Noradrenergic role in the self-administration of ethanol

Animal models of drug relapse and craving: From drug priming-induced reinstatement to incubation of craving after voluntary abstinence

High rates of relapse to drug use during abstinence is a defining feature of drug addiction. In abstinent drug users, drug relapse is often precipitated by acute exposure to the self-administered drug, drug-associated cues, stress, as well as by short-term and protracted withdrawal symptoms. In this review, we discuss different animal models that have been used to study behavioral and neuropharmacological mechanisms of these relapse-related phenomena. In the first part, we discuss relapse models in which abstinence is achieved through extinction training, including the established reinstatement model, as well as the reacquisition and resurgence models. In the second part, we discuss recent animal models in which drug relapse is assessed after either forced abstinence (e.g., the incubation of drug craving model) or voluntary (self-imposed) abstinence achieved either by introducing adverse consequences to ongoing drug self-administration (e.g., punishment) or by an alternative nondrug reward using a discrete choice (drug vs. palatable food) procedure. We conclude by briefly discussing the potential implications of the recent developments of animal models of drug relapse after voluntary abstinence to the development of medications for relapse prevention.

Prazosin + Naltrexone Decreases Alcohol Drinking More Effectively Than Does Either Drug Alone in P Rats with a Protracted History of Extensive Voluntary Alcohol Drinking, Dependence, and Multiple Withdrawals

BACKGROUND

Prazosin (PRZ; an α1 -adrenergic receptor antagonist) and naltrexone (NTX; a nonspecific opioid receptor antagonist) each decrease alcohol drinking when administered to rats selectively bred for high voluntary alcohol drinking (alcohol-preferring or "P"), and the combination of PRZ + NTX decreases alcohol drinking more effectively than does either drug alone. As drug responsiveness can depend on history of alcohol drinking and dependence, we investigated whether various schedules of PRZ and NTX administration, alone or in combination, are effective in decreasing alcohol drinking in male P rats with a history of protracted voluntary alcohol drinking, dependence, and repeated withdrawals closely resembling human alcoholism.

METHODS

Male P rats became alcohol-dependent during 1 year of ad libitum 24 h/d access to food, water, and 20% alcohol with repetitive temporary alcohol withdrawals. Four sequential studies then addressed effects of oral PRZ (2 mg/kg) and NTX (10 mg/kg), alone or together, on alcohol drinking during: (i) daily alcohol access with daily drug treatment, (ii) intermittent alcohol access with daily drug treatment, (iii) intermittent alcohol access with occasional drug treatment, and (iv) postdeprivation reinstatement of alcohol access.

RESULTS

The combination of PRZ + NTX consistently suppressed alcohol drinking during daily or intermittent alcohol access conditions and when drug treatment was either daily or occasional. PRZ + NTX was consistently more effective than either drug alone. The reduction in alcohol drinking was not due to sedation, motor effects, or malaise.

CONCLUSIONS

Both daily and "as-needed" treatment with PRZ + NTX are highly effective in suppressing daily, intermittent, and postdeprivation alcohol drinking in male P rats with a protracted history of alcohol dependence and repeated withdrawals. This drug combination may be especially effective for treating individuals with long histories of heavy alcohol abuse, dependence, and repeated relapse, as commonly encountered in clinical practice.

The dopamine β-hydroxylase inhibitor, nepicastat, reduces different alcohol-related behaviors in rats

BACKGROUND

Recent experimental data indicate that treatment with the selective dopamine β-hydroxylase inhibitor, nepicastat, suppressed different reward-related behaviors, including self-administration of chocolate and reinstatement of cocaine and chocolate seeking, in rats. This study was designed to extend to different alcohol-related behaviors the investigation on the "anti-addictive" properties of nepicastat.

METHODS

Sardinian alcohol-preferring (sP) rats, selectively bred for excessive alcohol consumption, were exposed to different procedures of alcohol drinking and self-administration.

RESULTS

Repeated treatment with nepicastat (0, 25, 50, and 100 mg/kg, intraperitoneally [i.p.], once daily for 10 consecutive days) produced a stable and dose-related reduction in daily alcohol intake in sP rats exposed to the homecage 2-bottle "alcohol (10% v/v) versus water" choice regimen with unlimited access. Acute treatment with nepicastat (0, 25, 50, and 100 mg/kg, i.p.) completely suppressed the "alcohol deprivation effect" (i.e., the temporary increase in alcohol intake occurring after a period of abstinence; model of alcohol relapse episodes) in sP rats exposed to the 2-bottle choice regimen. Acute treatment with nepicastat (0, 25, 50, and 100 mg/kg, i.p.) dose dependently and selectively reduced oral alcohol self-administration in sP rats trained to lever respond for alcohol (15% v/v) on a fixed ratio 4 schedule of reinforcement. Finally, combination of nepicastat (0, 50, and 100 mg/kg, i.p.) and alcohol (2 g/kg, intragastrically) did not alter spontaneous locomotor activity in sP rats.

