Mouse inbred strain differences in ethanol drinking to intoxication

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.

Reduced alcohol consumption in mice with access to a running wheel

Studies of the behavioral effects of alcohol in humans and rodent models have implicated a number of neurological pathways and genes. Separate studies have shown that certain regions of the brain are involved in behavioral responses to exercise. The aim of this study was to determine whether mice which normally voluntarily consume high amounts of alcohol (C57BL/6 strain) would exhibit reduced alcohol consumption when given access to a running wheel under two different models of voluntary consumption: unlimited access two-bottle choice and limited access drinking in the dark (DID). Under the two-bottle choice model, the animals voluntarily consumed less alcohol when a wheel was present in their cage. However, sex-specific differences emerged because female mice voluntarily consumed less alcohol when they have the opportunity to exercise on a running wheel, whereas male mice consumed less alcohol even if the running wheel was locked. There were no significant differences observed in alcohol metabolism or food consumption. Under the DID protocol, no differences in alcohol consumption were observed in the presence of a running wheel. These results suggest that exercise may be a useful approach to consider for treatment for some types of chronic human alcohol problem behaviors, but may be less applicable to human binge drinking.

Site-specific microinjection of baclofen into the anterior ventral tegmental area reduces binge-like ethanol intake in male C57BL/6J mice

The GABAB agonist baclofen has been shown to alter ethanol intake in human and animal studies (E. M. Moore et al., 2007). GABA-subB receptors are located within the ventral tegmental area (VTA; A. Imperato & G. DiChiara, 1986) and therefore may be involved in modulating voluntary ethanol intake. The present study assessed the effects of baclofen in a variation on a new mouse model of binge-like ethanol intake that takes advantage of the nocturnal nature of this species (J. S. Rhodes, K. Best, J. K. Belknap, D. A. Finn, & J. C. Crabbe, 2005; J. S. Rhodes et al., 2007). Baclofen or saline was microinjected into the anterior or posterior VTA of male C57BL/6J mice. Immediately afterward, mice were presented with ethanol, water, or sugar water using the Drinking in the Dark model, a procedure of fluid administration for 2 hr, 3 hr into the dark cycle). Fluid intake was recorded at 30, 60, 90, and 120 min; retro-orbital sinus bloods were sampled upon termination of the 120-min ethanol access period. Baclofen reduced binge-like ethanol intake when microinjected into the anterior VTA, whereas posterior VTA microinjections did not alter ethanol intake. Baclofen had no effect on water or sugar water intake when administered to anterior or posterior VTA. These results add to the growing literature suggesting that GABA-subB receptor systems are important in the modulation of binge-like ethanol intake and suggest that the GABA-subB receptor system may have different roles in anterior versus posterior VTA.

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.

Modulation of ethanol drinking-in-the-dark by mecamylamine and nicotinic acetylcholine receptor agonists in C57BL/6J mice

RATIONALE

Recent reports describe a restricted access ethanol consumption paradigm where C57Bl/6J mice drink until intoxicated. Termed "drinking in the dark" (DID), this paradigm has been used as a model of binge drinking. Although neuronal nicotinic acetylcholine receptors (nAChRs) have been implicated in alcohol drinking in rats pre-trained to self-administer ethanol, their role in binge-like ethanol consumption is unknown.

OBJECTIVES

To determine if nAChRs are involved in binge drinking as measured by the DID assay in C57Bl/6J mice.

MATERIALS AND METHODS

Adult male C57Bl/6J mice were injected i.p. with nicotinic receptor antagonists including mecamylamine, hexamethonium, dihydro-beta-erythroidine, and methyllycaconitine. Immediately following injection, mice were presented with 20% ethanol for 2 h in the DID assay to measure ethanol consumption. Nicotinic agonists including cytisine and nicotine were also evaluated. The effects of mecamylamine and nicotine on ethanol-induced dopaminergic neuronal activation in the VTA were evaluated via immunohistochemistry.

