Serotonin3 Receptor Antagonism of Alcohol Intake: Effects of Drinking Conditions

McKINZIE, D. L., R. EHA, R. COX, R. B. STEWART, W. DYR, J. M. MURPHY, W. J. McBRIDE, L. LUMENGAND T.-K. LI. Serotonin₃ receptor antagonism of alcohol intake: Effects of drinking conditions. ALCOHOL 15(4) 291–298, 1998.—The effects of 5-HT₃ receptor antagonists on ethanol intake were examined in the selectively bred alcohol-preferring P line of rats under continuous and limited access to 10% (v/v) ethanol with food and water ad lib. Single daily injections of either MDL 72222 (MDL) or ICS 205-930 (ICS) (0.01–3.0 mg/kg, SC) given 60 min before a 4-h scheduled access period for 4 consecutive days failed at all doses to alter the intake of a 10% (v/v) ethanol solution by P rats. However, multiple daily injections of either MDL (1–3 mg/kg, SC) or ICS (3.0 and 5.0 mg/kg, SC), given three times daily at 4-h intervals, significantly reduced ethanol intake under 24-h free-choice conditions on the first treatment day. Additionally, a single administration of 1.0 mg/kg MDL reduced 24-h free-choice ethanol intake by approximately 50% of control values and had no effect on 24-h saccharin intake. The effects of MDL were further examined in a 2-h schedule access paradigm in which rats received the access period at the same time every day (Fixed) or randomly during the dark cycle (Variable). Although 1.0 mg/kg MDL had little effect on ethanol drinking in the Fixed group, ethanol intake was reduced by 55% of control levels in the Variable group. Overall, the data indicate that drinking conditions influence the effectiveness of 5-HT₃ antagonists to reduce ethanol consumption. Furthermore, the results suggest that conditions, associated with limited access ethanol drinking, markedly reduce the actions of 5-HT₃ antagonists on ethanol intake.     

Histaminergic Activation of Endogenous Angiotensin II Fails to Inhibit Alcohol Intake in Rats

Demonstrations that alcohol intake can be inhibited by pharmacological activation of the renal renin–angiotensin system (RRA) or injection of angiotensin II (ANG II) in rats led to this study of a role for endogenous ANG II in inhibition of alcohol intake in rats. Relatively small doses of histamine, above threshold for eliciting drinking of water and activation of the RRA, were injected SC in adult male Sprague–Dawley rats with access to 3.0% alcohol in 45-min one-bottle alcohol tests and in two-bottle tests in which alcohol and water were available at the midpoint of the 12-h dark phase. The 0.312 and 1.25 mg/kg doses of SC histamine elevated plasma renin activity to levels similar to those in rats that had just eaten food. Neither dose of histamine affected alcohol intake in one-bottle tests. A relatively large 10 mg/kg dose of histamine increased alcohol intake in a one-bottle test, but decreased alcohol intake and increased water intake in two-bottle tests. The inhibitory effect of the 10 mg/kg dose of histamine on alcohol intake was completely blocked by SC 10 mg/kg losartan, a selective AT₁ angiotensin receptor antagonist. This 10 mg/kg dose of losartan given alone, however, failed to increase alcohol intake in one- or two-bottle tests. These results generally do not support a role for endogenous ANG II as an inhibitory physiological signal in the control of alcohol ingestion in rats, because histaminergic activation of RRA, using small but physiologically meaningful doses of histamine, failed to inhibit alcohol intake.     

Development of alcohol deprivation effect in rats: lack of correlation with saccharin drinking and locomotor activity.

The present study addressed the relationship between the parameters of saccharin drinking behaviour and locomotor activity in an open field environment and long-term alcohol self-administration. In a 22-day initiation phase, male Wistar rats were presented with increasing concentrations of ethanol (2-8%, v/v) in a choice with water. The rats were then given the choice between water and two ethanol solutions (8 and 16%). Every 28 days, ethanol was withdrawn for 5 days. The ethanol intake and the transient increase in ethanol consumption after each of six deprivation episodes (alcohol deprivation effect) was monitored and correlated with parameters of the subsequent saccharin drinking and open field tests. The total ethanol intake (g/kg/24 h) as well as the consumption of 16% ethanol were stable over time. However, the magnitude of the alcohol deprivation effect increased with the repeated deprivation episodes. None of the parameters measured in the open field or the saccharin drinking tests correlated with either ethanol consumption or the alcohol deprivation effect. These results suggest that (1) repeated episodes of ethanol deprivation may increase the magnitude of the alcohol deprivation effect, (2) neither saccharin drinking nor locomotor activity correlates with long-term ethanol drinking behaviour in rats.     

