Nucleus accumbens D2/3 receptors predict trait impulsivity and cocaine reinforcement

Medication-related impulse control and repetitive behaviors in Parkinson??s disease

PURPOSE OF REVIEW

A range of impulse control and repetitive behaviors presumed to be related to dopaminergic medications has been recognized in Parkinson's disease. These behaviors are linked by their incentive or reward-based and repetitive natures and overlap with addictions. The behaviors include pathological gambling, hypersexuality, compulsive shopping, and compulsive eating and are related to punding and compulsive medication use. In patients on dopamine agonists, these behaviors as a group are relatively common, can have potentially devastating psychosocial consequences and are commonly hidden.

RECENT FINDINGS

Recent studies have investigated prevalence rates and associated factors. The literature on these behaviors in Parkinson's disease, including definitions, epidemiology, pathophysiology and management, is reviewed. The relationship to medications, Parkinson's disease and individual susceptibility is examined.

SUMMARY

These behaviors can affect up to 14% of Parkinson's disease patients on dopamine agonists. Clinicians should warn patients prior to initiating dopamine agonists and enquire about these behaviors during follow up.

Neurobiology of addiction. An integrative review

Evidence that psychoactive substance use disorders, bulimia nervosa, pathological gambling, and sexual addiction share an underlying biopsychological process is summarized. Definitions are offered for addiction and addictive process, the latter being the proposed designation for the underlying biopsychological process that addictive disorders are hypothesized to share. The addictive process is introduced as an interaction of impairments in three functional systems: motivation-reward, affect regulation, and behavioral inhibition. An integrative review of the literature that addresses the neurobiology of addiction is then presented, organized according to the three functional systems that constitute the addictive process. The review is directed toward identifying candidate neurochemical substrates for the impairments in motivation-reward, affect regulation, and behavioral inhibition that could contribute to an addictive process.

The neurobiology and genetics of impulse control disorders: relationships to drug addictions

Impulse control disorders (ICDs), including pathological gambling, trichotillomania, kleptomania and others, have been conceptualized to lie along an impulsive-compulsive spectrum. Recent data have suggested that these disorders may be considered addictions. Here, we review the genetic and neuropathological bases of the impulse control disorders and consider the disorders within these non-mutually exclusive frameworks.

Isolated Flinders Sensitive Line rats have decreased dopamine D2 receptor mRNA

Social isolation has profound effects on animal behavior and dopamine systems. We investigated the effect of social isolation on the dopamine receptor and neuropeptide mRNAs in the brain reward system in an animal model of depression, the Flinders Sensitive Line rats and Sprague-Dawley controls. We demonstrate that socially isolated but not group housed Flinders sensitive line rats had lower dopamine D2 receptor mRNA levels compared with Sprague-Dawley rats. Isolated and group housed Flinders Sensitive Line rats had higher levels of dopamine D1 receptor and substance P and enkephalin but not dynorphin mRNAs when compared with Sprague-Dawley rats. Our findings of decreased dopamine D2 receptor levels in socially isolated Flinders Sensitive Line rats suggest that low D2 receptor expression may play a role in pathophysiology of depression.

Impulsive personality predicts dopamine-dependent changes in frontostriatal activity during component processes of working memory

Dopaminergic drugs affect a variety of cognitive processes, but the direction and extent of effects vary across individuals and tasks. Paradoxical effects are observed, by which the same drug causes cognitive enhancing as well as adverse effects. Here, we demonstrate that individual differences in impulsive personality account for the contrasting effects of dopaminergic drugs on working memory and associated frontostriatal activity. We observed that the dopamine D2 receptor agonist bromocriptine improved the flexible updating (switching) of relevant information in working memory in high-impulsive subjects, but not in low-impulsive subjects. These behavioral effects in high-impulsive subjects accompanied dissociable effects on frontostriatal activity. Bromocriptine modulated the striatum during switching but not during distraction from relevant information in working memory. Conversely, the lateral frontal cortex was modulated by bromocriptine during distraction but not during switching. The present results provide a key link between dopamine D2 receptor function, impulsivity, and frontostriatal activity during component processes of working memory.