Additive Reduction of Alcohol Drinking by 5-HT1A Antagonist WAY 100635 and Serotonin Uptake Blocker Fluoxetine in Alcohol-Preferring P Rats

We found previously that alcohol-preferring (P) rats have fewer serotonin (5-HT) neurons and fibers in key brain regions than alcoholnonpreferring (NP) rats. Because 5-HT uptake blockers increase synaptic 5-HT content and 5-HT_1A receptor antagonists increase 5-HT release by disinhibiting 5-HT autoinnervation, in the present study, our intent was to determine whether increased synaptic 5-HT content and/or 5-HT release in P rats would effectively reduce alcohol consumption. In experiment 1, the 5-HT antagonist WAY 100635 (WAY) was tested on adult female P rats maintained on 24-hr free-choice access to ethanol (10% v/v) and water. Twice daily doses of WAY (0.05, 0.1, 0.5, and 1.0 mg/kg, subcutaneously) were administered to each rat in a counterbalanced order. Baseline ethanol intake, derived from the mean ethanol intakes of the three previous non-drug days, was approximately 8 g/kg/day. Results indicated that 0.05,0.1, and 0.5 mg/kg doses of WAY reduced 24-hr ethanol drinking by 25-30% ( p < 0.01) without affecting 24-hr water intake or body weight In the second experiment, the effects of WAY (0.5 mg/kg), fluoxetine (1.0 mg/kg), or a combination of both were tested in another group of female P rats. WAY and fluoxetine, each alone, reduced ethanol drinking by around 20% and, when combined, decreased ethanol intake by 50%, whereas the body weight and the total fluid intake were not significantly affected. Taken together, these results indicate that both fluoxetine and WAY preferentially reduce ethanol drinking in the P line of rats and, when administered together, reduce ethanol intake in an additive manner. It is proposed that coadministration of these two compounds with distinct mechanisms of action may be a new strategy for reducing alcohol intake.     

The Alcohol Deprivation Effect in the Alcohol-Preferring P Rat under Free-Drinking and Operant Access Conditions

The alcohol-deprivation effect (ADE) was examined under 4-hr operant and 24-hr free-choice alcohol access in the alcohol-preferring (P) rat after deprivation intervals from 2 to 4 weeks. Results indicated that adult male P rats responding for 6 weeks on a concurrent FR-5/ FR-1 schedule of reinforcement for alcohol and water, respectively, and then deprived of alcohol for 2 weeks, demonstrated a 40% increase in alcohol responding during the first 60 min of alcohol reinstatement. The alcohol deprivation effect was temporary, however, as responding did not differ from baseline levels on the second day of reinstatement. In a second experiment, weanling male and female P rats received 7 weeks of continuous access to alcohol, beginning at 21 days of age, and were then deprived of alcohol for 4 weeks. On the first day of alcohol reinstatement, P rats exhibited a 40% to 45% increase from baseline alcohol drinking levels, with alcohol intake returning to baseline levels by the 3rd day of reinstatement. Although alcohol intake was higher in females than in males when adjustment was made for body weight, there were no gender differences in the magnitude of the alcohol deprivation effect. Taken together, these results indicate that the ADE is a long-lasting phenomenon that occurs under both operant and continuous access conditions in the P rat, and thus these rats may be useful models for the study of factors involved in relapse of alcohol drinking.     

Responding for Oral Ethanol after Naloxone Treatment by Alcohol-Preferring AA Rats

The present study examined the effect of a relatively nonselective opioid antagonist, naloxone, on lever pressing for oral ethanol by the alcohol-preferring AA rats. The AAs, housed continually in operant chambers with free access to food and water, learned to respond for 10% oral ethanol during daily 60-min alcohol access periods indicated by a stimulus light. The rats developed stable ethanol responding, resulting in mean ethanol intakes of 1.2 g/kg/60 min and measurable blood alcohol levels. In the first experiment, single systemic injections of naloxone (0.05–2.5 mg/kg) had no effect on the initial rate of responding; dose-dependent decreases were observed later during the alcohol access. The second experiment examined the effects of repeated injections of 0.5 and 2.5 mg/kg naloxone on 5 consecutive days. Naloxone suppressed responding dose-relatedly over the treatment days. In contrast to the effects of single injections, repeated injections with 2.5 mg/kg naloxone produced progressive decreases within the first minutes of access. The results suggest that naloxone may attenuate the reinforcing actions of ethanol.     

