The intermittent administration of ethanol during the juvenile period produces changes in the expression of hippocampal genes and proteins and deterioration of spatial memory

Acute activation of hemichannels by ethanol leads to Ca2+-dependent gliotransmitter release in astrocytes

Multiple studies have demonstrated that acute ethanol consumption alters brain function and cognition. Nevertheless, the mechanisms underlying this phenomenon remain poorly understood. Astrocyte-mediated gliotransmission is crucial for hippocampal plasticity, and recently, the opening of hemichannels has been found to play a relevant role in this process. Hemichannels are plasma membrane channels composed of six connexins or seven pannexins, respectively, that oligomerize around a central pore. They serve as ionic and molecular exchange conduits between the cytoplasm and extracellular milieu, allowing the release of various paracrine substances, such as ATP, D-serine, and glutamate, and the entry of ions and other substances, such as Ca2+ and glucose. The persistent and exacerbated opening of hemichannels has been associated with the pathogenesis and progression of several brain diseases for at least three mechanisms. The uncontrolled activity of these channels could favor the collapse of ionic gradients and osmotic balance, the release of toxic levels of ATP or glutamate, cell swelling and plasma membrane breakdown and intracellular Ca2+ overload. Here, we evaluated whether acute ethanol exposure affects the activity of astrocyte hemichannels and the possible repercussions of this phenomenon on cytoplasmatic Ca2+ signaling and gliotransmitter release. Acute ethanol exposure triggered the rapid activation of connexin43 and pannexin1 hemichannels in astrocytes, as measured by time-lapse recordings of ethidium uptake. This heightened activity derived from a rapid rise in [Ca2+]i linked to extracellular Ca2+ influx and IP3-evoked Ca2+ release from intracellular Ca2+ stores. Relevantly, the acute ethanol-induced activation of hemichannels contributed to a persistent secondary increase in [Ca2+]i. The [Ca2+]i-dependent activation of hemichannels elicited by ethanol caused the increased release of ATP and glutamate in astroglial cultures and brain slices. Our findings offer fresh perspectives on the potential mechanisms behind acute alcohol-induced brain abnormalities and propose targeting connexin43 and pannexin1 hemichannels in astrocytes as a promising avenue to prevent deleterious consequences of alcohol consumption.

Assessing the Influence of Intermittent Alcohol Access on Acrylamide-Induced Neuronal Toxicity in an Experimental Rat Model

Tobacco and alcohol have been identified as health risk behaviors associated with significant unfavorable health consequences, ranking within the list of the top ten causes of mortality and disability-adjusted life years (DALY). The combustion of tobacco leads to the formation of acrylamide (ACR), which is well known for its neurotoxic effects. Similarly, alcohol consumption has also been widely recognized for its neurotoxic effects. Both substances can affect neurons and neuroglia cells through various pathways. This study sought to examine the impacts of co-administration of ACR and intermittent-access ethanol (IAE) consumption over a period of one month. The experimental group received 20 mg/kg of ACR, administered orally, along with IAE of 20% ethanol sessions lasting 24 h, three times per week. The cognitive outcomes were assessed utilizing the elevated plus maze (EPM), which was employed as a means of assessing the capability to learn and remember, the novel object recognition (NOR) test, which was employed to assess recognition memory, and the Y-maze, which was used to explore a new environment and navigate. Additionally, ELISA assays were performed to examine underlying mechanisms, including markers associated with inflammation (NF-κB, PGE2, and TNF-α), apoptosis (Bcl2, Bax, and Caspase-3), and oxidative stress (MDA, catalase, and GSH). These markers were assessed in the brain homogenate as part of the investigation. Furthermore, a histopathological study was conducted. The findings indicated that NF-κB levels increased significantly in the combination of ACR and IAE groups (ACR + IAE) compared to either the ACR-alone or IAE-alone groups. However, parallel changes were observed in TNF-α, PGE2, Bax, Bcl-2, Caspase-3, GSH, and CAT levels when comparing the ACR + IAE group to the ACR-alone group. Comparable alterations were noted between the ACR + IAE treatment and IAE-alone groups in TNF-α, Bcl-2, MDA, GSH, and CAT levels. Moreover, the histopathological analysis revealed significant changes between the ACR + IAE and the ACR- or IAE-alone groups. Regarding memory parameters assessed using tests including EPM, NOR, and Y-maze, considerable changes were observed across all treatment groups as opposed to the control. Surprisingly, there were no notable differences in the NOR and Y-maze tasks between the alone and combination treatment. Further study is necessary to explore the long-term alteration of co-administering ACR and IAE on behavior, memory, and neurotoxicity-related mechanisms, in order to elucidate their combined effects more clearly.