CONCLUSIONS

Together, these data extend to alcohol the capacity of nepicastat to suppress different behaviors motivated by natural stimuli and drugs of abuse.

Targeting the noradrenergic system for gender-sensitive medication development for tobacco dependence

INTRODUCTION

Tobacco use remains the leading cause of morbidity and mortality for both women and men in the United States, and women often experience poorer smoking cessation outcomes than men. Preliminary evidence suggests there are sex differences in medication effectiveness for smoking cessation. However, current medications do not take into account gender-sensitive treatment development and efficacy, underscoring the importance of this underdeveloped area of research.

METHODS

We reviewed preclinical and clinical evidence for gender differences in the inability to quit smoking by examining (a) the effect of increased negative affect and stress reactivity on smoking outcomes in women and (b) smoking for nicotine reinforcement in men. We also reviewed the current literature targeting the noradrenergic system as a novel gender-sensitive treatment strategy for tobacco dependence.

RESULTS

We hypothesize that noradrenergic agents that normalize noradrenergic activity may differentially attenuate stress reactivity in women and nicotine-related reinforcement in men, indicating that targeting the noradrenergic system for smoking cessation may be effective for both genders, with benefits operating through sex-specific mechanisms.

CONCLUSIONS

Converging lines of preclinical and clinical evidence suggest that gender-sensitive approaches to medication development for smoking cessation are a critical next step for addressing low quit rates and exacerbated health risks among women. Evidence reviewed indicates that smoking activates different brain systems modulated by noradrenergic activity in women versus men, and noradrenergic compounds may preferentially target these gender-sensitive systems.

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.

Chronic treatment with prazosin or duloxetine lessens concurrent anxiety-like behavior and alcohol intake: evidence of disrupted noradrenergic signaling in anxiety-related alcohol use

BACKGROUND

Alcohol use disorders have been linked to increased anxiety, and enhanced central noradrenergic signaling may partly explain this relationship. Pharmacological interventions believed to reduce the excitatory effects of norepinephrine have proven effective in attenuating ethanol intake in alcoholics as well as in rodent models of ethanol dependence. However, most preclinical investigations into the effectiveness of these drugs in decreasing ethanol intake have been limited to acute observations, and none have concurrently assessed their anxiolytic effects. The purpose of these studies was to examine the long-term effectiveness of pharmacological interventions presumed to decrease norepinephrine signaling on concomitant ethanol self-administration and anxiety-like behavior in adult rats with relatively high levels of antecedent anxiety-like behavior.

METHODS

Adult male Long-Evans rats self-administered ethanol on an intermittent access schedule for eight to ten weeks prior to being implanted with osmotic minipumps containing either an a1-adrenoreceptor antagonist (prazosin, 1.5 mg/kg/day), a β1/2-adrenoreceptor antagonist (propranolol, 2.5 mg/kg/day), a serotonin/norepinephrine reuptake inhibitor (duloxetine, 1.5 mg/kg/day) or vehicle (10% dimethyl sulfoxide). These drugs were continuously delivered across four weeks, during which animals continued to have intermittent access to ethanol. Anxiety-like behavior was assessed on the elevated plus maze before treatment and again near the end of the drug delivery period.

RESULTS

Our results indicate that chronic treatment with a low dose of prazosin or duloxetine significantly decreases ethanol self-administration (P < 0.05). Furthermore, this decrease in drinking is accompanied by significant reductions in the expression of anxiety-like behavior (P < 0.05).

CONCLUSIONS

These findings suggest that chronic treatment with putative inhibitors of central noradrenergic signaling may attenuate ethanol intake via a reduction in anxiety-like behavior.

The α1-adrenergic receptor antagonist, doxazosin, reduces alcohol drinking in alcohol-preferring (P) Rats

BACKGROUND

Evidence supports a role for the noradrenergic system in alcohol drinking in animals and humans. Our previous studies demonstrated the efficacy of prazosin, an α1-adrenergic antagonist, in decreasing alcohol drinking in rat models of alcohol dependence. Prazosin has also been shown to decrease alcohol drinking in treatment-seeking alcohol-dependent men. Clinically, the use of prazosin is limited by the requirement for multiple daily administrations, whereas doxazosin, a structurally similar α1-adrenergic antagonist, requires only once-daily dosing. In this study, we tested the hypothesis that doxazosin, like prazosin, would decrease alcohol drinking in rats selectively bred for alcohol preference (P line).

