Pharmacology of drug self-administration

Dissecting operant alcohol self-administration using saccharin-fading procedure

BACKGROUND

Although alcohol use disorder is a complex human pathology, the use of animal models represents an opportunity to study some aspects of this pathology. One of the most used paradigms to study the voluntary alcohol consumption in rodents is operant self-administration (OSA).

AIMS

In order to facilitate the performance of this paradigm, we aim to describe some critical steps of OSA under a saccharin-fading procedure.

MATERIAL & METHODS

We used 40 male Wistar rats to study the process of acquiring the operant response through a saccharin-fading procedure under a fixed ratio (FR1) schedule of reinforcement. Next, we analyze the alcohol introduction and concentration increase, the effect of an alcohol deprivation, and the analogy between this paradigm with the Drinking in the Dark-Multiple Scheduled Access paradigm.

RESULTS

During alcohol concentration increase, animals reduced their lever presses in accordance with the increase in alcohol concentration. On the contrary, the consumption measured in g·kg^-1 BW showed a great stability. The lever presses pattern within operant session changes with the introduction of different alcohol concentrations: at higher alcohol concentrations, animals tended to accumulate most of their presses in the initial period of the session.

DISCUSSION

We show the utility of fading with low concentrations of saccharin and the evolution of the operant response through the different concentrations of alcohol.

CONCLUSION

Taken together, our results aimed to dissect the acquisition and maintenance of OSA behavior as well as other related variables, to facilitate the understanding and performance of this paradigm.

Deep Brain Stimulation of the Subthalamic Nucleus Modulates Reward-Related Behavior: A Systematic Review

Deep brain stimulation of the subthalamic nucleus (STN-DBS) is an effective treatment for the motor symptoms of movement disorders including Parkinson's Disease (PD). Despite its therapeutic benefits, STN-DBS has been associated with adverse effects on mood and cognition. Specifically, apathy, which is defined as a loss of motivation, has been reported to emerge or to worsen following STN-DBS. However, it is often challenging to disentangle the effects of STN-DBS per se from concurrent reduction of dopamine replacement therapy, from underlying PD pathology or from disease progression. To this end, pre-clinical models allow for the dissociation of each of these factors, and to establish neural substrates underlying the emergence of motivational symptoms following STN-DBS. Here, we performed a systematic analysis of rodent studies assessing the effects of STN-DBS on reward seeking, reward motivation and reward consumption across a variety of behavioral paradigms. We find that STN-DBS decreases reward seeking in the majority of experiments, and we outline how design of the behavioral task and DBS parameters can influence experimental outcomes. While an early hypothesis posited that DBS acts as a "functional lesion," an analysis of lesions and inhibition of the STN revealed no consistent pattern on reward-related behavior. Thus, we discuss alternative mechanisms that could contribute to the amotivational effects of STN-DBS. We also argue that optogenetic-assisted circuit dissection could yield important insight into the effects of the STN on motivated behavior in health and disease. Understanding the mechanisms underlying the effects of STN-DBS on motivated behavior-will be critical for optimizing the clinical application of STN-DBS.

Nonhuman animal models of substance use disorders: Translational value and utility to basic science

BACKGROUND

The National Institute on Drug Abuse (NIDA) recently released a Request for Information (RFI) soliciting comments on nonhuman animal models of substance use disorders (SUD).

METHODS

A literature review was performed to address the four topics outlined in the RFI and one topic inspired by the RFI: (1) animal models that best recapitulate SUD, (2) animal models that best balance the trade-offs between resources and ecological validity, (3) animal models whose translational value are frequently misrepresented or overrepresented by the scientific community, (4) aspects of SUD that are not currently being modeled in animals, and (5) animal models that are optimal for examining the basic mechanisms by which drugs produce their abuse-related effects.

RESULTS

Models that employ response-contingent drug administration, use complex schedules of reinforcement, measure behaviors that mimic the distinguishing features of SUD, and use animals that are phylogenetically similar to humans have the greatest translational value. Models that produce stable and reproducible baselines of behavior, lessen the number of uncontrolled variables, and minimize the influence of extraneous factors are best at examining basic mechanisms contributing to drug reward and reinforcement.

CONCLUSIONS

Nonhuman animal models of SUD have undergone significant refinements to increase their utility for basic science and translational value for SUD. The existing literature describes numerous examples of how these models may best be utilized to answer mechanistic questions of drug reward and identify potential therapeutic interventions for SUD. Progress in the field could be accelerated by further collaborations between researchers using animals versus humans.

Understanding Addiction Using Animal Models

Drug addiction is a neuropsychiatric disorder with grave personal consequences that has an extraordinary global economic impact. Despite decades of research, the options available to treat addiction are often ineffective because our rudimentary understanding of drug-induced pathology in brain circuits and synaptic physiology inhibits the rational design of successful therapies. This understanding will arise first from animal models of addiction where experimentation at the level of circuits and molecular biology is possible. We will review the most common preclinical models of addictive behavior and discuss the advantages and disadvantages of each. This includes non-contingent models in which animals are passively exposed to rewarding substances, as well as widely used contingent models such as drug self-administration and relapse. For the latter, we elaborate on the different ways of mimicking craving and relapse, which include using acute stress, drug administration or exposure to cues and contexts previously paired with drug self-administration. We further describe paradigms where drug-taking is challenged by alternative rewards, such as appetitive foods or social interaction. In an attempt to better model the individual vulnerability to drug abuse that characterizes human addiction, the field has also established preclinical paradigms in which drug-induced behaviors are ranked by various criteria of drug use in the presence of negative consequences. Separation of more vulnerable animals according to these criteria, along with other innate predispositions including goal- or sign-tracking, sensation-seeking behavior or impulsivity, has established individual genetic susceptibilities to developing drug addiction and relapse vulnerability. We further examine current models of behavioral addictions such as gambling, a disorder included in the DSM-5, and exercise, mentioned in the DSM-5 but not included yet due to insufficient peer-reviewed evidence. Finally, after reviewing the face validity of the aforementioned models, we consider the most common standardized tests used by pharmaceutical companies to assess the addictive potential of a drug during clinical trials.

