Salvia miltiorrhiza extract inhibits alcohol absorption, preference, and discrimination in sP rats.

Experiment 1 of the present study investigated the ability of a standardized extract of Salvia miltiorrhiza in reducing voluntary ethanol intake in ethanol-preferring rats of the sP line. Ethanol intake occurred under the two-bottle free-choice regimen between 10% (v/v) ethanol and water in daily 4-h scheduled access periods; water was present 24 h/day. Intragastric administration of 200 mg/kg Salvia miltiorrhiza extract resulted in approximately 40% reduction in ethanol intake and preference throughout the 4-day treatment. This effect of Salvia miltiorrhiza extract was likely due to its ability of altering ethanol absorption from the gastrointestinal tract. Indeed, Experiments 2 and 3 of this study demonstrated that 200 mg/kg Salvia miltiorrhiza extract reduced blood ethanol levels (BELs) up to 60% in comparison to control rats, when ethanol was given IG, whereas it failed to modify BELs when ethanol was injected IP. The reducing effect of Salvia miltiorrhiza extract on ethanol absorption may have therefore resulted in an attenuated perception of the psychoactive effects of ethanol sought by ethanol-drinking rats. Consistently, the results of Experiment 4 of the present study demonstrated that a combination of 200 mg/kg Salvia miltiorrhiza extract IG and 1 or 2 g/kg ethanol IG resulted in a partial blockade of the discriminative stimulus effects of ethanol in sP rats trained to discriminate these doses of ethanol from water in a drug discrimination procedure. Collectively, the results are discussed as being suggestive that drugs curbing ethanol absorption from the gastrointestinal tract may constitute a novel strategy for controlling excessive alcohol consumption in human alcoholics.     

Effects of calcium channel blockers on pentylenetetrazol drug discrimination in rats.

The effects of the dihydropyridine L-type calcium channel blockers nitrendipine and nimodipine on the pentylenetetrazol (PTZ) drug discrimination, an operant model of anxiety, were investigated. Male Long-Evans rats were trained to discriminate PTZ (16 mg/kg, i.p.) from saline. Both nitrendipine (5.0-25 mg/kg, i.p.) and nimodipine (5.0-25 mg/kg, i.p.) partially substituted for the PTZ discriminative stimulus. However, pretreatment with nitrendipine (25 mg/kg, i.p.) or nimodipine (25 mg/kg, i.p.) produced no change in the PTZ dose-effect function. Rats were given a nutritionally balanced liquid diet containing 6.5% ethanol for 10 days. Rats selected the PTZ drug lever during withdrawal. Subchronic coadministration of nitrendipine (1.25-5.0 mg/kg, i.p., b.i.d.) with ethanol failed to dose-dependently reduce PTZ-lever responding, but it did reverse withdrawal signs. Acute administration of nitrendipine (5, 10, and 20 mg/kg, i.p.) produced marked suppression of lever responding, but it failed to significantly reduce levels of PTZ-lever responding. Although calcium channel blockers reduce signs of ethanol withdrawal, they also markedly reduce rates of behavior and produce no clear effects on anxiety-like behaviors induced by ethanol withdrawal.     

A Comparison of the Effects of the Opioid Antagonists Naltrexone,Naltrindole, and β-Funaltrexamine on Ethanol Consumption in the Rat

The effects of the universal opioid antagonist naltrexone were compared to the δ-selective opioid antagonist naltrindole and the μ-selective opioid antagonist β-funaltrexamine on ethanol consumption in the absence of food or fluid deprivation using a limited access procedure in Wistar rats. Both naltrexone, at doses of 0.1, 0.25, 0.5, 1.0, 3.0, and 10 mg/kg, and β-funaltrexamine, at doses of 5.0 and 20.0 mg/kg, significantly decreased consumption of a 6% ethanol solution compared to saline control groups. Naltrindole, at doses of 5.0 and 15.0 mg/kg, failed to significantly reduce ethanol consumption. In addition, the highest doses of naltrexone, which antagonize δ as well as μ-opioid receptors, did not differ significantly from the lowest doses in their ability to reduce ethanol consumption. These data suggest that ethanol consumption using the limited access paradigm in the outbred rat is modulated by μ rather than δ-opioid receptors. Although this is not consistent with other data showing that δ antagonists decrease ethanol consumption, it is suggested that these difference may be related to the alcohol-preferring rats used in those experiments.     