RESULTS

Mecamylamine dose dependently reduced ethanol consumption; whereas, the peripheral antagonist hexamethonium had no significant effect. Nicotinic agonists, cytisine and nicotine, reduced ethanol consumption. None of the effective nicotinic receptor drugs reduced sucrose drinking. Mecamylamine blocked ethanol activation of dopaminergic neurons while nicotine alone activated them without additional activation by ethanol.

CONCLUSIONS

Neuronal nAChRs are involved in ethanol consumption in the DID paradigm. The effects of mecamylamine, nicotine, and cytisine on ethanol intake appear to be specific because they do not reduce sucrose drinking. Mecamylamine reduces alcohol consumption by blocking activation of dopaminergic neurons; whereas, nicotinic agonists may activate the same reward pathway as alcohol.

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.

Chronic voluntary ethanol intake hypersensitizes 5-HT(1A) autoreceptors in C57BL/6J mice

Alcoholism is a complex disorder involving, among others, the serotoninergic (5-HT) system, mainly regulated by 5-HT(1A) autoreceptors in the dorsal raphe nucleus. 5-HT(1A) autoreceptor desensitization induced by chronic 5-HT reuptake inactivation has been associated with a decrease in ethanol intake in mice. We investigated here whether, conversely, chronic ethanol intake could induce 5-HT(1A) autoreceptor supersensitivity, thereby contributing to the maintenance of high ethanol consumption. C57BL/6J mice were subjected to a progressive ethanol intake procedure in a free-choice paradigm (3-10% ethanol versus tap water; 21 days) and 5-HT(1A) autoreceptor functional state was assessed using different approaches. Acute administration of the 5-HT(1A) receptor agonist ipsapirone decreased the rate of tryptophan hydroxylation in striatum, and this effect was significantly larger (+75%) in mice that drank ethanol than in those drinking water. Furthermore, ethanol intake produced both an increased potency (+45%) of ipsapirone to inhibit the firing of 5-HT neurons, and a raise (+35%) in 5-HT(1A) autoreceptor-mediated stimulation of [(35)S]GTP-gamma-S binding in the dorsal raphe nucleus. These data showed that chronic voluntary ethanol intake in C57BL/6J mice induced 5-HT(1A) autoreceptor supersensitivity, at the origin of a 5-HT neurotransmission deficit, which might be causally related to the addictive effects of ethanol intake.

Sizing up ethanol-induced plasticity: the role of small and large conductance calcium-activated potassium channels

Small (SK) and large conductance (BK) Ca(2+)-activated K(+) channels contribute to action potential repolarization, shape dendritic Ca(2+)spikes and postsynaptic responses, modulate the release of hormones and neurotransmitters, and contribute to hippocampal-dependent synaptic plasticity. Over the last decade, SK and BK channels have emerged as important targets for the development of acute ethanol tolerance and for altering neuronal excitability following chronic ethanol consumption. In this mini-review, we discuss new evidence implicating SK and BK channels in ethanol tolerance and ethanol-associated homeostatic plasticity. Findings from recent reports demonstrate that chronic ethanol produces a reduction in the function of SK channels in VTA dopaminergic and CA1 pyramidal neurons. It is hypothesized that the reduction in SK channel function increases the propensity for burst firing in VTA neurons and increases the likelihood for aberrant hyperexcitability during ethanol withdrawal in hippocampus. There is also increasing evidence supporting the idea that ethanol sensitivity of native BK channel results from differences in BK subunit composition, the proteolipid microenvironment, and molecular determinants of the channel-forming subunit itself. Moreover, these molecular entities play a substantial role in controlling the temporal component of ethanol-associated neuroadaptations in BK channels. Taken together, these studies suggest that SK and BK channels contribute to ethanol tolerance and adaptive plasticity.