Nicotine increases ethanol preference but decreases locomotor activity during the initial stages of chronic ethanol withdrawal

AIM: The ability of nicotine to modify withdrawal symptoms in rats chronically treated with alcohol, with respect to locomotor activity and ethanol or nicotine preference, has been evaluated in these studies. METHODS AND RESULTS: Preliminary studies showed that locomotor activity increased 8-9 h after withdrawal from chronic nicotine intoxication, which was dose specific; it occurred in rats administered 0.15 mg/kg or 0.6 mg/kg but not the 0.3 mg/kg nicotine dose. Administration of nicotine, either acutely (0.3 mg/kg) during ethanol withdrawal, or chronically (0.15, 0.3 or 0.6 mg/kg) during the chronic alcohol treatment procedure, diminished locomotor activity, which increases significantly, approximately 6-7 h after withdrawal, in rats chronically treated with alcohol. Rats which were chronically treated with alcohol alone or in combination with nicotine, 0.3 mg/kg, showed an increase in ethanol intake when the free choice was performed between ethanol 10% and tap water; on the contrary, when the free choice was performed between ethanol 10% versus nicotine, 0.3 mg/kg, results showed a decrease in ethanol preference and a concomitant increase in nicotine preference. CONCLUSION: These studies clearly identified the modulatory effects of nicotine, at specific doses, on both motility and preference in rat chronically co-administered nicotine and ethanol.     

Effects of D1 and D2 dopamine receptor agents on ethanol consumption in the high-alcohol-drinking (HAD) line of rats

Dopamine receptor agonists and antagonists were tested for effects on alcohol drinking in female HAD rats (n = 10) given limited access (4 h/day) to a 10% (v/v) ethanol solution. Food and water were available ad libitum. Subcutaneous drug injections were given 30–60 min before the ethanol access periods. The D₂ agonist quinpirole (0.04–2.0 mg/kg) caused a dose-dependent decrease in alcohol drinking throughout the 4-h period. Spiperone, a D₂ antagonist, had no effect during the initial part of the session, but by the fourth hour, the 10 μg/kg dose tended to increase alcohol intake and the 30 μg/kg dose reduced intake. The D₁ antagonist SCH-23390 (3–30 μg/kg) dose-dependently decreased ethanol drinking during the first hour of access. The D₁ agonist SKF-38393 (2–6 mg/kg) also decreased alcohol intake, but it was less effective than SCH-23390. The findings implicate both D₁ and D₂ receptors in the reinforcing effects of alcohol drinking by the HAD line of rats.     

Combination pharmacotherapy: a mixture of small doses of naltrexone, fluoxetine, and a thyrotropin-releasing hormone analogue reduces alcohol intake in three strains of alcohol-preferring rats

It is common to treat some diseases with more than one medication simultaneously. Since more than one neurotransmitter system is involved in alcohol-seeking behaviour, then a therapeutic approach that targets more than one system should be more effective in reducing alcohol intake than one addressing a single system. To test this hypothesis, we compared the efficacy of low doses of individual drugs reported to reduce voluntary alcohol drinking to the efficacy of a mixture of these agents at the same low doses in reducing alcohol intake in three strains of alcohol-preferring rats (P, HAD, and Fawn-Hooded). After establishment of a stable baseline for alcohol intake in a continuous access paradigm, each rat received separate single i.p. injections of relatively low doses of either naltrexone (2.0 mg/kg), fluoxetine (1.0 mg/kg), the thyrotropin-releasing hormone analogue TA-0910 (0.2 mg/kg), a mixture of all three drugs, or the vehicle at 09:30. Each rat received all treatments, with an inter-injection washout period of at least 3 days. Alcohol and water intakes were measured at 6 and 24 h, and food intake was measured at 24 h, after the injection. Our results show that individual drugs did not significantly affect food, water, or alcohol intake. However, the mixture significantly reduced alcohol intake in all three strains, but had no effect on food intake. Similar results were obtained when the HAD rats received an oral dose of the individual drugs or the mixture. When P rats were given an i.p. injection of the mixture for 10 consecutive days, there was a continued suppressing effect. These findings show that a combination treatment designed to target simultaneously serotonergic, dopaminergic, and opioidergic systems can reduce alcohol intake, even though the doses of the individual drugs in the mixture are relatively low and ineffective when given singly.     