The role of the orbitofrontal cortex in alcohol use, abuse, and dependence

One of the major functions of the orbitofrontal cortex (OFC) is to promote flexible motivated behavior. It is no surprise, therefore, that recent work has demonstrated a prominent impact of chronic drug use on the OFC and a potential role for OFC disruption in drug abuse and addiction. Among drugs of abuse, the use of alcohol is particularly salient with respect to OFC function. Although a number of studies in humans have implicated OFC dysregulation in alcohol use disorders, animal models investigating the association between OFC and alcohol use are only beginning to be developed, and there is still a great deal to be revealed. The goal of this review is to consider what is currently known regarding the role of the OFC in alcohol use and dependence. I will first provide a brief, general overview of current views of OFC function and its contributions to drug seeking and addiction. I will then discuss research to date related to the OFC and alcohol use, both in human clinical populations and in non-human models. Finally I will consider issues and strategies to guide future study that may identify this brain region as a key player in the transition from moderated to problematic alcohol use and dependence.

A Method for Evaluating the Reinforcing Properties of Ethanol in Rats without Water Deprivation, Saccharin Fading or Extended Access Training

Operant oral self-administration methods are commonly used to study the reinforcing properties of ethanol in animals. However, the standard methods require saccharin/sucrose fading, water deprivation and/or extended training to initiate operant responding in rats. This paper describes a novel and efficient method to quickly initiate operant responding for ethanol that is convenient for experimenters and does not require water deprivation or saccharin/sucrose fading, thus eliminating the potential confound of using sweeteners in ethanol operant self-administration studies. With this method, Wistar rats typically acquire and maintain self-administration of a 20% ethanol solution in less than two weeks of training. Furthermore, blood ethanol concentrations and rewards are positively correlated for a 30 min self-administration session. Moreover, naltrexone, an FDA-approved medication for alcohol dependence that has been shown to suppress ethanol self-administration in rodents, dose-dependently decreases alcohol intake and motivation to consume alcohol for rats self-administering 20% ethanol, thus validating the use of this new method to study the reinforcing properties of alcohol in rats.

Drug effects on multiple and concurrent schedules of ethanol- and food-maintained behaviour: context-dependent selectivity

BACKGROUND AND PURPOSE

Drugs that more potently or effectively reduce ethanol-maintained behaviour versus an alternative are considered selective and are considered promising pharmacotherapies for alcoholism. Such results are often obtained using separate groups or multiple schedules where ethanol and the alternative are available alone or sequentially. Recently, we observed that when ethanol and food were available sequentially under a multiple schedule, fluvoxamine and varenicline were selective; yet this selectivity disappeared when ethanol and food were concurrently available.

EXPERIMENTAL APPROACH

We examined the generality of these findings by comparing doses of several drugs required to decrease ethanol- and food-maintained responding under a multiple schedule and under a concurrent schedule. Effects were determined for chlordiazepoxide, 2,5-dimethoxy-4-iodoamphetamine (DOI), meta-chlorophenylpiperazine (mCPP), morphine, naltrexone and d-amphetamine.

KEY RESULTS

Under the multiple schedule, ED50 values for decreases in ethanol-maintained responding were significantly different and lower than ED50 s for decreases in food-maintained responding (demonstrating selectivity) for each drug except for chlordiazepoxide (which was equipotent) and naltrexone (which did not affect responding). However, this selectivity vanished or even inverted under the concurrent schedule, such that ED50 values for decreasing ethanol- and food-maintained responding were not different (or, following DOI, the ED50 for food-maintained responding was lower than for ethanol-maintained responding).

CONCLUSIONS AND IMPLICATIONS

Results are consistent with those seen following fluvoxamine and varenicline administration, and suggest that selectivity is assay-dependent. These results indicate the need for careful interpretation of selective drug effects, especially when obtained in situations where ethanol or the alternative is the only programmed reinforcement available.

Ceftriaxone and cefazolin attenuate the cue-primed reinstatement of alcohol-seeking

Alcohol consumption and the reinstatement of alcohol-seeking rely on glutamate and GABA transmission. Modulating these neurotransmitters may be a viable treatment strategy to prevent alcohol relapse. N-acetylcysteine (NAC) and the antibiotic ceftriaxone (CEF) alter the glial reuptake and release of glutamate while the antibiotic cefazolin (CEFAZ) modulates GABA signaling without affecting glutamate. Here, we used the extinction-reinstatement model of relapse to test the ability of these compounds to attenuate the reinstatement of alcohol-seeking. Male Sprague-Dawley rats were trained to self-administer 20% (v/v) alcohol in the home cage using an intermittent schedule (24 h on, 24 h off) for 12 sessions. Subsequently, animals self-administered alcohol during daily 45-min operant sessions for 26 sessions, followed by extinction training. We tested whether chronic administration of NAC, CEF, or CEFAZ attenuated the cue-primed reinstatement of alcohol-seeking. CEF and CEFAZ attenuated cue-primed reinstatement of alcohol-seeking while NAC had no effect. We subsequently investigated whether CEF and CEFAZ alter the self-administration of sucrose and chow pellets and if CEFAZ attenuates the reinstatement of cocaine-seeking. The operant self-administration of regular chow and sucrose was not altered by either CEF or CEFAZ. CEFAZ had no effect on cocaine reinstatement, a behavior that has been strongly tied to altered glutamate homeostasis in the nucleus accumbens. Thus the ability of CEFAZ to attenuate alcohol reinstatement likely does not involve the glial modulation of glutamate levels. The dampening of GABA transmission may be a common mechanism of action of cefazolin and ceftriaxone.

Wistar rats acquire and maintain self-administration of 20 % ethanol without water deprivation, saccharin/sucrose fading, or extended access training

RATIONALE

Operant self-administration (SA) is an important model of motivation to consume ethanol (EtOH), but low rates of voluntary consumption in rats are thought to necessitate water deprivation and saccharin/sucrose fading for acquisition of responding.

OBJECTIVES

Here, we sought to devise an effective model of SA that does not use water deprivation or saccharin/sucrose fading.

METHODS

First, we tested if Wistar rats would acquire and maintain SA behavior of 20 % EtOH under two conditions, water deprivation (WD) and non-water deprivation (NWD). Second, we tested the efficacy of our SA procedure by confirming a prior study which found that the NK1 antagonist L822429 specifically blocked stress-induced reinstatement of EtOH seeking but not SA. Finally, we assessed the effect of naltrexone, an FDA-approved medication for alcohol dependence that has been shown to suppress EtOH SA in rodents.

RESULTS

Lever presses (LPs) and rewards were consistent with previous reports that utilized WD and saccharin/sucrose fading. Similar to previous findings, we found that L822429 blocked stress-induced reinstatement but not baseline SA of 20 % EtOH. Moreover, naltrexone dose-dependently decreased alcohol intake and motivation to consume alcohol for rats that are self-administering 20 % EtOH.

