Developmental differences in the sensitivity of spontaneous and miniature IPSCs to ethanol

Endorsement of specific alcohol use disorder criterion items changes with age in individuals with persistent alcohol use disorders in 2 generations of the San Diego Prospective Study

BACKGROUND

Diagnostic and Statistical Manual (DSM) alcohol use disorder (AUD) criteria are written in broad enough terms to apply to diverse populations. The current analyses evaluate whether the endorsement of criteria changes with increasing age in individuals with persistent AUDs.

METHODS

Data regarding AUDs persisting across 3 timepoints between average ages of 31 and 43 were gathered about every 5 years from 318 interviews for 106 San Diego Prospective Study (SDPS) AUD male probands. Similar data regarding persistent AUDs across 2 timepoints were obtained from 136 interviews with 68 SDPS AUD offspring between average ages of 21 and 27. Changes in the endorsement of each AUD criterion were evaluated using Cochran's Q test.

RESULTS

For AUD probands across time, significant decreases were observed in the proportions endorsing 4 criteria (tolerance, withdrawal, failure to fulfill obligations, and using alcohol in hazardous situations). Increased rates of endorsement were documented for 3 criteria (drinking alcohol in higher amounts or for longer periods of time, spending a great deal of time regarding alcohol, and continued use despite social or interpersonal problems). Significant increases in rates of endorsements for offspring were seen for spending a great deal of time regarding alcohol and giving up or reducing important activities in order to drink.

CONCLUSIONS

These data indicate that the salience of many DSM AUD criterion items changed significantly with age in both SDPS generations among individuals with persistent AUDs. The current results support the need for additional systematic research to determine whether specific criterion items might need to be weighted differently in evaluating older and younger individuals with persistent AUDs.

Delta-opioid receptor-mediated modulation of excitability of individual hippocampal neurons: mechanisms involved

BACKGROUND

Delta-opioid receptor (DOR)-mediated modulation of hippocampal neural networks is involved in emotions, cognition, and in pathophysiology and treatment of mood disorders. In this study, we examined the effects of DOR agonist (SNC80) and antagonist (naltrindole) on the excitability of individual hippocampal neurons.

METHODS

Primary neuronal cultures were prepared from hippocampi of newborn rats and cultivated in vitro for 8-14 days (DIV8-14). The effects of SNC80 naltrindole on evoked and spontaneous action potentials (APs) were measured at DIV8-9 and DIV13-14, respectively.

RESULTS

SNC80 (100 µM) potentiated spontaneous AP firing and stimulated sodium current; naltrindole had opposite effects. The stimulatory effect of 100 µM of SNC80 was revoked by pre-administration of 1 µM of naltrindole. SNC80 and naltrindole induced similar inhibitory effects on the evoked AP firing and on the calcium current. Further, SNC80 inhibited both peak and sustained potassium currents. Naltrindole had no effect on potassium currents.

CONCLUSION

We suggest that the effects of naltrindole and high concentration of SNC80 on the sodium currents are mediated via DORs and underlying the changes in spontaneous activity. The inhibitory effects of SNC80 on calcium and potassium currents might also be DOR-dependent; these currents might mediate SNC80 effect on the evoked AP firing. The inhibitory effects of naltrindole on calcium and of low doses of SNC80 on sodium currents might be however DOR independent. The behavioral effects of SNC80 and naltrindole, observed in previous studies, might be mediated, at least in part, via the modulatory effect of these ligands on the excitability of hippocampal neurons.

Multiple sources of internal calcium stores mediate ethanol-induced presynaptic inhibitory GABA release in the central nucleus of the amygdala in mice

RATIONALE

Ethanol can enhance GABA release in various brain regions via presynaptic mechanisms. However, the presynaptic action of ethanol on inhibitory GABA release is still not well understood.

OBJECTIVES

Since calcium is required for neurotransmitter release from presynaptic terminals, the purpose of this study was to investigate the role of both internal and external calcium signaling in ethanol-induced enhancement of GABA release within the central amygdala nucleus (CeA) in acute brain slice preparations.

METHODS

Whole-cell patch clamp electrophysiology was used to record miniature GABA_A receptor-mediated inhibitory postsynaptic currents (mIPSCs) from CeA neurons. Ethanol-enhanced mIPSCs were recorded in the presence of antagonists that regulate internal and external calcium-mediated processes.

RESULTS

Bath-applied ethanol dose-dependently increased the mean frequency of mIPSCs without altering mIPSC amplitude. Ethanol-induced increases in mIPSC frequency were antagonized by dantrolene, 2-APB, and the endoplasmic reticulum calcium pump (SERCA) antagonists thapsigargin and cyclopiazonic acid (CPA). Blocking calcium release from mitochondria or via exocytosis with ruthenium red also attenuated mIPSCs while frequency was not altered in the presence of a non-selective calcium channel blocker cadmium. The L-type calcium blocker nifedipine, but not its analogue nimodipine, blocked ethanol-induced enhancement in CeA neurons.

CONCLUSIONS

These results demonstrate ethanol-induced presynaptic release of GABA is mediated by internal calcium stores and by disrupting neurotransmitter exocytosis within the CeA, a critical brain area involved in drugs of abuse and alcohol addiction.

Adolescent Vulnerability to Alcohol Use Disorder: Neurophysiological Mechanisms from Preclinical Studies

Adolescent alcohol use in human populations dramatically increases the likelihood of adult alcohol use disorder. This adolescent vulnerability is recapitulated in preclinical models which provide important opportunities to understand basic neurobiological mechanisms. We provide here an overview of GABAergic and glutamatergic neurotransmission and our current understanding of the sensitivity of these systems to adolescent ethanol exposure. As a whole, the preclinical literature suggests that adolescent vulnerability may be directly related to region-specific neurobiological processes that continue to develop during adolescence. These processes include the activity of intrinsic circuits within diverse brain regions (primarily represented by GABAergic neurotransmission) and activity-dependent regulation of synaptic strength at glutamatergic synapses. Furthermore, GABAergic and glutamatergic neurotransmission within regions/circuits that regulate cognitive function, emotion, and their integration appears to be the most vulnerable to adolescent ethanol exposure. Finally, using documented behavioral differences between adolescents and adults with respect to acute ethanol, we highlight additional circuits and regions for future study.

GABA and Glutamate Synaptic Coadaptations to Chronic Ethanol in the Striatum

Alcohol (ethanol) is a widely used and abused drug with approximately 90% of adults over the age of 18 consuming alcohol at some point in their lifetime. Alcohol exerts its actions through multiple neurotransmitter systems within the brain, most notably the GABAergic and glutamatergic systems. Alcohol's actions on GABAergic and glutamatergic neurotransmission have been suggested to underlie the acute behavioral effects of ethanol. The striatum is the primary input nucleus of the basal ganglia that plays a role in motor and reward systems. The effect of ethanol on GABAergic and glutamatergic neurotransmission within striatal circuitry has been thought to underlie ethanol taking, seeking, withdrawal and relapse. This chapter reviews the effects of ethanol on GABAergic and glutamatergic transmission, highlighting the dynamic changes in striatal circuitry from acute to chronic exposure and withdrawal.

