Selective Effects of Alcohol Drinking on Restraint-Induced Expression of Immediate Early Genes in Mouse Brain

BACKGROUND: Analysis of immediate early gene expression in brain is a common contemporary method for mapping changes in neuronal activation with cellular resolution. This method has been applied previously in models of involuntary alcohol exposure. In this study, immunohistochemical expression analysis of immediate early genes c-fos, fosB, and zif268 was performed in brain of C57BL/6J mice after voluntary alcohol consumption. METHODS: Mice were trained to consume 10% ethanol/10% sucrose, using a 30-min limited-access paradigm. Animals consumed approximately 1.5 g/kg of ethanol per session. Control animals consumed 10% sucrose solution. Gene expression was determined in half of the animals 1.5 hr after the drinking session. Gene expression in the remaining animals was determined after 0.5 hr of restraint stress, which is known to elevate expression of immediate early genes in many brain regions. Analysis of the stressed animals was also performed 1.5 hr after the drinking session. RESULTS: Blood alcohol concentrations were significantly reduced in animals exposed to restraint stress. However, stressed mice showed the greatest alcohol-induced changes in gene expression. Specifically, animals consuming ethanol/sucrose with subsequent exposure to restraint stress had lower c-Fos expression in the CA3 region of hippocampus, and higher c-Fos expression in nucleus accumbens than mice exposed to restraint stress after drinking the sucrose solution. Consumption of the ethanol/sucrose solution also significantly reduced FosB expression in the basolateral amygdala and lateral hypothalamus, and Zif268 expression in the CA1 region of the hippocampus of stressed animals. CONCLUSIONS: These data confirm previous observations showing selective effects of alcohol administration on immediate early gene expression. Furthermore, the effects of voluntary alcohol self-administration on immediate early gene expression differ from involuntary alcohol exposure and suggest several brain regions as substrates for alcohol consumption.     

Oral Ethanol Self-Administration in Free-Feeding Rhesus Monkeys

The ability of a conditioning procedure to establish oral ethanol self-administration in free-feeding rhesus monkeys was assessed. The conditioning procedure required the monkey to drink an ethanol solution in order to have access to a sweet orange-flavored solution. Following an average of 14 sessions under these conditions, the orange solution was no longer delivered and ethanol solution alone was made available in the sessions. During both the conditioning and the ethanol self-administration portions of the experiment each monkey was required to drink an average of 0.5 g/kg ethanol per session in order to continue in the experiment. Of the nine monkeys exposed to these contingencies, five monkeys continued to self-administer ethanol after the presentation of the orange drink was discontinued. However, two of these five monkeys decreased their ethanol solution intake below 0.5 g/kg within 3 weeks after the conditioning sessions had terminated. The three monkeys that sustained high ethanol intake were male and had histories of drug self-administration, suggesting that gender and drug history may influence the initiation of ethanol self-administration. Once ethanol self-administration was established, concentrations of ethanol from 4 to 15% (v/v) were made available. The monkeys consumed intoxicating amounts of ethanol, as indicated by average intakes ranging from 0.5 to 0.9 g/kg and blood ethanol levels over 100 mg/dl. These results demonstrate that ethanol self-administration can be established and maintained through the initial reinforcement of ethanol consumption by the contingent presentation of another reinforcing stimulus. However, the results of this study also indicate that individual differences may be an important determinant of animals initiating ethanol self-administration.     

Corticotropin-releasing factor acting on corticotropin-releasing factor receptor type 1 is critical for binge alcohol drinking in mice