Involvement of nicotinic acetylcholine receptors in the regulation of alcohol drinking in Wistar rats

The aim of the present study was to determine if nicotinic acetylcholine receptors (nAChRs) might be involved in the regulation of alcohol intake by Wistar rats. A non-selective nAChR agonist, nicotine, and a non-competitive nAChR antagonist, mecamylamine, were tested in alcohol-preferring Wistar rats maintained on a limited access (4 h/24 h) to ethanol (10%, v/v). In addition, the effects of nicotine and mecamylamine on intake of standard laboratory chow were studied in a separate control experiment. Nicotine (0.1-0.6 mg/kg, s.c.) decreased ethanol consumption, but had no effect on food intake. In contrast, mecamylamine (1-3 mg/kg, s.c.) did not alter ethanol drinking even at the dose (3 mg/kg) which significantly decreased food intake. These results suggest that activation of nAChRs may selectively reduce ethanol consumption in outbred Wistar rats.     

Time-dependent effect of ethanol upon discrimination behavior

The discriminative stimulus properties produced by ethanol were employed to demonstrate differences in discriminative performance over time in rats trained at different postinjection times. Thus, one group of rats was trained to discriminate between intraperitoneally administered 600 mg/kg ethanol and its distilled water vehicle at 6-min postadministration, whereas a second group of rats was trained to make this discrimination when trained at 30-min postinjection. Subsequent to reaching criterion performance, dose-response relations to doses of ethanol from 150-900 mg/kg were determined to be similar in both groups. This indicated that the discriminative stimulus effects at the two postadministration times were equally effective for training of behavioral responding to ethanol. The rats trained at 30 min postadministration maintained criterion level discrimination performance when tested at 6-, 15- and 60-min postinjection. In contrast, the rats trained at 6-min postadministration discriminated ethanol at a reduced level (40%) when tested at 30-min postinjection. These results suggest that the nature of the discriminable stimuli produced by a low dose of ethanol are different at 6-min and at 30-min postadministration. Evidence is cited to further suggest that the earlier stimuli are excitatory whereas the later stimuli are sedative.     

Effect of naltrexone on acute tolerance to ethanol in UChB rats.

The effect of naltrexone (a non-selective opioid receptor antagonist) on both alcohol consumption in a voluntary selection situation and acute tolerance to the motor impairment effect of ethanol was examined in female high alcohol-drinking (UChB) rats using the tilting plane test. In experiment 1, the effect of naltrexone on alcohol consumption was studied in UChB rats which were given a daily 1-h period access to a 10% (v/v) ethanol solution with food and water always available. Naltrexone in doses of 5 or 10 mg/kg intaperitoneal (i.p.) caused dose-dependent reduction in voluntary alcohol intake by 45% and 66%, respectively, without altering daily water intake. In experiment 2, the effect of naltrexone (5 mg/kg i.p.) on acute tolerance to motor impairment effect of a dose of 2.3 g ethanol/kg i.p. was examined. A comparison of control (C) and naltrexone (Nal) UChB groups indicated that naltrexone slowed the recovery of the motor activity and reduce acute tolerance development at comparable ethanol levels in cerebral blood. These results suggest a contribution of the opioid system to acute tolerance to ethanol.     

Effects of Hypericum perforatum extraction on alcohol intake in Marchigian Sardinian alcohol-preferring rats.

The present study investigated the effect of acute intragastric (i.g.) administration of dry Hypericum perforatum extract (HPE), containing 0.3% hypericin, on ethanol intake in genetically selected Marchigian Sardinian alcohol-preferring (msP) rats. The i.g. administration of HPE, 125 or 250 mg/kg, induced a 30-40% reduction in ethanol intake in rats offered 10% (v/v) ethanol for 2 h/day. The effect of these doses was selective, since they modified neither food intake nor food-associated drinking; neither did the same doses modify the rat's gross behaviour in the open-field test. A dose of 500 mg/kg frequently induced immobility and a general suppression of ingestive behaviour. In rats offered 10% ethanol for 12 h/day, ethanol intake following treatment with 250 mg/kg HPE was significantly lower than that of controls for up to 10 h. The effect on ethanol intake was not related to the antidepressant-like effect of HPE revealed in the forced swimming test. In this regard, the effect on ethanol intake was observed after a single administration of 125 mg/kg, whereas the antidepressant effect was observed only after repeated treatment with doses higher than 125 mg/kg HPE. The i.g. administration of HPE, 250 mg/kg, did not affect blood-alcohol levels following i.g. treatment with 0.7 g/kg ethanol, the amount usually ingested in a single drinking episode; thus, the effect is not related to changes in the pharmacokinetics of ethanol. The present study shows that HPE markedly reduces ethanol intake in msP rats, without significantly modifying food intake.     

