Compromised decision-making and increased gambling proneness following dietary serotonin depletion in rats

• Published in: Neuropharmacology 2012-03, Vol.62 (4), p.1640-1650
• Main Authors: Koot, S., Zoratto, F., Cassano, T., Colangeli, R., Laviola, G., van den Bos, R., Adriani, W.
• Format: Article
• Language: English
• Subjects: Animal model; Animals; Decision Making - physiology; Decision-making; Diet; Diet manipulation; Dopamine; Dopamine - metabolism; Gambling; Gambling - metabolism; Gambling - physiopathology; l-tryptophan; Male; Motivation; Operant behaviour; Prefrontal cortex; Prefrontal Cortex - metabolism; Rats; Rats, Wistar; Serotonin; Serotonin - metabolism; Tryptophan - deficiency
• ISSN: 0028-3908; 1873-7064
• DOI: 10.1016/j.neuropharm.2011.11.002

Psycho-genetic studies have revealed a role for the brain serotonin system in gambling proneness and poor decision-making. We assessed whether manipulation of brain serotonin levels in rats affected performance in operant-based tasks for decision-making and gambling proneness. Male Wistar rats were exposed to an l-tryptophan (TRP) deficient diet (0.0 g/kg; T− group) or to a control, l-tryptophan containing diet (2.8 g/kg; T+ group). The same rats were tested for decision-making performance in the rodent Iowa Gambling Task (rIGT) using home-cage operant panels, and subsequently for gambling proneness in a Probabilistic Delivery Task (rPDT) using classic Skinnerboxes. At sacrifice, monoamines and metabolites were evaluated with HPLC analysis, confirming a drastically reduced serotonin synthesis, as well as altered dopamine turnover in the prefrontal cortex of T− rats. As expected, control rats (T+) progressively chose the option with the best long-term payoff in the rIGT, and also shifted from “Large & Luck-Linked” (LLL) to “Small & Sure” (SS) reinforcers in the rPDT. In contrast, depleted animals (T−) exhibited a weaker improvement of performance in the rIGT and maintained a sub-optimal attraction for LLL reinforcer in the rPDT. Comparing individual performances in both tests, we found a significant correlation between the two tasks in control (T+) but not in depleted (T−) rats. The present study revealed that (1) brain 5-HT depletion leads to poor decision-making and to gambling proneness; (2) the relationship between these two traits, shown in the control group, was disrupted in 5-HT depleted rats. The data are discussed in terms of changes within forebrain loops involved in cognitive and motivational/affective processes. ► Problematic gambling behaviour is associated with poor decision-making in humans. ► l-tryptophan deficient diet was used in rats to reduce 5-HT synthesis during 45 days. ► 5-HT depleted rats did not improve their choice for a best long-term payoff in rIGT. ► Low 5-HT elicits risk-proneness (sub-optimal attraction towards binge reward) in rPDT. ► Relation between individual rIGT versus rPDT performance was disrupted by 5-HT depletion.