Behavioral neurobiology of alcohol addiction: recent advances and challenges

Diffusion tensor imaging in chronic head injury survivors: correlations with learning and memory indices

Diffusion tensor imaging (DTI) provides a unique insight into the cellular integrity of the brain. While conventional magnetic resonance imaging underestimates the extent of pathology following closed head injury, diffusion-weighted imaging has been shown to more accurately delineate the extent of cerebral damage. There have only been a few case studies of DTI in chronic head injury survivors. This study used DTI to investigate changes in anisotropy and diffusivity in survivors of head injury at least 6 months after their injury. The relationship between cognition and diffusion abnormality was also investigated. The voxel-based analysis revealed significant bilateral decreases in anisotropy, in major white matter tracts and association fibers in the temporal, frontal, parietal and occipital lobes. Statistically significant increases in diffusivity were also found in widespread areas of the cortex. A significant positive correlation was found between diffusivity and impairment of learning and memory in the left posterior cingulate, left hippocampal formation and left temporal, frontal and occipital cortex. The common pattern of abnormality despite heterogeneous injury mechanism and lesion location in the group suggests that these cellular changes reflect secondary insults. The importance of diffusion abnormalities in head injury outcome is emphasized by the significant correlation between a learning and memory index and diffusivity in areas known to subserve this cognitive function.

Recent advances in the development of treatments for alcohol and cocaine dependence: focus on topiramate and other modulators of GABA or glutamate function

Neuroscientific developments have promulgated interest in developing efficacious medications for the treatment of substance dependence. Previous pharmacological strategies that involve the use of relatively specific medications to alter corticomesolimbic dopaminergic neuronal activity--the critical pathway for expression of the reinforcing effects of abused drugs--have yielded modest efficacy in the treatment of alcohol dependence, and no medication has been established as a treatment for cocaine dependence. Since corticomesolimbic dopaminergic neurons interact with other neurotransmitters that modulate the effects of dopamine in the nucleus accumbens, would it not be possible to control these dopaminergic effects more reliably with a medication that acts contemporaneously on more than one neuromodulator of dopaminergic function? Further, since the long-term use of either alcohol or cocaine results in neuronal adaptations as a result of sensitisation, would the chances of effective therapy not be bolstered by administering a medication that was also able to mitigate these chronic effects? Thus, a new conceptual approach is needed. My proposal is that a medication--in this case topiramate--that principally potentiates inhibitory GABA(A) receptor-mediated input and antagonises excitatory glutamatergic afferents to the corticomesolimbic dopaminergic system should have therapeutic potential in treating either alcohol or cocaine dependence or perhaps both. This is because the principal neurochemical effects of topiramate would not only serve to decrease the acute reinforcing effects of alcohol or cocaine, but might also facilitate cessation of their use following a period of long-term use by decreasing neuronal sensitisation. This overview highlights the scientific concepts and clinical evidence for the development of topiramate in the treatment of alcohol dependence and introduces preliminary evidence to indicate that it might also have utility in treating cocaine dependence. Finally, to place the material on topiramate in context, information has been included on the utility and development of other medications that modulate GABA- or glutamate-mediated neuronal systems for the treatment of alcohol or cocaine dependence.

Reducing effect of the positive allosteric modulators of the GABA(B) receptor, CGP7930 and GS39783, on alcohol intake in alcohol-preferring rats

The gamma-aminobutyric acidB (GABA(B)) receptor full agonists, baclofen and CGP44532, have been found to suppress different aspects of alcohol drinking behavior, including acquisition and maintenance, in selectively bred Sardinian alcohol-preferring (sP) rats. The present study was designed to assess whether this capability extends to the recently synthesized, positive allosteric modulators of the GABA(B) receptor, 2,6-Di-tert-butyl-4-(3-hydroxy-2,2-dimethyl-propyl)-phenol (CGP7930) and N,N'-dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine (GS39783). In the "acquisition" experiments, CGP7930 (0, 25, 50 and 100 mg/kg; i.g.) and GS39783 (0, 6.25, 12.5 and 25 mg/kg; i.g.) were administered for 5 consecutive days to alcohol-naive sP rats. In the "maintenance" experiments, (0, 50 and 100 mg/kg; i.g.) and GS39783 (0, 50 and 100 mg/kg; i.g.) were administered for 5 consecutive days to alcohol-experienced sP rats. Alcohol intake was evaluated under the standard, homecage 2-bottle "alcohol (10%, v/v) vs water" regimen with unlimited access for 24 h/day. Both CGP7930 and GS39783 dose-dependently suppressed the acquisition of alcohol drinking behavior. In the "maintenance" experiments, CGP7930 and GS39783 reduced daily alcohol intake by 30-40% only at the highest dose when compared to vehicle-treated rats; this effect tended to vanish on continuing treatment. The results of the present study suggest that positive allosteric modulation of the GABA(B) receptor produced an effect on alcohol drinking behavior similar to that produced by GABA(B) receptor full agonists. These data also suggest that positive allosteric modulation of the GABA(B) receptor may constitute a potential strategy for developing new drugs for treating alcohol dependence.

Differential G-protein coupling to GABAB receptor in limbic areas of alcohol-preferring and -nonpreferring rats

The function of the gamma-aminobutyric acid(B) (GABAB) receptor, measured as baclofen-stimulated [35S]GTPgammaS binding, was evaluated in some brain regions of Sardinian alcohol-preferring (sP) and -nonpreferring (sNP) rats. EC50 value of baclofen-stimulated [35S]GTPgammaS in limbic areas was approximately 125% higher in alcohol-naive sP than sNP rats; voluntarily consumed alcohol reduced the EC50 value to a level similar to that of alcohol-naive sNP rats. These results suggest the presence of a genetically determined lower function of the GABAB receptor in limbic areas of sP than sNP rats; this differential functioning of the GABAB receptor may contribute to the opposite preference for alcohol in these rat lines.

Local effects of acute ethanol on dopamine neurotransmission in the ventral striatum in C57BL/6 mice

In this study, fast-scan cyclic voltammetry in brain slices was used to evaluate the effects of acute ethanol on dopamine terminal release and uptake in the nucleus accumbens of C57BL/6 mice. We found that pharmacologically relevant concentrations of ethanol (20 and 100 mM) did not alter electrically evoked dopamine release, while the highest concentration (200 mM) significantly decreased release (approximately 45%). No significant changes were observed in the rate of dopamine uptake after ethanol (20, 100 or 200 mM). In addition, it was established that a moderate dose (2 g/kg, i.p.) of ethanol did not alter the rate of dopamine synthesis, measured as L-dihydroxyphenylalanine (L-DOPA) accumulation. However, a high dose (5 g/kg, i.p.) of ethanol significantly increased the levels of L-DOPA to 60% above the control value. These data are consistent with earlier findings obtained in brain slices from rats; dopamine release, but not clearance, is affected by acute ethanol.

Hyperpolarization-activated cation current (Ih) is an ethanol target in midbrain dopamine neurons of mice

Ethanol stimulates the firing activity of midbrain dopamine (DA) neurons, leading to enhanced dopaminergic transmission in the mesolimbic system. This effect is thought to underlie the behavioral reinforcement of alcohol intake. Ethanol has been shown to directly enhance the intrinsic pacemaker activity of DA neurons, yet the cellular mechanism mediating this excitation remains poorly understood. The hyperpolarization-activated cation current, Ih, is known to contribute to the pacemaker firing of DA neurons. To determine the role of Ih in ethanol excitation of DA neurons, we performed patch-clamp recordings in acutely prepared mouse midbrain slices. Superfusion of ethanol increased the spontaneous firing frequency of DA neurons in a reversible fashion. Treatment with ZD7288, a blocker of Ih, irreversibly depressed basal firing frequency and significantly attenuated the stimulatory effect of ethanol on firing. Furthermore, ethanol reversibly augmented Ih amplitude and accelerated its activation kinetics. This effect of ethanol was accompanied by a shift in the voltage dependence of Ih activation to more depolarized potentials and an increase in the maximum Ih conductance. Cyclic AMP mediated the depolarizing shift in Ih activation but not the increase in the maximum conductance. Finally, repeated ethanol treatment in vivo induced downregulation of Ih density in DA neurons and an accompanying reduction in the magnitude of ethanol stimulation of firing. These results suggest an important role of Ih in the reinforcing actions of ethanol and in the neuroadaptations underlying escalation of alcohol consumption associated with alcoholism.