Type 2 Neural Progenitor Cell Activation Drives Reactive Neurogenesis after Binge-Like Alcohol Exposure in Adolescent Male Rats

Excessive alcohol consumption during adolescence remains a significant health concern as alcohol drinking during adolescence increases the likelihood of an alcohol use disorder in adulthood by fourfold. Binge drinking in adolescence is a particular problem as binge-pattern consumption is the biggest predictor of neurodegeneration from alcohol and adolescents are particularly susceptible to the damaging effects of alcohol. The adolescent hippocampus, in particular, is highly susceptible to alcohol-induced structural and functional effects, including volume and neuron loss. However, hippocampal structure and function may recover with abstinence and, like in adults, a reactive burst in hippocampal neurogenesis in abstinence may contribute to that recovery. As the mechanism of this reactive neurogenesis is not known, the current study investigated potential mechanisms of reactive neurogenesis in binge alcohol exposure in adolescent, male rats. In a screen for cell cycle perturbation, a dramatic increase in the number of cells in all phases of the cycle was observed at 7 days following binge ethanol exposure as compared to controls. However, the proportion of cells in each phase was not different between ethanol-exposed rats and controls, indicating that cell cycle dynamics are not responsible for the reactive burst in neurogenesis. Instead, the marked increase in hippocampal proliferation was shown to be due to a twofold increase in proliferating progenitor cells, specifically an increase in cells colabeled with the progenitor cell marker Sox2 and S-phase (proliferation) marker, BrdU, in ethanol-exposed rats. To further characterize the individual subtypes of neural progenitor cells (NPCs) affected by adolescent binge ethanol exposure, a fluorescent quadruple labeling technique was utilized to differentiate type 1, 2a, 2b, and 3 progenitor cells simultaneously. At one week into abstinence, animals in the ethanol exposure groups had an increase in proliferating type 2 (intermediate progenitors) and type 3 (neuroblast) progenitors but not type 1 neural stem cells. These results together suggest that activation of type 2 NPCs out of quiescence is likely the primary mechanism for reactive hippocampal neurogenesis following adolescent alcohol exposure.

Adolescent Alcohol Exposure Persistently Impacts Adult Neurobiology and Behavior

Adolescence is a developmental period when physical and cognitive abilities are optimized, when social skills are consolidated, and when sexuality, adolescent behaviors, and frontal cortical functions mature to adult levels. Adolescents also have unique responses to alcohol compared with adults, being less sensitive to ethanol sedative-motor responses that most likely contribute to binge drinking and blackouts. Population studies find that an early age of drinking onset correlates with increased lifetime risks for the development of alcohol dependence, violence, and injuries. Brain synapses, myelination, and neural circuits mature in adolescence to adult levels in parallel with increased reflection on the consequence of actions and reduced impulsivity and thrill seeking. Alcohol binge drinking could alter human development, but variations in genetics, peer groups, family structure, early life experiences, and the emergence of psychopathology in humans confound studies. As adolescence is common to mammalian species, preclinical models of binge drinking provide insight into the direct impact of alcohol on adolescent development. This review relates human findings to basic science studies, particularly the preclinical studies of the Neurobiology of Adolescent Drinking in Adulthood (NADIA) Consortium. These studies focus on persistent adult changes in neurobiology and behavior following adolescent intermittent ethanol (AIE), a model of underage drinking. NADIA studies and others find that AIE results in the following: increases in adult alcohol drinking, disinhibition, and social anxiety; altered adult synapses, cognition, and sleep; reduced adult neurogenesis, cholinergic, and serotonergic neurons; and increased neuroimmune gene expression and epigenetic modifiers of gene expression. Many of these effects are specific to adolescents and not found in parallel adult studies. AIE can cause a persistence of adolescent-like synaptic physiology, behavior, and sensitivity to alcohol into adulthood. Together, these findings support the hypothesis that adolescent binge drinking leads to long-lasting changes in the adult brain that increase risks of adult psychopathology, particularly for alcohol dependence.

Adolescent Alcohol Exposure: Burden of Epigenetic Reprogramming, Synaptic Remodeling, and Adult Psychopathology

Adolescence represents a crucial phase of synaptic maturation characterized by molecular changes in the developing brain that shape normal behavioral patterns. Epigenetic mechanisms play an important role in these neuromaturation processes. Perturbations of normal epigenetic programming during adolescence by ethanol can disrupt these molecular events, leading to synaptic remodeling and abnormal adult behaviors. Repeated exposure to binge levels of alcohol increases the risk for alcohol use disorder (AUD) and comorbid psychopathology including anxiety in adulthood. Recent studies in the field clearly suggest that adolescent alcohol exposure causes widespread and persistent changes in epigenetic, neurotrophic, and neuroimmune pathways in the brain. These changes are manifested by altered synaptic remodeling and neurogenesis in key brain regions leading to adult psychopathology such as anxiety and alcoholism. This review details the molecular mechanisms underlying adolescent alcohol exposure-induced changes in synaptic plasticity and the development of alcohol addiction-related phenotypes in adulthood.

Adolescent alcohol exposure and persistence of adolescent-typical phenotypes into adulthood: a mini-review

Alcohol use is typically initiated during adolescence, which, along with young adulthood, is a vulnerable period for the onset of high-risk drinking and alcohol abuse. Given across-species commonalities in certain fundamental neurobehavioral characteristics of adolescence, studies in laboratory animals such as the rat have proved useful to assess persisting consequences of repeated alcohol exposure. Despite limited research to date, reports of long-lasting effects of adolescent ethanol exposure are emerging, along with certain common themes. One repeated finding is that adolescent exposure to ethanol sometimes results in the persistence of adolescent-typical phenotypes into adulthood. Instances of adolescent-like persistence have been seen in terms of baseline behavioral, cognitive, electrophysiological and neuroanatomical characteristics, along with the retention of adolescent-typical sensitivities to acute ethanol challenge. These effects are generally not observed after comparable ethanol exposure in adulthood. Persistence of adolescent-typical phenotypes is not always evident, and may be related to regionally specific ethanol influences on the interplay between CNS excitation and inhibition critical for the timing of neuroplasticity.