Background: The corticotropin‐releasing factor (CRF) system has been implicated in the regulation of alcohol consumption. However, previous mouse knockout (KO) studies using continuous ethanol access have failed to conclusively confirm this. Recent studies have shown that CRF receptor type 1 (CRFR1) antagonists attenuate alcohol intake in the limited access “drinking in the dark” (DID) model of binge drinking. To avoid the potential nonspecific effects of antagonists, in this study, we tested alcohol drinking in CRFR1, CRFR2, CRF, and urocortin 1 (Ucn1) KO and corresponding wild‐type (WT) littermates using the DID paradigm. Methods: On days 1 to 3, the CRFR1, CRFR2, Ucn1, and CRF KO mice and their respective WT littermates were provided with 20% ethanol or 10% sucrose for 2 hours with water available at all other times. On day 4, access to ethanol or sucrose was increased to 4 hours. At the end of each drinking session, the volume of ethanol consumed was recorded, and at the conclusion of the last session, blood was also collected for blood ethanol concentration (BEC) analysis. Results: CRFR1 KO mice had lower alcohol intakes and BECs and higher intakes of sucrose compared with WTs. In contrast, CRFR2 KO mice, while having reduced intakes initially, had similar alcohol intakes on days 2 to 4 and similar BECs as the WTs. To determine the ligand responsible, Ucn1 and CRF KO and WT mice were tested next. While Ucn1 KOs had similar alcohol intakes and BECs to their WTs, CRF KO mice showed reduced alcohol consumption and lower BECs compared with WTs. Conclusions: Our results confirm that CRFR1 plays a key role in binge drinking and identify CRF as the ligand critically involved in excessive alcohol consumption.     

Time Course of Acamprosate Action on Operant Ethanol Self-Administration after Ethanol Deprivation

The effects of the new alcohol anticraving compound acamprosate on the alcohol deprivation effect were tested in an operant two-lever free choice paradigm with concurrent water. Two groups of rats were tested after long-term voluntary ethanol self-administration: the "continuous access" group consisting of animals that had continuous access to ethanol before operant testing; and the "limited access" group that was tested only after ethanol deprivation. The limited access group exhibited a strong alcohol deprivation effect with immediate high ethanol consumption and preference. Acamprosate (100, 200, or 400 mg/kg) dose-dependently reduced lever pressing for ethanol and, accordingly, ethanol consumption in both groups in a 23-hr session. The consumption-reducing effect was still evident at the end of the session. Ethanol preference was dose-dependently reduced during the first hour of the session, but returned to basal levels before the end of the 23-hr session in both groups. Thus, the time course of preference reduction was not identical with that of the reduction of ethanol consumption. Surprisingly, preference reduction was observed only after a considerable amount of ethanol had been consumed. These results suggest that the specific effect of preference reduction depended on the simultaneous presence of sufficient levels of acamprosate and ethanol, and that the longer-lasting reduction of ethanol consumption was the consequence of this experience.     

Chronic ethanol consumption by C57BL/6 mice promotes tolerance to its interoceptive cues and increases extracellular dopamine, an effect blocked by naltrexone

BACKGROUND: C57BL/6 (B6) mice voluntarily consume ethanol. Although preingestive factors might be accountable, the fact that B6 mice voluntarily consume sufficient ethanol to set the conditions for an ethanol-deprivation effect suggest that post-ingestive pharmacological induced changes also occur. In this study, we determined the amounts of ethanol voluntarily consumed by B6 mice and associated blood ethanol levels (BEL), the effects of this consumption on extracellular dopamine (DA) and how this was altered by naltrexone, as well as on its interoceptive discriminative cues. METHODS: In experiment 1, the amounts of 12% ethanol consumed at 2, 4, and 6 hr into the active phase of the circadian cycle and associated BEL were determined. In experiment 2, dialysate samples were collected for 1 hr to establish basal DA levels. Mice were then injected with saline or naltrexone (6 mg/kg) and given access to water and 12% ethanol or to water only, and samples were collected at 20-min intervals for the next 2 hr. In experiment 3, mice were trained to discriminate ethanol's interoceptive cues via operant techniques, and half were given 3 weeks access to ethanol and water, the other half water only. Ethanol-consuming and water control mice were again tested for their ability to discriminate the drug's interoceptive cues. RESULTS: Mice ingested nearly 6 g/kg of ethanol and attained BEL near 100 mg/100 mL by 6 hr into the active phase. Ethanol intake at 2-hr into the dark phase was approximately 2.5 g/kg, and increased DA to approximately 100% above basal levels. Naltrexone reduced ethanol consumption and blocked the DA increase. Ethanol consumption for 3 weeks attenuated its discriminative cues. CONCLUSIONS: B6 mice voluntarily consume sufficient ethanol (1) to produce intoxicating BEL; (2) to increase DA levels in nucleus accumbens, an effect blocked by naltrexone; and (3) to attenuate its discriminative cues.     

