Dopamine D2 receptor gene expression in rat lines selected for differences in voluntary alcohol consumption

Cannabidiol as a Modulator of the Development of Alcohol Tolerance in Rats

The study aimed to explore in vivo the influence of cannabidiol (CBD) on the development of alcohol tolerance in rats. Rats were treated with ethanol (3.0 g/kg, i.p.) and CBD (20 mg/kg, p.o.) for nine successive days, and rectal body temperature, sedation (sleeping time), and blood alcohol concentration (BAC) were measured. In the prefrontal cortex, hippocampus, and striatum, the cannabinoid (CB1R and CB2R) and dopaminergic (DRD1, DRD2, DRD4, DRD5) receptors’ mRNA level changes were analyzed using the quantitative RT-PCR method. CBD inhibited the development of tolerance to the hypothermic and sedative action of alcohol, coupled with BAC elevation. On a molecular level, the most pronounced effects of the CBD + ethanol interaction in the striatum were observed, where CBD reversed the downregulation of CB2R gene transcription caused by ethanol. For CB1R, DRD1, and DRD2 mRNAs, the CBD + ethanol interaction produced opposite effects than for CB2R ones. In turn, for the transcription of genes encoding dopaminergic receptors, the most potent effect of alcohol as CBD occurred in the hippocampus. However, the combined CBD and alcohol administration showed the same effect for each substance administered separately. Since tolerance is considered a prelude to drug addiction, obtained results allow us to emphasize the thesis that CBD can inhibit the development of alcohol dependence in rats.

Novel candidate genes for alcoholism--transcriptomic analysis of prefrontal medial cortex, hippocampus and nucleus accumbens of Warsaw alcohol-preferring and non-preferring rats

OBJECTIVE

Animal models provide opportunity to study neurobiological aspects of human alcoholism. Changes in gene expression have been implicated in mediating brain functions, including reward system and addiction. The current study aimed to identify genes that may underlie differential ethanol preference in Warsaw High Preferring (WHP) and Warsaw Low Preferring (WLP) rats.

METHODS

Microarray analysis comparing gene expression in nucleus accumbens (NAc), hippocampus (HP) and medial prefrontal cortex (mPFC) was performed in male WHP and WLP rats bred for differences in ethanol preference.

RESULTS

Differential and stable between biological repeats expression of 345, 254 and 129 transcripts in NAc, HP and mPFC was detected. Identified genes and processes included known mediators of ethanol response (Mx2, Fam111a, Itpr1, Gabra4, Agtr1a, LTP/LTD, renin-angiotensin signaling pathway), toxicity (Sult1c2a, Ces1, inflammatory response), as well as genes involved in regulation of important addiction-related brain systems such as dopamine, tachykinin or acetylcholine (Gng7, Tac4, Slc5a7).

CONCLUSIONS

The identified candidate genes may underlie differential ethanol preference in an animal model of alcoholism.

COMMENT

Names of genes are written in italics, while names of proteins are written in standard font. Names of human genes/proteins are written in all capital letters. Names of rodent genes/proteins are written in capital letter followed by small letters.

The dopamine system and alcohol dependence

Alcohol dependence is a common mental disorder that is associated with substantial disease burden. Current efforts at prevention and treatment of alcohol dependence are of very limited effectiveness. A better understanding of the biological mechanisms underlying dependence is essential to improving the outcomes of treatment and prevention initiatives. To date, most of the efforts have focused on the key role of the dopamine system in the complex etiological network of alcohol dependence. This review summarizes current research about the relationships between alcohol consumption and the dopaminergic system. We find that many of the currently available studies have contradictory results, presumably due to differences in methodology, non-linear dosage effects, use of different samples, and the possible confounding effects of other neurotransmitter systems.

Animal models for medications development targeting alcohol abuse using selectively bred rat lines: neurobiological and pharmacological validity

The purpose of this review paper is to present evidence that rat animal models of alcoholism provide an ideal platform for developing and screening medications that target alcohol abuse and dependence. The focus is on the 5 oldest international rat lines that have been selectively bred for a high alcohol-consumption phenotype. The behavioral and neurochemical phenotypes of these rat lines are reviewed and placed in the context of the clinical literature. The paper presents behavioral models for assessing the efficacy of pharmaceuticals for the treatment of alcohol abuse and dependence in rodents, with particular emphasis on rats. Drugs that have been tested for their effectiveness in reducing alcohol/ethanol consumption and/or self-administration by these rat lines and their putative site of action are summarized. The paper also presents some current and future directions for developing pharmacological treatments targeting alcohol abuse and dependence.