The gamma-aminobutyric acid-B receptor agonist baclofen attenuates responding for ethanol in ethanol-dependent rats

BACKGROUND: Gamma-aminobutyric acid-B (GABA(B)) receptor agonists have been shown to suppress operant self-administration of ethanol in nondependent rats. However, little work has focused on the effects of GABA(B) receptor agonists on self-administration of ethanol in dependent animals. METHODS: In the present experiment, the GABA(B) receptor agonist baclofen was tested for the ability to modulate both fixed- (FR) and progressive-ratio (PR) responding for ethanol in rats while nondependent and subsequently after ethanol dependence induction. Following the acquisition and stabilization of baseline operant ethanol self-administration and after dependence induction, baclofen [0.0, 0.5, 1, 2, and 4 mg/kg, intraperitoneal (IP)] was tested on FR-1 responding for ethanol. The ability of baclofen (2.0 mg/kg) to affect responding under a PR schedule of reinforcement was also evaluated. Dependence was induced in the animals by subjecting them to a 1-month intermittent vapor-exposure period in which animals were exposed to ethanol vapor for 14 h/d. Following the 1-month period, the vapor-exposed animals resumed FR-1 and PR baclofen drug testing (doses as described above) in the operant chambers at a time point corresponding to the animals being 6 hours into withdrawal (i.e., 6 hours after the ethanol vapor had been discontinued for that day). RESULTS: Baclofen (0.0, 0.5, 1, 2, and 4 mg/kg, IP) dose-dependently decreased ethanol self-administration in both nondependent and dependent rats on a FR schedule of reinforcement. However, the dose of baclofen that significantly reduced responding for ethanol was shifted to the left in the ethanol vapor-exposed animals, indicating an increased sensitivity to baclofen in animals that were chronically exposed to ethanol. When tested using a PR schedule of reinforcement, there was a significant increase in the breakpoint for the vapor-exposed animals (i.e., the animals were willing to work more in a dependent state). Baclofen (2.0 mg/kg, IP) suppressed intake for both nondependent and dependent animals. CONCLUSIONS: Ethanol dependence produced increased self-administration of ethanol as reflected in increased ethanol intake and increased responding on a PR schedule of reinforcement. As baclofen suppressed ethanol self-administration and showed evidence of increased potency in dependent animals, the present experiment suggests that the GABA(B) receptor could be a potential pharmacotherapeutic target for the treatment of chronic alcoholism.     

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 drinking by alcohol-preferring rats increases the sensitivity of the posterior ventral tegmental area to the reinforcing effects of ethanol

BACKGROUND: The ventral tegmental area (VTA) is involved in regulating ethanol drinking, and the posterior VTA seems to be a neuroanatomical substrate that mediates the reinforcing effects of ethanol in ethanol-naive Wistar and ethanol-naive alcohol-preferring (P) rats. The objective of this study was to test the hypothesis that chronic ethanol drinking increases the sensitivity of the posterior VTA to the reinforcing effects of ethanol. METHODS: Two groups of female P rats (one given water as its sole source of fluid and the other given 24-hr free-choice access to 15% ethanol and water for at least 8 weeks) were stereotaxically implanted with guide cannulae aimed at the posterior VTA. One week after surgery, rats were placed in standard two-lever (active and inactive) operant chambers and connected to the microinfusion system. Depression of the active lever produced the infusion of 100 nl of artificial cerebrospinal fluid (CSF) or ethanol. The ethanol-naive and chronic ethanol-drinking groups were assigned to subgroups to receive artificial CSF or 25, 50, 75, or 125 mg/dl of ethanol (n = 6-9/dose/group) to self-infuse (FR1 schedule) during the 4-hr sessions given every other day. RESULTS: Compared with the infusions of artificial CSF, the control group reliably (p < 0.05) self-infused 75 and 125 mg/dl of ethanol but not the lower concentrations. The ethanol-drinking group had significantly (p < 0.05) higher self-infusions of 50, 75, and 125 mg/dl of ethanol than artificial CSF during the four acquisition sessions; the number of infusions of all three doses was higher in the ethanol-drinking group than in the ethanol-naive group. Both groups decreased responding on the active lever when artificial CSF was substituted for ethanol, and both groups demonstrated robust reinstatement of responding on the active lever when ethanol was restored. CONCLUSIONS: Chronic ethanol drinking by P rats increased the sensitivity of the posterior VTA to the reinforcing effects of ethanol.     