CONCLUSIONS

Our findings provide a method for voluntary oral EtOH SA in rats that is convenient for experimenters and eliminates the potential confound of sweeteners in EtOH-operant SA studies. Unlike models that use intermittent access to 20 % EtOH, this method does not induce escalation, and based on pharmacological experiments, it appears to be driven by the positive reinforcing effects of EtOH.

Appropriate experimental approaches for predicting abuse potential and addictive qualities in preclinical drug discovery

INTRODUCTION

Drug abuse is an increasing social and public health issue, putting the onus on drug developers and regulatory agencies to ensure that the abuse potential of novel drugs is adequately assessed prior to product launch.

AREAS COVERED

This review summarizes the core preclinical data that frequently contribute to building an understanding of abuse potential for a new molecular entity, in addition to highlighting models that can provide increased resolution regarding the level of risk. Second, an important distinction between abuse potential and addiction potential is drawn, with comments on how preclinical models can inform on each.

EXPERT OPINION

While the currently adopted preclinical models possess strong predictive validity, there are areas for future refinement and research. These areas include a more refined use of self-administration models to assess relative reinforcement; and the need for open innovation in pursuing improvements. There is also the need for careful scientifically driven application of models rather than a standardization of methodologies, and the need to explore the opportunities that may exist for enhancing the value of physical dependence and withdrawal studies by focusing on withdrawal-induced drug seeking, rather than broad symptomology.

Ghrelin knockout mice show decreased voluntary alcohol consumption and reduced ethanol-induced conditioned place preference

Recent work suggests that stomach-derived hormone ghrelin receptor (GHS-R1A) antagonism may reduce motivational aspects of ethanol intake. In the current study we hypothesized that the endogenous GHS-R1A agonist ghrelin modulates alcohol reward mechanisms. For this purpose ethanol-induced conditioned place preference (CPP), ethanol-induced locomotor stimulation and voluntary ethanol consumption in a two-bottle choice drinking paradigm were examined under conditions where ghrelin and its receptor were blocked, either using ghrelin knockout (KO) mice or the specific ghrelin receptor (GHS-R1A) antagonist "JMV2959". We showed that ghrelin KO mice displayed lower ethanol-induced CPP than their wild-type (WT) littermates. Consistently, when injected during CPP-acquisition, JMV2959 reduced CPP-expression in C57BL/6 mice. In addition, ethanol-induced locomotor stimulation was lower in ghrelin KO mice. Moreover, GHS-R1A blockade, using JMV2959, reduced alcohol-stimulated locomotion only in WT but not in ghrelin KO mice. When alcohol consumption and preference were assessed using the two-bottle choice test, both genetic deletion of ghrelin and pharmacological antagonism of the GHS-R1A (JMV2959) reduced voluntary alcohol consumption and preference. Finally, JMV2959-induced reduction of alcohol intake was only observed in WT but not in ghrelin KO mice. Taken together, these results suggest that ghrelin neurotransmission is necessary for the stimulatory effect of ethanol to occur, whereas lack of ghrelin leads to changes that reduce the voluntary intake as well as conditioned reward by ethanol. Our findings reveal a major, novel role for ghrelin in mediating ethanol behavior, and add to growing evidence that ghrelin is a key mediator of the effects of multiple abused drugs.

Neuronal nicotinic acetylcholine receptors: common molecular substrates of nicotine and alcohol dependence

Alcohol and nicotine are often co-abused. As many as 80-95% of alcoholics are also smokers, suggesting that ethanol and nicotine, the primary addictive component of tobacco smoke, may functionally interact in the central nervous system and/or share a common mechanism of action. While nicotine initiates dependence by binding to and activating neuronal nicotinic acetylcholine receptors (nAChRs), ligand-gated cation channels normally activated by endogenous acetylcholine (ACh), ethanol is much less specific with the ability to modulate multiple gene products including those encoding voltage-gated ion channels, and excitatory/inhibitory neurotransmitter receptors. However, emerging data indicate that ethanol interacts with nAChRs, both directly and indirectly, in the mesocorticolimbic dopaminergic (DAergic) reward circuitry to affect brain reward systems. Like nicotine, ethanol activates DAergic neurons of the ventral tegmental area (VTA) which project to the nucleus accumbens (NAc). Blockade of VTA nAChRs reduces ethanol-mediated activation of DAergic neurons, NAc DA release, consumption, and operant responding for ethanol in rodents. Thus, ethanol may increase ACh release into the VTA driving activation of DAergic neurons through nAChRs. In addition, ethanol potentiates distinct nAChR subtype responses to ACh and nicotine in vitro and in DAergic neurons. The smoking cessation therapeutic and nAChR partial agonist, varenicline, reduces alcohol consumption in heavy drinking smokers and rodent models of alcohol consumption. Finally, single nucleotide polymorphisms in nAChR subunit genes are associated with alcohol dependence phenotypes and smoking behaviors in human populations. Together, results from pre-clinical, clinical, and genetic studies indicate that nAChRs may have an inherent role in the abusive properties of ethanol, as well as in nicotine and alcohol co-dependence.

Effects of removing food on maintenance of drinking initiated by pairings of sipper and food

Two experiments evaluated the effects of removing food presentations on the maintenance of drinking induced by experience with sipper - food pairings. In Exp 1, ethanol drinking was induced in non-deprived Long-Evans rats by Pavlovian conditioning procedures employing an ethanol sipper as conditioned stimulus (CS) and food pellet as unconditioned stimulus (US). The Paired/Ethanol group received presentations of the ethanol sipper CS followed immediately by the response-independent presentation of the food pellet US. The Random/Ethanol group received the ethanol sipper CS and food US randomly with respect to one another. For both groups, the concentration of ethanol in the sipper CS [(3%, 4%, 6%, 8% (vol./vol.)] was increased across sessions, and, as in previous studies employing low concentrations of ethanol in non-deprived rats (i.e., maintained with free access to food in their home cages), the two procedures induced comparable levels of sipper CS-directed ethanol drinking. Removing food US presentations had no effect on sipper CS-directed ethanol drinking in either group. In Exp 2, groups of non-deprived Long-Evans rats were trained either with water or ethanol in the sipper CS paired with food US. Removing food US presentations had no effect on ethanol drinking in the Paired/Ethanol group, but water drinking in the Paired/Water group declined systematically across sessions. Results indicate that food US presentations contribute to the maintenance of water drinking but not to the maintenance of ethanol drinking. Implications for accounts of ethanol drinking based on Pavlovian sign-tracking, behavioral economics and intermittent sipper procedures are considered.