The mesolimbic dopamine system: the final common pathway for the reinforcing effect of drugs of abuse?

In this review we will critically assess the hypothesis that the reinforcing effect of virtually all drugs of abuse is primarily dependent on activation of the mesolimbic dopamine system. The focus is on five classes of abused drugs: psychostimulants, opiates, ethanol, cannabinoids and nicotine. For each of these drug classes, the pharmacological and physiological mechanisms underlying the direct or indirect influence on mesolimbic dopamine transmission will be reviewed. Next, we evaluate behavioral pharmacological experiments that specifically assess the influence of activation of the mesolimbic dopamine system on drug reinforcement, with particular emphasis on animal experiments using drug self-administration paradigms. There is overwhelming evidence that all five classes of abused drugs increase dopamine transmission in limbic regions of the brain through interactions with a variety of transporters, ionotropic receptors and metabotropic receptors. Behavioral pharmacological experiments indicate that increased dopamine transmission is clearly both necessary and sufficient to promote psychostimulant reinforcement. For the other four classes of abused substances, self-administration experiments suggest that although increasing mesolimbic dopamine transmission plays an important role in the reinforcing effects of opiates, ethanol, cannabinoids and nicotine, there are also dopamine-independent processes that contribute significantly to the reinforcing effects of these compounds.

Stress enhancement of craving during sobriety: a risk for relapse

This report of the proceedings of a symposium presented at the 2004 Research Society on Alcoholism Meeting provides evidence linking stress during sobriety to craving that increases the risk for relapse. The initial presentation by Rajita Sinha summarized clinical evidence for the hypothesis that there is an increased sensitivity to stress-induced craving in alcoholics. During early abstinence, alcoholics who were confronted with stressful circumstances showed increased susceptibility for relapse. George Breese presented data demonstrating that stress could substitute for repeated withdrawals from chronic ethanol to induce anxiety-like behavior. This persistent adaptive change induced by multiple withdrawals allowed stress to induce an anxiety-like response that was absent in animals that were not previously exposed to chronic ethanol. Subsequently, Amanda Roberts reviewed evidence that increased drinking induced by stress was dependent on corticotropin-releasing factor (CRF). In addition, rats that were stressed during protracted abstinence exhibited anxiety-like behavior that was also dependent on CRF. Christopher Dayas indicated that stress increases the reinstatement of an alcohol-related cue. Moreover, this effect was enhanced by previous alcohol dependence. These interactive effects between stress and alcohol-related environmental stimuli depended on concurrent activation of endogenous opioid and CRF systems. A.D. Lê covered information that indicated that stress facilitated reinstatement to alcohol responding and summarized the influence of multiple deprivations on this interaction. David Overstreet provided evidence that restraint stress during repeated alcohol deprivations increases voluntary drinking in alcohol-preferring (P) rats that results in withdrawal-induced anxiety that is not observed in the absence of stress. Testing of drugs on the stress-induced voluntary drinking implicated serotonin and CRF involvement in the sensitized response. Collectively, the presentations provided convincing support for an involvement of stress in the cause of relapse and continuing alcohol abuse and suggested novel pharmacological approaches for treating relapse induced by stress.

Alcohol and adolescent suicide

Adolescent suicide is a major public health problem. In this review, the authors discuss different aspects of the relation between alcohol abuse and suicidal behavior in adolescents, including epidemiology, role of family history, comorbidity, gender differences, neurobiology, treatment, and prevention. In the general population, about 2,000 adolescents in the United States die by suicide each year. Suicide continually ranks as the second or third leading cause of death of persons between the ages of 15 and 34 years old. The suicide rate in young people has more than doubled during the period from 1956 to 1993. This increasing suicide rate has been blamed on the increase of adolescent alcohol abuse. Availability of alcohol and guns at home may contribute to suicide risk in adolescents. Comorbid psychopathology, which is common among adolescent alcohol abusers, substantially increases risk for suicide completions and attempts. Depressed adolescents may use alcohol to self-medicate depressive symptoms. Alcohol abuse and suicidal behavior in adolescents and in adults has been found to have biochemical, genetic, and psychological correlates. Ideally, treatment of adolescents who receive a diagnosis of an alcohol use disorder and co-occurring suicidality should follow an integrated protocol that addresses both conditions. Future studies of psychological and neurobiological mechanisms of suicidality in adolescents with alcohol and/or substance abuse are merited.

Baclofen-induced reduction of alcohol reinforcement in alcohol-preferring rats

Recent studies have demonstrated that treatment with the gamma-aminobutyric acid (GABA(B)) receptor agonist, baclofen, reduces alcohol intake in selectively bred Sardinian alcohol-preferring rats tested under the homecage two-bottle "alcohol versus water" choice regimen. This study was designed to investigate whether baclofen also reduces alcohol-reinforcing effects in Sardinian alcohol-preferring rats. To this aim, sP rats were trained to lever press for oral alcohol (15%, vol/vol) or sucrose (0.3%, wt/vol; included as alternative reinforcer to evaluate the specificity of baclofen effect on alcohol reinforcement) under a fixed ratio schedule of 4. Once steady levels of alcohol or sucrose self-administration behavior were established, the effects of acutely administered baclofen (0, 1.7, and 3 mg/kg, intraperitoneal [ip]) and naloxone (0, 1, and 3 mg/kg, ip; included as reference compound) on alcohol- or sucrose-reinforced responding were evaluated. Baclofen administration dose dependently, although not specifically, reduced alcohol-reinforced responding to an extent comparable to that of naloxone. Baclofen also produced a dose-dependent and specific delay in the onset of alcohol-reinforced responding, suggesting that it suppressed the rats' motivation to start drinking alcohol. These data are discussed in terms of adding further support to the hypothesized involvement of the GABA(B) receptor in the neural system mediating alcohol reinforcement. These data are also in agreement with the results of recent preliminary clinical studies suggesting that baclofen may have therapeutic efficacy in the treatment of alcohol dependence.

Helplessness in the tail suspension test is associated with an increase in ethanol intake and its rewarding effect in female mice

BACKGROUND

Depression is frequently observed in drug abusers. However, depression may be a primary factor of predisposition to drug abuse or a consequence of drug abuse. The aim of this study was to analyze the influence of a preexisting depressive-like state/helplessness on subsequent alcohol responsiveness in mice.

METHODS

Male and female CD1 mice were selected according to their immobility time in the tail suspension test, and only mice with "high immobility" and "low immobility" time were retained. Using a two-bottle free-choice paradigm, these mice were given continuous access to tap water or solutions of ethanol (3-20% v/v), quinine (12.5-50 mg/liter), or sucrose (1-4% w/v). In female mice, rewarding and aversive effects of ethanol (1.5 and 3 g/kg, intraperitoneally) were also investigated using the conditioned place preference and the conditioned taste aversion paradigms.

RESULTS

Female mice were more immobile and drank more ethanol than male mice. No striking sex difference was observed in quinine consumption. Sucrose intake was higher in female than in male mice, whatever the solution concentration. At the 4% concentrated solution, a sucrose-induced increase in daily fluid intake was observed only in female mice. Female mice with high immobility time (HI) consumed more ethanol at the highest concentration than female mice with low immobility time (LI), whereas no difference was observed between HI and LI male mice. Moreover, whereas LI female mice failed to express place conditioning induced by the 3-g/kg dose of ethanol, HI female mice were strongly responsive to the rewarding effect of this high ethanol dose. Ethanol dose-dependently induced a conditioned taste aversion with a similar magnitude in both LI and HI female mice.

