Modifying drug-reinforced behavior by altering the economic conditions of the drug and a nondrug reinforcer

Animal Models of the Behavioral Symptoms of Substance Use Disorders

To more effectively manage substance use disorders, it is imperative to understand the neural, genetic, and psychological underpinnings of addictive behavior. To contribute to this understanding, considerable efforts have been made to develop translational animal models that capture key behavioral characteristics of addiction on the basis of DSM5 criteria of substance use disorders. In this review, we summarize empirical evidence for the occurrence of addiction-like behavior in animals. These symptoms include escalation of drug use, neurocognitive deficits, resistance to extinction, exaggerated motivation for drugs, increased reinstatement of drug seeking after extinction, preference for drugs over nondrug rewards, and resistance to punishment. The occurrence of addiction-like behavior in laboratory animals has opened the opportunity to investigate the neural, genetic, and psychological background of key aspects of addiction, which may ultimately contribute to the prevention and treatment of substance use disorders.

The effect of economy type on demand and preference for cocaine and saccharin in rats

BACKGROUND

Economy type is an important determinant of reinforcer value. This study investigated the effect of open and closed economies on demand and preference for cocaine and saccharin in rats.

METHODS

In the first phase, rats were trained to lever press for cocaine infusions or saccharin. The number of presses required for each reinforcer increased across sessions. Cocaine and saccharin economy type was manipulated over groups by varying post-session availability of these reinforcers. One group of rats had three hours' post-session access to unlimited cocaine (open economy). A second group had three hours' post-session access to unlimited saccharin. A third group had no post-session access to either reinforcer (closed economy). In a second phase, rats in the three conditions could make mutually exclusive choices for cocaine or saccharin.

RESULTS

Post-session access to saccharin caused saccharin demand to become more elastic. Post-session access to cocaine had no effect on demand for cocaine but made demand for saccharin more elastic. Results from the choice phase generally paralleled those from the demand phase, the main finding being that post-session saccharin access caused an increase in cocaine preference.

CONCLUSIONS

These results show that manipulating economy type can affect cocaine and non-drug reinforcers differently. Opening the saccharin economy decreased saccharin's value. Opening the cocaine economy did not decrease cocaine's value, but instead led to a devaluation of saccharin. These results suggest that cocaine choice may be determined not only by the reinforcers immediately available, but also by those reinforcers' broader contexts of availability.

Effects of the nicotinic agonist varenicline, nicotinic antagonist r-bPiDI, and DAT inhibitor (R)-modafinil on co-use of ethanol and nicotine in female P rats

RATIONALE

Co-users of alcohol and nicotine are the largest group of polysubstance users worldwide. Commonalities in mechanisms of action for ethanol (EtOH) and nicotine proposes the possibility of developing a single pharmacotherapeutic to treat co-use.

OBJECTIVES

Toward developing a preclinical model of co-use, female alcohol-preferring (P) rats were trained for voluntary EtOH drinking and i.v. nicotine self-administration in three phases: (1) EtOH alone (0 vs. 15%, two-bottle choice), (2) nicotine alone (0.03 mg/kg/infusion, active vs. inactive lever), and (3) concurrent access to both EtOH and nicotine. Using this model, we examined the effects of (1) varenicline, a nicotinic acetylcholine receptor (nAChR) partial agonist with high affinity for the α4β2* subtype; (2) r-bPiDI, a subtype-selective antagonist at α6β2* nAChRs; and (3) (R)-modafinil, an atypical inhibitor of the dopamine transporter (DAT).

RESULTS

In phases 1 and 2, pharmacologically relevant intake of EtOH and nicotine was achieved. In the concurrent access phase (phase 3), EtOH consumption decreased while nicotine intake increased relative to phases 1 and 2. For drug pretreatments, in the EtOH access phase (phase 1), (R)-modafinil (100 mg/kg) decreased EtOH consumption, with no effect on water consumption. In the concurrent access phase, varenicline (3 mg/kg), r-bPiDI (20 mg/kg), and (R)-modafinil (100 mg/kg) decreased nicotine self-administration but did not alter EtOH consumption, water consumption, or inactive lever pressing.

CONCLUSIONS

These results indicate that therapeutics which may be useful for smoking cessation via selective inhibition of α4β2* or α6β2* nAChRs, or DAT inhibition, may not be sufficient to treat EtOH and nicotine co-use.

The Neuroeconomics of Tobacco Demand: An Initial Investigation of the Neural Correlates of Cigarette Cost-Benefit Decision Making in Male Smokers

How the brain processes cigarette cost-benefit decision making remains largely unknown. Using functional magnetic resonance imaging (fMRI), this study investigated the neural correlates of decisions for cigarettes (0–10 cigarettes) at varying levels of price during a Cigarette Purchase Task (CPT) in male regular smokers (N = 35). Differential neural activity was examined between choices classified as inelastic, elastic, and suppressed demand, operationalized as consumption unaffected by cost, partially suppressed by cost, and entirely suppressed by cost, respectively. Decisions reflecting elastic demand, putatively the most effortful decisions, elicited greater activation in regions associated with inhibition and planning (e.g., middle frontal gyrus and inferior frontal gyrus), craving and interoceptive processing (anterior insula), and conflict monitoring (e.g., anterior cingulate cortex). Exploratory examination in a harmonized dataset of both cigarette and alcohol demand (N = 59) suggested common neural activation patterns across commodities, particularly in the anterior insula, caudate, anterior cingulate, medial frontal gyrus, and dorsolateral prefrontal cortex. Collectively, these findings provide initial validation of a CPT fMRI paradigm; reveal the interplay of brain regions associated with executive functioning, incentive salience, and interoceptive processing in cigarette decision making; and add to the literature implicating the insula as a key brain region in addiction.

Characterizing the relationship between increases in the cost of nicotine and decreases in nicotine content in adult male rats: implications for tobacco regulation

BACKGROUND

A large reduction in the nicotine content of cigarettes may benefit public health by reducing the rate and the prevalence of smoking. A behavioral economics framework suggests that a decrease in nicotine content may be considered an increase in the unit price of nicotine (unit price = reinforcer cost/reinforcer magnitude). Increasing the price of cigarettes (i.e., increasing reinforcer cost) would be considered an equivalent change in unit price to reducing nicotine content (i.e., reducing reinforcer magnitude).

OBJECTIVES

The goal of the present experiments was to characterize the relationship between increases in nicotine cost and decreases in nicotine dose.

MATERIALS AND METHODS

A rat self-administration model was used to assess this relationship across three experiments, with an emphasis on very low nicotine doses to model a potential nicotine reduction policy. Cost was manipulated via changes in the number of responses required to earn an infusion.

RESULTS

Results show that increases in the cost of nicotine and decreases in nicotine content were not equivalent manipulations. Nicotine consumption was more sensitive to nicotine dose than to nicotine cost. Nicotine consumption was also not equivalent across a variety of cost and dose combinations forming a single unit price.

CONCLUSIONS

Results of the present studies suggest that nicotine reduction is likely to have a large impact on nicotine exposure from cigarettes.

Varenicline decreases nicotine but not alcohol self-administration in genetically selected Marchigian Sardinian alcohol-preferring (msP) rats

BACKGROUND

Alcohol and nicotine are largely co-abused. Here, we investigated whether concurrent exposure to both addictive drugs influences each other's consumption and whether varenicline attenuates alcohol consumption in the presence of nicotine.

METHODS

Marchigian Sardinian alcohol-preferring (msP) rats trained to simultaneously self-administer oral alcohol (10% v/v) and intravenous nicotine (30μg/kg/inf) were used. Additional groups of rats were trained to self-administer either alcohol or nicotine. Further, msP rats were also trained to self-administer nicotine followed by 22-h/day access to alcohol and water in a two bottle free choice paradigm or water alone. The effects of varenicline (0.0, 0.3, 1.0, 3.0mg/kg, p.o.) on alcohol and nicotine consumption were tested.