Long-Evans rats acquire operant self-administration of 20% ethanol without sucrose fading

A major obstacle in the development of new medications for the treatment of alcohol use disorders (AUDs) has been the lack of preclinical, oral ethanol consumption paradigms that elicit high consumption. We have previously shown that rats exposed to 20% ethanol intermittently in a two-bottle choice paradigm will consume two times more ethanol than those given continuous access without the use of water deprivation or sucrose fading (5-6 g/kg every 24 h vs 2-3 g/kg every 24 h, respectively). In this study, we have adapted the model to an operant self-administration paradigm. Long-Evans rats were given access to 20% ethanol in overnight sessions on one of two schedules: (1) intermittent (Monday, Wednesday, and Friday) or (2) daily (Monday through Friday). With the progression of the overnight sessions, both groups showed a steady escalation in drinking (3-6 g/kg every 14 h) without the use of a sucrose-fading procedure. Following the acquisition phase, the 20% ethanol groups consumed significantly more ethanol than did animals trained to consume 10% ethanol with a sucrose fade (1.5 vs 0.7 g/kg every 30 min) and reached significantly higher blood ethanol concentrations. In addition, training history (20% ethanol vs 10% ethanol with sucrose fade) had a significant effect on the subsequent self-administration of higher concentrations of ethanol. Administration of the pharmacological stressor yohimbine following extinction caused a significant reinstatement of ethanol-seeking behavior. Both 20% ethanol models show promise and are amenable to the study of maintenance, motivation, and reinstatement. Furthermore, training animals to lever press for ethanol without the use of sucrose fading removes a potential confound from self-administration studies.

Crucial role of alpha4 and alpha6 nicotinic acetylcholine receptor subunits from ventral tegmental area in systemic nicotine self-administration

The identification of the molecular mechanisms involved in nicotine addiction and its cognitive consequences is a worldwide priority for public health. Novel in vivo paradigms were developed to match this aim. Although the beta2 subunit of the neuronal nicotinic acetylcholine receptor (nAChR) has been shown to play a crucial role in mediating the reinforcement properties of nicotine, little is known about the contribution of the different alpha subunit partners of beta2 (i.e., alpha4 and alpha6), the homo-pentameric alpha7, and the brain areas other than the ventral tegmental area (VTA) involved in nicotine reinforcement. In this study, nicotine (8.7-52.6 microg free base/kg/inf) self-administration was investigated with drug-naive mice deleted (KO) for the beta2, alpha4, alpha6 and alpha7 subunit genes, their wild-type (WT) controls, and KO mice in which the corresponding nAChR subunit was selectively re-expressed using a lentiviral vector (VEC mice). We show that WT mice, beta2-VEC mice with the beta2 subunit re-expressed exclusively in the VTA, alpha4-VEC mice with selective alpha4 re-expression in the VTA, alpha6-VEC mice with selective alpha6 re-expression in the VTA, and alpha7-KO mice promptly self-administer nicotine intravenously, whereas beta2-KO, beta2-VEC in the substantia nigra, alpha4-KO and alpha6-KO mice do not respond to nicotine. We thus define the necessary and sufficient role of alpha4beta2- and alpha6beta2-subunit containing nicotinic receptors (alpha4beta2*- and alpha6beta2*-nAChRs), but not alpha7*-nAChRs, present in cell bodies of the VTA, and their axons, for systemic nicotine reinforcement in drug-naive mice.

Drug addiction

Many drugs of abuse, including cannabinoids, opioids, alcohol and nicotine, can alter the levels of endocannabinoids in the brain. Recent studies show that release of endocannabinoids in the ventral tegmental area can modulate the reward-related effects of dopamine and might therefore be an important neurobiological mechanism underlying drug addiction. There is strong evidence that the endocannabinoid system is involved in drug-seeking behavior (especially behavior that is reinforced by drug-related cues), as well as in the mechanisms that underlie relapse to drug use. The cannabinoid CB(1) antagonist/inverse agonist rimonabant has been shown to reduce the behavioral effects of stimuli associated with drugs of abuse, including nicotine, alcohol, cocaine, and marijuana. Thus, the endocannabinoid system represents a promising target for development of new treatments for drug addiction.

Using drug-discrimination techniques to study the abuse-related effects of psychoactive drugs in rats

Drug-discrimination (DD) techniques can be used to study abuse-related effects by establishing the interoceptive effects of a training drug (e.g., cocaine) as a cue for performing a specific operant response (e.g., lever pressing reinforced by food). During training with this protocol, pressing one lever is reinforced when the training drug is injected before the start of the session, and responding on a second lever is reinforced when vehicle is injected before the session. Lever choice during test sessions can then be used as an indication of whether a novel drug has effects similar to the training drug, or whether a potential therapeutic alters the effects of the training drug. Although training can be lengthy (up to several months), the pharmacological specificity of DD procedures make them a perfect complement to other techniques used to study drug-abuse phenomena, such as intravenous self-administration and conditioned place-preference procedures.

Self-administration of cannabinoids by experimental animals and human marijuana smokers

Drug self-administration behavior has been one of the most direct and productive approaches for studying the reinforcing effects of psychoactive drugs, which are critical in determining their abuse potential. Cannabinoids, which are usually abused by humans in the form of marijuana, have become the most frequently abused illicit class of drugs in the United States. The early elucidation of the structure and stereochemistry of delta-9-tetrahydrocannabinol (THC) in 1964, which is now recognized as the principal psychoactive ingredient in marijuana, activated cannabinoid research worldwide. This review examines advances in research on cannabinoid self-administration behavior by humans and laboratory animals. There have been numerous laboratory demonstrations of the reinforcing effects of cannabinoids in human subjects, but reliable self-administration of cannabinoids by laboratory animals has only recently been demonstrated. It has now been shown that strong and persistent self-administration behavior can be maintained in experimentally and drug-naïve squirrel monkeys by doses of THC comparable to those in marijuana smoke inhaled by humans. Furthermore, reinforcing effects of some synthetic CB1 cannabinoid agonists have been recently reported using intravenous and intracerebroventricular self-administration procedures in rats and mice. These findings support previous conclusions that THC has a pronounced abuse liability comparable to other drugs of abuse under certain experimental conditions. Self-administration of THC by squirrel monkeys provides the most reliable animal model for human marijuana abuse available to date. This animal model now makes it possible to study the relative abuse liability of other natural and synthetic cannabinoids and to preclinically assess new therapeutic strategies for the treatment or prevention of marijuana abuse in humans.