Schedule-induced alcohol intake during adolescence sex dependently impairs hippocampal synaptic plasticity and spatial memory

In a previous study, we demonstrated that intermittent ethanol administration in male adolescent animals impaired hippocampus-dependent spatial memory, particularly under conditions of excessive ethanol administration. In this current study, we subjected adolescent male and female Wistar rats an alcohol schedule-induced drinking (SID) procedure to obtain an elevated rate of alcohol self-administration and assessed their hippocampus-dependent spatial memory. We also studied hippocampal synaptic transmission and plasticity, as well as the expression levels of several genes involved in these mechanisms. Both male and female rats exhibited similar drinking patterns throughout the sessions of the SID protocol reaching similar blood alcohol levels in all the groups. However, only male rats that consumed alcohol showed spatial memory deficits which correlated with inhibition of hippocampal synaptic plasticity as long-term potentiation. In contrast, alcohol did not modify hippocampal gene expression of AMPA and NMDA glutamate receptor subunits, although there are differences in the expression levels of several genes relevant to synaptic plasticity mechanisms underlying learning and memory processes, related to alcohol consumption as Ephb2, sex differences as Pi3k or the interaction of both factors such as Pten. In conclusion, elevated alcohol intake during adolescence seems to have a negative impact on spatial memory and hippocampal synaptic plasticity in a sex dependent manner, even both sexes exhibit similar blood alcohol concentrations and drinking patterns.

Proteome-Wide Analysis of the Hippocampus in Adult Mice with Learning and Memory Impairment Caused by Chronic Ethanol Exposure

Alcohol consumption may cause various impairments in the brain. The hippocampus is particularly vulnerable to alcohol exposure, which may cause learning and memory deficits. Recently, proteomics analysis has become a popular approach to explore the pathogenesis of various diseases. The present study was conducted to investigate protein expression alteration in the hippocampus and to identify the molecular mechanisms underlying ethanol-induced learning and memory impairments. Mouse models of chronic ethanol intoxication were established by intragastrical administration for 28 consecutive days, and hippocampal neuronal damage was assessed by Nissl staining. Recognition memory was evaluated by Novel object recognition and Morris water maze tests, and hippocampus tissues were collected for label-free quantitative proteomics and analyzed using bioinformatics methods. Our study showed that chronic ethanol exposure prompted marked changes in protein expression in the hippocampus. We identified 32 differentially expressed proteins, of which 21 were upregulated and 11 downregulated. Gene Ontology analysis suggested that the identified differentially proteins were mainly involved in cytoskeleton and signal transduction mechanisms. Further verification using Western blotting and real-time quantitative PCR revealed that the hippocampal CTSL (cathepsin L), and PVALB (Parvalbumin) showed strongest expression changes, the latter being specifically expressed in GABAergic interneurons. These two proteins might serve as candidate protein biomarkers, providing new prospects for the diagnosis and treatment of ethanol-induced learning and memory disorders.

Butyric Acid Precursor Tributyrin Modulates Hippocampal Synaptic Plasticity and Prevents Spatial Memory Deficits: Role of PPARγ and AMPK

BACKGROUND

Short chain fatty acids (SCFA), such as butyric acid (BA), derived from the intestinal fermentation of dietary fiber and contained in dairy products, are gaining interest in relation to their possible beneficial effects on neuropsychological disorders.

METHODS

C57BL/6J male mice were used to investigate the effect of tributyrin (TB), a prodrug of BA, on hippocampus (HIP)-dependent spatial memory, HIP synaptic transmission and plasticity mechanisms, and the expression of genes and proteins relevant to HIP glutamatergic transmission.