RESULTS

In a self-administration paradigm, msP rats showed a significantly high level of alcohol and nicotine intake when the drugs were administered alone. However, when access to both drugs occurred concomitantly, the number of nicotine infusions self-administered was significantly decreased. Nicotine self-administration was markedly reduced by varenicline regardless of whether it was self-administered alone or concurrently with alcohol. In a two bottle choice test, varenicline significantly decreased nicotine self-administration but had no influence on alcohol consumption.

CONCLUSION

Varenicline is highly efficacious in decreasing nicotine self-administration either alone or in combination with alcohol. However, varenicline failed to influence both operant responding for alcohol and home-cage alcohol drinking in msP animals. Taken together, our findings suggest that the effects of varenicline could be specific to nicotine under conditions where excessive alcohol drinking is facilitated by genetic factors as in msP rats.

Contingency Management and Deliberative Decision-Making Processes

Contingency management is an effective treatment for drug addiction. The current explanation for its success is rooted in alternative reinforcement theory. We suggest that alternative reinforcement theory is inadequate to explain the success of contingency management and produce a model based on demand curves that show how little the monetary rewards offered in this treatment would affect drug use. Instead, we offer an explanation of its success based on the concept that it accesses deliberative decision-making processes. We suggest that contingency management is effective because it offers a concrete and immediate alternative to using drugs, which engages deliberative processes, improves the ability of those deliberative processes to attend to non-drug options, and offsets more automatic action-selection systems. This theory makes explicit predictions that can be tested, suggests which users will be most helped by contingency management, and suggests improvements in its implementation.

Drug self-administration studies: a novel reinforcement schedule enhances choice

Relative reinforcing effects of different ethanol and different cocaine doses were studied under concurrent independent fixed-ratio (FR) schedules and concurrent nonindependent FR schedules with rhesus monkeys. Nonindependent FR schedules differed from independent FR schedules in that responses on either side counted towards the FR requirements of two concurrently presented choices. Thus, responses on the right operandum counted toward completion of both right and left FR schedules and, symmetrically, responses on the left did the same. Nonindependent schedules allow the number of responses per drug delivery to vary considerably, unlike independent schedules, thereby making the number of responses per delivery a sensitive dependent variable. In contrast, standard independent schedules do not allow responses per drug delivery to vary; the required number of responses is an independent variable. Three rhesus monkeys were subjects, and choices between different doses of ethanol or cocaine were studied. Larger doses maintained higher response rates than smaller doses - consistent with previous choice studies. By using nonindependent schedules, however, graded responses per drug delivery and increased switching between sides were obtained, providing additional data and useful measures of choice.

Peer influences on drug self-administration: an econometric analysis in socially housed rats

Social-learning theories of substance use propose that members of peer groups influence the drug use of other members by selectively modeling, reinforcing, and punishing either abstinence-related or drug-related behaviors. The objective of the present study was to examine the social influences on cocaine self-administration in isolated and socially housed rats, under conditions where the socially housed rats were tested simultaneously with their partner in the same chamber. To this end, male rats were obtained at weaning and housed in isolated or pair-housed conditions for 6 weeks. Rats were then implanted with intravenous catheters and cocaine self-administration was examined in custom-built operant conditioning chambers that allowed two rats to be tested simultaneously. For some socially housed subjects, both rats had simultaneous access to cocaine; for others, only one rat of the pair had access to cocaine. An econometric analysis was applied to the data, and the reinforcing strength of cocaine was measured by examining consumption (i.e. quantity demanded) and elasticity of demand as a function of price, which was manipulated by varying the dose and ratio requirements on a fixed ratio schedule of reinforcement. Cocaine consumption decreased as a function of price in all groups. Elasticity of demand did not vary across groups, but consumption was significantly lower in socially housed rats paired with a rat without access to cocaine. These data suggest that the presence of an abstaining peer decreases the reinforcing strength of cocaine, thus supporting the development of social interventions in drug abuse prevention and treatment programs.

Response deprivation, reinforcement, and economics

Reinforcement of an instrumental response results not from a special kind of response consequence known as a reinforcer, but from a special kind of schedule known as a response-deprivation schedule. Under the requirements of a response-deprivation schedule, the baseline rate of the instrumental response permits less than the baseline rate of the contingent response. Because reinforcement occurs only if the schedule deprives the organism of the contingent response, reinforcement cannot result from any intrinsic property of the contingent response or any property relative to the instrumental response. Two typical effects of response-deprivation schedules-facilitation of the instrumental response and suppression of the contingent response-are discussed in terms of economic concepts and models of instrumental performance. It is suggested that response deprivation makes the contingent response function as an economic good, the instrumental response as currency.

Effects of 2-AG on the reinforcing properties of wheel activity in obese and lean Zucker rats

The endocannabinoid system plays a role in obesity, primarily by its role in food reward. Activity, also involved in obesity, seems to be at least partially controlled by the endocannabinoid system, but the relevant behavioral and neurochemical mechanisms have not been well established. This study represents an attempt to begin elucidating these mechanisms by examining the effects of an endogenous cannabinoid ligand, 2-arachidonoylglycerol (2-AG), on the reinforcing properties of exercise reinforcement in lean and obese Zucker rats. Ten obese and 10 lean Zucker rats pressed a locked door under a progressive ratio schedule of reinforcement that, when unlocked, provided access to a running wheel for 2-min periods. After baseline breakpoints were established, doses of 2-AG (0.3-3 mg/kg) were administered before experimental sessions. Obese rats exhibited lower breakpoints for wheel activity, lower response rates, and fewer revolutions compared with lean rats. 2-AG decreased breakpoints, response rates, and revolutions for obese rats, and revolutions only for lean rats. These data suggest that 2-AG may reduce the reinforcing properties of activity, and that obese Zuckers may show a greater sensitivity to 2-AG. The data also suggest that endocannabinoids may play a role in the reinforcing properties of exercise.

Design, synthesis, and subtype selectivity of 3,6-disubstituted β-carbolines at Bz/GABA(A)ergic receptors. SAR and studies directed toward agents for treatment of alcohol abuse

A series of 3,6-disubstituted β-carbolines was synthesized and evaluated for their in vitro affinities at α(x)β(3)γ(2) GABA(A)/benzodiazepine receptor subtypes by radioligand binding assays in search of α(1) subtype selective ligands to treat alcohol abuse. Analogues of β-carboline-3-carboxylate-t-butyl ester (βCCt, 1) were synthesized via a CDI-mediated process and the related 6-substituted β-carboline-3-carboxylates 6 including WYS8 (7) were synthesized via a Sonogashira or Stille coupling processes from 6-iodo-βCCt (5). The bivalent ligands of βCCt (32 and 33) were also designed and prepared via a palladium-catalyzed homocoupling process to expand the structure-activity relationships (SAR) to larger ligands. Based on the pharmacophore/receptor model, a preliminary SAR study on 34 analogues illustrated that large substituents at position-6 of the β-carbolines were well tolerated. As expected, these groups are proposed to project into the extracellular domain (L(Di) region) of GABA(A)/Bz receptors (see 32 and 33). Moreover, substituents located at position-3 of the β-carboline nucleus exhibited a conserved stereo interaction in lipophilic pocket L(1), while N(2) presumably underwent a hydrogen bonding interaction with H(1). Three novel β-carboline ligands (βCCt, 3PBC and WYS8), which preferentially bound to α1 BzR subtypes permitted a comparison of the pharmacological efficacies with a range of classical BzR antagonists (flumazenil, ZK93426) from several different structural groups and indicated these β-carbolines were 'near GABA neutral antagonists'. Based on the SAR, the most potent (in vitro) α(1) selective ligand was the 6-substituted acetylenyl βCCt (WYS8, 7). Earlier both βCCt and 3PBC had been shown to reduce alcohol self-administration in alcohol preferring (P) and high alcohol drinking (HAD) rats but had little or no effect on sucrose self-administration.(1-3) Moreover, these two β-carbolines were orally active, and in addition, were anxiolytic in P rats but were only weakly anxiolytic in rodents. These data prompted the synthesis of the β-carbolines presented here.