The glucocorticoid receptor as a potential target to reduce cocaine abuse

Several findings suggest that glucocorticoid hormones are involved in determining the propensity of an individual to develop cocaine abuse. These hormones activate two related transcription factors, the glucocorticoid receptor (GR) and the mineralocorticoid receptor. In this study, we show that the selective inactivation of the GR gene in the brains of mice profoundly flattened the dose-response function for cocaine intravenous self-administration and suppressed sensitization, two experimental procedures considered relevant models of addiction. Furthermore, administration of a GR antagonist dose-dependently reduced the motivation to self-administer cocaine. Importantly, the absence of GR did not modify the basal behavioral and molecular effects of cocaine but selectively modified the excessive response to the drug spontaneously present in certain vulnerable individuals or induced by repeated drug exposure in others. In conclusion, we provide the first genetic evidence that the GR gene can modulate cocaine abuse. This suggests that targeting GR function in the brain could provide new therapeutic strategies to treat cocaine addiction for which there is no available treatment.

Assessing the stimulant effects of alcohol in humans

The stimulant effects of alcohol were assessed in humans. Twenty social drinkers were tested in dyads in the laboratory on three separate occasions, held 7 days apart. For their first session, one-third of the group consumed a dose of alcohol that was calculated to reach a target peak blood alcohol concentration (BAC) of 0.05 g/dl, one-third of the group consumed placebo-alcohol, and one-third consumed diet Sprite. For alcohol and placebo-alcohol conditions, subjects were told that they may or may not be given alcohol. For the soda condition, subjects were told they were consuming soda. Subjective stimulation, activity levels, and speech production were assessed over a 15-min period after beverage consumption (posttreatment) and compared to measurements taken prior to beverage consumption (baseline). Scores on the stimulant subscale of the Biphasic Alcohol Effects Scale (BAES) were significantly greater for the alcohol condition relative to the soda condition. There was also a trend for stimulant scores to be greater for the alcohol condition relative to the placebo-alcohol condition. Activity levels were significantly greater for the alcohol condition compared to either the placebo-alcohol or soda conditions. There were no group differences found for speech production. Subjective stimulant score and activity levels were not correlated. Peak BAC obtained in subjects who consumed alcohol was not correlated with either subjective stimulant scores or activity levels. Activity levels may provide a useful behavioral assay for assessing the stimulant effects of alcohol in humans.

Regional differences within the rat ventral tegmental area for muscimol self-infusions

The present study examined the effects of activating GABA(A) receptors in the anterior and posterior regions of the ventral tegmental area (VTA) on operant reinforcement behavior, using the technique of intracranial self-administration. Rats were given the opportunity to self-administer vehicle alone (artificial CSF) and vehicle containing 25, 50, and 100 microM muscimol, a GABA(A) agonist, into the anterior or posterior VTA during four sessions (3 h/session) in standard two-lever operant chambers. Rats received five times greater infusions of 50 and 100 microM muscimol than vehicle into the posterior VTA; both doses significantly increased responding above vehicle levels on the active and inactive (control) levers equally. When the response requirement for muscimol infusions was increased from a fixed-ratio 1 (FR1) to FR3 in a single-lever chamber, the total session responses increased approximately twofold. Muscimol was not self-infused when cannula placements were in the anterior VTA. The self-infusion of muscimol into the posterior VTA was attenuated by coadministration of picrotoxin. Overall, the results suggest that the activation of GABA(A) receptors in the posterior VTA produces goal-directed behavior.

The paradoxical hedonic valence of acute ethanol withdrawal (hangover) states in rats: place and taste conditioning

The hedonic valence of EtOH's delayed effects, usually referred to as "hangover," was assessed 18 h after a 4 g/kg injection using both place and taste learning tasks. In the place conditioning task two CS-,CS+ intervals were used (48 h and 144 h); within each treatment interval, experimentally induced "hangover" was paired with the initially nonpreferred conditioning compartment for half of the experimental group (N = 10 rats) and with the initially preferred conditioning compartment for the half (N = 10 rats). Saline injections were paired with placement in the alternate conditioning compartment. A third group (N = 10 rats) was conditioned with milliliter equivalent volumes of saline on both sides. A conditioned place preference was conditioned with the hangover state-induced interoceptive stimuli. Attempts were made to taste condition 24 rats with the interoceptive stimulus attributes of hangover. Experimentally induced hangover was associated with an adipsogenic state, defined as a significant decline in voluntary intake of both saccharin and water, which prevented taste conditioning.

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.

Thyrotropin-releasing hormone analog TA-0910 reduces voluntary alcohol intake of P rats subchronically in a limited scheduled access paradigm

We previously reported that single intraperitoneal injections of the thyrotropin-releasing hormone analog TA-0910 dose-dependently reduce alcohol intake in alcohol-preferring (P) rats in a free-choice continuous access protocol. We later showed, using the same protocol, that a transient tolerance develops to this effect after several consecutive, once-daily injections. In the present study, P rats that had been accustomed to continuous access to alcohol were acclimated to a limited scheduled access protocol in which alcohol was available only between 10 and 11 AM. This resulted in an elevated rate of alcohol intake. Rats were then injected once daily with TA-0910 (0.75 mg/kg) or an equal volume of a saline vehicle at 9:45 AM for 12 consecutive days. After 11 days of scheduled access, rats were allowed continuous access to alcohol. Intake of alcohol and water was measured each day at 11:00 AM. Compared with vehicle, TA-0910 reduced alcohol intake on the 11 days of scheduled access and during the first hour of day 12 when continuous access was restored, but did not reduce total (24 hr) alcohol intake on day 12. Data from this experiment show that TA-0910 reduces alcohol intake over a long period of time in a limited scheduled access protocol.

