Urocortin 1 microinjection into the mouse lateral septum regulates the acquisition and expression of alcohol consumption

Mu-opioid receptors in septum mediate the development of behavioural sensitization to a single morphine exposure in male rats

Behavioural sensitization (BS) is characterized by enhanced psychomotor responses to a dose of substance of abuse after prior repeated exposure. We previously reported that BS can be induced by a single injection of morphine in rats, whereas septal nuclei are specifically involved in the development phase of BS. Here, we demonstrated that intra-LS or intra-MS microinjections also incubated BS to a systemic morphine injection in a cross-sensitization fashion, whereas inactivation of either subdivision of septal nuclei (LS: lateral septum; MS: medial septum) can negate this ability of morphine. Then, non-selective (naloxone) and selective (μ-, δ- and κ-)opioid receptor antagonists were directly delivered into LS or MS, respectively, ahead of a morphine microinjection, whereas only μ-opioid receptors in both LS and MS play indispensable roles in mediating the BS development. Finally, there was a pronounced elevation in the levels of the monoamines (i.e. dopamine, homovanillic acid, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid) in the septum, 8 h after a morphine injection detected with a HPLC-ECD method, suggesting that dopaminergi and serotoninergic systems are implicated in the BS formation. Our studies demonstrated that septal nuclei critically participate in the BS development. Essentially, μ- instead of δ- or κ-opioid receptors in LS and MS mediate sensitization to opiates.

Effect of acute alcohol intoxication on scale-free neural activity in the lateral septum in rats

Electrophysiological recordings of brain activity show both oscillatory dynamics that typically are analyzed in the time-frequency domain to describe brain oscillatory phenomena and scale-free arrhythmic activity defined as neural noise. Recent studies consider this arrhythmic fractal dynamics of neural noise as a sensitive biomarker of a number of cognitive processes, activity of neurotransmitter systems, changes that accompany neurodegenerative and psychiatric disorders including alcohol use disorder. We tested the changes in neural noise induced by acute alcohol intoxication in the lateral septum for the entire spectrum (1–200 Hz) of local field potential signal and for frequency specific ranges (delta, theta, beta, gamma and epsilon bands). Five male Wistar rats were implanted with intracranial electrodes and local field potential signal was measured for baseline activity and activity induced by acute ethanol intoxication (2 g/kg). Change in neural noise dynamics was assessed as a change in the slope of linear regression fit of power spectral density curves in double logarithmic scale. In our study alcohol resulted in lower incline of scale-free activity in the lateral septum for high frequency range and for the whole spectrum, which is interpreted generally as increase in neural noise and change in neuronal processing in a more stochastic way initiated by the acute alcohol intoxication. At the same time, we observed decrease in neural noise for low frequency range. The observed changes may be related to the shift of the excitatory-inhibitory balance towards inhibition and changes in neurotransmission mostly in the GABAergic system. Scale-free activity was sensitive in the conditions of acute alcohol intoxication, therefore to understand its role in alcohol use disorder we need more data and studies on the underlying processes. Future studies should include simultaneous recordings and analysis of arrhythmic dynamics with the oscillatory and multiunit spiking activity in the lateral septum. It can reveal the contribution of different-scale processes in changes driven by acute alcohol intoxication and clarify the specific electrophysiological mechanisms.

The corticotropin releasing factor binding protein: A strange case of Dr. Jekyll and Mr. Hyde in the stress system?

The corticotropin releasing factor (CRF) exerts its effects by acting on its receptors and on the binding protein (CRFBP). Extensive literature suggests a role of CRF in alcohol use disorder (AUD). Less is known about the specific role, if any, of CRFBP in AUD. In this review, we summarize recent interdisciplinary efforts toward identifying the contribution of CRFBP in mediating CRF activation. The role of CRFBP in alcohol-related behaviors has been evaluated with the ultimate goal of designing effective novel therapeutic strategies for AUD. A series of in vitro, in vivo, ex vivo, and genetic studies presented here provides initial evidence that CRFBP may possess both inhibitory and excitatory roles, and supports the original hypothesis that it represents a novel pharmacological target for the treatment of AUD. This report summarizes the proceedings of one of the talks at the Young Investigator Award symposium at the Alcoholism and Stress: A Framework for Future Treatment Strategies Conference, Volterra, Italy.

Corticotropin Releasing Factor in the Bed Nucleus of the Stria Terminalis in Socially Defeated and Non-stressed Mice with a History of Chronic Alcohol Intake

Stress exposure has been identified as one risk factor for alcohol abuse that may facilitate the transition from social or regulated use to the development of alcohol dependence. Preclinical studies have shown that dysregulation of the corticotropin releasing factor (CRF) neurotransmission has been implicated in stress-related psychopathologies such as depression and anxiety, and may affect alcohol consumption. The bed nucleus of the stria terminalis (BNST) contains CRF-producing neurons which seem to be sensitive to stress. In this study, adult male C57BL/6 mice previously defeated in resident-intruder confrontations were evaluated in the elevated plus-maze and tail suspension test. Mice were also tested for sweet solution intake before and after social stress. After having had continuous access to ethanol (20% weight/volume) for 4 weeks, control and stressed mice had CRF type 1 (CRFR1) or type 2 (CRFR2) receptor antagonists infused into the BNST and then had access to ethanol for 24 h. In separate cohorts of control and stressed mice, we assessed mRNA levels of BNST CRF, CRFR1 and CRFR2. Stressed mice increased their intake of sweet solution after ten sessions of social defeat and showed reduced activity in the open arms of the elevated plus-maze. When tested for ethanol consumption, stressed mice persistently drank significantly more than controls during the 4 weeks of access. Also, social stress induced higher BNST CRF mRNA levels. The selective blockade of BNST CRFR1 with CP376,395 effectively reduced alcohol drinking in non-stressed mice, whereas the selective CRFR2 antagonist astressin2B produced a dose-dependent increase in ethanol consumption in both non-stressed controls and stressed mice. The 10-day episodic defeat stress used here elicited anxiety- but not depressive-like behaviors, and promoted an increase in ethanol drinking. CRF-CRFR1 signaling in the BNST seems to underlie ethanol intake in non-stressed mice, whereas CRFR2 modulates alcohol consumption in both socially defeated and non-stressed mice with a history of chronic intake.

Corticotropin-Releasing Factor (CRF) and Addictive Behaviors

Drug addiction is a complex disorder that is characterized by compulsivity to seek and take the drug, loss of control in limiting intake of the drug, and emergence of a withdrawal syndrome in the absence of the drug. The transition from casual drug use to dependence is mediated by changes in reward and brain stress functions and has been linked to a shift from positive reinforcement to negative reinforcement. The recruitment of brain stress systems mediates the negative emotional state produced by dependence that drives drug seeking through negative reinforcement mechanisms, defined as the "dark side" of addiction. In this chapter we focus on behavioral and cellular neuropharmacological studies that have implicated brain stress systems (i.e., corticotropin-releasing factor [CRF]) in the transition to addiction and the predominant brain regions involved. We also discuss the implication of CRF recruitment in compulsive eating disorders.