Stimulated dopamine overflow and alpha-synuclein expression in the nucleus accumbens core distinguish rats bred for differential ethanol preference

The key neurochemical systems and structures involved in the predisposition to substance abuse and preference to ethanol (EtOH) are not known in detail but clearly dopamine (DA) is an important modulator of addiction. Recent data indicate that alpha-synuclein (alpha-syn), a pre-synaptic protein, plays a role in regulation of DA release from the pre-synaptic terminals in striatum and the expression of this protein is different after drug abuse or following abstinence. In the present work, we analysed stimulated DA overflow in the dorsal and ventral striatum in EtOH naïve alko alchohol (AA) and alko non-alchohol (ANA) rats selected for more than 100 generations for their differential EtOH preference. In the same structures, we studied the expression of alpha-syn using western blotting. AA rats, in comparison with ANA rats, showed a marked reduction of stimulated peak DA overflow and higher levels of alpha-syn in the nucleus accumbens core. In the same structure, DA re-uptake was increased in AA rats in comparison with ANA rats. The effects of EtOH at low (0.1 g/kg) and higher (3 mg/kg) doses on DA overflow measured in the nucleus accumbens shell were similar in both lines. These results indicate that high expression of alpha-syn may contribute to the reduced DA overflow and the possible activation of re-uptake in the nucleus accumbens core of AA rats in comparison with ANA rats.

Cortical dopamine D(1) receptors in type 1 and type 2 alcoholics measured with human whole hemisphere autoradiography

A large body of evidence indicates the importance of dopamine (DA) activation for ethanol reinforcement, and animal models of alcoholism have implied the involvement of DA D(1) receptors in this context. We studied cortical DA D(1) receptors in nine type 1 alcoholics (late-onset, binge-drinker), eight type 2 alcoholics (early-onset, antisocial) and 10 controls by using [(3)H]SCH23390 as a radioligand in postmortem human whole hemisphere autoradiography. We also evaluated correlations of DA D(1) receptors between the cortical and subcortical areas and between cortical DA transporters and DA D(2) and D(3) receptors by comparing the present results to our earlier studies. On the average, type 2 alcoholics were younger and had more violent causes of death than type 1 alcoholics and controls. There were no statistically significant differences between the groups, suggesting that cortical DA D(1) receptors do not play a major role in alcoholism. However, among type 2 alcoholics, the binding was consistently lower (8.6%-22.3%) than among controls, and the effect sizes showed a large effect in the anterior cingulate (0.90) and frontal (0.87) cortices. Interestingly, among type 2 alcoholics, the correlation of DA D(1) receptors between two ventral midbrain structures (substantia nigra and amygdala) and anterior cingulate cortex was significantly negative, whereas in the type 1 alcoholics and controls, the correlations were significantly positive.

Accumbal FosB/DeltaFosB immunoreactivity and conditioned place preference in alcohol-preferring AA rats and alcohol-avoiding ANA rats treated repeatedly with cocaine

Transcription factor DeltaFosB has been implicated in the psychomotor responses and rewarding effects of drugs of abuse. In the present study, we compared the effects of cocaine on the expression of DeltaFosB-like proteins by immunohistochemistry in striatal brain areas of alcohol-preferring (AA) and alcohol-avoiding (ANA) rats. Cocaine was administered using a previously verified treatment paradigm that sensitized the locomotor response to cocaine in AA but not in ANA rats. We also studied the rewarding effects of cocaine with a conditioned place preference (CPP) paradigm in both lines of rats. Cocaine treatment increased the FosB/DeltaFosB immunoreactivity (IR) in the nucleus accumbens of AA rats but not in ANA rats. In addition, after repeated saline injections the accumbal FosB/DeltaFosB IR was significantly greater in saline-injected AA rats than in ANA rats. In the caudate-putamen cocaine significantly increased FosB/DeltaFosB IR, but no differences were found between the rats of two lines. In the CPP experiment, AA rats treated with cocaine 2.5 mg/kg preferred the cocaine-associated compartment, in contrast to ANA rats, which did not show such a preference. In conclusion, our findings show that AA rats are more sensitive to cocaine than ANA rats, and suggest that one possible mediator for this increased sensitivity could be the increased expression of fosB-derived proteins in the nucleus accumbens of AA rats.

