Attenuation by antidepressant drugs of alcohol intake in rats

Postdependent state in rats as a model for medication development in alcoholism

Rational development of novel therapeutic strategies for alcoholism requires understanding of its underlying neurobiology and pathophysiology. Obtaining this knowledge largely relies on animal studies. Thus, choosing the appropriate animal model is one of the most critical steps in pre-clinical medication development. Among the range of animal models that have been used to investigate excessive alcohol consumption in rodents, the postdependent model stands out. It was specifically developed to test the role of negative affect as a key driving force in a perpetuating addiction cycle for alcoholism. Here, we will describe our approach to make rats dependent via chronic intermittent exposure to alcohol, discuss the validity of this model, and compare it with other commonly used animal models of alcoholism. We will summarize evidence that postdependent rats fulfill several criteria of a 'Diagnostic and Statistical Manual of Mental Disorders IV/V-like' diagnostic system. Importantly, these animals show long-lasting excessive consumption of and increased motivation for alcohol, and evidence for loss of control over alcohol intake. Our conclusion that postdependent rats are an excellent model for medication development for alcoholism is underscored by a summary of more than two dozen pharmacological tests aimed at reversing these abnormal alcohol responses. We will end with open questions on the use of this model. In the tradition of the Sanchis-Segura and Spanagel review, we provide comic strips that illustrate the postdependent procedure and relevant phenotypes in this review.

Fluoxetine, desipramine, and the dual antidepressant milnacipran reduce alcohol self-administration and/or relapse in dependent rats

A few clinical studies have shown that dual antidepressants (serotonergic (5-HT) and noradrenergic (NE) transporter inhibitors, SNRIs) may be effective in alcoholism treatment. We studied the effect of the dual antidepressant milnacipran on ethanol operant self-administration in acutely withdrawn ethanol-dependent and in -non-dependent Wistar rats, and used fluoxetine and desipramine to dissect both 5-HT and NE components, respectively, in the effect of milnacipran. Milnacipran was also tested for relapse after protracted abstinence and on ethanol-induced (1.0 g/kg) conditioned place preference in control rats and ethanol-induced locomotor sensitization in DBA/2J female mice. Milnacipran dose dependently (5-40 mg/kg) attenuated the increased ethanol self-administration observed during early withdrawal and was more potent in preventing reinstatement in dependent rats after protracted abstinence as compared with non-dependent rats. Desipramine and fluoxetine (10 mg/kg) blocked ethanol self-administration during early withdrawal, and recovery was delayed in dependent animals, indicating a potent effect. Ethanol self-administration was also reduced 1 day after treatment with desipramine and fluoxetine but not with milnacipran. Finally, milnacipran prevented ethanol-induced place preference in ethanol-naive rats and reduced the magnitude of ethanol-induced sensitization associated with a delayed induction in mice. Desipramine (20 mg/kg) countered sensitization development and reduced its expression at 1 week after treatment; fluoxetine (10 mg/kg) reduced sensitization expression. Thus, 5-HT and NE transmissions during sensitization expression may mediate the effect of milnacipran on sensitization induction. These results support that SNRIs may have a potential use in alcoholism treatment.

Effect of DOV 102,677 on the volitional consumption of ethanol by Myers' high ethanol-preferring rat

BACKGROUND

Inhibitors of monoamine neurotransmitter transporters are well established as antidepressants. However, the evidence that single (serotonin) or dual (serotonin-norepinephrine) neurotransmitter uptake inhibitors can treat ethanol abuse, either as a comorbidity with depression or as a separate entity, is inconsistent. Drugs that have, in addition, the ability to inhibit dopamine uptake may have an advantage in the treatment of alcohol abuse. Therefore, the inhibitor of norepinephrine, serotonin and dopamine uptake, DOV 102,677, was tested for its effects on the volitional consumption of ethanol by an ethanol-preferring rat strain.

METHODS

Myers' high ethanol-preferring rats were screened by a 10-day, 3 to 30% step-up test and then given free access to the preferred concentration of ethanol in a 3-bottle choice task. Consumption of ethanol (g/kg), water, food, and body weight were measured daily during a 3-day predrug treatment period, a 3-day treatment period, and a 3-day posttreatment period. Additional Sprague-Dawley rats were observed for 24 hours for the behavioral effects of 2.0 mg/kg s.c. reserpine after a 30-minute pretreatment with different doses of DOV 102,677.

RESULTS

The triple monoamine uptake inhibitor DOV 102,677 dose-dependently decreased the volitional consumption of ethanol by as much as 71.2% (20 mg/kg i.p., b.i.d.) over 3 days of administration. This effect carried over into the posttreatment period. Similarly, the proportion of ethanol to total fluids consumed declined by 66.2% (20 mg/kg s.c., b.i.d.), while food consumption and body weight were unaltered. In contrast, amperozide (2 mg/kg i.p., b.i.d.) suppressed the amount of ethanol consumed by 56%, while naltrexone (5 mg/kg i.p., b.i.d.) was without effect. DOV 102,677 (40 mg/kg s.c.) inhibited reserpine-induced akinesia and ptosis, but not hypothermia in Sprague-Dawley rats, consistent with its transient inhibition of serotonin transport, and more long-lived inhibition of norepinephrine and dopamine uptake.