Involvement of lateral septum in alcohol's dopamine-elevating effect in the rat

Drugs of abuse share the ability to increase extracellular dopamine (DA) levels in the mesolimbic DA system. This effect has been linked to positive and reinforcing experiences of drug consumption and is presumed to be of importance for continued use, as well as for the development of dependence and addiction. Previous rat studies from our lab have implicated a neuronal circuitry involving glycine receptors in nucleus accumbens (nAc) and, secondarily, nicotinic acetylcholine receptors in the ventral tegmental area (VTA) in ethanol's (EtOH) DA-elevating effect. The work presented here, performed in male Wistar rats, suggests that the lateral septum (LS), which has previously been associated with different aspects of EtOH-related behaviour, is involved as well. In vivo microdialysis methodology demonstrated that blocking the generation of action potentials in LS using tetrodotoxin prevented a DA increase in nAc after accumbal EtOH perfusion. Retrograde tracing and polymerase chain reaction (PCR) were used to identify and characterize cells projecting to VTA from nAc/LS and from LS to nAc. Based on the PCR results, cells projecting from both LS/nAc to anterior VTA and from LS to nAc were mainly GABAergic neurons expressing glycine receptors, and these cells are presumed to be involved in mediating the DA-elevating effect of EtOH. These results provide further evidence implicating LS in the reinforcing effects of EtOH. Additional studies are needed to investigate LS involvement in EtOH consumption behaviour and its potential role in the development of dependence and addiction.

Control of chronic excessive alcohol drinking by genetic manipulation of the Edinger-Westphal nucleus urocortin-1 neuropeptide system

Midbrain neurons of the centrally projecting Edinger-Westphal nucleus (EWcp) are activated by alcohol, and enriched with stress-responsive neuropeptide modulators (including the paralog of corticotropin-releasing factor, urocortin-1). Evidence suggests that EWcp neurons promote behavioral processes for alcohol-seeking and consumption, but a definitive role for these cells remains elusive. Here we combined targeted viral manipulations and gene array profiling of EWcp neurons with mass behavioral phenotyping in C57BL/6 J mice to directly define the links between EWcp-specific urocortin-1 expression and voluntary binge alcohol intake, demonstrating a specific importance for EWcp urocortin-1 activity in escalation of alcohol intake.

An Update on CRF Mechanisms Underlying Alcohol Use Disorders and Dependence

Alcohol is the most commonly used and abused substance worldwide. The emergence of alcohol use disorders, and alcohol dependence in particular, is accompanied by functional changes in brain reward and stress systems, which contribute to escalated alcohol drinking and seeking. Corticotropin-releasing factor (CRF) systems have been critically implied in the transition toward problematic alcohol drinking and alcohol dependence. This review will discuss how dysregulation of CRF function contributes to the vulnerability for escalated alcohol drinking and other consequences of alcohol consumption, based on preclinical evidence. CRF signaling, mostly via CRF1 receptors, seems to be particularly important in conditions of excessive alcohol taking and seeking, including during early and protracted withdrawal, relapse, as well as during withdrawal-induced anxiety and escalated aggression promoted by alcohol. Modulation of CRF1 function seems to exert a less prominent role over low to moderate alcohol intake, or to species-typical behaviors. While CRF mechanisms in the hypothalamic-pituitary-adrenal axis have some contribution to the neurobiology of alcohol abuse and dependence, a pivotal role for extra-hypothalamic CRF pathways, particularly in the extended amygdala, is well characterized. More recent studies further suggest a direct modulation of brain reward function by CRF signaling in the ventral tegmental area, nucleus accumbens, and the prefrontal cortex, among other structures. This review will further discuss a putative role for other components of the CRF system that contribute for the overall balance of CRF function in reward and stress pathways, including CRF2 receptors, CRF-binding protein, and urocortins, a family of CRF-related peptides.

Rodent models and mechanisms of voluntary binge-like ethanol consumption: Examples, opportunities, and strategies for preclinical research

Binge ethanol consumption has widespread negative consequences for global public health. Rodent models offer exceptional power to explore the neurobiology underlying and affected by binge-like drinking as well as target potential prevention, intervention, and treatment strategies. An important characteristic of these models is their ability to consistently produce pharmacologically-relevant blood ethanol concentration. This review examines the current available rodent models of voluntary, pre-dependent binge-like ethanol consumption and their utility in various research strategies. Studies have demonstrated that a diverse array of neurotransmitters regulate binge-like drinking, resembling some findings from other drinking models. Furthermore, repeated binge-like drinking recruits neuroadaptive mechanisms in mesolimbocortical reward circuitry. New opportunities that these models offer in the current context of mechanistic research are also discussed.

Preclinical evidence implicating corticotropin-releasing factor signaling in ethanol consumption and neuroadaptation

The results of many studies support the influence of the corticotropin-releasing factor (CRF) system on ethanol (EtOH) consumption and EtOH-induced neuroadaptations that are critical in the addiction process. This review summarizes the preclinical data in this area after first providing an overview of the components of the CRF system. This complex system involves hypothalamic and extra-hypothalamic mechanisms that play a role in the central and peripheral consequences of stressors, including EtOH and other drugs of abuse. In addition, several endogenous ligands and targets make up this system and show differences in their involvement in EtOH drinking and in the effects of chronic or repeated EtOH treatment. In general, genetic and pharmacological approaches paint a consistent picture of the importance of CRF signaling via type 1 CRF receptors (CRF(1)) in EtOH-induced neuroadaptations that result in higher levels of intake, encourage alcohol seeking during abstinence and alter EtOH sensitivity. Furthermore, genetic findings in rodents, non-human primates and humans have provided some evidence of associations of genetic polymorphisms in CRF-related genes with EtOH drinking, although additional data are needed. These results suggest that CRF(1) antagonists have potential as pharmacotherapeutics for alcohol use disorders. However, given the broad and important role of these receptors in adaptation to environmental and other challenges, full antagonist effects may be too profound and consideration should be given to treatments with modulatory effects.

Reduction of ethanol intake by corticotropin-releasing factor receptor-1 antagonist in "heavy-drinking" mice in a free-choice paradigm

RATIONALE

We hypothesized that the corticotropin-releasing factor (CRF) system is hyperresponsive in animals with high ethanol intake, which exhibits a reduction of ethanol intake when administered with a CRF1 receptor antagonist.

METHODS

Outbred Swiss mice were subjected to a long-term, three-bottle, free-choice paradigm (5 and 10 % [v/v] ethanol and water) that consisted of four phases: acquisition (AC; 10 weeks), withdrawal (W; 2 weeks), reexposure (RE; 2 weeks), and quinine-adulteration (AD; 2 weeks). Based on individual ethanol intake, the mice were classified into three groups: A group, preference for ethanol and persistently high consumption during AD phase; B group, preference for ethanol and a reduction of ethanol intake in the AD phase; and C group; preference for water during all phases. A control group only had access to water. CRF1 receptor messenger RNA (mRNA) levels in the amygdala and the effect of the CRF1 receptor antagonist CP-154,526 on ethanol and water intake in the subgroups were studied.

