Strain differences in alcohol-induced neurochemical plasticity: a role for accumbens glutamate in alcohol intake

Different contributions of dopamine D1 and D2 receptor activity to alcohol potentiation of brain stimulation reward in C57BL/6J and DBA/2J mice

C57BL/6J (C57) and DBA/2J (DBA) mice respond differently to drugs that affect dopamine systems, including alcohol. The current study compared effects of D1 and D2 receptor agonists and antagonists, and the interaction between D1/D2 antagonists and alcohol, on intracranial self-stimulation in male C57 and DBA mice to determine the role of dopamine receptors in the effects of alcohol on brain stimulation reward (BSR). In the initial strain comparison, dose effects on BSR thresholds and maximum operant response rates were determined for the D1 receptor agonist SKF-82958 (±-6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine; 0.1-0.56 mg/kg) and antagonist SCH 23390 (+-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepinehydrochloride; 0.003-0.056 mg/kg), and the D2 receptor agonist quinpirole (0.1-3.0 mg/kg) and antagonist raclopride (0.01-0.56 mg/kg). For the alcohol interaction, SCH 23390 (0.003 mg/kg) or raclopride (0.03 mg/kg) was given before alcohol (0.6-2.4 g/kg p.o.). D1 antagonism dose-dependently elevated and SKF-82958 dose-dependently lowered BSR threshold in both strains; DBA mice were more sensitive to SKF-82958 effects. D2 antagonism dose-dependently elevated BSR threshold only in C57 mice. Low doses of quinpirole elevated BSR threshold equally in both strains, whereas higher doses of quinpirole lowered BSR threshold only in C57 mice. SCH 23390, but not raclopride, prevented lowering of BSR threshold by alcohol in DBA mice. Conversely, raclopride, but not SCH 23390, prevented alcohol potentiation of BSR in C57 mice. These results extend C57 and DBA strain differences to D1/D2 sensitivity of BSR, and suggest differential involvement of D1 and D2 receptors in the acute rewarding effects of alcohol in these two mouse strains.

Enhancement of alcohol drinking in mice depends on alterations in RNA editing of serotonin 2C receptors

Serotonin 2C receptors (5-HT(2C)R) are G-protein-coupled receptors with various actions, including involvement in drug addiction. 5-HT2CR undergoes mRNA editing, converting genomically encoded adenosine residues to inosines via adenosine deaminases acting on RNA (ADARs). Here we show that enhanced alcohol drinking behaviour in mice is associated with the degree of 5-HT(2C)R mRNA editing in the nucleus accumbens and dorsal raphe nuceus, brain regions important for reward and addiction. Following chronic alcohol vapour exposure, voluntary alcohol intake increased in C57BL/6J mice, but remained unchanged in C3H/HeJ and DBA/2J mice. 5-HT(2C)R mRNA editing frequency in both regions increased significantly in C57BL/6J mice, as did expressions of 5-HT(2C)R, ADAR1 and ADAR2, but not in other strains. Moreover, mice that exclusively express the unedited isoform (INI) of 5-HT(2C)R mRNA on a C57BL/6J background did not exhibit increased alcohol intake compared with wild-type mice. Our results indicate that alterations in 5-HT(2C)R mRNA editing underlie alcohol preference in mice.

Exploring the role of central astrocytic glutamate uptake in ethanol reward in mice

BACKGROUND

Alcoholism is associated with specific brain abnormalities revealed through postmortem studies, including a reduction in glial cell number and dysregulated glutamatergic neurotransmission. Whether these abnormalities contribute to the etiology of alcoholism, are consequences of alcohol use, or both is still unknown.

METHODS

We investigated the role of astrocytic glutamate uptake in ethanol (EtOH) binge drinking in mice, using the "drinking in the dark" (DID) paradigm by blocking the astrocytic glutamate transporter (GLT-1) with intracerebroventricular (ICV) administration of dihydrokainic acid (DHK). To determine whether astrocytic glutamate uptake regulates the conditioned rewarding effects of EtOH, we examined the effects of ICV DHK on the acquisition and expression of EtOH-induced conditioned place preference.

RESULTS

Blocking central astrocytic glutamate uptake selectively attenuated EtOH binge drinking behavior in mice. DHK did not alter the acquisition or expression of preference for EtOH-associated cues, indicating that reduced astrocytic glutamate trafficking may decrease binge-like drinking without altering the conditioned rewarding effects of EtOH.

CONCLUSIONS

Several alternative conclusions are plausible, however, interpreting these data in the context of the human literature, these findings suggest that the reduction of glia in the alcoholic brain may not be a predisposing factor to developing alcoholism and could be a consequence of EtOH toxicity that decreases excessive EtOH intake.

Effects of ceftriaxone on chronic ethanol consumption: a potential role for xCT and GLT1 modulation of glutamate levels in male P rats

Alterations in glutamatergic neurotransmission have been suggested to affect many aspects of neuroplasticity associated with alcohol/drug addiction. We have previously shown that ceftriaxone, a β-lactam antibiotic known to upregulate glutamate transporter 1 (GLT1), reduced ethanol intake after 5 weeks of free choice ethanol drinking paradigm in male alcohol-preferring (P) rats. Evidence suggests that differential effects involving alterations of glutamatergic neurotransmission occur after long-term ethanol consumption. In this study, we tested whether the efficacy of administration of ceftriaxone persists after 14 weeks of free access to 15 and 30 % ethanol in male P rats. After 14 weeks of ethanol consumption, male P rats were administered ceftriaxone (100 mg/kg, intraperitoneal (i.p.)) or saline vehicle for 5 days. We found that ceftriaxone treatment resulted in a significant reduction in ethanol intake starting from day 2 (48 h after the first i.p. injections of ceftriaxone) through day 14, 10 days after final injection. Western blot analysis of brain samples from animals euthanized 24 h after treatment with the last dose of ceftriaxone revealed a significant upregulation of cystine/glutamate exchanger (xCT) and GLT1 levels in prefrontal cortex, nucleus accumbens, and amygdala as compared to saline vehicle-treated group. These findings demonstrated the effectiveness of ceftriaxone in attenuating ethanol intake in a chronic consumption paradigm. These might be due in part through the upregulation of both xCT and GLT1 levels in brain reward regions. Thus, the drug has a potential therapeutic action for the treatment of alcohol dependence.

Influence of adolescent heavy session drinking on the systemic and brain innate immune system

AIMS

The aim of the study was to evaluate rat models of intermittent alcohol abuse (heavy session/'heavy session' drinking) in relation to inflammatory changes in specific brain regions as well as in the periphery. Furthermore, the study was aimed to assess whether there are inflammatory changes in the blood of human intermittent alcohol abusers who might be associated with changes in neuronal circuitry in the brain, as assessed by functional magnetic resonance imaging (fMRI), which cause adverse effects on memory and learning.

METHODS

Various regimes of intermittent alcohol administration have been used in rat models, which vary with respect to the dose and duration of ethanol administration as well as the time of abstinence. Immunohistological methods were used to identify activated microglia in specific brain regions. The response of isolated alveolar macrophages to in vitro stimuli was assessed by the assay of nitric oxide and the pro-inflammatory cytokines IL-6 and TNFα. Blood samples were collected from university students who had been heavy session drinkers for 2 years to assess whether there was an inflammatory cytokine profile that correlated with cognitive test scores as well as fMRI findings.

RESULTS

The extent of microglia activation appears to depend on the doses and duration of ethanol administration. In addition, there is activation of phagocytic cells in the periphery, e.g. alveolar macrophages, in the rat models of heavy session drinking. Changes in the plasma levels of pro- and anti-inflammatory cytokines were present in heavy session drinking students, although no changes were identified in specific cognitive tests (which may be because of compensatory changes in the prefrontal cortex, as identified by fMRI).

CONCLUSION

Changes in the cytokine levels induced by intermittent ethanol abuse may provoke inflammatory pathways in specific brain regions, such as hippocampus and prefrontal cortex (particularly during the stage of active neurogenesis in the adolescent brain), which might induce cognitive impairment in susceptible individuals.