METHODS

Adult male P rats were given 2 h/d scheduled access to a 2-bottle choice (15% v/v alcohol vs. water) session 5 d/wk (M-F), with food and water available ad libitum 24 h/d. Rats were injected with doxazosin (0 to 10 mg/kg, IP) 40 minutes prior to initiation of the alcohol access session in 3 trials (of 3, 5, and 5 consecutive days) each separated by 5 to 8 weeks. The third trial included 1 day without alcohol access (for locomotor testing), and 1 day of a single hour of alcohol access (for plasma alcohol determination).

RESULTS

Doxazosin significantly reduced alcohol intake in all 3 trials. The 5 mg/kg dose consistently reduced alcohol intake, increased water drinking, did not affect locomotor activity, and resulted in lower plasma alcohol concentrations, suggesting that the doxazosin-induced reduction in alcohol drinking was not dependent on a motor impairment or an alteration in alcohol clearance.

CONCLUSIONS

Doxazosin decreases voluntary alcohol consumption by male alcohol-preferring (P) rats, supporting a role for the noradrenergic system in alcohol drinking in P rats and suggesting that doxazosin could potentially be an effective once-daily pharmacotherapeutic agent for the treatment of alcohol use disorders.

Effects of prazosin, an α1-adrenergic receptor antagonist, on the seeking and intake of alcohol and sucrose in alcohol-preferring (P) rats

BACKGROUND

Previous studies show that prazosin, an α(1) -adrenergic receptor antagonist, decreases alcohol drinking in animal models of alcohol use and dependence [Rasmussen et al. (2009) Alcohol Clin Exp Res 3:264-272; Walker et al. (2008) Alcohol 42:91-97] and in alcohol-dependent men [Simpson et al. (2009) Alcohol Clin Exp Res 33:255-263]. This study extended these findings by using a paradigm that allows for separate assessment of prazosin on motivation to seek versus consume alcohol or sucrose in selectively bred rats.

METHODS

Alcohol-preferring (P) rats were trained to complete an operant response that resulted in access to either 2% sucrose or 10% alcohol. A 4-week Seeking Test Phase examined responding in single, weekly extinction sessions when no reinforcer could be obtained. A 4-week Drinking Test Phase consisted of rats lever-pressing to "pay" a specified amount up front to gain access to unlimited alcohol (or sucrose) for a 20-minute period. On Seeking and Drinking test days, prazosin (0.0, 0.5, 1.0, and 1.5 mg/kg) was administered intraperitoneally 30 minutes prior to behavioral sessions.

RESULTS

Rats were self-administering an average of 0.9 (±0.09) g/kg alcohol on vehicle test day and had pharmacologically relevant blood ethanol concentrations. Prazosin significantly decreased alcohol seeking at all doses tested. The highest dose of prazosin also increased the latency to first response for alcohol and decreased alcohol intake. While sucrose-seeking and intake were similarly affected by prazosin, the high dose of prazosin did not increase response latency.

CONCLUSIONS

These findings are consistent with and extend previous research and suggest that prazosin decreases motivation to initiate and engage in alcohol consumption. The specificity of prazosin in attenuating the initiation of alcohol- but not sucrose-seeking suggests that this effect is not because of prazosin-induced motor-impairment or malaise. Together with previous findings, these data suggest that prazosin may be an effective pharmacotherapy, with specific application in people that drink excessively or have a genetic predisposition to alcohol abuse.

The alpha1-adrenergic receptor antagonist, prazosin, reduces alcohol drinking in alcohol-preferring (P) rats

BACKGROUND

Preliminary evidence suggest that noradrenergic signaling may play a role in mediating alcohol drinking behavior in both humans and rats. Accordingly, we tested the hypothesis that blockade of alpha(1)-adrenergic receptors will suppress alcohol drinking in rats selectively bred for alcohol preference (P line).

METHODS

Adult male P rats were given 24-hour access to food and water and scheduled access to a 15% (v/v) alcohol solution for 2 hours daily. Rats were injected IP with the alpha(1)-adrenergic receptor antagonist, prazosin (0, 0.5, 1.0, 1.5, or 2.0 mg/kg body weight), once a day at 15 minutes prior to onset of the daily 2-hour 2-bottle choice, alcohol versus water, access period for 2 consecutive days and then 3 weeks later for 5 consecutive days.

RESULTS

Prazosin significantly reduced (p < 0.01) alcohol intake during the initial 2 daily administrations, and this reduction of alcohol intake was maintained for 5 consecutive days by daily prazosin treatment in the subsequent more prolonged trial (p < 0.05). The prazosin-induced reduction of alcohol intake was not dependent upon drug-induced motor impairment since increases in water drinking (p < 0.05) were exhibited during the 2-hour access periods during both 2- and 5-day prazosin treatment.