RESULTS

CRF1 transcript levels were higher in the B group than in the control group. The highest dose of CP-154,526 reduced ethanol intake and preference, with no changes in water consumption, in the A group compared with vehicle. The B group exhibited a reduction of both ethanol and water intake, with no changes in preference. The C group exhibited no changes in response to the CRF1 antagonist.

CONCLUSIONS

CRF1 receptors appear to be involved in ethanol consumption in mice with high ethanol consumption, and CRF system-mediated neuroadaptations depend on drinking profiles.

Corticotropin releasing factor: a key role in the neurobiology of addiction

Drug addiction is a chronically relapsing disorder characterized by loss of control over intake and dysregulation of stress-related brain emotional systems. Since the discovery by Wylie Vale and his colleagues of corticotropin-releasing factor (CRF) and the structurally-related urocortins, CRF systems have emerged as mediators of the body's response to stress. Relatedly, CRF systems have a prominent role in driving addiction via actions in the central extended amygdala, producing anxiety-like behavior, reward deficits, excessive, compulsive-like drug self-administration and stress-induced reinstatement of drug seeking. CRF neuron activation in the medial prefrontal cortex may also contribute to the loss of control. Polymorphisms in CRF system molecules are associated with drug use phenotypes in humans, often in interaction with stress history. Drug discovery efforts have yielded brain-penetrant CRF1 antagonists with activity in preclinical models of addiction. The results support the hypothesis that brain CRF-CRF1 systems contribute to the etiology and maintenance of addiction.

Increased anxiety in corticotropin-releasing factor type 2 receptor-null mice requires recent acute stress exposure and is associated with dysregulated serotonergic activity in limbic brain areas

Background

Corticotropin-releasing factor type 2 receptors (CRFR2) are suggested to facilitate successful recovery from stress to maintain mental health. They are abundant in the midbrain raphe nuclei, where they regulate serotonergic neuronal activity and have been demonstrated to mediate behavioural consequences of stress. Here, we describe behavioural and serotonergic responses consistent with maladaptive recovery from stressful challenge in CRFR2-null mice.

Results

CRFR2-null mice showed similar anxiety levels to control mice before and immediately after acute restraint stress, and also after cessation of chronic stress. However, they showed increased anxiety by 24 hours after restraint, whether or not they had been chronically stressed.

Serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) contents were quantified and the level of 5-HIAA in the caudal dorsal raphe nucleus (DRN) was increased under basal conditions in CRFR2-null mice, indicating increased 5-HT turnover. Twenty-four hours following restraint, 5-HIAA was decreased only in CRFR2-null mice, suggesting that they had not fully recovered from the challenge. In efferent limbic structures, CRFR2-null mice showed lower levels of basal 5-HT in the lateral septum and subiculum, and again showed a differential response to restraint stress from controls.

Local cerebral glucose utilization (LCMRglu) revealed decreased neuronal activity in the DRN of CRFR2-null mice under basal conditions. Following 5-HT receptor agonist challenge, LCMRglu responses indicated that 5-HT_1A receptor responses in the DRN were attenuated in CRFR2-null mice. However, postsynaptic 5-HT receptor responses in forebrain regions were intact.

Conclusions

These results suggest that CRFR2 are required for proper functionality of 5-HT_1A receptors in the raphe nuclei, and are key to successful recovery from stress. This disrupted serotonergic function in CRFR2-null mice likely contributes to their stress-sensitive phenotype. The 5-HT content in lateral septum and subiculum was notably altered. These areas are important for anxiety, and are also implicated in reward and the pathophysiology of addiction. The role of CRFR2 in stress-related psychopathologies deserves further consideration.

Inhibition of VTA neurons activates the centrally projecting Edinger-Westphal nucleus: evidence of a stress-reward link?

The primary site of urocortin 1 (Ucn1) expression in the brain is the centrally projecting Edinger-Westphal nucleus. The EWcp is innervated by dopaminergic neurons of the ventral tegmental area (VTA). To investigate whether activity of EWcp is regulated by the VTA, we investigated the effects of local pharmacological inhibition of VTA activity on the induction of Fos immunoreactivity in the EWcp of male C57BL/6J mice. A unilateral intracranial administration of the GABA agonist muscimol aimed at the VTA resulted in increased number of Fos-positive cells in the EWcp. This induction was lower than that produced by an intraperitoneal injection of 2.5 g/kg of ethanol. To investigate whether inhibition of dopaminergic neurons was responsible for induction of Fos, a second experiment was performed where the dopamine agonist quinpirole was unilaterally injected targeting the VTA. Injections of quinpirole also significantly induced Fos in the EWcp neurons. The induction occurred only on the side of the EWcp ipsilateral to the VTA injection. These results indicate that activity of EWcp is inhibited by tonic activity of dopaminergic VTA neurons, and that unilateral projections of VTA onto Ucn1-containing EWcp neurons provide a link between systems regulating approach and avoidance behaviors.

Binge ethanol-drinking potentiates corticotropin releasing factor R1 receptor activity in the ventral tegmental area

BACKGROUND

Corticotropin releasing factor (CRF) and urocortin play an important role in many stress responses and also can regulate ethanol (EtOH) intake. Adaptations in CRF signaling in the central amygdala promote EtOH consumption after long-term EtOH intake in dependent animals and also after brief periods of binge EtOH intake. Thus, even brief episodes of EtOH consumption can alter the function of the CRF system, allowing CRF to regulate EtOH intake. Here, we examined whether brief binge EtOH consumption leads to CRF receptor adaptations within the ventral tegmental area (VTA), a structure involved in signaling rewarding and aversive events and important in the development and expression of drug and alcohol addiction.

METHODS

We utilized a mouse model of binge drinking known as drinking in the dark (DID), where C57BL/6J mice drink approximately 6 g/kg in 4 hours and achieve blood EtOH concentrations of approximately 100 mg/dl, which is equivalent to binge drinking in humans. We used ex vivo whole-cell recordings from putative VTA dopamine (DA) neurons to examine CRF regulation of NMDA receptor (NMDAR) currents. We also examined the impact of CRF receptor antagonist injection in the VTA on binge EtOH intake.

RESULTS

Ex vivo whole-cell recordings from putative VTA DA neurons showed enhanced CRF-mediated potentiation of NMDAR currents in juvenile mice that consumed EtOH in the DID procedure. CRF-induced potentiation of NMDAR currents in EtOH-drinking mice was blocked by administration of CP-154,526 (3 μM), a selective CRF1 receptor antagonist. Furthermore, intra-VTA infusion of CP-154,526 (1 μg) significantly reduced binge EtOH consumption in adult mice. These results were not due to alterations of VTA NMDAR number or function, suggesting that binge drinking may enhance signaling through VTA CRF1 receptors onto NMDARs.

