Effects of d-amphetamine on risk choice in rats depend on the manner in which the expected reward value is varied

Methamphetamine increases risky choice in rats, but only when magnitude and probability of reinforcement are manipulated within a session

Risky choice is associated with maladaptive behaviors, particularly substance use disorders. Current animal models of risky choice are often confounded by other constructs like behavioral flexibility and suboptimal choice. The purpose of the current experiment was to determine if the psychostimulant methamphetamine, a drug whose popularity has increased in recent years, increases risky choice in an equivalent expected value (EEV) task. In the EEV task, rats are given a choice between two reinforcer alternatives that differ in magnitude and probability of delivery, but have equivalent expected value. Forty-eight Sprague Dawley rats were tested in three versions of the EEV task. In the first version of the EEV task, both reinforcer magnitude and probability were adjusted across blocks of trials for both alternatives. In the second and the third versions of the EEV task, reinforcer magnitude was held constant across each block of trials (either 1 vs. 2 pellets or 4 vs. 5 pellets). We found that male rats preferred the "riskier" option, except when reinforcer magnitudes were held constant at 4 and 5 pellets across each block of trials. Methamphetamine (0.5 mg/kg) increased preference for the risky option in both males and females, but only when both reinforcer magnitude and probability were manipulated across blocks of trials for each alternative. The current results demonstrate that both magnitude of reinforcement and probability of reinforcement interact to influence risky choice. Overall, this study provides additional support for using reinforcers with expected value to measure risky choice.

Effects of methamphetamine on probability discounting in rats using concurrent chains

How stimulant drugs affect risky choice and the role of reinforcement magnitude has been an important question for research on impulsivity. This study investigated rats' responding on a rapid acquisition, concurrent chains, probability discounting task under methamphetamine administration. In each block of four sessions, probability of reinforcement delivery was unequal (0.5/1.0, 1.0/0.5) or equal, (1.0/1.0, 0.5/0.5) while amount of reinforcement was constant and unequal. This allowed for an estimate of probability discounting and the magnitude effect (where larger reinforcers are discounted at a greater rate) in each block. Baseline, acute and chronic methamphetamine administration, and re-establish baseline phases were completed. Rats showed sensitivity to probability and magnitude in baseline, as well as a magnitude effect whereby preference for the larger reinforcement was greater with 100% than 50% reinforcement probability. Acute methamphetamine dose-dependently reduced the probability effect. There were no effects of chronic administration and only probability discounting was maintained in the re-establish baseline phase. This was the first procedure to find a magnitude effect with rats in a probability discounting procedure and demonstrates that acute methamphetamine reduces both the probability and magnitude effects which increases propensity for risky choice.

Dopamine receptors regulate preference between high-effort and high-risk rewards

RATIONALE

Optimal decision-making necessitates evaluation of multiple rewards that are each offset by distinct costs, such as high effort requirement or high risk of failure. The neurotransmitter dopamine is fundamental toward these cost-benefit analyses, and D1-like and D2-like dopamine receptors differently modulate the reward-discounting effects of both effort and risk. However, measuring the role of dopamine in regulating decision-making between options associated with distinct costs exceeds the scope of traditional rodent economic decision-making paradigms.

OBJECTIVES

We developed the effort vs probability economic conflict task (EvP) to model multimodal economic decision-making in rats. This task measures choice between two rewards of uniform magnitude associated with either a high effort requirement or risk of reward omission. We then tested the modulatory effects of systemic cocaine and D1/D2 blockade or activation on the preference between high-effort and high-risk alternatives.

METHODS

In the EvP, two reinforcers of equal magnitude are associated with either (1) an effort requirement that increases throughout the session (1, 5, 10, and 20 lever presses), or (2) a low probability of reward receipt (25% of probabilistic choices). Critically, the reinforcer for each choice is comparable (one pellet), which eliminates the influence of magnitude discrimination on the decision-making process. After establishing the task, the dopamine transporter blocker cocaine and D1/D2 antagonists and agonists were administered prior to EvP performance.

RESULTS

Preference shifted away from either effortful or probabilistic choice when either option became more costly, and this preference was highly variable between subjects and stable over time. Cocaine, D1 activation, and D2 blockade produced limited, dose-dependent shifts in choice preference contingent on high or low effort conditions. In contrast, D2 activation across multiple doses evoked a robust shift from effortful to risky choice that was evident even when clearly disadvantageous.

CONCLUSIONS

The EvP clearly demonstrates that rats can evaluate distinct effortful or risky costs associated with rewards of comparable magnitude, and shift preference away from either option with increasing cost. This preference is more tightly linked to D2 than D1 receptor manipulation, suggesting D2-like receptors as a possible therapeutic target for maladaptive biases toward risk-taking over effort.

