Ethanol drinking following 6-OHDA lesions of nucleus accumbens and tuberculum olfactorium of the rat

Alcohol and the dopamine system

The mesolimbic dopamine pathway plays a major role in drug reinforcement and is likely involved also in the development of drug addiction. Ethanol, like most addictive drugs, acutely activates the mesolimbic dopamine system and releases dopamine, and ethanol-associated stimuli also appear to trigger dopamine release. In addition, chronic exposure to ethanol reduces the baseline function of the mesolimbic dopamine system. The molecular mechanisms underlying ethanol´s interaction with this system remain, however, to be unveiled. Here research on the actions of ethanol in the mesolimbic dopamine system, focusing on the involvement of cystein-loop ligand-gated ion channels, opiate receptors, gastric peptides and acetaldehyde is briefly reviewed. In summary, a great complexity as regards ethanol´s mechanism(s) of action along the mesolimbic dopamine system has been revealed. Consequently, several new targets and possibilities for pharmacotherapies for alcohol use disorder have emerged.

REM sleep behavior and olfactory dysfunction: improving the utility and translation of animal models in the search for neuroprotective therapies for Parkinson's disease

Parkinson's disease (PD) is a heterogeneous neurodegenerative disease that belongs to the family of synucleiopathies, varying in age, symptoms and progression. Hallmark of the disease is the accumulation of misfolded α-synuclein protein (α-Syn) in neuronal and non-neuronal brain cells. In past decades, diagnosis and treatment of PD has focused on motor deficits, which for the clinical endpoint, have contributed to the prevalence of deficits in the nigrostriatal dopaminergic system and animal models related to motor behavior to study disease. However, clinical trials have failed to translate results from animal models into effective treatments. PD as a multisystem disorder therefore requires additional assessment of motor and non-motor symptoms. Braak's staging revealed early α-Syn pathology in pontine brainstem and olfactory circuits controlling rapid eye movement sleep behavior disorder (RBD) and olfaction, respectively. Recent converging evidence from multicenter clinical studies supports that RBD is the most important risk factor for prodromal PD and the conduct of neuroprotective therapeutic trials in RBD-enriched cohorts has been recommended. Animal models of RBD and olfaction dysfunction can aid to fill the gap in translational research.

The nucleus accumbens and alcoholism: a target for deep brain stimulation

Alcohol use disorder (AUD) is a difficult to treat condition with a significant global public health and cost burden. The nucleus accumbens (NAc) has been implicated in AUD and identified as an ideal target for deep brain stimulation (DBS). There are promising preclinical animal studies of DBS for alcohol consumption as well as some initial human clinical studies that have shown some promise at reducing alcohol-related cravings and, in some instances, achieving long-term abstinence. In this review, the authors discuss the evidence and concepts supporting the role of the NAc in AUD, summarize the findings from published NAc DBS studies in animal models and humans, and consider the challenges and propose future directions for neuromodulation of the NAc for the treatment of AUD.

Delay discounting for sucrose in alcohol-preferring and nonpreferring rats using a sipper tube within-sessions task

BACKGROUND

Delay discounting (DD) is a measure of impulsivity that quantifies preference for a small reward delivered immediately over a large reward delivered after a delay. It has been hypothesized that impulsivity is an endophenotype associated with increased risk for development of alcohol use disorders (AUDs); however, a causal role of impulsivity is difficult to determine with human studies. We tested this hypothesis by assessing the degree of DD present in alcohol-naïve rats selectively bred for either high- or low-alcohol preference.

METHODS

A novel adaptation of a within-sessions DD procedure was used to compare impulsivity differences between male alcohol-preferring (P) and nonpreferring (NP) rat lines (n = 6 per line) using a 5% sucrose reward. Animals chose between 2 options: 2-second sipper tube access delivered immediately (small reward) or 8-second access after a variable delay (large reward). Each 50-minute session consisted of 5 blocks of ten 60-second trials. Within each session, the delay to the large reward increased in each block of trials. Delays were gradually increased over 3 sets to attain a final delay set of 3, 8, 15, 18, and 25 seconds.

RESULTS

Prior to starting delays, there were no significant differences between lines in sucrose consumption or percent choice for the large reward, and both lines exhibited a clear preference for the large reward. After delays were initiated, choice for the large reward decreased as the delay to its presentation increased. Although discounting of the large, delayed reward was observed for both lines, the degree of discounting, or "impulsivity," was greater for P rats compared with NP rats.

CONCLUSIONS

P rats are more impulsive for sucrose rewards before exposure to alcohol compared with NP rats. Thus, individuals genetically predisposed toward developing AUDs may be more likely to engage in impulsive decision making prior to alcohol exposure.

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.

Reduced ethanol consumption by alcohol-preferring (P) rats following pharmacological silencing and deep brain stimulation of the nucleus accumbens shell

OBJECT

There is increasing interest in deep brain stimulation (DBS) for the treatment of addiction. Initial testing must be conducted in animals, and the alcohol-preferring (P) rat meets the criteria for an animal model of alcoholism. This study is composed of 2 experiments designed to examine the effects of 1) pharmacological inactivation and 2) DBS of the nucleus accumbens shell (AcbSh) on the consumption of alcohol by P rats.

METHODS

In the first experiment, the effects of reversible inactivation of the AcbSh were investigated by administering intracranial injections of γ-aminobutyric acid (GABA) agonists. Bilateral microinjections of drug were administered to the AcbSh in P rats (8-10 rats/group), after which the animals were placed in operant chambers containing 2 levers--one used to administer water and the other to administer 15% EtOH--to examine the acquisition and maintenance of oral EtOH self-administration. In the second experiment, a DBS electrode was placed in each P rat's left AcbSh. The animals then received 100 or 200 μA (3-4 rats/group) of DBS to examine the effect on daily consumption of oral EtOH in a free-access paradigm.

RESULTS

In the first experiment, pharmacological silencing of the AcbSh with GABA agonists did not decrease the acquisition of EtOH drinking behavior but did reduce EtOH consumption by 55% in chronically drinking rats. Similarly, in the second experiment, 200 μA of DBS consistently reduced EtOH intake by 47% in chronically drinking rats. The amount of EtOH consumption returned to baseline levels following termination of therapy in both experiments.