CONCLUSIONS

Altered CRF1 receptor-mediated signaling in the VTA promotes binge-like EtOH consumption in mice, which supports the idea that CRF1 receptors may therefore be a promising pharmacological target for reducing binge drinking in humans.

CRF1 receptor signaling regulates food and fluid intake in the drinking-in-the-dark model of binge alcohol consumption

BACKGROUND

Several recent studies implementing the standard "drinking-in-the-dark" (DID) model of short-term binge-like ethanol (EtOH) intake in C57BL/6J mice highlighted a role for the stress-related neuropeptide corticotropin-releasing factor (CRF) and its primary binding partner, the CRF type-1 (CRF1) receptor.

METHODS

We evaluated the selectivity of CRF1 involvement in binge-like EtOH intake by interrupting CRF1 function via pharmacological and genetic methods in a slightly modified 2-bottle choice DID model that allowed calculation of an EtOH preference ratio. In addition to determining EtOH intake and preference, we also measured consumption of food and H2 O during the DID period, both in the presence and absence of EtOH and sweet tastant solutions.

RESULTS

Treatment with either of the CRF1-selective antagonists CP-376,395 (CP; 10 to 20 mg/kg, i.p.) or NBI-27914 (10 to 30 mg/kg, i.p.) decreased intake of 15% EtOH in male C57BL/6J mice, but did so in the absence of a concomitant decrease in EtOH preference. These findings were replicated genetically in a CRF1 knockout (KO) mouse model (also on a C57BL/6J background). In contrast to effects on EtOH intake, pharmacological blockade of CRF1 with CP increased intake of 10% sucrose, consistent with previous findings in CRF1 KO mice. Finally, pharmacological and genetic disruption of CRF1 activity significantly reduced feeding and/or total caloric intake in all experiments, confirming the existence of nonspecific effects.

CONCLUSIONS

Our findings indicate that blockade of CRF1 receptors does not exert specific effects on EtOH intake in the DID paradigm, and that slight modifications to this procedure, as well as additional consummatory control experiments, may be useful when evaluating the selectivity of pharmacological and genetic manipulations on binge-like EtOH intake.

Signaling pathways mediating alcohol effects

Ethanol's effects on intracellular signaling pathways contribute to acute effects of ethanol as well as to neuroadaptive responses to repeated ethanol exposure. In this chapter we review recent discoveries that demonstrate how ethanol alters signaling pathways involving several receptor tyrosine kinases and intracellular tyrosine and serine-threonine kinases, with consequences for regulation of cell surface receptor function, gene expression, protein translation, neuronal excitability and animal behavior. We also describe recent work that demonstrates a key role for ethanol in regulating the function of scaffolding proteins that organize signaling complexes into functional units. Finally, we review recent exciting studies demonstrating ethanol modulation of DNA and histone modification and the expression of microRNAs, indicating epigenetic mechanisms by which ethanol regulates neuronal gene expression and addictive behaviors.

Chronic self-administration of alcohol results in elevated ΔFosB: comparison of hybrid mice with distinct drinking patterns

Background

The inability to reduce or regulate alcohol intake is a hallmark symptom for alcohol use disorders. Research on novel behavioral and genetic models of experience-induced changes in drinking will further our knowledge on alcohol use disorders. Distinct alcohol self-administration behaviors were previously observed when comparing two F1 hybrid strains of mice: C57BL/6J x NZB/B1NJ (BxN) show reduced alcohol preference after experience with high concentrations of alcohol and periods of abstinence while C57BL/6J x FVB/NJ (BxF) show sustained alcohol preference. These phenotypes are interesting because these hybrids demonstrate the occurrence of genetic additivity (BxN) and overdominance (BxF) in ethanol intake in an experience dependent manner. Specifically, BxF exhibit sustained alcohol preference and BxN exhibit reduced alcohol preference after experience with high ethanol concentrations; however, experience with low ethanol concentrations produce sustained alcohol preference for both hybrids. In the present study, we tested the hypothesis that these phenotypes are represented by differential production of the inducible transcription factor, ΔFosB, in reward, aversion, and stress related brain regions.

Results

Changes in neuronal plasticity (as measured by ΔFosB levels) were experience dependent, as well as brain region and genotype specific, further supporting that neuronal circuitry underlies motivational aspects of ethanol consumption. BxN mice exhibiting reduced alcohol preference had lower ΔFosB levels in the Edinger-Westphal nucleus than mice exhibiting sustained alcohol preference, and increased ΔFosB levels in central medial amygdala as compared with control mice. BxN mice showing sustained alcohol preference exhibited higher ΔFosB levels in the ventral tegmental area, Edinger-Westphal nucleus, and amygdala (central and lateral divisions). Moreover, in BxN mice ΔFosB levels in the Edinger-Westphal nucleus and ventral tegmental regions significantly positively correlated with ethanol preference and intake. Additionally, hierarchical clustering analysis revealed that many ethanol-naïve mice with overall low ΔFosB levels are in a cluster, whereas many mice displaying sustained alcohol preference with overall high ΔFosB levels are in a cluster together.

Conclusions

By comparing and contrasting two alcohol phenotypes, this study demonstrates that the reward- and stress-related circuits (including the Edinger-Westphal nucleus, ventral tegmental area, amygdala) undergo significant plasticity that manifests as reduced alcohol preference.

Stress-related neuropeptides and addictive behaviors: beyond the usual suspects

Addictive disorders are chronic, relapsing conditions that cause extensive disease burden. Genetic factors partly account for susceptibility to addiction, but environmental factors such as stressful experiences and prolonged exposure of the brain to addictive drugs promote its development. Progression to addiction involves neuroadaptations within neurocircuitry that mediates stress responses and is influenced by several peptidergic neuromodulators. While corticotrophin releasing factor is the prototypic member of this class, recent work has identified several additional stress-related neuropeptides that play an important role in regulation of drug intake and relapse, including the urocortins, nociceptin, substance P, and neuropeptide S. Here, we review this emerging literature, discussing to what extent the properties of these neuromodulators are shared or distinct and considering their potential as drug targets.

Systems genetics of the lateral septal nucleus in mouse: heritability, genetic control, and covariation with behavioral and morphological traits

The lateral septum has strong efferent projections to hypothalamic and midbrain regions, and has been associated with modulation of social behavior, anxiety, fear conditioning, memory-related behaviors, and the mesolimbic reward pathways. Understanding natural variation of lateral septal anatomy and function, as well as its genetic modulation, may provide important insights into individual differences in these evolutionarily important functions. Here we address these issues by using efficient and unbiased stereological probes to estimate the volume of the lateral septum in the BXD line of recombinant inbred mice. Lateral septum volume is a highly variable trait, with a 2.5-fold difference among animals. We find that this trait covaries with a number of behavioral and physiological phenotypes, many of which have already been associated with behaviors modulated by the lateral septum, such as spatial learning, anxiety, and reward-seeking. Heritability of lateral septal volume is moderate (h(2) = 0.52), and much of the heritable variation is caused by a locus on the distal portion of chromosome (Chr) 1. Composite interval analysis identified a secondary interval on Chr 2 that works additively with the Chr 1 locus to increase lateral septum volume. Using bioinformatic resources, we identified plausible candidate genes in both intervals that may influence the volume of this key nucleus, as well as associated behaviors.