CONCLUSIONS

The results indicate that the noradrenergic system plays a role in mediating alcohol drinking in rats of the P line and suggest that prazosin--a safe, well-characterized, and well-tolerated drug--may be an effective pharmacotherapeutic agent for the treatment of alcohol use disorders.

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.

Role of alpha-2 adrenoceptors in stress-induced reinstatement of alcohol seeking and alcohol self-administration in rats

RATIONALE AND OBJECTIVES

Alpha-2 adrenoceptors are known to be involved in stress-induced reinstatement of heroin and cocaine seeking in laboratory animals. Here, we studied the involvement of these receptors in stress-induced reinstatement of alcohol seeking by using an agonist (lofexidine) and an antagonist (yohimbine) of these receptors, which inhibit and activate, respectively, noradrenaline transmission. We also tested the effect of lofexidine and yohimbine on alcohol self-administration. Lofexidine is used clinically for treating opiate withdrawal symptoms and yohimbine induces stress-like responses in humans and non-humans.

METHODS

Rats were trained to self-administer alcohol (12% w/v, 1 h/day) and after extinction of the alcohol-reinforced behavior, they were tested for the effect of lofexidine (0, 0.05 and 0.1 mg/kg, IP) on reinstatement of alcohol seeking induced by intermittent footshock stress (10 min, 0.8 mA) or for the effect of yohimbine (0, 1.25 and 2.5 mg/kg, IP) on reinstatement of alcohol seeking. Other rats were trained to self-administer alcohol, and after stable responding, the effects of lofexidine and yohimbine on alcohol self-administration were determined.

RESULTS

Pretreatment with lofexidine (0.05 mg/kg and 0.1 mg/kg) attenuated stress-induced reinstatement of alcohol seeking and also decreased alcohol self-administration. In contrast, yohimbine pretreatment potently reinstated alcohol seeking after extinction and also induced a profound increase in alcohol self-administration.

CONCLUSIONS

Results indicate that activation of alpha-2 adrencoceptors is involved in both stress-induced reinstatement of alcohol seeking and alcohol self-administration. To the degree that the present results are relevant to human alcoholism, alpha-2 adrencoceptor agonists should be considered in the treatment of alcohol dependence.

Clozapine reduces alcohol drinking in Syrian golden hamsters

Alcohol abuse contributes substantially to the overall morbidity of schizophrenia. While typical antipsychotic medications do not limit alcohol use in patients with schizophrenia, emerging data suggest that the atypical antipsychotic clozapine does. To further elucidate the effects of these antipsychotics on alcohol use, we initiated a study in alcohol-preferring rodents. Syrian golden hamsters were given free-choice, unlimited access to alcohol. Nine days of treatment (s.c. injection) with clozapine (2-4 mg/kg/day), but not haloperidol (0.2-0.4 mg/kg/day), reduced alcohol drinking. Clozapine reduced alcohol drinking by 88% (from 11.3+/-1.7 to 1.4+/-0.2 g/kg/day) while increasing both water and food intake. Alcohol drinking gradually (during 24 days) returned toward baseline in the clozapine-treated animals when vehicle was substituted for clozapine. Further increasing the doses of haloperidol (0.6-1.0 mg/kg/day) had no effect on alcohol drinking; moreover, very low doses of haloperidol (0.025-0.1 mg/kg/day) tested in separate groups of hamsters also had no effect on alcohol drinking. This study demonstrates that clozapine, but not haloperidol, can effectively and reversibly decrease alcohol consumption in alcohol-preferring hamsters. The results are compatible with the observations that clozapine, but not haloperidol, limits alcohol use in patients with schizophrenia. These data further suggest that clozapine may serve as a prototype for developing novel treatments for alcohol abuse.

Neuromodulatory role of the endocannabinoid signaling system in alcoholism: an overview