The Reinforcing Effects of Ethanol Are Altered by the Endogenous Neurosteroid, Allopregnanolone

We examined the effect of systemic administration of the endog-enously occurring progesterone metabolite, allopregnanolone, on oral self-administration of ethanol by male rats. Rats were trained to perform an operant response for presentation of 0.1 ml of a solution of 10% ethanol in water using the sucrose fading technique. After acquisition of stable lever-press responding on a fixed-ratio 4 schedule, subjects received subcutaneous injections of 1,3, or 10 mg/kg of allopregnanolone, or vehicle, 20 min prior to the self-administration session. Pretreatment with 3 mg/kg, but not 1 or 10 mg/kg, increased the mean total number of lever press responses made to obtain ethanol, and therefore increased the mean total number of ethanol presentations. The number of responses and response rate were examined as a function of the number of “runs” within the 30-min session; a “run” was defined as a series of consecutive responses with an interresponse interval of <1 min. The increase in total responses after 3 mg/kg was due in part to an increased number of responses for the first run of the session, with no effect on response rates. However, the higher dose of 10 mg/kg decreased response rates within the first run. Thus, allopregnanolone alters ethanol-reinforced responding at concentrations lower than those that depress rates of responding. The effects of administration of the ben-zodiazepene, diazepam, were determined for comparison with those of the neurosteroid. The subcutaneous injection of 0.3, 1.0, or 3.0 mg/kg of diazepam did not produce any clear dose-dependent changes in measures of ethanol-reinforced operant responding, supporting the suggestion of differences in the contribution of the benzodiazepene and neurosteroid binding sites to GABA_A receptor function. The results indicate that exogenous administration of allopregnanolone dose-dependently alters ethanol-reinforced operant responding, and suggest that this endogenously occurring neurosteroid could mediate some of the reinforcing effects of ethanol.     

GABA Antagonist and Benzodiazepine Partial Inverse Agonist Reduce Motivated Responding for Ethanol

Brain γ-aminobutyric acid (GABA) systems have long been associated with the behavioral actions of ethanol. This study investigated the effects of GABAergic agents on ethanol reinforcement. Rats were trained to orally self-administer ethanol in a 30-min, free-choice operant task. Responses at one of two levers produced contingent access to ethanol (10% w/v) or water. Pretreatment with RO 154513, a benzodlazepine inverse agonist (0.375 to 3.0 mg/kg ip), selectively reduced responses for ethanol, and a higher dose of RO 15-4513 (6.0 mg/kg) reduced both ethanol and water responses. Self-administration of saccharin in a free-choice task with access to saccharin (0.05%) and water was unaffected by RO 15-4513, suggesting that the effects of RO 15-4513 on ethanol reinforcement may not necessarily generalize to other reinforcers. Isopropylbicyclophosphate (IPPO), a picrotoxin ligand (5 and 10 μ g/kg ip), selectively reduced responses for ethanol in alcohol-preferring, nonpreferring and Wistar rats. However, the highest dose of IPPO (20 μ g/kg) reduced both ethanol and water responses. Chlordiazepoxide, a benzodiazepine, did not reduce responses for ethanol in the selectively bred animals, suggesting that this drug does not substitute for the reinforcing properties associated with acute ethanol intake. Together, these results suggest that compounds that act at the benzodiazepine inverse agonist and picrotoxin sites of the GABA/benzodiazepine receptor complex may decrease motivated responding for ethanol.     