CONCLUSIONS

DOV 102,677 significantly decreased the volitional consumption of ethanol with minimal alterations in the intake of food or on body weight in an ethanol-preferring rat strain, suggesting that triple reuptake inhibitors may find utility in treating alcohol abuse.

Reduced DAT- and DBH-immunostaining in the limbic system of Sardinian alcohol-preferring rats

We have recently shown that tyrosine-hydroxylase immunostaining (TH-IM) is selectively decreased in the cingulate cortex and in the shell of the nucleus accumbens (nAcc) of Sardinian alcohol-preferring rats (sP) when compared with Sardinian alcohol-non preferring (sNP) and Wistar (W) rats. Since these regions contain both dopamine and noradrenaline (NA) fibers, clarification of the dopaminergic and noradrenergic contribution to the decreased TH-immunoreactivity was needed. To this aim, we carried out the present immunohistochemistry study using two antibodies raised against dopamine beta-hydroxylase (DBH), the enzyme responsible for the conversion of dopamine into noradrenaline, and against the dopamine transporter (DAT), as markers for noradrenergic and dopaminergic fibers, respectively. The results show that DBH-immunostaining (DBH-IM) and DAT-immunostaining (DAT-IM) were both lower in the cingulate cortex of the sP rats with respect to sNP and W rats. In the shell of the nAcc a reduced DAT-IM in sP rats was found, while the DBH-IM did not differ between the three lines of rats. The analysis of the cell-body area of noradrenergic neurons in the locus coeruleus, revealed no differences between sP, sNP and W rats. These results indicate a selective reduction of the terminal innervation in the mesocorticolimbic dopamine and NA systems in sP rats. This genetically-determined difference may be involved in the opposite alcohol preference and consumption of sP and sNP rats.

Haloperidol administered subchronically reduces the alcohol-deprivation effect in mice

During the pre-experimental phase, hybrid (CBA x C57BL) male mice having had 16 weeks free access to food, water and flavored 30% alcohol were deprived of alcohol for 3 days. The next day they were given free choice between similarly flavored water and 30% alcohol. The mice were divided into two subgroups having (HD) or lacking (LD) the deprivation-induced elevation in alcohol intake during the first 1.5 h of renewed access compared with their intake during the last 22.5 h of first postdeprivation day. In Experiment 1, alcohol naive, LD, and HD mice received daily injections of haloperidol (Haldol; 1 mg/kg) or vehicle during 14 days of abstinence. The behavior of the mice was evaluated in an exploratory cross-maze and inescapable slip funnel test a day after the 13th injection (before the 14th injection). On the first postinjection day, the mice were again given a free choice between flavored water and alcohol. In Experiment 2, all the mice were administered with vehicle during the first 13 days of abstinence. On 14th day, they received an injection of haloperidol (1 mg/kg) or vehicle and a day later were given choice between flavored water and alcohol. Unlike a single injection, the subchronic administration of haloperidol lowered the alcohol intake by HD mice with a more prominent decrease seen during the first 1.5 h than during the last 22.5 h of first postdeprivation day. The alcohol-deprivation effect in HD mice decreased by 79% after subchronic haloperidol. No significant change in alcohol intake was found in alcohol-naive and LD mice. Water intake did not vary systematically. Among the groups, the effect of subchronic haloperidol on the alcohol-deprivation effect did not parallel changes in most of the measures of exploratory or avoidance behavior. It is proposed that haloperidol administered subchronically may attenuate motivation for alcohol.

Lack of effect of dopamine D2 blockade on ethanol intake in selected and unselected strains of rats

Previous research has suggested that brain catecholamines may be involved in regulating ethanol intake. This study was designed to look more specifically at dopamine (DA) and whether DA D2 receptor blockade with the antagonist pimozide would alter ethanol consumption in rats. Subjects were male Maudsley Reactive and Wistar rats, the former previously shown to consume larger amounts of ethanol than the latter. Both strains were screened for ethanol intake by presentation of ethanol solutions (free choice with water) in increasing steps from 2% to 10% (v/v) on an alternate-day schedule. Following the screening period, animals were switched to a schedule of everyday presentation of the 10% (v/v) ethanol solution (free choice with water) for 10 baseline days. Animals were then divided into high and low drinking levels according to whether their mean baseline ethanol intake (g/kg) fell within +/- 0.5 SD of the mean intake of their group (Maudsley Reactives: mean = 2.55 g/kg, low drinkers < 1.63, high drinkers > 3.47; Wistars: mean = 2.17 g/kg, low drinkers < 1.53, high drinkers > 2.82). The animals were assigned to one of five treatment groups for 5 subsequent days where they received IP injections of pimozide (0.08, 0.24, or 0.48 mg/kg), tartaric acid, or saline. Following the treatment period, ethanol consumption was recorded for 5 posttreatment days. No significant differences due to treatment were observed for either intake or preference of ethanol across treatments, drinking groups, or strains. The results obtained in the present study suggested that interference in DA neurotransmission through administration of the D2 antagonist pimozide does not significantly alter ethanol consumption in either MR or Wistar animals.