Demand for sucrose in the genetically obese Zucker (fa/fa) rat

Obese Zucker rats (fa/fa) eat more food than lean controls in free-feeding conditions, which strongly influences their phenotypic expression. Few studies, however, characterize their food consumption in environments that are more representative of foraging conditions, e.g., how effort plays a role in food procurement. This study examined the reinforcing efficacy of sucrose in obese Zucker rats by varying the responses required to obtain single sucrose pellets. Male Zucker rats (15 lean, 14 obese) lever-pressed under eight fixed ratio (FR) schedules of sucrose reinforcement, in which the number of lever-presses required to gain access to a single sucrose pellet varied from 1 to 300. Linear and exponential demand equations, which characterize the value of a reinforcer by its sensitivity to price (FR), were fit to the number of food reinforcers and responses made. Free food consumption was also examined. Obese Zuckers, compared to leans, consumed more food under free-feeding conditions. Moreover, they had higher levels of consumption and response output, but only at low FR values. Both groups were equally sensitive to price increases at higher FR values. This suggests that environmental conditions may interact with genes in the expression of food reinforcer efficacy.

Operant self-administration models for testing the neuropharmacological basis of ethanol consumption in rats

Operant self-administration procedures are used to assess the neural basis of ethanol-seeking behavior under a wide range of experimental conditions. In general, rats do not spontaneously self-administer ethanol in pharmacologically meaningful amounts. This unit provides a step-by-step guide for training rats to self-administer quantities of ethanol that produce moderate to high blood-alcohol content. Different protocols are used for rats that are genetically heterogeneous versus rats that are selectively bred for high alcohol preference. Also, these protocols have different sets of advantages and disadvantages in terms of the ability to control for caloric intake and taste of solutions in operant testing. Basic self-administration protocols can also be altered to focus on different aspects of the motivational properties of ethanol (for example, those related to dependence). This unit provides multiple protocols that lead to alcohol intake in rats, which can be pharmacologically probed relative to a variety of control conditions.

Effects of different accessibility of reinforcement schedules on choice in humans

Based on the delay-reduction hypothesis, a less profitable schedule should be rejected if its duration exceeds the mean delay to reinforcement. It should be accepted if its duration is shorter than the mean delay. This was tested for humans, using a successive-choice schedule. The accessibility of the less profitable (variable-interval 18 s) schedule was varied by changing the duration (in terms of a fixed interval) of the waiting-time component preceding its presentation. Forty-eight students were randomly assigned to three groups. In Phase 1, the duration of the less profitable schedule equaled the mean delay to reinforcement in all groups. In Phase 2, waiting time preceding the less profitable schedule was reduced in Group 1 and increased in Group 2. Thus, the schedule was correlated either with a relative delay increase (Group 1) or a delay reduction (Group 2). In Group 3, conditions remained unchanged. As predicted, acceptance of the less profitable schedule decreased in Group 1 and increased in Group 2. The increased acceptance in Group 2 was accompanied by a decreased acceptance of the more profitable (variable-interval 3 s) schedule, resembling a pattern of negative contrast. Response rates were higher under the component preceding (a) the more profitable schedule in Group 1 and (b) the less profitable schedule in Group 2. Implications for the modification of human choice behavior are discussed.

Food reinforcement, delay discounting and obesity

Choice is a central construct in behavioral economics, with choice research divided into choice of concurrent alternative reinforcers, which is conceptualized as relative reinforcing value, or choice of small immediate versus larger delayed rewards, usually of the same commodity, which is conceptualized as delay of gratification and delay discounting. Relative reinforcing value, delay of gratification and delay discounting paradigms can be used to study obesity, which involves strong motivation to obtain and consume food reinforcers. Strong food reinforcement and difficulties in delay of gratification are risk factors for child weight gain, and both are related to individual differences in overweight/obesity. Delay discounting interacts with food reinforcement to predict energy intake. We provide a selective review of research on each of these areas, and argue that the division of choice into reinforcing value versus delay discounting is based on an arbitrary definition based on the temporality of choices. We present a model that integrates reinforcing value and delay discounting approaches. Implications of this theoretical approach to better understand excess energy intake and obesity are discussed. The paper represents an invited review by a symposium, award winner or keynote speaker at the Society for the Study of Ingestive Behavior [SSIB] Annual Meeting in Portland, July 2009.

The behavioral economics of drug dependence: towards the consilience of economics and behavioral neuroscience

In this chapter, we review the research in this growing field by first discussing the concepts related to price and consumption (demand), its applications to the study of drug consumption and drug seeking, and the impact of other commodities on drug consumption. We then review the discounting of future commodities and events among the addicted, review the most recent research examining the neural correlates of discounting, and describe and review the new theory of addiction that results from that research. We conclude by addressing the next research steps that these advances engender.

Supply of a nondrug substitute reduces escalated heroin consumption

Escalation of drug consumption-a hallmark of addiction-has been hypothesized to be associated with a relative devaluation of alternative nondrug rewards and thus with a decrease in their ability to compete with or to substitute for the drug. In a behavioral economic framework, decreased substitutability of nondrug rewards for drug would explain why drug consumption is behaviorally dominant and relatively resistant to change (eg price-inelastic) in drug-addicted individuals. The goal of the present study was to test this hypothesis using a validated rat model of heroin intake escalation. Escalation was precipitated by long (6 h, long access (LgA)), but not short (1 h, short access (ShA)), daily access to i.v. heroin self-administration. After escalation, the effects of price (ie fixed-ratio value) on heroin consumption were assessed under two alternative reward conditions: in the presence or absence of a nondrug substitute for heroin (ie four freely available chow pellets). As expected, escalated heroin consumption by LgA rats was less sensitive to price than heroin consumption by ShA rats, showing that heroin had acquired greater reinforcing strength during escalation. However, supplying a substitute during access to heroin was sufficient to reverse this post-escalation increase in the reinforcing effectiveness of heroin. Thus, escalated heroin consumption is not associated with a decreased sensitivity to competing nondrug rewards. Escalated drug use may therefore persist, not so much because of a relative devaluation of nondrug substitutes, but because of a loss or reduction of their availability.

Preclinical models to evaluate potential pharmacotherapeutic agents in treating alcoholism and studying the neuropharmacological bases of ethanol-seeking behaviors in rats

The unit outlines four basic protocols designed to systematically evaluate the capacity of potential pharmacotherapeutic agents to effectively treat alcohol addiction and dependence in rats. Also included are procedures designed to study the neural mechanisms regulating alcohol-seeking behaviors.

Effects of delay to reinforcement on the choice between cocaine and food in rhesus monkeys

RATIONALE

Although a delay between behavior and reinforcer has been shown to weaken behavior, little is known about the effects of delay on drug choice.

OBJECTIVES

The present study examined effects of delay between lever press and reinforcer presentation on the choice between a drug and non-drug reinforcer and between different drug doses.

MATERIALS AND METHODS

Monkeys (n=4) were allowed to choose 32 times/day between cocaine and four food pellets. The delay between lever press and a preferred dose of cocaine (0.05 mg/kg/injection) was increased systematically from 0 to 240 s, while the delay to food remained at 0 s. A second group of monkeys (n=4) was allowed to choose between 0.05 mg/kg/injection and a lower dose of cocaine (0.025 mg/kg/injection). Next, a delay that resulted in less than 20% choice of 0.05 mg/kg/injection cocaine was selected and delay to the alternative was varied.

RESULTS

Results were similar across groups. The choice of 0.05 mg/kg/injection approximated 100% at 0 delay and decreased to near 0 as delay increased. As the delay to alternative was subsequently increased from 0 to 240 s, choice of 0.05 mg/kg/injection increased, though full cocaine choice was not generally restored. The delay estimated to maintain 50% choice (indifference point) was lower for the cocaine-food choice (mean=64 s) than for the cocaine-cocaine choice (mean=207 s).