The current review evaluates the evidence that some of the pharmacological and behavioral effects of ethanol (EtOH), including EtOH-preferring behavior, may be mediated through the endocannabinoid signaling system. The recent advances in the understanding of the neurobiological basis of alcoholism suggest that the pharmacological and behavioral effects of EtOH are mediated through its action on neuronal signal transduction pathways and ligand-gated ion channels, receptor systems, and receptors that are coupled to G-proteins. The identification of a G-protein-coupled receptor, namely, the cannabinoid receptor (CB1 receptor) that was activated by Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the major psychoactive component of marijuana, led to the discovery of endogenous cannabinoid agonists. To date, two fatty acid derivatives identified to be arachidonylethanolamide (AEA) and 2-arachidonylglycerol (2-AG) have been isolated from both nervous and peripheral tissues. Both these compounds have been shown to mimic the pharmacological and behavioral effects of Delta(9)-THC. The involvement of the endocannabinoid signaling system in the development of tolerance to the drugs of abuse including EtOH has not been known until recently. Recent studies from our laboratory have demonstrated for the first time the down-regulation of CB1 receptor function and its signal transduction by chronic EtOH. The observed down-regulation of CB1 receptor binding and its signal transduction results from the persistent stimulation of the receptors by the endogenous CB1 receptor agonists, AEA and 2-AG, the synthesis of which has been found to be increased by chronic EtOH treatment. This enhanced formation of endocannabinoids may subsequently influence the release of neurotransmitters. It was found that the DBA/2 mice, known to avoid EtOH intake, have significantly reduced brain-CB1-receptor function consistent with other studies, where the CB1 receptor antagonist SR141716A has been shown to block voluntary EtOH intake in rodents. Similarly, activation of the CB1 receptor system promoted alcohol craving, suggesting a role for the CB1 receptor gene in excessive EtOH drinking behavior and development of alcoholism. Ongoing investigations may lead to the development of potential therapeutic strategies for the treatment of alcoholism.

Effects of d-fenfluramine and metergoline on responding for conditioned reward and the response potentiating effect of nucleus accumbens d-amphetamine

These studies investigated the effects of the 5-hydroxytryptamine (5-HT) releaser, and re-uptake inhibitor, d-fenfluramine, and the non-selective 5-HT receptor antagonist metergoline, on responding for conditioned reward (CR), and on the potentiation of responding for CR following amphetamine injected into the nucleus accumbens. Water deprived rats were trained to associate a compound stimulus with water delivery during a conditioning phase. During a test phase, water was not delivered but the compound stimulus was delivered according to a random ratio 2 schedule following a response on one of two levers; responding on the other lever was not reinforced. Overall, rats responded at a higher rate on the lever delivering the CR. d-Amphetamine (1, 3 and 10 micrograms) injected into the nucleus accumbens dose-dependently enhanced responding on the CR lever. Treatment with d-fenfluramine (0.5 and 1 mg/kg) reduced responding for the CR, and abolished the potentiating effect of d-amphetamine. Responding on the inactive lever was also reduced by 1 mg/kg but not 0.5 mg/kg d-fenfluramine. The reduction of d-amphetamine's effect on responding for CR was prevented by prior treatment with the 5-HT receptor antagonist metergoline (1 mg/kg). Control experiments showed that changes in thirst and motor performance, as well as deficits in learning ability, cannot account for the effects of d-fenfluramine in this paradigm. In a separate experiment, 1 mg/kg metergoline failed to enhance responding for CR, and to augment the response potentiating effect of a low dose (2 micrograms) of d-amphetamine injected into the nucleus accumbens.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol, monoamines, and affect

Evidence suggests that ethanol self-administration is directly related to central norepinephrine (NE) activity and inversely related to central serotonin (5-HT) activity. Normal male volunteers participated in a placebo controlled crossover design to assess the effects of 1-tyrosine (TY) and 1-tryptophan (TP) (precursors of catecholamines and 5-HT, respectively) in combination with ethanol, on several neurobehavioral measures. Ethanol by itself produced negative effects on several dimensions of mood. Dysphoria was potentiated by TP in combination with ethanol and either unchanged or attenuated by the combination of TY and ethanol. Ethanol impaired verbal recall, and neither TP nor TY in combination with ethanol altered that impairment. The results are consistent with the hypothesis that 5-HT mediates some of the negative mood effects produced by ethanol or antagonizes some of its positive effects, while NE at least partly mediates ethanol's positive effects on mood. Ethanol's impairment of verbal memory appears to be mediated by mechanisms outside the monoamine systems.

Noradrenergic system: effect of DSP4 and FLA-57 on ethanol intake in ethanol preferring rats

Ethanol preferring rats (male Long-Evans; n = 6) were selected as drinking rats (DR) and treated with DSP4 (50 mg.kg-1 IP) at the end of the preference selection. Two more groups received DSP4 (50 mg.kg-1 IP) + the inhibitor of dopamine beta-hydroxylase FLA-57 (1 mg.kg-1.d-1 during two weeks), IP (n = 5) or FLA-57 alone (1 mg.kg-1.d-1 during two weeks IP) (n = 5). The control DR group (n = 6) received NaCl 0.9%. 3H-Noradrenaline uptake was studied at the 17th day of treatment in DR, treated or not with DSP4, and in ethanol naive rats treated (n = 6) or not (n = 6) with DSP4 (50 mg.kg-1, IP) DSP4 does not modify ethanol intake in DR, and both treated groups (DR or ethanol naive rats). 3H-Noradrenaline uptake was decreased (about 60%), both in cortex and hippocampus. But the association of FLA-57 and DSP4 decreases both ethanol and fluid intakes. It was suggested 1) that the 40% of intact neurons was able to compensate the DSP4-induced noradrenergic neurons destruction, 2) that the destruction of noradrenergic pathways (FLA-57 + DSP4) is associated with a decrease in ethanol intake but also in fluid intakes, suggesting finally 3) that the modulation of ethanol intake by the noradrenergic system was partial or indirect.