Alcoholism abolishes the growth hormone response to sumatriptan administration in man

To assess the possible influence of alcoholism on serotonergic control of growth hormone (GH) secretion, 6 mg of the 5-HT1D serotonergic receptor agonist, sumatriptan, was injected subcutaneously in a group of nine normal controls (aged 32 to 49 years) and in nine age-matched nondepressed male alcoholic subjects after 10 to 25 days of abstinence from alcohol. During the same period, subjects were also tested with GH-releasing hormone ([GHRH] 1 microgram/kg body weight in an intravenous [i.v.] bolus) and L-arginine, which releases GH from somatostatin inhibition (50 g in 50 mL normal saline over 30 minutes) to determine whether GH secretion in response to alternate secretagogues is preserved in alcoholics. A control test with administration of normal saline instead of drug treatments was also performed. Plasma GH levels were recorded over 2 hours in all tests. Administration of placebo did not change plasma GH levels in any subject. Similar GH responses were observed in normal controls and alcoholic subjects when GHRH or arginine were administered. A significant GH increase was observed in normal controls after sumatriptan injection; in contrast, GH secretion was not modified by sumatriptan administration in alcoholic patients. These data show that alcoholism is associated with an impairment in the serotonergic-stimulatory regulation of GH secretion, whereas GH responses to direct pituitary stimulation with GHRH or to release from somatostatinergic inhibition with arginine appear to be preserved in alcoholics.

New drugs for the treatment of experimental alcoholism

This article presents a current overview of the efforts to suppress pharmacologically the craving, dependence, or other factors associated with the self-selection of alcohol in an experimental animal. The contemporary status of the pharmacotherapy of experimental alcoholism similarly is described for different animal models of alcohol drinking. An evaluation is presented of several classes of drug for their efficacy in ameliorating the volitional ingestion of alcohol in the presence of an alternative fluid. Currently, two main experimental animal models of alcoholism are being used in this endeavor: (a) genetic lines or substrains of high alcohol preferring or high drinking rats; and (b) strains of nondrinking or low alcohol preferring rats which are induced chemically to prefer alcohol. Because of technical, methodological, and other issues surrounding the procedures used to assess the efficacy of a drug in reducing alcohol intake, several of the newer findings remain controversial. For example, serious side effects on the intake of food, caloric regulation, motor activity, or other functions would preclude the clinical utility of the drug. However, several drugs which affect monoaminergic neurons as well as opioid systems in the brain now seem to offer promise as agents which do possess clinical benefits. Two of these drugs, FG5606 (amperozide) and FG 5893 are essentially "antialcoholic" or anticraving and are without any significant side effects on cerebral mechanisms responsible for hunger, caloric intake, motor activity, or other physiological process. Amperozide, a 5-HT2 receptor antagonist with dopamine releasing properties, is particularly notable because of its irreversible nature in attenuating alcohol preference for months after its administration. It is concluded that future pharmacological research on presently available and newly developed compounds will provide exciting opportunities to the clinician who can utilize a particular drug as an adjunctive tool in the therapeutic treatment of the alcoholic individual.

Alcohol drinking in rats treated with 5,7-dihydroxytryptamine: effect of 8-OH-DPAT and tropisetron (ICS 205-930)

5,7-Dihydroxytryptamine (5,7-DHT) was administered ICV to Wistar male rats. Lesioned rats displayed higher preference for ETOH than sham-lesioned animals. Among 5,7-DHT-pretreated rats 38% became high-preferring, while only 22% of sham-lesioned rats displayed this behavioural pattern (p < 0.05). Both 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; the agonist of serotonin 5-HT1A receptors) and tropisetron (ICS 205-930, the antagonist of 5-HT3 receptors) reduced ETOH consumption in high-preferring, sham-lesioned rats. However, in 5,7-DHT rats the effect of 8-OH-DPAT was completely abolished, while tropisetron retained its antipreference activity. Therefore, it seems that 5-HT1A autoreceptors are critically involved in 8-OH-DPAT action, while 5-HT3 receptor sites responsible for tropisetron action are located beyond the 5-HT system.

Alcohol, the reward system and dependence

Evidence is presented to show that multiple neurotransmitter systems of the brain reward systems including GABA, glutamate, dopamine, serotonin and opioid peptides are involved in alcohol reinforcement. Dependence is associated with changes in many of these same systems, but also with changes in other neurotransmitters, such as brain corticotropin releasing factor. A midbrain forebrain circuitry that involves parts of the nucleus accumbens and amygdala is hypothesized to be the focus for the neuropharmacology of alcohol reinforcement.

Alcohol drinking in rats is attenuated by the mixed 5-HT1 agonist/5-HT2 antagonist FG 5893