The effect of cannabinoid CB(1) receptor antagonist rimonabant (SR-141716) on ethanol drinking in high-preferring rats.

The present study investigated the effect of the cannabinoid CB(1) receptor antagonist, rimonabant (SR-141716) on ethanol intake in selectively bred alcohol-preferring Warsaw High-Preferring rats. Ethanol (10% vol/vol) and food were available in daily 4-h limited access period while water was available ad libitum. The administration (i.p.) of single 2.5 and 5.0-mg/kg doses of rimonabant preferentially reduced ethanol intake, whereas a 10mg/kg dose of rimonabant similarly reduced both ethanol and food intake. Our result extends the suppressive effect of cannabinoid CB(1) receptor antagonist to the ethanol drinking behavior in Warsaw High-Preferring line of rats. The result also supports a growing body of literature indicating that the cannabinoid CB(1) receptor is involved in motivational and appetitive properties of ethanol.     

Discriminative stimulus effects of ethanol: Lack of antagonism with N-methyl-d-aspartate and d-cycloserine

Several drug discrimination studies reported that both competitive and uncompetitive NMDA receptor antagonist substituted for ethanol stimulus in rats. In the present study we examined if compounds that act as agonists at the NMDA receptor complex, d-cycloserine (a partial agonist at the glycine positive modulatory site) and N-methyl-d-aspartate (an agonist at the glutamate binding site), could antagonize the discriminative stimulus effects of ethanol. Rats were trained to discriminate between IP administered 1.0 g/kg of ethanol (10% v/v) and saline under a sweetened milk-reinforced fixed ratio 10 (FR10) schedule of reinforcement. When the animals met the discriminative criteria, antagonism tests were conducted with d-cycloserine (0.3–10.0 mg/kg, IP) and N-methyl-d-aspartate (15.0–60.0 mg/kg, IP). Neither d-cycloserine nor N-methyl-d-aspartate antagonized the ethanol-mediated discriminative stimulus effects. In addition, d-cycloserine (3.0–300.0 mg/kg, IP) did not substitute for ethanol. These results indicate that at least certain agonists at the NMDA receptor complex do not attenuate the ethanol interoceptive cue in the rat.     

Naltrexone treatment produces dose-related effects on food and water intake but daily alcohol consumption is not affected

Abstract

There is evidence that naltrexone, an opioid antagonist, affects alcohol and food consumption. Though food intake is inherently involved when naltrexone effects on alcohol consumption have been studied, the differential effect of this opioid antagonist on both food and alcohol intake has not yet been reported. The present study analyzed the effect of a single daily dose of naltrexone on alcohol, food and water intake when these substances were available on a continuous basis. Wistar male rats were treated with s.c. injections of either naltrexone (2 or 10 mg/kg/day/rat) or a saline solution, 0.2 ml/day/rat for 7 days. This period was followed by a lapse of 7 days with no treatment (PT period), and this sequence of naltrexone or saline treatment followed by a period without treatment was repeated four times. Neither 2 mg/kg nor 10 mg/kg of naltrexone affected alcohol consumption, though the higher dose of naltrexone (10 mg/kg) increased food intake with respect to both the PT periods and the saline group and decreased water consumption with respect to the corresponding PT periods. Naltrexone at 2 mg/kg produced a decrease in food intake but only with respect to the PT periods. These results suggest that the effects of a single dose of naltrexone on alcohol consumption may not be evident when 24-h access to alcohol is assessed; however, naltrexone may produce different dose-related effects on food and water intake, suggesting that they may be mediated by distinct opioid system mechanisms.     