Increased extracellular glutamate in the nucleus accumbens promotes excessive ethanol drinking in ethanol dependent mice

Using a well-established model of ethanol dependence and relapse, this study examined adaptations in glutamatergic transmission in the nucleus accumbens (NAc) and their role in regulating voluntary ethanol drinking. Mice were first trained to drink ethanol in a free-choice, limited access (2 h/day) paradigm. One group (EtOH mice) received repeated weekly cycles of chronic intermittent ethanol (CIE) exposure with intervening weeks of test drinking sessions, whereas the remaining mice (CTL mice) were similarly treated but did not receive CIE treatment. Over repeated cycles of CIE exposure, EtOH mice exhibited significant escalation in drinking (up to ∼3.5 g/kg), whereas drinking remained relatively stable at baseline levels (2-2.5 g/kg) in CTL mice. Using in vivo microdialysis procedures, extracellular glutamate (GLUEX) levels in the NAc were increased approximately twofold in EtOH mice compared with CTL mice, and this difference was observed 7 days after final CIE exposure, indicating that this hyperglutamatergic state persisted beyond acute withdrawal. This finding prompted additional studies examining the effects of pharmacologically manipulating GLUEX in the NAc on ethanol drinking in the CIE model. The non-selective glutamate reuptake antagonist, threo-β-benzyloxyaspartate (TBOA), was bilaterally microinjected into the NAc and found to dose-dependently increase drinking in nondependent (CTL) mice to levels attained by dependent (EtOH) mice. TBOA also further increased drinking in EtOH mice. In contrast, reducing glutamatergic transmission in the NAc via bilateral injections of the metabotropic glutamate receptor-2/3 agonist LY379268 reduced drinking in dependent (EtOH) mice to nondependent (CTL) levels, whereas having a more modest effect in decreasing ethanol consumption in CTL mice. Taken together, these data support an important role of glutamatergic transmission in the NAc in regulating ethanol drinking. Additionally, these results indicate that ethanol dependence produces adaptations that favor elevated glutamate activity in the NAc which, in turn, promote excessive levels of ethanol consumption associated with dependence.

Adenosine and glutamate in neuroglial interaction: implications for circadian disorders and alcoholism

Recent studies have demonstrated that the function of glia is not restricted to the support of neuronal function. In fact, astrocytes are essential for neuronal activity in the brain and play an important role in the regulation of complex behavior. Astrocytes actively participate in synapse formation and brain information processing by releasing and uptaking glutamate, D-serine, adenosine 5'-triphosphate (ATP), and adenosine. In the central nervous system, adenosine-mediated neuronal activity modulates the actions of other neurotransmitter systems. Adenosinergic fine-tuning of the glutamate system in particular has been shown to regulate circadian rhythmicity and sleep, as well as alcohol-related behavior and drinking. Adenosine gates both photic (light-induced) glutamatergic and nonphotic (alerting) input to the circadian clock located in the suprachiasmatic nucleus of the hypothalamus. Astrocytic, SNARE-mediated ATP release provides the extracellular adenosine that drives homeostatic sleep. Acute ethanol increases extracellular adenosine, which mediates the ataxic and hypnotic/sedative effects of alcohol, while chronic ethanol leads to downregulated adenosine signaling that underlies insomnia, a major predictor of relapse. Studies using mice lacking the equilibrative nucleoside transporter 1 have illuminated how adenosine functions through neuroglial interactions involving glutamate uptake transporter GLT-1 [referred to as excitatory amino acid transporter 2 (EAAT2) in human] and possibly water channel aquaporin 4 to regulate ethanol sensitivity, reward-related motivational processes, and alcohol intake.

Neurochemical mechanisms of alcohol withdrawal

Alcohol dependence encompasses a serious medical and societal problem that constitutes a major public health concern. A serious consequence of dependence is the emergence of symptoms associated with the alcohol withdrawal syndrome when drinking is abruptly terminated or substantially reduced. Clinical features of alcohol withdrawal include signs of central nervous system hyperexcitability, heightened autonomic nervous system activation, and a constellation of symptoms contributing to psychologic discomfort and negative affect. The development of alcohol dependence is a complex and dynamic process that ultimately reflects a maladaptive neurophysiologic state. Perturbations in a wide range of neurochemical systems, including glutamate, γ-aminobutyric acid, monoamines, a host of neuropeptide systems, and various ion channels produced by the chronic presence of alcohol ultimately compromise the functional integrity of the brain. These neuroadaptations not only underlie the emergence and expression of many alcohol withdrawal symptoms, but also contribute to enhanced relapse vulnerability as well as perpetuation of uncontrolled excessive drinking. This chapter highlights the hallmark features of the alcohol withdrawal syndrome, and describes neuroadaptations in a wide array of neurotransmitter and neuromodulator systems (amino acid and monoamine neurotransmitter, neuropeptide systems, and various ion channels) as they relate to the expression of various signs and symptoms of alcohol withdrawal, as well as their relationship to the significant clinical problem of relapse and uncontrolled dangerous drinking.

Greater ethanol-induced locomotor activation in DBA/2J versus C57BL/6J mice is not predicted by presynaptic striatal dopamine dynamics

A large body of research has aimed to determine the neurochemical factors driving differential sensitivity to ethanol between individuals in an attempt to find predictors of ethanol abuse vulnerability. Here we find that the locomotor activating effects of ethanol are markedly greater in DBA/2J compared to C57BL/6J mice, although it is unclear as to what neurochemical differences between strains mediate this behavior. Dopamine elevations in the nucleus accumbens and caudate-putamen regulate locomotor behavior for most drugs, including ethanol; thus, we aimed to determine if differences in these regions predict strain differences in ethanol-induced locomotor activity. Previous studies suggest that ethanol interacts with the dopamine transporter, potentially mediating its locomotor activating effects; however, we found that ethanol had no effects on dopamine uptake in either strain. Ex vivo voltammetry allows for the determination of ethanol effects on presynaptic dopamine terminals, independent of drug-induced changes in firing rates of afferent inputs from either dopamine neurons or other neurotransmitter systems. However, differences in striatal dopamine dynamics did not predict the locomotor-activating effects of ethanol, since the inhibitory effects of ethanol on dopamine release were similar between strains. There were differences in presynaptic dopamine function between strains, with faster dopamine clearance in the caudate-putamen of DBA/2J mice; however, it is unclear how this difference relates to locomotor behavior. Because of the role of the dopamine system in reinforcement and reward learning, differences in dopamine signaling between the strains could have implications for addiction-related behaviors that extend beyond ethanol effects in the striatum.

Imbalances in prefrontal cortex CC-Homer1 versus CC-Homer2 expression promote cocaine preference

Homer postsynaptic scaffolding proteins regulate forebrain glutamate transmission and thus, are likely molecular candidates mediating hypofrontality in addiction. Protracted withdrawal from cocaine experience increases the relative expression of Homer2 versus Homer1 isoforms within medial prefrontal cortex (mPFC). Thus, this study used virus-mediated gene transfer strategies to investigate the functional relevance of an imbalance in mPFC Homer1/2 expression as it relates to various measures of sensorimotor, cognitive, emotional and motivational processing, as well as accompanying alterations in extracellular glutamate in C57BL/6J mice. mPFC Homer2b overexpression elevated basal glutamate content and blunted cocaine-induced glutamate release within the mPFC, whereas Homer2b knockdown produced the opposite effects. Despite altering mPFC glutamate, Homer2b knockdown failed to influence cocaine-elicited conditioned place preferences, nor did it produce consistent effects on any other behavioral measures. In contrast, elevating the relative expression of Homer2b versus Homer1 within mPFC, by overexpressing Homer2b or knocking down Homer1c, shifted the dose-response function for cocaine-conditioned reward to the left, without affecting cocaine locomotion or sensitization. Intriguingly, both these transgenic manipulations produced glutamate anomalies within the nucleus accumbens (NAC) of cocaine-naive animals that are reminiscent of those observed in cocaine experienced animals, including reduced basal extracellular glutamate content, reduced Homer1/2 and glutamate receptor expression, and augmented cocaine-elicited glutamate release. Together, these data provide novel evidence in support of opposing roles for constitutively expressed Homer1 and Homer2 isoforms in regulating mPFC glutamate transmission in vivo and support the hypothesis that cocaine-elicited increases in the relative amount of mPFC Homer2 versus Homer1 signaling produces abnormalities in NAC glutamate transmission that enhance vulnerability to cocaine reward.

Alcohol drinking and deprivation alter basal extracellular glutamate concentrations and clearance in the mesolimbic system of alcohol-preferring (P) rats

The present study determined the effects of voluntary ethanol drinking and deprivation on basal extracellular glutamate concentrations and clearance in the mesolimbic system and tested the hypothesis that chronic ethanol drinking would persistently increase basal glutamate neurotransmission. Three groups of alcohol-preferring (P) rats were used: 'water group (WG),' 'ethanol maintenance group (MG; 24-hour free choice water versus 15% ethanol)' and 'ethanol deprivation group (DG; 2 weeks of deprivation).' Quantitative microdialysis and Western blots were conducted to measure basal extracellular glutamate concentrations, clearance and proteins associated with glutamate clearance. Chronic alcohol drinking produced a 70-100% increase of basal extracellular glutamate concentrations in the posterior ventral tegmental area (4.0 versus 7.0 μM) and nucleus accumbens shell (3.0 versus 6.0 μM). Glutamate clearances were reduced by 30-40% in both regions of MG rats compared with WG rats. In addition, Western blots revealed a 40-45% decrease of excitatory amino transporter 1 (EAAT1) protein, but no significant changes in the levels of EAAT2 or cystine-glutamate antiporter in these regions of MG versus WG rats. The enhanced glutamate concentrations returned to control levels, accompanied by a recovery of glutamate clearance following deprivation. These results indicated that chronic alcohol drinking enhanced extracellular glutamate concentrations in the mesolimbic system, as a result, in part, of reduced clearance, suggesting that enhanced glutamate neurotransmission may contribute to the maintenance of alcohol drinking. However, because the increased glutamate levels returned to normal after deprivation, elevated glutamate neurotransmission may not contribute to the initiation of relapse drinking.