Escalating ethanol intake is associated with altered corticostriatal BDNF expression

Alcoholism is a chronically relapsing condition, indicative of long-term neuronal adaptations maintaining the disease even after prolonged abstinence. Previously, we identified brain-derived neurotrophic factor (BDNF) in the dorsal striatum as the central mediator of a homeostatic mechanism which is activated by acute alcohol (ethanol) exposure and functions to decrease the sensitivity of rodents to ethanol-related behaviors. We hypothesized that extensive exposure to ethanol would result in dysregulation of this BDNF-mediated protective mechanism, accompanied by heightened ethanol intake. In this study, we demonstrate that while a single bout of ethanol intake increases BDNF mRNA expression in the dorsal striatum, this effect is no longer observed after 6 weeks of daily ethanol access. Additionally, 6 weeks of ethanol consumption decreases BDNF in the cortex, a main source of BDNF for the striatum. Importantly, these ethanol-induced changes in BDNF levels are not ameliorated by 2 weeks' abstinence. Together, these data suggest that the BDNF pathway, which is activated following a single bout of ethanol drinking, breaks down by the end of 6 weeks of access and does not recover its protective function after a 2-week deprivation period. These results suggest that the persistence of altered BDNF signaling may contribute to the inflexibility of addictive behaviors.

Effects of food availability and administration of orexigenic and anorectic agents on elevated ethanol drinking associated with drinking in the dark procedures

BACKGROUND

Drinking in the dark (DID) procedures have recently been developed to induce high levels of ethanol drinking in C57BL/6J mice, which result in blood ethanol concentrations reaching levels that have measurable affects on physiology and/or behavior. The present study determined if increased ethanol drinking associated with DID procedures may be motivated by caloric need rather than by the postingestive pharmacological effects of ethanol. To this end, food availability was manipulated or mice were given peripheral administration of orexigenic or anorectic agents during DID procedures.

METHODS

C57BL/6J had 2-hours of access to the 20% (v/v) ethanol solution beginning 3-hours into the dark cycle on days 1 to 3, and 4-hours of access to the ethanol bottle on day 4 of DID procedures. In Experiment 1, the effects of food deprivation on ethanol consumption during DID procedures was assessed. In Experiments 2 and 3, mice were given intraperitoneal (i.p.) injection of the orexigenic peptide ghrelin (0, 10 or 30 mg/kg) or the anorectic protein leptin (0 or 20 microg/g), respectively, before access to ethanol on day 4 of DID procedures. In Experiment 4, hourly consumption of food and a 0.05% saccharin solution were assessed over a period of hours that included those used with DID procedures.

RESULTS

Consistent with previous research, mice achieved blood ethanol concentrations (BECs) that ranged between 100 and 150 mg% on day 4 of DID experiments. Neither food deprivation nor administration of orexigenic or anorectic compounds significantly altered ethanol drinking with DID procedures. Interestingly, mice exhibited their highest level of food and saccharin solution consumption during hours that overlapped with DID procedures.

CONCLUSIONS

The present observations are inconsistent with the hypothesis that C57BL/6J mice consume large amounts of ethanol during DID procedures in order to satisfy a caloric need.

Using drinking in the dark to model prenatal binge-like exposure to ethanol in C57BL/6J mice

Animal models of prenatal ethanol exposure are necessary to more fully understand the effects of ethanol on the developing embryo/fetus. However, most models employ procedures that may produce additional maternal stress beyond that produced by ethanol alone. We employed a daily limited-access ethanol intake model called Drinking in the Dark (DID) to assess the effects of voluntary maternal binge-like ethanol intake on the developing mouse. Evidence suggests that binge exposure may be particularly harmful to the embryo/fetus, perhaps due to the relatively higher blood ethanol concentrations achieved. Pregnant females had mean daily ethanol intakes ranging from 4.2 to 6.4 g/kg ethanol over gestation, producing blood ethanol concentrations ranging from 115 to 182 mg/dL. This level of ethanol intake produced behavioral alterations among adolescent offspring that disappeared by adulthood, including altered sensitivity to ethanol's hypnotic actions. The DID model may provide a useful tool for studying the effects of prenatal ethanol exposure in mice.

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.