Effects of repeated morphine treatment on metabolism of cerebral dopamine and serotonin in alcohol-preferring AA and alcohol-avoiding ANA rats

The alcohol-preferring AA (Alko Alcohol) rats are more rapidly sensitized to the locomotor activity-stimulating effects of small doses of morphine than the alcohol-avoiding ANA (Alko Non-Alcohol) rats. To study the involvement of dopaminergic and serotonergic transmission in this behaviour, the effects of acute morphine (1 mg/kg) challenge on the concentrations of dopamine (DA), 5-hydroxytryptamine (5-HT, serotonin) and their metabolites were estimated in three dopaminergic areas in AA and ANA rats on the fourth day after a 3-day morphine or saline treatment. Acute administration of morphine enhanced DA metabolism in the caudate-putamen in the AA, but not in the ANA, rats; in the nucleus accumbens and in the olfactory tubercle the acute effect of morphine was similar in rats of both lines. Morphine pretreatment did not significantly enhance acute morphine's effects on DA metabolites in any of the brain areas studied in rats of either line. Acute administration of morphine enhanced brain 5-HT metabolism in the AA rats but not in the ANA rats, but after repeated treatment it induced no enhancement of 5-HT metabolism. With the methods used, no significant differences were found between the AA and ANA rats in the effects of repeated morphine on cerebral dopaminergic or serotonergic mechanisms which could account for the different behavioural sensitization found previously in rats of these lines. However, both monoamines studied might be involved in the acute locomotor stimulatory effects of morphine.     

Kudzu root extract suppresses voluntary alcohol intake and alcohol withdrawal symptoms in P rats receiving free access to water and alcohol

Alcohol-preferring (P) rats, given free choice to drink water or 15% alcohol, drank 7-10 g of alcohol/kg/day, giving blood alcohol values ranging from 16 to 24 mg/dL. Body weight and food and total fluid intake values in control and alcohol-drinking P rats did not differ significantly, while water intake was inversely related to the amount of alcohol consumed. Alcohol withdrawal after 50 days of alcohol drinking caused withdrawal symptoms such as hypersensitivity, poor landing coordination, and tremors. A daily 0.5, 0.75, and 1.0 g/kg dose of kudzu root (KdR) did not affect body weight and food and water intake values in control (no alcohol) P rats. Subchronic feeding of relatively higher KdR doses (0.75 and 1.0 g/kg) caused a 25-30% reduction in weight gain. The 0.5 g/kg KdR dose caused a 50-60% reduction in alcohol consumption, abolished the development of alcohol withdrawal symptoms, but did not affect blood alcohol levels. The higher KdR doses did not further reduce alcohol consumption. Alcohol suppressed the weight-reducing effects of KdR. The KdR extract used in this study contained 150 mg/g of puerarin, 13 mg/g of daidzin, 4 mg/g of daidzein, 3 mg/g of genistin, 0.2 mg/g of genistein, and 1 mg/g of glycetin. Blood and liver samples contained mostly puerarin and a trace amount of daidzein that may have been formed by the hydrolysis of daidzin by liver enzymes. An important observation was that brain samples obtained from KdR-fed or alcohol + KdR-fed rats did not contain any of the KdR isoflavones. Thus, KdR isoflavones suppressed alcohol drinking and withdrawal symptoms without entering the brain.     

Manipulations of the renin-angiotensin system and intake of a sweetened alcoholic beverage among rats.