Neuroimmunophilin GPI-1046 reduces ethanol consumption in part through activation of GLT1 in alcohol-preferring rats

We have previously shown that ceftriaxone, β-lactam antibiotic known to upregulate glutamate transporter 1 (GLT1), reduced ethanol intake in alcohol-preferring (P) rats. GLT1 is a glial glutamate transporter that regulates the majority of extracellular glutamate uptake. We tested in this study the effects of neuroimmunophilin GPI-1046 (3-(3-pyridyl)-1-propyl (2S)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidinecarboxylate), known also to upregulate GLT1 expression, in ethanol intake in P rats. Male P rats had concurrent access to free choice of 15% and 30% ethanol, water, and food for five weeks. On Week 6, P rats continued in this drinking and food regimen and they were administered either 10 or 20mg/kg GPI-1046 (i.p.), or a vehicle for five consecutive days. Body weight, ethanol intake, and water consumption were measured daily for 8 days starting on Day 1 of GPI-1046 or vehicle i.p. injections. We have also tested the effect of GPI-1046 (20mg/kg) on daily sucrose (10%) intake. The data revealed significant dose-dependent effects in the reduction of ethanol intake starting 48 h after the first treatment with GPI-1046 throughout treatment and post-treatment periods. There were also dose-dependent increases in water intake. However, GPI-1046 treatment did not affect the body weight of all animals nor sucrose intake. Importantly, GPI-1046 (20mg/kg) increased GLT1 level compared to all groups in nucleus accumbens core (NAc-core). Alternatively, GPI-1046 (10mg/kg) upregulated GLT1 level in NAc-core compared to vehicle (ethanol naïve) group. Moreover, both doses of GPI-1046 increased significantly GLT1 level in the prefrontal cortex (PFC) compared to ethanol naïve vehicle group. GPI-1046 (20mg/kg) increased GLT1 level in PFC compared to naïve control group that was exposed to water and food only. These findings demonstrated that neuroimmunophilin GPI-1046 attenuates ethanol intake in part through the upregulation of GLT1 in PFC and NAc-core.

Alcohol affects the brain's resting-state network in social drinkers

Acute alcohol intake is known to enhance inhibition through facilitation of GABA(A) receptors, which are present in 40% of the synapses all over the brain. Evidence suggests that enhanced GABAergic transmission leads to increased large-scale brain connectivity. Our hypothesis is that acute alcohol intake would increase the functional connectivity of the human brain resting-state network (RSN). To test our hypothesis, electroencephalographic (EEG) measurements were recorded from healthy social drinkers at rest, during eyes-open and eyes-closed sessions, after administering to them an alcoholic beverage or placebo respectively. Salivary alcohol and cortisol served to measure the inebriation and stress levels. By calculating Magnitude Square Coherence (MSC) on standardized Low Resolution Electromagnetic Tomography (sLORETA) solutions, we formed cortical networks over several frequency bands, which were then analyzed in the context of functional connectivity and graph theory. MSC was increased (p<0.05, corrected with False Discovery Rate, FDR corrected) in alpha, beta (eyes-open) and theta bands (eyes-closed) following acute alcohol intake. Graph parameters were accordingly altered in these bands quantifying the effect of alcohol on the structure of brain networks; global efficiency and density were higher and path length was lower during alcohol (vs. placebo, p<0.05). Salivary alcohol concentration was positively correlated with the density of the network in beta band. The degree of specific nodes was elevated following alcohol (vs. placebo). Our findings support the hypothesis that short-term inebriation considerably increases large-scale connectivity in the RSN. The increased baseline functional connectivity can -at least partially- be attributed to the alcohol-induced disruption of the delicate balance between inhibitory and excitatory neurotransmission in favor of inhibitory influences. Thus, it is suggested that short-term inebriation is associated, as expected, to increased GABA transmission and functional connectivity, while long-term alcohol consumption may be linked to exactly the opposite effect.

GABAB receptor activation attenuates the stimulant but not mesolimbic dopamine response to ethanol in FAST mice

Neural processes influenced by γ-aminobutyric acid B (GABA(B)) receptors appear to contribute to acute ethanol sensitivity, including the difference between lines of mice bred for extreme sensitivity (FAST) or insensitivity (SLOW) to the locomotor stimulant effect of ethanol. One goal of the current study was to determine whether selection of the FAST and SLOW lines resulted in changes in GABA(B) receptor function, since the lines differ in sensitivity to the GABA(B) receptor agonist baclofen and baclofen attenuates the stimulant response to ethanol in FAST mice. A second goal was to determine whether the baclofen-induced reduction in ethanol stimulation in FAST mice is associated with an attenuation of the mesolimbic dopamine response to ethanol. In Experiment 1, the FAST and SLOW lines were found to not differ in GABA(B) receptor function (measured by baclofen-stimulated [(35)S]GTPγS binding) in whole brain or in several regional preparations, except in the striatum in one of the two replicate sets of selected lines. In Experiment 2, baclofen-induced attenuation of the locomotor stimulant response to ethanol in FAST mice was not accompanied by a reduction in dopamine levels in the nucleus accumbens, as measured by microdialysis. These data suggest that, overall, GABA(B) receptor function does not play an integral role in the genetic difference in ethanol sensitivity between the FAST and SLOW lines. Further, although GABA(B) receptors do modulate the locomotor stimulant response to ethanol in FAST mice, this effect does not appear to be due to a reduction in tonic dopamine signaling in the nucleus accumbens.

Extended access to cocaine self-administration results in reduced glutamate function within the medial prefrontal cortex

Previous studies have shown that brief access to cocaine yields an increase in D2 receptor binding in the medial prefrontal cortex (mPFC), but that extended access to cocaine results in normalized binding of D2 receptors (i.e. the D2 binding returned to control levels). Extended-access conditions have also been shown to produce increased expression of the NR2 subunit of the N-Methyl-D-aspartate receptor in the mPFC. These results implicate disrupted glutamate and dopamine function within this area. Therefore, in the present study, we monitored glutamate and dopamine content within the mPFC during, or 24 hours after, cocaine self-administration in animals that experienced various amounts of exposure to the drug. Naïve subjects showed decreased glutamate and increased dopamine levels within the mPFC during cocaine self-administration. Exposure to seven 1-hour daily cocaine self-administration sessions did not alter the response to self-administered cocaine, but resulted in decreased basal dopamine levels. While exposure to 17 1-hour sessions also resulted in reduced basal dopamine levels, these animals showed increased dopaminergic, but completely diminished glutamatergic, response to self-administered cocaine. Finally, exposure to 17 cocaine self-administration sessions, the last 10 of which being 6-hour sessions, resulted in diminished glutamatergic response to self-administered cocaine and reduced basal glutamate levels within the mPFC while normalizing (i.e. causing a return to control levels) both the dopaminergic response to self-administered cocaine as well as basal dopamine levels within this area. These data demonstrate directly that the transition to escalated cocaine use involves progressive changes in dopamine and glutamate function within the mPFC.

Solution-Focused Brief Therapy for Depression and Alcohol Dependence

This case study employs solution-focused brief therapy (SFBT) to alleviate depressive symptoms in an alcohol-dependent patient with comorbid personality disorder. Alcohol dependence and depression are frequent comorbid conditions in patients presenting for treatment. For some of these, personality disorders may further complicate treatment and even present a barrier to patients seeking or being offered treatment. In the case described, the patient only sought treatment after his gingivitis led to discovery of liver damage. In addition to SFBT, the patient was prescribed acamprosate to assist with abstinence from alcohol and fluoxetine for depression. Following three sessions of SFBT spaced at 1-month intervals, the patient reported maintaining abstinence from alcohol. His symptoms of depression as measured by Depression Anxiety Stress Scale reduced from severe to normal range, and he reported a reduction in the frequency and intensity of dark thoughts that had previously plagued him when sober. Outcomes were maintained 12 months following treatment.