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

The effect of bromocriptine (stimulant of dopaminergic D2 receptors) on the daily consumption of 10% v/v ethanol solution, distilled water, and solid food, under free-choice conditions, was measured in nine genetically low (UChA) and six high ethanol consumer (UChB) adult female rats. Animals were housed in individual cages and maintained at room temperature of 23 +/- 1 degree C and with 12/12 h dark/light rhythm. The consumption of ethanol solution, water, and solid food was measured in pretreatment, treatment, and posttreatment periods of 3 days (Tuesday through Thursday) of 3 consecutive weeks. During the treatment period rats received daily a single oral dose of 8 mg of bromocriptine mesylate (Sandoz) suspended in 1 ml of water per kg of body weight. Data analysis was performed with a method previously reported, which allows to recognize specific effect of ethanol intake, depurated from the effects on calories and/or water consumption. Results showed that all UChB rats decreased significantly and specifically the consumption of ethanol solution during the treatment period compared to the pretreatment period (mean: -58 +/- 15%) and recovered the pretreatment consumption in the posttreatment period, without significant changes in the consumption of food and/or total water. The only significant change observed in UChA rats was a decrease of the consumption of solid food (mean: -15 +/- 5%). Results are consistent with the idea that a dopaminergic D2 synapsis participates in the neural network responsible for satiation with ethanol.

Discriminative stimulus effects of dopaminergic agents in rhesus monkeys

Recent reports have shown that treatment with dopamine reuptake inhibitors can selectively decrease responding maintained by low doses of cocaine in rhesus monkeys. This may occur because response-independent delivery of a reuptake inhibitor and response-dependent cocaine have common effects. One behavioral effect that dopamine reuptake inhibitors and cocaine share is their ability to serve as a discriminative stimulus. To compare discriminative effects of several dopaminergic agents with their ability to attenuate cocaine-maintained responding, three rhesus monkeys were first trained to discriminate intravenous injections of cocaine (0.1 mg/kg) from saline. Following generalization testing with various doses of cocaine (0.001-1.0 mg/kg), the relative potencies of phentermine (0.03-1.0 mg/kg), d-amphetamine (0.01-1.0 mg/kg), GBR 12,909 (0.01-1.0 mg/kg), and buspirone (0.03-0.56 mg/kg) to substitute for cocaine were assessed. Each drug except buspirone resulted in predominantly cocaine-appropriate responding at doses that were generally without rate-decreasing effect. The ED50 for the ability of these drugs to substitute for cocaine exhibited the same rank order as that for their effectiveness in decreasing cocaine-maintained responding. Thus, the current results show that the potencies of dopaminergic drugs to decrease cocaine-maintained responding and substitute for cocaine in a drug discrimination paradigm are related.

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

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

Effect of ethanol on extracellular 5-HT and glutamate in the nucleus accumbens and prefrontal cortex: comparison between the Lewis and Fischer 344 rat strains

The present study investigated the impact of systemic (i.p.) ethanol administration on extracellular levels of serotonin and glutamate in the prefrontal cortex and the nucleus accumbens in Lewis and Fischer 344 rat strains using in vivo microdialysis. At 1.0 g/kg, ethanol elicited a significant increase in nucleus accumbens-dialysate levels of both 5-HT (44% +/- 16, P = 0.002) and glutmate (90% +/- 43, P = 0.009) in Lewis rats. In Fischer rats, there was no increase in 5-HT (6% +/- 7: P = 0.5), and a trend toward an increase in glutamate (88% +/- 46: P = 0.1). The 0.5 and 2.0 g/kg doses did not result in any significant change in extracellular 5-HT or glutamate in the nucleus accumbens or prefrontal cortex of either strain. The basal levels of glutamate, in both brain regions, were significantly lower in Lewis than in Fischer 344 rats. The basal levels of 5-HT were also lower in the nucleus accumbens of Lewis rats. These findings suggest that enhanced sensitivity of the mesoaccumbens 5-HT or glutamate systems to ethanol and/or inherent low basal levels of 5-HT or glutamate activity may be associated with the predisposition to alcohol-drinking behavior seen in Lewis rats.

Effects of an acute dose of ethanol on dopaminergic and serotonergic systems from rat cerebral cortex and striatum

Intraperitoneal injection 10 min before sacrifice of 1.5 g ethanol/kg weight produced an increase in rat striatal levels of homovanillic acid (HVA) (p < 0.05) but did not affect the striatal concentrations of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA). A similar ethanol treatment led to decreases in 5-HT (p < 0.05) and 5-HIAA (p < 0.05) from cerebral cortex (prefrontal and anterior cingulate areas). The results point to several ethanol-linked alterations in central serotonergic and dopaminergic systems.

Effects of chronic alcohol consumption and aging on dopamine D2 receptors in Fischer 344 rats

Aging and chronic alcohol consumption are each accompanied by significant changes in dopamine and dopamine receptors. This study extended previous work by investigating the combined effects of chronic alcoholism and aging on total dopamine D2 receptors in brain areas associated with the nigrostriatal and mesocorticolimbic systems. In addition, the effects of chronic alcohol consumption and aging on the high-affinity state of D2 receptors and their conversion to the low-affinity form is included. Quantitative autoradiography was used to assess [3H]spiperone-labeled D2 receptors in tissue sections from 5- to 14- and 24-month Fischer 344 rats that were pair-fed a control or 6.6% (v/v) ethanol-containing liquid diet for 6 weeks. In addition, D2 receptors were determined in rats given the control liquid diet ad libitum. The results of these experiments demonstrated age-related changes in the nigrostriatal system. There was an age-related loss of total dopamine D2 receptors in the rostral and caudal striatum (approximately 25% decrease in Bmax). This decline in D2 receptors may be associated with changes in motor function. Despite the age-related decline in D2 receptors, there were no significant differences in the proportion of striatal receptors in the high-affinity form or in their conversion to the low-affinity state. Both aging and chronic alcohol consumption produced significant changes in the concentration of D2 receptors in brain areas associated with the mesocorticolimbic system. That is, the specific binding of [3H]spiperone was decreased in the frontal cortex of aged rats. In addition, chronic alcoholism was associated with a significant increase (approximately 20%) in the Bmax for D2 receptors in the nucleus accumbens. Nonetheless, neither age nor chronic alcohol consumption altered the proportion of high-affinity D2 receptors in the nucleus accumbens or their conversion to the lower affinity state. The observed changes in D2 receptors in the frontal cortex and nucleus accumbens are of interest because of the involvement of the mesocorticolimbic dopamine areas in the rewarding properties of alcohol and other drugs of abuse. Although aging and chronic alcoholism both produced significant changes in dopamine D2 receptor concentrations, alcohol did not accentuate the age-related loss of D2 receptors. We cannot eliminate the possibility that a more prolonged exposure of higher ethanol dose may potentiate age-related changes in the dopaminergic system.

