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Gambling Rats: Insight into Impulsive and Addictive Behavior | Neuropsychopharmacology
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If either the 1st or 2nd response sequence during the drug-seeking period is performed incorrectly indicated by dashed lines , no tone is presented, and the animal would have to restart the puzzle from the beginning. Credit: Singer et al. More information: Journal of Neuroscience Conditioned negative reinforcement involves the pairing of a previously neutral stimulus with the aversive stimulus effects of withdrawal or abstinence Table 3.
One approach to the development of animal models that has gained wide acceptance in the research community is that they should have construct validity or predictive validity, in which the model mimics specific signs or symptoms associated with a particular psychopathological condition. Animal models of a complete syndrome of a human psychiatric disorder are unlikely to be possible either conceptually or practically. Certain areas of the human condition are obviously difficult to model in animals, like kleptomania, child abuse, etc.
From a practical standpoint, psychiatric disorders are based on a classification of diseases that is complex and constantly evolving.
Such disorders often have multiple subtypes and diverse etiologies, and many of them are in fact constellations of many different disorders. Any animal model that attempts to reproduce entire syndromes of the human condition would require multiple endpoints, making the practical study of the underlying mechanisms very difficult. The reliance of animal models on a given observable also eliminates a fundamental problem associated with animal models of human psychopathology — the frustration of attempting to provide complete validation of an entire syndrome. More definitive information related to a specific domain of addiction can be generated, thus increasing the confidence of cross-species validity.
This framework also leads to a more pragmatic approach to the study of the neurobiological mechanisms of the behavior in question. Further on in the section, however, these observables are linked to the actual criteria for addiction in the Diagnostic and Statistical Manual of Mental Disorders, 4th edition DSM IV , and human clinical laboratory models of addiction.
The particular behavioral parameter being assessed in an animal model may or may not be a particular symptom of the disorder, but it still must be defined objectively and observed reliably. The behavior being analyzed may actually be found in both pathological and nonpathological states but still have predictive validity.
A good example of such a situation is the widespread, and sometimes misguided, use of drug reinforcement or reward as a definitive animal model of addiction. Drug reinforcement does not necessarily lead to addiction. Take, for instance, a social drinker who does not develop alcoholism. What is Addiction? Animal models of substance use have made a significant contribution to our understanding of drug addiction. Modeling gambling processes in non-human subjects could likewise facilitate our understanding of the drive to gamble, and stimulate the development of pharmacotherapies.
Clinically, one of the most common tests of gambling-related decision-making is the Iowa Gambling Task IGT , in which subjects choose from four decks of cards to win money or points Bechara et al, Two of the decks are associated with bigger immediate rewards but disproportionately large losses. The correct approach is therefore to favour decks which deliver smaller amounts but also lower penalties, thereby leading to greater long-term gain.
Animal Models for Examining Social Influences on Drug Addiction, Volume 140
Using the IGT as a template, novel rodent models of gambling behaviour have been developed in which rats play against the clock to earn as many sugar pellets as possible by sampling between four different options. The amount of reward available on each option varies in size 1—4 pellets.
The reinforcement schedules are fixed such that the larger pellet options are associated with a greater frequency or duration of time-outs, decreasing their net worth. Rats must therefore learn to avoid risky options associated with larger rewards, analogous to the optimal strategy on the IGT.
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Furthermore, such choice behaviour can be modulated by drugs which target the serotonin and dopamine systems, with a D 2 receptor antagonist enhancing performance, while amphetamine and a serotonin 1A receptor agonist impair choice Zeeb et al, Human and animal studies indicate that highly impulsive individuals, particularly those showing elevated levels of motor impulsivity, are more vulnerable to both cocaine dependency and PG Verdejo-Garcia et al, Whether this form of impulsivity represents an endophenotype for chemical and behavioural addictions remains an interesting hypothesis now open to empirical verification.
Demonstrating that rodents can engage in a decision-making process reminiscent of gambling, and that such decision-making can be pharmacologically modified, is certainly a step forward. As with research into substance abuse, however, it will be important to dissociate the act of performing a potentially-addictive behaviour and actually exhibiting symptoms of dependence.
Some of the DSM-IV criteria for drug dependency have been translated into behavioural measurements applied to rats self-administering cocaine, theoretically demarcating dependent subjects Belin et al, A future challenge for the field will be to create a similar standard for gambling models to help identify subjects exhibiting a PG-like phenotype.