Over the last three decades, the neurotransmitter serotonin (5-HT) has been implicated in the etiological mechanisms underlying the excessive drinking of ethyl alcohol. Recently, the 5-HT2 antagonist amperozide was found to reduce selectively the high intake of alcohol in the cyanamide-induced drinking rat without any adverse side effects. The purpose of the present study was to determine the action on alcohol drinking of the novel second-generation amperozide-like drug, which is a mixed 5-HT1 agonist/5-HT2 antagonist, FG 5893 (2-[4-[4,4-bis(4-fluorophenyl)butyl]-1-piperazinyl]-3-pyridinecarb oxylic acid methyl ester). To induce preference for alcohol in Sprague-Dawley rats, the enzyme aldehyde dehydrogenase was inhibited by cyanamide administered in the absence of alcohol in a dose of 10 mg/kg twice a day over three days. A standard three-bottle preference test was used in which water and a maximally preferred concentration of alcohol were offered to each animal. Following control tests of alcohol preference for 3 days, either a saline control vehicle or FG 5893 in a dose of 0.5, 1.0, or 2.5 mg/kg was administered subcutaneously at 1600 and 2200 for 3 consecutive days. Whereas control injections of saline were without effect on alcohol consumption, all doses of FG 5893 significantly reduced the 24-h intake of alcohol in terms of both absolute g/kg and proportion of alcohol to total fluid intake. Further, the 1.0 and 2.5 mg/kg doses of FG 5893 continued to suppress alcohol consumption over two 4-day tests immediately following the injection sequence and after a 40-day interval.(ABSTRACT TRUNCATED AT 250 WORDS)

SDZ-205,152, a novel dopamine receptor agonist, reduces oral ethanol self-administration in rats

The effects of SDZ-205,152, a synthetic mixed D1/D2 dopamine receptor agonist, was investigated in rats trained to orally self-administer ethanol (10% w/v) in a free-choice, two-lever operant task. Pretreatment with SDZ-205,152, at doses of 0.5-5.0 mg/kg subcutaneously 30 min prior to limited access to 10% ethanol and water, selectively reduced ethanol-reinforced responding without affecting responses for water. These results demonstrate that ethanol-reinforced responding was attenuated by SDZ-205,152 and suggests that dopamine neural systems may mediate, in part, the reinforcing properties associated with voluntary ethanol self-administration.

Reducing the desire to drink. Pharmacology and neurobiology

The past decade has witnessed major advances in understanding of neural functioning and neurobiological bases of alcohol consumption. Concurrent with this, a range of exciting investigations have been conducted on pharmacologic agents that may curb drinking behavior. Research is reviewed on several promising medications influencing neurotransmitter and endocrine systems with particular attention to the serotonergic and opioid systems. Following this overview, recommendations are offered regarding research methodology to support future pharmacotherapy trials.

Platelets 3H 5-HT uptake in descendants from alcoholic patients: a potential risk factor for alcohol dependence?

We studied platelet 3H-serotonin uptake in 32 former alcoholics, withdrawn for from 1 month to 22 years, in their descendants (21.7 +/- 1.6 years old, n = 17; 10.9 +/- 0.7 years old; n = 19), and in respective control groups, paired in age and sex. All of the alcoholics presented high 3H-serotonin uptake (Vmax = 10.88 +/- 4.23 pmoles/10(8)pl/30 sec., vs. 0.93 +/- 0.15 pmole/10(8)pl/30 sec. Their descendants also showed high platelet serotonin uptake: 3.94 +/- 1.44 pmoles/10(8)pl/30 sec., vs. 0.93 +/- 0.15 pmoles/10(8)pl/30 sec. for adult descendants, and 5.99 +/- 2.23 vs. 0.84 +/- 0.15 pmole/10(8)pl/30 sec. for young descendants. All subjects were free of alcoholisation (biological parameters studied were blood ethanol concentration, gamma glutamyl transferase and mean corpuscular volume), and dependence of former alcoholics was evaluate by using, a posteriori, the CAGE test. In descendants, 28% of the subjects have Vmax values higher than the highest of the control group. Alcohol, in vitro, (54 mM) did not affect serotonin uptake in any group. These results indicate that in descendants of alcoholics, platelet serotonin uptake is altered, without modification of sensitivity to ethanol. The genetic basis of alcohol dependence could be linked with the platelet serotonin transport.

Effect of ethanol administration and withdrawal on serotonin receptor subtypes and receptor-mediated phosphoinositide hydrolysis in rat brain

The effect of short-term (15 days) and long-term (60 days) ethanol treatment and withdrawal on agonist-stimulated phosphoinositide (Pl) hydrolysis, serotonin receptor subtypes (5HT1A and 5HT2), and alpha 1-adrenergic receptors were studied in rat cerebral cortex. Short-term ethanol treatment had no significant effect on serotonin (5HT), norepinephrine (NE), and calcium ionophore (A23187)-stimulated [3H]-inositol-1-phosphate ([3H]-IP1) formation and 5-HT2 receptors as measured by 125I-lysergic acid diethylamide (125I-LSD) binding, in rat cerebral cortex. However, 15 days of ethanol treatment, followed by 24 hr of withdrawal resulted in a decrease in Bmax of 125I-LSD binding without significant change in KD, as well as a decrease in 5HT-stimulated [3H]-IP1 formation in rat cerebral cortex. 5HT1A and alpha 1-adrenergic receptors were determined by using [3H]-8-hydroxy-2-(di-N-propylamino)tetralin and [3H]-prazosin as radioligand, respectively. We also observed that long-term ethanol treatment had no significant effect on Bmax and KD of 5HT2, 5HT1A, and alpha 1-adrenergic receptors, as well as NE and A23187-stimulated [3H]-IP1 formation, but significantly decreased the 5HT-stimulated [3H]-IP1 formation in rat cerebral cortex. It is possible that a decrease in 5HT-induced PI turnover after long-term ethanol exposure may be due to a decrease in coupling of 5HT2 receptors to G protein or PLC enzyme, whereas the decrease in 5HT-induced PI turnover after withdrawal may be due to a decrease in functional 5HT2 receptor number.