Effects of Morphine and Naloxone on Ethanol- and Sucrose-Reinforced Responding in Nondeprived Rats

In the following series of experiments, effects of morphine (0.1, 0.3, 1.0, 3.0, and 10.0 mg/kg) and naloxone (0.1, 0.3, and 1.0 mg/kg) were assessed in nondeprived rats trained to leverpress with 10% ethanol, sweetened ethanol, or 5% sucrose and water as the reinforcers. Morphine, at doses of 0.1, 0.3, and 1.0 mg/kg had little effect on responding with ethanol or sweetened ethanol available on a fixed ratio 4 (FR4) schedule of reinforcement, but at the 3.0 mg/kg dose, morphine suppressed responding to near zero. Similar results were obtained when 10% ethanol and water were available on a concurrent FR4 FR4 schedule of reinforcement. When 5% sucrose and water were available concurrently, morphine suppressed responding at 3.0 and 10 mg/kg. Naloxone (0.1, 0.3, and 1.0 mg/kg) decreased responding for ethanol, sweetened ethanol, and sucrose solutions in a dose-dependent manner. Naloxone decreased total number of responses/session by shortening the duration of responding without affecting momentary rate. Overall, the data suggest that the endogenous opioid system plays a role in the ability of ethanol to reinforce operant behavior. However, this role does not appear to be specific to ethanol because similar results were observed with sucrose reinforcement. Failure to find enhanced ethanol intakes following morphine injections in the operant situation suggests that the method used to measure ethanol self-administration makes a difference in assessing the effects of drugs on ethanol intake.     

Ethanol- and sucrose-reinforced appetitive and consummatory responding in HAD1, HAD2, and P rats

INTRODUCTION: Ethanol-preferring (P) rats and high-alcohol-drinking (HAD1 and HAD2) rats have been selectively bred to consume greater amounts of ethanol than nonselected rat strains. These three rat lines also show increased levels of responding for ethanol in operant paradigms that assess a combined appetitive/consummatory response. METHODS: The present experiment used a model of reinforced responding that procedurally separates the appetitive, or seeking, response requirement from consummatory responding to compare seeking and intake responding in P and HAD rats. Subjects (n = 7 or 8 per group) were trained to make 25 lever-press responses, which were followed by 20 min of access to a sipper tube spout containing either 10% ethanol (10E) or (in separate groups of subjects) 3% sucrose (3S). After training, a single nonreinforced session was conducted to assess the limit to appetitive responding under extinction conditions. After this single nonreinforced session, three successive across-session breakpoint determinations were made for 10E and 3S by increasing the response requirement over days until subjects failed to complete the requirement. A final extinction session was then conducted. RESULTS: Appetitive responding during both the nonreinforced and breakpoint sessions indicated that P rats made significantly more responses overall than HAD rats in both the ethanol and sucrose groups. P rats also consumed more sucrose than HAD rats, with no differences in ethanol consumption between the lines (1.0-1.5 g/kg/20 min). Appetitive responding in the HAD rats in the ethanol groups was comparable to that reported previously for nonselected Long-Evans rats. CONCLUSIONS: These findings indicate that appetitive and consummatory processes are distinct and that P rats have an increased tendency to both seek and drink ethanol and sucrose solutions, making this selected line useful when modeling both "craving" and "loss of control" related behaviors involved in excessive alcohol consumption.     

Operant self-administration of ethanol in Sardinian alcohol-preferring rats

BACKGROUND: "Work" for ethanol, that is, the ability of a laboratory animal to press a lever to gain access to ethanol, has been proposed as (a) a requirement for definition of an animal model of alcoholism and (b) a measure of ethanol-reinforcing properties. The present study evaluated oral self-administration of ethanol under an operant (lever pressing) procedure in selectively bred Sardinian alcohol-preferring (sP) and alcohol-nonpreferring (sNP) rats. METHODS: Rats from both lines were initiated to self-administer 10% ethanol, on a fixed ratio 1 schedule and in daily 30 min sessions, by using the Samson sucrose fading procedure. Subsequently, rats were exposed to increasing concentrations of ethanol up to 30% on a fixed ratio 4 schedule. Finally, the extinction responding for ethanol, defined as the maximal number of lever responses reached by each rat in the absence of ethanol reinforcement, was determined. RESULTS: The results indicated that sP rats acquired and maintained lever pressing for ethanol, self-administering mean amounts of ethanol in the range of 0.6 to 1.1 g/kg/session, which gave rise to mean blood ethanol levels in the 30 to 45 mg% range. Extinction responding for ethanol in sP rats averaged 73. In contrast, once sucrose was faded out, sNP rats displayed minimal levels of responding for ethanol, and extinction responding averaged 6. CONCLUSIONS: The results of the present study extend to the sP/sNP rat lines the finding that ethanol can be established as a reinforcer in selectively bred alcohol-preferring rats, whereas it has modest, if any, reinforcing properties in alcohol-nonpreferring rats.     