GABAergic contributions to alcohol responsivity during adolescence: insights from preclinical and clinical studies

There is a considerable body of literature demonstrating that adolescence is a unique age period, which includes rapid and dramatic maturation of behavioral, cognitive, hormonal and neurobiological systems. Most notably, adolescence is also a period of unique responsiveness to alcohol effects, with both hyposensitivity and hypersensitivity observed to the various effects of alcohol. Multiple neurotransmitter systems are undergoing fine-tuning during this critical period of brain development, including those that contribute to the rewarding effects of drugs of abuse. The role of developmental maturation of the γ-amino-butyric acid (GABA) system, however, has received less attention in contributing to age-specific alcohol sensitivities. This review integrates GABA findings from human magnetic resonance spectroscopy studies as they may translate to understanding adolescent-specific responsiveness to alcohol effects. Better understanding of the vulnerability of the GABA system both during adolescent development, and in psychiatric conditions that include alcohol dependence, could point to a putative mechanism, boosting brain GABA, that may have increased effectiveness for treating alcohol use disorders.

Developmental changes in the acute ethanol sensitivity of glutamatergic and GABAergic transmission in the BNST

Glutamatergic and GABAergic transmission undergo significant changes during adolescence. Receptors for both of these transmitters (NMDAR, and GABAA) are known to be key targets for the acute effects of ethanol in adults. The current study set out to investigate the acute effects of ethanol on both NMDAR-mediated excitatory transmission and GABAergic inhibitory transmission within the bed nucleus of the stria terminalis (BNST) across age. The BNST is an area of the brain implicated in the negative reinforcing properties associated with alcohol dependence, and the BNST plays a critical role in stress-induced relapse. Therefore, assessing the developmental regulation of ethanol sensitivity in this key brain region is important to understanding the progression of ethanol dependence. To do this, whole-cell recordings of isolated NMDAR-evoked excitatory postsynaptic currents (eEPSCs) or evoked GABAergic inhibitory postsynaptic currents (eIPSCs) were performed on BNST neurons in slices from 4- or 8-week-old male C57BL/6J mice. Ethanol (50 mm) produced greater inhibition of NMDAR-eEPSCs in adolescent mice than in adult mice. This enhanced sensitivity in adolescence was not a result of shifts in function of the GluN2B subunit of the NMDAR, measured by Ro25-6981 inhibition and decay kinetics measured across age. Adolescent mice also exhibited greater ethanol sensitivity of GABAergic transmission, as ethanol (50 mm) enhanced eIPSCs in the BNST of adolescent but not adult mice. Collectively, this work illustrates that a moderate dose of ethanol produces greater inhibition of transmission in the BNST (through greater excitatory inhibition and enhancement of inhibitory transmission) in adolescents compared to adults. Given the role of the BNST in alcohol dependence, these developmental changes in acute ethanol sensitivity could accelerate neuroadaptations that result from chronic ethanol use during the critical period of adolescence.

Anxiolytic effects of the GABA(A) receptor partial agonist, L-838,417: impact of age, test context familiarity, and stress

The partial α2,3,5 GABA(A) receptor agonist, L-838,417 has been reported to have anxiolytic effects in adult rodents. Although maturational differences exist for the GABA(A) receptor subunits, the anxiolytic effects of L-838,417 have not been tested in younger animals. The goal of the present experiments was to determine whether L-838,417 reverses anxiety-like behavior induced by either an unfamiliar environment (Experiment 1) or repeated restraint stress (Experiment 2) differentially in adolescent and adult, male and female Sprague-Dawley rats using a modified social interaction test. In Experiment 1, rats were injected with 0, 0.5, 1.0, 2.0, or 4.0 mg/kg L-838,417, i.p. and tested 30 min later in an unfamiliar test context for 10 min. In Experiment 2, rats were exposed to restraint stress (90 min daily for 5 days). Immediately after the last restraint session, animals were injected with L-838,417 and placed alone for 30 min in the test apparatus to familiarize them to this context prior to the 10 min social interaction test. In Experiment 1, L-838,417 produced anxiolytic effects in adults at 1.0 mg/kg, as indexed by a transformation of social avoidance into preference and an increase in social investigation. In adolescents, a dose of 2.0 mg/kg eliminated social avoidance, but had no anxiolytic effects on social investigation. Testing under familiar circumstances (Experiment 2) after repeated restraint stress eliminated age differences in sensitivity to L-838,417, with 0.5 mg/kg reversing the anxiogenic effects of prior stress regardless of age, but with doses ≥ 1 mg/kg decreasing social investigation, an effect possibly due in part to locomotor-impairing effects of this compound. Although locomotor activity was suppressed in both experiments, higher doses of L-838,417 were necessary to suppress locomotor activity in Experiment 1. Thus, anxiolytic effects of L-838,417 were found to be context-, age-, and stress-dependent.

Imbalanced synaptic plasticity induced spatial cognition impairment in male offspring rats treated with chronic prenatal ethanol exposure

BACKGROUND

As chronic prenatal ethanol (EtOH) exposure (CPEE) may cause deficiencies in a variety of behavioral and cognitive functions, the aim of present study is to investigate the effects of CPEE on spatial learning and memory and examine the action of CPEE on synaptic plasticity balance in the hippocampus of adolescent male rats.

METHODS

The animal model was produced by EtOH exposure throughout gestational period with 4 g/kg bodyweight, while the male offspring rats were used in the study. Morris water maze (MWM) test was performed, and then, long-term potentiation (LTP) and depotentiation were recorded from Schaffer collaterals to CA1 region in the hippocampus.

RESULTS

It was shown that escape latencies in learning period and re-acquisition period were prolonged in CPEE-treated group compared with that in control group. Furthermore, LTP was drastically inhibited, and depotentiation was distinctly enhanced in CPEE-treated group compared with that in control group.

CONCLUSIONS

It is suggested that the balance between cognitive stability and flexibility was broken by the bidirectional effects of long-term synaptic plasticity. In addition, the spatial cognition was attenuated by the alteration of synaptic plasticity balance in CPEE-treated male adolescent rats.

Ethanol-enhanced GABA release: a focus on G protein-coupled receptors

While research on the actions of ethanol at the GABAergic synapse has focused on postsynaptic mechanisms, recent data have demonstrated that ethanol also facilitates GABA release from presynaptic terminals in many, but not all, brain regions. The ability of ethanol to increase GABA release can be regulated by different G protein-coupled receptors (GPCRs), such as the cannabinoid-1 receptor, corticotropin-releasing factor 1 receptor, GABA(B) receptor, and the 5-hydroxytryptamine 2C receptor. The intracellular messengers linked to these GPCRs, including the calcium that is released from internal stores, also play a role in ethanol-enhanced GABA release. Hypotheses are proposed to explain how ethanol interacts with the GPCR pathways to increase GABA release and how this interaction contributes to the brain region specificity of ethanol-enhanced GABA release. Defining the mechanism of ethanol-facilitated GABA release will further our understanding of the GABAergic profile of ethanol and increase our knowledge of how GABAergic neurotransmission may contribute to the intoxicating effects of alcohol and to alcohol dependence.