CONCLUSIONS

Pharmacological silencing and DBS of the AcbSh reduced EtOH intake after chronic EtOH use had been established in rodents. The AcbSh is a neuroanatomical substrate for the reinforcing effects of alcohol and may be a target for surgical intervention in cases of alcoholism.

Electrolytic lesions of the medial nucleus accumbens shell selectively decrease ethanol consumption without altering preference in a limited access procedure in C57BL/6J mice

The central extended amygdala (cExtA) is a limbic region proposed to play a key role in drug and alcohol addiction and to contain the medial nucleus accumbens shell (MNAc shell). The aim of this study was to examine the involvement of the MNAc shell in ethanol and sucrose consumption in a limited and free access procedure in the C57BL/6J (B6) mouse. Separate groups of mice received bilateral electrolytic lesions of the MNAc shell or sham surgery, and following recovery from surgery, were allowed to voluntarily consume ethanol (15% v/v) in a 2 h limited access 2-bottle-choice procedure. Following 1 week of limited access ethanol consumption, mice were given 1 week of limited access sucrose consumption. A separate group of lesioned and sham mice were given free access (24 h) to ethanol in a 2-bottle choice procedure and were run in parallel to the mice receiving limited access consumption. Electrolytic lesions of the MNAc shell decreased ethanol (but not sucrose) consumption in a limited access procedure, but did not alter free access ethanol consumption. These results suggest that the MNAc shell is a component of the underlying neural circuitry contributing to limited access alcohol consumption in the B6 mouse.

Endogenous nociceptin (orphanin FQ) suppresses basal hedonic state and acute reward responses to methamphetamine and ethanol, but facilitates chronic responses

The opioid peptide nociceptin (orphanin FQ) suppresses drug reward, drug self-administration, and impedes some of the processes believed to underlie the transition to addiction. As virtually all previous studies have used administration of nociceptin receptor agonists to evaluate the role of nociceptin on addiction-like behavior, the current study used a pharmacological (nociceptin receptor antagonist) and genetic (nociceptin receptor knockout mice) approach to elucidate the role of endogenous nociceptin. The nociceptin receptor antagonist UFP-101 induced a modest place preference, and enhanced the conditioned place preference induced by methamphetamine. In agreement with this, nociceptin receptor knockout mice had slightly enhanced methamphetamine and ethanol conditioned place preferences compared to wild-type mice. This effect did not appear to depend on differences in learning ability, as nociceptin receptor knockout mice had slightly weaker-conditioned place aversions to lithium chloride, the kappa-opioid receptor agonist, U50488H, and the general opiate antagonist, naloxone. The development of behavioral sensitization to methamphetamine was lower in nociceptin receptor knockout mice, and attenuated by UFP-101 administration to wild-type mice. Additionally, ethanol consumption and preference in a two-bottle choice test was lower in nociceptin receptor knockout mice, though ethanol-stimulated locomotion was stronger. Whereas the rewarding effect of methamphetamine and ethanol following chronic treatment, as measured by place conditioning, strengthened in wild-type mice, this effect was absent in nociceptin receptor knockout mice. These results suggest that endogenous N/OFQ suppresses basal and drug-stimulated increases in hedonic state, and plays either a permissive or facilitatory role in the development of addiction.

Microarray analysis of the effects of a gamma-protein kinase C null mutation on gene expression in striatum: a role for transthyretin in mutant phenotypes

A constitutive null mutation of the neural-specific isotype of protein kinase C (gamma-PKC) in mice produces alterations in behavioral traits and responses to ethanol suggesting that gamma-PKC-mediated phosphorylation is essential for regulation of some behaviors. However, it is possible that some of the effects of gamma-PKC gene deletion also may be due to altered gene expression. To examine alterations in gene expression, microarray analyses were performed on striatal tissue from wild types and mutants. A total of 143 genes and ESTs were identified as potential candidates related to differences between null mutants and wild types. Confirmation studies using qRT-PCR indicated that the expression of transthyretin was increased about 8-fold in striatum of naïve mutants compared to wild types. The effect of chronic ethanol treatment on transthyretin expression was analyzed because gamma-PKC mutants do not develop tolerance to chronic ethanol treatment. Ethanol treatment of mutants reversed the dramatic increase in transthyretin expression seen in naïve and control-diet treated mutants, but did not affect transthyretin expression in wild types.

Dopamine and serotonin content in select brain regions of weanling and adult alcohol drinking rat lines

The objective of the present study was to examine innate differences in the tissue content of dopamine (DA), serotonin (5-HT) and their metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) in five brain regions of weanling and adult alcohol-preferring (P), alcohol-nonpreferring (NP), high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) selected rat lines. Adult male and weanling (postnatal day 25) male rats were killed by decapitation and brains were rapidly dissected for the following regions: olfactory tubercles (OTU), nucleus accumbens (ACB), septum (SEP), anterior cerebral cortex (ACTX) and amygdala (AMYG). Tissue extracts were assayed by HPLC with electrochemical detection. Due to significantly higher content levels in the adults, adult and weanling animals were analyzed separately. Significant differences were found in the ACB and OTU between the adult lines in both DA and 5-HT content, with P and HAD rats having lower levels than NP and LAD rats, respectively. Significant differences in DA content between the weanling lines were also found in the OTU, with P and HAD rats having lower DA levels than NP and LAD rats, respectively. These results confirm previous findings of an association between innate low DA content in select limbic regions and high alcohol drinking behavior.

The role of mesolimbic dopamine in the development and maintenance of ethanol reinforcement

The neurobiological processes by which ethanol seeking and consumption are established and maintained are thought to involve areas of the brain that mediate motivated behavior, such as the mesolimbic dopamine system. The mesolimbic dopamine system is comprised of cells that originate in the ventral tegmental area (VTA) and project to several forebrain regions, including a prominent terminal area, the nucleus accumbens (NAcc). The NAcc has been subdivided into core and shell subregions. Both areas receive converging excitatory input from the cortex and amygdala and dopamine input from the VTA, with the accumbal medium spiny neuron situated to integrate the signals. Although forced ethanol administration enhances dopamine activity in the NAcc, conclusions regarding the role of mesolimbic dopamine in ethanol reinforcement cannot be made from these experiments. Behavioral experiments consistently show that pharmacological manipulations of the dopamine transmission in the NAcc alter responding for ethanol, although ethanol reinforcement is maintained after lesions of the accumbal dopamine system. Additionally, extracellular dopamine increases in the NAcc during operant self-administration of ethanol, which is consistent with a role of dopamine in ethanol reinforcement. Behavioral studies that distinguish appetitive responding from ethanol consumption show that dopamine is important in ethanol-seeking behavior, whereas neurochemical studies suggest that accumbal dopamine is also important during ethanol consumption before pharmacological effects occur. Cellular studies suggest that ethanol alters synaptic plasticity in the mesolimbic system, possibly through dopaminergic mechanisms, and this may underlie the development of ethanol reinforcement. Thus, anatomical, pharmacological, neurochemical, cellular, and behavioral studies are more clearly defining the role of mesolimbic dopamine in ethanol reinforcement.