CONCLUSIONS

The findings indicate that female CD1 mice tend to drink greater amounts of ethanol or sucrose solutions than male CD1 mice, suggesting that female mice may be a better model of excessive alcohol intake. Furthermore, no relationship was found between immobility scores and ethanol consumption in male mice. On the contrary, within female mice, HI mice consumed higher amounts of ethanol than LI mice probably because they experienced greater rewarding effects of ethanol. The present results support the hypothesis that depressive-like responses may predispose to ethanol abuse in female mice.

Ethanol exposure decreases glutamate uptake in the nucleus accumbens

BACKGROUND

An increased level of extracellular glutamate is a key neurochemical feature associated with ethanol exposure and withdrawal.

METHODS

In the current study, extracellular levels of glutamate and glutamate transport in the nucleus accumbens were assayed 24 hr after repeated ethanol exposure (1 g/kg ip daily for 7 days) with use of in vivo no-net-flux microdialysis and in vitro [(3)H]glutamate uptake, respectively.

RESULTS

Microdialysis revealed higher extracellular glutamate concentrations in the nucleus accumbens of rats that were given ethanol. The increase in basal extracellular glutamate levels was accounted for in part by a decrease in the in vivo probe recovery of glutamate. Moreover, an in vitro accumbens slice preparation measuring [(3)H]glutamate uptake revealed that Na(+)-dependent [(3)H]glutamate uptake was significantly reduced 24 hr after 7 days of repeated ethanol exposure. The ethanol-induced deficit in glutamate uptake was not associated with decreased total tissue levels of the transporters GLAST or GLT1. The in vivo and in vitro ethanol-induced changes in glutamate levels and uptake returned to control levels 14 days after discontinuing 7 days of repeated ethanol exposure.

CONCLUSIONS

These results suggest that the previously reported increases in extracellular glutamate induced by ethanol exposure may be due in part to deficits in glutamate transport.

Effects of injections of 8-hydroxy-2-(di-n-propylamino)tetralin or muscimol in the median raphe nucleus on c-fos mRNA in the rat brain

Inhibition of the median raphe nucleus (MRN) by the local injection of 5-HT(1A) or GABA(A) receptor agonists produces strong activational effects on feeding, drinking and locomotor activity. Using an animal model of relapse, we have shown that intra-MRN injection of the 5-HT(1A) autoreceptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) reinstates alcohol seeking in rats. The circuitry underlying the behavioral effects of intra-MRN injection of these drugs is not known. In order to identify the brain areas that may be involved, we measured levels of mRNA of the immediate early gene c-fos in discrete nuclei of the rat brain following intra-MRN infusions of these drugs. Male Wistar rats received intra-MRN infusions of 8-OH-DPAT (1 mug), muscimol (25 ng) or saline vehicle immediately prior to placement in locomotor activity chambers. Thirty minutes later, they were decapitated, and their brains processed for in situ hybridization of c-fos mRNA. In agreement with previous reports, injections of 8-OH-DPAT or muscimol into the MRN resulted in large increases in locomotor activity. Intra-MRN injections of these drugs increased c-fos in a number of brain nuclei previously shown to be involved in the rewarding effects of drugs of abuse in a regionally specific manner. Both drugs significantly increased the expression of c-fos mRNA in the medial frontal cortex, nucleus accumbens, lateral septum, dorsal bed nucleus of the stria terminalis and ventral tegmental area. In the ventral hippocampus, only 8-OH-DPAT increased c-fos, while in the basolateral nucleus of the amygdala and locus coeruleus, it was increased only by muscimol. These results are discussed in terms of the projections of the MRN and the pathways involved in relapse to alcohol and drug seeking.

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

RATIONALE AND OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Dissecting the genetic effect of the CRH system on anxiety and stress-related behaviour

Corticotropin-releasing hormone (CRH) plays a central role in the adaptation of the body to stress. CRH integrates the endocrine, autonomic and behavioural responses to stress acting as a secretagogue within the line of the hypothalamic pituitary adrenocortical (HPA) system and as a neurotransmitter modulating synaptic transmission in the central nervous system. Accumulating evidence suggests that the neuroendocrine and behavioural symptoms observed in patients suffering from major depression are at least in part linked to a hyperactivity of the CRH system. Genetic modifications of the CRH system by conventional and conditional gene targeting strategies in the mouse allowed us to study the endogenous mechanisms underlying HPA system regulation and CRH-related neuronal circuitries involved in pathways mediating anxiety and stress-related behaviour.

Effect of operant self-administration of 10% ethanol plus 10% sucrose on dopamine and ethanol concentrations in the nucleus accumbens

Although operant ethanol self-administration can increase accumbal dopamine activity, the relationship between dopamine and ethanol levels during consumption remains unclear. We trained Long-Evans rats to self-administer escalating concentrations of ethanol (with 10% sucrose) over 7 days, during which two to four lever presses resulted in 20 min of access to the solution with no further response requirements. Accumbal microdialysis was performed in rats self-administering 10% ethanol (plus 10% sucrose) or 10% sucrose alone. Most ethanol (1.6 +/- 0.2 g/kg) and sucrose intake occurred during the first 10 min of access. Sucrose ingestion did not induce significant changes in dopamine concentrations. Dopamine levels increased within the first 5 min of ethanol availability followed by a return to baseline, whereas brain ethanol levels reached peak concentration more than 40 min later. We found significant correlations between intake and dopamine concentration during the initial 10 min of consumption. Furthermore, ethanol-conditioned rats consuming 10% sucrose showed no effect of ethanol expectation on dopamine activity. The transient rise in dopamine during ethanol ingestion suggests that the dopamine response was not solely due to the pharmacological properties of ethanol. The dopamine response may be related to the stimulus properties of ethanol presentation, which were strongest during consumption.

Cannabinoid CB1 receptor antagonism reduces conditioned reinstatement of ethanol-seeking behavior in rats

The endocannabinoid system is involved in a variety of effects of drugs of misuse, and blockade of the cannabinoid CB1 receptor by selective antagonists elicits marked reductions in opioid and alcohol self-administration. The present study was designed to extend our knowledge of the role of the cannabinoid CB1 receptor in the modulation of alcohol misuse vulnerability in rats. Accordingly, using nonselected Wistar rats and genetically selected Marchigian Sardinian alcohol-preferring (msP) rats, we investigated the effect of the CB1 antagonist SR141716A on operant alcohol self-administration and on reinstatement of alcohol-seeking behavior by environmental conditioning factors. In addition, in situ hybridization studies in both strains were performed to measure cannabinoid CB1 receptor mRNA in different brain areas of these animals. Results showed that intraperitoneal administration of SR141716A (0.03, 1.0 and 3.0 mg/kg) markedly inhibits ethanol self-administration and conditioned reinstatement of ethanol-seeking behavior in both strains of rats. ED50 analysis showed significantly higher sensitivity (P < 0.05) to the effect of SR141716A in msP rats than in heterogeneous Wistar rats. In situ hybridization studies revealed that, compared with Wistar rats, msP animals have consistently greater cannabinoid CB1 receptor mRNA expression in a number of brain areas, including the frontoparietal cortex, caudate-putamen and hippocampus (CA1 and dentate gyrus areas). In conclusion, we provide clear evidence that blockade of CB1 receptors reduces both ethanol self-administration and conditioned reinstatement of alcohol-seeking behavior in rats. In addition, current pharmacological and neuroanatomical data suggest that an altered function of the CB1 receptor system exists between genetically selected alcohol-preferring msP rats and a heterogeneous animal population.