Effects of chronic alcohol consumption and aging on dopamine D1 receptors in Fischer 344 rats

The present study examined the hypothesis that chronic alcoholism augments the age-related loss of dopamine D1 receptors. This hypothesis was investigated because previous studies reported that both aging and chronic alcoholism produce significant changes in dopaminergic systems, and because chronic alcoholism potentiates some age-related CNS losses. In addition, this study investigated the effects of aging on D1 receptors in animals 1 and 7 days after withdrawal from chronic ethanol. Quantitative autoradiography was used to measure [3H]SCH 23390 binding to D1 receptors in brain areas associated with both the nigrostriatal and mesocorticolimbic dopamine systems. Receptors were assessed in 5-, 14-, and 24-month-old male Fischer 344 rats that were pair-fed a control or 6.6% (v/v) ethanol-containing liquid diet for 6 weeks. The results of these studies demonstrated that aging is associated with a significant decline in D1 receptors in the rostral and caudal striatum, and substantia nigra of both control and ethanol-fed rats. These receptor changes in the nigrostriatal system may be associated with motor abnormalities. In addition, there was an age-related decline in D1 receptors in two brain areas of the mesocorticolimbic system: the nucleus accumbens and frontal cortex. The latter findings may be important because of the involvement of this system with the rewarding properties of ethanol and other drugs of abuse. There were no age-related differences in the response of D1 receptors to ethanol withdrawal in the caudal and rostral striatum, substantia nigra, and nucleus accumbens.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Ethanol enhancement of the motor-stimulating effect of nicotine in the rat

Although ethanol stimulates locomotion in mice, it has been difficult to demonstrate such an action in rats. In contrast, nicotine has been shown to enhance locomotion, including ipsiversive rotation in nigral-lesioned rats. We found no significant effect of ethanol alone on rat rotation at doses of 0.125, 0.50, 1.0, and 2.0 g/kg, IP, during a 30-min observation period. However, there was a dose-dependent effect of ethanol enhancing the rotation induced by nicotine (0.4 mg/kg, SC) given 30 min after the ethanol. The interaction of ethanol and nicotine on locomotion most likely involves the release of dopamine and may be related to the motor abnormalities sometimes seen clinically.

Current concepts of ethanol dependence

Alcohol dependence is considered to be divisible into two types (although the divisions between these are indistinct). These are psychological dependence, in which the rewarding effects of alcohol play a primary role, and chemical dependence, in which adaptive changes in the brain initiate punishing effects on withdrawal of alcohol, and suppression of these becomes the primary motive for using the drug. The neurochemical basis for the rewarding effects of alcohol may be the potentiation of GABA at GABAA receptors (causing relaxation) and release of dopamine from mesolimbic neurones (causing euphoria). The adaptive changes which cause the alcohol withdrawal syndrome are not known for certain, but alterations in GABAA receptors, NMDA receptors and voltage-operated calcium channels all have a claim. However, it is distinctly doubtful whether these all contribute to the negatively reinforcing effects of alcohol that are important in chemical dependence, although they may be important in other pathological effects of alcohol abuse. Current research badly needs better communication between basic scientists and clinicians to establish research goals and to improve current models.

Biphasic effect of ethanol on extracellular accumulation of glutamate in the hippocampus and the nucleus accumbens

The effect of systemic ethanol administration on the extracellular levels of glutamate in the hippocampus and nucleus accumbens of conscious rats was assessed using microdialysis. At 0.5 g/kg, ethanol caused a sustained increase in the levels of glutamate in both regions. Following 1.0 g/kg, response was observed in the nucleus accumbens while a trend towards a decrease in glutamate levels occurred in hippocampus. Injection of 2.0 g/kg ethanol decreased these levels in both regions. These findings suggest a relationship between the previously reported biphasic behavioral consequence of ethanol and its effect on glutamatergic neurotransmission.

Initiation and maintenance of oral ethanol self-administration in female Sprague-Dawley rats

Group-housed female Sprague-Dawley rats were trained to self-administer 5% ethanol (v/v) in a large self-administration chamber (100 x 40 x 40 cm) following three different initiation methods. The procedures were 1) an ethanol injection procedure, 2) a sucrose substitution procedure, and 3) a prandial drinking technique. Only the prandial drinking method served to maintain responding for ethanol in the absence of water deprivation or sweetening of the alcohol solution. Rats trained using this technique showed a large preference for 5% ethanol over water and a significant increase in locomotor activity while responding for 5% ethanol but not while responding for water. When the concentration of ethanol was increased from 1% to 32%, the amount of ethanol ingested increased up to a maximum of 1.233 +/- 0.3 g/kg of 32% ethanol, and response rates and number of ethanol deliveries followed an inverted U-shaped curve. Appreciable blood ethanol levels were detected immediately following self-administration of 8% ethanol. These results show that, in female Sprague-Dawley rats under the experimental conditions described, the prandial drinking technique was the most effective in inducing stable oral ethanol self-administration and suggest that under these conditions and in these subjects ethanol was acting as a positive reinforcer.

Neuropeptides and alcohol addiction in monkeys

Neuropeptides have been implicated in experimental drug addiction. Desglycinamide (Arg8) vasopressin (DGAVP) attenuates heroin and cocaine intake during initiation of drug self-administration in rats. beta-Endorphin is self-administered in rats and a role of endogenous opioids in cocaine reward has been proposed. The present studies deal with voluntary alcohol consumption in monkeys under free choice conditions. Monkeys initiated alcohol drinking within a few days and after a stable drinking pattern was acquired increased their ethanol consumption during a short period following interruption of the alcohol supply (relapse). The alcohol drinking behavior seems under the control of reinforcement principles. DGAVP reduced the acquisition of alcohol drinking in the majority of treated monkeys. Initiation of alcohol drinking induced modifications in neuroendocrine homeostasis e.g. an increased plasma beta-endorphin. Both the opioid antagonist naltrexone and the opioid agonist morphine dose-dependently decreased alcohol intake during continuous supply and after imposed abstinence. The monkeys were more sensitive to both drugs after imposed abstinence. The effects are interpreted in the context of the endorphin compensation hypothesis of addictive behavior. It is suggested that endorphins may be particularly implicated in craving for addictive drugs and in relapse of addictive behavior.