Effects of dopaminergic agents on alcohol consumption by rats in a limited access paradigm

The effects of several dopaminergic drugs on alcohol consumption were studied in free-feeding rats using a limited access paradigm. Ascending doses of amphetamine (0.1, 0.3 and 1.0 mg/kg), haloperidol (0.1, 0.3 and 1.0 mg/kg), SKF 38393 (a D1 receptor agonist - 0.3, 1.0 and 3.0 mg/kg), quinpirole (LY 171555, a D2 receptor agonist - 0.03, 0.1 and 0.3 mg/kg), SCH 23,390 (a D1 receptor blocker, 0.003, 0.01, 0.03 and 0.1 mg/kg) and spiperone (a D2 receptor blocker, 0.003, 0.01, 0.03 and 0.1 mg/kg) were administered IP to rats approximately 30 min prior to their 1-h per day access to alcohol. Each dose was administered for 5 successive days, and the effects of the drugs were compared to those of respective saline or 0.4% lactic acid solution controls. Although there was an overall significant dose effect of amphetamine on alcohol consumption, no single dose altered alcohol consumption significantly from baseline. SKF 38,393 specifically decreased alcohol consumption at the highest dose of 3 mg/kg. Quinpirole significantly increased water consumption at the highest dose but had no effect on alcohol consumption. The antagonist haloperidol decreased alcohol consumption but only at doses that also reduced water consumption. The specific antagonists SCH 23,390 and spiperone decreased water consumption at the highest doses tested without modifying alcohol consumption. Taken together, these data suggest that dopamine does not play as critical a role in mediating the reinforcing effects of alcohol (insofar as they are reflected by alcohol consumption) as it does in relation to other psychoactive drugs, particularly the psychomotor stimulants.

A microcomputer controlled data acquisition system for research on feeding and drinking behavior in rats

This paper describes an inexpensive, reliable computer controlled data collection system designed for the continuous monitoring of feeding and drinking behavior in rats. This system will be useful in areas of behavioral pharmacology research requiring a detailed analysis of food and fluid intake. The configuration described herein was developed for research on the "microstructure" of alcohol drinking behavior. Variables examined include: alcohol bout size, frequency and duration, interbout intervals as well as the temporal pattern of intake and its relationship to food and water consumption. Detailed analysis of behavior using this technique will enhance our ability to interpret the nature of changes in alcohol oriented behavior produced by pharmacological manipulations, aid in the development of specific hypotheses related to the regulation of alcohol drinking behavior and provide a means of testing these hypotheses.

Ethanol induces rotational behavior in 6-hydroxydopamine lesioned mice

Mice with unilateral striatal lesions created by 6-hydroxydopamine (6HDA) injection were screened for rotational (circling) behavior in response to injection of amphetamine and apomorphine. Those that rotated ipsilaterally in response to amphetamine and contralaterally in response to apomorphine were subsequently challenged with 1 to 3 g/kg (i.p.) ethanol. Surprisingly, ethanol induced dose related contralateral (apomorphine-like) rotation which, despite gross intoxication, was quite marked in most animals. No significant correlation was found between the number of turns made following ethanol and made after apomorphine or amphetamine.

A time-dependent biphasic effect of an acute ethanol injection on 3-methoxy 4-hydroxyphenylethylene glycol sulfate in rat brain

The present experiment demonstrated that acute administration of ethanol appeared to have a biphasic effect on the accumulation of 3-methoxy-4-hydroxyphenylethylene glycol sulfate (MHPG-SO4) in rat brain. The magnitude of these alterations in MHPG-SO4 levels was also observed to be highly correlated with peripheral blood ethanol levels. Since levels of MHPG-SO4 are considered to be an index of noradrenergic activity, the findings suggest that ethanol may affect norepinephrine activity in a specific dose- and time-dependent manner. These results are discussed in reference to previous reports describing apparent divergent effects on norepinephrine. Possible mechanisms for the biphasic actions are also suggested.