RESULTS

Ex vivo studies, carried out in HIP slices, revealed that TB can transform early-LTP into late-LTP (l-LTP) and to rescue LTP-inhibition induced by scopolamine. The facilitation of l-LTP induced by TB was blocked both by GW9662 (a PPARγ antagonist) and C-Compound (an AMPK inhibitor), suggesting the involvement of both PPARγ and AMPK on TB effects. Moreover, 48-hour intake of a diet containing 1% TB prevented, in adolescent but not in adult mice, scopolamine-induced impairment of HIP-dependent spatial memory. In the adolescent HIP, TB upregulated gene expression levels of Pparg, leptin, and adiponectin receptors, and that of the glutamate receptor subunits AMPA-2, NMDA-1, NMDA-2A, and NMDA-2B.

CONCLUSIONS

Our study shows that TB has a positive influence on LTP and HIP-dependent spatial memory, which suggests that BA may have beneficial effects on memory.

Effects of binge drinking and the anti-inflammatory drug indomethacin on spatial memory and cognitive flexibility in mice

In previous research, we found that chronic-intermittent ethanol administration (CIEA), a model of binge drinking, impaired emotional memory in mice, and this impairment was counteracted by the anti-inflammatory drug indomethacin. In the present study, we evaluated the effects of CIEA on spatial memory and cognitive flexibility in adolescent mice of both sexes. Animals were randomly assigned to one of four groups for each sex: SS (saline + saline), SA (saline + alcohol), SI (saline + indomethacin), and AI (alcohol + indomethacin). They were injected with saline, ethanol (3 g/kg) or indomethacin (10 mg/kg) for the first three days of each week, throughout three weeks. 96 h after treatment, subjects learnt a standard water maze task on five consecutive days (4-day training and 1-day probe trial). One day later, mice underwent a reversal task for evaluating spatial cognitive flexibility. Animals receiving alcohol (SA and AI groups) did not differ from controls (SS groups) during the standard task, but animals treated with indomethacin performed better than controls, both in the acquisition trials and the probe trial. During the reversal task, no significant differences between alcohol groups and controls were observed, but the indomethacin group showed significant lower escape latencies than controls. No sex differences were found in either task. In conclusion, binge drinking does not impair spatial memory or spatial cognitive flexibility, while the anti-inflammatory indomethacin improves both, showing that the effects of alcohol and indomethacin on spatial memory (dependent on hippocampus) are different to those they exert on emotional memory (dependent on amygdala).

The interactions of alcohol and cocaine regulate the expression of genes involved in the GABAergic, glutamatergic and endocannabinoid systems of male and female rats

Although the pharmacological and behavioural interactions between cocaine and alcohol are well established, less is known about how polyconsumption of these drugs affects the neurotransmitter systems involved in their psychoactive effects and in particular, in the process of addiction. Here, rats of both sexes at two stages of development were studied under a chronic regime of intravenous cocaine and/or alcohol administration. Brain samples from the medial prefrontal cortex, nucleus accumbens, hippocampus and amygdala were extracted to analyse the mRNA expression of genes encoding subunits of the GABA, NMDA and AMPA receptors, as well as the expression of the CB1 receptor, and that of enzymes related to the biosynthesis and degradation of endocannabinoids. Moreover, two synaptic scaffold proteins related to GABA and NMDA receptors, gephyrin and PSD-95, were quantified in Western blots. Significant interactions between cocaine and alcohol were common, affecting the GABAergic and endocannabinoid systems in the medial prefrontal cortex and amygdala of young adults, whereas such interactions were evident in the glutamatergic and endocannabinoid systems in adults, as well as a more pronounced sex effect. Significant interactions between these drugs affecting the scaffold proteins were evident in the medial prefrontal cortex and nucleus accumbens of young adults, and in the nucleus accumbens and amygdala of adults, but not in the hippocampus. These results highlight the importance of considering the interactions between cocaine and alcohol on neurotransmitter systems in the context of polyconsumption, specifically when treating problems of abuse of these two substances.