Suppressing effect of the cannabinoid CB1 receptor antagonist, SR 141716, on alcohol's motivational properties in alcohol-preferring rats

Administration of the cannabinoid CB(1) receptor antagonist, SR 141716 [N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxamide], has been reported to reduce alcohol intake and alcohol self-administration in different models of excessive alcohol consumption, including the selectively bred Sardinian alcohol-preferring (sP) rats. The present study investigated whether SR 141716 was also capable of decreasing, in this rat line, alcohol's motivational properties. Extinction responding for alcohol, defined as the maximal number of lever responses reached in the absence of alcohol in rats trained to lever-press for alcohol, was used as index of alcohol's motivational properties. Rats were initially trained to lever-press for oral alcohol (15%, v/v) under a fixed ratio (FR) schedule of FR4. Once self-administration behavior was established, extinction sessions were conducted. SR 141716 (0, 0.3, 1 and 3 mg/kg; i.p.) was acutely administered before extinction sessions. In order to assess the specificity of SR 141716 action on extinction responding for alcohol, a separate group of sP rats was trained to lever-press for a 3% (w/v) sucrose solution under an FR4 schedule. SR 141716 administration produced a dose-dependent, virtually complete suppression of extinction responding for alcohol. In contrast, extinction responding for sucrose was not significantly altered by treatment with SR 141716. Further to the consummatory aspects, these results also extend the suppressing effect of SR 141716 to the appetitive aspects of alcohol drinking behavior in sP rats. The results also implicate the cannabinoid CB1 receptor in the neural substrate mediating alcohol's motivational properties in this rat line.

An overview of the development of medications including novel anticonvulsants for the treatment of alcohol dependence

The development of treatments for alcohol dependence has been significantly complicated by the multiple actions of ethanol at the neurotransmitter level, heterogeneity among patients with alcohol dependence, the complexity of defining and measuring the phenomenon of craving, and the challenge of quantifying alcohol intake in patients. Increasingly, anticonvulsant medications are showing promise for the safe and effective amelioration of alcohol withdrawal symptoms. Furthermore, there is evidence that anticonvulsant medications are promising treatments for reducing drinking and preventing relapse among alcohol-dependent individuals. In recent years, many medications have been evaluated for the treatment of alcohol dependence, including those that interact with dopaminergic, serotonergic, opioid or glutamate and/or GABA systems. So far, naltrexone, acamprosate and, more recently, the anticonvulsant, topiramate, have shown some efficacy for the treatment of heterogeneous populations of individuals with alcohol dependence. Both ondansetron and sertraline appear to have some efficacy in treating different subgroups of alcoholic.

Progress in the development of topiramate for treating alcohol dependence: from a hypothesis to a proof-of-concept study

Advances in neuroscientific knowledge have evoked interest in developing effective medications for the treatment of alcohol dependence. Pharmacological approaches that involve the use of relatively specific medications at a particular neuronal target to modulate corticomesolimbic dopamine neuronal activity, the critical pathway for expression of the reinforcing effects of abused drugs, have yielded modest efficacy in the treatment of alcohol dependence. A new approach is needed. Because corticomesolimbic dopamine neurons interact with a variety of neurotransmitters that modulate its effects in the nucleus accumbens, it might be possible to more reliably control these dopaminergic effects with a medication that acted contemporaneously on more than one neuromodulator of dopamine function. Additionally, because alcohol use results in neuronal adaptations due to sensitization, the chances of effective therapy might be bolstered by administering a medication that also has utility with mitigating its chronic effects. My proposed conceptual framework suggests that a medication that facilitates inhibitory gamma-aminobutyric acid-A input and antagonizes excitatory glutaminergic afferents to the nucleus accumbens would have pharmacotherapeutic potential in treating the alcohol dependence syndrome because these effects would act contemporaneously to suppress corticomesolimbic dopamine release. Through similar effects, topiramate might also aid chronic drinkers to wean themselves off alcohol and might ameliorate the symptoms of alcohol withdrawal. This commentary highlights the scientific concepts and clinical evidence for the development of topiramate in the treatment of alcohol dependence.

CB1 receptor knockout mice display reduced ethanol-induced conditioned place preference and increased striatal dopamine D2 receptors

Cannabinoids and ethanol activate the same reward pathways, and recent advances in the understanding of the neurobiological basis of alcoholism suggest that the CB1 receptor system may play a key role in the reinforcing effects of ethanol and in modulating ethanol intake. In the present study, male CB1 receptors knockout mice generated on a CD1 background displayed decreased ethanol-induced conditioned place preference (CPP) compared to wild-type (CB1(+/+)) mice. Ethanol (0.5, 1.0, 1.5, and 2.0 g/kg) induced significant CPP in CB1(+/+) mice at all doses tested, whereas it induced significant CPP only at the highest dose of ethanol (2.0 g/kg) in CB1(-/-) mice. However, there was no genotypic difference in cocaine (20 mg/kg)-induced CPP. There was also no genotypic difference, neither in cocaine (10-50 mg/kg) nor in D-amphetamine (1.2-5 mg/kg)-induced locomotor effects. In addition, mutant and wild-type mice did not differ in sensitivity to the anxiolytic effects of ethanol (1.5 g/kg) when tested using the elevated plus maze. Interestingly, this decrease in ethanol efficacy to induce CPP in CB1(-/-) mice was correlated with an increase in D2/D3 receptors, as determined by [3H]raclopride binding, whereas there was no difference in D1-like receptors, as determined by [3H]SCH23390 binding, measured in the striatum from drug-naive mice. This increase in D2/D3 binding sites observed in CB1 knockout mice was associated with an altered locomotor response to the D2/D3 agonist quinpirole (low doses 0.02-0.1 mg/kg) but not to an alteration of quinpirole (0.1-1.0 mg/kg)-induced CPP compared to wild-type mice. Altogether, the present results indicate that lifelong deletion of CB1 receptors reduced ethanol-induced CPP and that these reduced rewarding effects of ethanol are correlated to an overexpression of striatal dopamine D2 receptors.

GDNF and Addiction

Biochemical adaptations to drugs of abuse and alcohol are especially profound in midbrain dopaminergic neurons. Long-lasting molecular and structural changes in mesolimbic dopaminergic neurons that result from chronic exposure to drugs of abuse and alcohol are thought to underlie adverse behaviors such as compulsive drug seeking and relapse. Recent studies suggest that a subset of these changes is prevented/reversed by activation of the glial cell line-derived neurotrophic factor (GDNF) signaling pathway. Behavioral effects of drugs of abuse such as cocaine and alcohol are also negatively regulated by GDNF: inhibition of the endogenous GDNF pathway enhances the activity of drugs of abuse, while administration of GDNF reduces the severity of the effects. In this review, we summarize the data implicating GDNF as a negative regulator of drug and alcohol addiction. We also provide evidence to suggest that therapies that activate GDNF signaling may be useful for the treatment of drug and alcohol addiction.

Magnetic resonance detects brainstem changes in chronic, active heavy drinkers

Neuropathological and neuroimaging studies show cortical and subcortical volume loss in alcohol-dependent individuals. Using quantitative magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopic imaging ((1)H MRSI), we studied the size and potential cellular injury of the brainstem in untreated heavy alcohol drinkers. The brainstem is considered critical in the development and maintenance of drug and alcohol dependence. Two methods of brainstem size determination were compared: standard volumetry vs. midsagittal MR image area measurement. Heavy drinkers (n=12) and light drinkers (n=10) were compared with MRI; (1)H MRSI brainstem data were obtained from a subset of this cohort. Chronic heavy drinking was associated with significantly smaller midsagittal areas of the brainstem, midbrain, and pons, and with significantly smaller overall brainstem volume. Heavy drinking was also associated with significantly lower ratios of N-acetyl-aspartate and choline-containing metabolites compared with creatine-containing compounds in the brainstem, independent of brainstem atrophy. Additionally, brainstem volume and midsagittal brainstem area were correlated (r=0.78). These structural and metabolite findings are consistent with neuronal injury in the brainstem of untreated chronic heavy drinkers. The results also indicate that the midsagittal MRI brainstem area is an easily determined and reliable indicator of brainstem volume.

The clock gene Per2 influences the glutamatergic system and modulates alcohol consumption

Period (Per) genes are involved in regulation of the circadian clock and are thought to modulate several brain functions. We demonstrate that Per2(Brdm1) mutant mice, which have a deletion in the PAS domain of the Per2 protein, show alterations in the glutamatergic system. Lowered expression of the glutamate transporter Eaat1 is observed in these animals, leading to reduced uptake of glutamate by astrocytes. As a consequence, glutamate levels increase in the extracellular space of Per2(Brdm1) mutant mouse brains. This is accompanied by increased alcohol intake in these animals. In humans, variations of the PER2 gene are associated with regulation of alcohol consumption. Acamprosate, a drug used to prevent craving and relapse in alcoholic patients is thought to act by dampening a hyper-glutamatergic state. This drug reduced augmented glutamate levels and normalized increased alcohol consumption in Per2(Brdm1) mutant mice. Collectively, these data establish glutamate as a link between dysfunction of the circadian clock gene Per2 and enhanced alcohol intake.