Standard laboratory rats were maintained on a daily regimen involving deprivation of fluids for 22 h followed by a 2-h opportunity to drink water and a sweetened alcoholic beverage. Angiotensin II, in doses ranging from 0.1 to 1.25 mg/kg, dose relatedly decreased rats' mean intake of ethanol. All doses increased rats' mean intake of water. Angiotensin II, 0.25 mg/kg, reliably reduced intake of ethanol when it was presented alone during the 1st h of the daily 2-h drinking session, and reliably increased intake of water when it was subsequently presented alone during the 2nd h. Thus the reduction in intake of ethanol seen when the alcoholic beverage is presented concurrently with water is probably not merely due to the increase in intake of water. Lisinopril, an angiotensin converting enzyme inhibitor, in doses of 0.3, 1.0, and 3.0 mg/kg, dose relatedly decreased intake of ethanol, but only after several days of injections. Concurrent intake of water was increased dose relatedly. When injections of lisinopril ceased, intakes of both ethanol and water took several days to return to control levels. Pretreatment with lisinopril, 3.0 mg/kg, for 8 days, had no effect on subsequent intakes of either water or ethanol. Lisinopril, 3.0 mg/kg, had no effect on rats' intake of a sweet solution without ethanol. These results confirm previous work and extend the data base supporting the idea that the renin-angiotensin system plays a role in modulating intake of ethanol.     

alpha1-noradrenergic receptor antagonism blocks dependence-induced increases in responding for ethanol.

The purpose of this study was to test the hypothesis that blockade of alpha1-adrenergic receptors may suppress the excessive ethanol consumption associated with acute withdrawal in ethanol-dependent rats. Following the acquisition and stabilization of operant ethanol self-administration in male Wistar rats, dependence was induced in half the animals by subjecting them to a 4-week intermittent vapor exposure period in which animals were exposed to ethanol vapor for 14h/day. Subsequent to dependence induction, the effect of alpha1-noradrenergic receptor antagonist prazosin (0.0, 0.25, 0.5, 1, 1.5, and 2.0mg/kg IP) was tested on operant responding for ethanol in vapor-exposed and control rats during acute withdrawal. In ethanol-dependent animals, prazosin significantly suppressed responding at the 1.5 and 2.0mg/kg doses, whereas only the 2.0mg/kg dose was effective in nondependent animals, identifying an increase in the sensitivity to prazosin in dependent animals. Conversely, at the lowest dose tested (0.25mg/kg), prazosin increased responding in nondependent animals, which is consistent with the effect of anxiolytics on ethanol self-administration in nondependent animals. None of the doses tested reliably affected concurrent water self-administration. These results suggest the involvement of the noradrenergic system in the excessive alcohol drinking seen during acute withdrawal in ethanol-dependent rats.     

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.     

The α2-adrenergic receptor agonist,clonidine, reduces alcohol drinking in alcohol-preferring (P) rats

Evidence suggests that noradrenergic signaling may play a role in mediating alcohol-drinking behavior in both rodents and humans. We have investigated this possibility by administering clonidine to alcohol-drinking rats selectively bred for alcohol preference (P line). Clonidine is an α₂-adrenergic receptor agonist which, at low doses, inhibits noradrenergic signaling by decreasing norepinephrine release from presynaptic noradrenergic neurons. Adult male P rats were given 24 h access to food and water and scheduled access to a 15% (v/v) alcohol solution for 2 h daily. Rats received intra-peritoneal (IP) injections with clonidine (0, 10, 20, 40, or 80 μg/kg body weight [BW], 10–11 rats/treatment group) once/day at 30 min prior to onset of the daily 2 h alcohol access period for 2 consecutive days. Clonidine, in doses of 40 or 80 μg/kg BW, significantly reduced alcohol intake on both days of treatment (p < 0.001). Two weeks later, rats were treated with clonidine for 5 consecutive days and clonidine, in doses of 40 or 80 μg/kg BW, reduced alcohol intake on all 5 treatment days (p < 0.001). Clonidine did not alter water consumption during the daily 2 h free-choice between alcohol and water. In a separate group of male P rats, clonidine (40 μg/kg BW) suppressed intake of a saccharin solution (0.04 g/L). These results are consistent with and complement our previous findings that the α₁-adrenergic receptor antagonist, prazosin, decreases voluntary alcohol drinking in alcohol-preferring rats, but suggests that effects of clonidine may not be specific for alcohol. The results suggest that although activation of the noradrenergic system plays an important role in mediating voluntary alcohol drinking, care is needed in selecting which drugs to use to suppress central noradrenergic signaling in order to maximize the selectivity of the drugs for treating alcohol-use disorders.     