CONCLUSIONS

This experiment demonstrates that the choice between cocaine and a non-drug or drug alternative can be modified by increasing the interval between behavior and drug injection. Overall, the results are consistent with a temporal discounting model of drug choice.

Intermittent presentations of ethanol sipper tube induce ethanol drinking in rats

AIMS

Intermittent presentations of the ethanol sipper have been reported to induce more ethanol drinking in rats than when the ethanol sipper was continuously available during the session. This intermittent sipper effect was observed in a social drinking situation, in which subjects experienced intermittent opportunities to interact briefly with a conspecific rat. The objective of this study was to evaluate the effects of the intermittent sipper procedure in situations providing for intermittent presentations of food, and, in addition, in situations that do not provide for intermittent presentations of another rewarding event.

METHODS

Four groups of male Long-Evans hooded rats, arranged in a 2 x 2 factorial design with two levels of Sipper Procedure (Intermittent vs Continuous) and two levels of Food procedure (Food vs No Food), were trained in drinking chambers. During each daily session, Intermittent Sipper groups received access to the ethanol sipper during each of 25 trials of 10 s each, while Continuous Sipper groups had access to the ethanol sipper during the entire session (approximately 30 min). During each session, Food groups received 25 presentations of food pellets while No Food groups received no food pellets. Ethanol concentrations in the sipper [3, 4, 6, 8, and 10% (vol./vol.)] increased across sessions.

RESULTS

More rapid escalation of ethanol intake was observed in the Intermittent Sipper groups than in the Continuous Sipper groups, and this effect was observed in both the Food and No Food conditions (P's < 0.05), which did not differ from one another.

CONCLUSIONS

Intermittent Sipper procedures provide less access to the ethanol sipper, yet induced more ethanol drinking than Continuous Sipper procedures. The intermittent sipper effect is not dependent on presentations of food. Implications for schedule-induced polydipsia and Pavlovian autoshaping are discussed.

Selective GABAA ??5 Benzodiazepine Inverse Agonist Antagonizes the Neurobehavioral Actions of Alcohol

BACKGROUND

Previous research has implicated the alpha5-containing GABAA receptors of the hippocampus in the reinforcing properties of alcohol. In the present study, a selective GABAA alpha5 benzodiazepine inverse agonist (e.g., RY 023) was used in a series of in vivo and in vitro studies to determine the significance of the alpha5-receptor in the neurobehavioral actions of alcohol.

METHODS

In experiment one, systemic injections of RY 023 (1 to 10 mg/kg IP) dose-dependently reduced ethanol-maintained responding by 52% to 86% of controls, whereas bilateral hippocampal infusions (0.3 to 20 microg) reduced responding by 66% to 84% of controls. Saccharin responding was reduced only with the highest intraperitoneal (e.g., 10 mg) and microinjected (e.g., 20 microg) doses. In experiment two, RY 023 (3.0 to 15 mg/kg IP) reversed the motor-impairing effects of a moderate dose of alcohol (0.75 g/kg) on an oscillating bar task in the absence of intrinsic effects. In the open field, RY 023 (3.0 to 7.5 mg/kg) produced intrinsic effects alone but attenuated the suppression of the 1.25 g/kg ethanol dose. Because the diazepam-insensitive receptors (e.g., alpha4 and alpha6) have been suggested to play a role in alcohol motor impairing and sedative actions, experiment three compared the efficacy of RY 023 with Ro 15-4513 and two prototypical benzodiazepine antagonists (e.g., flumazenil and ZK 93426) across the alpha4beta3gamma2-, alpha5beta3gamma2-, and alpha6beta3gamma2-receptor subtypes in Xenopus oocytes.

RESULTS

RY 023 produced classic inverse agonism at all receptor subtypes, whereas Ro15-4513 and the two antagonists displayed a neutral or agonistic profile at the diazepam-insensitive receptors.

CONCLUSIONS

Overall, the results extend our previous findings by demonstrating that an alpha5-subtype ligand is capable of attenuating not only the rewarding action of alcohol but also its motor impairing and sedative effects. We propose that these actions are mediated in part by the alpha5-receptors of the hippocampus. The hippocampal alpha5-receptors could represent novel targets in understanding the neuromechanisms regulating the neurobehavioral actions of alcohol in humans.

Labor supply and consumption of food in a closed economy under a range of fixed- and random-ratio schedules: tests of unit price

The behavioral economic concept of unit price predicts that consumption and response output (labor supply) are determined by the unit price at which a good is available regardless of the value of the cost and benefit components of the unit price ratio. Experiment 1 assessed 4 pigeons' consumption and response output at a range of unit prices. In one condition, food was available according to a range of fixed-ratio schedules, whereas in the other condition, food was available according to a range of random-ratio schedules. Consistent with unit price predictions, consumption and response output were approximately equivalent across schedule types within the lower range of unit prices. However, at Unit Prices 64 (ratio value = 192) and greater, considerably more consumption and response output were observed in the random-ratio condition. Experiment 2 replicated these findings with 4 pigeons using the rapid demand curve assay procedure that is commonly used in the behavioral economics literature. Findings are integrated with two mathematical models of behavior under variable reinforcer delays.

Adherence Across Behavioral Domains in Treatment Promoting Smoking Cessation Plus Weight Control

The authors tested whether adherence to simultaneous health behavior changes was unitary or domain specific among 76 women who modified smoking, eating, and physical activity to accomplish smoking cessation plus weight control. Random-effects regression analyses showed that adherence to both smoking and diet plans declined linearly and covaried positively; their association tended to grow stronger over time. In contrast, physical activity plan adherence did not change over time and was unrelated to other domains. At the end of treatment, 65%, 30.5%, and 25% adhered well or excellently to smoking, diet, and activity treatments, respectively. Findings support both unitary and domain-specific aspects of adherence and suggest that among smokers, smoking and eating behaviors may have similarities unshared by physical activity.

On the learning curve: the emerging evidence supporting cognitive-behavioral therapies for adolescent substance abuse

AIMS

Cognitive-behavioral therapy (CBT) approaches to intervention for adolescent substance use disorders has been limited and formal controlled clinical efficacy trials have been rare. Moreover, the early literature on the efficacy of CBT for adolescent substance abuse has been characterized by significant methodological limitations. Recent innovations in the treatment of adolescent substance abuse and the recent completion of several randomized clinical trials has brightened the picture with respect to establishing the empirical support for CBT. The aim of this review is to integrate the findings from controlled trials of CBT for adolescent substance abuse.

METHOD

Studies representing randomized clinical trials were reviewed using criteria provided by Lonigan et al. and Nathan & Gorman as a guide.

FINDINGS AND CONCLUSIONS

Despite some prominent differences in design and methodology, the studies reviewed provide consistent empirical evidence that group and individual CBT are associated with significant and clinically meaningful reductions in adolescent substance use. The evidence for the efficacy of group therapy is particularly important, countering the assertion that aggregating problem youths into group treatment settings is associated with iatrogenic effects. The findings from the randomized trials reviewed represent significant developments in treatment outcome research and lay the foundation for validating CBT for adolescent substance use disorders. Future research directions include improving short- and long-term outcomes, enhancing treatment motivation and engagement, and identifying mechanisms and processes associated with positive change, especially for youths with comorbid conditions.

Randomized controlled trial for behavioral smoking and weight control treatment: effect of concurrent versus sequential intervention

The authors compared simultaneous versus sequential approaches to multiple health behavior change in diet, exercise, and cigarette smoking. Female regular smokers (N = 315) randomized to 3 conditions received 16 weeks of behavioral smoking treatment, quit smoking at Week 5, and were followed for 9 months after quit date. Weight management was omitted for control and was added to the 1st 8 weeks for early diet (ED) and the final 8 weeks for late diet (LD). ED lacked lasting effect on weight gain, whereas LD initially lacked but gradually acquired a weight-suppression effect that stabilized (p = .004). Behavioral weight control did not undermine smoking cessation and, when initiated after the smoking quit date, slowed the rate of weight gain, supporting a sequential approach.