Ethanol operant self-administration in rats is regulated by adenosine A2 receptors

BACKGROUND

Recent findings suggest that adenosine is involved in the neural and behavioral effects of ethanol (EtOH). Studies in neural cell culture show that EtOH, via activation of adenosine A2 receptors, triggers cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) signaling and CRE (cAMP regulatory element)-mediated gene expression and that this effect is blocked by inhibiting G-protein betagamma subunits. Recently, we reported that expression of a betagamma inhibitor in the nucleus accumbens (NAc) reduces EtOH drinking in rats. The NAc expresses high levels of the adenosine A2A receptor in GABAergic medium spiny neurons. If the reinforcing effects of EtOH are mediated through an A2 activation of cAMP/PKA signaling via betagamma, then A2 receptor blockade should attenuate EtOH consumption. Here we tested this hypothesis. Because adenosine A2 and dopamine D2 receptors are coexpressed in neurons of the NAc, we compared the effects of A2 blockade with those of D2 receptor blockade.

METHODS

Male Long-Evans rats were trained to self-administer 10% EtOH in daily 30-min sessions with an active and an inactive lever. Separate groups of rats were given the D2 antagonist eticlopride (0.005, 0.007, and 0.01 mg/kg), the A2 antagonist 3,7-dimethyl-1-propargylxanthine (DMPX; 1, 3, 5, 7, 10, and 20 mg/kg), and the A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 0.125, 0.25, and 0.5 mg/kg) by systemic injection.

RESULTS

Eticlopride dose-dependently reduced EtOH drinking. DMPX showed a bimodal effect: 10 and 20 mg/kg decreased, but 1 mg/kg increased, EtOH consumption. DPCPX was without effect.

CONCLUSIONS

In support of our hypothesis, the A2 antagonist DMPX attenuated EtOH self-administration. Low doses of the A2 antagonist enhanced EtOH drinking, consistent with the possibility that rats increase EtOH self-administration to overcome partial A2 blockade. The D2 antagonist eticlopride also decreased EtOH self-administration. These data provide the first evidence that pharmacological modulation of adenosine A2 receptors can regulate EtOH consumption in rats.

Pharmacotherapy for alcohol-related disorders: what clinicians should know

Alcohol-related disorders are a major public health problem in the United States. Alcohol interacts with several neurotransmitter systems causing both acute and chronic effects in the brain. While the mainstay of treatment of alcohol-related disorders, with the exception of alcohol withdrawal, has historically been psychosocial, pharmacotherapy is increasingly being investigated and incorporated into standard clinical practice. Patients with alcohol use disorders and comorbid psychiatric conditions, most commonly depressive and anxiety disorders, can benefit from symptom-targeted pharmacotherapy, even if the patient fails to achieve abstinence from alcohol. Although benzodiazepines remain the treatment of choice to treat alcohol withdrawal, a variety of other agents is being investigated, particularly in the outpatient setting. Further randomized clinical trials of alcohol-related disorder pharmacotherapy, particularly of comorbid subpopulations, are needed to better inform clinical decision making. The routine exclusion of alcohol-dependent patients from pharmacotherapy trials of psychiatric disorders presents a barrier to gathering more data. Recommendations for future research are discussed.

State-dependency in C. elegans

Memory and the expression of learned behaviors by an organism are often triggered by contextual cues that resemble those that were present when the initial learning occurred. In state-dependent learning, the cue eliciting a learned behavior is a neuroactive drug; behaviors initially learned during exposure to centrally acting compounds such as ethanol are subsequently recalled better if the drug stimulus is again present during testing. Although state-dependent learning is well documented in many vertebrate systems, the molecular mechanisms underlying state-dependent learning and other forms of contextual learning are not understood. Here we demonstrate and present a genetic analysis of state- dependent adaptation in Caenorhabditis elegans. C. elegans normally exhibits adaptation, or reduced behavioral response, to an olfactory stimulus after prior exposure to the stimulus. If the adaptation to the olfactory stimulus is acquired during ethanol administration, the adaptation is subsequently displayed only if the ethanol stimulus is again present. cat-1 and cat-2 mutant animals are defective in dopaminergic neuron signaling and are impaired in state dependency, indicating that dopamine functions in state-dependent adaptation in C. elegans.

Decreased expression of NEFH and PCP4/PEP19 in the prefrontal cortex of alcoholics

Patients with alcoholism exhibit behavioral adaptations to ethanol such as tolerance, dependence, and addiction. Molecular mechanisms that underlie these altered behavioral responses to ethanol are largely unclear. We have performed oligonucleotide microarray analysis in postmortem prefrontal cortices of alcoholics. Among about 12,000 genes represented on microarray, a total of 79 genes showed differential expression changes in alcoholics compared with control subjects, consisting of 54 up- and 25 down-regulated genes. Altered expressions in alcoholics were observed in genes having a wide range of biological functions. The remarkable findings were up-regulation of myelin-related genes and molecular chaperones in alcoholics. Among the genes identified, decreased expressions of NEFH and PCP4/PEP19 were further examined. NEFH encodes a component of neurofilament protein in neurons. PCP4/PEP19 encodes protein involved in calcium signaling and neuronal apoptosis. Observation of their down-regulations in alcoholics in microarray analysis was confirmed by real-time quantitative RT-PCR, and was also confirmed in the independent set of postmortem brains of alcoholics. The present results may provide some insights into understanding the mechanism of ethanol-induced altered behavioral responses at the molecular level.

Topiramate-induced neuromodulation of cortico-mesolimbic dopamine function: a new vista for the treatment of comorbid alcohol and nicotine dependence?

Alcohol and nicotine dependence are commonly occurring disorders that together represent the most important preventable causes of morbidity and mortality in the United States. While there have been differences of opinion as to which disorder to treat first when they occur, there is growing evidence that a management strategy addressing both conditions contemporaneously would be optimal. Advances in the neurosciences have demonstrated not only that the reinforcing effects of both alcohol and nicotine are mediated by similar mechanisms resulting in enhanced activity of the cortico-mesolimbic dopamine system, but that their neurochemical interactions can lead to an aggregation of these effects. Despite this striking neurobiological overlap between alcohol and nicotine consumption, few studies have sought to take advantage of this commonality by devising a pharmacological approach that serves to treat both disorders. The results of our proof-of-concept study showed that topiramate is a promising medication for the treatment of both alcohol and nicotine dependence, presumably by its ability to modulate cortico-mesolimbic dopamine function profoundly; however, other mechanisms might also contribute to this effect. Further studies are ongoing to establish and extend topiramate's efficacy in the treatment of each and both disorders.

The glucocorticoid receptor antagonist mifepristone reduces ethanol intake in rats under limited access conditions

There is a substantial amount of evidence indicating control over ethanol intake by steroid hormones, particularly adrenal glucocorticoids. Thus far, however, studies employing pharmacological methods have failed to find effects of glucocorticoid receptor blockade on voluntary ethanol consumption. Since length of ethanol access period can influence ethanol consumption levels as well as potential pharmacological effects in such studies, the present study was conducted to determine the effects of acute administration of the glucocorticoid receptor (GR) antagonist mifepristone on voluntary ethanol intake under limited access conditions. Rats were fluid restricted and given concurrent access to 10% ethanol and water in a two-bottle choice paradigm for 1 h/day, 5 days a week. Both fluids were available ad libitum during the remaining 2 days per week. Administration of mifepristone (1, 5 and 20 mg/kg i.p.) immediately prior to the limited access two-bottle access period dose-dependently suppressed ethanol intake (maximum 40% at 20 mg/kg). The mineralcorticoid receptor (MR) antagonist spironolactone (10, 25 and 50 mg/kg i.p.) was without effect on ethanol intake, and neither compound had an effect on water intake. These data confirm an active role of GRs in modulating voluntary ethanol consumption, particularly under conditions of limited access.

