Objective: Investigating the effect of chronic administration of the dopamine D_2/3 agonist ropinirole on a cued model of gambling behaviour in rats. 

Background: Dopamine D_2/3 agonists are successfully used to treat the motor symptoms of Parkinson’s Disease (PD), either as adjunct to L-DOPA, or as stand alone treatments. However, these dopamine agonists may lead to impulse control disorders (ICD) including pathological gambling in some patients. We have previously observed that chronic ropinirole increased choice of uncertain options on the rat Betting Task (rBT), a paradigm that captures aspects of risk aversion. In contrast, ropinirole transiently increased premature responses, a measure of motor impulsivity observed in models of addiction, without influencing choice on the rat Gambling Task (rGT). The rGT is a rodent analogue of the Iowa Gambling Task used clinically to assess decision making under risk in which rats choose between four options, each associated with differing probabilities of reward and punishment. Repeated exposure to cues that predict reward with maximal uncertainty may sensitize the dopamine system and predispose subjects to addiction disorders such as gambling. Although win-associated stimuli are salient in casinos, they are not featured on the original version of the rGT, which may explain the lack of effect of ropinirole on choice in the uncued task. We therefore tested if chronic ropinirole would increase choice of risky options on a cued version of the rGT. Win-associated cues were previously shown to increase rats’ preference for the riskier options on this task. 

Methods: Subjects were 40 male rats performing the cued rGT and implanted with an osmotic pump delivering either ropinirole (5mg/kg/day) or saline for 28 days. 

Results: Ropinirole led to a larger and more long-lasting increase in premature responses on the cued rGT with no effect on choice, consistent with results on the original rGT.

Conclusions: Together with other data, our results suggest that the rGT and the rBT may model decision-making deficits linked to different disorders. Chronic ropinirole increases preference for uncertainty on the rBT, potentially akin to problem gambling behaviour, whereas this drug increases impulsivity on the rGT, which may represent an endophenotype for impulse control disorders or drug addiction. 

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MDS Abstracts - https://www.mdsabstracts.org/abstract/adding-cues-to-a-rat-gambling-task-potentiates-the-increase-in-premature-responding-in-response-to-chronic-d23-agonist-ropinirole-without-mitigating-preference-for-risk/