Manipulation of catechol-O-methyl-transferase (COMT) activity to influence the attenuation of substance seeking behavior, a subtype of Reward Deficiency Syndrome (RDS), is dependent upon gene polymorphisms: A hypothesis

There are common genetic mechanisms responsible for both drug effects and subsequent seeking behavior. In 1996, we coined the term Reward Deficiency Syndrome (RDS). Past and current treatment of substance seeking behavior, a subtype of Reward Deficiency Syndrome (RDS), is considered by most to be inadequate. Recently, we evaluated a complex named Synaptamine [Haveos (SG8839R)]. The main difference with an older studied variant and the latest variant is the inclusion of a proprietary form of Rhodiola rosea, a known catechol-O-methyl-transferase inhibitor (COMT) to potentially enhance the activity of presynaptic released dopamine. In this regard, based on the current literature we hypothesize that manipulation of catechol-O-methyl-transferase (COMT) activity to influence the attenuation of substance seeking behavior, is dependent upon gene polymorphisms. In this regard we hypothesize that carrying the LL genotype with low COMT activity should as theorized, increase the reward induced by substance-induced dopamine release and may indeed increase the propensity to type 1 alcoholism and possibly other drugs that activate the dopaminergic system. Thus when alcohol is present in low COMT LL genotype, increasing COMT activity, not inhibiting it should assist in the reduction of social consumption or abuse. Alternatively, under physiological conditions (no psychoactive substances present (e.g. alcohol) carrying the DRD2 A1 allele with associated low D2 receptors should, as theorized, increase craving behavior because of a low or hypodopaminergic state causing the individual to seek out substances that increase the release of dopamine for subsequent activation of unbound D2 sites in the nucleus accumbens. Thus, in the absence of alcohol or other psychoactive drugs (dopamine releasers), especially during recovery or rehabilitation, decreasing, not increasing COMT activity, should result in enhanced synaptic dopamine as physiologically released, thereby proliferating D2 receptors while reducing stress, increasing well-being, reducing craving behavior and preventing relapse. Based on this hypothesis, we believe that adding the COMT inhibitor R. rosea (as Rhodimin) to our amino-acid and chromium combination in DUI offenders and other illegal drug-related crimes, increases the potential for more targeted neurochemical rebalancing and enhanced relapse prevention. Finally, we hypothesize that these data coupled together provide evidence that the combination of enkephalinase inhibition, neurotransmitter precursor loading, brain tryptophan enhancing and COMT inhibition as well as DNA analysis of the individual's genome, may be useful as an adjunct to therapy when used in outpatient recovery, specifically to assist in reducing craving behavior and preventing relapse.

The alcohol-preferring AA and alcohol-avoiding ANA rats: neurobiology of the regulation of alcohol drinking

The AA (alko, alcohol) and ANA (alko, non-alcohol) rat lines were among the earliest rodent lines produced by bidirectional selection for ethanol preference. The purpose of this review is to highlight the strategies for understanding the neurobiological factors underlying differential alcohol-drinking behavior in these lines. Most early work evaluated functioning of the major neurotransmitter systems implicated in drug reward in the lines. No consistent line differences were found in the dopaminergic system either under baseline conditions or after ethanol challenges. However, increased opioidergic tone in the ventral striatum and a deficiency in endocannabinoid signaling in the prefrontal cortex of AA rats may comprise mechanisms leading to increased ethanol consumption. Because complex behaviors, such as ethanol drinking, are not likely to be controlled by single factors, system-oriented molecular-profiling strategies have been used recently. Microarray based expression analysis of AA and ANA brains and novel data-mining strategies provide a system biological view that allows us to formulate a hypothesis on the mechanism underlying selection for ethanol preference. Two main factors appear active in the selection: a recruitment of signal transduction networks, including mitogen-activated protein kinases and calcium pathways and involving transcription factors such as Creb, Myc and Max, to mediate ethanol reinforcement and plasticity. The second factor acts on the mitochondrion and most likely provides metabolic flexibility for alternative substrate utilization in the presence of low amounts of ethanol.

EFFECTS OF ARIPIPRAZOLE ON ALCOHOL INTAKE IN AN ANIMAL MODEL OF HIGH-ALCOHOL DRINKING

AIMS

This study examined the effects of aripiprazole, a novel atypical antipsychotic drug with partial agonist properties at dopamine D2 receptors, on the voluntary limited access alcohol drinking of alcohol-preferring AA (Alko, Alcohol) rats.

