Conditioned taste aversion learning: implications for animal models of drug abuse

Drugs of abuse are typically discussed in terms of their rewarding effects and how these effects mediate drug taking. However, these drugs produce aversive effects that could have an important role in the overall acceptability of a drug and its likelihood of being self-administered. Rewarding and aversive effects, then, could be interpreted as separate behavioral effects, with the balance of the two determining overall drug acceptability. Interestingly, the role of aversive effects on drug acceptability in the self-administration preparation has received limited attention in this context. This chapter examines the aversive effects of drugs and discusses their role in drug taking. If these aversive effects serve a protective function, manipulations that alter or decrease these effects could have implications for drug taking. Several factors have been reported to alter conditioned taste aversion (CTA) learning, a preparation used in the assessment of the aversive effects of drugs in general. Two of these factors, drug history and strain, are reviewed here. By reviewing these, we intend to demonstrate the protective nature of aversive effects in the initiation and escalation of drug taking and to provide evidence that reductions in aversive effects could produce changes in patterns of drug self-administration that could lead to an increased vulnerability to abuse drugs by altering the reward-aversion balance. The aim of this chapter is not to question the importance of rewarding effects in self-administration but rather to provide evidence that aversive effects are an important factor that needs to be considered in discussions of drug-taking behavior.

MK-801 prevents the increased NMDA-NR1 and NR2B subunits mRNA expression observed in the hippocampus of rats tolerant to diazepam

The chronic diazepam administration in rats has been show from our previous results, to produce an increased synaptic plasticity. Furthermore, this occurs with a concomitant over expression of the mRNA NR1 and NR2B N-methyl-D-aspartate receptor subunits. MK-801, a non-competitive antagonist of N-methyl-D-aspartate receptor, impairs both the development of conditioned tolerance to diazepam and the hippocampal long-term potentiation generation. In the present study, we have further investigated the hippocampal glutamatergic transmission in the development of tolerance to diazepam. Our results demonstrate that the development of tolerance to the hypolocomotive effect of diazepam, along with the increased hippocampal synaptic plasticity and the associated over expression of the mRNA NR1 and NR2B N-methyl-D-aspartate receptor subunits, were blocked by previous MK-801 administration. We suggest that the participation of hippocampal glutamatergic transmission is relevant to increased hippocampal synaptic plasticity, the latter being a neurobiological mechanism behind the development of the conditioned tolerance to diazepam.

Adolescent substance use disorders and comorbidity

It is imperative to know what risk factors are more likely to appear during specific developmental stages so that identification and interventions can be used to decrease the risk for future SUD. Continued surveying of risk factors that can occur at any stage in childhood are important to ensure that other risk factors are anticipated and intervened upon as well. Multiple risk factors increase the magnitude of the risk for SUD, and therefore all risk factors should be detected to convert these to protective factors. Screening instruments that can assess risk factors found to increase the risk for substance abuse can be found in examples, such as the Drug Usage Screening Instrument [81] and the Problem-Oriented Screening Instrument for Teenagers. The detection of risk factors by primary care providers is becoming increasingly important. However, other professionals are beginning to recognize that early recognition and treatment can enable a youth to go on to a productive life in other arenas as well. Drug courts and diversion programs are beginning to treat first-time offenders and their families rather than taking the punitive approach. These have proven to be very successful. Primary care physicians also should become familiar with motivational enhancement therapy when confronting a youth with a suspected substance abuse problem [57]. This method has proven to be more effective in getting youth into treatment than the direct, confrontational style, which often puts the youth in a defensive mode. Motivational enhancement therapy includes interventions that are delivered in a neutral and empathetic way. The six components of motivational enhancement therapy (also called FRAMES) include: Feedback on personal impairment Emphasis on personal responsibility Clear advice to change Menu of alternative options Empathy as a counseling style Self-efficacy In this way, a clinician can elicit pros and cons, give advice, provide choices, practice empathy, clarify goals, and remove barriers. This technique allows youth to be less defensive and more proactive. Monti et al. [59] have demonstrated that this technique has been useful in getting youth into treatment. Primary care physicians can use instruments that will assess the possibility of both externalizing (e.g., ADHD) and internalizing (e.g., depression and anxiety) disorders. Examples of this type of instrument are the Auchenbach child behavior checklist, teacher report form, and youth self-report form, which survey symptoms for these disorders [1]. Social anxiety disorder can be detected by asking whether the prelatency child went into new situations willingly and tended to hang back or whether the child had difficulty separating from his or her parents. Other questions to ask are whether the child tended to isolate or was fearful of speaking in front of the class. Of course, any bruising or behavior that suggests exposure to adult-related sexual acts may cause concern for physical or sexual abuse and possible PTSD. However, interest in sex earlier than expected for the age of the child may also indicate the possibility of bipolar disorder. These children have many symptoms of ADHD with a high degree of irritability and may seem boastful or grandiose. They may be "daredevils" with no fear of dangerous consequences. Referral to a specialist is necessary to evaluate these children further. Because substance use at age 14 or 15 years can be predicted by academic and social behavior at ages 7 to 9 years, early detection of poor social skills and learning difficulties is essential [43]. Learning disorders can be uncovered by asking the school to do an evaluation. However, schools having economic problems may not be able to accommodate all requests. A parent may have to pay a private provider to complete this workup because insurance companies seldom pay for educational testing. Learning disorders may go undetected because many school systems opt to use a higher deviation from the full-scale IQ to detect learning problems. For instance, if a student has an IQ of 115, the standard nationally recommended deviation from this IQ to detect a learning disorder is 15. Therefore, any child who scores 100 or less on an achievement test should be considered to have a learning disorder. Some schools prefer to use a deviation of up to 23 so that learning disorders are not detected. Few schools screen for processing problems, including auditory and visual motor processing problems, processing speed, comprehension, and short-term and long-term memory problems. This is extremely important because ADHD can be confused with an auditory processing problem. Stimulants may help this condition, but accommodations must be made to ensure continued success. Early-intervention programs, such as Drug Abuse Resistance Education (DARE), proved to be ineffective because the programs did not target components that have been shown to predict future drug use [54]. One program that has targeted these components, normative beliefs, lifestyle-behavior incongruence, and commitment is the All Stars program [39,40]. A strong initial dosage with booster interventions for at least 2 years is also important [10]. Before a child is diagnosed with oppositional defiant disorder or conduct disorder, every effort should be made to detect any underlying psychiatric disorder that has not been treated and therefore may look like a conduct disorder (e.g., bipolar disorder). Proper psychopharmacologic interventions should be made for psychiatric disorders. If one drug has been ineffective, another untreated psychiatric disorder may be present, and it is always important to tease out what remaining symptoms are present after a therapeutic trial has been tried. It is important to form a team approach so that all risk factors can be approached. Members of the team often include a primary care physician, a child psychologist, the parents, the patient, a teacher, a school counselor, a child psychiatrist, and sometimes a pediatric neurologist. No one member of the treatment team can provide all of the necessary services to prevent the future risk for substance abuse.