Ethanol up-regulates nucleus accumbens neuronal activity dependent pentraxin (Narp): implications for alcohol-induced behavioral plasticity

Neuronal activity dependent pentraxin (Narp) interacts with α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) glutamate receptors to facilitate excitatory synapse formation by aggregating them at established synapses. Alcohol is well-characterized to influence central glutamatergic transmission, including AMPA receptor function. Herein, we examined the influence of injected and ingested alcohol upon Narp protein expression, as well as basal Narp expression in mouse lines selectively bred for high blood alcohol concentrations under limited access conditions. Alcohol up-regulated accumbens Narp levels, concomitant with increases in levels of the GluR1 AMPA receptor subunit. However, accumbens Narp or GluR1 levels did not vary as a function of selectively bred genotype. We next employed a Narp knock-out (KO) strategy to begin to understand the behavioral relevance of alcohol-induced changes in protein expression in several assays of alcohol reward. Compared to wild-type mice, Narp KO animals: fail to escalate daily intake of high alcohol concentrations under free-access conditions; shift their preference away from high alcohol concentrations with repeated alcohol experience; exhibit a conditioned place-aversion in response to the repeated pairing of 3 g/kg alcohol with a distinct environment and fail to exhibit alcohol-induced locomotor hyperactivity following repeated alcohol treatment. Narp deletion did not influence the daily intake of either food or water, nor did it alter any aspect of spontaneous or alcohol-induced motor activity, including the development of tolerance to its motor-impairing effects with repeated treatment. Taken together, these data indicate that Narp induction, and presumably subsequent aggregation of AMPA receptors, may be important for neuroplasticity within limbic subcircuits mediating or maintaining the rewarding properties of alcohol.

Effects of alcohol on the membrane excitability and synaptic transmission of medium spiny neurons in the nucleus accumbens

Chronic and excessive alcohol drinking lead to alcohol dependence and loss of control over alcohol consumption, with serious detrimental health consequences. Chronic alcohol exposure followed by protracted withdrawal causes profound alterations in the brain reward system that leads to marked changes in reinforcement mechanisms and motivational state. These long-lasting neuroadaptations are thought to contribute to the development of cravings and relapse. The nucleus accumbens (NAcc), a central component of the brain reward system, plays a critical role in alcohol-induced neuroadaptive changes underlying alcohol-seeking behaviors. Here we review the findings that chronic alcohol exposure produces long-lasting neuroadaptive changes in various ion channels that govern intrinsic membrane properties and neuronal excitability, as well as excitatory and inhibitory synaptic transmission in the NAcc that underlie alcohol-seeking behavior during protracted withdrawal.

Nucleus accumbens mGluR5-associated signaling regulates binge alcohol drinking under drinking-in-the-dark procedures

BACKGROUND

Alcohol increases the expression of Group 1 metabotropic glutamate receptors (mGluRs) and their associated scaffolding protein Homer2 and stimulates phosphatidylinositol 3-kinase (PI3K) within the nucleus accumbens (NAC). Moreover, functional studies suggest that NAC Group 1 mGluR/Homer2/PI3K signaling may be a potential target for pharmacotherapeutic intervention in alcoholism.

METHODS

Immunoblotting was conducted to examine the effects of alcohol consumption under drinking-in-the-dark (DID) procedures on Group 1 mGluR-associated proteins in C57BL/6J (B6) mice. Follow-up behavioral studies examined the importance of Group 1 mGluR/Homer2/PI3K signaling within the NAC shell for limited-access alcohol drinking. Finally, immunoblotting examined whether the NAC expression of Group 1 mGluR-associated proteins is a genetic correlate of high alcohol drinking using a selectively bred high DID (HDID-1) mouse line.

RESULTS

Limited-access alcohol drinking under DID procedures up-regulated NAC shell Homer2 levels, concomitant with increases in mGluR5 and NR2B. Intra-NAC shell blockade of mGluR5, Homer2, or PI3K signaling, as well as transgenic disruption of the Homer binding site on mGluR5, decreased alcohol consumption in B6 mice. Moreover, transgenic disruption of the Homer binding site on mGluR5 and Homer2 deletion both prevented the attenuating effect of mGluR5 and PI3K blockade upon intake. Finally, the basal NAC shell protein expression of mGluR1 and Homer2 was increased in offspring of HDID-1 animals.

CONCLUSIONS

Taken together, these data further implicate Group 1 mGluR signaling through Homer2 within the NAC in excessive alcohol consumption.

Brain region-specific gene expression changes after chronic intermittent ethanol exposure and early withdrawal in C57BL/6J mice

Neuroadaptations that participate in the ontogeny of alcohol dependence are likely a result of altered gene expression in various brain regions. The present study investigated brain region-specific changes in the pattern and magnitude of gene expression immediately following chronic intermittent ethanol (CIE) exposure and 8 hours following final ethanol exposure [i.e. early withdrawal (EWD)]. High-density oligonucleotide microarrays (Affymetrix 430A 2.0, Affymetrix, Santa Clara, CA, USA) and bioinformatics analysis were used to characterize gene expression and function in the prefrontal cortex (PFC), hippocampus (HPC) and nucleus accumbens (NAc) of C57BL/6J mice (Jackson Laboratories, Bar Harbor, ME, USA). Gene expression levels were determined using gene chip robust multi-array average followed by statistical analysis of microarrays and validated by quantitative real-time reverse transcription polymerase chain reaction and Western blot analysis. Results indicated that immediately following CIE exposure, changes in gene expression were strikingly greater in the PFC (284 genes) compared with the HPC (16 genes) and NAc (32 genes). Bioinformatics analysis revealed that most of the transcriptionally responsive genes in the PFC were involved in Ras/MAPK signaling, notch signaling or ubiquitination. In contrast, during EWD, changes in gene expression were greatest in the HPC (139 genes) compared with the PFC (four genes) and NAc (eight genes). The most transcriptionally responsive genes in the HPC were involved in mRNA processing or actin dynamics. Of the few genes detected in the NAc, the most representatives were involved in circadian rhythms. Overall, these findings indicate that brain region-specific and time-dependent neuroadaptive alterations in gene expression play an integral role in the development of alcohol dependence and withdrawal.

Alpha4 subunit-containing GABAA receptors in the accumbens shell contribute to the reinforcing effects of alcohol

The α4βδ gamma-aminobutyric acid A receptor (GABA(A) R) has been proposed to mediate the rewarding effects of low-to-moderate concentrations of alcohol (ethanol) that approximate those achieved by social drinking. If this is true, then this receptor should be necessary for the reinforcing effects of ethanol as assessed in an instrumental self-administration procedure in which rats are trained to lever press for oral ethanol. We used viral-mediated RNA interference to transiently reduce expression of the α4 GABA(A) R subunit in the shell region of the nucleus accumbens (NAc). We found that responding for ethanol was significantly reduced after α4 reductions in the NAc shell, but not NAc core. This reduction was specific to ethanol, as responding for sucrose was not altered. The presence of ethanol was also required as unreinforced responding for ethanol in subjects previously trained to respond for ethanol (i.e. responding during an extinction test) was not altered. In addition, responding during reinforced sessions was not altered during the initial 5 minutes of the session, but decreased after 5 minutes, following multiple reinforced responses. Together, these findings indicate that the α4 GABA(A) R subunit in the NAc shell is necessary for the instrumental reinforcing effects of oral ethanol, further supporting a role for α4-containing GABA(A) Rs in the rewarding/reinforcing effects of ethanol. Possible pharmacological and non-pharmacological explanations for these effects are considered.

Reduced alcohol intake and reward associated with impaired endocannabinoid signaling in mice with a deletion of the glutamate transporter GLAST

A hyperglutamatergic state has been hypothesized to drive escalation of alcohol intake. This hypothesis predicts that an impairment of glutamate clearance through inactivation of the astrocytic glutamate transporter, GLAST (EAAT1), will result in escalation of alcohol consumption. Here, we used mice with a deletion of GLAST to test this prediction. WT and GLAST KO mice were tested for alcohol consumption using two-bottle free-choice drinking. Alcohol reward was evaluated using conditioned place preference (CPP). Sensitivity to depressant alcohol effects was tested using the accelerating rotarod, alcohol-induced hypothermia, and loss of righting reflex. Extracellular glutamate was measured using microdialysis, and striatal slice electrophysiology was carried out to examine plasticity of the cortico-striatal pathway as a model system in which adaptations to the constitutive GLAST deletion can be studied. Contrary to our hypothesis, GLAST KO mice showed markedly decreased alcohol consumption, and lacked CPP for alcohol, despite a higher locomotor response to this drug. Alcohol-induced ataxia, hypothermia, and sedation were unaffected. In striatal slices from GLAST KO mice, long-term depression (LTD) induced by high frequency stimulation, or by post-synaptic depolarization combined with the l-type calcium channel activator FPL 64176 was absent. In contrast, normal synaptic depression was observed after application of the cannabinoid 1 (CB1) receptor agonist WIN55,212-2. Constitutive deletion of GLAST unexpectedly results in markedly reduced alcohol consumption and preference, associated with markedly reduced alcohol reward. Endocannabinoid signaling appears to be down-regulated upstream of the CB1 receptor as a result of the GLAST deletion, and is a candidate mechanism behind the reduction of alcohol reward observed.