Suppression of alcohol intake by chronic naloxone treatment in P rats: tolerance development and elevation of opiate receptor binding

BACKGROUND: This study was planned to determine the feasibility of using a slow release naloxone preparation to treat alcoholism, because compliance with medication is a significant problem in alcoholics. METHODS: Experiments were performed in alcohol-preferring P rats maintained either on continuous access or on limited access (1 hr/day) to alcohol with water and food provided ad libitum. Naloxone (Nx) was administered either by twice daily subcutaneous injections or by slow release (1.1 mg/kg/hr) osmotic minipump. In limited access experiments, Nx was injected immediately before access to alcohol. RESULTS: An initial experiment estimated the dose-effect curve for Nx subcutaneous suppression on alcohol intake. Nx (2.5-20 mg/kg) had a stronger effect during the first 2 hr after injection (ED50 = 2.1 mg/kg); however, the effect was more modest on 24-hr consumption. Similar results were found with chronic Nx treatment. Low doses of Nx (0.5 and 2.0 mg/kg) injected immediately before limited access to alcohol produced almost complete suppression of alcohol intake for at least 14 consecutive days. However, 14 days of treatment with 26 mg/kg/day by minipump or injection produced an initial 50% suppression of 24-hr alcohol intake with the gradual development of tolerance. An acute challenge with Nx immediately after the pumps were scheduled to be empty provided additional evidence of tolerance development in chronically Nx-treated rats. Brain micro-opiate receptors, estimated autoradiographically by using the ligand [3H][D-Ala2,N-Me-Phe4, Gly-ol5][tyrosyl-3,5-3H]-enkephalin, showed that rats chronically exposed to Nx and showing tolerance to Nx suppression of drinking exhibited 17% to 250% increases in [3H][D-Ala2,N-Me-Phe4, Gly-ol5][tyrosyl-3,5-3H]-enkephalin binding. CONCLUSIONS: High doses of Nx are required to suppress continuous access alcohol consumption in P rats, and tolerance develops to the ethanol consumption-suppressing effect of Nx that may be related to increases in micro-opiate receptors.     

Microdialysis of dopamine in the nucleus accumbens of alcohol-preferring (P) rats during anticipation and operant self-administration of ethanol

BACKGROUND: The present study was designed to test directly whether a contextual stimulus for access to ethanol would acquire the ability to enhance locomotor activity and dopamine efflux in the nucleus accumbens (NAc) of alcohol-preferring (P) rats. The study also explored the association between elevated locomotor activity and NAc dopamine efflux during operant self-administration of ethanol. METHODS: Adult female P rats were randomly assigned to operantly self-administer either 15% (v/v) ethanol or 0.0125% (w/v) saccharin. Both groups were trained in a daily 30-min two-lever concurrent operant task (FR-3) to orally self-administer ethanol or saccharin, with water on the alternate lever. A third (control) group was trained to self-administer water on both levers. All groups were also acclimated in the operant chambers to periods of habituation, anticipation, and postadministration. RESULTS: Compared with controls, the ethanol group, but not the saccharin group, showed significant increases in locomotor activity as well as increased NAc dopamine efflux during the first 10 min of the anticipation period. During the first 10 min of the self-administration period, locomotor activity was significantly increased in both the ethanol and saccharin groups compared with control values. The ethanol group, but not the saccharin group, showed significant increases in NAc dopamine efflux during the 20th and 30th min of the self-administration period and during the first 10 min of the postadministration period. CONCLUSIONS: The findings suggest that acquisition of signal-induced anticipation of self-administered ethanol is associated with increases in locomotor activity and extracellular levels of dopamine in the NAc of P rats. Such associations may be important to the development and maintenance of ethanol-seeking behaviors. The findings also indicate that operant self-administration of ethanol is associated with increases in extracellular levels of dopamine in the NAc of P rats.     