Identification of a BK channel auxiliary protein controlling molecular and behavioral tolerance to alcohol

Tolerance, described as the loss of drug effectiveness over time, is an important component of addiction. The degree of acute behavioral tolerance to alcohol exhibited by a naïve subject can predict the likelihood of alcohol abuse. Thus, the determinants of acute tolerance are important to understand. Calcium- and voltage-gated (BK) potassium channels, consisting of pore forming alpha and modulatory beta subunits, are targets of ethanol (EtOH) action. Here, we examine the role, at the molecular, cellular, and behavioral levels, of the BK beta4 subunit in acute tolerance. Single channel recordings in HEK-293 cells show that, in the absence of beta4, EtOH potentiation of activity exhibits acute tolerance, which is blocked by coexpressing the beta4 subunit. BK channels in acutely isolated medium spiny neurons from WT mice (in which the beta4 subunit is well-represented) exhibit little tolerance. In contrast, neuronal BK channels from beta4 knockout (KO) mice do display acute tolerance. Brain slice recordings showed tolerance to EtOH's effects on spike patterning in KO but not in WT mice. In addition, beta4 KO mice develop rapid tolerance to EtOH's locomotor effects, whereas WT mice do not. Finally, in a restricted access ethanol self-administration assay, beta4 KO mice drink more than their WT counterparts. Taken together, these data indicate that the beta4 subunit controls ethanol tolerance at the molecular, cellular, and behavioral levels, and could determine individual differences in alcohol abuse and alcoholism, as well as represent a therapeutic target for alcoholism.

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.

Ethanol intake patterns in female mice: influence of allopregnanolone and the inhibition of its synthesis

The neurosteroid allopregnanolone (ALLO) is a positive modulator of GABA(A) receptors that exhibits a psychopharmacological profile similar to ethanol (i.e., anxiolytic, sedative-hypnotic). Based on research suggesting that manipulation of ALLO levels altered ethanol self-administration in male rodents, the current studies determined whether exogenous ALLO administration or the inhibition of its synthesis in vivo modulated ethanol intake patterns in female C57BL/6J mice. Lickometer circuits collected temporal lick records of ethanol (10%, v/v) and water consumption during daily 2h limited access sessions. Following the establishment of stable ethanol intake, studies examined the effect of an acute ALLO challenge (3.2-24.0 mg/kg) or a 7-day blockade of ALLO production with finasteride (FIN; 50 or 100 mg/kg) on ethanol intake in a within-subjects design. In contrast to results in male mice, ethanol dose (g/kg), ethanol preference and most of the bout parameters were unaltered by ALLO pretreatment in female mice. Ethanol intake in females also was recalcitrant to 7-day treatment with 50 mg/kg FIN, whereas 100 mg/kg FIN significantly reduced the ethanol dose consumed by 35%. The FIN-attenuated ethanol intake was attributable to a significant decrease in bout frequency (up to 45%), with lick patterns indicating reduced maintenance of consumption throughout the 2-h session. FIN also produced a dose-dependent decrease in brain ALLO levels. In conjunction with data in male mice, the present findings indicate that there are sex differences in the physiological regulation of ethanol intake patterns by GABAergic neurosteroids.

Increase in free choice oral ethanol self-administration in catechol-o-methyltransferase gene-disrupted male mice

The effect of catechol-O-methyltransferase (Comt) gene disruption on the voluntary oral consumption of water, ethanol (2.5-20%, v/v) and cocaine (0.1-0.8 mg/ml) was studied in the free-choice, two-bottle paradigm in male and female mice. Solutions containing ethanol or cocaine, or tap water were available ad libitum from drinking burettes for 4 weeks. Catechol-O-methyltransferase-deficient male mice consumed significantly more ethanol than their wild-type male littermates. In contrast, female mice did not show genotype differences in the consumption of ethanol solutions. During the cocaine experiment, male mice developed either a side preference or an aversion that obscured cocaine consumption. This pattern of drinking was not dependent on Comt genotype. In female mice, Comt genotype was not associated with cocaine consumption. In conclusion, disruption of Comt gene influenced ethanol consumption in a gender-dependent manner in mice, supporting the hypothesis that low catechol-O-methyltransferase activity is one of the predisposing factors for high alcohol consumption in males.