Influence of dopaminergic and serotonergic neurons on intravenous ethanol self-administration in the rat

Rats implanted with chronic indwelling intravenous catheters and allowed access to a self-administration apparatus learned to self-inject intravenous ethanol. Ethanol concentrations of 0.5, 1.0, and 2.0%, corresponding to a dose/injection of 1, 2, and 4 mg/kg, respectively, were consistently self-injected. Self-injection was not acquired or maintained with ethanol doses of 0.5 or 8 mg/kg/injection. Saline replacement of ethanol reservoirs led to marked increases in lever-pressing response in animals self-injecting 1, 2, and 4 mg/kg ethanol/injection but not with 0.5 or 8 mg/kg/injection. Neurotoxin-induced lesions of dopamine-(DA) containing neurons in nucleus accumbens septi failed to alter the acquisition or maintenance of ethanol self-injection. Pretreatment with haloperidol (0.05 and 0.1 mg/kg, SC) failed to alter hourly or daily self-injection rates. On the other hand, p-chlorophenylalanine pretreatment increased, while fluoxetine (2.5 and 5.0 mg/kg) administration significantly reduced, self-injected intravenous ethanol. These data suggest that ethanol is self-injected by the rat in a narrow dose range and that 5-hydroxytryptamine (5-HT), but not DA-containing neurons, subserves some function in the reinforcing or aversive affects of ethanol.

Ethanol intake and 3H-serotonin uptake I: A study in Fawn-Hooded rats

Ethanol intake and synaptosomal 3H-serotonin uptake were studied in male Fawn-Hooded and Sprague-Dawley rats. Fawn-Hooded rats consumed more alcohol and more water than Sprague-Dawley rats. Plasma alcohol levels of Sprague-Dawley rats were not detectable but were about 5 mg/dl in Fawn-Hooded rats. Ethanol intake increased the Vmax of serotonin uptake in Fawn-Hooded rats in hippocampus and cortex, but not in thalamus. In Fawn-Hooded rats, serotonin uptake (Vmax) was higher than in Sprague-Dawley rats cortex. Ethanol intake reduced the Vmax of serotonin uptake in Fawn-Hooded rats in hippocampus and cortex. In cortex, the carrier affinity for serotonin was increased in alcoholized Fawn-Hooded rats. These results indicate that synaptosomal 3H-serotonin uptake is affected by ethanol intake. In Fawn-Hooded rats, high ethanol consumption is associated with high serotonin uptake. In rats presenting high serotonin uptake, alcoholisation reduces 3H-serotonin internalisation in synaptosomes, indicating a specific sensitivity to alcohol intake of serotonin uptake system.

Effects of fluoxetine and desipramine on palatability-induced ethanol consumption in the alcohol-nonpreferring (NP) line of rats

Three groups of NP rats (n = 5/group) received food, water and one of 3 Polycose solutions ad lib. One group received a solution containing 3% (w/v) Polycose, 0.125% (w/v) saccharin, 0.5% (w/v) NaCl (3% POL solution) to which ethanol was gradually added over three weeks until the concentration of 10% (v/v) ethanol (E) was reached (3% POL + E group). Alcohol ingestion by the 3% POL + E group reached an average of 9 g of ethanol/kg b. wt./day; the rats attained average blood alcohol concentrations of 61 +/- 8 mg%. One control group (3% POL) was given the same solution as above but without ethanol. The second control group (17% POL) had access to a 17.6% Polycose solution supplemented with 0.125% saccharin and 0.5% NaCl and was isocaloric to the 3% POL + E solution. Although the three groups differed significantly in the amounts of food and Polycose solutions consumed, their total caloric intakes were equivalent. The IP administration of the serotonin (5-HT) uptake inhibitor fluoxetine (5 and 10 mg/kg) significantly reduced drinking of the group receiving the 3% POL + E solution by 23% and 67%, respectively, but did not alter intakes of the Polycose solutions by the 3% or 17% POL control groups. The IP administration of the norepinephrine (NE) uptake inhibitor desipramine (5 and 10 mg/kg) significantly reduced intake of the Polycose solution by the 17% POL group by 52 and 83%, respectively, but only the 10 mg/kg dose attenuated drinking of the solutions by the 3% POL and 3% POL + E groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of p-chlorophenylalanine on the voluntary consumption of ethanol, water and solid food by UChA and UChB rats

The immediate and the long-lasting effects of PCPA (126 mg/kg IP for 3 days) on the voluntary consumption of 10% v/v ethanol solution, water and solid food were studied in genetically low (UChA) and high (UChB) ethanol consumer rats. Data were analysed according to the method proposed by the authors for recognizing specific effects on ethanol consumption. Results confirmed immediate specific decrease of ethanol consumption in UChB rats, while a nonspecific decrease of it was observed in UChA rats. In UChB rats ethanol consumption recovered the basic level about nine days after the first dose. By contradistincion, in UChA rats a significant specific increase of ethanol consumption, starting at the first week after the treatment, was observed. During this period 12 out of 21 UChA rats reached an ethanol consumption level commonly observed in UChB rats, and 10 of them recovered the pretreatment level in 15 to 30 weeks. The other 2 maintained the high consumption until 38 weeks of observation. At that time the serotonin content of cortex and hippocampus of these 2 rats was normal.