Oxysterols Modulate the Acute Effects of Ethanol on Hippocampal N-Methyl-d-Aspartate Receptors, Long-Term Potentiation, and Learning

Ethanol is a noncompetitive inhibitor of N-methyl-d-aspartate receptors (NMDARs) and acutely disrupts hippocampal synaptic plasticity and learning. In the present study, we examined the effects of oxysterol positive allosteric modulators (PAMs) of NMDARs on ethanol-mediated inhibition of NMDARs, block of long-term potentiation (LTP) and long-term depression (LTD) in rat hippocampal slices, and defects in one-trial learning in vivo. We found that 24S-hydroxycholesterol and a synthetic oxysterol analog, SGE-301, overcame effects of ethanol on NMDAR-mediated synaptic responses in the CA1 region but did not alter acute effects of ethanol on LTD; the synthetic oxysterol, however, overcame acute inhibition of LTP. In addition, both oxysterols overcame persistent effects of ethanol on LTP in vitro, and the synthetic analog reversed defects in one-trial inhibitory avoidance learning in vivo. These results indicate that effects of ethanol on both LTP and LTD arise by complex mechanisms beyond NMDAR antagonism and that oxysterol NMDAR PAMS may represent a novel approach for preventing and reversing acute ethanol-mediated changes in cognition.

Protective effect of apple polyphenols on chronic ethanol exposure-induced neural injury in rats

Apple polyphenols (AP) have attracted much attention due to their various bioactivities. In this study, the protective effect of AP against chronic ethanol exposure-induced neural injury as well as the possible mechanisms were investigated. Body weight, daily average food intake and daily average fluid intake were measured and daily average ethanol consumption was calculated. The influences of AP on motor behavior and memory were detected by locomotor activity test, rotarod test, beam walking test, and Y maze test and novel object recognition test, respectively. The changes of blood ethanol concentration and the oxidative stress were also measured. AP improved chronic ethanol exposure-induced the inhibition of body weight and the decrease of daily average food intake, but did not influence the daily average fluid intake and the daily average ethanol intake, indicating that the improve effect of AP did not result from the decrease of ethanol intake. Motor activity and motor coordination were not influenced after chronic ethanol exposure though the blood ethanol concentration was higher than that in control group. AP improved significantly chronic ethanol-induced the memory impairment and the hippocampal CA1 neurons damage. Further studies found that AP decreased the contents of NO and MDA and increased the levels of T-AOC and GSH in the hippocampus of rats. These results suggest that AP exerts a protective effect against chronic ethanol-induced memory impairment through improving the oxidative stress in the hippocampus.

Inhibitors of cellular stress overcome acute effects of ethanol on hippocampal plasticity and learning

Ethanol intoxication can produce marked changes in cognitive function including states in which the ability to learn and remember new information is completely disrupted. These defects likely reflect changes in the synaptic plasticity thought to underlie memory formation. We have studied mechanisms contributing to the adverse effects of ethanol on hippocampal long-term potentiation (LTP) and provided evidence that ethanol-mediated LTP inhibition involves a form of metaplasticity resulting from local metabolism of ethanol to acetaldehyde and untimely activation of N-methyl-d-aspartate receptors (NMDARs), both of which are neuronal stressors. In the present studies, we sought to understand the role of cellular stress in LTP defects, and demonstrate that ethanol's effects on LTP in the CA1 hippocampal region are overcome by agents that inhibit cellular stress responses, including ISRIB, a specific inhibitor of integrated stress responses, and GW3965, an agonist that acts at liver X receptors (LXRs) and dampens cellular stress. The agents that alter LTP inhibition also prevent the adverse effects of acute ethanol on one trial inhibitory avoidance learning. Unexpectedly, we found that the LXR agonist but not ISRIB overcomes effects of ethanol on synaptic responses mediated by N-methyl-d-aspartate receptors (NMDARs). These results have implications for understanding the adverse effects of ethanol and possibly for identifying novel paths to treatments that can prevent or overcome ethanol-induced cognitive dysfunction.