Norepinephrine turnover and voluntary consumption of ethanol in the rat

The effect of a centrally acting noradrenergic agonist on voluntary ethanol intake was investigated in the laboratory rat. Doses of 1.5, 7.5, 15 and 25 mg/kg of FLA-136 were administered to animals chronically exposed to ethanol on a free choice basis. Administration of the highest dose of the drug brought about a 40% reduction in voluntary ethanol intake with no significant effect on total fluid consumption. These results would seem to indicate a possible functional relationship between rate of norepinephrine turnover and amounts of ethanol voluntarily consumed by the laboratory rat.

Effects of alcohol on cerebrospinal fluid norepinephrine in rhesus monkeys

Alcohol (1-3 g/kg) significantly increased the concentration of cerebrospinal fluid (CSF) norepinephrine (NE) in rhesus monkeys. This effect is consistent with the previously demonstrated activational and possible antidepressant effect of low doses of alcohol. The greatest increase was observed in subjects with low baseline levels of CSF NE. Individual differences in activation or euphoria could be related to differential increases in CSF NE following alcohol consumption.

Selective depletion of norepinephrine in brain by N-2-chloroethyl-N-ethyl-2-bromobenzylamine fails to alter the voluntary consumption of ethanol in rats

The effects of the selective norepinephrine neurotoxin, DSP-4, on the maintenance of voluntary consumption of ethanol was tested in male Long-Evans rats. The drug, DSP-4, produced a 51% reduction in whole brain levels of NE without affecting the consumption of ethanol. These results, however, do not rule out a role for NE in mediating this behavior.

The influence of haloperidol and aminooxyacetic acid on etonitazene, alcohol, diazepam and barbital consumption

Four groups of rats were given free choice between water and solutions of either 3 micrograms/ml etonitazene, 5% ethanol (v/v), 0.1 mg/ml diazepam or 3 mg/ml barbital for 10-14 days. With the exception of barbital, some rats spontaneously preferred the drug solutions to water. This preference was reduced by addition of 7 micrograms/ml haolperidol. In a forced drug fluid consumption procedure, the daily administration of 15 mg/kg i.p. of the gamma-aminobutyric acid (GABA)-transaminase blocker aminooxyacetic acid (AOAA) led to a reduction of ethanol and diazepam intake, but not of etonitazene and barbital. It is suggested that the diminished consumption of ethanol and diazepam as caused by GABA-T-inhibition may also be mediated by dopamine which seems to act indirectly, via benzodiazepine receptors and GABA neurons.

Attenuation by antidepressant drugs of alcohol intake in rats

Ethanol preferring rats were selected and showed a constant voluntary intake of a 12% ethanol solution during 14 days (about 5 g/kg body weight daily). These alcohol preferring rats were daily IP injected during two weeks with different antidepressant drugs, according to their specificity of action: nomifensine (5 and 10 mg/kg) and maprotiline (2.5 and 5 mg/kg) (dopamine uptake inhibitors), desipramine and metapramine (5 and 10 mg/kg) (noradrenaline uptake inhibitors) clomipramine and doxepin (5 and 10 mg/kg) (serotonin uptake inhibitors). Only desipramine, 5 and 10 mg/kg, metapramine, 10 mg/kg, clomipramine, 5 and 10 mg/kg and doxepin, 10 mg/kg, were able to reduce significantly the ethanol intake. These drugs specifically inhibit noradrenaline or serotonin uptake. These data lead us to think that norepinephrine and/or serotonin, but not dopamine, are involved in the voluntary intake of alcohol.

Zimeldine: a review of its effects on ethanol consumption

This review evaluates the literature and describes an extensive series of experiments which examined the effects of zimeldine , its metabolite norzimeldine and other serotonin and norepinephrine reuptake inhibitors on voluntary ethanol consumption in rats. The results of these experiments indicate that drugs which specifically inhibit serotonin reuptake are capable of decreasing voluntary ethanol consumption. The behavioral mechanism through which these drugs exert their effects seems to be extinction of the primary reinforcing properties of alcohol. These effects seem to be partially attenuated both by drugs which modulate the norepinephrine system as well as by the serotonin postsynaptic receptor blocker methergoline. The data presented in this review are discussed in terms of the involvement of the serotonin and norepinephrine systems in the mechanism of action of these drugs. In addition, several alternative hypotheses concerning the nature of the phenomenon are offered. Finally, the implications of these data for the possible development of a treatment procedure for problem drinkers is discussed.