Risk-Based Decision Making: A Systematic Scoping Review of Animal Models and a Pilot Study on the Effects of Sleep Deprivation in Rats

Animals, including humans, frequently make decisions involving risk or uncertainty. Different strategies in these decisions can be advantageous depending the circumstances. Short sleep duration seems to be associated with more risky decisions in humans. Animal models for risk-based decision making can increase mechanistic understanding, but very little data is available concerning the effects of sleep. We combined primary- and meta-research to explore the relationship between sleep and risk-based decision making in animals. Our first objective was to create an overview of the available animal models for risky decision making. We performed a systematic scoping review. Our searches in Pubmed and Psychinfo retrieved 712 references, of which 235 were included. Animal models for risk-based decision making have been described for rodents, non-human primates, birds, pigs and honey-bees. We discuss task designs and model validity. Our second objective was to apply this knowledge and perform a pilot study on the effect of sleep deprivation. We trained and tested male Wistar rats on a probability discounting task; a “safe” lever always resulted in 1 reward, a “risky” lever resulted in 4 or no rewards. Rats adapted their preferences to variations in reward probabilities (p < 0.001), but 12 h of sleep deprivation during the light phase did not clearly alter risk preference (p = 0.21).

Neurobiological changes in striatal glutamate are associated with trait impulsivity of differential reinforcement of low-rate-response behavior in male rats

Impulsive action can be measured using rat's responses on a differential reinforcement of low-rate-response (DRL) task in which performance may be varied between rats. Nevertheless, neurobiological profiles underlying the trait impulsivity of DRL behavior remain largely unknown. Here, in vivo non-invasive proton magnetic resonance spectroscopy (¹H-MRS) and Western blot assay were performed to assess neurobiological changes in the dorsal striatum (DS) and nucleus accumbens (NAc) in relation to individual differences in DRL behavior. A cohort of rats was subjected to acquire a DRL task over 14 daily sessions. High impulsive (HI) and low impulsive (LI) rats were screened by behavioral measures displaying a lower response efficiency and performing more nonreinforced responses in HI rats and vice versa. MRS measurements indicated that the HI group had a lower NAc glutamate (Glu) level than did the LI group, whereas no such difference was found in the other five metabolites in this area. Moreover, no intergroup difference was observed in any metabolite in the DS. The results of Western blot assay revealed that protein expressions of GluN1 (but not GluN2B) subunit of N-methyl-D-aspartate receptors in the DS and NAc were higher in the HI group than in the LI group. This inherent timing impulsivity was not attributed to risky behavioral propensity because both Hl and LI rats could acquire a risk-dependent choice. The findings of this study, supported by certain correlations among behavioral, brain imaging, and neuroreceptor indices, provide evidence of the neurobiological changes of striatal Glu underlying trait impulsive action of DRL behavior.

Challenges and Opportunities in Animal Models of Gambling-like Behavior

In the past several years, there has been an explosion of interest in animal models of risk-based decision-making, a fundamental process associated with gambling disorder. While early work focused on establishing various tasks for assaying decision-making, current studies are determining the (subtle and not-so-subtle) influence of cues in driving risky decisions to better understand problem gambling. In addition, these decision-making paradigms are now being used to investigate comorbid conditions such as substance dependence or brain injury and replicating observations from human patients. These animal models have now developed to a point where therapeutic interventions may be assessed for not just gambling disorder, but also a number of other conditions which engender risky decision-making.

Examining the neurochemical underpinnings of animal models of risky choice: Methodological and analytic considerations

Because risky choice is associated with several psychiatric conditions, recent research has focused on examining the underlying neurochemical processes that control risk-based decision-making. Not surprisingly, several tasks have been developed to study the neural mechanisms involved in risky choice. The current review will briefly discuss the major tasks used to measure risky choice and will summarize the contribution of several major neurotransmitter systems to this behavior. To date, the most common measures of risky choice are the probability discounting task, the risky decision task, and the rat gambling task. Across these three tasks, the contribution of the dopaminergic system has been most studied, although the effects of serotonergic, adrenergic, cholinergic, and glutamatergic ligands will be discussed. Drug effects across these tasks have been inconsistent, which makes determining the precise role of neurotransmitter systems in risky choice somewhat difficult. Furthermore, procedural differences can modulate drug effects in these procedures, and the way data are analyzed can alter the interpretations one makes concerning pharmacological manipulations. By taking these methodological/analytic considerations into account, we may better elucidate the neurochemistry of risky decision-making. (PsycINFO Database Record (c) 2019 APA, all rights reserved).