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.

Lower CSF homovanillic acid levels in depressed patients with a history of alcoholism

Major depression and alcoholism are often comorbid, resulting in more impairment and more suicidal behavior compared with either diagnosis alone. This study compared clinical features and cerebrospinal fluid (CSF) monoamine metabolites in depressed subjects with and without a history of alcoholism and healthy volunteers. We hypothesized that depressed subjects with a history of alcoholism would be more aggressive, impulsive, and suicidal than depressed subjects without a history of alcoholism, and would have lower CSF monoamine metabolite levels. We compared 63 subjects with a current major depressive episode (MDE) and a history of alcoholism, 72 subjects with a current MDE but without a history of alcoholism, and 22 healthy volunteers. Participants with a history of alcoholism were in remission for at least 6 months. All subjects were free from prescribed medications known to affect brain serotonin, dopamine, or norepinephrine systems for a minimum of 14 days. Depressive symptoms, lifetime aggression, impulsivity, Axis II disorders, and suicidal behavior were assessed. CSF was sampled and homovanillic acid (HVA), 5-hydroxyindolacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) were assayed by high-performance lipid chromatography with electrochemical detection. Depressed subjects with a history of alcoholism did not differ from depressed subjects without a history of alcoholism in current severity of depressive symptoms, or in past suicidal behavior. Depressed subjects with a history of alcoholism had lower CSF HVA levels, and higher lifetime aggression and current suicide ideation scale scores and were more likely to be tobacco smokers compared with depressed subjects without a history of alcoholism. Low HVA was present after adjustment for sex, aggression and depression scores, cigarette smoking, antisocial and borderline personality disorders, psychomotor retardation, and delusions. Controls had CSF HVA levels intermediate between the two depressed groups. We found no group difference in CSF 5-HIAA and MHPG levels. In individuals with current MDE, those with a history of comorbid alcoholism had lower CSF HVA levels compared with those without a history of alcoholism. Low CSF HVA suggests that impaired dopaminergic activity is associated with a history of alcoholism in persons with current MDE.

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.

The acquisition and maintenance of voluntary ethanol drinking in the rat: effects of dopaminergic lesions and naloxone

Wistar male rats were microinfused bilaterally with 6-hydroxydopamine or vehicle into the ventral tegmental area. After recovery, ethanol drinking was established using a sucrose-fading paradigm, i.e. rats were given twice a day access to drinks containing increasing amounts of ethanol and decreasing amounts of sucrose. Mean daily intakes at each ethanol/sucrose concentration were similar irrespective of the level of dopamine depletion that, in some animals, reached 80-90%. The percentage of rats testing as ethanol preferers in a two-bottle choice test also appeared similar in both the lesioned and control groups. After completing the sucrose-fading protocol, all rats were switched to one access per day during which they were presented with a drink containing 10% ethanol with 5% sucrose. Naloxone administration (15 min before the daily access period) decreased ethanol beverage consumption by about 50%, irrespective of the level of dopamine depletion. Total daily water intake was not altered by naloxone. In a two-bottle choice situation, naloxone suppressed intake of an ethanol drink (10% ethanol/5% sucrose), but not the intake of 5% sucrose alone. Thus, a lesion of the dopaminergic cell bodies that results in extensive depletion of dopamine in mesolimbic target regions produced no measurable effect on intake of the sweetened ethanol drinks during the acquisition phase of the sucrose-fading paradigm. Furthermore, during the maintenance phase of drinking, the marked effect of naloxone in inhibiting ethanol beverage ingestion (but not water ingestion or sucrose alone solutions) occurred despite extensive loss of dopaminergic innervation to telencephalic target regions. A preliminary account of these experiments appeared in an abstract form and as an Internet publication. (Supported by NIAAA grants P50-03510 and T32-0720).

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.

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.

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

Morphine induces a larger locomotor stimulation in the alcohol-preferring AA rats than in the alcohol-avoiding ANA rats. We have now studied the acute effects of morphine (1 and 3 mg/kg) on metabolism of dopamine and serotonin (5-HT) in the dorsal and ventral striatum of the AA and ANA rats. The basal level of dopamine release, as reflected by the concentration of dopamine metabolite 3-methoxytyramine (3-MT), was lower in the caudate-putamen and nucleus accumbens of the AA rats than in the ANA rats. In the caudate-putamen, morphine increased dopamine metabolism and release more in the AA than in the ANA rats. In the nucleus accumbens and olfactory tubercle, the effects of morphine on dopamine metabolism and release did not differ between the rat lines. Morphine elevated the metabolism of 5-HT in the caudate-putamen and nucleus accumbens of the AA but not in those of the ANA rats. The results suggest that the larger morphine-induced psychomotor stimulation of the AA rats in comparison with the ANA rats is associated with the larger effect of morphine on dopamine metabolism in the caudate-putamen and 5-HT metabolism in the caudate-putamen and nucleus accumbens. Furthermore, low basal dopamine release may play a role in the high alcohol-preference of AA rats.