Suppressing effect of the cannabinoid CB1 receptor antagonist, SR147778, on alcohol intake and motivational properties of alcohol in alcohol-preferring sP rats

AIMS: The present study investigated the effect of the newly synthesized cannabinoid CB(1) receptor antagonist, SR147778, on alcohol intake and the motivational properties of alcohol in selectively bred Sardinian alcohol-preferring (sP) rats. METHODS AND RESULTS: In Experiment 1, the repeated administration of SR147778 (0.3-3 mg/kg twice daily, i.p.) specifically suppressed the acquisition of alcohol drinking behaviour in alcohol-naive rats exposed to the two-bottle "alcohol vs water" choice regimen for 24 h/day. In Experiment 2, an acute administration of SR147778 (2.5-10 mg/kg, i.p.) specifically reduced alcohol intake in alcohol-experienced rats that were given alcohol and water under the two-bottle choice regimen in daily sessions of 4 h. In Experiment 3, an acute administration of SR147778 (0.3-3 mg/kg, i.p.) suppressed the "alcohol deprivation effect", i.e. the extra-intake of alcohol occurring after a period of alcohol abstinence. In Experiment 4, an acute administration of SR147778 (0.3-3 mg/kg, i.p.) specifically suppressed the extinction responding for alcohol, i.e. the maximal number of lever responses reached in the absence of alcohol in rats trained to lever-press for alcohol (measure of the motivational properties of alcohol). In Experiment 5, the combination of 3 mg/kg of SR147778 (i.p.) and 0.5 g/kg of alcohol (i.p.), a dose comparable with those usually consumed by sP rats in each drinking binge, failed to induce any conditioned taste aversion. CONCLUSION: Taken together, these results extend to SR147778 the anti-alcohol profile of the prototype cannabinoid CB(1) receptor antagonist, rimonabant (SR141716), and strengthen the hypothesis that the cannabinoid CB(1) receptor is part of the neural substrate mediating alcohol intake and the motivational properties of alcohol.     

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.     

Apomorphine and 7-OH DPAT reduce ethanol intake of P and HAD rats

Adult male rats of the alcohol-preferring (P) line (N = 10) and high alcohol drinking (HAD) line (N = 12) were used to study the effects of IP administration of 0.125–0.50 mg/kg 7-OH DPAT (a putative D₃ agonist) and 0.25–1.0 mg/kg apomorphine (a dopamine agonist with 50-fold higher affinities for the D₁ and D₂ receptors than for the D₃ receptor) on the concurrent intakes of 10% (v/v) ethanol and 0.0125% (g/v) saccharin during a daily 4-h scheduled access period. Control intakes by the P rats for the 4-h period were 17.9±0.5 and 7.2±0.4 ml for the ethanol and saccharin solutions, respectively. For the HAD line, ethanol consumption was 18.7±0.2 ml and saccharin intake was 8.7±1.6 ml for the 4-h period. In terms of grams ethanol/kg body wt., the 4-h intakes were 2.2±0.2 for the P line and 3.0±0.3 for the HAD rats. Both P and HAD rats consumed approximately 40% of their total ethanol intake in the first 15 min of access while consuming only about 15% of their total saccharin intake during this 15-min period. The putative D₃ agonist 7-OH DPAT produced a decrease in ethanol intake in the first h to 45–55% of control levels for the P rat (p < 0.01) and to 25–70% of control values in the HAD line (p < 0.001). Apomorphine caused a dose-dependent decrease in ethanol intake in the first hour to 15–70% of control values in the P rat (p < 0.001) and to 25–60% of control levels in the HAD line (p < 0.001). Saccharin and 4-h food intakes for both lines were not altered by either 7-OH DPAT or apomorphine. Overall, these results suggest that D₂ and D₃ dopamine receptors may play a role in mediating alcohol drinking behavior of the selectively bred HAD and P lines of rats.     