Body Mass Index and Alcohol Use

BACKGROUND

Obesity, inactivity and being overweight are leading causes of morbidity and mortality in the United States. The relationship between eating, overeating, and addiction have been discussed, debated and more recently investigated. We have hypothesized that drugs of abuse compete with food for brain reward sites. Overeating and obesity may act as protective factors reducing drug reward and addiction.

METHODS

In the first part of this study, 374 charts of all active weight management patients in a 12-month period were examined. Demographic information, laboratory testing, psychiatric diagnostic interview, alcohol and drug history were reviewed. A detailed alcohol use, abuse, dependence history was present in 298 charts as part of the pre-bariatric evaluation. The relationship between BMI and alcohol use among female patients (n = 298) was then analyzed.

RESULTS

We found a significant (p <.05) inverse relationship between BMI and alcohol consumption. The more obese the patient was, the less alcohol they consumed. The percentage of women who consumed alcohol in the past year decreased as BMI level increased. These results confirmed our surgeons' perception that it is rare to find a morbidly obese patient excluded for bariatric surgery because of excessive alcohol consumption.

CONCLUSIONS

Obese patients have lower rates of alcohol use than found in the general population of women. As BMI increases, lower rates of alcohol consumption are found. Overeating may compete with alcohol for brain reward sites, making alcohol ingestion less reinforcing.

Ethanol-maintained responding of rats is more resistant to change in a context with added non-drug reinforcement

Alternative non-drug reinforcers reliably decrease drug-maintained responding in self-administration procedures. Studies of the resistance to change of food-maintained behavior, however, have found that responding in the presence of a stimulus associated with an alternative reinforcer is more resistant to disruption. This increase in persistence occurs despite lower response rates when the alternative reinforcer is present. The present experiment examined if, in addition to decreasing response rates, an alternative non-drug reinforcer also increases the persistence of drug-maintained responding. Rats self-administered oral ethanol in a multiple schedule of reinforcement in which responding was reinforced in two components signaled by different stimuli. In one component, response-independent food was delivered in addition to the earned ethanol. The effects of the alternative food reinforcer on response rates and resistance to extinction in the two components were examined. As in previous experiments on the resistance to change of food-maintained operant behavior, response rates were lower, but more resistant to extinction in the presence of the stimulus associated with the alternative reinforcer. These findings suggest that all the reinforcers obtained in a context in which drugs are consumed may contribute to the persistence of drug seeking in that context. This increase in persistence may occur even if the alternative reinforcers interfere with drug seeking.

Applying a behavioral economic framework to understanding adolescent smoking

Adolescents' choice to smoke may depend on substitute reinforcers for smoking, complementary activities to smoking, and individual differences in reinforcer value. The influence of these variables on smoking was determined among 983 adolescents. Substitutes were school involvement, academic performance, physical activity, and sports team participation: complements were peer smoking and substance use; delay discounting assessed individual differences in reinforcer value. Latent growth modeling indicated that substitute reinforcers reduced the odds of smoking progression almost two-fold, complementary reinforcers increased the odds by 1.14. and delay discounting indirectly influenced the odds of smoking progression through complementary reinforcers. Adolescents who smoke may have fewer reinforcers that protect against smoking and more reinforcers that promote smoking. Discounting of future rewards affects smoking through reinforcer type.

GABA(A) and opioid receptors of the central nucleus of the amygdala selectively regulate ethanol-maintained behaviors

The present study tested the hypothesis that GABA(A) and opioid receptors within the central nucleus of the amygdala (CeA) regulate ethanol (EtOH), but not sucrose-maintained responding. To accomplish this, betaCCt, a mixed benzodiazepine (BDZ) agonist-antagonist with binding selectivity at the alpha1 subunit-containing GABA(A) receptor, and the nonselective opioid antagonist, naltrexone, were bilaterally infused directly into the CeA of alcohol-preferring rats. The results demonstrated that in HAD-1 and P rat lines, betaCCt (5-60 microg) reduced EtOH-maintained responding by 56-89% of control levels. On day 2, betaCCt (10-40 microg) continued to suppress EtOH maintained responding in HAD-1 rats by as much as 60-85% of control levels. Similarly, naltrexone (0.5-30 microg) reduced EtOH-maintained responding by 56-75% of control levels in P rats. betaCCt and naltrexone exhibited neuroanatomical and reinforcer specificity within the CeA. Specifically, no effects on EtOH-maintained responding were observed following infusion into the caudate putamen (CPu), a locus several millimeters dorsal to the CeA. Additionally, responding maintained by sucrose, when presented concurrently with ethanol (EtOH) or presented alone, was not altered by betaCCt. Naltrexone reduced sucrose-maintained responding only under the 5 microg dose condition when sucrose was presented alone, however, it did not alter sucrose responding when given concurrently with EtOH. These results support the hypothesis that GABA(A) and opioid receptors within the CeA can selectively regulate EtOH-maintained responding. The CeA may represent a novel target site in the development of prototypical GABA(A) and opioidergic receptor ligands, which selectively reduce alcohol abuse in humans.

Central opioid receptors differentially regulate the nalmefene-induced suppression of ethanol- and saccharin-reinforced behaviors in alcohol-preferring (P) rats

The exact opioid-sensitive receptors participating in EtOH-seeking behaviors remains unclear. Previous studies have reported higher densities of micro-opioid receptor binding in the nucleus accumbens (NACC) of P relative to NP rats; however, no differences were seen in delta-receptor binding. In contrast to the NACC, substantially lower levels of micro-receptor binding have been observed in the ventral tegmental area (VTA) of both P and NP rats, albeit no line differences have been observed. In the present study, opioid receptors in the NACC, VTA, and hippocampus were evaluated for their capacity to regulate both EtOH- and saccharin-motivated behaviors in the genetically selected alcohol-preferring (P) rat. To accomplish this, nalmefene, an opiate antagonist with preferential binding affinity for the micro-opioid receptor was unilaterally or bilaterally infused during concurrent availability of 1 h daily EtOH (10% v/v) and saccharin (0.025 or 0.050% w/v) solutions. Rats performed under a two-lever fixed ratio (FR) schedule in which four responses on one lever produced the EtOH solution, and four on a second lever produced the saccharin solution. The results demonstrated that when responding maintained by both EtOH and saccharin are matched at basal levels, unilateral (1-60 microg) or bilateral (0.5-10 microg) microinjections of nalmefene into the NACC produced selective dose-dependent reductions on responding maintained by EtOH. Unilateral (40, 60 microg) and bilateral (10 microg) VTA infusions were also observed to selectively reduced EtOH responding; however, greater nalmefene doses were required and the magnitude of suppression on EtOH responding was markedly less compared with the NACC. The greater sensitivity of nalmefene to suppress EtOH responding in the NACC is likely due to the greater number of opioid receptors in the NACC relative to the VTA. Only bilateral infusion of the 40 microg dose in the NACC and VTA suppressed responding maintained by both EtOH and saccharin. In contrast, intrahippocampal infusions dose dependently suppressed EtOH- and saccharin-maintained responding over a range of doses (1-20 microg). The present study provides evidence that nalmefene suppresses EtOH-motivated behaviors via blockade of opioid receptors within the NACC and VTA, and under various dose conditions both reinforcer and neuroanatomical specificity can be observed.

Sugars: hedonic aspects, neuroregulation, and energy balance

The prevalence of obesity has increased dramatically in recent years in the United States, with similar patterns seen in several other countries. Although there are several potential explanations for this dramatic increase in obesity, dietary influences are a contributing factor. An inverse correlation between dietary sugar intake and body mass index has been reported, suggesting beneficial effects of carbohydrate intake on body mass index. In this review we discuss how sugars interact with regulatory neurochemicals in the brain to affect both energy intake and energy expenditure. These neurochemicals appear to be involved in dietary selection, and sugars and palatable substances affect neurochemical changes in the brain. For example, rats that drink sucrose solutions for 3 wk have major changes in neuronal activity in the limbic area of the brain, a region involved in pleasure and other emotions. We also investigate the relations between sucrose (and other sweet substances), drugs of abuse, and the mesolimbic dopaminergic system. The presence of sucrose in an animal's cage can affect the animals desire to self-administer drugs of abuse. Also, an animal's level of sucrose preference can predict its desire to self-administer cocaine. Such data suggest a relation between sweet taste and drug reward, although the relevance to humans is unclear. Finally, we address the influence of sugar on body weight control. For example, sucrose feeding for 2 wk decreases the efficiency of energy utilization and increases gene expression of uncoupling protein 3 in muscle, suggesting that sucrose may influence uncoupling protein 3 activity and contribute to changes in metabolic efficiency and thus regulation of body weight.