Treating neonatal rats with 6-hydroxydopamine induced an increase in voluntary alcohol consumption

Brain dopamine (DA) and serotonin (5-HT) neurotransmission have been implicated in the mediation of alcohol-seeking behavior. We examined the effects of treatment of neonatal rats (3 days after birth) with the neurotoxin 6-hydroxydopamine (6-OHDA; 100 microg/10 microl, intracerebroventricularly) on the relationship between the levels of neurotransmitters and alcohol drinking behavior at the age of 14 weeks. 6-OHDA treatment reduced the levels of DA and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens (ACC), frontal cortex, striatum (STR), tegmentum/substantia nigra, and dorsal raphe nucleus. 5-HT levels in the ACC and STR were increased in the 6-OHDA-treated rats. 6-OHDA-treated rats showed increased alcohol consumption. There was a significant change in the ratio of [5-hydroxyindoleacetic acid]/[5-HT] in the ACC and STR of the treated rats, but no difference in the ratio of [DOPAC]/[DA] between the sham-operated controls and treated rats. 6-OHDA-treated rats had dopaminergic dysfunction in the five brain regions related to the reward system, in part, and a decrease in 5-HT turnover, including the accumulation of 5-HT in the ACC and STR. Furthermore, basal extracellular releases of DA and 5-HT of the ACC were significantly lower in the 6-OHDA-treated rats, compared with the controls. It was suggested that alcohol seeking behavior is associated with the alterations of dopaminergic neurons and the release of 5-HT in the mesocorticolimbic system.

Drinking patterns in genetic low-alcohol-drinking (LAD) rats after systemic cyanamide and cerebral injections of THP or 6-OHDA

A key question related to the role of acetaldehyde and aldehyde adducts in alcoholism concerns their relationship to the genetic mechanisms underlying drinking. Experimentally, the low-alcohol-drinking (LAD) rat represents a standard rodent model having a strong aversion to alcohol. In these experiments, preferences for water vs. alcohol, offered in concentrations from 3% to 30%, were determined over 10 days in adult LAD rats (N = 6 per group). Then a saline vehicle or either 10 or 20 mg/kg of the aldehyde dehydrogenase (AIDH) inhibitor, cyanamide, was injected s.c. twice daily for 3 days. Secondly, either 0.5 or 1.0 microg of tetrahydropapaveroline (THP) was infused i.c.v. twice daily for 3 days in LAD rats (N = 8) and, as a genetic control, THP also was infused identically in Sprague-Dawley (SD) rats (N = 8). The results showed that the lower and higher doses of cyanamide augmented alcohol intakes in 33% and 50% of the LAD rats, respectively, with the patterns of drinking resembling that of genetic high-alcohol-drinking HAD or P rats. Although i.c.v. infusions of THP had little effect on alcohol preference of LAD rats, alcohol drinking was enhanced significantly in the SD rats. In a supplementary study, 200 microg of 6-hydroxydopamine (6-OHDA) also was infused i.c.v. in LAD rats (N = 7) on two consecutive days; no change occurred in the characteristic aversion to alcohol. These findings suggest that in certain individuals, a perturbation in the synthesis of AIDH can modify the genetically based aversion to alcohol, thus precipitating the liability for alcoholism. In that neither THP nor 6-OHDA lesioning exerted any effect on the genetic nondrinking LAD animal suggests that an unknown endogenous factor in the brain must underlie the cyanamide-induced shift to alcohol preference. We conclude that the genetic elements that normally prevent the progression to addictive drinking in most individuals appear to be invariant and irreversible.

Putative oxidative metabolites of 1-methyl-6-hydroxy-1,2,3,4-tetrahydro-beta-carboline of potential relevance to the addictive and neurodegenerative consequences of ethanol abuse

Ethanol is metabolized in the brain by catalase/H2O2 to yield acetaldehyde and by an ethanol-inducible form of cytochrome P450 (P450 IIE1) in a reaction that yields oxygen radicals. Within the cytoplasm of serotonergic axon terminals these metabolic pathways together provide conditions for the endogenous synthesis of 1-methyl-6-hydroxy-1,2,3,4-tetrahydro-beta-carboline (1), by reaction of acetaldehyde with unbound 5-hydroxytryptamine (5-HT), and for the oxygen radical-mediated oxidation of this alkaloid. The major initial product of the hydroxyl radical (HO.)-mediated oxidation of 1 in the presence of free glutathione (GSH), a constituent of nerve terminals and axons, is 8-S-glutathionyl-1-methyl-1,2,3,4-tetrahydro-beta-carboline-5,6-dione (6). When administered into the brains of mice, 6 is a potent toxin (LD50 = 2.9 microg) and evokes episodes of hyperactivity and tremor. Compound 6 binds at the GABA(B) receptor and evokes elevated release and turnover of several neurotransmitters. Furthermore, the GABA(B) receptor antagonist phaclofen attenuates the behavioral response caused by intracerebral administration of 6. These observations suggest that 6 might be an inverse agonist at the GABA(B) receptor site. Accordingly, it is speculated that ethanol drinking might potentiate formation of 6 that contributes to elevated release of several neurotransmitters including dopamine (DA) and endogenous opioids in regions of the brain innervated by serotonergic axon terminals. Subsequent interactions of DA and opioids with their receptors might be related to the initial development of dependence on ethanol. Redox cycling of 6 (and of several putative secondary metabolites) in the presence of intraneuronal antioxidants and molecular oxygen to produce elevated fluxes of cytotoxic reduced oxygen species might contribute to the degeneration of serotonergic pathways. Low levels of 5-HT in certain brain regions of the rat predisposes these animals to drink or augments drinking. Accordingly, 6, formed as a result of ethanol metabolism in the cytoplasm of certain serotonergic axon terminals, might contribute to the initial development of dependence on ethanol, by mediating DA and opioid release, and long-term preference and addiction to the fluid as a result of the progressive degeneration of these neurons.

Amphetamine and fenfluramine suppress ethanol intake in ethanol-dependent rats

Alcohol intake or preference for alcohol has been attributed to concomitant dopamine and serotonin dysfunction in rats. Amphetamine and fenfluramine, administered alone, have been shown to reduce food and fluid intake as well as alcohol consumption while acute coadministration of these agents has been shown to suppress audiogenic seizure in rats withdrawn from alcohol. The present study was designed to assess the effectiveness of chronic amphetamine and fenfluramine coadministration on reducing alcohol intake. Chronic coadministration of amphetamine (2 mg/kg) and fenfluramine (8 mg/kg) reduced alcohol consumption during choice trials in both alcohol-dependent and alcohol-nondependent rats while not affecting water intake. The findings indicate that coadministration of amphetamine and fenfluramine, a treatment effective in reducing alcohol withdrawal seizures, also selectively attenuates alcohol consumption.