Blood Ethanol Concentrations in Rats Drinking Sucrose/Ethanol Solutions

BACKGROUND: The addition of sucrose to ethanol solutions results in a substantial increase in ethanol self-administration by rats that are deprived of neither food nor water. However, if sucrose alters ethanol absorption or metabolism, resulting in blood ethanol concentrations (BECs) not different from those resulting from lower intakes of ethanol/water solutions, then the usefulness of sucrose/ethanol mixtures in increasing ethanol consumption is questionable. The present study was conducted to determine whether the addition of sucrose to ethanol solutions altered BECs in an operant self-administration paradigm. METHODS: Tail blood (from male Long-Evans rats) was collected 30 min after the intake of four different solutions, i.e., 5% sucrose/20% ethanol, 5% sucrose/10% ethanol, 2% sucrose/10% ethanol, and 10% ethanol. RESULTS: Ethanol intakes (mean, 1.57+/-0.21 g/kg) and BECs (mean, 78.4+/-9.3 mg/100 ml) were highest when 5% sucrose was added to the ethanol solution. Moreover, the ratios between ethanol intakes and resulting BECs were approximately the same for all solutions. CONCLUSIONS: These findings indicate that, under the conditions of this procedure, the BEC reached is dependent on the amount of ethanol consumed and is not influenced by the addition of sucrose to the solution.     

Antagonism of Ethanol Intoxication in Rats by Inhibitors of Phenylethanolamine N-Methyltransferase

The probable involvement of brain epinephrine in the expression of the acute sedative and intoxicating effects of ethanol and pentobarbital is demonstrated. Two selective inhibitors of phenylethanolamine N-methyltransferase (PNMT), LY134046 and LY78335, proved to be potent and long-lasting antagonists of ethanol intoxication in rats. Acute antagonism of pentobarbital-induced intoxication was observed with LY134046. The present results are compatible with a role for central epinephrine synthesis in ethanol and pentobarbital-induced sedation and intoxication in rats.     

The cyclic AMP/protein kinase A signal transduction pathway modulates tolerance to sedative and hypothermic effects of ethanol

Background: An expanding body of literature indicates the important role of the cAMP/PKA signaling pathway in establishing initial sensitivity to alcohol as well as being involved in certain forms of tolerance to ethanol. The use of mice with heterozygous inactivation of the Gnas gene encoding Gsα allowed us to explore the relationship between tolerance to ethanol and cAMP/PKA signaling. Methods: Mice with the targeted disruption of one Gsα allele were compared with wild‐type littermates in their initial sensitivity to ethanol‐induced sedation and hypothermia and then monitored for the development of tolerance during two subsequent bouts of intoxication. Components of the cAMP/PKA signaling pathway were analyzed in ethanol‐naïve mice and again following the development of tolerance to ethanol to better understand the contribution of this signaling pathway to the acquisition of tolerance. Results: During the initial exposure to ethanol, mice with the targeted disruption of one Gsα allele (Gnas) were more sensitive to the sedative effects of ethanol compared with wild‐type littermates. Wild‐type mice developed within‐session tolerance to ethanol‐induced hypothermia whereas Gnas mice did not. Following the subsequent ethanol treatments, wild‐type mice developed between‐session tolerance to the sedative effects of ethanol to a greater degree than mice with heterozygous inactivation of the Gnas gene. The development of tolerance to the sedative effects of ethanol was accompanied by increased expression of phospho‐CREB in the cerebellum, hippocampus, and frontal cortex. No changes in phospho‐CREB expression were detected in these brain regions in mice with heterozygous inactivation of the Gnas gene. Conclusion: The results show that cAMP/PKA signal transduction modulates sensitivity to sedative and hypothermic effects of ethanol. This signal transduction system also influences the acquisition of within‐session and between‐session tolerance. The mechanism through which cAMP/PKA signaling modulates the development of tolerance remains to be elucidated but may involve changes in phospho‐CREB expression.     

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.     

