• Energy Research

The purpose of the present study was to determine the acute effects of the anticraving compound acamprosate (calcium acetylhomotaurinate) and the closely related compound homotaurine on ethanol intake and ethanol-stimulated dopamine release in the nucleus accumbens. Male rats were treated with acamprosate (200 or 400 mg/kg intraperitoneally, i.p.) or homotaurine (10, 50, or 100 mg/kg i.p.) 15 min prior to access to 10% ethanol and water for 1 h in a two-bottle choice restricted access paradigm. A separate group of rats was implanted with microdialysis probes in the nucleus accumbens and given an acute injection of ethanol (1.5 g/kg i.p.) that was preceded by saline, acamprosate, or homotaurine. Acamprosate and homotaurine dose-dependently reduced ethanol intake and preference. These compounds also delayed or suppressed ethanol-stimulated increases in nucleus accumbens dopamine release, suggesting that acamprosate and homotaurine may reduce ethanol intake by interfering with the ability of ethanol to activate the mesolimbic dopamine reward system.

Several of the actions of ethanol are mediated by gamma-aminobutyrate type A (GABA(A)) receptors. Here we demonstrated that mutant mice lacking protein kinase C epsilon (PKCepsilon) were more sensitive than wild-type littermates to the acute behavioral effects of ethanol and other drugs that allosterically activate GABA(A) receptors. GABA(A) receptors in membranes isolated from the frontal cortex of PKCepsilon null mice were also supersensitive to allosteric activation by ethanol and flunitrazepam. In addition, these mutant mice showed markedly reduced ethanol self-administration. These findings indicate that inhibition of PKCepsilon increases sensitivity of GABA(A) receptors to ethanol and allosteric modulators. Pharmacological agents that inhibit PKCepsilon may be useful for treatment of alcoholism and may provide a non-sedating alternative for enhancing GABA(A) receptor function to treat other disorders such as anxiety and epilepsy.

AbstractLong‐term alcohol exposure produces neuroadaptations that contribute to the progression of alcohol abuse disorders. Chronic alcohol consumption results in strengthened excitatory neurotransmission and increased α‐amino‐3‐hydroxyl‐5‐methyl‐4‐isoxazole‐propionate receptors (AMPA) receptor signaling in animal models. However, the mechanistic role of enhanced AMPA receptor activity in alcohol‐reinforcement and alcohol‐seeking behavior remains unclear. This study examined the role of enhanced AMPA receptor function using the selective positive allosteric modulator, aniracetam, in modulating operant alcohol self‐administration and cue‐induced reinstatement. Male alcohol‐preferring (P‐) rats, trained to self‐administer alcohol (15%, v/v) versus water were pre‐treated with aniracetam to assess effects on maintenance of alcohol self‐administration. To determine reinforcer specificity, P‐rats were trained to self‐administer sucrose (0.8%, w/v) versus water, and effects of aniracetam were tested. The role of aniracetam in modulating relapse of alcohol‐seeking was assessed using a response contingent cue‐induced reinstatement procedure in P‐rats trained to self‐administer 15% alcohol. Aniracetam pre‐treatment significantly increased alcohol‐reinforced responses relative to vehicle treatment. This increase was not attributed to aniracetam‐induced hyperactivity as aniracetam pre‐treatment did not alter locomotor activity. AMPA receptor involvement was confirmed because 6,7‐dinitroquinoxaline‐2,3‐dione (AMPA receptor antagonist) blocked the aniracetam‐induced increase in alcohol self‐administration. Aniracetam did not alter sucrose‐reinforced responses in sucrose‐trained P‐rats, suggesting that enhanced AMPA receptor activity is selective in modulating the reinforcing function of alcohol. Finally, aniracetam pre‐treatment potentiated cue‐induced reinstatement of alcohol‐seeking behavior versus vehicle‐treated P‐rats. These data suggest that enhanced glutamate activity at AMPA receptors may be key in facilitating alcohol consumption and seeking behavior, which could ultimately contribute to the development of alcohol abuse disorders.