Adenosine and glutamate signaling in neuron-glial interactions: implications in alcoholism and sleep disorders

Recent studies have demonstrated that the function of glia is not restricted to the support of neuronal function. Especially, astrocytes are essential for neuronal activity in the brain. Astrocytes actively participate in synapse formation and brain information processing by releasing or uptaking gliotransmitters such as glutamate, d-serine, adenosine 5'-triphosphate (ATP), and adenosine. In the central nervous system, adenosine plays an important role in regulating neuronal activity as well as in controlling other neurotransmitter systems such as GABA, glutamate, and dopamine. Ethanol (EtOH) increases extracellular adenosine levels, which regulates the ataxic and hypnotic/sedative (somnogenic) effects of EtOH. Adenosine signaling is also involved in the homeostasis of major inhibitory/excitatory neurotransmission (i.e., GABA or glutamate) through neuron-glial interactions, which regulates the effect of EtOH and sleep. Adenosine transporters or astrocytic SNARE-mediated transmitter release regulates extracellular or synaptic adenosine levels. Adenosine then exerts its function through several adenosine receptors and regulates glutamate levels in the brain. This review presents novel findings on how neuron-glial interactions, particularly adenosinergic signaling and glutamate uptake activity involving glutamate transporter 1 (GLT1), are implicated in alcoholism and sleep disorders.

Distinct neurochemical adaptations within the nucleus accumbens produced by a history of self-administered vs non-contingently administered intravenous methamphetamine

Methamphetamine is a highly addictive psychomotor stimulant yet the neurobiological consequences of methamphetamine self-administration remain under-characterized. Thus, we employed microdialysis in rats trained to self-administer intravenous (IV) infusions of methamphetamine (METH-SA) or saline (SAL) and a group of rats receiving non-contingent IV infusions of methamphetamine (METH-NC) at 1 or 21 days withdrawal to determine the dopamine and glutamate responses in the nucleus accumbens (NAC) to a 2 mg/kg methamphetamine intraperitoneal challenge. Furthermore, basal NAC extracellular glutamate content was assessed employing no net-flux procedures in these three groups at both time points. At both 1- and 21-day withdrawal points, methamphetamine elicited a rise in extracellular dopamine in SAL animals and this effect was sensitized in METH-NC rats. However, METH-SA animals showed a much greater sensitized dopamine response to the drug challenge compared with the other groups. Additionally, acute methamphetamine decreased extracellular glutamate in both SAL and METH-NC animals at both time-points. In contrast, METH-SA rats exhibited a modest and delayed rise in glutamate at 1-day withdrawal and this rise was sensitized at 21 days withdrawal. Finally, no net-flux microdialysis revealed elevated basal glutamate and increased extraction fraction at both withdrawal time-points in METH-SA rats. Although METH-NC rats exhibited no change in the glutamate extraction fraction, they exhibited a time-dependent elevation in basal glutamate levels. These data illustrate for the first time that a history of methamphetamine self-administration produces enduring changes in NAC neurotransmission and that non-pharmacological factors have a critical role in the expression of these methamphetamine-induced neurochemical adaptations.

The effects of chronic ethanol self-administration on hippocampal serotonin transporter density in monkeys

Evidence for an interaction between alcohol consumption and the serotonin system has been observed repeatedly in both humans and animal models yet the specific relationship between the two remains unclear. Research has focused primarily on the serotonin transporter (SERT) due in part to its role in regulating extracellular levels of serotonin. The hippocampal formation is heavily innervated by ascending serotonin fibers and is a major component of the neurocircuitry involved in mediating the reinforcing effects of alcohol. The current study investigated the effects of chronic ethanol self-administration on hippocampal SERT in a layer and field specific manner using a monkey model of human alcohol consumption. [(3)H]Citalopram was used to measure hippocampal SERT density in male cynomolgus macaques that voluntarily self-administered ethanol for 18 months. Hippocampal [(3)H]citalopram binding was less dense in ethanol drinkers than in controls, with the greatest effect observed in the molecular layer of the dentate gyrus. SERT density was not correlated with measures of ethanol consumption or blood ethanol concentrations, suggesting the possibility that a threshold level of consumption had been met. The lower hippocampal SERT density observed suggests that chronic ethanol consumption is associated with altered serotonergic modulation of hippocampal neurotransmission.

Ethanol increases glutamate neurotransmission in the posterior ventral tegmental area of female wistar rats

BACKGROUND

The posterior ventral tegmental area (pVTA) mediates the reinforcing and stimulating effects of ethanol (EtOH). Electrophysiological studies indicated that exposure to EtOH increased glutamate synaptic function in the VTA. This study determined the neurochemical effects of both acute and repeated EtOH exposure on glutamate neurotransmission in the pVTA.

METHODS

Adult female Wistar rats were implanted with microdialysis probes in the pVTA. During microdialysis, rats received acute intraperitoneal (i.p.) injection of saline or EtOH (0.5, 1.0, or 2.0 g/kg), and extracellular glutamate levels were measured in the pVTA. The effects of repeated daily injections of EtOH (0.5, 1.0, or 2.0 g/kg) on basal extracellular glutamate concentrations in the pVTA and on glutamate response to a subsequent EtOH challenge were also examined.

RESULTS

The injection of 0.5 g/kg EtOH significantly increased (120 to 125% of baseline), whereas injection of 2.0 g/kg EtOH significantly decreased (80% of baseline) extracellular glutamate levels in the pVTA. The dose of 1.0 g/kg EtOH did not alter extracellular glutamate levels. Seven repeated daily injections of each dose of EtOH increased basal extracellular glutamate concentrations (from 4.1 ± 0.5 to 9.2 ± 0.5 μM) and reduced glutamate clearance in the pVTA (from 30 ± 2 to 17 ± 2%), but failed to alter glutamate response to a 2.0 g/kg EtOH challenge.

CONCLUSIONS

The results suggest that the low dose of EtOH can stimulate the release of glutamate in the pVTA, and repeated EtOH administration increased basal glutamate transmission in the pVTA, as a result of reduced glutamate clearance.

Severity of drinking as a predictor of efficacy of the combination of ondansetron and topiramate in rat models of ethanol consumption and relapse

RATIONALE

Alcohol dependence is the third leading cause of preventable death in the USA. While single-agent pharmacotherapies have variable efficacy, medication combinations may produce additive effects by modulating multiple neural pathways.

OBJECTIVES

Here, we examined in animal models of ethanol consumption and relapse the combined effects of ondansetron (a serotonin-3 antagonist) and topiramate (a GABA/glutamate modulator), two medications with demonstrated efficacy for treating alcohol dependence, hypothesizing that their combination would produce a more efficacious response.

METHODS

The effects of acutely administered ondansetron (0-0.01 mg/kg) and topiramate (0-10 mg/kg) alone and in combination on ethanol consumption were examined in alcohol preferring (P) rats (N = 20) and in rats from their background strain (Wistars, N = 20) using a 24-h access free-choice paradigm. Next, we examined their ability to prevent an increase in ethanol consumption following a deprivation period (i.e., an animal model of relapse).

RESULTS

Whether administered alone or combined with ondansetron, topiramate produced a similar modest but persistent reduction in ethanol consumption. However, an analysis of efficacy by drinking level revealed that the combination was superior to topiramate alone in heavy-drinking P rats, but was without effect in lighter-drinking P rats and Wistar rats. Both topiramate alone and the combination blocked the alcohol deprivation effect in both Wistar and P rats with the combination tending to produce a greater decrease than topiramate alone.

CONCLUSIONS

The combination of ondansetron and topiramate may be a promising treatment for preventing relapse and for treating alcohol dependence in heavy-, but not lighter-drinkers.