The Alcohol Deprivation Effect in C57BL/6J Mice is Observed Using Operant Self-Administration Procedures and is Modulated by CRF-1 Receptor Signaling

Background: The alcohol deprivation effect (ADE) is characterized by transient excessive alcohol consumption upon reinstatement of ethanol following a period of ethanol deprivation. While this phenomenon has been observed in rats using both bottle drinking (consummatory behavior) and operant self‐administration (consummatory and appetitive “ethanol‐seeking” behavior) procedures, ADE studies in mice have primarily relied on bottle drinking measures. Furthermore, the neurochemical pathways that modulate the ADE are not well understood. Therefore, we determined whether the ADE can be observed in C57BL/6J mice using operant self‐administration procedures and if expression of the ADE is modulated by the corticotropin releasing factor‐1 (CRF‐1) receptor. Methods: C57BL/6J mice were trained in a 2‐hour operant self‐administration paradigm to lever press for 10% ethanol or water on separate response keys. Between operant sessions, mice had access to ethanol in their homecage. Once stable responding occurred, mice were deprived of ethanol for 4 days and were then retested with ethanol in the operant paradigm for 3 consecutive days. Next, to assess the role of the CRF‐1 receptor, mice were given intraperitoneal (i.p.) injection (0, 10, or 20 mg/kg) of the CRF‐1 receptor antagonist CP‐154,526 30 minutes before ADE testing. Additional experiments assessed (i) ADE responding in which the alternate response lever was inactive, (ii) the effects of CP‐154,526 on self‐administration of a 1% sucrose solution following 4 days of deprivation, and (iii) ADE responding in which mice did not received i.p. injections throughout the experiment. Results: Mice exhibited a significant increase in postdeprivation lever responding for ethanol with either a water reinforced or inactive alternate lever. Interestingly, i.p. injection of a 10 mg/kg dose of CP‐154,526 protected against the ADE while not affecting lever responding for a sucrose solution. Finally, baseline and deprivation‐induced increases of ethanol reinforced lever responding were greater in mice not given i.p. injections. Conclusions: The ADE in C57BL/6J mice can be modeled using the operant self‐administration paradigm and increased ethanol self‐administration associated with the ADE is modulated by CRF‐1 receptor signaling.     

Suppression of Alcohol Intake after Administration of the Chinese Herbal Medicine, NPI-028, and Its Derivatives

The Chinese herbal medicine, NPI-028, has been used for centuries in China to counteract alcohol intoxication. The present study used a number of different experimental conditions to determine whether NPI-028 and its derivatives might selectively influence alcohol intake in rodents that naturally exhibit high alcohol intakes. It was determined that intraperitoneal (IP) injections of NPI-028 (0.5, 0.75, and 1.0 g/kg) suppressed alcohol intake by up to 30% in both alcohol-preferring P and Fawn-Hooded (FH) rats during a continuous access schedule. These injections did not significantly affect food or water intakes, nor did the highest dose of NPI-028 (1 g/kg) alter blood ethanol levels after an IP injection of 2.5 g/kg of ethanol. In P rats, it was found that NPI-028 was orally active with the dose of 1.5 g/kg having a greater effect on ethanol intake than the 1.0 g/kg dose; once again, food and water intakes were not significantly altered. In FH rats maintained on a limited access schedule (1 hr/day), alcohol intake was completely abolished by 1.5 g/kg of NPI-028. Chronic IP administration of NPI-028 (0.75 g/kg) for four consecutive days in FH rats maintained on a continuous access schedule did not lead to any diminution of its alcohol-suppressant effects. Thus, NPI-028 has significant effects on alcohol intake without much effect on water and food intake, and tolerance does not readily develop to these effects. The IP administration of a partially purified extract (NPI-031) of NPI-028, obtained by countercurrent chromatography, also dose-dependently suppressed ethanol intake in FH rats, but the highest dose (200 mg/kg) also significantly decreased food intake. Finally, the IP administration of puerarin (NPI-31G), an isoflavone isolated from NPI-031 by countercurrent chromatography, significantly reduced ethanol intake in FH rats without affecting food or water intake. Therefore, NPI-028 and one of its pure components, NPI-031G, selectively reduced ethanol intake in alcohol-preferring rats.     