Neurochemical and neurostructural plasticity in alcoholism

The behavioral manifestations of alcoholism are primarily attributable to the numerous and lasting adaptations that occur in the brain as a result of chronic heavy alcohol consumption. As will be reviewed here, these adaptations include alcohol-induced plasticity in chemical neurotransmission, density and morphology of dendritic spines, as well as neurodegeneration and cerebral atrophy. Within the context of these neuroadaptations that have been observed in both human and animal studies, we will discuss how these changes potentially contribute to the cognitive and behavioral dysfunctions that are hallmark features of alcoholism, as well as how they reveal novel potential pharmacological targets for the treatment of this disorder.

The role of early life experience and species differences in alcohol intake in microtine rodents

Social relationships have important effects on alcohol drinking. There are conflicting reports, however, about whether early-life family structure plays an important role in moderating alcohol use in humans. We have previously modeled social facilitation of alcohol drinking in peers in socially monogamous prairie voles. We have also modeled the effects of family structure on the development of adult social and emotional behaviors. Here we assessed whether alcohol intake would differ in prairie voles reared by both parents compared to those reared by a single mother. We also assessed whether meadow voles, a closely related species that do not form lasting reproductive partnerships, would differ in alcohol drinking or in the effect of social influence on drinking. Prairie voles were reared either bi-parentally (BP) or by a single mother (SM). BP- and SM-reared adult prairie voles and BP-reared adult meadow voles were given limited access to a choice between alcohol (10%) and water over four days and assessed for drinking behavior in social and non-social drinking environments. While alcohol preference was not different between species, meadow voles drank significantly lower doses than prairie voles. Meadow voles also had significantly higher blood ethanol concentrations than prairie voles after receiving the same dose, suggesting differences in ethanol metabolism. Both species, regardless of rearing condition, consumed more alcohol in the social drinking condition than the non-social condition. Early life family structure did not significantly affect any measure. Greater drinking in the social condition indicates that alcohol intake is influenced similarly in both species by the presence of a peer. While the ability of prairie voles to model humans may be limited, the lack of differences in alcohol drinking in BP- and SM-reared prairie voles lends biological support to human studies demonstrating no effect of single-parenting on alcohol abuse.

Urocortins: CRF's siblings and their potential role in anxiety, depression and alcohol drinking behavior

It is widely accepted that stress, anxiety, depression and alcohol abuse-related disorders are in large part controlled by corticotropin-releasing factor (CRF) receptors. However, evidence is accumulating that some of the actions on these receptors are mediated not by CRF, but by a family of related Urocortin (Ucn) peptides Ucn1, Ucn2 and Ucn3. The initial narrow focus on CRF as the potential main player acting on CRF receptors appears outdated. Instead it is suggested that CRF and the individual Ucns act in a complementary and brain region-specific fashion to regulate anxiety-related behaviors and alcohol consumption. This review, based on a symposium held in 2011 at the research meeting on "Alcoholism and Stress" in Volterra, Italy, highlights recent evidence for regulation of these behaviors by Ucns. In studies on stress and anxiety, the roles of Ucns, and in particular Ucn1, appear more visible in experiments analyzing adaptation to stressors rather than testing basal anxiety states. Based on these studies, we propose that the contribution of Ucn1 to regulating mood follows a U-like pattern with both high and low activity of Ucn1 contributing to high anxiety states. In studies on alcohol use disorders, the CRF system appears to regulate not only dependence-induced drinking, but also binge drinking and even basal consumption of alcohol. While dependence-induced and binge drinking rely on the actions of CRF on CRFR1 receptors, alcohol consumption in models of these behaviors is inhibited by actions of Ucns on CRFR2. In contrast, alcohol preference is positively influenced by actions of Ucn1, which is capable of acting on both CRFR1 and CRFR2. Because of complex distribution of Ucns in the nervous system, advances in this field will critically depend on development of new tools allowing site-specific analyses of the roles of Ucns and CRF.

Characterization of Genetic Differences within the Centrally Projecting Edinger-Westphal Nucleus of C57BL/6J and DBA/2J Mice by Expression Profiling

Detailed examination of the midbrain Edinger–Westphal (EW) nucleus revealed the existence of two distinct nuclei. One population of EW preganglionic (EWpg) neurons was found to control oculomotor functions, and a separate population of EW centrally projecting (EWcp) neurons was found to contain stress- and feeding-related neuropeptides. Although it has been shown that EWcp neurons are highly responsive to drugs of abuse and behavioral stress, a genetic characterization of the EWcp was needed. To identify genetic differences in the EWcp of inbred mouse strains that differ in behaviors relevant to EWcp function, we used publicly available tools from the Allen Brain Atlas to identify 68 transcripts that were selectively expressed in the EWcp, and examined their expression within tissue punch microdissection samples containing the EWcp of adult male C57BL/6J (B6) and DBA/2J (D2) mice. Using 96-well quantitative real-time PCR (qPCR) arrays that included the EWcp-specific genes, several other genes of interest, and five housekeeping genes, we identified strain differences in expression of 11 EWcp-specific genes (BC023892, Btg3, Bves, Cart, Cck, Ghsr, Neto1, Postn, Ptprn, Rcn1, and Ucn), two immediate early genes (Egr1 and Fos), and one dopamine-related gene (Drd5). All significant expression differences were greater in B6 vs. D2 mice, and several of these were verified either at the protein level using immunohistochemistry (IHC) or in silico using microarray data sets from whole brain and other brain areas. These results demonstrate a significant advance in our understanding of the EWcp on three levels. First, we generated a list of EWcp-specific genes (most of which had not yet been reported within the EWcp in the literature) that will be informative for future studies of EWcp function. Second, due to similarity in results from qPCR and IHC, we revealed that strain differences in basal EWcp neuropeptide content are accounted for by differential transcription and number of peptidergic neurons, rather than by differential rates of peptide release. And third, our identification of differentially expressed EWcp-specific genes between B6 and D2 mice may hold powerful insight into the neurogenetic contributions of the EWcp to stress- and addiction-related behaviors.