Effects of naltrexone on the acquisition of alcohol intake in male and female periadolescent and adult alcohol-preferring (P) rats

The objective of this study was to compare the effects of naltrexone (NTX) on the acquisition of alcohol drinking, during periadolescence and adulthood in rats using a rodent model of alcoholism. Periadolescent and adult alcohol-preferring (P) rats of both sexes were given access to water and 15% (v/v) alcohol 24-hr/day for 45 days. Alcohol access started at 1200 hr on post-natal day (PND) 30 for the periadolescent rats and approximately PND 90 for the adult rats. Subcutaneous (SC) injections of NTX (0, 5, 10, 20, and 30 mg/kg) were administered daily between 1600-1700 hr to separate groups of animals during the first 10 days of alcohol access. During the treatment period, differential effects on alcohol intake were seen between periadolescent and adult animals: (a) lower doses of NTX were more effective in the periadolescent than the adult P rats, and (b) greater tolerance to repeated dosing was displayed by adult, compared with periadolescent, rats. By the 20h day of alcohol access there were no significant differences between the NTX dose groups. Additionally, there were no sex of animal differences at the ages tested. These findings indicate that the endogenous opioid system(s) mediating alcohol intake are developmentally present in periadolescent P rats, such that NTX not only interfered with the acquisition of alcohol intake by adolescent P rats but appeared to also have a greater effect than that observed in adult P rats. Therefore, NTX may serve as an effective treatment in reducing alcohol abuse and dependence in genetically, and perhaps environmentally, at-risk youth.     

Differential efficacy of serotonergic drugs FG5974, FG5893, and amperozide in reducing alcohol drinking in P rats

Amperozide (FG5606), a 5-HT₂ receptor antagonist, is well known to suppress alcohol consumption in different rat models of drinking. The present study compared the efficacy of three drugs, FG5974, FG5893, and amperozide, which have differential affinities for 5-HT_1A and 5-HT_2A receptors, on alcohol drinking in the genetic alcohol-preferring (P) rat. After preference for alcohol vs. water was determined over 10 days when concentrations of alcohol were increased from 3% to 30%, the maximal concentration of alcohol preferred by each animal was selected for drug testing. A 4-day predrug preference test was followed by SC injection of the saline control vehicle or doses of 1.0 and 2.5 mg/kg FG5974, FG5893, or amperozide given at 1600 and 2200 h for 4 days. Alcohol preference testing concluded with a final 4-day interval. A total daily dose of 5.0 mg/kg FG5974 reduced absolute g/kg intake of alcohol and proportional intakes of the P rats significantly; the lower dose of FG5974 also reduced alcohol drinking significantly following treatment. The mixed 5-HT_1A agonist/5-HT_2A antagonist, FG5893, which suppresses drinking in cyanamide-treated rats, was without effect on alcohol ingested by the P rats. However, amperozide caused a dose-dependent decline in both absolute intakes and proportion of alcohol that was more intense than that of FG5974. The control vehicle failed to alter alcohol drinking and, like the FG compounds, did not affect food intake or body weight. Although the inhibition of alcohol drinking by amperozide corresponds precisely with previous findings, the effect of FG5974 contrasts to results obtained with a structurally analogous drug FG5893. Thus, the genetic strain of rat as well as the nature of the chemical characteristics of a 5-HT agonist/antagonist will determine the differential efficacy of a drug in influencing the volitional drinking of alcohol.     