GABAergic transmission modulates ethanol excitation of ventral tegmental area dopamine neurons

Activation of the dopaminergic (DA) neurons of the ventral tegmental area (VTA) by ethanol has been implicated in its rewarding and reinforcing effects. We previously demonstrated that ethanol enhances GABA release onto VTA-DA neurons via activation of 5-HT2C receptors and subsequent release of calcium from intracellular stores. Here we demonstrate that excitation of VTA-DA neurons by ethanol is limited by an ethanol-enhancement in GABA release. In this study, we performed whole-cell voltage clamp recordings of miniature inhibitory postsynaptic currents (mIPSCs) and cell-attached recordings of action potential firing from VTA-DA neurons in midbrain slices from young Long Evans rats. Acute exposure to ethanol (75 mM) transiently enhanced the firing rate of VTA-DA neurons as well as the frequency of mIPSCs. Simultaneous blockade of both GABA(A) and GABA(B) receptors (Picrotoxin (75 μM) and SCH50911 (20 μM)) disinhibited VTA-DA firing rate whereas a GABA(A) agonist (muscimol, 1 μM) strongly inhibited firing rate. In the presence of picrotoxin, ethanol enhanced VTA-DA firing rate more than in the absence of picrotoxin. Additionally, a sub-maximal concentration of muscimol together with ethanol inhibited VTA-DA firing rate more than muscimol alone. DAMGO (3 μM) inhibited mIPSC frequency but did not block the ethanol-enhancement in mIPSC frequency. DAMGO (1 and 3 μM) had no effect on VTA-DA firing rate. Naltrexone (60 μM) had no effect on basal or ethanol-enhancement of mIPSC frequency. Additionally, naltrexone (20 and 60 μM) did not block the ethanol-enhancement in VTA-DA firing rate. Overall, the present results indicate that the ethanol enhancement in GABA release onto VTA-DA neurons limits the stimulatory effect of ethanol on VTA-DA neuron activity and may have implications for the rewarding properties of ethanol.

Differential sensitivity of hippocampal interneurons to ethanol in adolescent and adult rats

Ethanol (EtOH) promotes GABAergic synaptic transmission in the central nervous system. We have shown that EtOH enhances the frequency of GABA(A) receptor-mediated spontaneous inhibitory postsynaptic currents less powerfully in hippocampal CA1 pyramidal neurons from adolescent animals compared with those from adults. However, we have also shown that EtOH promotes the firing of hippocampal interneurons, located in stratum lacunosum moleculare (SLM), from adolescent animals more potently than in those from adults. Thus the latter finding would seem to be inconsistent with the former. To understand this apparent inconsistency, we have now assessed the effects of EtOH on a different subpopulation of hippocampal interneurons, those with somata located in the stratum oriens (SO). We found that EtOH-induced enhancement of the frequency of spontaneous action potentials (sAPs) was less in interneurons from adolescent rats compared with those from adults. In addition, EtOH-induced reduction of the afterhyperpolarization decay time constant (τ(slow)) was less pronounced in interneurons from adolescent rats, as was the EtOH-induced increase in the amplitude of the hyperpolarization-activated cation current, I(h). The effect of EtOH on sAP firing frequency was blocked by application of the I(h) antagonist 4-ethylphenylamino-1,2-dimethyl-6-methylaminopyrimidinium chloride (ZD7288). These results indicate that although EtOH promotes the firing of hippocampal interneurons, through promotion of I(h), the developmental expression of this effect differs between interneurons with somata located in the SO and SLM.

Roles of neural stem cells and adult neurogenesis in adolescent alcohol use disorders

This review discusses the contributions of a newly considered form of plasticity, the ongoing production of new neurons from neural stem cells, or adult neurogenesis, within the context of neuropathologies that occur with excessive alcohol intake in the adolescents. Neural stem cells and adult neurogenesis are now thought to contribute to the structural integrity of the hippocampus, a limbic system region involved in learning, memory, behavioral control, and mood. In adolescents with alcohol use disorders (AUDs), the hippocampus appears to be particularly vulnerable to the neurodegenerative effects of alcohol, but the role of neural stem cells and adult neurogenesis in alcoholic neuropathology has only recently been considered. This review encompasses a brief overview of neural stem cells and the processes involved in adult neurogenesis, how neural stem cells are affected by alcohol, and possible differences in the neurogenic niche between adults and adolescents. Specifically, what is known about developmental differences in adult neurogenesis between the adult and adolescent is gleaned from the literature, as well as how alcohol affects this process differently among the age groups. Finally, this review suggests differences that may exist in the neurogenic niche between adults and adolescents and how these differences may contribute to the susceptibility of the adolescent hippocampus to damage. However, many more studies are needed to discern whether these developmental differences contribute to the vulnerability of the adolescent to developing an AUD.

Research on alcohol and adolescent brain development: opportunities and future directions

In the past 15 years, both human and animal studies have advanced our understanding of the effects of adolescent alcohol exposure on behavioral and neural development, particularly in the areas of the ontogeny of initial sensitivity and tolerance to alcohol, the consequences of adolescent alcohol exposure on subsequent drinking patterns, as well as cognitive and neural function. Despite these advances, there are still substantial gaps in our understanding of whether heavy adolescent drinking interferes with normal brain development at the cellular and molecular level, and if so, how these changes may translate into patterns of brain connectivity that result in the emergence of alcohol use disorders. This article discusses our current knowledge of the cellular and molecular brain changes that stem from heavy alcohol exposure, including binge patterns, during adolescence. Progress has been made in linking the behavioral effects of adolescent drinking to underlying cellular and molecular mechanisms. However, it is suggested that future research on the etiology and consequences of adolescent drinking use an integrative approach to this problem by combining multiple levels, including genetic, cellular and molecular, systems (neuroimaging), and behavioral, with an emphasis on integrating the different levels of analysis.