Effects of a non-drug reinforcer, saccharin, on oral self-administration of phencyclidine in male and female rhesus monkeys

RATIONALE

Previous research with male subjects has demonstrated that alternative non-drug reinforcers reduce self-administration of drugs of abuse under a wide variety of conditions. Recent findings indicate sex differences in drug self-administration, and females may be more responsive to the suppressive effects of pharmacological treatment strategies than males; however, it is not known whether or not there are similar sex differences in the effect of behavioral interventions, such as non-drug reinforcers, on drug self-administration.

OBJECTIVES

The goal of this research was to determine whether the suppressive effects of non-drug reinforcers vary as a function of sex using behavioral economic measures in rhesus monkeys.

METHODS

During daily 3-h sessions, seven male and seven female adult rhesus monkeys orally self-administered concurrently available phencyclidine (PCP) and water, PCP and saccharin, or saccharin and water, from two separate spouts, under a series of fixed-ratio (FR) values. The FR value was varied from 4 to 8, 16, 32, 64, and 128, and the demand (consumption x FR) for PCP was measured in order to determine the effect of concurrent access to saccharin (versus water).

RESULTS

The availability of saccharin resulted in reduced PCP self-administration compared with the condition when water was available in both males and females. Consumption of PCP and saccharin was similar between the sexes under the two conditions when water was concurrently available. When saccharin was available with PCP, PCP responses and deliveries were reduced in both sexes at low to intermediate FR values, but the amount of PCP consumed (mg/kg) was reduced significantly more in females than in males only at FR 32.

CONCLUSIONS

. Non-drug reinforcers are an effective treatment for drug abuse in females as well as males over a range of PCP FR values. Males show elevated drug-maintained responding compared with females, but when differential body weights are considered (mg/kg) females consume more than males only under limited schedule parameters.

Relation between choice of ethanol concentration and response rates under progressive- and fixed-ratio schedules: studies with rhesus monkeys

RATIONALE

A fundamental problem in the study of drugs as reinforcers is the evaluation of a drug's relative reinforcing effects and changes in such effects. Relative reinforcing effects can be measured by determining the preference for one drug dose relative to another drug dose. However, in IV drug self-administration studies technical limitations make direct comparisons between drug doses difficult. An alternative procedure is to measure the relative persistence of behavior across increases in schedule size.

OBJECTIVE

To develop a more rapid method to measure the relative persistence of behavior. Instead of increasing the schedule size across sessions, schedule size was increased within sessions by use of a progressive-ratio schedule (PR).

METHODS

Male rhesus monkeys orally self-administered ethanol during daily 3-h sessions. At each concentration responding was measured with fixed-ratio (FR) 8 schedules to obtain baseline values. Subsequently behavior was studied with a PR schedule. Relative persistence of behavior was calculated by dividing the mean response rate under the PR schedule by the mean response rate under the FR8 schedules. To compare these findings with results of choice between concentrations, monkeys were given concurrent access to pairs of ethanol concentrations.

RESULTS

The relative persistence of behavior increased with increases in drug concentration. When two concentrations were concurrently available, the higher concentration maintained higher response rates.

CONCLUSIONS

The relative persistence of behavior can be efficiently measured by dividing the response rate under the PR schedule by the response rate under the FR schedule. Measures of relative persistence corresponded well with measures of choice and show that relative reinforcing effects increase as dose increases.

Smoked heroin in rhesus monkeys: effects of heroin extinction and fluid availability on measures of heroin seeking

The purpose of the present study was to evaluate the reinforcing effects of smoked heroin in nonopioid-dependent nonhuman primates when an alternative reinforcer, sweetened fluid, was made available. Four adult male rhesus monkeys lived in three chambers, with heroin self-administration (0, 0.3, and 0.6 mg/kg) specific to one end of the chamber, oral sweetened fluid self-administration specific to the other end chamber, and no commodity available in the middle chamber. The length of time monkeys spent in the drug-associated chamber provided one measure of drug seeking (i.e., location preference). During self-administration sessions, a second-order schedule of reinforcement was used, with responding during the first component maintained by a brief presentation of the stimuli associated with reinforcement. Responding during the second component was maintained by a delivery of the reinforcer, and the associated stimuli. Responding during the first component provided a second measure of drug seeking. Monkeys also had choice trials each day, when they could choose to work for either commodity. Choice behavior provided a third measure of drug seeking. Each experimental day consisted of a smoking session (four smoking trials), a sweetened fluid session (four fluid trials), and a choice session (four choice trials). Monkeys typically completed all four smoking trials each day when either of the active heroin doses was available. They chose both heroin doses over fluid on 3.5 of the four choice trials, and they had a location preference for the heroin chamber. Under baseline conditions, the number of acquisition responses and the number of consumption responses (inhalations) were greater for the high dose of heroin compared to the low dose of heroin. Further, it took longer to extinguish the responding for the high dose of heroin compared to the low dose of heroin when a vehicle was substituted. During heroin extinction, acquisition responding for fluid increased, the number of fluid choices increased, and location preference shifted to the fluid chamber. These data suggest that in nondependent rhesus monkeys, measures of heroin seeking decreased when heroin was not available and seeking behavior shifted to the available alternative commodity.

Sensitivity of nicotine-containing and de-nicotinized cigarette consumption to alternative non-drug reinforcement: a behavioral economic analysis

A previous report from our laboratory showed similar measures of reinforcing efficacy for nicotine-containing and de-nicotinized cigarettes when each cigarette type was presented alone. The present experiment further compared the reinforcing efficacy of nicotine-containing and de-nicotinized cigarettes by assessing the effects of alternative non-drug reinforcement on self-administration of both cigarette types. Eight human subjects responded on a progressive-ratio schedule in which the number of plunger pulls required for standardized cigarette puffs increased across sessions. Responding for the two types of cigarette was examined when each was available alone and when the concurrent opportunity to earn money was available. Consumption of nicotine-containing and de-nicotinized cigarettes was decreased by both increases in price and by the concurrent availability of money. The two cigarettes types did not differ in their sensitivity to price or alternative non-drug reinforcement. These results replicate our previous report of similar measures of reinforcing efficacy for the two cigarette types when each was presented alone, and extend our previous findings to a choice situation involving an alternative non-drug reinforcer. These data suggest the importance of further examination of non-pharmacological variables in the maintenance of drug taking and the sensitivity of drug taking to alternative non-drug sources of reinforcement. Factors potentially contributing to the maintenance of smoking the de-nicotinized cigarettes (i.e. conditioned reinforcement, primary reinforcement by respiratory stimulation, instructional control, demand characteristics) are also discussed.

Oral drug self-administration: an overview of laboratory animal studies

Many abused drugs can be established as orally delivered reinforcers for rhesus monkeys and other animals. Benzodiazepines, barbiturates, opioids, psychomotor stimulants, dissociative anesthetics, and ethanol can come to serve as reinforcers when taken by mouth. The principal problems in establishing drugs as reinforcers by the oral route of administration are (1) aversive taste, (2) delay in onset of central nervous system effects, and (3) consumption of low volumes of drug solution. Strategies have been devised to successfully overcome these problems, and orally delivered drugs can be established as effective reinforcers. Reinforcing actions are demonstrated by consumption of greater volumes of drug solution than volumes of the water vehicle, and supporting evidence for reinforcing effects consists of the maintenance of behavior under intermittent schedules of reinforcement and the generation of orderly dose-response functions. This article presents an overview of studies of behavior reinforced by oral drug reinforcement. Factors that control oral drug intake include dose, schedule of reinforcement, food restriction, and alternative reinforcers. Many drugs, administered by the experimenter, can alter oral drug reinforcement. Relative reinforcing effects can be assessed by choice procedures and by persistence of behavior across increases in schedule size. In general, reinforcing effects increase directly with dose. Rhesus monkeys prefer combinations of reinforcing drugs to the component drugs. The taste of drug solutions may act as a conditioned reinforcer and a discriminative stimulus. Consequences of drug intake include tolerance and physiological dependence. Findings with orally self-administered drugs are similar to many findings with other positive reinforcers, including intravenously self-administered drugs.

