Opioidergic and dopaminergic manipulation of gambling tendencies: a preliminary study in male recreational gamblers

Abstract

Gambling is characterized by cognitive distortions in the processing of chance and skill that are exacerbated in pathological gambling. Opioid and dopamine dysregulation is implicated in pathological gambling, but it is unclear whether these neurotransmitters modulate gambling distortions. The objective of the current study was to assess the effects of the opioid receptor antagonist naltrexone and the dopamine D2 receptor antagonist haloperidol on gambling behavior. Male recreational gamblers (n = 62) were assigned to receive single oral doses of naltrexone 50 mg, haloperidol 2 mg or placebo, in a parallel-groups design. At 2.5 h post-dosing, participants completed a slot machine task to elicit monetary wins, "near-misses," and a manipulation of personal choice, and a roulette game to elicit two biases in sequential processing, the gambler's fallacy and the hot hand belief. Psychophysiological responses (electrodermal activity and heart rate) were taken during the slot machine task, and plasma prolactin increase was assessed. The tasks successfully induced the gambling effects of interest. Some of these effects differed across treatment groups, although the direction of effect was not in line with our predictions. Differences were driven by the naltrexone group, which displayed a greater physiological response to wins, and marginally higher confidence ratings on winning streaks. Prolactin levels increased in the naltrexone group, but did not differ between haloperidol and placebo, implying that naltrexone but not haloperidol may have been functionally active at these doses. Our results support opioid modulation of cognition during gambling-like tasks, but did not support the more specific hypothesis that naltrexone may act to ameliorate cognitive distortions.

Keywords: addiction; decision-making; haloperidol; motivation; naltrexone; pathological gambling; psychophysiology; reward.

Figure 1

The slot machine task displayed two reels, with the same six icons on each reel. Each trial involved a fixed £0.15 p wager. After a selection phase in which either the computer or the participant chose one of the icons on the left reel as the “play icon,” the right reel spun for a variable anticipation phase. The right reel decelerated and came to a standstill. If the right reel stopped on the chosen play icon, i.e., the reels were aligned on the central payline, the subject won £1. If the right reel stopped on a different icon (5/6 trials), the participant lost their wager. In the analysis of these non-wins, we distinguished near-misses (with the play icon either side of the payline) and full-misses (with the play icon more than one position from the payline).

Figure 2

The roulette task presented a color choice (red or blue) on each trial, followed by a confidence rating. The roulette wheel then spun, and the outcome and feedback were presented. A history bar across the top of the screen indicated the last ten outcomes, to alleviate any working memory requirements.

Figure 3

Prolactin levels (mU/L) at T1 (baseline) and T2 (start of testing period). Naltrexone significantly increased prolactin levels. Error bars indicate standard errors of the means.

Figure 4

Motivational ratings on the slot machine task showed an outcome (near-miss, full-miss) by control (participant-chosen, computer-chosen) interaction, whereby participant-chosen near-misses increased motivation to continue relative to the computer-chosen near-misses, in the placebo group (and haloperidol group), and this was attenuated in the naltrexone group. Error bars indicate standard error of the mean. ^*p < 0.08.

Figure 5

Psychophysiological responses on the slot machine task: (A) Naltrexone significantly increased post-outcome EDA following wins compared to both non-win outcomes (collapsing across choice conditions). (B) The naltrexone group displayed marginally elevated post-outcome HR deceleration following wins compared to non-wins (collapsing across choice conditions). Error bars indicate standard error of the mean.

Figure 6

Confidence ratings on the roulette task as a function of winning streak length show a marginal difference between the naltrexone and placebo groups. Error bars indicate standard error of the mean.