Effect of Hypericum perforatum CO2 extract on the motivational properties of ethanol in alcohol-preferring rats

AIMS: Extracts of Hypericum perforatum (HPE) attenuate voluntary ethanol intake in different lines of alcohol-preferring rats. The present study evaluated the effect of the intragastric (IG) administration of a CO(2) Hypericum perforatum extract (HPCO(2)) on operant ethanol self-administration, as well as on voluntary ethanol intake, after a period of ethanol deprivation in genetically selected Marchigian Sardinian alcohol-preferring rats. METHODS: HPCO2 was administered by means of an indwelling IG catheter, 1 h before the tests. For the self-administration experiments, the rats were trained to self-administer 10% (v/v) ethanol in 30-min daily sessions under a fixed ratio 1 schedule of reinforcement. HPCO2 was also tested on 0.2% w/v saccharin self-administration. For the ethanol deprivation experiments, rats that had a previous experience with voluntary ethanol drinking were deprived of ethanol for 9 days, whereas water and food were freely available; HPCO2 was given by IG injection 1 h before the ethanol re-presentation. RESULTS: HPCO2 in doses of 31 or 125 mg/kg but not 7 mg/kg, significantly reduced ethanol self-administration, while it did not modify saccharin self-administration. The same doses of the extract abolished the increased ethanol intake following ethanol deprivation. CONCLUSIONS: These findings provide evidence that HPCO2 markedly reduces the reinforcing properties of ethanol in the self-administration paradigm, as well as the increase of ethanol intake following ethanol deprivation. These findings further support the view that the use of HPE may represent an interesting pharmacological approach in the treatment of alcohol abuse and alcoholism.     

Nicotinic receptor ligands reduce ethanol intake by high alcohol-drinking HAD-2 rats

Neuronal nicotinic acetylcholine receptors (nAChRs) are implicated in the reinforcing effects of many drugs of abuse, including ethanol. The present study examined the efficacy of cytisine, a nAChR partial agonist, and lobeline, a putative nAChR antagonist, on the maintenance of ethanol drinking by HAD-2 rats. Adult male HAD-2 rats were given access to ethanol (15 and 30%, with ad libitum access to water and food) 22 h/day for 12 weeks, beginning at 60 days of age, after which cytisine (0.0, 0.5, and 1.5 mg/kg) was tested for 3 consecutive days. The rats were given an 18-day washout period and were then tested with lobeline (0.0, 1.0, and 5.0 mg/kg) for 3 consecutive days. Ethanol intake was measured at 1, 4, and 22 h postinjection. Rats were injected intraperitoneally just before lights out (1200 h). There was a significant main effect of cytisine treatment on the second test day, with the 1.5 mg/kg dose significantly reducing ethanol intake at the 1- and 4-h time-points, relative to saline, and the 0.5 mg/kg dose inducing a significant reduction at the 4-h time-point. Conversely, lobeline treatment resulted in significant main effects of treatment for all three time-points within each test day, with the 5.0 mg/kg dose significantly reducing ethanol intake, relative to saline, at each time-point within each test day. These findings provide further evidence that activity at the nAChR influences ethanol intake and is a promising target for pharmacotherapy development for the treatment of alcohol dependence and relapse.     

Attenuation of ethanol withdrawal signs by high doses of L-arginine in rats

AIMS: Effects of l-arginine, a nitric oxide (NO) precursor, on ethanol withdrawal syndrome were investigated in rats. METHODS: Ethanol (7.2% v/v) was given to rats by a liquid diet for 16 days. l-Arginine (250, 500 and 1000 mg/kg) or saline were injected into rats intraperitoneally 20 min before ethanol withdrawal. All injections were repeated 30 min before the 6th h of the observation period. The effects of l-arginine on ethanol withdrawal syndrome were evaluated during the first 6 h of ethanol withdrawal. RESULTS: l-Arginine (250 mg/kg) potentiated significantly vertical and ambulatory locomotor activities at only the 30th minute of the observation period. l-Arginine (500 and 1000 mg/kg) inhibited behavioural signs of ethanol withdrawal significantly. l-Arginine (1000 mg/kg) also prolonged the latency and attenuated the intensity of audiogenic seizures. This dose of l-arginine also reduced both vertical and ambulatory locomotor hyperactivity of the rats from the 2nd hour of ethanol withdrawal. l-Arginine (1000 mg/kg) did not produce any significant change in the locomotor activities of the naive (non-ethanol-dependent) rats. CONCLUSIONS: Our results indicate that l-arginine at high doses alleviates the signs of ethanol withdrawal syndrome in rats.