Effects of chronic ethanol treatment and ethanol withdrawal on [3H]SCH23390 binding to rat striatal membranes

The effects of chronic ethanol administration and ethanol withdrawal on the kinetic and pharmacological properties of [3H]SCH23390 binding sites and the labelling of central dopamine D-1 receptors were studied in the striatum of the rat. Chronic 40 day ethanol treatment produced a statistically significant decrease (p < 0.05) in maximum binding (Bmax) on striatal dopamine D-1 receptors of the rat, KD remaining unaltered. The withdrawal of ethanol did not affect the kinetic binding parameters. The rank order of potency in displacing the specific [3H]SCH23390 binding of several dopamine antagonists, agonists and serotonin-related drugs was consistent with the pharmacological profile of dopamine D-1 receptors. Chronic ethanol treatment led to a statistically significant increase in receptor affinity (lower Ki than controls) for (+)-butaclamol (p < 0.05). Ethanol withdrawal for 24 hr increased the affinity of [3H]SCH23390-labeled binding sites for norepinephrine. The addition of 0.03-0.68 M ethanol in vitro had no significant effects on [3H]SCH23390 binding in striatal preparations taken from both control and ethanol-treated rats. The results show that rat striatal [3H]SCH23390-labelled binding sites are affected by different conditions of ethanol exposure, possibly suggesting the medication of striatal dopamine pathways in the responses to ethanol intoxication.

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

Amperozide (FG5606), a 5-HT2 receptor antagonist, is well known to suppress alcohol consumption in different rat models of drinking. The present study compared the efficacy of three drugs, FG5974, FG5893, and amperozide, which have differential affinities for 5-HT1A and 5-HT2A receptors, on alcohol drinking in the genetic alcohol-preferring (P) rat. After preference for alcohol vs. water was determined over 10 days when concentrations of alcohol were increased from 3% to 30%, the maximal concentration of alcohol preferred by each animal was selected for drug testing. A 4-day predrug preference test was followed by SC injection of the saline control vehicle or doses of 1.0 and 2.5 mg/kg FG5974, FG5893, or amperozide given at 1600 and 2200 h for 4 days. Alcohol preference testing concluded with a final 4-day interval. A total daily dose of 5.0 mg/kg FG5974 reduced absolute g/kg intake of alcohol and proportional intakes of the P rats significantly; the lower dose of FG5974 also reduced alcohol drinking significantly following treatment. The mixed 5-HT1A agonist/5-HT2A antagonist, FG5893, which suppresses drinking in cyanamide-treated rats, was without effect on alcohol ingested by the P rats. However, amperozide caused a dose-dependent decline in both absolute intakes and proportion of alcohol that was more intense than that of FG5974. The control vehicle failed to alter alcohol drinking and, like the FG compounds, did not affect food intake or body weight. Although the inhibition of alcohol drinking by amperozide corresponds precisely with previous findings, the effect of FG5974 contrasts to results obtained with a structurally analogous drug FG5893. Thus, the genetic strain of rat as well as the nature of the chemical characteristics of a 5-HT agonist/antagonist will determine the differential efficacy of a drug in influencing the volitional drinking of alcohol.

Influence of glutathione on the oxidation of 1-methyl-6-hydroxy-1,2,3,4-tetrahydro-beta-carboline: chemistry of potential relevance to the addictive and neurodegenerative consequences of ethanol use

Recent evidence suggests that intraneuronal metabolism of ethanol by catalase/H2O2 and an ethanol-inducible form of cytochrome P450 together generate acetaldehyde and oxygen radicals including the hydroxyl radical (HO.). Within the cytoplasm of serotonergic neurons, these metabolic processes would thus provide acetaldehyde, which would react with unbound 5-hydroxytryptamine (5-HT) to give 1-methyl-6-hydroxy-1,2,3,4-tetrahydro-beta-carboline (1), known to be formed at elevated levels in the brain following ethanol drinking, and HO. necessary to oxidize this alkaloid. In this study, it is demonstrated that the HO.-mediated oxidation of 1 at physiological pH yields 1-methyl-1,2,3,4-tetrahydro-beta-carboline-5,6-dione (8) that reacts avidly with free glutathione (GSH), a significant constituent of axons and nerve terminals, to give diastereomers of 8-S-glutathionyl-1-methyl-1,2,3,4-tetrahydro-beta-carboline-5,6-dione (9A and 9B). In the presence of free GSH, ascorbic acid, other intraneuronal antioxidants/reductants, and molecular oxygen diastereomers, 9A/9B redox cycle in reactions that generate H2O2 and, via trace transition metal ion catalyzed decomposition of the latter compound, HO.. Further reactions of 9A/9B with GSH and/or HO. generate several additional glutathionyl conjugates that also redox cycle in the presence of intraneuronal reductants and molecular oxygen forming H2O2 and HO.. Thus, intraneuronal formation of 1 and HO. as a consequence of ethanol drinking and resultant endogenous synthesis of 8,9A, and 9B would, based on these in vitro chemical studies, be expected to generate elevated fluxes of H2O2 and HO. leading to oxidative damage to serotonergic axons and nerve terminals and the irreversible loss of GSH, both of which occur in the brain as a consequence of ethanol drinking. Furthermore, deficiencies of 5-HT and loss of certain serotonergic pathways in the brain have been linked to the preference for and addiction to ethanol.

Effect of ethanol on extracellular dopamine in nucleus accumbens: comparison between Lewis and Fischer 344 rat strains

The purpose of this study was to examine the differential effects of intraperitoneal ethanol on the mesoaccumbens dopamine (DA) system in Fischer 344 and Lewis rat strains, utilizing microdialysis in awake animals. At the lowest dose tested (0.5 g/kg), there were no changes in extracellular DA in the nucleus accumbens in either strain. There was a differential response to the intermediate dose of 1 g/kg ethanol, with an 84% increase in extracellular DA in the Fischer, but no change in Lewis rats. The highest dose administered (2 g/kg) did not induce significant increases in DA in either strain. These data demonstrate that the mesoaccumbens DA systems of Fischer and Lewis rat strains differ in their susceptibility to activation by ethanol, and suggest that the higher alcohol preference of Lewis rats is not associated with an enhanced DAergic response to acute experimental administration of ethanol.