Circadian Timing of Ethanol Exposure Exerts Enduring Effects on Subsequent Ad Libitum Consumption in C57 Mice

Background:  There is a daily rhythm in the voluntary intake of ethanol in mice, with greatest consumption in the early night and lowest intake during the day. The role of daily timing of ethanol exposure on the development and control of long-term ethanol self-administration has been neglected. The present study examines these issues using C57BL/6J mice.
Methods:  Mice were repeatedly exposed to 10% ethanol for 2 hours early in the night or day for several weeks. Subsequently, ethanol was available at the opposite time (Expt 1) or 24 hours daily (Expts 1 and 2). Lick sensors recorded the patterns of drinking activity in Experiment 2.
Results:  Mice exposed to ethanol during the night drink more than mice exposed during the day. Prior history did not affect ethanol intake when the schedule was reversed. Under 24-hour exposure conditions, mice with a history of drinking during the night consumed significantly more than mice drinking during the day. The circadian patterns of drinking were not altered.
Conclusions:  These results demonstrate that the daily timing of ethanol exposure exerts enduring effects of self-administration of ethanol in mice. Understanding how circadian rhythms regulate ethanol consumption may be valuable for modifying subsequent intake.     

Breakpoint Determination and Ethanol Self-Administration Using an Across-Session Progressive Ratio Procedure in the Rat

BACKGROUND: Progressive ratio schedules are used to determine the "breakpoint" or limit to the amount of "work" that a subject is willing to perform to obtain a reinforcer. Reinforcing efficacy is inferred from the breakpoint values, which are typically measured in a single session by increasing the number of responses required for successive reinforcer presentations. This procedure is not feasible, however, when assessing the reinforcing efficacy of a substance that can change as a function of its physiological actions during self-administration, as in the case of ethanol. METHODS: The present study made use of a procedure that increased the response requirement across single daily sessions rather than within a session. Completion of the response requirement in each daily session resulted in the presentation of a drinking tube that allowed for self-administration of ethanol for a 20-min period. This procedure made possible the assessment of ethanol-directed appetitive (number of lever presses) and consummatory (number of licks and intake volume) behaviors. Reliable responding for 10% ethanol was initiated using sucrose-substitution on a fixed ratio (FR) 4 schedule in male Long Evans rats. Then four successive breakpoint determinations were made which were separated by a return to the FR4 schedule to re-establish baseline responding. RESULTS: The results indicated that there was an increase in breakpoint values from the first to the second determination, which was then stable over the following three determinations. Individual rats reached breakpoints as high as 240 lever presses to receive access to 10% ethanol and maintained ethanol intake over sessions in the 1.0 g/kg range. Ethanol intake (g/kg), however, was stable across all four determinations (mean 0.86 +/- 0.06 to 1.01 +/- 0.10). Moreover, ethanol intake was not related to the preceding appetitive responding, as no differences between intake on the session before a breakpoint (high FR) and the following baseline period (FR4) were observed. CONCLUSIONS: This model provides an assessment of the distinct mechanisms that mediate ethanol-seeking versus ethanol consumption in subjects that drink measurable amounts of ethanol, with the appetitive behaviors not altered by the pharmacological effects of ethanol.     

Preclinical Evaluation of Riluzole: Assessments of Ethanol Self-Administration and Ethanol Withdrawal Symptoms