Chronic morphine treatment exaggerates the suppressive effects of sucrose and cocaine, but not lithium chloride, on saccharin intake in Sprague-Dawley rats

Three experiments examined the effect of chronic morphine treatment on cocaine-, sucrose-, and lithium chloride (LiCl)-induced suppression of saccharin intake in Sprague-Dawley rats. All rats were either water- or food-deprived and then implanted subcutaneously with 1 morphine (75 mg) or vehicle pellet for 5 days. They were then given brief access to 0.15% saccharin and soon thereafter injected with either cocaine (10 mg/kg s.c.), LiCl (0.009 M, 1.33 ml/100 g body weight i.p.), or saline, or, in Experiment 2, given a 2nd access period to either a preferred 1.0 M sucrose solution or the same 0.15% saccharin solution. There was 1 taste-drug or taste-taste pairing per day for a number of days. The results showed that a history of chronic morphine treatment exaggerated the suppressive effects of a rewarding sucrose solution and cocaine but not those of the aversive agent, LiCl. These data provide further support for the reward comparison hypothesis.

The suppressive effects of sucrose and cocaine, but not lithium chloride, are greater in Lewis than in Fischer rats: evidence for the reward comparison hypothesis

Rats suppress intake of a saccharin conditioned stimulus (CS) when it is paired with an aversive unconditioned stimulus (US), an appetitive US, or a drug of abuse such as morphine or cocaine. It is unclear, however, whether the reduction in intake induced by these drugs is mediated by their aversive or their rewarding properties. The present set of experiments addressed this question by comparing the suppressive effects of a known aversive US (LiCl), a known reinforcing US (sucrose), and a drug of abuse (cocaine) in two strains of rats (i.e., Lewis and Fischer 344 rats) that differ in their preference for rewarding stimuli. The results show that, although both strains readily acquired a LiCl-induced conditioned taste aversion (CTA), the suppressive effects of sucrose and cocaine were robust in the drug-preferring Lewis rats and absent in the Fischer rats. These data argue against a CTA account and in favor of the reward comparison hypothesis.

Activating properties of cocaine and cocaethylene in a behavioral preparation of Drosophila melanogaster

The use of Drosophila as a model to study the behavioral consequences of stimulant drugs was analyzed in an active preparation of decapitated Drosophila. Application of cocaine and cocaethylene to discrete nerve cord cells regulating motor programs of behavior produced striking patterns of behavioral activity in a concentration-related manner. In general, intense circling behavior and significant wing buzzing activity were distinguishable behavioral markers in flies treated with mM concentrations of cocaine or cocaethylene. The significant changes in motor behavior induced by stimulant drugs in decapitated flies were not reproduced by the application of apomorphine, a direct dopamine (DA) agonist, or octopamine, a naturally occurring transmitter in arthropods. Because both cocaine and cocaethylene interfere with DA reuptake in mammals, we characterized the role of DA receptors mediating increased stereotypy and motor behavior in flies. Coadministration of SCH-23390, a specific D1 receptor antagonist, significantly attenuated the behavior-activating properties of cocaine and cocaethylene in this active experimental preparation. Therefore, the receptor protein mediating the behavioral responses to stimulant drugs in Drosophila is pharmacologically similar to the mammalian D1 subtype. In rats, cocaine- and cocaethylene-induced behavioral activity is complex, with increasing evidence that the D1 receptor interacts significantly with N-methyl-D-aspartate (NMDA) receptor pathways to produce an altered behavioral phenotype. To further characterize additional receptor subtypes targeted by the actions of cocaine and cocaethylene, we pretreated flies with MK-801 and dextromethorphan. Both of these drugs are potent, selective noncompetitive NMDA receptor antagonists. Interestingly, MK-801 and dextromethorphan profoundly reduced the behavior-activating properties of cocaine and cocaethylene in Drosophila. Therefore, as in rats, the NMDA (and D1) receptor pathways in this arthropod represent obligatory targets for the behavioral effects of stimulant drugs.