Emotional memory impairment produced by binge drinking in mice is counteracted by the anti-inflammatory indomethacin

The Binge Drinking (BD) pattern of alcohol consumption, prevalent in adolescents and young adults, has been associated with memory impairment. In addition, evidence shows that alcohol abuse causes neuroinflammation, which may contribute to the brain damage produced by alcohol and explain its cognitive consequences. In this study, we evaluated the effectiveness of the anti-inflammatory indomethacin in counteracting the memory impairment produced by alcohol (ethanol) in adolescent mice of both sexes. Animals were randomly assigned to one of four groups for each sex: SS (saline + saline), SA (saline + alcohol), SI (saline + indomethacin) and AI (alcohol + indomethacin). They were injected acutely (Experiment 1) or chronically intermittent (Experiment 2) with saline, ethanol (3 g/kg) and indomethacin (10 mg/kg). All subjects were evaluated in an inhibitory avoidance task 96 h after treatment. With acute administration, SA groups showed significantly lower Test latencies than SS groups, while AI groups had similar latencies to controls. The chronic-intermittent administration of alcohol, an animal model of BD, produced significant emotional memory impairment -blocking learning in males- which was counteracted by indomethacin, as the AI groups had similar latencies to the SS groups. No significant differences were observed in locomotor activity or analgesia. In conclusion, alcohol BD (one or several episodes) impairs emotional memory in mice. This impairment is not secondary to the effects of alcohol BD on locomotor activity or pain sensitivity, and it is counteracted by indomethacin. Therefore, the memory impairment produced by alcohol BD seems to be mediated, in part, by neuroinflammatory processes. These findings open a window for new treatments for alcohol use disorders.

Effects of Intermittent versus Chronic-Moderate Ethanol Administration during Adolescence in the Adult Hippocampal Phosphoproteome

Alcohol consumption during adolescence is known to cause different impairments in the hippocampus that could lead to persistent deficits in adulthood. A common pattern of alcohol use in adolescents consists of excessive and intermittent alcohol consumption over a very short period of time (binge drinking). Protein phosphorylation is a mechanism underlying memory processes and we have previously demonstrated changes in the rat hippocampal phosphoproteome after a single dose of ethanol; however, studies showing the phosphoprotein alterations in the hippocampus after repeated exposition to alcohol are limited. This study focuses on the identification of the phosphoproteins differentially regulated in the adolescent rat hippocampus after repeated ethanol administration by comparing different patterns of alcohol treatments according to dose and frequency of administration ((i) moderate dose-chronic use, (ii) low dose-intermittent use, and (iii) high dose-intermittent use). We have used a proteomic approach, including phosphoprotein enrichment by immobilized metal affinity chromatography, which revealed 21 proteins differentially affected depending on the pattern of alcohol treatment used. Many of these proteins are included in glycolysis and glucagon signaling pathways and are also involved in neurodegeneration, which could reinforce the role of metabolic alterations in the neural damage induced by repeated alcohol exposure during adolescence.

Understanding Addiction Using Animal Models

Drug addiction is a neuropsychiatric disorder with grave personal consequences that has an extraordinary global economic impact. Despite decades of research, the options available to treat addiction are often ineffective because our rudimentary understanding of drug-induced pathology in brain circuits and synaptic physiology inhibits the rational design of successful therapies. This understanding will arise first from animal models of addiction where experimentation at the level of circuits and molecular biology is possible. We will review the most common preclinical models of addictive behavior and discuss the advantages and disadvantages of each. This includes non-contingent models in which animals are passively exposed to rewarding substances, as well as widely used contingent models such as drug self-administration and relapse. For the latter, we elaborate on the different ways of mimicking craving and relapse, which include using acute stress, drug administration or exposure to cues and contexts previously paired with drug self-administration. We further describe paradigms where drug-taking is challenged by alternative rewards, such as appetitive foods or social interaction. In an attempt to better model the individual vulnerability to drug abuse that characterizes human addiction, the field has also established preclinical paradigms in which drug-induced behaviors are ranked by various criteria of drug use in the presence of negative consequences. Separation of more vulnerable animals according to these criteria, along with other innate predispositions including goal- or sign-tracking, sensation-seeking behavior or impulsivity, has established individual genetic susceptibilities to developing drug addiction and relapse vulnerability. We further examine current models of behavioral addictions such as gambling, a disorder included in the DSM-5, and exercise, mentioned in the DSM-5 but not included yet due to insufficient peer-reviewed evidence. Finally, after reviewing the face validity of the aforementioned models, we consider the most common standardized tests used by pharmaceutical companies to assess the addictive potential of a drug during clinical trials.