Background:  Many of the neurobehavioral effects of ethanol are mediated by inhibition of excitatory N -methyl- d -aspartate (NMDA) and enhancement of inhibitory γ-amino-butyric-acid (GABA) receptor systems. There is growing interest in drugs that alter these systems as potential medications for problems associated with alcoholism. The drug riluzole, approved for treatment of amyotrophic lateral sclerosis (ALS), inhibits NMDA and enhances GABA_A receptor system activity. This study was designed to determine the preclinical efficacy of riluzole to modulate ethanol self-administration and withdrawal.
Methods:  Male C57BL/6J mice were trained to lever press on a concurrent fixed-ratio 1 schedule of ethanol (10% v/v) versus water reinforcement during daily 16-hour sessions. Riluzole (1 to 40 mg/kg, IP) was evaluated on ethanol self-administration after acute and chronic (2 week) treatment. To determine if riluzole influences ethanol withdrawal-associated seizures, mice were fed an ethanol-containing or control liquid diet for 18 days. The effects of a single injection of riluzole (30 mg/kg) were examined on handling-induced convulsions after ethanol withdrawal.
Results:  Acute riluzole (30 and 40 mg/kg) reduced ethanol self-administration during the first 4 hours of the session, which corresponds to the known pharmacokinetics of this drug. Ethanol self-administration was also reduced by riluzole after chronic treatment. Riluzole (30 mg/kg) significantly decreased the severity of ethanol-induced convulsions 2 hours after ethanol withdrawal.
Conclusions:  These results demonstrate that riluzole decreases ethanol self-administration and may reduce ethanol withdrawal severity in mice. Thus, riluzole may have utility in the treatment of problems associated with alcoholism.     

Intravenous Self-Administration of Ethanol in β-Endorphin-Deficient Mice

Extensive research on both human alcoholics and in animal models of alcoholism has implicated the release of endogenous opioids in the consumption of ethanol. Various experiments using opioid antagonists have indicated that these drugs cause both humans and animals to decrease their consumption of ethanol. However, it remains unclear exactly which of the endogenous opioids mediates the rewarding effects of ethanol. The present experiment used intravenous self-administration of ethanol to determine whether β -endorphin (BE)-deficient mice differed from wild-type (WT) mice in ethanol self-administration. The BE-deficient mice completely lack BE, but are otherwise similar to the WT mice. By using intravenous self-administration, we were able to rule out any ability of BE to mediate differences in ethanol consumption via palatability factors alone. Both types of mice were 7 generations backcrossed onto a C57BL/6J inbred strain background. During nine daily, 2-hr free-operant sessions, 14 BE-deficient and 17 WT mice could nosepoke for 75 mg/kg ethanol infusions delivered intravenously on an fixed-ratio 3 schedule with a 2-sec time-out after each reinforcer delivery. Reinforcer delivery occurred following nosepokes in only one of two holes. Contrary to what was expected, BE-deficient mice acquired selective operant responding for ethanol, whereas WT mice did not. Although the two genotypes did not differ in either operant or locomotor behavior during the first session, by the end of the nine sessions, BE deficient mice were reliably nosepoking for ethanol, whereas WT mice were not. These findings may indicate that BE is not essential for the postingestive reinforcing effects of ethanol in these animals.     

Initiation of Ethanol Reinforcement using a Sucrose-Substitution Procedure in Food- and Water-Sated Rats

Rats, maintained on free access to both food and water, were trained to press a lever to obtain a 20% sucrose solution. When presentation of the sucrose solution was maintaining responding, low ethanol concentrations were added to the solution. Over 25 sessions, the solution presented as reinforcement was gradually reduced in sucrose concentration until a 10% ethanol solution with no sucrose was presented. Following this initiation procedure, ethanol concentrations up to and including 40% ethanol were found to maintain responding. At the higher ethanol concentrations, the rats consumed doses of ethanol between 0.90 and 0.95 g/kg in the 30-min session. When a concurrent choice between ethanol and water was available in the operant chamber, the rats responded on the lever associated with 10% ethanol presentation. Home cage preference between ethanol and water was found to be altered following the operant ethanol experience with the rats acceptability for 10% ethanol increased prior to the start of the experiment. This initiation procedure provides another manner in which ethanol reinforcement can be instigated in animals that have not been either food- or fluid-deprived. It is hypothesized that mechanisms which may regulate the intravascular and intragastric self-administration of ethanol may also be operating when the oral route is employed.     

