Determinants of Choice in Animal Models of Gambling

Gambling Disorder is a debilitating mental illness that can cause significant harm. Rodent models of gambling behaviour have been developed in order to probe the neural mechanisms underlying maladaptive patterns of risk-based choice. The effects of changes in the dopamine neurotransmitter system have been heavily investigated using these models, due to observed phenotypic similarity with substance use disorders. It is necessary however, to first understand how rats unaffected by prior pharmacological or neurological manipulation make choices in these tasks. The aim of this thesis is to determine the relative importance of different behavioural and learning variables in the development and expression of suboptimal choice behaviour in rats, and to provide preliminary data regarding the role of dopaminergic signalling in these behaviours. Investigations with the rodent Iowa Gambling Task revealed a consistent insensitivity to the timeout punishments that serve as a defining feature of this task, with systemic administration of d-amphetamine at doses of 1-1.5mg/kg shown to increase choice of a larger but less frequent reward, independent of the presence or absence of delay punishments. Using a protocol derived from experiments previously conducted in pigeons, rats were shown to produce suboptimal choice behaviour without prior pharmacological intervention. Systemic amphetamine prior to choice in this task was found to cause a similar increase in risky choice in a subset of these animals, with doses of 1-1.5mg/kg increasing preference for a choice option that provided larger but less frequent reward. Using a task design with increasing response requirements to earn reward, rats were shown to exhibit a greater response rate when given the opportunity to earn a large probabilistic reward, relative to when reward magnitude was consistent. Amphetamine was not observed to impact performance in these animals, but did produce an increase in response rates in those rats not experiencing the large probabilistic reward. These results suggest the effect of dopaminergic manipulations likely depend on the manner in which rats learn and express choice behaviour across these different models, where amphetamine treatment may act to shift the balance of behavioural control between available response strategies