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.

Spiroxatrine augments fluoxetine-induced reduction of ethanol intake by the P line of rats

The present study was undertaken to determine if spiroxatrine, a reported 5-HT1A antagonist, could block the attenuating effects of fluoxetine (a 5-HT uptake inhibitor) on voluntary ethanol intake by the selectively bred alcohol-preferring P line of rats. Fluoxetine (10 mg/kg, IP) significantly reduced the intake of 10% ethanol by P rats approximately 50% during the 4-hour period of alcohol availability. Spiroxatrine (4 mg/kg, IP) was without effect on ethanol intake when given alone. However, when given 5 minutes before fluoxetine (10 mg/kg, IP), this dose of spiroxatrine augmented the reduction of ethanol intake to approximately 15% of control values after 4 hours. Similar experiments conducted with 1 mg/kg (IP) 8-hydroxy-2(di-N-propylamino) tetralin (DPAT) demonstrated that this 5-HT1A agonist also enhanced the attenuating effects of fluoxetine on ethanol intake. Likewise, spiroxatrine augmented the DPAT reduction of alcohol intake. Spiroxatrine enhanced the effect of DPAT and fluoxetine on food intake as it did on ethanol intake. The results suggest that spiroxatrine behaved as a partial agonist and/or modulator and not as an antagonist at 5-HT1A receptors under the present experimental conditions.

Serotonin and ethanol preference

This chapter brings together evidence indicating the involvement of serotonin (5-HT) in ethanol preference using data mainly obtained from selectively bred alcohol-preferring and alcohol-nonpreferring lines of rodents. Although several laboratories have established rodent lines that will consume large quantities of ethanol daily, only one line thus far has been established that satisfied all the criteria for an animal model of alcoholism and that would be suitable for studying the biological basis of ethanol preference. This is the P line of alcohol-preferring rats that: (1) freely consumes 5-9 g ethanol/kg body wt/day; (2) drinks sufficient alcohol to produce intoxicating blood alcohol concentrations; (3) works to obtain alcohol; (4) self-administers ethanol for its CNS pharmacological effects; and (5) develops chronic tolerance to and dependence on alcohol with free-choice drinking. Relative to the NP line of alcohol-nonpreferring rats, the P rat has lower 5-HT levels in several CNS regions, including some, such as the nucleus accumbens, hypothalamus, and frontal cortex, which are involved in the brain reward circuitry. Furthermore, both acute and chronic ethanol administration have effects on the 5-HT pathway from the dorsal raphe nucleus to the nucleus accumbens in the P rat. Pharmacological studies have demonstrated that fluoxetine, a serotonin uptake inhibitor, reduced the oral consumption or intragastric self-administration of alcohol in the P rats. In addition, administration of a 5-HT1B agonist also attenuated the oral intake of ethanol by P rats. It is hypothesized that the serotonergic pathway from the dorsal raphe nucleus to the nucleus accumbens is involved in the reinforcing actions of alcohol in the P line of rats.

Serotonin uptake blockers and voluntary alcohol consumption. A review of recent studies

Previous research demonstrated that serotonin uptake blockers (e.g., zimeldine, sertraline, fluoxetine) reduce voluntary ethanol consumption in rats and humans. However, the mechanism of action of these compounds is not well understood. It has been suggested, for example, that serotonin uptake blockade interferes with the processes that mediate the reinforcement derived from ethanol ingestion. On the other hand, there is considerable experimental evidence that suggests that the effects on alcohol intake may be an expression of a more general inhibitory role that serotonin plays in consummatory behavior. This chapter presents evidence that suggests that serotonin uptake blockers may affect ethanol intake, in part via a reduction of food intake. Current issues concerning the central versus peripheral mediation of these effects, receptor specificity, as well as alternate mechanisms of action are considered.

Effects of Ro 15-4513, fluoxetine and desipramine on the intake of ethanol, water and food by the alcohol-preferring (P) and -nonpreferring (NP) lines of rats

The effects of the IP administration of RO 15-4513 (1, 2 and 4 mg/kg), fluoxetine (5 and 10 mg/kg) and desipramine (5 and 10 mg/kg) on the intake of 10% ethanol, H2O and food were determined in the selectively bred alcohol-preferring (P) and -nonpreferring (NP) lines of rats with daily access to fluids being limited to single 2-hour sessions. The imidazobenzodiazepine Ro 15-4513 (a partial inverse benzodiazepine agonist) significantly reduced the intake of 10% ethanol by the P rats to 50-60% of control levels in the first 30 minutes without altering food or H2O intake. The attenuating actions of 2 mg/kg Ro 15-4513 on ethanol intake could be completely blocked by the central benzodiazepine receptor antagonist Ro 15-1788 (10 mg/kg). Ro 15-1788, by itself, produced no effects on alcohol and H2O consumption. The 5 mg/kg dose of fluoxetine significantly reduced 10% ethanol intake by the P rats to 20% of control values without altering either H2O or food consumption. The 10 mg/kg dose of fluoxetine further reduced ethanol intake by the P rats, but this dose also reduced daily food intake to approximately 70% of normal. Desipramine at both doses significantly (p less than 0.05) reduced both ethanol and food uptake by the P rats and had a tendency to reduce H2O consumption as well. In general, the three drugs had effects in the NP rats similar to those observed for the P group, although the effects on 10% ethanol intake were difficult to compare because of the low, variable intake of alcohol by the NP group.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluoxetine increases the extracellular levels of serotonin in the nucleus accumbens