Effect of the selective NMDA NR2B antagonist, ifenprodil, on acute tolerance to ethanol-induced motor impairment in adolescent and adult rats

Background: Adolescent rats have been observed to be less sensitive than adults to a number of acute ethanol effects, including ethanol‐induced motor impairment. These adolescent insensitivities may be related in part to the more rapid emergence of within session (acute) tolerance in adolescents than adults. Adolescent‐related alterations in neural systems that serve as ethanol target sites, including changes in NMDA receptor subunit expression, may influence the responsiveness of adolescents to acute ethanol effects. This study explored the role of NMDA NR2B receptors in the development of acute tolerance to ethanol‐induced motor impairment in male adolescent [postnatal day (P)28–30] and adult (P68–70) Sprague–Dawley rats. Methods: Motor‐impairing effects of ethanol on the stationary inclined plane and blood ethanol concentrations (BECs) were examined following challenge at each age with a functionally equivalent ethanol dose (adolescents: 2.25 g/kg; adults: 1.5 g/kg). Data were collected at two postinjection intervals (10 or 60 minutes) to compare rate of recovery from ethanol intoxication with BEC declines using the Radlow approach ( Radlow, 1994 ) and changes in motor impairment/BEC ratios over time for assessing acute tolerance. Results: Both vehicle‐treated adolescent and adult animals showed similar acute tolerance development to the motor‐impairing effects of ethanol at these functionally equivalent doses on the stationary inclined plane, as indexed by an increasing time‐dependent dissociation between BECs and ethanol‐induced motor impairment, with motor impairment declining faster than BECs, as well as by significant declines in motor impairment/BEC ratios over time. Acute tolerance development was reliably blocked by administration of the NR2B antagonist, ifenprodil, (5.0 mg/kg), in adult rats, whereas adolescents were affected by a higher dose (10.0 mg/kg). Conclusions: These data support the suggestion that alterations in NMDA receptor systems occurring during adolescence may contribute to reduced sensitivity to ethanol by enhancing the expression of acute tolerance development in adolescents relative to adults.     

Ethanol consumption and place-preference conditioning in the alcohol-preferring C57BL/6 mouse: relationship with motor activity patterns

Ethanol place-preference conditioning (PC) was conducted in drug-naive and ethanol pre-exposed female and male C57BL/6J (C57) mice to assess whether environmental cues can develop positive incentive value for ethanol-preferring animals when associated with administration of ethanol. After 12 days episodic access to free-choice ethanol and/or water self-administration, mice received eight ethanol injections (1.75 g/kg/i.p.) 5 min before placement in their nonpreferred PC chamber and eight saline injections paired with their preferred chamber. Control mice received eight saline injections (20 ml/kg) in both their preferred and nonpreferred chambers. Mice of both sexes developed strong ethanol PC. Correlational analysis indicated that the strength of ethanol PC for mice with a prior ethanol drinking experience was inversely related to the amount of ethanol consumed regardless of gender. Furthermore, depending on gender and previous ethanol drinking experience, ethanol PC was differentially related to initial baseline motor activity, the initial motor response to ethanol, or rapid change in the motor response to ethanol. Thus, a complicated relationship between neural systems that mediate ethanol reward and motor activity may exist as suggested by current addiction theory.     

Increased consumption but not operant self-administration of ethanol in mice lacking the RIIbeta subunit of protein kinase A

BACKGROUND: Accumulating evidence indicates that adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) is involved in the neurobiological responses to ethanol. Previous reports indicate that mice lacking the RIIbeta subunit of PKA (RIIbeta(-/-)) voluntarily consume more ethanol than wild-type controls (RIIbeta(+/+)) using 2-bottle testing procedures. Although such procedures primarily measure consummatory behavior, operant self-administration procedures allow analysis of consummatory as well as appetitive or "ethanol-seeking" behavior (i.e., lever pressing is required to gain access to the ethanol solution). Therefore, we determined whether the high ethanol consumption characteristic of RIIbeta(-/-) mice would be complemented by increased appetitive ethanol-seeking behavior in an operant paradigm. METHODS: RIIbeta(-/-) (n=8) and RIIbeta(+/+) (n=8) mice were initially sucrose-faded until they were lever responding for nonsweetened ethanol (10, 14, and 18%). Following the self-administration testing, RIIbeta(+/+) and RIIbeta(-/-) mice were given access to 2 bottles, one containing water and the other ethanol to replicate the voluntary ethanol drinking data previously from our laboratory. Finally, immediately after voluntary consumption all mice were again tested for self-administration of 10% ethanol. Alterations in the reinforcement schedule were also explored as RIIbeta(+/+) and RIIbeta(-/-) mice were tested for self-administration of 10% ethanol at FR-3 and FR-5 schedules. RESULTS: The RIIbeta(-/-) mice displayed lower operant responding for ethanol and food reinforcement compared with RIIbeta(+/+) controls. However, this effect was driven by a significant increase in lever responses made by female RIIbeta(+/+) mice. When the excessive lever responses of the female RIIbeta(+/+) mice are accounted for, the RIIbeta(-/-) mice show ethanol lever responses comparable to controls. Following operant self-administration testing, RIIbeta(-/-) mice of both sexes consumed more ethanol solution compared with RIIbeta(+/+) mice during 2-bottle testing. CONCLUSIONS: Increased ingestion of ethanol by RIIbeta(-/-) mice is likely the result of altered PKA activity within neuronal pathways that control ethanol-consummatory behaviors. Conversely, the RIIbeta subunit of PKA appears not to play a critical role in neuronal pathways that regulate appetitive behaviors directed at obtaining ethanol. Finally, increased operant self-administration of food and ethanol by female wild-type mice was absent in female RIIbeta(-/-) mice, suggesting that normal PKA signaling may be part of a general, and sex-dependent, mechanism involved with reinforcement-seeking behavior.     