Changes in extracellular levels of glutamate in the nucleus accumbens after ethanol-induced behavioral sensitization in adolescent and adult mice

Repeated administration of low doses of ethanol gradually increases locomotor responses to ethanol in adult Swiss mice. This phenomenon is known as behavioral sensitization. However, we have shown that adolescent Swiss mice show either behavioral tolerance or no sensitization after repeated ethanol injections. Although the mesolimbic dopamine system has been extensively implicated in behavioral sensitization, several studies have demonstrated an important role of glutamatergic transmission in this phenomenon. In addition, relatively few studies have examined the role of developmental factors in behavioral sensitization to ethanol. To examine the relationship between age differences in behavioral sensitization to ethanol and the neurochemical adaptations related to glutamate within nucleus accumbens (NAc), in vivo microdialysis was conducted in adolescent and adult Swiss mice treated with ethanol (1.8 g/kg) or saline for 15 days and subsequently challenged with an acute dose (1.8 g/kg) of ethanol 6 days later. Consistent with previous findings, only adult mice demonstrated evidence of behavioral sensitization. However, ethanol-treated adolescent mice demonstrated a 196.1 ± 40.0% peak increase in extracellular levels of glutamate in the NAc after ethanol challenge in comparison with the basal values, whereas ethanol-treated adult mice demonstrated a 52.2 ± 6.2% reduction in extracellular levels of glutamate in the NAc after ethanol challenge. These observations suggest an age-dependent inverse relationship between behavioral and glutamatergic responses to repeated ethanol exposure.

Binge drinking +/- chronic nicotine administration alters extracellular glutamate and arginine levels in the nucleus accumbens of adult male and female Wistar rats

AIMS

The effect of 'binge drinking' coupled or not with chronic nicotine administration on nucleus accumbens (NAc) glutamate, arginine, taurine and hydroxyl radical levels has been investigated in these present studies.

METHODS AND RESULTS

Ethanol, 2 or 3 g/kg, has been administered to male or female adult rats in a 'binge-type' regime for 3 weeks, +/- nicotine, and changes in glutamate, arginine and taurine content in the NAc, assayed by microdialysis after a further dose of ethanol. The basal concentration of NAc glutamate increased 8-fold in the female adult rats but did not change significantly after further doses of ethanol. In contrast, the male adult rats showed no changes in basal glutamate content but exhibited a dose-dependent increase in NAc glutamate after further doses of ethanol. NAc arginine basal levels decreased significantly in both male and female adult rats after further doses of ethanol. Co-administration of nicotine modified the toxicity of ethanol as exemplified by diminishment of both the basal NAc glutamate release as well as modifying the release of this excitatory amino acid after further ethanol doses, particularly in female rats. In addition, the marked changes in arginine release after further ethanol doses were less evident. There was no evidence for increased hydroxyl radical production in the NAc after 'binge drinking' +/- nicotine.

CONCLUSION

There appeared to be a greater vulnerability to ethanol toxicity in female adult rats after 'binge drinking'. It remains unclear whether the increased release of glutamate during the microdialysis evokes activation of inducible nitric oxide synthase (iNOS), which would utilize arginine in the formation of nitric oxide.

Ceftriaxone, a beta-lactam antibiotic, reduces ethanol consumption in alcohol-preferring rats

AIMS

Changes in glutamatergic transmission affect many aspects of neuroplasticity associated with ethanol and drug addiction. For instance, ethanol- and drug-seeking behavior is promoted by increased glutamate transmission in key regions of the motive circuit. We hypothesized that because glutamate transporter 1 (GLT1) is responsible for the removal of most extracellular glutamate, up-regulation or activation of GLT1 would attenuate ethanol consumption.

METHODS

Alcohol-preferring (P) rats were given 24 h/day concurrent access to 15 and 30% ethanol, water and food for 7 weeks. During Week 6, P rats received either 25, 50, 100 or 200 mg/kg ceftriaxone (CEF, i.p.), a β-lactam antibiotic known to elevate GLT1 expression, or a saline vehicle for five consecutive days. Water intake, ethanol consumption and body weight were measured daily for 15 days starting on Day 1 of injections. We also tested the effects of CEF (100 and 200 mg/kg, i.p.) on daily sucrose (10%) consumption as a control for motivated behavioral drinking.

RESULTS

Statistical analyses revealed a significant reduction in daily ethanol, but not sucrose, consumption following CEF treatment. During the post treatment period, there was a recovery of ethanol intake across days. Dose-dependent increases in water intake were manifest concurrent with the CEF-induced decreases in ethanol intake. Nevertheless, CEF did not affect body weight. An examination of a subset of the CEF-treated ethanol-drinking rats, on the third day post CEF treatment, revealed increases in GTL1 expression levels within the prefrontal cortex and nucleus accumbens.

CONCLUSIONS

These results indicate that CEF effectively reduces ethanol intake, possibly through activation of GLT1, and may be a potential therapeutic drug for alcohol addiction treatment.

Role of the serotonergic system in alcohol dependence: from animal models to clinics

Alcohol dependence remains among the most common substance abuse problems worldwide, and compulsive alcohol consumption is a significant public health concern. Alcohol is an addictive drug that alters brain function through interactions with multiple neurotransmitter systems. These neurotransmitter systems mediate the reinforcing effects of alcohol. Specifically, the serotonergic system is important in mediating alcohol reward, preference, dependence, and craving. In this review chapter, we first discuss the serotonin system as it relates to alcoholism, and then outline interactions between this system and other neurotransmitter systems. We emphasize the serotonin transporter and its possible role in alcoholism, then present several serotonergic receptors and discuss their contribution to alcoholism, and finally assess the serotonin system as a target for pharmacotherapy, with an emphasis on current and potential treatments.

Accumbens Homer2-mediated signaling: a factor contributing to mouse strain differences in alcohol drinking?

Alcohol-induced increases in nucleus accumbens glutamate actively regulate alcohol consumption, and the alcohol responsiveness of corticoaccumbens glutamate systems relates to genetic variance in alcohol reward. Here, we extend earlier data for inbred mouse strain differences in accumbens glutamate by examining for differences in basal and alcohol-induced changes in the striatal expression of glutamate-related signaling molecules between inbred C57BL/6J and DBA2/J mice. Repeated alcohol treatment (8 × 2 g/kg) increased the expression of Group1 metabotropic glutamate receptors, the NR2a/b subunits of the N-methyl-D-aspartate receptor, Homer2a/b, as well as the activated forms of protein kinase C (PKC) epsilon and phosphoinositol-3-kinase within ventral, but not dorsal, striatum. Regardless of prior alcohol experience, C57BL/6J mice exhibited higher accumbens levels of mGluR1/5, Homer2a/b, NR2a and activated kinases vs. DBA2/J mice, whereas an alcohol-induced rise in dorsal striatum mGluR1/5 expression was observed only in C57BL/6J mice. We next employed virus-mediated gene transfer approaches to ascertain the functional relevance of the observed strain difference in accumbens Homer2 expression for B6/D2 differences in alcohol-induced glutamate sensitization, as well as alcohol preference/intake. Manipulating nucleus accumbens shell Homer2b expression actively regulated these measures in C57BL/6J mice, whereas DBA2/J mice were relatively insensitive to the neurochemical and behavioral effects of virus-mediated changes in Homer2 expression. These data support the over-arching hypothesis that augmented accumbens Homer2-mediated glutamate signaling may be an endophenotype related to genetic variance in alcohol consumption. If relevant to humans, such data pose polymorphisms affecting glutamate receptor/Homer2 signaling in the etiology of alcoholism.

Metabotropic glutamate receptor 5 activity in the nucleus accumbens is required for the maintenance of ethanol self-administration in a rat genetic model of high alcohol intake

BACKGROUND

Systemic modulation of Group I and II metabotropic glutamate receptors (mGluRs) regulate ethanol self-administration in a variety of animal models. Although these receptors are expressed in reward-related brain regions, the anatomical specificity of their functional involvement in ethanol self-administration remains to be characterized. This study sought to evaluate the functional role of Group I (mGluR5) and Group II (mGluR2/3) in mesocorticolimbic brain regions in ethanol self-administration.

METHODS

Alcohol-preferring (P) rats, a genetic model of high alcohol drinking, were trained to self-administer ethanol (15% v/v) versus water in operant conditioning chambers. Effects of brain site-specific infusion of the mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP) and the mGluR2/3 agonist were then assessed on the maintenance of self-administration.

RESULTS

Microinjection of the mGluR5 antagonist MPEP in the nucleus accumbens reduced ethanol self-administration at a dose that did not alter locomotor activity. By contrast, infusion of the mGluR2/3 agonist LY379268 in the nucleus accumbens reduced self-administration and produced nonspecific reductions in locomotor activity. The mGluR5 involvement showed anatomical specificity as evidenced by lack of effect of MPEP infusion in the dorsomedial caudate or medial prefrontal cortex on ethanol self-administration. To determine reinforcer specificity, P-rats were trained to self-administer sucrose (.4% w/v) versus water, and effects of intra-accumbens MPEP were tested. The MPEP did not alter sucrose self-administration or motor behavior.

