Orbitofrontal or accumbens dopamine depletion does not affect risk-based decision making in rats

Abstract

Considerable evidence has implicated dopamine (DA) signals in target regions of midbrain DA neurons such as the medial prefrontal cortex or the core region of the nucleus accumbens in controlling risk-based decision-making. However, to date little is known about the contribution of DA in the orbitofrontal cortex (OFC) and the medial shell region of the nucleus accumbens (AcbS) to risk-based decision-making. Here we examined in rats the effects of 6-hydroxydopamine-induced DA depletions of the OFC and AcbS on risky choice using an instrumental two-lever choice task that requires the assessment of fixed within-session reward probabilities that were shifted across subsequent sessions, i.e., rats had to choose between two levers, a small/ certain lever that delivered one certain food reward (one pellet at p = 1) and a large/risky lever that delivered a larger uncertain food reward with decreasing probabilities across subsequent sessions (four pellets at p = 0. 75, 0.5, 0.25, 0.125, 0.0625). Results show that systemic administration of amphetamine or cocaine increased the preference for the large/risky lever. Results further demonstrate that, like sham controls, rats with OFC or AcbS DA depletion were sensitive to changes in probabilities for obtaining the large/risky reward across sessions and displayed probabilistic discounting. These findings point to the view that the basal capacity to evaluate the magnitude and likelihood of rewards associated with alternative courses of action as well as long-term changes of reward probabilities does not rely on DA input to the AcbS or OFC.

Foraging with the frontal cortex: A cross-species evaluation of reward-guided behavior

“…Similar to effort-and delay-discounting paradigms, the preferred, larger reward is associated with at-first equal probability of 100%, but then decreasing probabilities of reward through subsequent blocks of trials. Such probabilistic discounting assays have been utilized to explore dissociations within rodent frontal cortex in risk, concluding that PL, but not OFC, is involved in probabilistic discounting [92,93], with dopamine in OFC similarly not involved in this kind of decision making in rats [94].…”

Enhanced Risky Choice in Male Rats Elicited by the Acute Pharmacological Stressor Yohimbine Involves Prefrontal Dopamine D1 Receptor Activation

“…In Experiment 1, we analyzed the effects of yohimbine and corticosterone on risk-based decision-making in rats after single or combined systemic administration. To this end, we used a risk discounting task in which rats had to choose between a certain/small reward lever that always delivered 1 pellet and a risky/large reward lever that delivered 4 pellets with a decreasing probability in subsequent trials ( Cardinal and Howes, 2005 ; St Onge and Floresco, 2009 ; Mai and Hauber, 2012 , 2015 ). In view of evidence that NA activity alone or in concert with glucocorticoids mediates stressor effects on cognitive function ( van Stegeren et al, 2007 ; Schwabe et al, 2010 ), we hypothesized that yohimbine would enhance risky choice, an effect that could be further augmented by co-administration of corticosterone.…”