Naltrexone treatment produces dose-related effects on food and water intake but daily alcohol consumption is not affected

There is evidence that naltrexone, an opioid antagonist, affects alcohol and food consumption. Though food intake is inherently involved when naltrexone effects on alcohol consumption have been studied, the differential effect of this opioid antagonist on both food and alcohol intake has not yet been reported. The present study analyzed the effect of a single daily dose of naltrexone on alcohol, food and water intake when these substances were available on a continuous basis. Wistar male rats were treated with s.c. injections of either naltrexone (2 or 10 mg/kg/day/rat) or a saline solution, 0.2 ml/day/rat for 7 days. This period was followed by a lapse of 7 days with no treatment (PT period), and this sequence of naltrexone or saline treatment followed by a period without treatment was repeated four times. Neither 2 mg/kg nor 10 mg/kg of naltrexone affected alcohol consumption, though the higher dose of naltrexone (10 mg/kg) increased food intake with respect to both the PT periods and the saline group and decreased water consumption with respect to the corresponding PT periods. Naltrexone at 2 mg/kg produced a decrease in food intake but only with respect to the PT periods. These results suggest that the effects of a single dose of naltrexone on alcohol consumption may not be evident when 24-h access to alcohol is assessed; however, naltrexone may produce different dose-related effects on food and water intake, suggesting that they may be mediated by distinct opioid system mechanisms.     

Morphine and naloxone modulate intake of ethanol

Rats, deprived of food and water for 18 hr, were given an opportunity to drink water and sweetened ethanol solution for 1 hr prior to being fed and watered for 5 hr, daily. One group received water and sucrose solution without ethanol and other groups received water and sucrose solution with 3, 6, 12 or 24% ethanol. Prior to some days' opportunities to drink, rats were injected with morphine (2.5 mg/kg), naloxone (10 mg/kg), or saline. Morphine increased intake of solutions containing ethanol as compared to intake under placebo. Naloxone reduced intakes of both fluids. Since morphine only increased sucrose solution intake when it contained ethanol, it was concluded that increments in opioid activity increase rats' avidity for ethanol.     

The NMDA receptor antagonist MK-801 produces ethanol-like discrimination in the rat

Two groups of rats, one derived from N/Nih stock and the second from the (putatively) serotonin-compromised Fawn-Hooded line, were trained to discriminate ethanol from its vehicle in a drug discrimination paradigm. Once each of the two groups attained discrimination criterion, dose-response relationships with lower doses of ethanol indicated that the Fawn-Hooded rats were less sensitive (ED₅₀ value = 579.5 mg/kg) than the N/Nih rats (ED₅₀ = 371.4 mg/kg). Testing of various doses of the NMDA (N-methyl-D-aspartate) receptor antagonist MK-801 produced complete generalization in each group of animals, with a similar difference in ED₅₀ values between N/Nih and Fawn-Hooded lines. These results extend previous ethanol-to-MK-801 generalization reported in pigeons, and are discussed in light of a possible NMDA-mediated contribution to the ethanol-induced discriminative stimulus cues.     

Morphine and diprenorphine together potentiate intake of alcoholic beverages

Water-deprived rats were given a daily opportunity to take water or an ethanol solution. Prior to some opportunities to drink, some were injected with morphine (across procedures either 2.0, 7.5, or 20.0 mg/kg), diprenorphine (from 0.001 to 10.0 mg/kg), or a combination of diprenorphine and morphine. The small dose of morphine increased intake of alcoholic beverage and the large dose decreased intake, confirming previous observations. Diprenorphine, across a wide range of doses, increased intake of ethanol solution. Morphine and diprenorphine together produced more intake than either given alone. Diprenorphine reversed the depressing effects of large doses of morphine on intake of ethanol solution. Since diprenorphine is an antagonist with respect to opioid analgesia and behavioral depression and an agonist with respect to intake of alcoholic beverages, and since it potentiates the small dose morphine effect, it is concluded that only some effects of morphine are related to opioid-potentiation of intake of alcoholic beverages.     

Effects of 5,7-dihydroxytryptamine lesion of the dorsal raphe nucleus on ethanol discrimination in the rat.