METHODS

AA rats were taught to drink 10% alcohol in a 4 h limited access paradigm. Effects of acute aripiprazole (0, 0.3, 1.0, and 3.0 mg/kg) on the limited access alcohol drinking were studied. In repeated treatment experiment, aripiprazole (0, 1.0, and 6.0 mg/kg) was administered once daily over five successive days. To reveal any effect by aripiprazole not selective for alcohol drinking, 0.025% saccharin solution was substituted for alcohol during the 4 h limited access, and acute treatments were repeated. The effects of aripiprazole on ambulatory locomotor activity were tested with doses that were used in the acute experiments.

RESULTS

Acute aripiprazole at the doses of 0.3, 1.0, and 3.0 mg/kg had no effect on alcohol drinking. Repeated treatment with the aripiprazole dose of 6.0 mg/kg significantly diminished alcohol drinking at the 1 h time point. This dose had no effect on saccharin drinking when given acutely. Acute aripiprazole at the doses of 1.0, 3.0, and 6.0 mg/kg significantly suppressed locomotor activity.

CONCLUSIONS

Aripiprazole decreased limited access alcohol drinking in AA rats, but only at a high dose that also strongly suppressed locomotor activity.

Dopamine and alcoholism: neurobiological basis of ethanol abuse

The role of the dopamine (DA) system in brain reward mechanisms and the development of substance abuse has been well established. We review earlier animal and human studies on DA and alcoholism with some relevant issues relating to those studies. The present animal and human data suggest several alterations in the DA system in the context of alcoholism. Receptor studies imply that DA D(2) receptor density and function are lower at least among type 1 alcoholics, which suggests that they could benefit from drugs that enhance DAergic activity, such as partial DA agonists. These drugs could help to restore suboptimal levels of DAergic activity by reducing both the craving for alcohol in abstinence and the euphoria subsequent to alcohol's release of DA in the nucleus accumbens (NAC), thus providing negative reinforcement for relapse.

Alcoholism and the dopaminergic system: a review

Alcohol as well as other substances of abuse are reinforcing substances which manifest their effects through activation of the mesolimbic dopaminergic reward pathways of the brain. In animal genetic models of alcoholism, reduced dopamine levels and D2 dopamine receptor (DRD2) numbers have been found in the brains of alcohol-preferring animals. Dopamine receptor agonists reduce alcohol consumption, whereas antagonists, in general, show the opposite effect. Moreover, quantitative trait loci studies in animals suggest the DRD2 gene and the region proximate to this locus is a chromosomal "hot spot" for alcohol-related behaviors. Human studies provide additional support for connection between alcohol dependence and CNS dopaminergic function. In endocrinological studies, using dopamine receptor agonists, reduced dopaminergic activity has been found in more severe and more genetic types of alcoholics. Brain imaging studies are similarly revealing a diminished dopaminergic tone in alcoholics. Treatment of alcoholics with dopamine receptor agonists shows reduced alcohol consumption and improvements in other outcome measures. Molecular genetic studies in humans have identified an association of the Al allele of the DRD2 gene with alcoholism. Moreover, a diminished central dopaminergic function has been found in DRD2 A1 allele subjects using pharmacological, electrophysiological and neuropsychological studies. Further, treatment of alcoholics with a dopamine receptor agonist showed more salutary effects on alcoholics who carry than those who do not carry the DRD2 A1 allele. The A1 allele has also been associated with substance use disorders other than alcoholism, including and cocaine and nicotine dependence and polysubstance abuse. The emerging evidence suggests that the DRD2 is a reinforcement or reward gene. It could represent one of the most prominent single-gene determinants of susceptibility to severe substance abuse. However, the environment and other genes, when combined, still play the larger role.