Metabotropic glutamate receptor subtype-5 (mGluR5) activity regulates a variety of behavioral pathologies associated with alcohol addiction. The main goal of this study was to determine if mGluR5 regulates the induction of ethanol-induced locomotor sensitization, which is a model of experience-dependent plasticity following initial exposure to drugs of abuse. The extracellular signal-regulated kinase (ERK1/2) pathway is downstream of mGluR5 and implicated in alcohol addiction; however, its role in sensitization remains unexplored. We sought to determine if mGluR5-mediated changes in ethanol-induced sensitization are associated with changes in ERK1/2 phosphorylation (pERK1/2) in specific brain regions. Adult male DBA/2 J mice were tested for acute locomotor response to ethanol (0 or 2 g/kg, IP) followed by a 9-day induction period in which the mGluR5 antagonist MPEP (0 or 30 mg/kg, IP) was administered prior to ethanol (0 or 2.5 g/kg, IP). One day later, ethanol (2 g/kg) produced a robust within- and between-group increase in locomotor activity, indicating sensitization in mice that received MPEP (0 mg/kg) during induction. MPEP (30 mg/kg) treatment during induction resulted in locomotor response to ethanol (2 g/kg) challenge that was equivalent to an acute response, indicating full blockade of sensitization. Sensitization was associated with increased pERK1/2 immunoreactivity (IR) in nucleus accumbens shell (AcbSh) and a reduction in lateral habenula (LHb), both of which were blocked by MPEP treatment during induction. Sensitization was also associated with mGluR5-independent increases in pERK1/2 IR in the nucleus accumbens core and decreases in the dentate gyrus and lateral septum. These data indicate that mGluR5 activity is required for the induction of ethanol locomotor sensitization and associated changes in ERK1/2 phosphorylation in the AcbSh and LHb, which raises the hypothesis that mGluR5-mediated cell signaling in these brain regions may mediate the induction of sensitization. Elucidating mechanisms of sensitization may increase understanding of how ethanol hijacks behavioral functions during the development of addiction.

Background: Activation of GABAA receptors in the amygdala or nucleus accumbens produces discriminative stimulus effects that substitute fully for those of systemically administered ethanol. This study was conducted to determine if GABAA receptors in the amygdala and nucleus accumbens interactively modulate ethanol discrimination.Methods: Male Long‐Evans rats were trained to discriminate between intraperitoneal injections of ethanol (1 g/kg) and saline on a 2‐lever drug discrimination task. The rats were then surgically implanted with bilateral injection cannulae aimed at the nucleus accumbens and the amygdala.Results: Infusion of the GABAA agonist muscimol in the nucleus accumbens resulted in full substitution for systemically administered ethanol. Concurrent infusion of the GABAA antagonist bicuculline in the amygdala shifted the muscimol substitution curve in the nucleus accumbens 10‐fold to the right.Conclusions: These results indicate that blockade of GABAA receptors in the amygdala significantly reduces the potency of the GABAA agonist in the nucleus accumbens. This suggests that the ethanol‐like stimulus effects of GABAA receptor activation in the nucleus accumbens are modulated by GABAA receptor activity in the amygdala. These data support the hypothesis that the addictive stimulus properties of alcohol are mediated by GABAergic transmission in a neural circuit involving the amygdala and nucleus accumbens.

Background: This work was conducted in an effort to establish an oral intake model system in which the effects of ethanol insult that occur during early stages of embryogenesis can be easily examined and in which agents that may modulate ethanol's teratogenicity can be readily tested in vivo. The model system described utilizes the alcohol deprivation effect to obtain teratogenic levels of maternal ethanol intake on days 7 and 8 of pregnancy in C57Bl/6J mice. Ocular defects including microphthalmia and uveal coloboma, which have previously been shown to result from ethanol administered by gavage or via intraperitoneal injection on these days, served as the developmental end point for this study. The ocular defects are readily identifiable and their degree of severity is expected to correlate with concurrently developing defects of the central nervous system (CNS).Methods: Female C57Bl/6J mice were maintained on an ethanol‐containing (4.8% v/v) liquid diet for 14 days and then mated during a subsequent abstinence period. Mice were then reexposed to ethanol on days 7 and 8 of pregnancy only. Control as well as ethanol‐exposed dams were killed on their 14th day of pregnancy. Fetuses were then weighed, measured for crown rump length, photographed, and analyzed for ocular abnormalities. Globe size, palpebral fissure length, and pupil size and shape were noted for both the right and left eyes of all fetuses and informative comparisons were made.Results: This exposure paradigm resulted in peak maternal blood alcohol concentrations that ranged from 170 to 220 mg/dL on gestational day (GD) 8. Compared with the GD 14 fetuses from the normal control group, the pair‐fed, acquisition controls, as well as the ethanol‐exposed fetuses, were developmentally delayed and had reduced weights. Confirming previous studies, comparison of similarly staged control and treated GD 8 embryos illustrated reductions in the size of the forebrain in the latter. Subsequent ocular malformations were noted in 33% of the right eyes and 25% of the left eyes of the 103 GD 14 ethanol‐exposed fetuses examined. This incidence of defects is twice that observed in the control groups. Additionally, it was found that the palpebral fissure length is directly correlated with globe size.Conclusions: The high incidence of readily identifiable ocular malformations produced by oral ethanol intake in this model and their relevance to human fetal alcohol spectrum disorders (FASD) makes this an excellent system for utilization in experiments involving factors administered to the embryo that might alter ethanol's teratogenic effects. Additionally, the fact that early ethanol insult yields ocular and forebrain abnormalities that are developmentally associated allows efficient specimen selection for subsequent detailed analyses of CNS effects in this in vivo mammalian FASD model.