It has been shown that ethanol produces a complex interoceptive cue in rodents with distinct GABAergic, glutamatergic, and serotonergic (5-hydroxytryptamine, 5-HT) components. The present study aimed to examine the contribution of the 5-HT system originating in the dorsal raphe nucleus (DRN) to the discriminative stimulus effects of ethanol in male Wistar rats. Therefore, selective lesions of 5-HT neurons in the DRN were induced by microinfusions of 5,7-dihydroxytryptamine. The DRN- and sham-lesioned rats were trained to discriminate ethanol (1.0 g/kg) from saline in a standard two-lever drug discrimination procedure. Acquisition of ethanol discrimination and discrimination performance after consumption of lower doses of ethanol did not differ between the groups. In substitution tests, diazepam (0.5-2.5 mg/kg), a nonselective benzodiazepine receptor agonist, partially generalized from the ethanol cue in both groups. In contrast, m-chlorophenylpiperazine (0.1-0.9 mg/kg), a mixed 5-HT(1B/2C) receptor agonist, did not mimic the ethanol cue. The drug decreased response rates in both groups, but this effect was more evident in the sham-lesioned group. A 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propyloamino)-tetraline (0.05-0.4 mg/kg), did not produce significant increase in ethanol-appropriate responding in either group. These results may indicate that 5-HT neurons of the DRN are not critically involved in ethanol discrimination in the rat.     

The neuropeptide-Y Y5 receptor antagonist L-152,804 decreases alcohol self-administration in inbred alcohol-preferring (iP) rats.

Neuropeptide-Y (NPY) is the most abundant and widely distributed peptide in the mammalian central nervous system and increases feeding behavior through actions at the Y5 receptor subtype. Recent pharmacological evidence indicates that NPY activity at this receptor subtype can modulate ethanol reinforcement. The purpose of this study was to determine if NPY Y5 receptor antagonism reduces ethanol self-administration and reinforcement in a rodent genetic animal model of alcoholism. Selectively inbred alcohol-preferring (iP) rats were trained to voluntarily consume ethanol (10% vol/vol) versus H2O in a 24-h two-bottle choice test. An additional group of iP rats was trained in operant ethanol self-administration to lever press on a fixed-ratio 1 schedule for ethanol (10% vol/vol) reinforcement. Following establishment of baseline intake or ethanol-reinforced responding, iP rats were injected with L-152,804 (0-20 mg/kg) prior to two-bottle or operant ethanol self-administration sessions. In the two-bottle choice test, L-152,804 (3 and 10 mg/kg, ip) significantly reduced ethanol intake (g/kg) at 4- and 6-h postinjection and had no effect on food intake. In the operant procedure, L-152,804 (10 and 20 mg/kg, ip) significantly reduced both the dosage of self-administered ethanol (g/kg/1-h) and the total number of ethanol-reinforced responses. No effect was observed on latency to the first response or the number of inactive lever presses. These results indicate that blockade of NPY Y5 receptor activity decreases both voluntary ethanol drinking and ethanol reinforcement in a rodent genetic animal model of alcoholism. For this reason, NPY Y5 receptor antagonists may be useful in medical management of alcohol abuse and alcoholism in the human population.     

Opioids in the perifornical lateral hypothalamus suppress ethanol drinking

The opioid system is known to enhance motivated behaviors, including ethanol drinking and food ingestion, by acting in various reward-related brain regions, such as the nucleus accumbens, ventral tegmental area and medial hypothalamus. There is indirect evidence, however, suggesting that opioid peptides may act differently in the perifornical lateral hypothalamus (PF/LH), causing a suppression of consummatory behavior. Using brain-cannulated Sprague–Dawley rats trained to voluntarily drink 7% ethanol, the present study tested the hypothesis that opioids in the PF/LH can reduce the consumption of ethanol, with animals receiving PF/LH injections of the δ-opioid receptor agonist D-Ala2-met-enkephalinamide (DALA), the μ-receptor agonist [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO), the κ-receptor agonist (±)-trans-U-50,488 methanesulfonate (U-50,488H), or the general opioid antagonist methylated naloxone (m-naloxone). The consumption of ethanol, lab chow, and water was monitored for 4 h after injection. The results showed that the three opioid receptor agonists injected into the PF/LH specifically and significantly reduced ethanol intake, while causing little change in chow or water intake, and the opposite effect, enhanced ethanol intake, was observed with the opioid antagonist. Of the three opioid agonists, the δ-agonist appears to produce the most consistent and long-lasting suppression of consumption. This effect was not observed with injections 2 mm dorsal to this area, focusing attention on the PF/LH as the main site of action. These results suggest that the opioid peptides have a specific role in the PF/LH of reducing ethanol drinking, which is distinct from their more commonly observed appetitive actions in other brain areas. The additional finding, that m-naloxone in the PF/LH stimulates ethanol intake in contrast to its generally suppressive effect in other regions, focuses attention on this hypothalamic area and its distinctive role in contributing to the variable effects sometimes observed with opioid antagonist therapy for alcoholism.     