The effects of acute and chronic ethanol exposure on presynaptic and postsynaptic gamma-aminobutyric acid (GABA) neurotransmission in cultured cortical and hippocampal neurons

Decades after ethanol was first described as a gamma-aminobutyric acid (GABA) mimetic, the precise mechanisms that produce the acute effects of ethanol and the physiological adaptations that underlie ethanol tolerance and dependence remain unclear. Although a substantial body of evidence suggests that ethanol acts on GABAergic neurotransmission to enhance inhibition in the central nervous system, the precise mechanisms underlying the physiological effects of both acute and chronic ethanol exposure are still under investigation. We have used in vitro ethanol exposure followed by recording of miniature inhibitory postsynaptic currents (mIPSCs) to determine whether acute or chronic ethanol exposure directly alters synaptic GABA(A) receptor (GABA(A)R) function or GABA release in cultured cortical and hippocampal neurons. Acute ethanol exposure slightly increased the duration of mIPSCs in hippocampal neurons but did not alter mIPSC kinetics in cortical neurons. Acute ethanol exposure did not change mIPSC frequency in either hippocampal or cortical neurons. One day of chronic ethanol exposure produced a transient decrease in mIPSC duration in cortical neurons but did not alter mIPSC kinetics in hippocampal neurons. Chronic ethanol exposure did not change mIPSC frequency in either hippocampal or cortical neurons. Chronic ethanol exposure also did not produce substantial cross-tolerance to a benzodiazepine in either hippocampal or cortical neurons. The results suggest that ethanol exposure in vitro has limited effects on synaptic GABA(A)R function and action potential-independent GABA release in cultured neurons and that ethanol exposure in cultured cortical and hippocampal neurons may not reproduce all the effects that occur in vivo and in acute brain slices.

Neurobiological mechanisms contributing to alcohol-stress-anxiety interactions

This article summarizes the proceedings of a symposium that was presented at a conference entitled "Alcoholism and Stress: A Framework for Future Treatment Strategies." The conference was held in Volterra, Italy on May 6-9, 2008 and this symposium was chaired by Jeff L. Weiner. The overall goal of this session was to review recent findings that may shed new light on the neurobiological mechanisms that underlie the complex relationships between stress, anxiety, and alcoholism. Dr. Danny Winder described a novel interaction between D1 receptor activation and the corticotrophin-releasing factor (CRF) system that leads to an increase in glutamatergic synaptic transmission in the bed nucleus of the stria terminalis. Dr. Marisa Roberto presented recent data describing how protein kinase C epsilon, ethanol, and CRF interact to alter GABAergic inhibition in the central nucleus of the amygdala. Dr. Jeff Weiner presented recent advances in our understanding of inhibitory circuitry within the basolateral amygdala (BLA) and how acute ethanol exposure enhances GABAergic inhibition in these pathways. Finally, Dr. Brian McCool discussed recent findings on complementary glutamatergic and GABAergic adaptations to chronic ethanol exposure and withdrawal in the BLA. Collectively, these investigators have identified novel mechanisms through which neurotransmitter and neuropeptide systems interact to modulate synaptic activity in stress and anxiety circuits. Their studies have also begun to describe how acute and chronic ethanol exposure influence excitatory and inhibitory synaptic communication in these pathways. These findings point toward a number of novel neurobiological targets that may prove useful for the development of more effective treatment strategies for alcohol use disorders.

Modulation of GABAergic and glutamatergic transmission by ethanol in the developing neocortex: an in vitro test of the excessive inhibition hypothesis of fetal alcohol spectrum disorder

Exposure to ethanol during development triggers neuronal cell death and this is thought to play a central role in the pathophysiology of fetal alcohol spectrum disorder (FASD). Studies suggest that ethanol-induced neurodegeneration during the period of synaptogenesis results from widespread potentiation of GABA(A) receptors and inhibition of NMDA receptors throughout the brain, with neocortical layer II being particularly sensitive. Here, we tested whether ethanol modulates the function of these receptors during this developmental period using patch-clamp electrophysiological and Ca(2+) imaging techniques in acute slices from postnatal day 7-9 rats. We focused on pyramidal neurons in layer II of the parietal cortex (with layer III as a control). Ethanol (70mM) increased spontaneous action potential-dependent GABA release in layer II (but not layer III) neurons without affecting postsynaptic GABA(A) receptors. Protein and mRNA expression for both the Cl(-) importer, NKCC1, and the Cl(-) exporter, KCC2, were detected in layer II/III neurons. Perforated-patch experiments demonstrated that E(Cl)((-)) is shifted to the right of E(m); activation of GABA(A) receptors with muscimol depolarized E(m), decreased action potential firing, and minimally increased [Ca(2+)](i). However, the ethanol-induced increase of GABAergic transmission did not affect neuronal excitability. Ethanol had no effect on currents exogenously evoked by NMDA or AMPA receptor-mediated spontaneous excitatory postsynaptic currents. Acute application of ethanol in the absence of receptor antagonists minimally increased [Ca(2+)](i). These findings are inconsistent with the excessive inhibition model of ethanol-induced neurodegeneration, supporting the view that ethanol damages developing neurons via more complex mechanisms that vary among specific neuronal populations.

The novel micro-opioid receptor antagonist, [N-allyl-Dmt(1)]endomorphin-2, attenuates the enhancement of GABAergic neurotransmission by ethanol

AIMS

We investigated the effects of [N-allyl-Dmt(1)]endomorphin-2 (TL-319), a novel and highly potent micro-opioid receptor antagonist, on ethanol (EtOH)-induced enhancement of GABA(A) receptor-mediated synaptic activity in the hippocampus.

METHODS

Evoked and spontaneous inhibitory postsynaptic currents (eIPSCs and sIPSCs) were isolated from CA1 pyramidal cells from brain slices of male rats using whole-cell patch-clamp techniques.

RESULTS

TL-319 had no effect on the baseline amplitude of eIPSCs or the frequency of sIPSCs. However, it induced a dose-dependent suppression of an ethanol-induced increase of sIPSC frequency with full reversal at concentrations of 500 nM and higher. The non-specific competitive opioid receptor antagonist naltrexone also suppressed EtOH-induced increases in sIPSC frequency but only at a concentration of 60 microM.

CONCLUSION

These data indicate that blockade of micro-opioid receptors by low concentrations of [N-allyl-Dmt(1)]endomorphin-2 can reverse ethanol-induced increases in GABAergic neurotransmission and possibly alter its anxiolytic or sedative effects. This suggests the possibility that high potency opioid antagonists may emerge as possible candidate compounds for the treatment of ethanol addiction.

Developmental sensitivity of hippocampal interneurons to ethanol: involvement of the hyperpolarization-activated current, Ih

Ethanol (EtOH) has powerful effects on GABA(A) receptor-mediated neurotransmission, and we have previously shown that EtOH-induced enhancement of GABA(A) receptor-mediated synaptic transmission in the hippocampus is developmentally regulated. Because synaptic inhibition is determined in part by the firing properties of interneurons, we have investigated the mechanisms whereby EtOH influences the spontaneous firing characteristics and hyperpolarization-activated cation current (Ih) of hippocampal interneurons located in the near to the border of stratum lacunosum moleculare and s. radiatum of adolescent and adult rats. EtOH did not affect current injection-induced action potentials of interneurons that do not exhibit spontaneous firing. However, in neurons that fire spontaneously, EtOH enhanced the frequency of spontaneous action potentials (sAPs) in a concentration-dependent manner, an effect that was more pronounced in interneurons from adolescent rats, compared with adult rats. EtOH also modulated the afterhyperpolarization (AHP) that follows sAPs by shortening the tau(slow) decay time constant, and this effect was more pronounced in slices from adolescent rats. EtOH increased Ih amplitudes, accelerated Ih activation kinetics, and increased the maximal Ih conductance in interneurons from animals in both age groups. These effects were also more pronounced in interneurons from adolescents and persisted in the presence of glutamatergic and GABAergic blockers. However, EtOH failed to affect sAP firing in the presence of ZD7288 or cesium chloride. These results suggest that Ih may be of mechanistic significance in the effect of EtOH on interneuron spontaneous firing.