The neurobiology of binge-like ethanol drinking: evidence from rodent models

Binge alcohol (ethanol) drinking is a destructive pattern of ethanol consumption that may precipitate ethanol dependence-a chronic, debilitating, and prevalent health problem. While an abundance of research has focused on the neurochemical underpinnings of ethanol dependence, relatively little is known about the mechanisms underlying the heavy consumption characteristic of binge ethanol drinking. Recently, a simple preclinical model termed "drinking in the dark" (DID) was developed to examine binge-like ethanol consumption in a rodent population. This assay capitalizes on the predisposition of C57BL/6J mice to voluntarily consume substantial quantities of a high concentration (20% v/v) ethanol solution, resulting in pharmacologically relevant blood ethanol concentrations (BECs). This review provides a comprehensive overview of recent literature utilizing this model to investigate the neuromodulatory systems that may influence binge ethanol drinking. Studies examining the glutamatergic and opioidergic systems not only provide evidence for these systems in the modulation of binge-like ethanol consumption, but also suggest this preclinical model has predictive validity and may be an appropriate tool for screening novel pharmacological compounds aimed at treating binge ethanol drinking in the human population. Additionally, this review presents evidence for the involvement of the GABAergic, dopaminergic, nicotinic, and endocannabinoid systems in modulating binge-like ethanol consumption. Finally, recent evidence shows that corticotropin-releasing factor (CRF), agouti-related protein (AgRP), neuropeptide Y (NPY), and ghrelin are also implicated as impacting this pattern of ethanol consumption.

Preclinical studies of alcohol binge drinking

Binge drinking is prevalent and has serious biomedical consequences. In children, adolescents, and young adults, it is a prominent risk factor for later development of alcohol-use disorders. Many preclinical models have been employed to study the genetic risks for and biomedical consequences of alcohol drinking. However, these models historically did not result in blood-alcohol concentrations (BACs) exceeding 80 mg%; this relatively modest level is the threshold that currently defines a binge session, according to the NIAAA and CDC. Nevertheless, in alcohol-dependent rodents, binge drinking has been well documented. Key neurobiological substrates localized to brain reward and stress systems have been identified. Studies of newer models of binge drinking without dependence are reviewed here. In these models, rodents, non-human primates, and flies will drink enough to reach high BACs. They often display observable signs of intoxication. The neurobiological consequences of these episodes of binge drinking without dependence are reviewed, and preliminary evidence for roles for GABA, glutamate, opioid peptides, and corticotropin releasing factor are discussed, as is the need for more work to identify the antecedents and consequences of binge drinking in both animal models and humans.

The complexity of alcohol drinking: studies in rodent genetic models

Risk for alcohol dependence in humans has substantial genetic contributions. Successful rodent models generally attempt to address only selected features of the human diagnosis. Most such models target the phenotype of oral administration of alcohol solutions, usually consumption of or preference for an alcohol solution versus water. Data from rats and mice for more than 50 years have shown genetic influences on preference drinking and related phenotypes. This paper summarizes some key findings from that extensive literature. Much has been learned, including the genomic location and possible identity of several genes influencing preference drinking. We report new information from congenic lines confirming QTLs for drinking on mouse chromosomes 2 and 9. There are many strengths of the various phenotypic assays used to study drinking, but there are also some weaknesses. One major weakness, the lack of drinking excessively enough to become intoxicated, has recently been addressed with a new genetic animal model, mouse lines selectively bred for their high and intoxicating blood alcohol levels after a limited period of drinking in the circadian dark. We report here results from a second replicate of that selection and compare them with the first replicate.

CRF-1 antagonist and CRF-2 agonist decrease binge-like ethanol drinking in C57BL/6J mice independent of the HPA axis

Recent evidence suggests that corticotropin-releasing factor (CRF) receptor (CRFR) signaling is involved in modulating binge-like ethanol consumption in C57BL/6J mice. In this report, a series of experiments were performed to further characterize the role of CRFR signaling in binge-like ethanol consumption. The role of central CRFR signaling was assessed with intracerebroventricular (i.c.v.) infusion of the nonselective CRFR antagonist, alpha-helical CRF(9-41) (0, 1, 5, 10 microg/1 microl). The contribution of central CRF type 2 receptor (CRF(2)R) signaling was assessed with i.c.v. infusion of the selective CRF(2)R agonist, urocortin (Ucn) 3 (0, 0.05, 0.1, or 0.5 microg/1 microl). The role of the hypothalamic-pituitary-adrenal (HPA) axis was assessed by pretreating mice with intraperitoneal (i.p.) injection of (1) the corticosterone synthesis inhibitor, metyrapone (0, 50, 100, 150 mg/kg) or (2) the glucocorticoid receptor antagonist, mifepristone (0, 25, 50 mg/kg), and (3) by using radioimmunoassay to determine whether binge-like ethanol intake influenced plasma corticosterone levels. Finally, we determined whether the ability of the CRF(1)R antagonist, CP-154,526 (CP; 0, 10, 15 mg/kg, i.p.), to blunt binge-like drinking required normal HPA axis signaling by comparing the effectiveness of CP in adrenalectomized (ADX) and normal mice. Results showed that i.c.v. infusion of a 1 microg dose of alpha-helical CRF(9-41) significantly attenuated binge-like ethanol consumption relative to vehicle treatment, and i.c.v. infusion of Ucn 3 dose-dependently blunted binge-like drinking. On the other hand, metyrapone nonselectively reduced both ethanol and sucrose consumption, mifepristone did not alter ethanol drinking, and binge-like drinking did not correlate with plasma corticosterone levels. Finally, i.p. injection of CP significantly attenuated binge-like ethanol intake in both ADX and normal mice. Together, these results suggest that binge-like ethanol intake in C57BL/6J mice is modulated by CRF(1)R and CRF(2)R signaling, such that blockade of CRF(1)R or activation of CRF(2)R effectively reduces excessive ethanol intake. Furthermore, normal HPA axis signaling is not necessary to achieve binge-like drinking behavior.

The role of CRF and CRF-related peptides in the dark side of addiction

Drug addiction is a chronically relapsing disorder characterized by a compulsion to seek and take drugs, the development of dependence, and the manifestation of a negative emotional state when the drug is removed. Activation of brain stress systems is hypothesized to be a key element of the negative emotional state produced by dependence that drives drug-seeking through negative reinforcement mechanisms, defined as the "dark side" of addiction. The focus of the present review is on the role of corticotropin-releasing factor (CRF) and CRF-related peptides in the dark side of addiction. CRF is a key mediator of the hormonal, autonomic, and behavior responses to stressors. Emphasis is placed on the role of CRF in extrahypothalamic systems in the extended amygdala, including the central nucleus of the amygdala, bed nucleus of the stria terminalis, and a transition area in the shell of the nucleus accumbens, in the dark side of addiction. The urocortin/CRF(2) systems have been less explored, but results suggest their role in the neuroadaptation associated with chronic drug use, sometimes in opposition to the effects produced by the CRF(1) receptor. Compelling evidence argues that the CRF stress system, including its activation of the hypothalamic-pituitary-adrenal axis, plays a key role in engaging the transition to dependence and maintaining dependence once it is initiated. Understanding the role of the CRF systems in addiction not only provides insight into the neurobiology of the dark side of addiction, but also provides novel targets for identifying vulnerability to addiction and the treatment of addiction.