REDUCTION OF VOLUNTARY ETHANOL INTAKE IN ETHANOL-PREFERRING sP RATS BY THE CANNABINOID ANTAGONIST SR-141716

The present study assessed the efficacy of the cannabinoid CB₁receptor antagonist, SR-141716, in reducing voluntary ethanolintake in selectively bred Sardinian alcohol-preferring (sP)rats. Ethanol (10%, v/v) and food were available in daily 4hscheduled access periods; water was present 24 h/day. The acuteadministration of a 2.5 and a 5 mg/kg dose of SR-141716 selectivelyreduced ethanol intake, whereas a 10 mg/kg dose of SR-141716reduced to a similar extent both ethanol and food intake. Theseresults suggest that the cannabinoid CB₁ receptor is involvedin the mediation of the ethanol-reinforcing effects in sP rats.     

THE EFFECT OF DIAZEPAM ON VOLUNTARY ETHANOL INTAKE IN A RAT MODEL OF ALCOHOLISM

This paper reports the effects of a diazepam treatment on voluntaryethanol intake in rats included in an animal model of alcoholism.In a first dose-seeking experiment, rats had a choice between10% (w/v) ethanol and water for 24 h each week. Single dosesof diazepam between 2 and 20 mg/kg injected i.p. prior to the24-h choice caused a dose-dependent decrease in voluntary ethanolintake from 3.2±0.4 g/kg/day down to 2.3±0.3 g/kg/day(P<0.01) after a dose of 20 mg/kg. In a second experiment,psychological dependence was induced by a 1-year intermittentexposure to ethanol (a choice between 10% ethanol and waterfor 24 h each week, followed by an i.p. injection of 2.0 g/kgof ethanol). After this year, the rats were given a continuouschoice between ethanol and water. A 3-week treatment with diazepam(20 mg/kg/day, i.p.) was started in week 68, during which perioda choice of 10% (w/v) ethanol was available only on the firstand the last days of treatment. On the first day of the diazepamtreatment, ethanol intake was decreased from a pre-experimentalvalue of 2.7±0.3 g/kg/day to 1.2±0.1 g/kg/day(P<0.001). On the last day of the treatment, voluntary intakewas higher than before the treatment (3.8±0.27 g/kg/day,P<0.01). Ethanol intake remained elevated during the weekafter the end of the diazepam treatment (P<0.05). When singledoses of diazepam (20 mg/kg) were re-tested 10 and 19 weeksafter the treatment, there was no decrease in ethanol intake,indicating that the initial effect had not been re-established.     

HAD and LAD rats respond differently to stimulating effect but not discriminative effects of ethanol.

The drug discrimination paradigm (DD) was used to evaluate behavioral differences of rats selectively bred for differential ethanol drinking preferences. Seventh-generation high alcohol-drinking (HAD) and low alcohol-drinking (LAD) rats were trained to discriminate between ethanol (0.5 g/kg, IP) and saline vehicle, following a 2-min presession interval (PI), using an FR-10 schedule of reinforcement. The HAD line was more responsive than the LAD line to the stimulating effect of ethanol as measured by total response rates. ED50 values of 0.239 and 0.244 g/kg for the HAD and LAD lines, respectively, do not reflect any difference in the discriminative effects of ethanol. Response rates during DD indicated a dissociation of rate-increasing effects and discriminative performance following ethanol. In addition to differential drinking preference, these data suggest that selective breeding for the HAD and LAD animals also involves the stimulant action of ethanol but not on the discriminative effects.