Long-Evans rats (N = 3) were trained to lever press on a fixed-ratio 4 (FR 4) schedule with ethanol (10% v/v) presented as the reinforcer. Each rat received a total of six bilateral nucleus accumbens microinjections, one per week. They were tested with one physiological saline control, three 20.0-microgram/brain d-amphetamine, and two 6.0-microgram/brain quinpirole injections given 10 min prior to operant sessions. Ethanol-reinforced responding terminated after approximately 10 min during control sessions. Microinjections of the D2 agonist quinpirole and the nonspecific dopamine (DA) agonist d-amphetamine increased total responding but produced slowed response rates that continued for 45-60 min. The slowed response rate produced by d-amphetamine resulted in a peak increase in interresponse times (IRTs) between 8-10 s, whereas quinpirole increased IRTs in the 14- to 16-s range, indicating that nonspecific DA activation resulted in higher rates of ethanol-reinforced responding than specific D2 activation although both drugs decreased local response rates. These data indicate that the amount and temporal extent of ethanol-reinforced responding are increased by microinjections of DA agonists in the nucleus accumbens and support the hypothesis that DA activity in this region is involved in the regulation of ethanol-reinforced responding.

The interoceptive effects of alcohol are major determinants of addiction liability. Metabotropic glutamate (mGlu) receptors are widely expressed in striatal circuits known to modulate drug-seeking. Given that the interoceptive effects of drugs can be important determinants of abuse liability, we hypothesized that striatal mGlu receptors modulate the interoceptive effects of alcohol. Using drug discrimination learning, rats were trained to discriminate alcohol (1 g/kg, i.g.) versus water. We found that systemic antagonism of metabotropic glutamate subtype 5 (mGlu5) receptors [10 mg/kg 2-methyl-6-(phenylethynyl)pyridine (MPEP) and 3 mg/kg 3-((2-methyl-1,3-thiazol-4-yl)ethynyl)pyridine], but not mGlu1 receptors ([0.3–3 mg/kg JNJ16259685) (3,4-dihydro-2H-pyrano[2,3]β-quinolin-7-yl)(cis-4-methoxycyclohexyl) methanone)], inhibited the discriminative stimulus effects of alcohol. Furthermore, mGlu5 receptor antagonism (10 mg/kg MPEP) significantly inhibited neuronal activity in the nucleus accumbens core as levels of the transcription factor c-Fos were significantly reduced. Accordingly, targeted inhibition of mGlu5 receptors (20 μg of MPEP) in the nucleus accumbens core blunted the discriminative stimulus effects of alcohol (1 g/kg). Anatomical specificity was confirmed by the lack of effect of inhibition of mGlu5 receptors (10–30 μg of MPEP) in the dorsomedial caudate–putamen and the similar cytological expression patterns and relative density of mGlu5 receptors between the brain regions. Functional involvement of intra-accumbens mGlu5 receptors was confirmed as activation of mGlu5 receptors [10 μg of (RS)-2-amino-2-(2-chloro-5-hydroxyphenyl)acetic acid sodium salt] enhanced the discriminative stimulus effects of a low alcohol dose (0.5 g/kg), and mGlu5 receptor inhibition (20 μg of MPEP) prevented the agonist-induced enhancement. These results show that mGlu5 receptor activity in the nucleus accumbens is required for the expression of the interoceptive effects of alcohol.