Postnatal developmental profile of urocortin 1 and cocaine- and amphetamine-regulated transcript in the perioculomotor region of C57BL/6J mice

Urocortin 1 (Ucn 1) is an endogenous corticotropin releasing factor (CRF)-related peptide. Ucn 1 is most highly expressed in the perioculomotor urocortin containing neurons (pIIIu), previously known as the non-preganglionic Edinger-Westphal nucleus (npEW). Various studies indicate that these cells are involved in stress adaptation and the regulation of ethanol (EtOH) intake. However, the developmental trajectory of these neurons remained unexamined. Expression of the cocaine- and amphetamine-regulated transcript (CART), which co-localizes with Ucn 1 in the perioculomotor area (pIII) has been examined prenatally, but not postnatally. The goal of the current study was to characterize the ontogenetic profile of Ucn 1 and CART during postnatal development in C57BL/6J (B6) mice. B6 mice were bred, and brains were collected at postnatal days (PND) 1, 4, 8, 12, 16, 24 and 45. Brightfield immunohistochemical staining for Ucn 1 and CART showed that Ucn 1-immunoreactivity (ir) was absent at PND 1, while CART-ir was already apparent in pIIIu at birth, a finding indicating that although the pIIIu neurons have already migrated to their adult position, Ucn 1 expression is triggered in them at later postnatal stages. Ucn 1-ir gradually increased with age, approaching adult levels at PND 16. This developmental profile was confirmed by double-immunofluorescence, which showed that Ucn 1 was absent in CART-positive cells of pIII at PND 4 and that Ucn 1 and CART are strongly but not completely co-localized in pIII at PND 24. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis confirmed that Ucn 1 mRNA levels are significantly lower at PND 4 and PND 12 than in adult animals. The lack of brain Ucn 1 immunoreactivity at birth and the gradual postnatal increase in Ucn 1 in pIIIu suggests that this peptide plays a greater behavioral role in adulthood than during the early postnatal development of an organism.

Increased perioculomotor urocortin 1 immunoreactivity in genetically selected alcohol preferring rats

INTRODUCTION

Urocortin 1 (Ucn 1) is an endogenous peptide related to the corticotropin-releasing factor (CRF). Ucn 1 is mainly expressed in the perioculomotor area (pIII), and its involvement in alcohol self-administration is well confirmed in mice. In other species, the relationship between the perioculomotor Ucn 1-containing population of neurons (pIIIu) and alcohol consumption needs further investigation. The pIII also has a significant subpopulation of dopaminergic neurons. Because of dopamine's (DA) role in addiction, it is important to evaluate whether this subpopulation of neurons contributes to addiction-related phenotypes. Furthermore, the effects of gender on the relationship between Ucn 1 and tyrosine hydroxylase (TH) in pIII and alcohol preference in rats have not been previously assessed.

METHODS

To address these issues, we compared 2 Sardinian alcohol-preferring sublines of rats, a population maintained at the Scripps Research Institute (Scr:sP) and a population maintained at University of Camerino-Marchigian Sardinian preferring rats (msP), to corresponding nonselectively bred Wistar rats of both sexes. Ucn 1- and TH-positive cells were detected on coronal midbrain sections from 6- to 8-week-old alcohol-naïve animals using brightfield and fluorescent immunohistochemistry. Ucn 1- and TH-positive cells in pIII were counted in the perioculomotor area, averaged across 2 to 3 sets, and binned into 3 bregma levels.

RESULTS

Results demonstrated increased average counts of Ucn 1-positive cells in the middle bregma level in preferring male rats compared to Wistar controls and no difference in TH-positive cell counts in pIII. In addition, fluorescent double labeling revealed no colocalization of Ucn 1-positive and TH-positive neurons. Ucn 1 but not TH distribution was influenced by gender with female animals expressing more Ucn 1-positive cells than male animals in the peak bregma level.

CONCLUSIONS

These findings extend previous reports of increased Ucn 1-positive cell distribution in preferring lines of animals. They indicate that Ucn1 contributes to increased alcohol consumption across different species and that this contribution could be gender specific. The results also suggest that Ucn1 regulates positive reinforcing rather than aversive properties of alcohol and that these effects could be mediated by CRF(2) receptors, independent of direct actions of DA.

Stress-related neuropeptides and alcoholism: CRH, NPY, and beyond

This article summarizes the proceedings of a symposium held at the conference on "Alcoholism and Stress: A Framework for Future Treatment Strategies" in Volterra, Italy, May 6-9, 2008. Chaired by Markus Heilig and Roberto Ciccocioppo, this symposium offered a forum for the presentation of recent data linking neuropetidergic neurotransmission to the regulation of different alcohol-related behaviors in animals and in humans. Dr. Donald Gehlert described the development of a new corticotrophin-releasing factor receptor 1 antagonist and showed its efficacy in reducing alcohol consumption and stress-induced relapse in different animal models of alcohol abuse. Dr. Andrey Ryabinin reviewed recent findings in his laboratory, indicating a role of the urocortin 1 receptor system in the regulation of alcohol intake. Dr. Annika Thorsell showed data supporting the significance of the neuropeptide Y receptor system in the modulation of behaviors associated with a history of ethanol intoxication. Dr. Roberto Ciccocioppo focused his presentation on the nociceptin/orphanin FQ (N/OFQ) receptors as treatment targets for alcoholism. Finally, Dr. Markus Heilig showed recent preclinical and clinical evidence suggesting that neurokinin 1 antagonism may represent a promising new treatment for alcoholism. Collectively, these investigators highlighted the significance of neuropeptidergic neurotransmission in the regulation of neurobiological mechanisms of alcohol addiction. Data also revealed the importance of these systems as treatment targets for the development of new medication for alcoholism.

Central urocortin 3 administration decreases limited-access ethanol intake in nondependent mice

Stress and alcohol abuse are co-related. Acute alcohol is anxiolytic and stress is cited as a factor in relapse to alcohol use. A primary mediator of the stress response is the neuropeptide corticotropin-releasing factor (CRF). The CRF family of endogenous ligands includes urocortin 3 (Ucn 3), which binds selectively to the CRF type 2 receptor and has been implicated in ethanol consumption in dependent and withdrawing rats. The objective of this study was to examine the effect of Ucn 3, delivered centrally to nondependent mice, on limited-access ethanol consumption. Adult C57BL/6J mice were trained to self-administer 10% ethanol during daily, 2-h limited-access sessions, using lickometers to assess drinking patterns for both ethanol and water. Sterile saline or 0.3, 1, or 3 nmol of Ucn 3 was microinjected into the lateral ventricle immediately before the limited-access session in a within-subjects design. There was a significant decrease in ethanol (both ml and g/kg), but not water, intake following Ucn 3 treatment, explained by a change in size of the largest lick run. Food intake at both 2 h and 24 h after injection was statistically unaffected by Ucn 3 administration. These results establish a role for CRF type 2 receptors in a nondependent mouse model of ethanol self-administration.