Prefrontal levels of 5-HIAA, but not dopamine, predict alcohol consumption in male Wistar rats following 6-OHDA lesions

To examine the effects of dopamine (DA) on alcohol consumption, male Wistar rats were subjected either to 6-OHDA lesions of the frontal cortex (MPFC) or to a sham lesion/no lesion. Following surgery, rats were trained to drink alcohol on a sucrose-fading paradigm over the course of 6 weeks, at the completion of which they consumed a solution of 3% sucrose/10% alcohol. Daily consumption of alcohol was computed for each rat. Animals were sacrificed and the MPFC, nucleus accumbens (NA), and ventral tegmentum (VTA) were removed. Levels of DA and its metabolites (i.e., HVA and DOPAC), norepinephrine (NE), and serotonin (5-HT) and its metabolite (i.e., 5-HIAA) were measured for each brain region using HPLC with electrochemical detection. Post hoc analyses were run examining the relationship of DA and its metabolites, 5-HT and its metabolite (5-HIAA), and norepinephrine (NE) in the MPFC, NA, and VTA with alcohol consumption. The 6-OHDA lesions depleted DA to 74.5% of control levels in the MPFC, but did not significantly affect alcohol consumption. Post hoc analyses found that the "high" alcohol consumption group had significantly reduced levels of MPFC 5-HIAA in comparison to the "low" consumption group, but that there was no relationship of 5-HIAA levels in the VTA or NA to alcohol consumption. These findings suggest that MPFC DA is not critically involved in the regulation of alcohol consumption. They further suggest that MPFC serotonergic systems may play an important role in the regulation of alcohol consumption, although future experimentation directly manipulating 5-HT systems in the MPFC will be required to fully assess these findings.

Effects of ibotenic acid lesions of the ventral striatum and the medial prefrontal cortex on ethanol consumption in the rat

The purpose of this study was to to assess the effect on ethanol drinking of ibotenic acid lesions in the medial prefrontal cortex and the ventral striatum of female rats with continuous access to water and a 6% ethanol solution. Ibotenic acid infusions in the prefrontal cortex did not affect ethanol intake at any time, but a significant increase in water intake was observed on the third postoperative week. Ventral striatal lesions significantly increased ethanol intake during the first 2 postoperative weeks. On the third week consumption was not significantly different from vehicle-infused controls. Apparently, then, severe excitoxic injury to the ventral striatum is compatible with normal, or increased, intake of ethanol; in contrast, similar lesions reduce the intake of other drugs of abuse such as psychostimulants and opioids.

Low-dose effect of ethanol on locomotor activity induced by activation of the mesolimbic system

Four experiments were designed to study the ability of 0.5 g/kg ethanol (EtOH) intraperitoneally to modify locomotor activity induced by drugs that interact with different sites in the mesolimbic system (MLS) of male Sprague-Dawley rats. Locomotor activity was measured in a doughnut-shaped circular arena after various treatments. EtOH alone did not alter locomotor activity in any of the experiments. Amphetamine (AMP, intraperitoneally or intraaccumbens) increased locomotor activity in a dose-dependent manner, and the presence of EtOH attenuated AMP-induced locomotor activity. Bilateral infusion of GABAA antagonist picrotoxin (PIC) into the ventral tegmental area also increased locomotor activity in a dose-dependent manner, and the presence of EtOH attenuated PIC-induced locomotor activity. On the other hand, the interaction between bilateral infusion of mu-receptor agonist Tyr-D-Ala-Gly-NMe-Phe-Gly-ol (DAGO) and EtOH on locomotor activity is complex. The highest dose of DAGO that significantly increased locomotor activity was not affected by the presence of EtOH. But, with lower doses of DAGO that either had no effect or a small increase in locomotor activity, the combination of EtOH and DAGO increased and attenuated locomotor activity, respectively. Results from this study support our hypothesis that a low dose of EtOH that does not modify behavior can interact with neurotransmitter systems in the brain and modify drug-induced locomotor activity. Modification of this drug-induced locomotor activity by a low dose of EtOH is dependent on the rate of ongoing locomotor behavior induced by drug and the neurotransmitter substrate that the drug modified to induce locomotor behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of dopamine in drug abuse viewed from the perspective of its role in motivation

Drugs of abuse share with conventional reinforcers the activation of specific neural pathways in the CNS that are the substrate of their motivational properties. Dopamine is recognized as the transmitter of one such neural pathway, being involved in at least three major aspects of motivation: modulation of motivational state, acquisition (incentive learning) and expression of incentive properties by motivational stimuli. Drugs of abuse of different pharmacological classes stimulate in the low dose range dopamine transmission particularly in the ventral striatum. Apart from psychostimulants, the evidence that stimulation of dopamine transmission by drugs of abuse provides the primary motivational stimulus for drug self-administration is either unconvincing or negative. However, stimulation of dopamine transmission is essential for the activational properties of drugs of abuse and might be instrumental for the acquisition of responding to drug-related incentive stimuli (incentive learning). Dopamine is involved in the induction and in the expression of behavioural sensitization by repeated exposure to various drugs of abuse. Sensitization to the dopamine-stimulant properties of specific drug classes leading to facilitation of incentive learning of drug-related stimuli might account for the strong control over behaviour exerted by these stimuli in the addiction state. Withdrawal from drugs of abuse results in a reduction in basal dopamine transmission in vivo and in reduced responding for conventional reinforcers. Although these changes are likely to be the expression of a state of dependence of the dopamine system their contribution to the motivational state of drug addiction is unclear.

Alcohol drinking in rats injected ICV with 6-OHDA: effect of 8-OHDPAT and tropisetron (ICS 205930)

6-Hydroxydopamine (6-OHDA) was administered ICV to Wistar male rats. Lesioned animals displayed lower preference for ethanol (ETOH) than sham-operated rats. Among 6-OHDA lesioned rats only 9% became high-preferring whereas 20% of sham-operated animals became high-preferring ones. Both tropisetron (the antagonist of 5-HT3 receptors) and 8-OHDPAT (the 5-HT1A receptor agonist) reduced ETOH drinking in high-preferring rats. However, in 6-OHDA lesioned rats the effect of tropisetron was reduced although 8-OHDA retained its effect on ETOH consumption. These results suggest that brain DA neurons are involved in tropisetron action but are not responsible for antipreference effect of 8-OHDPAT.