The role of protein kinase A in the ethanol-induced increase in spontaneous GABA release onto cerebellar Purkinje neurons

Ethanol increases miniature inhibitory postsynaptic current frequency and decreases the paired-pulse ratio, which suggests that ethanol increases both spontaneous and evoked GABA release, respectively. We have shown previously that ethanol increases GABA release at the rat interneuron-Purkinje cell synapse and that this ethanol effect involves calcium release from internal stores; however, further exploration of the mechanism responsible for ethanol-enhanced GABA release was needed. We found that a cannabinoid receptor 1 (CB1) agonist, WIN-55212, and a GABA(B) receptor agonist, baclofen, decreased baseline spontaneous GABA release and prevented ethanol from increasing spontaneous GABA release. The CB1 receptor and GABA(B) receptor are Galpha i-linked G protein-coupled receptors with common downstream messengers that include adenylate cyclase and protein kinase A (PKA). Adenylate cyclase and PKA antagonists blocked ethanol from increasing spontaneous GABA release, whereas a PKA antagonist limited to the postsynaptic neuron did not block ethanol from increasing spontaneous GABA release. These results suggest that presynaptic PKA plays an essential role in ethanol-enhanced spontaneous GABA release. Similar to ethanol, we found that the mechanism of the cannabinoid-mediated decrease in spontaneous GABA release involves internal calcium stores and PKA. A PKA antagonist decreased baseline spontaneous GABA release. This effect was reduced after incubating the slice with a calcium chelator, BAPTA-AM, but was unaffected when BAPTA was limited to the postsynaptic neuron. This suggests that the PKA antagonist is acting through a presynaptic, calcium-dependent mechanism to decrease spontaneous GABA release. Overall, these results suggest that PKA activation is necessary for ethanol to increase spontaneous GABA release.

Ethanol decreases Purkinje neuron excitability by increasing GABA release in rat cerebellar slices

Cerebellar Purkinje neurons (PNs) receive inhibitory GABAergic input from stellate and basket cells, which are located in the outer and inner portions of the molecular layer, respectively. Ethanol (EtOH) was recently shown to increase GABAergic transmission at PNs via a mechanism that involves enhanced calcium release from presynaptic internal stores (J Pharmacol Exp Ther 323:356-364, 2007). Here, we further characterized the effect of EtOH on GABA release and assessed its impact on PN excitability. Using whole-cell patch-clamp electrophysiological techniques in cerebellar vermis parasagittal slices, we found that EtOH acutely increases the frequency but not the amplitude or half-width of miniature and spontaneous inhibitory postsynaptic currents (IPSCs). EtOH significantly increased the amplitude and decreased the paired pulse ratio of IPSCs evoked by stimulation in the outer but not inner molecular layer. In current clamp, EtOH decreased both the amplitude of excitatory postsynaptic potentials evoked in PNs by granule cell axon stimulation and the number of action potentials triggered by these events; these effects depended on GABA(A) receptor activation because they were not observed in presence of bicuculline. Loose-patch cell-attached PN recordings revealed that neither the spontaneous action potential firing frequency nor the coefficient of variation of the interspike interval was altered by acute EtOH exposure. These findings suggest that EtOH differentially affects GABAergic transmission at stellate cell- and basket cell-to-PN synapses and that it modulates PN firing triggered by granule cell axonal input. These effects could be in part responsible for the cerebellar impairments associated with acute EtOH intoxication.

A psychobiological framework of the substrates that mediate nicotine use during adolescence

Adolescents are especially likely to initiate tobacco use and are more vulnerable to long-term nicotine dependence. A unifying hypothesis is proposed based largely on animals studies that adolescents, as compared to adults, experience enhanced short-term positive and reduced aversive effects of nicotine, as well as less negative effects during nicotine withdrawal. Thus, during adolescence the strong positive effects of nicotine are inadequately balanced by negative effects that contribute to nicotine dependence in adults. This review provides a neural framework to explain developmental differences within the mesolimbic pathway based on the established role of dopamine in addiction. This pathway originates in the ventral tegmental area (VTA) and terminates in the nucleus accumbens (NAcc) where dopamine is increased by nicotine but decreased during withdrawal. During adolescence, excitatory glutamatergic systems that facilitate dopamine are overdeveloped, whereas inhibitory GABAergic systems are underdeveloped. Thus, it is hypothesized that adolescents display enhanced nicotine reward and reduced withdrawal via enhanced excitation and reduced inhibition of VTA cell bodies that release dopamine in the NAcc. Although this framework focuses on adolescents and adults, it may also apply to the understanding of enhanced vulnerability to nicotine in adults that were previously exposed to nicotine during adolescence. The hypothesis presented in this review suggests that the clinical diagnostic criteria developed for nicotine dependence in adults, based primarily on withdrawal, may be inappropriate during adolescence when nicotine withdrawal does not appear to play a major role in nicotine use. Furthermore, treatment strategies involving nicotine replacement may be harmful for adolescents because it may cause enhanced vulnerability to nicotine dependence later in adulthood.

Ethanol enhances GABAergic transmission onto dopamine neurons in the ventral tegmental area of the rat

BACKGROUND

Activation of the dopaminergic (DA) neurons of the ventral tegmental area (VTA) by ethanol has been implicated in its rewarding and reinforcing effects. At most central synapses, ethanol generally increases inhibitory synaptic transmission; however, no studies have explored the effect of acute ethanol on GABAergic transmission in the VTA.

METHODS

Whole-cell patch clamp recordings of inhibitory postsynaptic currents (IPSCs) from VTA-DA neurons in midbrain slices from young rats.

RESULTS

Acute exposure of VTA-DA neurons to ethanol (25 to 50 mM) robustly enhanced GABAergic spontaneous and miniature IPSC frequency while inducing a slight enhancement of spontaneous IPSC (sIPSC) amplitude. Ethanol (50 mM) enhanced paired-pulse depression of evoked IPSCs, further suggesting enhanced GABA release onto VTA-DA neurons. The frequency of sIPSCs was suppressed by the GABA(B) agonist, baclofen (1.25 microM) and enhanced by the antagonist, SCH50911 (20 microM); however, neither appeared to modulate or occlude the effects of ethanol on sIPSC frequency.