Development of an alcohol deprivation and escalation effect in C57BL/6J mice

BACKGROUND: Relapse-like drinking has been studied through the expression of the alcohol deprivation effect (ADE), which is measured by a pronounced increase in ethanol preference and consumption after imposed abstinence. No studies have characterized the ADE in C57BL/6J (B6) mice. The present study examined the effects of length and number of deprivations on the expression of the ADE in B6 mice. METHODS: Adult male B6 mice received 24-hour continuous access to ethanol and water for 6 weeks (baseline). Experiment 1 determined the ADE in mice receiving weekly access to 15% ethanol (i.e., exposed 1 day a week and deprived during the other 6 days) for a total of 10 weeks. Experiments 2 and 3 determined the ADE after a single 2-week deprivation period in mice receiving a single concentration of 15% ethanol or multiple concentrations of 7.5, 15, and 30% ethanol, respectively, followed by weekly access to their respective ethanol solutions for 10 weeks. Experiment 4 determined the ADE after a single 2-week deprivation period, followed by daily access to 15% ethanol. Mice never deprived of ethanol (i.e., continuous access) were used as age-matched drinking controls. RESULTS: The ADE was observed after the initial 6-day deprivation period and was profoundly enhanced (i.e., escalation of the ADE) following weekly reexposure to 15% ethanol. Compared with a single concentration of 15% ethanol, concurrent access to multiple ethanol concentrations resulted in a near 2-fold increase in baseline ethanol consumption. Regardless of having access to single or multiple concentrations of ethanol, the ADE was not observed immediately after a 2-week deprivation period. The ADE was observed (although to a lesser magnitude and duration) following weekly reexposure to single or multiple concentrations of ethanol. Alternatively, following a 2-week deprivation period, mice receiving daily access to 15% ethanol showed a significant decrease in ethanol intake and preference (i.e., negative ADE). CONCLUSIONS: Short-term deprivations followed by repeated intermittent (weekly) reexposure to ethanol produces a robust ADE in B6 mice. Increasing the initial deprivation length to 2 weeks produces various opposing effects, including erasure of an initial ADE, diminished expression and magnitude of the ADE following weekly exposure, and complete reversal of the ADE following daily exposure to ethanol.     

Effects of Ethanol on Hepatic Blood Flow in the Rat

Hepatic blood flow measured by indocyanine green clearance was studied in rats after an acute intoxicating dose of ethanol (2 g/kg) or after chronic ethanol administration by feeding with alcohol liquid diets. Acute intoxication to normal animals did not modify hepatic blood flow. In chronically alcohol-fed rats, hepatic blood flow was significantly decreased when measured after 15 hr of abstinence. If ethanol was not withdrawn and an acute dose of ethanol was given before the indocyanine green clearance, a decreased hepatic blood flow was not observed. It is suggested that the reduction of hepatic blood flow in recently abstinent chronically alcohol-treated animals is related to the withdrawal syndrome.