Genetics of alcoholism: simultaneous presentation of a chocolate drink diminishes alcohol preference in high drinking HAD rats

Through selective crossbreeding of the N/Nih heterogeneous stock of rats, two genetic lines of rats have been developed that are categorized by their preference for ethyl alcohol as high alcohol drinking (HAD) and low alcohol drinking (LAD) animals. Corresponding to other strains of rat bred for alcohol selection or rejection, they were subdivided on the basis of their intake of a solution of 10% alcohol vs. water. The present experiments were designed to determine whether the HAD-1 and LAD-1 lines are similar to the P and NP rats in their profile of alcohol consumption. Five successive three-bottle preference tests for alcohol drinking in the presence of water were undertaken in both HAD (n = 9) and LAD (n = 10) rats as follows: 10% alcohol for 5 days; 3-30% concentrations of alcohol increased over 11 days; the maximally preferred concentration of alcohol for 5 days; this maximally preferred concentration of alcohol plus either chocolate Slender for 5 days, or an aspartame solution for 5 days. The intake of alcohol of the LAD rats during the 10% test was 0.4 g/kg/day, whereas during the 3-30% test, the maximum intake was 1.7 g/kg/day; their maximally preferred concentrations ranged between 7% and 9% alcohol. In contrast, the intake of 10% alcohol of the HAD rats was 6.5 g/kg/day, whereas during the 3-30% test the mean daily intake was 6.6 g/kg/day; the maximally preferred solutions of the HAD rats ranged between 13 to 20%, with the mean maximum intake of 10.57 g/kg/day reached at the 20% concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ventral striatal 6-OHDA lesions or amphetamine sensitization on ethanol consumption in the rat

Female rats with continuous access to water and 6% ethanol were given bilateral ventral striatal 6-OHDA infusions, which induced pronounced striatal depletions of dopamine. The postoperative ethanol consumption of these rats was not significantly affected in comparison to vehicle-infused controls. In a second experiment, female rats received escalating doses of d-amphetamine over a 5-week period (from 1 to 9 mg/kg/injection). Control females were given saline injections. Following a 3-month drug-free interval, the females were given access to ethanol, the concentration of which was gradually increased from 2% to 12% with weekly intervals. Amphetamine-sensitized rats consumed significantly more alcohol than the saline-treated controls. Taken together, these results suggest that striatal dopaminergic mechanisms, while not necessary for basal ethanol drinking, can facilitate alcohol drinking.

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)

Irreversible suppression of alcohol drinking in cyanamide-treated rats after sustained delivery of the 5-HT2 antagonist amperozide

The purpose of this study was to evaluate the long-term effect of sustained treatment with amperozide, which has been shown to attenuate the volitional drinking of ethyl alcohol in the rat without side effects. Preference for alcohol first was induced pharmacologically in Sprague-Dawley rats by the inhibitor of aldehyde dehydrogenase, cyanamide, administered in a dose of 10 mg/kg twice daily for 3 days. Then following a standard preference test, each rat was offered water and its maximally preferred concentration of alcohol which ranged from 7% to 15%. Following a 4-day pre-drug test, saline control vehicle or amperozide was administered for 7 days by an osmotic minipump implanted in the intrascapular space. A single dose of 208 micrograms/kg/h (i.e., 5.0 mg/kg/day) was selected on the basis of a prior dose response study of amperozide. During the interval of sustained release of amperozide, the consumption of alcohol declined significantly in terms of both absolute g/kg intake and proportion of alcohol to water. When the preference of the rats was retested at 4, 30, 70, 110, and 140 day intervals after the pump had exhausted amperozide, the absolute g/kg consumption of alcohol continued to decline significantly. Unlike other drugs, amperozide did not produce any side effects, particularly on the intake of food or water or on body weight, which suggests a pharmacological specificity of its action.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of tolerance to ethanol-induced dopamine release in the rat ventral striatum

The effect of ethanol challenge on the extracellular concentrations of dopamine, 3,4-dihydroxy-phenylacetic acid and homovanillic acid was studied in the ventral striatum of rats repeatedly treated with ethanol. Ethanol-treated animals (1 g/kg i.p. twice a day for 12 days) developed marked tolerance to the behavioral signs of ethanol intoxication when challenged with ethanol (2 g/kg i.p.). However, in ethanol-treated animals the increased output of dopamine and metabolites after ethanol challenge (1 or 2 g/kg i.p.) was not statistically different from that observed in saline-treated rats. These results indicate that tolerance does not develop to the ethanol-induced stimulation of dopamine release and support the hypothesis that activation of the mesolimbic dopamine system contributes to the reinforcing properties of ethanol.

Effect of dopamine agonists and antagonists on ethanol-reinforced behavior: the involvement of the nucleus accumbens

Rats initiated to self-administer 10% ethanol (v/v) in an operant situation using the sucrose-substitution technique received bilateral n. accumbens or caudate nucleus microinjections of d-amphetamine (4, 10, and 20 micrograms/brain), quinpirole (4 micrograms/brain), and/or raclopride (0.1, 0.5, and 1.0 micrograms/brain). Only microinjections into the n. accumbens produced changes in rate and pattern of responding. With d-amphetamine, an increase in total responding and a slowing of initial response rate was seen, whereas with raclopride administration a dose-related decrease in total responding was observed with no alteration in momentary response rates. Drug-dependent behavioral rate and pattern differences suggest that DA activity in the n. accumbens influences ethanol reinforced behavior.

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.

Age dependent development of ethanol drinking in rats after inhibition of aldehyde dehydrogenase

The purpose of this experiment was to determine the temporal characteristics associated with the age-related development of volitional consumption of ethanol induced by the pharmacological inhibition of aldehyde dehydrogenase (AlDH). To induce preference for ethanol, the AlDH inhibitor, cyanamide, was administered to male Sprague-Dawley rats which were 30 days of age. Cyanamide (n = 8) was injected subcutaneously twice daily in a dose of 10 mg/kg over a period of 3 days while the control group (n = 6) received the saline vehicle solution according to the same schedule. Then at 50, 70, 90, and 110 days of age, both groups of rats were given a standard 11-day test of preference for water versus ethanol offered in concentrations ranging from 3% through 30%. The results showed that at 70 days of age the preference for ethanol increased above the level of the 50-day test in terms of absolute g/kg intakes and proportion of ethanol to water consumed over the lower range of 3% through 15% concentrations. During the tests at 90 and 110 days of age, the cyanamide-treated rats further increased their preference for ethanol significantly over the levels at the 70-day test in terms of both g/kg and proportional intakes. The pattern of drinking of ethanol offered in the higher concentrations of 25% and 30% was unrelated to the age of the rats and the overall intakes were significantly higher than those of the lower concentrations. These findings demonstrate that the enzymatic inhibition of AlDH systematically acts in a delayed fashion to shift the pattern of preference for ethanol which is contingent on the maturation of the animal. In this instance, the volitional intake of ethanol in the cyanamide-treated rats reached its maximal level by 90-110 days of age. It is proposed that an endocrine mechanism involved in gonadal maturation may function in the intense shift in alcohol drinking.