CONCLUSIONS

The present results indicate that ethanol increases postsynaptic GABA(A) receptor sensitivity, enhances action potential-independent GABA release onto VTA-DA neurons, and that this latter effect is independent of GABA(B) auto-receptor inhibition of GABA release.

Differential effects of acute alcohol on EEG and sedative responses in adolescent and adult Wistar rats

Age-related developmental differences in sensitivity to the acute effects of alcohol may play an important role in the development of alcoholism. The present study was designed to evaluate the acute effects of alcohol on cortical electroencephalogram (EEG) in adolescent (P36) and adult (P78) Wistar rats. Five minutes of EEG was recorded after administration of 0, 0.75 or 1.5 g/kg alcohol. The righting reflex was performed to measure the sedative effects of alcohol (3.5 g/kg) and total sleeping time for each rat. Our results showed that alcohol (1.5 g/kg) increased power in the 1-2 Hz band and decreased the power in the 32-50 Hz band in the parietal cortical region of adolescent rats. Alcohol (1.5 g/kg) also increased stability of the EEG power in the slow-wave frequency bands (2-4 Hz, 4-6 Hz, and 6-8 Hz) of adolescent rats. In the frontal cortex of adult rats, but not in adolescent rats, alcohol (1.5 or 0.75 g/kg) decreased the power in the 16-32 Hz frequency band. Alcohol (1.5 g/kg) differentially increased power in a multiple of slow-wave frequency bands (2-4 Hz and 4-6 Hz) in the parietal cortex of adult rats as compared to adolescent rats. Adolescent rats were shown significantly shorter sleeping time and higher blood alcohol levels after regaining reflex than adult rats. Our results provide additional evidence of age-related differences in the effects of acute alcohol on cortical EEG, sedation and tolerance.

Ethanol dually modulates GABAergic synaptic transmission onto dopaminergic neurons in ventral tegmental area: role of mu-opioid receptors

The mesolimbic dopaminergic system, originating from the ventral tegmental area (VTA) is implicated in the rewarding properties of ethanol. VTA dopaminergic neurons are under the tonic control of GABAergic innervations. Application of GABAergic agents changes ethanol consumption. However, it is unclear how acute ethanol modulates GABAergic inputs to dopaminergic neurons in the VTA. This report describes ethanol at clinically relevant concentrations (10-40 mM) dually modulates inhibitory postsynaptic currents (IPSCs). IPSCs were mediated by GABA(A) receptors and were recorded from VTA dopaminergic neurons in acute midbrain slices of rats. Acute application of ethanol reduced the amplitude and increased the paired pulse ratio of evoked IPSCs. Ethanol lowered the frequency but not the amplitude of spontaneous IPSCs. Nevertheless, ethanol had no effect on miniature IPSCs recorded in the presence of tetrodotoxin. These data indicate that ethanol inhibits GABAergic synaptic transmission to dopaminergic neurons by presynaptic mechanisms, and that ethanol inhibition depends on the firing of GABAergic neurons. Application of CGP 52432, a GABA(B) receptor antagonist, did not change ethanol inhibition of IPSCs. Tyr-d-Ala-Gly-N-Me-Phe-Gly-ol enkephalin (DAMGO), a mu-opioid receptor agonist, conversely, silenced VTA GABAergic neurons and inhibited IPSCs. Of note, in the presence of a saturating concentration of DAMGO (3 microM), ethanol potentiated the remaining IPSCs. Thus, ethanol dually modulates GABAergic transmission to dopaminergic neurons in the VTA. Ethanol modulation depends on the activity of VTA GABAergic neurons, which were inhibited by the activation of mu-opioid receptors. This dual modulation of GABAergic transmission by ethanol may be an important mechanism underlying alcohol addiction.

Neurobiological processes in adolescent addictive disorders

The purpose of this review is to summarize the neurobiological factors involved in the etiology of adolescent addiction and present evidence implicating various mechanisms in its development. Adolescents are at heightened risk for experimentation with substances, and early experimentation is associated with higher rates of SUD in adulthood. Both normative (e.g., immature frontal-limbic connections, immature frontal lobe development) and non-normative (e.g., lowered serotonergic function, abnormal hypothalamic-pituitary-adrenal axis function) neurobiological developmental factors can predispose adolescents to a heightened risk for SUD. In addition, a normative imbalance in the adolescent neurobiological motivational system may be caused by the relative underdevelopment of suppressive mechanisms when compared to stimulatory systems. These neurobiological liabilities may correspond to neurobehavioral impairments in decision-making, affiliation with deviant peers and externalizing behavior; these and other cognitive and behavioral traits converge with neurobiological factors to increase SUD risk. The progression to SUD acts as an amplifying feedback loop, where the development of SUD results in reciprocal impairments in neurobehavioral and neurobiological processes. A clearer understanding of adolescent neurobiology is a necessary step in the development of prevention and treatment interventions for adolescent SUD.

Distinct mechanisms of ethanol potentiation of local and paracapsular GABAergic synapses in the rat basolateral amygdala

Converging lines of behavioral and pharmacological evidence suggest that GABAergic synapses in the basolateral amygdala (BLA) may play an integral role in mediating the anxiolytic effects of ethanol (EtOH). Since anxiety is thought to play an important role in the development of, and relapse to, alcoholism, elucidating the mechanisms through which EtOH modulates GABAergic synaptic transmission in the BLA may be fundamental in understanding the etiology of this disease. A recent study in mice has shown that principal cells within the BLA receive inhibitory input from two distinct types of GABAergic interneurons: a loosely distributed population of local interneurons and a dense network of paracapsular (pcs) GABAergic cells clustered along the external capsule border. Here, we sought to confirm the presence of these two populations of GABAergic synapses in the rat BLA and evaluate their ethanol sensitivity. Our results suggest that rat BLA pyramidal cells receive distinct inhibitory input from local and pcs interneurons and that EtOH potentiates both populations of synapses, albeit via distinct mechanisms. EtOH enhancement of local inhibitory postsynaptic currents (IPSCs) was associated with a significant decrease in paired-pulse ratio (PPR) and was significantly potentiated by the GABA(B) receptor antagonist SCH 50911 [(+)-(S)-5,5-dimethylmorpholinyl-2-acetic acid], consistent with a facilitation of GABA release from presynaptic terminals. Conversely, EtOH enhancement of pcs IPSCs did not alter PPR and was not enhanced by SCH 50911 but was inhibited by blockade of noradrenergic receptors. Collectively, these data reveal that EtOH can potentiate GABAergic inhibitory synaptic transmission in the rat BLA through at least two distinct pathways.