Intravenous Ethanol Self-administration in C57BL/6J and DBA/2J Mice

Two strains of mice, C57BL/6J (B6) and DBA/2J (D2) were allowed to self-administer intravenous (iv) ethanol. These two strains were selected because they differ greatly in their preference for drinking ethanol solutions: 86 mice are preferrers, whereas D2 mice are avoiders of ethanol. Of interest was whether these strains would also differ in self-administration of iv ethanol when taste factors presumably do not influence consumption. Mice were trained with either 60, 75, or 90 mg/kg per infusion. Mice from both strains acquired nosepoking for all of these doses on an FR-3 schedule of reinforcement during 2-hr daily sessions. Additionally, mice in both strains acquired an equal preference for nosepoking on the side resulting in ethanol infusions, compared with the side that had no scheduled consequence, although B6 mice took somewhat more ethanol early in training than did D2 mice. Mice in both strains achieved equal levels of responding at the conclusion of training, when response rates had stabilized. A subset of animals were then tested at doses of ethanol ranging from 25 to 125 mg/kg per infusion. Although their responding tended to decrease over time regardless of changes in the unit dose of ethanol, these mice showed lower response rates for higher doses of ethanol, and less responding for saline than for ethanol. Together, these findings imply that iv ethanol has reinforcing properties in both these strains, despite the strain difference in preference for oral ethanol. Self-administration of iv ethanol in mice may prove a valuable addition to existing animal models for the study of ethanol reward.     

Hypericum perforatum CO2 extract and opioid receptor antagonists act synergistically to reduce ethanol intake in alcohol-preferring rats

BACKGROUND: Hypericum perforatum extracts attenuate ethanol intake in alcohol-preferring rats. The opioid receptor antagonists, naloxone and naltrexone, reduce ethanol intake in rats and humans. The combination of different agents that reduce ethanol intake has been proposed as an approach to the pharmacotherapy of alcoholism. This study evaluated the effect on ethanol intake of the combined administration of a CO2 H. perforatum extract and naloxone or naltrexone in genetically selected Marchigian Sardinian alcohol-preferring rats. METHODS: Ten percent (v/v) ethanol intake was offered 2 hr per day at the beginning of the dark phase of the reverse light-dark cycle. H. perforatum CO2 extract was given intragastrically, 1 hr before access to ethanol. Naloxone or naltrexone was given by intraperitoneal injection 10 min before the extract. RESULTS: H. perforatum CO2 extract reduced ethanol intake at 31 or 125 mg/kg, but not 7 mg/kg. These doses neither modified food or water intake during access to ethanol, nor reduce 0.2% saccharin intake. Naloxone reduced ethanol and food intake at 3 or 5 mg/kg, but not 1 mg/kg. When naloxone 1 mg/kg was combined with the three doses of H. perforatum CO2 extract, the attenuation of ethanol intake was more pronounced than that observed after the administration of the extract alone. Alcohol intake was also significantly reduced by 7 mg/kg of H. perforatum CO2 extract combined with naloxone 1 mg/kg. The combined treatments never modified the rat's locomotor activity nor the simultaneous intake of food, water or 0.2% saccharin. Naltrexone reduced ethanol intake at 1 and 3 mg/kg, but not at 0.5 mg/kg. When naltrexone 0.5 mg/kg was combined with H. perforatum CO2 extract 7 mg/kg, ethanol intake was markedly reduced. CONCLUSIONS: These findings provide evidence that H. perforatum CO2 extract and opiate receptor antagonists act synergistically to induce a pronounced and selective reduction of voluntary ethanol consumption in alcohol-preferring rats.     

Neuropeptide-Y Y5 receptors modulate the onset and maintenance of operant ethanol self-administration