Different sensitivity to the motor-stimulating effect of amphetamine in Sardinian alcohol-preferring and non-preferring rats

The selective breeding of rodents on the basis of ethanol intake and preference has led to the development of lines of alcohol-preferring and non-preferring animals. The divergent degree of alcohol preference and consumption displayed by these lines of animals appears to be related, among other factors, to the genetic differences in dopaminergic neurotransmission. Moreover, in genetically unselected rats, a positive correlation has been found between alcohol preference and several amphetamine effects, including the stimulation of motor hyperactivity, thus suggesting the hypothesis that a common neural pathway might underlie some aspects in both of the amphetamine-induced hypermotility and alcohol preference. In the present study, we compared the motor-stimulating effect of amphetamine, which is mediated by the release of dopamine in the nucleus accumbens and in the corpus striatum in two lines of rats selectively bred for high and low ethanol preference, the Sardinian alcohol-preferring (sP) and the Sardinian alcohol-non-preferring (sNP) rats, respectively. The results show that sP rats are less sensitive to the motor-stimulant effect of amphetamine with respect to sNP rats, thus suggesting a negative correlation between this behavioural response and alcohol preference. The present results might be explained by the previously reported reduced density of dopamine receptors in the nucleus accumbens of sP rats and are consistent with the view that alcohol preference is associated with a deficient dopaminergic transmission. Moreover, they are consistent with the hypothesis that alcohol preference and amphetamine motor effect share a common neural substrate and that hereditary factors determine individual variations in its sensitivity.

Flupenthixol as a potential pharmacotreatment of alcohol and cocaine abuse/dependence

Preclinical and clinical studies suggest that the mesolimbic dopamine system plays a major role in mediating the reinforcing effects of drugs of abuse, including alcohol and psychostimulants, and that pharmacological blockade of dopamine D1 and/or D2 receptors may reduce intake of these drugs, as well as relapse rates. The neuroleptic flupenthixol, which has dopamine D1 and D2 receptor antagonist properties and which may be given intramuscularly in order to improve compliance, has been studied as a possible anti-craving drug in substance abuse disorders. Flupenthixol has been shown to attenuate the discriminative stimulus effects of psychostimulants, as well as their intake in animal models of drug abuse. In addition, the compound was found to reduce alcohol intake in a rat model of alcoholism, but the 'anti-alcohol' effect appeared to be only weakly selective and nonspecific. Clinically, the drug has been studied in alcoholics, cocaine addicts and in patients with comorbid psychiatric disorders. Although the data base is still limited and a number of recent trials have not been completely analyzed, these studies suggest that flupenthixol may be useful in decreasing cocaine consumption. Recent studies in alcoholism, however, have shown disappointing results. A number of pilot studies suggest that probably the most promising area may be the treatment of substance abuse/dependence in patients with comorbid psychiatric disorders. Future studies should focus on dosing issues, the differentiation between short- and long-term effects and the identification of subgroups of patients with particular psychopathology.

The role of opioid-dopamine interactions in the induction and maintenance of ethanol consumption

1. Alcohol is one of the most widely used recreational drugs, but also one of the most widely abused, causing vast economic, social and personal damage. 2. Several animal models are available to study the reinforcing mechanisms that are the basis of the abuse liability of ethanol. Innate differences in opioid or dopamine neurotransmission may enhance the abuse liability of ethanol, as indicated by animal and human studies. 3. Opioid antagonists have been shown to be effective, both experimentally and clinically, in decreasing ethanol consumption, presumably since ethanol induces the release of endogenous opioid peptides in vivo. However, ethanol may also stimulate the formation of opiate-like compounds, which could interact with opioid (or dopamine) receptors. Ethanol may cause changes in neurotransmission mediated via opioid receptors that determines whether alcohol abuse is more or less likely. 4. Ethanol appears to facilitate dopamine release by increasing opioidergic activity, disinhibiting dopaminergic neurons (by inhibition of GABAergic neurotransmission) via mu-opioid receptors in the ventral tegmental area (VTA) and delta-opioid receptors in the nucleus accumbens (NAcc). The effects of ethanol would be antagonised by presynaptic kappa-opioid receptors present on dopaminergic terminals in the NAcc. 5. Mesolimbic dopamine release induced by ethanol consumption seems to indicate ethanol-related stimuli are important, focussing attention on and enabling learning of the stimuli. However, studies indicate that there are redundant pathways, and neural pathways 'downstream' of the mesolimbic dopamine system, which also enable the reinforcing properties of ethanol to be mediated.