Calcium Release from Presynaptic Internal Stores Is Required for Ethanol to Increase Spontaneous γ-Aminobutyric Acid Release onto Cerebellum Purkinje Neurons

Recent data have demonstrated that ethanol increases gamma-aminobutyric acid (GABA) release in many brain regions, but little is known about the mechanism responsible for this action. Consistent with previous results, ethanol increased miniature inhibitory postsynaptic current (mIPSC) frequency at the interneuron-Purkinje cell synapse in the slice and in mechanically dissociated neurons. These data suggest that ethanol is increasing spontaneous GABA release at this synapse. It is generally accepted that ethanol increases levels of intracellular calcium and that changes in intracellular calcium can alter neurotransmitter release. Therefore, we examined the contribution of calcium-dependent pathways to the effect of ethanol on spontaneous GABA release at the interneuron-Purkinje cell synapse. Ethanol continued to increase mIPSC frequency in a nominally calcium-free extracellular solution and in the presence of a voltage-dependent calcium channel inhibitor, cadmium chloride. These data suggest that influx of extracellular calcium does not play a critical role in the mechanism of ethanol-enhanced spontaneous GABA release. However, a sarco/endoplasmic-reticulum calcium ATPase pump inhibitor (thapsigargin), an inositol 1,4,5-trisphosphate receptor antagonist (2-aminoethoxydiphenylborate) and a ryanodine receptor antagonist (ryanodine) significantly reduced the ability of ethanol to increase mIPSC frequency. In addition, ethanol was still able to increase mIPSC frequency in the presence of intracellular 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) and a cannabinoid receptor antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM-251); thus, retrograde messengers are not involved in ethanol-enhanced spontaneous GABA release. Overall, these data suggest that calcium release from presynaptic internal stores plays a vital role in the mechanism of ethanol-enhanced spontaneous GABA release at the interneuron-Purkinje cell synapse.

Chronic ethanol exposure during adolescence increases basal dopamine in the nucleus accumbens septi during adulthood

BACKGROUND

In humans, adolescent exposure to alcohol is associated with the onset of adult alcohol dependency and suggests that early use potentiates vulnerability to addiction. The aim of the present study was to address whether chronic ethanol exposure during adolescence would alter nucleus accumbens septi (NAcc) dopamine (DA) levels in the adult brain.

METHODS

Rats were injected daily from postnatal day (PND) 30 to 50 with either 0.75 g/kg/i.p. ethanol or saline followed by an ethanol-abstinent period from PND 51 to 65. Changes in extracellular DA levels in the anterior NAcc shell were measured via the no net flux (NNF) paradigm.

RESULTS

Extracellular DA levels were greater in rats chronically treated with ethanol during adolescence (6.5 nM DA) in comparison with saline-exposed controls (3.6 nM DA). There were no differences in extraction fraction (E(d)), an indirect measure of DA reuptake, between ethanol-treated (87%) and nontreated (68%) rats.

CONCLUSIONS

Together these findings suggest that changes in extracellular DA may be an underlying physiological mechanism in adolescent vulnerability to the rewarding properties of ethanol.

Magnitude and ethanol sensitivity of tonic GABAA receptor-mediated inhibition in dentate gyrus changes from adolescence to adulthood

Ethanol consumption by adolescents is a public health problem of striking importance. Educational and clinical efforts to address this problem have been aided by recent neurobehavioral studies indicating that ethanol disrupts memory and memory-related brain functions more powerfully in adolescent animals than in adults. Still, the mechanisms underlying this developmental sensitivity remain unclear. GABA(A) receptor (GABA(A)R)-mediated neurotransmission in the hippocampal formation, particularly that which is driven by extrasynaptic GABA(A)Rs, is enhanced by pharmacologically relevant concentrations of ethanol, and may be, in part, responsible for the modulation of memory and memory-related circuit plasticity. Using hippocampal slices from adolescent and adult rats, we have shown that tonic current mediated by extrasynaptic GABA(A)Rs is larger in dentate gyrus granule cells from adult animals than in those from adolescents and that 30 mM ethanol enhances inhibitory tonic current more in cells from adolescent rats than in those from adults. It is possible that more powerful promotion of tonic GABA(A)R-mediated inhibition by ethanol in the dentate gyrus of adolescent rats, compared with adults, contributes to the developmental differences that have previously been observed with respect to ethanol-induced memory impairment and reduction of synaptic plasticity.

Adolescence, glucocorticoids and alcohol

This review examines the evidence that glucocorticoids are involved, during both adolescence and adulthood, in the cognitive deficits caused by long-term alcohol consumption and in the mechanism(s) of alcohol dependence. During adolescence, the hypothalamopituitary-adrenal (HPA) axis undergoes well-characterized changes in basal activity and many of these are influenced by alcohol consumption. While the former have been fairly well studied, there is little information about whether alcohol effects on the HPA in adolescents differ from those in adults. The means by which glucocorticoids may influence alcohol-related neurotoxicity are presented, and potential differences between adolescence and adults in this regard noted. The substantial evidence for involvement of glucocorticoids in alcohol-induced cognitive deficits is described, with particular reference to the consequences of alcohol withdrawal. The use of immature organotypic cultures of rodent brain in the study of alcohol neurotoxicity is considered in detail, and the information obtained from this methodology concerning the role of glucocorticoid receptors and excitable membrane proteins in this neurotoxicity. The influence of glucocorticoids on alcohol consumption and possible contributions to alcohol dependence are then considered. In conclusion, more information concerning the effects of glucocorticoids on plasticity and alcohol neurotoxicity during the adolescent period is needed.

Ethanol potentiates GABAergic synaptic transmission in a postsynaptic neuron/synaptic bouton preparation from basolateral amygdala

Interactions between ethanol and synaptic transmission mediated by gamma -amino-N-butyric acid (GABA) have been suggested to contribute to alcohol intoxication. Ethanol effects on postsynaptic GABAA receptors have been the major focus of this line of research. There is increasing evidence that ethanol potentiation of GABAergic transmission involves increased GABA release from presynaptic terminals. In the present study, a mechanically isolated neuron/bouton preparation from the basolateral amygdala was used to examine the effects of ethanol on spontaneous GABAergic synaptic currents elicited by GABA release from the presynaptic terminals. We found that ethanol application produced a rapid increase in the frequency of spontaneous GABAergic synaptic currents. An acute tolerance to ethanol was also observed, and this tolerance involved GABAB receptor activation. The ethanol-induced potentiation did not involve alterations in the function of postsynaptic GABAA receptors and was independent of presynaptic action potential firing. These findings indicate that ethanol potentiates GABA release, most likely via a direct action on presynaptic boutons.