Effects of chronic ethanol consumption on G proteins in brain areas associated with the nigrostriatal and mesolimbic dopamine systems

This study examined the effects of chronic ethanol consumption on the content of G proteins in brain areas associated with the nigrostriatal and mesolimbic dopamine systems of male Fischer 344 rats, aged 3, 5, or 13 months at the time of killing. In addition, G protein mRNA was assessed in 3-month-old rats. G proteins were examined in ethanol-fed rats because a number of studies have implicated these proteins with both the acute and chronic effects of ethanol. Brain areas associated with the nigrostriatal and mesolimbic dopamine systems were examined because of the evidence that these systems are sensitive to ethanol. The brain areas examined include the substantia nigra (SN), striatum (ST), globus pallidus (GP), frontal cortex (FCX), nucleus accumbens (NA), ventral tegmental area (VTA), and ventral pallidum (VP). These experiments demonstrated that the 3-month-old rats that consumed a 6.6% (v/v) ethanol-containing liquid diet for 4 weeks had a significant (approximately 30-40%) increase in the mRNA content of Gi3 alpha in the FCX, VTA, and VP, and a significant (approximately 20%) decrease of that for G0 alpha in the SN. Nonetheless, the content of the G0 alpha protein subunit was not altered. In addition, there were no significant differences in the content of the proteins detected by antibodies to Gs alpha, G0 alpha, Gi1 alpha/Gi2 alpha, and G0 alpha/Gi3 alpha in the FCX, NA, and ST of similarly treated older rats (5 and 13 months). The content of mRNA for the other G proteins examined in the seven brain areas of 3-month-old rats was unaffected by chronic ethanol exposure.

Firing patterns of nucleus accumbens neurons during cocaine self-administration in rats

The firing patterns of neurons in the nucleus accumbens (NA) were recorded in rats trained to self-administer cocaine via response contingent intravenous drug infusions. Recordings were obtained from permanently implanted multiple electrode arrays (8 microwires) inserted bilaterally into the NA and/or ventral striatum (NA-VS) in animals exhibiting stable responding (inter-infusion intervals, INT) during test sessions consisting of 16-30 drug delivery episodes. Electronically isolated and identified NA-VS neurons showed distinct patterns of phasic increases in firing relative to the occurrence of the reinforced lever press. Two particular firing patterns, however, were repeatedly encountered in different animals. In one type, a marked increase was observed in discharge following response contingent drug delivery. A second firing pattern showed two distinct temporally separated brief firing peaks (bursts), one immediately prior to the initiation of responding, and the other a brief discharge commencing within 200 ms after the initiation of drug delivery. The time between firing peaks was found to be modifiable by changing the response/reward (FR) ratio for drug delivery. A third finding was that the correlates of the self-administration response were not solely the result of drug infusion since, (1) phasic firing increases were not observed when the drug was delivered non-contingently during the same session and, (2) the emergence of patterns was frequently delayed within the session until after drug self-administration behavior stabilized at regular INTs. The findings are discussed in terms of the significance of NA-VS neuron firing correlates for the initiation and maintenance of cocaine self-administration.

Neuroscience research: how has it contributed to our understanding of alcohol abuse and alcoholism? A review

Alcohol abuse and alcoholism are the greatest substance abuse problems in the United States today and contribute to numerous medical and social problems. To deal with many of these problems, an understanding of how alcohol acts on the brain is extremely important. Advances in neuroscience research have provided significant clues about where and how alcohol works on the brain. Alcohol clearly acts on membrane function, altering such processes as ion movements and neurotransmitter interactions with their receptors. Although these alcohol-induced alterations are presumed to relate to changes in behavior, this has not been clearly established. However, alcohol research is on the threshold of making a giant leap forward in our understanding the etiology of alcoholism.

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.

Effects of morphine on acquisition and maintenance of ethanol and water intake patterns in rats

Two experiments were conducted to assess the effects of chronic subcutaneous injections of morphine (1.0 mg/kg) or saline on the pattern and amount of sweetened ethanol and water intake in fluid restricted Long-Evans rats. Following daily injections, 2-h two-bottle choice tests were conducted with water and an ethanol solution (15% ethanol v/v in 5% sucrose w/v). During a 20-day acquisition phase (Experiment 1), ethanol intake patterns and amounts did not differ between saline (n = 6) and morphine (n = 6) groups. Both groups exhibited ethanol intake patterns that decreased exponentially throughout the session suggesting control by fluid restriction procedures. Morphine decreased water intake during initial periods of each session and increased intake during later periods. In Experiment 2, morphine and saline injections were reversed across three phases with the same rats. Morphine increased total ethanol consumption during the first few days of each 15-day phase, but the groups did not differ thereafter, and the initial increases produced no statistically significant group differences. Additionally, morphine augmented ethanol intake in early portions of sessions, while water intake was decreased and increased during early and later portions of each session, respectively. Analysis of the data from the last 5 days of each phase indicated that, when injected with morphine, the group which received saline during acquisition consumed significantly more ethanol solution than the group injected with morphine during acquisition. The effect on patterns of water and ethanol intake were observed, regardless of the drug injected during acquisition.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of chronic ethanol consumption on the mesolimbic and nigrostriatal dopamine systems

Both the mesolimbic dopamine system, which is involved with the rewarding properties of several drugs of abuse, and the nigrostriatal dopamine system, which is involved with motor function, appear to be sensitive to the effects of ethanol. In order to determine which components of the mesolimbic and nigrostriatal dopamine systems are adversely affected by chronic ethanol consumption, we assessed dopamine and DOPAC (3,4-dihydroxyphenylacetic acid) concentration and D1 and D2 receptors in several dopaminergic brain areas. These studies demonstrated that consumption of a 6.6% (v/v) ethanol-containing lipid diet for 1 month affected several components of the mesolimbic dopamine system in 3-month-old Fisher 344 rats and fewer components of the nigrostriatal dopamine system. Specifically, there was a 1.6- to 2.6-fold increase in the concentration of DOPAC in the nucleus accumbens (NA), frontal cortex (FCX), ventral tegmental area (VTA), and substantia nigra (SN). While the increase in DOPAC in the FCX and VTA was paralleled by a similar increase in dopamine, there was a significant deficiency of dopamine in the SN. These results suggest that there is an increase in dopamine turnover in the FCX, VTA, NA, and SN, which is accompanied by increased dopamine synthesis in the former two regions. Studies of dopamine receptors in control and ethanol-fed rats demonstrated a 25% loss of D1 receptors in the NA. No significant differences were found in D1 receptors in the striatum or globus pallidus. In addition, there were no differences in the number of total D2 receptors or in the conversion of the high to low affinity state of D2 receptors in the nucleus accumbens and striatum.(ABSTRACT TRUNCATED AT 250 WORDS)