Intact neurogenesis is required for benefits of exercise on spatial memory but not motor performance or contextual fear conditioning in C57BL/6J mice

The mammalian hippocampus continues to generate new neurons throughout life. Experiences such as exercise, anti-depressants, and stress regulate levels of neurogenesis. Exercise increases adult hippocampal neurogenesis and enhances behavioral performance on rotarod, contextual fear and water maze in rodents. To directly test whether intact neurogenesis is required for gains in behavioral performance from exercise in C57BL/6J mice, neurogenesis was reduced using focal gamma irradiation (3 sessions of 5 Gy). Two months after treatment, mice (total n=42 males and 42 females) (Irradiated or Sham), were placed with or without running wheels (Runner or Sedentary) for 54 days. The first 10 days mice received daily injections of bromodeoxyuridine (BrdU) to label dividing cells. The last 14 days mice were tested on water maze (two trials per day for 5 days, then 1 h later probe test), rotarod (four trials per day for 3 days), and contextual fear conditioning (2 days), then measured for neurogenesis using immunohistochemical detection of BrdU and neuronal nuclear protein (NeuN) mature neuronal marker. Consistent with previous studies, in Sham animals, running increased neurogenesis fourfold and gains in performance were observed for the water maze (spatial learning and memory), rotarod (motor performance), and contextual fear (conditioning). These positive results provided the reference to determine whether gains in performance were blocked by irradiation. Irradiation reduced neurogenesis by 50% in both groups, Runner and Sedentary. Irradiation did not affect running or baseline performance on any task. Minimal changes in microglia associated with inflammation (using immunohistochemical detection of cd68) were detected at the time of behavioral testing. Irradiation did not reduce gains in performance on rotarod or contextual fear, however it eliminated gain in performance on the water maze. Results support the hypothesis that intact exercise-induced hippocampal neurogenesis is required for improved spatial memory, but not motor performance or contextual fear in C57BL/6J mice.

Voluntary ethanol consumption in 22 inbred mouse strains

Inbred strains are genetically stable across time and laboratories, allowing scientists to accumulate a record of phenotypes, including physiological characteristics and behaviors. To date, the C57/C58 family of inbred mouse strains has been identified as having the highest innate ethanol consumption, but some lineages have rarely or never been surveyed. Thus, the purpose of the present experiment was to measure ethanol preference and intake in 22 inbred mouse strains, some of which have never been tested for ethanol consumption. Male and female mice (A/J, BALB/cByJ, BTBR+T(tf/tf), BUB/BnJ, C57BL/6J, C57BLKS/J, C58/J, CZECH/Ei, DBA/2J, FVB/NJ, I/LnJ, LP/J, MA/MyJ, NOD/LtJ, NON/LtJ, NZB/B1NJ, NZW/LacJ, PERA/Ei, RIIIS/J, SEA/GnJ, SM/J, and 129S1/SvlmJ) were individually housed and given unlimited access in a two-bottle choice procedure to one bottle containing tap water and a second containing increasing concentrations of ethanol (3%, 6%, 10%), 0.2% saccharin, and then increasing concentrations of ethanol (3%, 6%, 10%) plus 0.2% saccharin. Mice were given access to each novel solution for a total of 4 days, with a bottle side change every other day. Consistent with previous studies, C57BL/6J (B6) mice consumed an ethanol dose of >10g/kg/day whereas DBA/2J (D2) mice consumed <2g/kg/day. No strain voluntarily consumed greater doses of ethanol than B6 mice. Although the C58 and C57BLKS strains showed high ethanol consumption levels that were comparable to B6 mice, the BUB and BTBR strains exhibited low ethanol intakes similar to D2 mice. The addition of 0.2% saccharin to the ethanol solutions significantly increased ethanol intake by most strains and altered the strain distribution pattern. Strong positive correlations (rs> or =0.83) were determined between consumption of the unsweetened versus sweetened ethanol solutions. Consumption of saccharin alone was significantly positively correlated with the sweetened ethanol solutions (rs=0.62-0.81), but the correlation with unsweetened ethanol solutions was considerably lower (rs=0.37-0.45). These results add new strains to the strain mean database that will facilitate the identification of genetic relationships between voluntary ethanol consumption, saccharin preference, and other phenotypes.