CONCLUSIONS

These results suggest that mGluR5 activity specifically in the nucleus accumbens is required for the maintenance of ethanol self-administration in individuals with genetic risk for high alcohol consumption.

Alcohol during adolescence selectively alters immediate and long-term behavior and neurochemistry

Alcohol use increases across adolescence and is a concern in the United States. In humans, males and females consume different amounts of alcohol depending on the age of initiation, and the long-term consequences of early ethanol consumption are not readily understood. The purpose of our work was to better understand the immediate and long-term impact of ethanol exposure during adolescence and the effects it can have on behavior and dopaminergic responsivity. We have assessed sex differences in voluntary ethanol consumption during adolescence and adulthood and the influence of binge ethanol exposure during adolescence. We have observed that males are sensitive to passive social influences that mediate voluntary ethanol consumption, and early ethanol exposure induces long-term changes in responsivity to ethanol in adulthood. Exposure to moderate doses of ethanol during adolescence produced alterations in dopamine in the nucleus accumbens septi during adolescence and later in adulthood. Taken together, all of these data indicate that the adolescent brain is sensitive to the impact of early ethanol exposure during this critical developmental period.

Contribution of early environmental stress to alcoholism vulnerability

The most problematic aspects of alcohol abuse disorder are excessive alcohol consumption and the inability to refrain from alcohol consumption during attempted abstinence. The root causes that predispose certain individuals to these problems are poorly understood but are believed to be produced by a combination of genetic and environmental factors. Early environmental trauma alters neurodevelopmental trajectories that can predispose an individual to a number of neuropsychiatric disorders, including substance abuse. Prenatal stress (PNS) is a well-established protocol that produces perturbations in nervous system development, resulting in behavioral alterations that include hyperresponsiveness to stress, novelty, and psychomotor stimulant drugs (e.g., cocaine, amphetamine). Moreover, PNS animals exhibit enduring alterations in basal and cocaine-induced changes in dopamine and glutamate transmission within limbic structures, which exhibit pathology in drug addiction and alcoholism, suggesting that these alterations may contribute to an increased propensity to self-administer large amounts of drugs of abuse or to relapse after periods of drug withdrawal. Given that cocaine and alcohol have actions on common limbic neural substrates (albeit by different mechanisms), we hypothesized that PNS would elevate the motivation for, and consumption of, alcohol. Accordingly, we have found that male C57BL/6J mice subject to PNS exhibit higher operant responding and consume more alcohol during alcohol reinforcement as adults. Alterations in glutamate and dopamine neurotransmission within the forebrain structures appear to contribute to the PNS-induced predisposition to high alcohol intake and are induced by excessive alcohol intake. Accordingly, we are exploring the interactions between neurochemical changes produced by PNS and changes induced by consumption of alcohol in adulthood to model the biological bases of high vulnerability to alcohol abuse.

Alcohol, cocaine, and brain stimulation-reward in C57Bl6/J and DBA2/J mice

BACKGROUND

Pleasure and reward are critical features of alcohol drinking that are difficult to measure in animal studies. Intracranial self-stimulation (ICSS) is a behavioral method for studying the effects of drugs directly on the neural circuitry that underlies brain reward. These experiments had 2 objectives: first, to establish the effects of alcohol on ICSS responding in the C57Bl6/J (C57) and DBA2/J (DBA) mouse strains; and second, to compare these effects to those of the psychostimulant cocaine.

METHODS

Male C57 and DBA mice were implanted with unipolar stimulating electrodes in the lateral hypothalamus and conditioned to spin a wheel for reinforcement by the delivery of rewarding electrical stimulation (i.e., brain stimulation-reward or BSR). Using the curve-shift method, the BSR threshold (theta(0)) was determined immediately before and after oral gavage with alcohol (0.3, 0.6, 1.0, 1.7 g/kg) or water. Blood alcohol concentration (BAC) was measured to determine the influence of alcohol metabolism on BSR threshold. Separately, mice were administered cocaine (1.0, 3.0, 10.0, 30.0 mg/kg) or saline intraperitoneally.

RESULTS

In C57 mice, the 0.6 g/kg dose of alcohol lowered BSR thresholds by about 20%, during the rising (up to 40 mg/dl), but not falling, phase of BAC. When given to the DBA mice, alcohol lowered BSR thresholds over the entire dose range; the largest reduction was by about 50%. Cocaine lowered BSR thresholds in both strains. However, cocaine was more potent in DBA mice than in C57 mice as revealed by a leftward shift in the cocaine dose-response curve. For both alcohol and cocaine, effects on BSR threshold were dissociable from effects on operant response rates.

CONCLUSIONS

In C57 and DBA mice, reductions in BSR threshold reflect the ability of alcohol to potentiate the neural mechanisms of brain reward. The DBA mice are more sensitive to the reward-potentiating effects of both alcohol and cocaine, suggesting that there are mouse strain differences in the neural mechanisms of brain reward that can be measured with the ICSS technique.

Differential effects of chronic ethanol consumption and withdrawal on homer/glutamate receptor expression in subregions of the accumbens and amygdala of P rats

BACKGROUND

Homer proteins are constituents of scaffolding complexes that regulate the trafficking and function of central Group1 metabotropic glutamate receptors (mGluRs) and N-methyl-d-aspartate (NMDA) receptors. Research supports the involvement of these proteins in ethanol-induced neuroplasticity in mouse. In this study, we examined the effects of short versus long-term withdrawal from chronic ethanol consumption on Homer and glutamate receptor protein expression within striatal and amygdala subregions of selectively bred, alcohol-preferring P rats.

METHODS

For 6 months, male P rats had concurrent access to 15% and 30% ethanol solutions under intermittent (IA: 4 d/wk) or continuous (CA: 7 d/wk) access conditions in their home cage. Rats were killed 24 hours (short withdrawal: SW) or 4 weeks (long withdrawal: LW) after termination of ethanol access, subregions of interest were micropunched and tissue processed for detection of Group1 mGluRs, NR2 subunits of the NMDA receptor and Homer protein expression.

RESULTS

Within the nucleus accumbens (NAC), limited changes in NR2a and NR2b expression were detected in the shell (NACsh), whereas substantial changes were observed for Homer2a/b, mGluRs as well as NR2a and NR2b subunits in the core (NACc). Within the amygdala, no changes were detected in the basolateral subregion, whereas substantial changes, many paralleling those observed in the NACc, were detected in the central nucleus (CeA) subregion. In addition, most of the changes observed in the CeA, but not NACc, were present in both SW and LW rats.

CONCLUSIONS

Overall, these subregion specific, ethanol-induced increases in mGluR/Homer2/NR2 expression within the NAC and amygdala suggest changes in glutamatergic plasticity had taken place. This may be a result of learning and subsequent memory formation of ethanol's rewarding effects in these brain structures, which may, in part, mediate the chronic relapsing nature of alcohol abuse.

Binge drinking upregulates accumbens mGluR5-Homer2-PI3K signaling: functional implications for alcoholism

The glutamate receptor-associated protein Homer2 regulates alcohol-induced neuroplasticity within the nucleus accumbens (NAC), but the precise intracellular signaling cascades involved are not known. This study examined the role for NAC metabotropic glutamate receptor (mGluR)-Homer2-phosphatidylinositol 3-kinase (PI3K) signaling in regulating excessive alcohol consumption within the context of the scheduled high alcohol consumption (SHAC) model of binge alcohol drinking. Repeated bouts of binge drinking ( approximately 1.5 g/kg per 30 min) elevated NAC Homer2a/b expression and increased PI3K activity in this region. Virus-mediated knockdown of NAC Homer2b expression attenuated alcohol intake, as did an intra-NAC infusion of the mGluR5 antagonist MPEP [2-methyl-6-(phenylethynyl)pyridine hydrochloride] (0.1-1 microg/side) and the PI3K antagonist wortmannin (50 ng/side), supporting necessary roles for mGluR5/Homer2/PI3K in binge alcohol drinking. Moreover, when compared with wild-type littermates, transgenic mice with an F1128R point mutation in mGluR5 that markedly reduces Homer binding exhibited a 50% reduction in binge alcohol drinking, which was related to reduced NAC basal PI3K activity. Consistent with the hypothesis that mGluR5-Homer-PI3K signaling may be a mechanism governing excessive alcohol intake, the "anti-binge" effects of MPEP and wortmannin were not additive, nor were they observed in the mGluR5(F1128R) transgenic mice. Finally, mice genetically selected for a high versus low SHAC phenotype differed in NAC mGluR, Homer2, and PI3K activity, consistent with the hypothesis that augmented NAC mGluR5-Homer2-PI3K signaling predisposes a high binge alcohol-drinking phenotype. Together, these data point to an important role for NAC mGluR5-Homer2-PI3K signaling in regulating binge-like alcohol consumption that has relevance for our understanding of the neurobiology of alcoholism and its pharmacotherapy.