Forebrain noradrenaline and oral self-administration of ethanol by rats

The effects of 6-hydroxydopamine-induced depletion of forebrain noradrenaline (NA) on oral intake of ethanol were studied in male Wistar rats. Prior depletion of NA produced a smaller and significantly less variable intake of a concentrated solution of ethanol than that of control rats, and this effect was not accompanied by hyperreactivity to aversive solutions of quinine. NA-depleted rats also displayed rejection 'thresholds' for ethanol solutions that were significantly lower than those of controls. Depletion of forebrain NA did not, however, affect the punishing effects of ethanol injections measured in the conditioned taste aversion paradigm. In contrast to these effects of NA depletion on initiation of ethanol intake, depletion of forebrain NA after a preference for ethanol had been established failed to affect subsequent intake of ethanol. These results suggest that forebrain NA is involved in the initiation of ethanol intake by naive rats but not in the maintenance of established patterns of intake by experienced rats. Possible mechanisms for this differential involvement of NA are discussed.

Actions of drugs of abuse on brain reward systems: a reconsideration with specific attention to alcohol

Research in the areas of intracranial self-stimulation and drug self-administration has provided a substantial data base that has contributed to our understanding of brain reward mechanisms. In a recent article, Wise [83] argued that dopamine is the catecholamine critically involved in the central mediation of reward. The present paper attempts to examine the available data with particular reference to alcohol, but also with reference to opiates, and argues that the reinforcing effects of at least these drugs are primarily and directly mediated by noradrenergic rather than dopaminergic systems in the brain. It also argues, in direct contrast to Wise, that in the context of these drugs, dopamine seems to play a minor if not negligible role.

Central norepinephrine metabolism during alcohol intoxication in addicts and healthy volunteers

The concentrations of the major norepinephrine metabolite, 3-methoxy-4-hydroxyphenylethylene glycol (MOPEG), in lumbar cerebrospinal fluid of alcoholic patients were markedly elevated during intoxication and successively declined during 1 and 3 weeks of abstinence. During intoxication the MOPEG concentration in cerebrospinal fluid showed a statistically significant correlation with the blood alcohol concentration. In healthy volunteers who received 80 grams of ethanol, the MOPEG concentration in cerebrospinal fluid increased significantly. Healthy subjects sampled during intoxication had significantly higher concentrations of MOPEG in the cerebrospinal fluid than did subjects sampled after the end of intoxication. The results indicate that alcohol administration markedly stimulates norepinephrine metabolism in the central nervous system in human subjects possibly by increasing unit impulse activity of central noradrenergic neurons.

Intragastric drug self-administration by rats exposed successively to morphine and ethanol

Male Sprague-Dawley rats were implanted with intragastric cannulas for self-administration of drug solutions by bar-pressing on a continuous reinforcement schedule in 10-hour daily sessions. Similar levels of responding were observed for doses per infusion of 3.0 mg/kg morphine sulfate and 25 mg/kg ethanol in separate groups of rats. When rats that showed self-administration of a morphine solution over a 5-day period were than given access instead to ethanol for 5 days, the number of infusions taken did not deviate significantly between the two periods. However, rats selected from a small minority that failed to take morphine under these conditions also failed to manifest ethanol self-administration behavior. The data can be seen to support a possible concurrence or similarity between innate factors determining acceptance or rejection of morphine and ethanol as objects of self-administration behavior.

Reinforcement with intragastric infusions of ethanol: blocking effect of FLA 57

Suppression of oral intake of ethanol by FLA 57 has been reported for rats and was attributed to an inhibition of dopamine beta-hydroxylase. We have demonstrated the ability of FLA 57 (50 mg/kg, IP) to suppress bar-pressing for intragastric (IG) delivery of doses of ethanol (25 mg/kg). This indicates that the effect on oral intake of ethanol may not be attributed to a taste factor, e.g., a decreased palatability of the ethanol solution. The same dose of FLA 57 did not suppress responding for IG doses of sweet milk. Thus, there was not an impairment of appetitive behavior in general through some nonspecific depressant or toxic action. Furthermore, the primary reinforcing action of ethanol, when used to establish a buzzer as a conditioned reinforcer through repeated pairings, was blocked if FLA 57 was given before pairings. This was evidenced by a failure of such rats to bar-press above the baseline level in a later test of conditioned reinforcement, which contrasted with the increased responding seen for rats receiving saline instead of FLA 57 before ethanol. These data support the previous findings on oral ethanol and confirm that FLA 57 can impair the mechanism by which ethanol produces positive reinforcement in rats.

Intraventricular self-administration of acetaldehyde, but not ethanol, in naive laboratory rats

For 11 consecutive days, naive rats were maintained in operant chambers where they were given the opportunity to self-administer acetaldehyde (1,2, or 5% v/v), ethanol (2 or 10% v/v), or pH control solutions directly into the cerebral ventricles. Only the animals that had access to the 2 and 5% acetaldehyde solutions showed rates of lever pressing significantly higher than controls. It is suggested that acetaldehyde rather than ethanol itself may mediate the positive reinforcing effects of ethanol in the brain.