Dissociable effects of ethanol consumption during the light and dark phase in adolescent and adult Wistar rats

In adolescence, high levels of drinking over short episodes (binge drinking) is commonly seen in a proportion of the population. Because adolescence is an important neurodevelopmental period, the effects of binge drinking on brain and behavior has become a significant health concern. However, robust animal models of binge drinking in rats are still being developed and therefore further efforts are needed to optimize paradigms for inducing maximal self-administration of alcohol. In the present experiment, 1-h limited-access self-administration sessions were instituted to model excessive drinking behavior in adolescent and adult Wistar rats. In addition to age, the involvement of sex and phase within the light/dark cycle (i.e., drinking in the light or dark) on sweetened 5% ethanol intake were also evaluated over 14 limited-access sessions using a between-groups design. The results of the experiment showed that over 14 limited-access sessions, sweetened ethanol intake (g/kg) was significantly higher for adolescents compared to adults. Females were also found to drink more sweetened ethanol as compared to males. Additionally, drinking in the light produced a robust increase in sweetened ethanol intake (g/kg) in adolescents, as compared to adults during the light phase and as compared to both adolescent and adult rats drinking in the dark. Furthermore, the increase in ethanol consumption observed in adolescents drinking during the light phase was dissociable from sweetened solution intake patterns. These results identify that age, sex, and time of day all significantly influence consumption of sweetened ethanol in Wistar rats. Knowledge of these parameters should be useful for future experiments attempting to evaluate the effects of self-administered ethanol exposure in adult and adolescent rats.

Blockade of the corticotropin releasing factor type 1 receptor attenuates elevated ethanol drinking associated with drinking in the dark procedures

BACKGROUND

Drinking in the dark (DID) procedures have recently been developed to induce high levels of ethanol drinking in C57BL/6J mice, which result in blood ethanol concentrations (BECs) reaching levels that have measurable affects on physiology and/or behavior. The present experiments determined whether the increased ethanol drinking caused by DID procedures can be attenuated by pretreatment with CP-154,526; a corticotropin releasing factor type-1 (CRF1) receptor antagonist.

METHODS

In Experiment 1, male C57BL/6J mice received ethanol (20% v/v) in place of water for 4 hours, beginning with 3 hours into the dark cycle. On the fourth day, mice were given an intraperitoneal injection of one of the 4 doses of CP-154,526 (0, 1, 3, 10 mg/kg) 30 minutes before receiving their ethanol bottle. In Experiment 2, C57BL/6J mice had 2 hours of access to the 20% ethanol solution, beginning with 3 hours into the dark cycle on days 1 to 3, and 4 hours of access to the ethanol bottle on day 4 of DID procedures. Mice were given an intraperitoneal injection of one of the 4 doses of CP-154,526 (0, 1, 3, 10 mg/kg) 30 minutes before receiving their ethanol bottle on day 4. Tail blood samples were collected immediately after the 4-hour ethanol access period on the fourth day of each experiment. Additional control experiments assessed the effects of CP-154,526 on 4-hour consumption of a 10% (w/v) sucrose solution and open-field locomotor activity.

RESULTS

In Experiment 1, the vehicle-treated group consumed approximately 4.0 g/kg/4 h of ethanol and achieved BECs of approximately 30 mg%. Furthermore, pretreatment with the CRF1 receptor antagonist did not alter ethanol consumption. On the other hand, procedures used in Experiment 2 resulted in vehicle-treated mice consuming approximately 6.0 g/kg/4 h of ethanol with BECs of about 80 mg%. Additionally, the 10 mg/kg dose of CP-154,526 significantly reduced ethanol consumption and BECs to approximately 3.0 g/kg/4 h and 27 mg%, respectively, relative to vehicle-treated mice. Importantly, the 10 mg/kg dose of the CRF1R antagonist did not significantly alter 4-hour sucrose consumption or locomotor activity.

CONCLUSIONS

These data indicate that CRF1R signaling modulates high, but not moderate, levels of ethanol drinking associated with DID procedures.