Deletion of agouti-related protein blunts ethanol self-administration and binge-like drinking in mice

The melanocortin (MC) system is composed of peptides that are cleaved from the polypeptide precursor proopiomelanocortin (POMC). Recent pharmacological and genetic evidence suggests that melanocortin receptor (MCR) signaling modulates neurobiological responses to ethanol and ethanol intake. Agouti-related protein (AgRP) is synthesized by neurons in the arcuate nucleus of the hypothalamus and is a natural antagonist of MCRs. Because central administration of the functionally active AgRP fragment AgRP-(83-132) increases ethanol intake by C57BL/6 J mice, we determined if mutant mice lacking normal production of AgRP (AgRP(-/-)) and maintained on a C57BL/6 J genetic background would show reduced self-administration of ethanol relative to littermate wild-type (AgRP(+/+)) mice. AgRP(-/-) mice showed reduced 8% (v/v) ethanol-reinforced lever-pressing behavior relative to AgRP(+/+) mice in daily 2-h sessions, but normal sucrose-, saccharin- and water-reinforced lever-pressing. Similarly, AgRP(-/-) mice showed reduced consumption of 8% ethanol in a two-bottle limited access test (2 h/day), although this effect was largely sex-dependent. Using drinking-in-the-dark (DID) procedures, AgRP(-/-) mice showed blunted binge-like drinking of 20% (v/v) ethanol which was associated with lower blood ethanol levels (85 mg/dl) relative to AgRP(+/+) mice (133 mg/dl) after 4 h of intake. AgRP(-/-) mice showed normal ethanol metabolism and did not show altered sensitivity to the sedative effects of ethanol. These observations with genetically altered mice are consistent with previous pharmacological data and suggest that endogenous AgRP signaling modulates the reinforcing properties of ethanol and binge-like ethanol drinking.

Agonism of the endocannabinoid system modulates binge-like alcohol intake in male C57BL/6J mice: involvement of the posterior ventral tegmental area

Recent studies have indicated a role for the endocannabinoid system in the behavioral and physiological effects of alcohol (ethanol), particularly ethanol seeking behaviors. However, its role in modulating binge-like intake and/or the mechanism by which it may exert these effects remain poorly understood. The current study used a newly developed strain-specific animal model of binge drinking, dubbed 'Drinking In the Dark' (DID), to determine if facilitation of the endocannabinoid system with the synthetic cannabinoid agonist WIN 55-212,2 (WIN) modulates binge-like ethanol intake in male C57BL/6J (B6) mice. Based on the results of these systemic (i.p.) manipulations, and evidence in support of the involvement of subregions of the Ventral Tegmental Area (VTA) in governing self-administration of ethanol (Rodd-Henricks et al., (2000) Psychopharmacology (Berl) 149(3):217-224) as well as binge-like intake using the DID model (Moore & Boehm, (2009 Behav Neurosci 123(3):555-563), we extended these findings to evaluate the role of the endocannabinoid system within the anterior and posterior sub regions of the VTA using site-specific microinjections. Consistent with previous research, the lowest systemic dose of WIN (0.5 mg/kg) significantly increased ethanol intake in the first 30 minutes of access whereas the two highest doses (1 and 2 mg/kg) decreased ethanol intake within this time interval. Intra-posterior ventral tegmental area (pVTA) (but not aVTA (anterior ventral tegmental area) microinjections elicited time-dependent and dose-dependent increases (0.25 and 0.5 mug/side) and decreases (2.5 mug/side) in ethanol intake. Importantly, follow-up studies revealed that in some cases alterations in fluid consumption may have been influenced by competing locomotor activity (or inactivity). The present data are consistent with previous research in that agonism of the endocannabinoid system increases ethanol intake in rodents and implicate the pVTA in the modulation of drinking to intoxication. Moreover, the dose-dependent alterations in locomotor activity emphasize the importance of directly assessing multiple (possibly competing) behaviors when evaluating drug effects on voluntary consumption.

A line of mice selected for high blood ethanol concentrations shows drinking in the dark to intoxication

BACKGROUND

Many animal models of alcoholism have targeted aspects of excessive alcohol intake (abuse) and dependence. In the rodent, models aimed at increasing alcohol self-administration have used genetic or environmental manipulations, or their combination. Strictly genetic manipulations (e.g., comparison of inbred strains or targeted mutants, selective breeding) have not yielded rat or mouse genotypes that will regularly and voluntarily drink alcohol to the point of intoxication. Although some behavioral manipulations (e.g., scheduling or limiting access to alcohol, adding a sweetener) will induce mice or rats to drink enough alcohol to become intoxicated, these typically require significant food or water restriction or a long time to develop. We report progress toward the development of a new genetic animal model for high levels of alcohol drinking.

METHODS

High Drinking in the Dark (HDID-1) mice have been selectively bred for high blood ethanol concentrations (BEC, ideally exceeding 100 mg%) resulting from the ingestion of a 20% alcohol solution.

RESULTS

After 11 generations of selection, more than 56% of the population now exceeds this BEC after a 4-hour drinking session in which a single bottle containing 20% ethanol is available. The dose of ethanol consumed also produced quantifiable signs of intoxication.

CONCLUSIONS

These mice will be useful for mechanistic studies of the biological and genetic contributions to excessive drinking.

Review. Neurogenetic studies of alcohol addiction

Neurogenetic studies of alcohol dependence have relied substantially on genetic animal models, particularly rodents. Studies of inbred strains, selectively bred lines and mutants bearing genes whose function has been targeted for over or under expression are reviewed. Studies focused on gene expression changes are the most recent contributors to this literature, and some genetic effects may work through epigenetic mechanisms. In a few instances, interesting parallels have been revealed between genetic risk in humans and studies in non-human animal models. Future approaches are likely to be increasingly complex.

Acute effects of acamprosate and MPEP on ethanol Drinking-in-the-Dark in male C57BL/6J mice

BACKGROUND

Recently, a simple procedure in mice, Drinking-in-the-Dark (DID), was hypothesized to have value for medication development for human alcoholism. In DID, mice are offered intermittent, limited access to ethanol over a series of days during the dark phase that results in rapid drinking to intoxication in predisposed genotypes.

METHODS

We measured the effects of acamprosate or MPEP, metabotropic glutamate 5 receptor (mGluR5) antagonist, on intake of 20% ethanol, plain tap water or 10% sugar water using the DID procedure in male C57BL/6J mice.

RESULTS

Acamprosate (100, 200, 300, or 400 mg/kg) dose dependently decreased ethanol drinking with 300 mg/kg reducing ethanol intake by approximately 20% without affecting intake of plain water or 10% sugar water. MPEP (1, 3, 5, 10, 20, or 40 mg/kg) was more potent than acamprosate with 20 mg/kg reducing ethanol intake by approximately 20% and for longer duration without affecting intake of plain water or 10% sugar water.

CONCLUSIONS

These results support the hypothesis that mGluR5 signaling plays a role in excessive ethanol intake in DID and suggest DID may have value for screening novel compounds that reduce overactive glutamate signaling for potential pharmaceutical treatment of excessive ethanol drinking behavior.