Community reinforcement and family training (CRAFT): engaging unmotivated drug users in treatment

Although motivation for drug abuse treatment is a substantial problem, unilateral intervention through concerned significant others (CSOs) represents a promising method for engaging unmotivated individuals. The Community Reinforcement and Family Training (CRAFT) program, based on principles of reinforcement was developed for this specific purpose. In Phase I, CSOs received the CRAFT intervention, whereby they were taught skills for modifying a loved one's drug-using behavior and for enhancing treatment engagement. CSOs were evaluated at 3 and 6 months. In Phase II, engaged drug users received treatment using the Community Reinforcement Approach (CRA). A total of 62 CSOs participated in this evaluation of the effectiveness of CRAFT. CSOs completed, on average, 87% of offered treatment sessions. During the 6-month study period, 74% succeeded in engaging their resistant loved one in treatment. Reported abstinence both from illicit drugs and alcohol increased significantly for drug users engaged in treatment, but not for unengaged cases. All CSOs showed significant reduction in depression, anxiety, anger, and physical symptoms, with average scores dropping into the normal range on all measures. CRAFT provides a promising alternative to confrontational and detachment approaches in counseling CSOs to help their loved ones.

Three predictions of the economic concept of unit price in a choice context

Economic theory makes three predictions about consumption and response output in a choice situation: (a) When plotted on logarithmic coordinates, total consumption (i.e., summed across concurrent sources of reinforcement) should be a positively decelerating function, and total response output should be a bitonic function of unit price increases; (b) total consumption and response output should be determined by the value of the unit price ratio, independent of its cost and benefit components; and (c) when a reinforcer is available at the same unit price across all sources of reinforcement, consumption should be equal between these sources. These predictions were assessed in human cigarette smokers who earned cigarette puffs in a two-choice situation at a range of unit prices. In some sessions, smokers chose between different amounts of puffs, both available at identical unit prices. Individual subjects' data supported the first two predictions but failed to support the third. Instead, at low unit prices, the relatively larger reinforcer (and larger response requirement) was preferred, whereas at high unit prices, the smaller reinforcer (and smaller response requirement) was preferred. An expansion of unit price is proposed in which handling costs and the discounted value of reinforcers available according to ratio schedules are incorporated.

Ethanol and food pellet self-administration by baboons

During daily 23-h sessions, baboons had concurrent access to food pellets and an oral ethanol/dextrose solution. The effect of increasing the fixed-ratio or "cost" for pellets on pellet and fluid intake was examined when baboons had access to 2%, 4%, or 8% (w/v) ethanol. Increasing the response requirement for a pellet decreased pellet intake. The rate of decrease in pellet intake with increasing pellet cost was unaffected by the availability of ethanol solutions, which were either self-administered or given in investigator-planned doses. Increasing the response cost for pellets significantly increased self-administration of 4% ethanol. The effect of increasing the cost for fluid on fluid and pellet intake was examined when baboons had access to vehicle, 4% or 8% (w/v) ethanol. Although the total daily number of fluid deliveries was significantly greater when 4% ethanol was available, compared to vehicle, increasing the cost for a fluid delivery to 32 responses and above decreased intake of all three fluids similarly. Increasing the cost of ethanol did not affect food intake.

Ratio size and cocaine concentration effects on oral cocaine-reinforced behavior

Monkeys were given a choice between cocaine solutions and water under concurrent fixed-ratio reinforcement schedules. The operant response was spout contact. Six rhesus monkeys served as subjects. The cocaine concentration was varied from 0.0125 to 0.8 mg/ml, and the fixed-ratio value was varied from 8 to 128. Cocaine maintained higher response rates than did water over a wide range of conditions. Response rate and number of cocaine deliveries per session were inverted U-shaped functions of concentration. These functions were shifted to the right as the fixed ratio was increased. The number of cocaine deliveries was more persistent as fixed-ratio value was increased when the unit dose was larger rather than smaller. Cocaine consumption was analyzed as a function of unit price (fixed-ratio value divided by cocaine concentration), and unit price accounted for between 77% and 92% of the variance in cocaine consumption for individual monkeys. The current data support the claim that a drug's reinforcing effects increase directly with dose and underscore the need to gather parametric data when examining the effects of experimental manipulations on a drug-reinforced baseline.

Further analysis of choice between cocaine and food using the unit price model of behavioral economics

Behavioral economics defines unit price (UP) as the ratio of the response requirement to magnitude of reinforcer. When applied to drug self-administration, the UP model defines UP as the ratio of the response requirement to the unit dose of drug. This model makes two predictions about drug self-administration: increasing UP decreases consumption and consumption at a given UP will be constant regardless of the response requirement and dose that make up the UP. In previous experiments conducted in rhesus monkeys allowed to choose between an i.v. injection of cocaine and food, the UP model has failed to adequately predict drug consumption in that consumption varied (increased with dose) at a given UP. However, previous experiments have allowed a fixed number of choice trials/day, thereby imposing a procedural ceiling on consumption that may have influenced conformity to the UP model. In the present experiment, the number of choice trials available was varied in such a way that constant drug consumption was possible over the range of UPs tested. The response requirement for cocaine was varied between 15 and 1200 lever presses/injection and the dose of cocaine was varied between 0.05 and 0.2 mg/kg/inj, yielding UPs from 300 to 5600 responses/mg/kg. The response requirement for food was always 30. As predicted by the UP model, cocaine consumption decreased as UP increased. Moreover, in contrast to previous experiments, consumption did not vary significantly across the response requirement/dose combinations that made up a UP. A detailed analysis suggested that a decrease in magnitude of the alternative reinforcer (one rather than three food pellets), rather than the increase in trials, was responsible for the improved conformity to the UP model in the present experiment relative to previous experiments. Taken together with previous experiments, the present experiment suggests that conformity to the UP model of drug consumption in a choice situation is dependent upon the magnitude of alternative reinforcers that are available. Consumption was best predicted by the UP model when the magnitude of the alternative reinforcer was small.

Combined effects of buprenorphine and a nondrug alternative reinforcer on i.v. cocaine self-administration in rats maintained under FR schedules

Although previous studies have shown that pharmacological agents, such as buprenorphine, and alternative nondrug reinforcers, such as money or sweetened solutions, reduce cocaine self-administration, few studies have examined the combined effects of these two approaches. The purpose of the present study was to evaluate the effects of the opioid partial against buprenorphine (0.1 mg/kg) and concurrent access to either water or a glucose plus saccharin solution (G+S, 3% and 0.125% wt/vol) in rats self-administering intravenous (IV) cocaine (0.4 mg/kg per infusion) under fixed-ratio schedules (FR2, 8 or 32). One group had concurrent access to water and another group had concurrent access to G+S. After 3 consecutive days of stable cocaine self-administration, a single buprenorphine injection (0.1 mg/kg IV) was administered 30 min before the start of the experimental session for 3 consecutive days. To summarize the results, (1) the presence of an alternative non-drug reinforcer significantly reduced cocaine self-administration, (2) buprenorphine selectively decreased cocaine, but not water or G+S, self-administration; (3) the decrease in cocaine infusions by buprenorphine was greatest on the first day of buprenorphine administration; and (4) expressed as a percentage of baseline conditions, the combination of buprenorphine and G+S produced a greater decrease in cocaine self-administration than either buprenorphine or G+S alone. These results indicate that combined treatment with buprenorphine and concurrent access to a sweetened solution is a more effective strategy for reducing cocaine self-administration than either strategy alone.