Decreased alcohol self-administration and increased alcohol sensitivity and withdrawal in CB1 receptor knockout mice

Recent advances in the understanding of the neurobiological basis of alcohol dependence suggest that the endocannabinoid system may play a key role in the reinforcing effects of ethanol. In the present study, disruption of CB1 receptors in mice generated on a CD1 background decreased both ethanol consumption and preference. This decreased ethanol self-administration was associated with increased sensitivity to the acute intoxicating effects of ethanol. Mutant mice were more sensitive to the hypothermic and sedative/hypnotic effects of acute ethanol administration (1.5-4.0 g/kg), although plasma ethanol concentrations did not differ from those of controls. Moreover, wild-type mice exhibited normal locomotor activation caused by 1.0-2.5 g/kg injection of ethanol, whereas mutant mice displayed sedation in response to the injection of the same ethanol doses. The severity of alcohol withdrawal-induced convulsions was also increased in CB1(-/-) mice. Our results suggest that CB1 receptors participate in the regulation of ethanol drinking and demonstrate that their disruption lead to increased ethanol sensitivity and withdrawal severity.

mGluR5 antagonist MPEP reduces ethanol-seeking and relapse behavior

The glutamatergic system plays an important role in mediating neurobehavioral effects of ethanol. Metabotropic glutamate receptors subtype 5 (mGluR5) are modulators of glutamatergic neurotransmission and are abundant in brain regions known to be involved in ethanol self-administration. Here, we studied the effects of 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a highly potent, noncompetitive mGlu5 receptor antagonist, on voluntary ethanol consumption and relapse behavior. For this purpose, we used two models for the measurement of relapse behavior: (i) reinstatement of ethanol-seeking behavior by drug-associated cues and (ii) the alcohol deprivation effect in long-term ethanol-consuming rats. In the first set of experiments, rats were trained to lever press for ethanol in the presence of a distinct set of cues. After extinction, the animals were exposed to the respective cues that initiated reinstatement of responding. A response-contingent ethanol prime further enhanced responding compared to the conditioned cues alone. Under these conditions, MPEP (0, 1, 3, and 10 mg/kg) attenuated ethanol seeking significantly and in a dose-related manner. However, at the highest dose, MPEP also decreased the number of inactive lever responses. In the second set of experiments, rats with 1 year of ethanol experience and repeated deprivation phases were used. A subchronic treatment with MPEP (twice daily; 0, 3, and 10 mg/kg) resulted in a significant and dose-dependent reduction of the alcohol deprivation effect (ADE). Although the same MPEP treatment regimen decreased baseline drinking, this effect was not as pronounced as on the ADE. These results show in two commonly used models of relapse to ethanol that pharmacological targeting of mGlu5 receptors may be a promising approach for the treatment of alcoholism.

Sardinian alcohol-preferring rats show low 5-HT extraneuronal levels in the mPFC and no habituation in monoaminergic response to repeated ethanol consumption in the NAcS

Sardinian ethanol-preferring (sP), non-preferring (sNP), and Wistar rats show similar dopaminergic response to vanilla sugar consumption in nucleus accumbens shell (NAcS) and medial prefrontal cortex (mPFC), and similarly learn a vanilla sugar-sustained appetitive behavior. In this study we investigated whether in satiated sP, sNP, and Wistar rats vanilla sugar would also elicit a serotonergic response in NAcS and mPFC, and whether in these areas voluntary ethanol consumption would elicit dopaminergic and/or serotoninergic responses. In the NAcS, all rats showed similar serotonin increases in response to the two meals and similar development of rapid habituation. In the mPFC, Wistar and sNP rats showed similar serotonin increases after two vanilla sugar meals, while sP rats, which had low serotonin basal levels, did not show a serotonergic response. When presented with a 10% ethanol solution, Wistar and sP rats rapidly consumed it, while sNP rats did not. In the NAcS, Wistar and sP rats presented dopamine and serotonin increases in response to ethanol. However, while Wistar rats showed habituation in their response, sP rats did not. In the mPFC, ethanol induced similar dopamine increases in Wistar and sP rats; serotonin increases were observed only in Wistar rats. In conclusion, all three lines showed increased serotonin release in response to palatable food, but they profoundly differed in their response to ethanol. In fact, only Wistar and sP rats drank ethanol, Wistar rats showed a monoaminergic response similar to that obtained after palatable food, while sP rats did not develop habituation, suggesting that they perceived ethanol as a more relevant stimulus.

Chronic ethanol consumption reduces delta-and mu-opioid receptor-stimulated G-protein coupling in rat brain

BACKGROUND

Ethanol consumption is thought to enhance the release of endogenous opioids acting at opioid receptors (ORs) in the central nervous system. Prior studies have shown that chronic ethanol consumption in alcohol-preferring rats uncouples mu-ORs from Gi proteins. The purpose of this study was to investigate the potential for uncoupling of the delta- and the mu-OR after chronic ethanol consumption in a nonpreferring rat strain.

METHODS

We used radiohistochemical methods to study mu- and delta-OR-stimulated G-protein coupling in brain tissue of rats ingesting liquid diets containing 6.7% ethanol (v/v) for 16 days, as compared with 0% ethanol pair-fed control rats. Sections of brain from pair-fed and ethanol-treated rats were incubated with guanylyl 5'-[gamma-[35S]-thio]-triphosphate ([35S]-GTPgammaS) in the absence and presence of d-Pen2,d-Pen5 enkephalin (DPDPE), a delta-OR agonist, or Tyr-d-Ala-Gly-N(me)Phe-Gly-ol-enkephalin (DAMGO), a mu-OR agonist.

RESULTS

DPDPE significantly stimulated [35S]-GTPgammaS binding in the hippocampal dentate gyrus (DG), CA1, cerebellum, and inferior colliculus of untreated pair-fed controls. By contrast, DPDPE-stimulated [35S]-GTPgammaS binding was reduced significantly in those brain regions in the ethanol-consuming group. DAMGO stimulated [35S]-GTPgammaS binding in cortex, caudate, nucleus accumbens, DG, CA1, and superior and inferior colliculi, whereas the DG, CA1, and colliculi showed a significant reduction of binding after chronic ethanol. Basal [35S]-GTPgammaS binding was not different between the two diet groups. CONCLUSIONS These data are the first to demonstrate functional uncoupling of delta-ORs from G proteins after chronic ethanol consumption. Uncoupling may result from modulation of receptors, possibly by internalization or phosphorylation. Alterations in functional coupling of both delta- and mu-ORs and subsequent effects may contribute to continued ethanol consumption.

Acute effects of alcohol on larval zebrafish: a genetic system for large-scale screening

Larval zebrafish are used extensively for developmental genetic studies due to their salient features, such as small size, external development, optical transparency, and accessibility in large numbers. However, their use for the study of drug and alcohol abuse has not been explored. Here we investigated the response of larval zebrafish to acute treatment of alcohol. Our analyses showed that like adults, the larval zebrafish exhibited a dose-dependent locomotor response to ethanol: intermediate doses led to hyperactivity, whereas high doses have a neurodepressive effect resulting in hypoactivity and sedation. Alcohol also induced morphological changes of melanocytes, providing a visible cellular measure of the biological effects of alcohol in vivo. In addition, alcohol induced thigmotaxis behavior (preference for the edge of a compartment). In the behaviors we analyzed, genetic background influenced the locomotor responses to alcohol. The present study demonstrates that larval zebrafish exert a response to the acute treatment of alcohol, which is genetically modifiable. Therefore, the larval zebrafish represent a tractable vertebrate model system for a large-scale genetic analysis of the biological effects of alcohol.