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

Previous studies using genetic and lesion approaches have shown that the neuropeptide urocortin 1 (Ucn1) is involved in regulating alcohol consumption. Ucn1 is a corticotropin releasing factor (CRF) -like peptide that binds CRF1 and CRF2 receptors. Perioculomotor urocortin-containing neurons (pIIIu), also known as the non-preganglionic Edinger-Westphal nucleus, are the major source of Ucn1 in the brain and are known to innervate the lateral septum. Thus, the present study tested whether Ucn1 could regulate alcohol consumption through the lateral septum. In a series of experiments Ucn1 or CRF was bilaterally injected at various doses into the lateral septum of male C57BL/6J mice. Consumption of 20% volume/volume ethanol or water was tested immediately after the injections using a modification of a 2-h limited access sweetener-free "drinking-in-the-dark" procedure. Ucn1 significantly suppressed ethanol consumption when administered prior to the third ethanol drinking session (the expression phase of ethanol drinking) at doses as low as 6 pmol. Ethanol intake was differentially sensitive to Ucn1, as equivalent doses of this peptide did not suppress water consumption. In contrast, CRF suppressed both ethanol and water intake at 40 and 60 pmol, but not at lower doses. Repeated administration of Ucn1 during the acquisition of alcohol consumption showed that 40 pmol (but not 2 or 0.1 pmol) significantly attenuated ethanol intake. Repeated administration of Ucn1 also resulted in a decrease of ethanol intake in sham-injected animals, a finding suggesting that the suppressive effect of Ucn1 on ethanol intake can be conditioned. Taken together, these studies confirm the importance of lateral septum innervation by Ucn1 in the regulation of alcohol consumption.

The relationship between PROP and ethanol preferences: an evaluation of 4 inbred mouse strains

Ethanol's taste attributes undoubtedly contribute to the development of drug preference. Ethanol's taste is both sweet and bitter. Taster status for bitter 6-n-propylthiouracil (PROP) has been proposed as a genetic marker for alcoholism; however, human results are conflicting. We collected preference scores for both tastants in 4 mouse strains selected on the basis of previously reported taste preference, with the generally accepted idea that inbred mice show minimal within-strain variation. Eighty-eight male mice (22 per strain) participated. The strains were as follows: C57BL/6J, ethanol preferring; BALB/cJ, ethanol avoiding; SWR/J, PROP avoiding; and C3HeB/FeJ, PROP neutral. Using a brief-access (1-min trials) 2-bottle preference test, we assessed the taste response of each strain to PROP and ethanol on separate days. Although PROP avoiding versus neutral mice could be segregated into significantly different populations, this was not the case for ethanol avoiding versus preferring mice, and all strains showed high variability. On average, only BALB/cJ, SWR/J, and C3HeB/FeJ mice conformed to their literature-reported preferences; nonetheless, there were a substantial number of discordant animals. C57BL/6J did not conform to previous results, indicating that they are ethanol preferring. Finally, we did not observe a significant relationship between PROP and ethanol preferences across strains. The high variability per strain and the number of animals in disagreement with their respective literature-reported preference raise concerns regarding their utility for investigations underlying mechanisms of taste-mediated ingestive responses. Absent postingestive consequences, the brief-access results suggest a possible degree of previously masked polymorphisms in taste preferences or a more recent drift in underlying genetic factors. The absence of a relationship between PROP and ethanol indicates that the bitter quality in ethanol may be more highly related to other bitter compounds that are mediated by different genetic influences.

GABAergic modulation of binge-like ethanol intake in C57BL/6J mice

GABA receptor systems have long been implicated in alcoholism, and GABAergic drugs have demonstrated efficacy in altering alcohol intake in some rodent models. The present study was designed to assess the effects of baclofen, muscimol, and gaboxadol (THIP) in a variation on a new mouse model of binge-like ethanol intake. Three hours into their dark cycle, male and female C57BL/6J mice were given access to a 20% unsweetened ethanol solution for 2 h each day, for four days. On day five, mice received varying doses of baclofen, muscimol or THIP and were allowed access to 20% ethanol for 60 min. Baclofen dose-dependently increased binge-like ethanol intake, while both muscimol and THIP reduced ethanol intake. Subsequent studies testing the effect of baclofen, muscimol and THIP on water intake using the same procedure revealed that whereas baclofen had no significant effect, muscimol and THIP both reduced the measure. These results add to the growing literature suggesting a role for GABA receptor systems in the modulation of ethanol intake. However, whereas the role of GABA(B) receptor systems seems selective in the modulation of binge-like ethanol intake, the role for GABA(A) receptor systems appears to also extend to general fluid intake.