BACKGROUND: Neuropeptide Y (NPY) is the most abundant and widely distributed peptide in the mammalian central nervous system and increases feeding behavior at NPY Y1 or Y5 receptor subtypes. Recent pharmacological and mutant mouse data indicate that NPY activity at its receptors can influence ethanol self-administration, although the direction and strength of this influence are not clear. METHODS: Effects of the novel NPY Y5 receptor antagonist L-152,804 on the onset and maintenance of operant self-administration were examined in male C57BL/6J mice, which were trained to self-administer ethanol (10% v/v) versus water via the sucrose substitution method during 16 hr overnight sessions. After 4 months of baseline responding, mice were injected with L-152,804 (0, 10, 30, or 60 mg/kg, intraperitoneally) before operant sessions. Potential locomotor effects of L-152,804 and possible interaction with the sedative properties of ethanol also were examined. RESULTS: All three doses of L-152,804 significantly delayed the onset of ethanol-reinforced responding relative to vehicle injection. L-152,804 produced no effect on the total number of ethanol- or water-reinforced responses per 16 hr session. However, L-152,804 selectively modulated the temporal distribution of ethanol-reinforced responding depending on the dose (10 and 60 mg/kg) and time point measured in a manner consistent with blockade of ethanol reinforcement. Additional experiments determined that L-152,804 (10 or 60 mg/kg) did not alter spontaneous locomotor activity or influence the sedative effects of ethanol (4 g/kg). CONCLUSIONS: These results indicate that blockade NPY Y5 receptor activity modulates the onset and maintenance of ethanol self-administration. For this reason, NPY-Y5 receptor antagonists may be useful in medical management of alcohol abuse and alcoholism.     

Disruption of operant oral self-administration of ethanol, sucrose, and saccharin by the AMPA/kainate antagonist, NBQX, but not the AMPA antagonist, GYKI 52466

BACKGROUND: AMPAergic transmission has been suggested to be important in mediating the rewarding effects of drugs. We therefore examined the role of non-NMDA glutamate-receptors in mediating the reinforcing properties of ethanol in an oral self-administration paradigm. METHODS: The competitive antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)quinoxaline) and the non-competitive antagonist, GYKI 52466 (1-(4-aminophenyl)-4-methyl-7,8-methylene-dioxy-5H2,3- be nzodiazepine), were administered to animals previously trained to self-administer ethanol, sucrose, or saccharin, on a progressive ratio schedule. RESULTS: GYKI 52466 (5 & 10 mg/kg) had no effect on operant responding for ethanol, but increased spontaneous locomotor activity, whereas the highest doses of NBQX (3 & 6 mg/kg) significantly decreased operant responding and correspondingly decreased the breaking point in responding for ethanol on a progressive ratio schedule. NBQX (but not GYKI 52466) also significantly decreased operant responding for a food reinforcer (sucrose) as well as for a sweet tasting reinforcer (saccharin). Doses of NBQX that disrupted operant performance caused a significant reduction in locomotor activity, indicating that NBQX decreased ethanol self-administration only at doses which disrupt motor activity. CONCLUSIONS: These results suggest non-NMDA glutamate-receptors may not have a specific role in the maintenance of responding for an ethanol reinforcer, but may generally disrupt operant performance. Because, unlike GYKI 52466, NBQX possesses an action at central kainate receptors, these results suggest that kainate, but not AMPA (alpha-amino 3-hydroxy-5-methyl-4-isoxazole propionate) receptors may be important in mediating the reinforcing effects of ethanol.     

Ethanol Consumption Following Acute Treatment with Methysergide, Fluoxetine, Fenfluramine, and Their Combination

Methysergide (MS), a postsynaptic serotonin antagonist, was administered acutely in three experiments in relation to water or 5% ethanol solution intake of 24-hr, water-deprived male Sprague-Dawley rats. In the first experiment, MS significantly increased the consumption of ethanol at doses of 0.25, 2.0, and 4.0 mg/kg. Water intake was significantly increased by MS at the 2.0 mg/kg dose. In the second experiment, which was different from the first one in that MS was administered during the dark cycle, ethanol solution intake was again significantly increased at all three levels. In the third experiment, fenfluramine (FFL) and fluoxetine (FLU) were administered acutely (at 8 mg/kg) after MS (0.25 mg/kg) followed by measuring water or ethanol solution intake. FFL and FLU significantly decreased intake of both water and ethanol solution, a process that was significantly reversed by MS; to a greater degree for FLU (74%) than for FFL (57%). The successful use of MS in increasing ethanol intake in these studies may be due to the low doses used in comparison with earlier unsuccessful attempts. The procedure of treating 24-hr, water-deprived rats with acute doses of pre- and postsynaptic serotonin agonists and antagonists appears to be a useful model for further elucidation of their interaction in ethanol consummatory behavior.