The effects of an IP injection of the monoamine uptake inhibitor fluoxetine on the extracellular concentration of serotonin (5-HT), dopamine (DA), 5-hydroxyindoleacetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the nucleus accumbens of awake and freely moving rats were examined using a push-pull perfusion technique. Baseline values of 5-HT, 5-HIAA, DA, DOPAC and HVA in the perfusates were approximately 0.07, 13, 0.8, 49 and 12 pmol/hr, respectively. The IP administration of 5 and 10 mg/kg fluoxetine dose-dependently elevated the amounts of 5-HT 3- and 13-fold, respectively, in the push-pull perfusate, with the maximum reached within one hour after drug administration. Moreover, 10 mg/kg fluoxetine also significantly decreased the levels of 5-HIAA in the perfusate as much as 50% within 2-3 hours. On the other hand, no significant effect of 5 or 10 mg/kg fluoxetine was observed on the contents of DA, DOPAC and HVA in the push-pull perfusates. The data indicate that fluoxetine, in accord with its role as a 5-HT uptake inhibitor, increases the physiologically active pool of 5-HT in the nucleus accumbens under in vivo conditions.

A method for recognizing specific effects on ethanol intake by experimental animals

A method of mathematical treatment of data concerning changes in voluntary consumption of ethanol solution, water and solid food, induced by experimental treatments in animals, in order to recognize effects on mechanisms involved in specific appetite and satiety for calories, water and ethanol is proposed. The need of such method arises from the fact that several experimental treatments tested by the effects on ethanol consumption alter at the same time the appetite or satiety for calories and/or for water, as well as ingestive behavior. The results of testing the method with the data obtained by treatment of UChA and UChB rats with disulfiram or cyanamide were consistent with the expected ones.

GABA transmission, but not benzodiazepine receptor stimulation, modulates ethanol intake by rats

Adult male Long Evans were selected as ethanol preferring rats (DR) during 28 days. After this period, they were daily IP injected during 14 days with one of the next drugs: diazepam 1 mg.kg-1, alprazolam 1 mg.kg-1 (benzodiazepines), progabide 25 mg. kg-1 (GABA A and B agonist), nipecotic acid 150 mg.kg-1 (GABA uptake inhibitor), muscimol 0.2 mg.kg-1 (GABA A agonist), AOAA 10 mg.kg-1 (GABA decarboxylase inhibitor), baclofen 3 mg.kg-1 (GABA B agonist), or NaCl 0.9% (1 ml/200 g). During treatment, rats were isolated, had free access to food, and free choice between ethanol (12%) and water whose respective consumption were daily noted. Among treatments, only AOAA and baclofen were able to decrease significantly ethanol intake, without modifying total liquid intake. The action of these different drugs on GABA transmission and on ethanol intake was discussed. It was concluded that GABA A and benzodiazepine receptors were not implicated in ethanol intake, but that modulation of voluntary ethanol intake could be associated with a modification of GABA metabolism and/or stimulation of GABA B receptors. An intervention of GABA B receptors on noradrenergic pathways was also evoked.

Effects of serotonin uptake blockade on food, water, and ethanol consumption in rats

Previous research has demonstrated that the serotonin uptake blocker, zimeldine, reduced voluntary ethanol consumption in rats and humans. It has been suggested that zimeldine interfered with the processes that mediate the reinforcement derived from ethanol ingestion. However, there are considerable data which suggest that serotonergic pharmacological agents may produce a general inhibition of food and fluid consumption. The present investigation was therefore designed to directly examine the effects of zimeldine on food intake. The results indicated that zimeldine had a potent anorexic action. Furthermore, the drug appeared to primarily affect food intake, with secondary decreases in the fluid most closely associated with prandial drinking. The results were discussed in terms of the effects of serotonin uptake blockade on motivational processes in general.

Persistence of tolerance to a single dose of ethanol in the selectively-bred alcohol-preferring P rat

The persistence of tolerance to a single dose of ethanol was examined in the selectively-bred alcohol-preferring P line of rats. Tolerance was measured by a test that required trained rats to jump onto a descending platform to avoid footshock. On day 0, each trained rat received a single IP injection of 2.5 g ethanol/kg body weight and was tested every 15 minutes for recovery to a criterion of 75% of pre-alcohol training performance. The second ethanol injection of 2.5 g/kg and testing were carried out seven days later for one group (n = 12), and 14 days later for another group (n = 12). Tolerance was assessed by the differences in time required to recover to criterion performance and blood alcohol concentrations (BACs) at time of recovery on day 0 vs. day 7 and day 14. The mean recovery times and BACs on day 0 were 156 +/- 5 minutes and 222 +/- 6 mg%, respectively. The group injected on day 7 exhibited shorter recovery times of 113 +/- 4 minutes and higher BACs at recovery of 261 +/- 4 mg%, while the group injected on day 14 did not show any significant differences from the values obtained on day 0. In a second experiment, the persistence of tolerance in P rats was compared with that of rats from the alcohol-nonpreferring NP line and of stock Wistar rats (n = 6/group). All rats were trained and tested for recovery to criterion after 2.5 g ethanol/kg on day 0 as described for the first experiment. The rats were then injected with ethanol and tested for tolerance on three subsequent occasions.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of neonatal nomifensine exposure on adult behavior and brain monoamines in rats