Pharmacology of acamprosate: an overview

In the last years important advances have been made in the development of drugs for the treatment of alcohol addiction. Acamprosate (calcium bis-acetylhomotaurine) is one of the better established drugs in this field on the European market. This review focuses first on the pharmacokinetics of acamprosate. The published data and the recent advances in our knowledge on the mechanisms involved in the intestinal absorption and elimination of this drug are summarized. The importance of pharmacokinetics for the proper clinical use of acamprosate is highlighted. The anti-relapse as well as the well-known effects of acamprosate on ethanol intake are discussed. The recent experiments in animal models of conditioned withdrawal are reviewed. These experiments, explored for the first time the anticraving effect of the drug. Finally, the proposed hypotheses on the neuropharmacological mechanism of action of acamprosate are discussed. The discussion deals with the relative importance of various hypotheses as well as with the recent experiments that support them. It is pointed out that further research is necessary in order to clearly understand the mode of action of acamprosate as well as the neurobiological mechanisms involved in alcohol dependence.

Effect of chronic "binge cocaine" on basal levels and cocaine-induced increases of dopamine in the caudate putamen and nucleus accumbens of C57BL/6J and 129/J mice

In vivo microdialysis was used to measure the effect of chronic "binge" pattern cocaine administration on basal and cocaine-induced dopamine levels in the caudate putamen and nucleus accumbens of C57BL/6J and 129/J mice. Mice were implanted with a guide cannula in the caudate putamen or nucleus accumbens and after 4 days recovery, one group received "binge" pattern cocaine administration for 13 days (15 mg/kg x 3, i.p. at hourly intervals) while another group received saline in the same pattern. On the day before microdialysis, dialysis probes were lowered into the caudate putamen and nucleus accumbens. The next morning, after baseline dopamine collection, all animals received "binge" cocaine administration. Dialysates were collected every 20 min and dopamine content was determined by HPLC with electrochemical detection. In the basal condition, the mean level of dopamine in the dialysate from both brain regions of mice pretreated with "binge" pattern cocaine administration was significantly lower than that of the mice pretreated with saline administration. The absolute levels of dopamine achieved following "binge" pattern cocaine challenge were lower in the mice that had received chronic cocaine administration. However, when expressed as percent increase over baseline, the dopamine response to cocaine in the nucleus accumbens was significantly higher in mice that received chronic than in mice that received acute cocaine administration. Chronic cocaine administration led to a lowering of both basal dopamine and the absolute levels of cocaine-induced increases of dopamine in the two brain regions, but enhanced the percent increases over the baseline in response to cocaine in the nucleus accumbens of both mouse strains.

Role of GABA(B) receptor in alcohol dependence: reducing effect of baclofen on alcohol intake and alcohol motivational properties in rats and amelioration of alcohol withdrawal syndrome and alcohol craving in human alcoholics

The present paper describes the results of recent preclinical and clinical studies conducted in this laboratory in order to characterize the anti-alcohol properties of the GABA(B) receptor agonist, baclofen. At a preclinical level, the repeated administration of non-sedative doses of baclofen dose-dependently suppressed the acquisition and maintenance of alcohol drinking behavior in selectively bred Sardinian alcohol-preferring (sP) rats tested under the homecage, 2-bottle "alcohol vs water" choice regimen. Acute injection of baclofen completely blocked the temporary increase in voluntary alcohol intake occurring after a period of alcohol abstinence (the so-called alcohol deprivation effect, which models alcohol relapses in human alcoholics). Acute treatment with baclofen also dose-dependently suppressed extinction responding for alcohol (an index of motivation to consume alcohol) in sP rats trained to lever-press for oral alcohol self-administration. Taken together, these results suggest the involvement of the GABA(B) receptor in the neural substrate mediating alcohol intake and alcohol motivational properties in an animal model of excessive alcohol consumption. Further, acutely administered baclofen dose-dependently reduced the severity of alcohol withdrawal signs in Wistar rats made physically dependent upon alcohol. Preliminary clinical surveys suggest that the anti-alcohol properties of baclofen observed in rats may generalize to human alcoholics. Indeed, a double-blind survey demonstrated that repeated daily treatment with baclofen was associated, when compared to placebo, with a higher percentage of subjects totally abstinent from alcohol and a higher number of days of total abstinence. Treatment with baclofen also suppressed the number of daily drinks and decreased the obsessive and compulsive components of alcohol craving. Finally, a single non-sedative dose of baclofen resulted in the rapid disappearance of alcohol withdrawal symptomatology, including delirium tremens, in alcohol-dependent patients. In both clinical studies, baclofen was well tolerated with minimal side effects. These results suggest that baclofen may represent a potentially effective medication in the treatment of alcohol-dependent patients.

Gene-environment interplay in alcoholism and other substance abuse disorders: expressions of heritability and factors influencing vulnerability

Factors that confer predisposition and vulnerability for alcoholism and other substance abuse disorders may be described usefully within the gene-environment interplay framework. Thus, it is postulated that heritability provides a major contribution not only to alcohol but also to other substances of abuse. Studies of evoked potential amplitude reduction have provided a highly suitable and testable method for the assessment of both environmentally-determined and heritable characteristics pertaining to substance use and dependence. The different personal attributes that may co-exist with parental influence or exist in a shared, monozygotic relationship contribute to the final expression of addiction. In this connection, it appears that personality disorders are highly prevalent co-morbid conditions among addicted individuals, and, this co-morbidity is likely to be accounted for by multiple complex etiological relationships, not least in adolescent individuals. Co-morbidity associated with deficient executive functioning may be observed too in alcohol-related aggressiveness and crimes of violence. The successful intervention into alcohol dependence and craving brought about by baclofen in both human and animal studies elucidates glutamatergic mechanisms in alcoholism whereas the role of the dopamine transporter, in conjunction with both the noradrenergic and serotonergic transporters, are implicated in cocaine dependence and craving. The role of the cannabinoids in ontogeny through an influence upon the expression of key genes for the development of neurotransmitter systems must be considered. Finally, the particular form of behaviour/characteristic outcome due to childhood circumstance may lie with biological, gene-based determinants, for example individual characteristics of monoamine oxidase (MAO) activity levels, thereby rendering simple predictive measures both redundant and misguiding.

Molecular mechanisms of tolerance to and withdrawal of GABA(A) receptor modulators

Here, we summarize recent data pertaining to the effects of GABA(A) receptor modulators on the receptor gene expression in order to elucidate the molecular mechanisms behind tolerance and dependence induced by these drugs. Drug selectivity and intrinsic activity seems to be important to evidence at the molecular level the GABA(A) receptor tolerance. On the contrary, we suggested that all drug tested are equally potentially prone to induce dependence. Our results demonstrate that long-lasting exposure of GABA(A) receptors to endogenous steroids, benzodiazepines and ethanol, as well as their withdrawal, induce marked effects on receptor structure and function. These results suggest the possible synergic action between endogenous steroids and these drugs in modulating the functional activity of specific neuronal populations. We report here that endogenous steroids may play a crucial role in the action of ethanol on dopaminergic neurons.

Chronic Ethanol Consumption by C57BL/6 Mice Promotes Tolerance to Its Interoceptive Cues and Increases Extracellular Dopamine, an Effect Blocked by Naltrexone

BACKGROUND

C57BL/6 (B6) mice voluntarily consume ethanol. Although preingestive factors might be accountable, the fact that B6 mice voluntarily consume sufficient ethanol to set the conditions for an ethanol-deprivation effect suggest that post-ingestive pharmacological induced changes also occur. In this study, we determined the amounts of ethanol voluntarily consumed by B6 mice and associated blood ethanol levels (BEL), the effects of this consumption on extracellular dopamine (DA) and how this was altered by naltrexone, as well as on its interoceptive discriminative cues.

METHODS

In experiment 1, the amounts of 12% ethanol consumed at 2, 4, and 6 hr into the active phase of the circadian cycle and associated BEL were determined. In experiment 2, dialysate samples were collected for 1 hr to establish basal DA levels. Mice were then injected with saline or naltrexone (6 mg/kg) and given access to water and 12% ethanol or to water only, and samples were collected at 20-min intervals for the next 2 hr. In experiment 3, mice were trained to discriminate ethanol's interoceptive cues via operant techniques, and half were given 3 weeks access to ethanol and water, the other half water only. Ethanol-consuming and water control mice were again tested for their ability to discriminate the drug's interoceptive cues.

