Temporal discounting is a phenomenon where a reward loses its value as a function of time (e.g., a reward is more valuable immediately than when it delays in time). This is a type of intertemporal decision-making that has an association with impulsivity and self-control. Many pathologies exhibit higher discounting rates, meaning they discount more the values of rewards, such as addictive behaviors, bipolar disorder, attention-deficit/hyperactivity disorders, social anxiety disorders, and major depressive disorder, among others; thus, many studies look for the mechanism and neuromodulators of these decisions. This systematic review aims to investigate the association between pharmacological administration and changes in temporal discounting. A search was conducted in PubMed, Scopus, Web of Science, Science Direct and Cochrane. We used the PICO strategy: healthy humans (P-Participants) that received a pharmacological administration (I-Intervention) and the absence of a pharmacological administration or placebo (C-Comparison) to analyze the relationship between the pharmacological administration and the temporal discounting (O-outcome). Nineteen studies fulfilled the inclusion criteria. The most important findings were the involvement of dopamine modulation in a U-shape for choosing the delayed outcome (metoclopradime, haloperidol, and amisulpride). Furthermore, administration of tolcapone and high doses of d-amphetamine produced a preference for the delayed option. There was a time-dependent hydrocortisone effect in the preference for the immediate reward. Thus, it can be concluded that dopamine is a crucial modulator for temporal discounting, especially the D2 receptor, and cortisol also has an important time-dependent role in this type of decision. One of the limitations of this systematic review is the heterogeneity of the drugs used to assess the effect of temporal discounting.

Under certain circumstances, some nutrients can affect the synthesis of central neurotransmitters and potentially influence behavior. The objective of this study was to characterize the influence of tryptophan supplementation on anxiety-like behavior in zebrafish (Danio rerio) and to assess the suitability of a new formulation of standardized diet for enhancing the maintenance and performance of this species. To achieve this, the proportion of the amino acid tryptophan was experimentally modified through supplementation at 5%, 50%, and 100% of its original levels in the zebrafish diet. The investigation was conducted using the Y-maze test, light-dark preference test and inhibitory avoidance test. The results indicated that tryptophan supplementation did not lead to a reduction in anxiety-like behavior in any of the tests conducted, suggesting a direct relationship between the individual isolation of these animals and the predominance of this type of behavior. Furthermore, a significant difference was observed in the inhibitory avoidance test between groups with diets supplemented at 5% and 50%. The dietary modification did not alter the learning of natural anxiety, but in most animals, tryptophan supplementation led to a decrease in body mass.