Administration of MDMA to ethanol-deprived rats increases ethanol operant self-administration and dopamine release during reinstatement

Recreational use of (±)-3,4-methylenedioxymethamphetamine (MDMA, ecstasy) is often associated with other drugs, among which ethanol (EtOH) is one of the most common. However, little is known about how neurochemical sensitization produced by MDMA can modulate EtOH abuse. In this study we used EtOH operant self-administration tasks to investigate the effect of several low doses (0.33, 1.0 and 3.0 mg/kg) of MDMA in Dark Agouti rats. Motor activity was recorded after each MDMA administration. Changes in extracellular dopamine in the nucleus accumbens following a single EtOH injection (1.5 g/kg i.p.) were measured using intracerebral microdialysis in vivo after 1 wk of abstinence from EtOH, in order to mimic the dopaminergic response associated with reinstatement into EtOH consumption. Animals exposed to higher doses of MDMA (1.0 and 3.0 mg/kg) showed significantly enhanced EtOH self-administration during reinstatement and an increased EtOH-induced dopamine efflux. MDMA treatment acutely elevated motor activity after each administration in a dose-dependent manner. These findings suggest that repeated administration of MDMA, a relatively common drug of abuse, even at low doses, can alter subsequent vulnerability to EtOH consumption.

Chronic ethanol treatment potentiates ethanol-induced increases in interstitial nucleus accumbens endocannabinoid levels in rats

We employed in vivo microdialysis to characterize the effect of an ethanol challenge injection on endocannabinoid levels in the nucleus accumbens of ethanol-naïve and chronic ethanol-treated rats. Ethanol (0.75 and 2 g/kg, i.p.) dose-dependently increased dialysate 2-arachidonoylglycerol (to a maximum 157 +/- 20% of baseline) and decreased anandamide (to a minimum 52 +/- 9% of baseline) in ethanol-naïve rats. The endocannabinoid clearance inhibitor N-(4-hydrophenyl) arachidonoylamide (AM404; 3 mg/kg) potentiated ethanol effects on 2-arachidonoylglycerol levels but did not alter ethanol-induced decreases in anandamide. AM404 alone did not alter dialysate levels of either endocannabinoid. Then, we characterized the effect of ethanol challenge on nucleus accumbens endocannabinoid levels in rats previously maintained on an ethanol-containing liquid diet. Ethanol challenge produced a greater and more prolonged increase in 2-arachidonoylglycerol (to a maximum 394 +/- 135% of baseline) in ethanol-experienced than in ethanol-naïve rats. The profile in ethanol-experienced rats was similar to that produced by AM404 pre-treatment in ethanol-naïve rats. AM404 in ethanol-experienced rats led to a further enhancement in the 2-arachidonoylglycerol response to ethanol challenge (to a maximum 704 +/- 174% of baseline). Our findings demonstrate that ethanol-induced increases in nucleus accumbens 2-arachidonoylglycerol are potentiated in animals with a history of ethanol consumption.

Role of protein kinase C epsilon (PKCvarepsilon) in the reduction of ethanol reinforcement due to mGluR5 antagonism in the nucleus accumbens shell

RATIONALE

The type 5 metabotropic glutamate receptor (mGluR5) and the epsilon isoform of protein kinase C (PKCepsilon) regulate ethanol intake, and we have previously demonstrated that mGluR5 receptor antagonism reduces ethanol consumption via a PKCepsilon-dependent mechanism.

OBJECTIVES

We explored the potential neuroanatomical substrates of regulation of ethanol reinforcement by this mGluR5-PKCepsilon signaling pathway by infusing selective inhibitors of these proteins into the shell or core region of the nucleus accumbens (NAc).

METHODS

Male Wistar rats were trained to self-administer ethanol intravenously and received intra-NAc infusions of vehicle or the selective mGluR5 antagonist 3-((2-methyl-1,3-thiazol-4-yl)ethynyl)pyridine (MTEP) alone and in combination with a PKCepsilon translocation inhibitor (epsilonV1-2) or a scrambled control peptide (svarepsilonV1-2). The effects of intra-NAc MTEP on food-reinforced responding and open-field locomotor activity were also determined.

RESULTS

MTEP (1 microg/microl) had no effect on ethanol or food reinforcement or locomotor activity when infused into either region. MTEP (3 microg/microl) reduced ethanol reinforcement when infused into the NAc shell but not the core, and this effect was reversed by epsilonV1-2 (1 microg/microl) but not sepsilonV1-2 (1 microg/microl). In both regions, this concentration of MTEP did not alter food-reinforced responding or locomotor activity, and infusion of epsilonV1-2 alone did not alter ethanol reinforcement. MTEP (10 microg/microl) reduced locomotor activity when infused into the shell; therefore, this concentration was not further tested on responding for ethanol or food.

CONCLUSIONS

Blockade of mGluR5 receptors in the NAc shell reduces ethanol reinforcement via a PKCepsilon-dependent mechanism.

Electrolytic lesions of the medial nucleus accumbens shell selectively decrease ethanol consumption without altering preference in a limited access procedure in C57BL/6J mice

The central extended amygdala (cExtA) is a limbic region proposed to play a key role in drug and alcohol addiction and to contain the medial nucleus accumbens shell (MNAc shell). The aim of this study was to examine the involvement of the MNAc shell in ethanol and sucrose consumption in a limited and free access procedure in the C57BL/6J (B6) mouse. Separate groups of mice received bilateral electrolytic lesions of the MNAc shell or sham surgery, and following recovery from surgery, were allowed to voluntarily consume ethanol (15% v/v) in a 2 h limited access 2-bottle-choice procedure. Following 1 week of limited access ethanol consumption, mice were given 1 week of limited access sucrose consumption. A separate group of lesioned and sham mice were given free access (24 h) to ethanol in a 2-bottle choice procedure and were run in parallel to the mice receiving limited access consumption. Electrolytic lesions of the MNAc shell decreased ethanol (but not sucrose) consumption in a limited access procedure, but did not alter free access ethanol consumption. These results suggest that the MNAc shell is a component of the underlying neural circuitry contributing to limited access alcohol consumption in the B6 mouse.

Ethanol- and cocaine-induced locomotion are genetically related to increases in accumbal dopamine

Neuroanatomical research suggests that interactions between dopamine and glutamate within the mesolimbic dopamine system are involved in both drug-induced locomotor stimulation and addiction. Therefore, genetically determined differences in the locomotor responses to ethanol and cocaine may be related to differences in the effects of these drugs on this system. To test this, we measured drug-induced changes in dopamine and glutamate within the nucleus accumbens (NAcc), a major target of mesolimbic dopamine neurons, using in vivo microdialysis in selectively bred FAST and SLOW mouse lines, which were bred for extreme sensitivity (FAST) and insensitivity (SLOW) to the locomotor stimulant effects of ethanol. These mice also show a genetically correlated difference in stimulant response to cocaine (FAST > SLOW). Single injections of ethanol (2 g/kg) or cocaine (40 mg/kg) resulted in larger increases in dopamine within the NAcc in FAST compared with SLOW mice. There was no effect of either drug on NAcc glutamate levels. These experiments indicate that response of the mesolimbic dopamine system is genetically correlated with sensitivity to ethanol- and cocaine-induced locomotion. Because increased sensitivity to the stimulating effects of ethanol appears to be associated with greater risk for alcohol abuse, genetically determined differences in the mesolimbic dopamine response to ethanol may represent a critical underlying mechanism for increased genetic risk for alcoholism.

Targeting Homer genes using adeno-associated viral vector: lessons learned from behavioural and neurochemical studies

Over a decade of in-vitro data support a critical role for members of the Homer family of postsynaptic scaffolding proteins in regulating the functional architecture of glutamate synapses. Earlier studies of Homer knockout mice indicated a necessary role for Homer gene products in normal mesocorticolimbic glutamate transmission and behaviours associated therewith. The advent of adeno-associated viral vectors carrying cDNA for, or short hairpin RNA against, specific Homer isoforms enabled the site-directed targeting of Homers to neurons in the brain. This approach has allowed our groups to address developmental issues associated with conventional knockout mice, to confirm active roles for distinct Homer isoforms in regulating glutamate transmission in vivo, as well as in mediating a variety of behavioural processes. This review summarizes the existing data derived from our studies using adeno-associated viral vector-mediated neuronal targeting of Homer in rodents, implicating this family of proteins in drug and alcohol addiction, learning/memory and emotional processing.