Mmu and D2 receptor antisense oligonucleotides injected in nucleus accumbens suppress high alcohol intake in genetic drinking HEP rats

Numerous pharmacological and other studies have implicated both Mmu and dopamine receptor subtypes in alcohol consumption. In the genetic drinking rat as well as those chemically induced to drink, evidence has accrued that the abnormal intake of alcohol is underpined by these receptors in the brain. The purpose of this investigation was to demonstrate unequivocally that a biological impairment by antisense oligodeoxynucleotide (ODN) targeted specifically to these two receptor subtypes would disrupt ongoing alcohol drinking. In this project, a new strain of female and male high-ethanol preferring (HEP) rats was used that had free access to preferred concentrations of alcohol over water in a two choice paradigm. A guide cannula for a microinjection needle was first implanted bilaterally above the nucleus accumbens (NAC) of each rat. Following recovery, a dose of either 250 or 500 ng of the Mmu ODN or 500 ng D2ODN was microinjected into the NAC of the rat in a volume of 0.8-1.0 microl. A standard temporal sequence was used in which microinjections were given four times at successive 12-h intervals over a 2-day interval. The control mismatch ODNs corresponding to both the Mmu or D2 receptor antisense were microinjected identically at homologous sites in the NAC. Following the experiments, the brain of each rat was removed and sectioned in the coronal plane for histological analysis so that each microinjection site was identified. The results showed that the Mmu receptor antisense caused a significant dose dependent fall in free access alcohol drinking within 12 to 24 h following the initial microinjection. This decline often persisted for 1 to 2 days in terms of both g/kg intake and proportion of alcohol to water consumed. Similarly, the D2 receptor ODN likewise induced an intense and significant decline in both g/kg and proportion measures of alcohol intake. Since the corresponding mismatch ODN for both Mmu and D2 receptors exerted no effect on either of these measures of alcohol consumption, the specificity of molecular action of the respective antisense molecules on drinking behavior of the HEP rats was confirmed. Thus, these results provide the first unequivocal evidence that the genes for D2 and Mmu receptors are fundamentally involved in abnormal alcohol drinking in the genetically predisposed individual. Finally, important new anatomical evidence is introduced for the critical role of the NAC in the genetic basis of aberrant drinking of alcohol.

Alcohol preference and sensitivity are markedly reduced in mice lacking dopamine D2 receptors

Although dopaminergic transmission has been strongly implicated in alcohol self-administration, the involvement of specific dopamine receptor subtypes has not been well established. We studied the ethanol preference and sensitivity of D2-receptor-deficient mice to directly evaluate whether dopamine D2 receptors contribute to alcohol (ethanol) consumption. We report a marked aversion to ethanol in these mice, relative to the high preference and consumption exhibited by wild-type littermates. Sensitivity to ethanol-induced locomotor impairment was also reduced in these mutant mice, although they showed a normal locomotor depressant response to the dopamine D1 antagonist SCH-23390. These data demonstrate that dopamine signaling via D2 receptors is an essential component of the molecular pathway determining ethanol self-administration and sensitivity.

Regional CNS densities of serotonin and dopamine receptors in high alcohol-drinking (HAD) and low alcohol-drinking (LAD) rats

The densities of subtypes of serotonin (5-HT) and dopamine (DA) receptors were determined in the CNS of male alcohol-naive HAD and LAD lines of rats. Autoradiographic studies were undertaken to measure the densities of (a) 5-HT1A sites labelled with 2 nM [3H]8-OH DPAT, (b) 5-HT2A sites labelled with 2 nM [3H] ketanserin, (c) D1 sites labelled with 1 nM [3H]SCH23390, and (d) D2 sites labelled with 20 nM [3H]sulpiride. Membrane binding, using tissue combined from the olfactory bulb, olfactory tubercle, and nucleus accumbens, was carried out to determine Kd and Bmax values for the binding of 0.25-8.0 nM [3H]7-OH DPAT to D3 sites. Among the 14 regions measured for densities of 5-HT1A sites, no interline differences were found in the cerebral cortical regions or in the septal nuclei; however, within the hippocampus, 15-20% lower binding of [3H]8-OH DPAT was observed in the posterior dorsal CA3 and dentate gyrus of the HAD line. There were no interline differences in any of the 10 regions examined for [3H]ketanserin binding to 5-HT2A sites, or in the densities of D1 and D2 sites in the mesolimbic and nigrostriatal DA systems, except for a 35% higher density of D2 sites in the substantia nigra pars compacta of the HAD line. There were no interline differences in the Kd or Bmax values for [3H]7-OH DPAT binding to D3 sites. Overall, these results indicate that no marked interline differences are evident in the densities of 5-HT1A, 5-HT2A, D1, D2, and D3 receptors within the mesolimbic system that could be associated with the disparate alcohol drinking behaviors of the HAD and LAD rats.