particular signal. In the present review, I will focus on hippocampal LTD recorded in rodents and the effects of fetal alcohol exposure on this signal. A synthesis of the findings indicates that prenatal ethanol exposure disturbs LTD concurrently with LTP in offspring and that both glutamatergic and γ-aminobutyric acid (GABA) neurotransmissions are altered and contribute to LTD disturbances. Although the ultimate mode of action of ethanol on these two transmitter systems is not yet clear, novel suggestions have recently appeared in the literature.