Selective reduction by the 5-HT antagonist amperozide of alcohol preference induced in rats by systemic cyanamide

This investigation was undertaken to determine the effect of a unique psychotropic agent on the volitional drinking of alcohol induced pharmacologically in the rat by an inhibitor of aldehyde dehydrogenase. Following administration of cyanamide in a dose of 10 mg/kg twice daily for 3 days, the pattern of drinking of ethyl alcohol was determined in each of 12 Sprague-Dawley rats by means of a standard preference test for 3-30% alcohol vs. water. Then, each rat was offered water and its maximally preferred concentration of alcohol, which ranged from 7-15%. After a 4-day predrug test, either the saline control vehicle or the diphenylbutylpiperazinecarboxamide derivative, amperozide, was administered subcutaneously. The injections of amperozide were given b.i.d. at 1600 and 2200 h over 3 days in a dose of 0.5, 1.0, or 2.5 mg/kg. The intake of alcohol during the sequence of amperozide injections was significantly reduced in a dose-dependent manner in terms of both absolute g/kg and proportion of alcohol to water intake, whereas the saline control vehicle was without any effect on alcohol consumption. Although the highest dose of amperozide reduced the total intake of fluid due to the sharp decline in alcohol drinking, neither the consumption of food nor level of body weight was affected by any dose of the drug either during or after its administration. Because amperozide acts centrally on the synaptic activity of dopaminergic and serotonergic neurons in limbic system structures, it is envisaged that the drug ameliorates the aberrant drinking of alcohol by virtue of a direct effect on either one or both of these classes of neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Recent Advances in Pharmacological Research on Alcohol

Alcohol dependence is a major public health problem. Studies have shown that a person dependent on alcohol often coabuses other substances, such as cocaine. Cocaine is a powerful stimulant whereas ethanol is generally considered to be a depressant, with some stimulating properties. The subjective effects of these two substances in a dependent individual may often appear to be more similar than they are different. Animals also self-administer both substances. Basically, although both substances have anesthetic properties and both act to functionally increase catecholaminergic function, especially that of dopamine, there are some differences in their actions. Both alcohol and cocaine have various effects on several neurotransmitters and systems, which ultimately interact to produce the feeling of well-being avidly sought by many individuals today. This drive often eventually produces a dependence which has associated social and medical consequences. It seems likely that the neurochemical changes that ensue following abuse of these substances underlie the phenomena of dependence, tolerance, and subsequent withdrawal. The apparent similarities and differences between these two substances will be reviewed in this chapter.

Alcohol drinking attenuated by sertraline in rats with 6-OHDA or 5,7-DHT lesions of N. accumbens: a caloric response?

The purpose of this study was to elucidate further the role of serotonin (5-HT) in the preference for ethyl alcohol induced in the Sprague-Dawley rat by lesions of the N. accumbens. Following a standard preference test for 3-30% alcohol, dopaminergic or serotonergic neurons in the N. accumbens of the rat were lesioned bilaterally by 6-hydroxydopamine (6-OHDA) or 5,7-dihydroxytryptamine (5,7-DHT), respectively. After recovery postoperatively, each rat was offered water and its maximally preferred concentration of alcohol, which ranged from 7% to 11%. Following a 4-day pretest, either the saline control vehicle or the 5-HT reuptake inhibitor, sertraline, was injected subcutaneously in a dose of either 3.0 or 10 mg/kg b.i.d. at 0800 and 2000 h over the next 3 days. Alcohol preference during the injection sequence and for 4 days thereafter was significantly reduced by sertraline in terms of both absolute g/kg and proportion of alcohol to water intakes. Saline was without effect on alcohol drinking. Comparisons of the drinking profiles of serotonergic versus dopaminergic lesioned rats revealed a dose dependent response to sertraline only in the 5,7-DHT lesioned animals. Although sertraline did not alter water drinking, the consumption of food declined significantly during and after its administration with a decline in body weight also observed at the higher dose. These results suggest that in addition to dopaminergic neurons in the N. accumbens, the synaptic activity of 5-HT in this structure contributes to the aberrant drinking of alcohol. However, this interpretation is tempered by the fact that caloric intake was suppressed concomitantly by the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Drinking of high concentrations of ethanol versus palatable fluids in alcohol-preferring (P) rats: valid animal model of alcoholism

A genetically based animal model of alcoholism has been characterized in Wistar-derived rats in terms of their preference (P rats) or lack of preference (NP rats) for 10% ethanol over water. The present experiments were designed to determine: 1) whether a 10% solution of ethanol is the optimal concentration for differentiation of these lines; 2) what concentrations of ethanol are maximally preferred by P and NP rats; and 3) whether highly palatable fluids presented simultaneously with each rat's preferred solution of ethanol would alter the patterns of drinking by either the P or NP or both lines of rats. A three-bottle procedure was used to establish preference for ethanol in the presence of water as well as highly palatable solutions. The results showed that, when concentrations ranging from 3-30% were presented over a 12-day test interval, the mean absolute intake of ethanol of the P rats was 6.7 g/kg per day, with a maximum intake of 10.9 g/kg per day at the 25% concentration. These levels of intake were significantly higher than the 4.3 g/kg per day consumed during the presentation of the commonly used constant concentration of 10%. Similarly, the mean absolute intake of ethanol by the NP rats was also elevated significantly at concentrations of 15-30% (2.0 g/kg per day) above that consumed at the 10% concentration (0.4 g/kg).(ABSTRACT TRUNCATED AT 250 WORDS)