Normalized demand for drugs and other reinforcers

The concepts of behavioral economics have proven to be useful for understanding the environmental control of overall levels of responding for a variety of commodities, including reinforcement by drug self-administration. These general concepts have implications for the assessment of abuse liability and drug abuse intervention and the formulation of public policy on drug abuse. An essential requirement is the ability to compare the demand for different drugs directly in order to assess relative abuse liability, and to compare demand for the same drug under different environmental and biological interventions to assess their ability to reduce demand. Until now, such comparisons were hampered by the confounding effect of varying drug doses and potencies that prevent quantitative comparisons of demand elasticity--sensitivity of consumption and responding to the constraint of price (effort). In this paper we describe a procedure to normalize demand-curve analysis that permits dose- and potency-independent comparisons of demand across drugs. The procedure is shown to be effective for comparing drug demand within and across the drug classes. The technique permits a quantitative ordering of demand that is consistent with the peak levels of responding maintained by the drugs. The same technique is generalized for the comparison of other types of reinforcers under different biological conditions.

Concurrent self-administration of ethanol and an alternative nondrug reinforcer in monkeys: effects of income (session length) on demand for drug

Eight rhesus monkeys (Macaca mulata) were trained to self-administer orally delivered ethanol (8%) and saccharin (0.03 or 0.3% wt/vol) or water under concurrent fixed-ratio (FR) schedules. The FR requirement for saccharin was fixed at 32, while the FR for ethanol was varied (4, 8, 16, 32, 64 and 128) in a non-systematic order to assess demand for drug. Demand was defined as consumption plotted as a function of price (FR). Income was defined as the duration of access to available resources. Income was varied by allowing access to the concurrently available liquids 20, 60 or 180 min per day. Order of testing was counter-balanced across monkeys. Saccharin deliveries were much higher than ethanol deliveries under the 180-min income condition; however, they were lower than ethanol deliveries when income was reduced to 20 min and the ethanol FR was 4, 8 or 16. Thus, when the price of drug was relatively low, consumption of drug exceeded that of the nondrug reinforcer, and that relationship was reversed as income decreased. Saccharin deliveries sustained a proportionally greater reduction due to decreased income compared to ethanol deliveries. As income decreased from 180 to 20 min, saccharin deliveries were reduced by an average of 79.1% (across ethanol FR conditions) while ethanol deliveries were reduced by an average of 41.2 and 40.8% when concurrent saccharin or water were available, respectively; thus, drug self-administration was more resistant to income changes than saccharin. The demand for ethanol was shifted downward in a parallel fashion as income decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

The behavioral economics of concurrent drug reinforcers: a review and reanalysis of drug self-administration research

In economics, goods can function as substitutes, complements, or be independent of one another. These concepts refer to increases, decreases, or no change in the consumption of one item as the price of a second item increases. This review examined whether these economic terms can be used to describe relationships between concurrently available reinforcers in drug self-administration research. Sixteen drug self-administration studies that examined the effects of concurrent reinforcers were identified through a MEDLINE search. Across these studies, the following substances were employed: caffeinated coffee, cocaine, etonitazene, ethanol, heroin, food, methadone, morphine, nicotine cigarettes, pentobarbital, phencyclidine, sucrose and water. These studies were reanalyzed and the results were shown to be consistent with these economic notions. These analyses also showed that relationships among the concurrently available reinforcers were reliable within and across studies, that concurrently available reinforcers can affect each other asymmetrically, and that the relative price may determine the magnitude of effect for substitutes. These findings suggest that these economic concepts may be useful in characterizing the type and magnitude of interactions between concurrently available reinforcers and may suggest potential mechanisms that determine these relationships.

Effects of concurrent saccharin availability and buprenorphine pretreatment on demand for smoked cocaine base in rhesus monkeys

The effects of saccharin and the opioid partial agonist buprenorphine on cocaine base smoking were evaluated in five male rhesus monkeys. Monkeys completed a sequence of responding consisting of lever-press responses maintained under a fixed-ratio (FR) schedule followed by inhalation responses (FR5) on a smoking spout to gain access to a single delivery of volatilized cocaine base (1.0 mg/kg per delivery). Monkeys could receive a maximum of ten smoke deliveries per session. In the first experiment, either saccharin (0.03% wt/vol) or water was concurrently available under an FR1 schedule through a lip-operated drinking device. As lever FR values increased from 128 to 256, 512, 1024 and 2048, the number of cocaine smoke deliveries decreased. Cocaine intake was not statistically different when water versus saccharin was concurrently available. However, as cocaine consumption decreased, saccharin intake increased demonstrating that under these conditions, saccharin was substituting for cocaine as a reinforcer. On the first day that lidocaine replaced cocaine, all of the monkeys received the maximum number of smoke deliveries (ten) and saccharin intake increased. Lever-press responding gradually extinguished over days when lidocaine (1.0 mg/kg per delivery) was available with concurrent saccharin. In the second experiment, water was concurrently available with cocaine and buprenorphine (0.01 or 0.1 mg/kg) was administered intramuscularly (IM) 30 min before the start of the session. Although pretreatment with the lower dose of buprenorphine (0.01 mg/kg) had little effect on cocaine intake overall, individual differences in cocaine intake occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Unit price as a useful metric in analyzing effects of reinforcer magnitude

In this paper, we applied the behavioral-economic concept of unit price to the study of reinforcer magnitude in an attempt to provide a consistent account of the effects of reinforcer magnitude on behavior. Recent research in the experimental analysis of behavior and in behavioral pharmacology suggests that reinforcer magnitude interacts with the schedule of reinforcement to determine response rate and total consumption. The utility of the unit-price concept thus stems from its ability to quantify this interaction as a cost-benefit ratio (i.e., unit price = characteristics of the schedule of reinforcement divided by magnitude of reinforcement). Research employing the unit-price concept has shown that as unit price increases, a positively decelerating function exists for consumption (i.e., a function with an increasingly negative slope, when plotted on log coordinates) and a bitonic function exists for response rate. Based on these findings, the present analysis applied the unit-price concept to those studies of reinforcer magnitude and drug self-administration that examined the effects of reinforcer magnitude on response rate using simple schedules of reinforcement (e.g., fixed-ratio schedule). This resulted in three findings: (a) Reinforcer-magnitude manipulations and schedule manipulations interact in a manner that can be quantified in terms of unit price as benefit and cost factors, respectively; (b) different reinforcer-magnitude manipulations are functionally interchangeable as benefit factors in the unit-price ratio; and (c) these conclusions appear warranted despite the differences in reinforcers (food or drug), species (dogs, monkeys, or rats), and schedules (interval or ratio), and despite the fact that these studies were not designed for a unit-price analysis. In methodological terms, these results provide further evidence that employing the unit-price concept is a parsimonious method for examining the effects of reinforcer magnitude. In theoretical terms, these results suggest that a single process may underlie the effect of combined reinforcer-magnitude and schedule manipulations.

Behavioral economics: a novel experimental approach to the study of drug dependence

Drug abuse and dependence are among the most important problems facing society today. Understanding the determinants of drug abuse has been advanced by a considerable quantity of research on environmental and pharmacological factors that control drug taking in a variety of settings and species. Behavioral economics, which is the application of economic principles to the behavior of the individual, may have the potential to integrate a number of these empirical observations in a novel quantitative framework. In this paper the utility of behavioral economics for the study of drug dependence is reviewed. Specifically, we reviewed (i) the parsimony behavioral economics affords via the integration of variables, (ii) a ubiquitous behavioral process it has identified, (iii) the precise quantification of that behavioral process and its predictive utility, (iv) a novel independent variable suggested by behavioral economics, and (v) the utility of behavioral economic notions for the process of medication development. We conclude that behavioral economics provides a novel conceptual framework that has utility for the study of drug dependence.