Acute effects of naltrexone and GBR 12909 on ethanol drinking-in-the-dark in C57BL/6J mice

RATIONALE

Recently, a simple procedure was described, drinking in the dark (DID), in which C57BL/6J mice self-administer ethanol to the point of intoxication. The test consists of replacing the water with 20% ethanol in the home cage for 2 or 4 h early during the dark phase of the light/dark cycle.

OBJECTIVES

To determine whether the model displays predictive validity with naltrexone, and whether opioid or dopaminergic mechanisms mediate excessive drinking in the model.

MATERIALS AND METHODS

Naltrexone or GBR 12909 were administered via intraperitoneal injections immediately before offering ethanol solutions, plain tap water, or 10% sugar water to male C57BL/6J mice, and consumption was monitored over a 2- or 4-h period using the DID procedure.

RESULTS

Naltrexone (0.5, 1, or 2 mg/kg) dose dependently decreased ethanol drinking but these same doses had no significant effect on the consumption of plain water or 10% sugar water. GBR 12909 (5, 10, and 20 mg/kg) dose dependently reduced the consumption of ethanol and sugar water but had no effect on plain water drinking.

CONCLUSIONS

The DID model demonstrates predictive validity. Both opioid and dopamine signaling are involved in ethanol drinking to intoxication. Different physiological pathways mediate high ethanol drinking as compared to water or sugar water drinking in DID. DID may be a useful screening tool to find new alcoholism medications and to discover genetic and neurobiological mechanisms relevant to the human disorder.

Increased Drinking During Withdrawal From Intermittent Ethanol Exposure Is Blocked by the CRF Receptor Antagonist d-Phe-CRF(12?41)

BACKGROUND

Studies in rodents have determined that intermittent exposure to alcohol vapor can increase subsequent ethanol self-administration, measured with operant and 2-bottle choice procedures. Two key procedural factors in demonstrating increased alcohol intake are the establishment of stable alcohol self-administration before alcohol vapor exposure and the number of bouts of intermittent vapor exposure. The present studies provide additional behavioral validation and initial pharmacological validation of this withdrawal-associated drinking procedure.

METHODS

Studies at 2 different sites (Portland and Scripps) examined the effect of intermittent ethanol vapor exposure (3 cycles of 16 hours of ethanol vapor+8 hours air) on 2-hour limited access ethanol preference drinking in male C57BL/6 mice. Separate studies tested 10 or 15% (v/v) ethanol concentrations, and measured intake during the circadian dark. In one study, before measuring ethanol intake after the second bout of intermittent vapor exposure, mice were tested for handling-induced convulsions (HICs) indicative of physical dependence on ethanol. In a second study, the effect of bilateral infusions of the corticotropin-releasing factor (CRF) receptor antagonist D-Phe-CRF(12-41) (0.25 microg/0.5 microL) into the central nucleus of the amygdala (CeA) on ethanol intake was compared in vapor-exposed animals and air controls.

RESULTS

Intermittent ethanol vapor exposure significantly increased ethanol intake by 30 to 40%, and the mice had higher blood ethanol concentrations than controls. Intra-amygdala infusions of D-Phe-CRF(12-41) significantly decreased the withdrawal-associated increase in ethanol intake without altering ethanol consumption in controls. Following the second bout of intermittent vapor exposure, mice exhibited an increase in HICs, when compared with their own baseline scores or the air controls.

CONCLUSIONS

Intermittent alcohol vapor exposure significantly increased alcohol intake and produced signs of physical dependence. Initial pharmacological studies suggest that manipulation of the CRF system in the CeA can block this increased alcohol intake.