The aim of the study was to examine the effects of early postnatal exposure to nomifensine, an inhibitor of catecholamine uptake, on concurrent active (REM) sleep, on later alcohol related behavior and on monoamine concentrations in various brain regions of rats. For these purposes rats were given daily injections of 10 mg/kg nomifensine s.c. between the 7th and the 18th postnatal days. During the nomifensine exposure active sleep, expressed as a percentage of total sleeping time, was reduced. At one month of age, the nomifensine rats showed increased ambulation and had lower defecation scores in the open-field than the controls. Neonatal exposure to nomifensine increased voluntary intake of 10% (v/v) alcohol when the rats were 2-3 months of age. The rats, however, did not exhibit preservation in the T-maze, and similarly to control rats suppressed drinking 0.1 M lithium chloride even when thirsty. Measurement of cerebral monoamine concentrations at the age of 3 months suggested that neonatal nomifensine treatment interferes with the noradrenergic and serotonergic systems in several regions of the brain. Concentrations of noradrenaline and 5-hydroxyindoleacetic acid (5-HIAA) were decreased in the cerebral cortex and frontal cortex, concentration of 5-HIAA was decreased in the neostriatum, and concentrations of noradrenaline, 5-hydroxytryptamine (5-HT) and 5-HIAA were elevated in the lower brain stem. Taken together, these findings show that exposure to nomifensine during the 2nd and 3rd postnatal weeks suppresses neonatal active sleep, causes changes in the adult open-field behavior, and increases voluntary alcohol intake, perhaps due to a long-lasting alteration in brain monoamines.

Neonatal desipramine or zimeldine treatment causes long-lasting changes in brain monoaminergic systems and alcohol related behavior in rats

To study the relationship between neonatal antidepressant administration, active (REM) sleep and adult alcohol-related behavior, rat pups were treated daily with 5 mg/kg desipramine (DMI) or 25 mg/kg zimeldine SC from the 6th to the 19th postnatal days. Movement sensitive mattress ("SCSB") measurements showed that zimeldine treatment suppressed active sleep throughout the whole treatment period, but DMI was more effective during the first 8 days than during the last treatment days. At the age of 70 days, the zimeldine-treated rats expressed a selective increase of some components of activity in the open field test, and the DMI rats had a higher defecation score compared to the controls. Furthermore, the zimeldine-rats responded with a decrease in ambulation in the open field to an alcohol dose which generally stimulates locomotion in rats. At the age of 3 months the DMI and zimeldine rats showed increased voluntary intake of 10% (v/v) alcohol. Measurement of brain monoamines revealed that the neonatal treatment with DMI or zimeldine interfered with the normal development and function of the monoamine neuronal systems: the concentrations of noradrenaline, dopamine and 5-hydroxytryptamine (5-HT), and their metabolites were altered in several brain regions. The results thus suggest that neonatal treatment with DMI or zimeldine suppresses active sleep and has an influence on later alcohol-related behavior, possibly due to a long-lasting defect in brain monoaminergic transmission.

Test for decreased serotonin/tryptophan metabolite ratios in abstinent alcoholics

A segment of the population has a defect in the metabolism of tryptophan that causes a lowered concentration of serotonin in the central nervous system and indicates a predisposition towards chronic alcoholism. The metabolic defect in tryptophan metabolism is in the pathway between tryptophan and 5-hydroxyindoleacetic acid (5-HIAA) but not in the other pathways of tryptophan metabolism. A test using HPLC with amperometric detection was developed to detect the presence of an impaired serotonin metabolic pathway and therefore indicate a predisposition towards chronic alcoholism. The test used a ratio between 5-HIAA and two metabolites (indoleacetic acid and anthranilic acid) from the other pathways of tryptophan metabolism to indicate the presence or absence of an impaired serotonin metabolic pathway while correcting for variations in the concentration of urine.

Effects of prenatal alcohol exposure on neonatal sleep-wake behaviour and adult alcohol consumption in rats

Our previous experiments showed that suppression of early postnatal active (REM) sleep increases alcohol intake in adult rats. To study the effects of prenatal alcohol exposure on neonatal sleep-wake behaviour and adult alcohol consumption pregnant rat dams were given 7% to 12% alcohol, 1% sucrose solution, or tap water as a sole liquid throughout gestation. Sleep-wake behaviour of the pups was studied at 6, 8, 12 and 15 days of age by using a movement sensitive mattress. The offspring who were exposed to alcohol in utero had significantly less active sleep and more wakefulness from total recording time than the controls. Their quiet state was also interrupted more often by waking episodes. At the age of 2 months voluntary alcohol intake of the rats exposed prenatally to alcohol was elevated compared to the controls. These findings suggest that early postnatal active sleep and the neurotransmitter systems regulating it may be the means by which in utero alcohol exposure affects adult alcohol drinking.