RESULTS

Mice ingested nearly 6 g/kg of ethanol and attained BEL near 100 mg/100 mL by 6 hr into the active phase. Ethanol intake at 2-hr into the dark phase was approximately 2.5 g/kg, and increased DA to approximately 100% above basal levels. Naltrexone reduced ethanol consumption and blocked the DA increase. Ethanol consumption for 3 weeks attenuated its discriminative cues.

CONCLUSIONS

B6 mice voluntarily consume sufficient ethanol (1) to produce intoxicating BEL; (2) to increase DA levels in nucleus accumbens, an effect blocked by naltrexone; and (3) to attenuate its discriminative cues.

Effect of blockade of corticotropin-releasing factor receptors in the median raphe nucleus on stress-induced c-fos mRNA in the rat brain

Using a rat relapse model, we have shown that infusion of a corticotropin-releasing factor (CRF) receptor antagonist into the median raphe nucleus (MRN) blocks footshock stress-induced reinstatement of alcohol seeking in rats. The goal of the present study was to begin identifying brain sites potentially involved in this effect. For this purpose, we measured levels of c-fos mRNA in discrete nuclei of the rat brain following exposure to intermittent footshock, which was preceded by intra-MRN infusions of a CRF receptor antagonist, d-Phe CRF (0 or 50 ng). Exposure to intermittent footshock increased the expression of c-fos mRNA in a number of brain regions previously shown to be responsive to stressful stimuli. Pretreatment with d-Phe CRF in the MRN selectively attenuated the increases in c-fos mRNA induced by footshock in the central nucleus of the amygdala (CeA). These findings are consistent with previous data on the important role for the CeA in stress-induced reinstatement of drug seeking. These results also suggest that inhibition of CeA activity may contribute to the blockade of alcohol-seeking induced by footshock that we have observed following injections of d-Phe into the MRN.

Ethanol withdrawal reduces the number of spontaneously active ventral tegmental area dopamine neurons in conscious animals

Withdrawal from chronic ethanol treatment leads to a reduction in the electrical activity in dopamine (DA) neurons in the ventral tegmental area (VTA). However, there is disagreement on how the electrical activity is reduced (i.e., in the number of spontaneously active DA neurons or their firing rates and burst firing activity) and on the underlying mechanisms. The use of general anesthesia has been suggested to cause this discrepancy. In the present study, we demonstrate that ethanol withdrawal, in conscious animals, causes a reduction in the number of spontaneously active VTA DA neurons, but not in their firing rate or burst firing activity. Similar results were obtained in a previous study using anesthetized preparation, showing that general anesthesia does not cause this difference. Ethanol withdrawal-induced reduction in a number of spontaneously active VTA DA neurons could be mediated by depolarization inactivation because this effect was reversed by systemic administration of amphetamine, which inhibits VTA DA neurons by hyperpolarization. In addition, the withdrawal effect was normalized by acute ethanol administration, suggesting that the decrease in the number of spontaneously active VTA DA neurons represents an adaptational change to chronic ethanol treatment. Because the electrical activity of DA neurons controls the release of DA, it is possible that the decreased DA release during ethanol withdrawal observed in previous studies is caused by the reduction in the electrical activity of VTA DA neurons.

Haloperidol increases the disruptive effect of alcohol on spatial working memory in rats: a dopaminergic modulation in the medial prefrontal cortex

RATIONALE

The prefrontal cortex (PFC) has been considered the anatomic site for working memory. The medial portion of the PFC (mPFC) is also part of a "brain reward circuit" as constituted by the mesocorticolimbic dopaminergic system.

OBJECTIVE

This study examined the effects of acute administration of alcohol (ETOH) in the mPFC or systemically on the performance of 5-s or 1-h delayed tasks in an eight-arm radial maze. Effects of haloperidol (HAL), a dopamine antagonist, combined with ETOH, were also examined in a 1-h delayed task.

METHODS

Male Wistar rats trained in the radial maze and with bilateral cannulae implanted in the mPFC received intraperitoneal (IP) or intracortical (IC) drug administration.

RESULTS

As compared to saline (SAL) IC, ETOH IC in doses of 100 microg and 180 microg (5 min before session) increased significantly the number of errors in the 1-h and 5-s post-delay performance, respectively. HAL in doses with little or no effect alone IC (10 or 32 microg, 10 min before session) or IP (3.2 mg/kg, 35 min before session) increased the disruptive effect of ETOH IC (100 microg) on 1-h delayed task.

CONCLUSIONS

These results showed that ETOH administered directly in the mPFC disrupts short- and long-term spatial working memory. The increase of the disruptive effect of ETOH produced by a dopaminergic blockage, particularly in the mPFC, suggests that the dopaminergic neurotransmission in this cortical area might modulate ETOH effects on spatial working memory.

Nicotine increases alcohol self-administration and reinstates alcohol seeking in rats

RATIONALE AND OBJECTIVE

Alcohol and tobacco are often co-abused in humans and previous studies found that nicotine increases alcohol consumption in rats. Here, we studied whether nicotine would reinstate alcohol-taking behavior in drug-free rats and whether this effect would be enhanced by prior exposure to nicotine during alcohol self-administration training.

METHODS

Rats were trained to press a lever for alcohol (12% w/v, 1 h/day), and following stable alcohol intake groups of rats ( n=11-12) were given daily vehicle or nicotine (0.2, 0.4 or 0.8 mg/kg, SC) injections just prior to the self-administration sessions for 10 days. Rats were then given 6 days of alcohol self-administration in the absence of nicotine and an additional 5-10 drug-free days during which lever presses were not reinforced (extinction). Subsequently, rats were tested for reinstatement of alcohol seeking following exposure to priming injections of vehicle or nicotine (0.4 mg/kg, SC).

RESULTS

Nicotine increased alcohol self-administration in a dose- and time-dependent manner over the 10-day period. Nicotine also reinstated alcohol seeking after extinction of the alcohol-reinforced behavior, and this effect was strongly enhanced by prior nicotine exposure.

CONCLUSIONS

The present data extend previous studies on the effect of nicotine on alcohol self-administration, and further indicate that nicotine is an effective stimulus for reinstatement of alcohol seeking during drug-free periods.

Ethanol intake increases galanin mRNA in the hypothalamus and withdrawal decreases it

Alcoholism can be viewed as a motivational disorder that results from alterations in brain systems for ingestive behavior. Therefore, it was hypothesized that alcohol intake might alter the expression of hypothalamic peptides that stimulate feeding. Earlier studies showed that hypothalamic injection of the feeding-stimulatory peptide, galanin (GAL), increases the release of dopamine (DA) in the nucleus accumbens (NAc), as does systemic alcohol, leading to a focus on GAL. Results of this study demonstrate the following: (1). Ethanol, injected daily (0.8 g/kg 10% v/v) for 7 days in male rats, markedly increased the expression of GAL but not of neuropeptide Y (NPY). This occurred in specific hypothalamic nuclei, namely the dorsomedial nucleus (DMN), paraventricular nucleus (PVN) and perifornical lateral hypothalamus (PLH). (2). Rats induced to drink ethanol ad libitum, by gradually increasing the concentration from 1% to 9% v/v without adding sugar or flavoring, exhibited a similar stimulation of GAL mRNA in the PVN and GAL immunoreactivity in the DMN and PVN. (3). Rats given increasing ethanol concentrations, with 12 h access starting 4 h into the dark cycle, had a mean blood alcohol concentration of 18 mg/dl and exhibited a similar increase in GAL expression in the DMN and PVN. (4) Withdrawal from the opioid effects of 9% ethanol, produced by injection of naloxone (3 mg/kg sc), reversed this ethanol effect by significantly reducing GAL expression in the DMN and PLH below baseline levels. These studies suggest a possible role for hypothalamic GAL in alcohol abuse.