Pesticide exposure and the microbiota-gut-brain axis.

The gut microbiota exist within a dynamic ecosystem shaped by various factors that includes exposure to xenobiotics such as pesticides. It is widely regarded that the gut microbiota plays an essential role in maintaining host health, including a major influence on the brain and behaviour. Given the widespread use of pesticides in modern agriculture practices, it is important to assess the long-term collateral effects these xenobiotic exposures have on gut microbiota composition and function. Indeed, exposure studies using animal models have shown that pesticides can induce negative impacts on the host gut microbiota, physiology and health. In tandem, there is a growing body of literature showing that the effects of pesticide exposure can be extended to the manifestation of behavioural impairments in the host. With the increasing appreciation of the microbiota-gut-brain axis, in this review we assess whether pesticide-induced changes in gut microbiota composition profiles and functions could be driving these behavioural alterations. Currently, the diversity of pesticide type, exposure dose and variation in experimental designs hinders direct comparisons of studies presented. Although many insights presented, the mechanistic connection between the gut microbiota and behavioural changes remains insufficiently explored. Future experiments should therefore focus on causal mechanisms to examine the gut microbiota as the mediator of the behavioural impairments observed in the host following pesticide exposure.

Rats choose alcohol over social reward in an operant choice procedure.

The interaction between social factors and alcohol addiction is complex, with potential for both positive and negative contributions to drug use and abstinence. Positive social connections are an important component in successful abstinence, and yet the social context of alcohol use can also lead to relapse. Recently it was shown that rats overwhelmingly choose social reward over methamphetamine, cocaine, and heroin in a discrete choice procedure, and that prolonged choice for social reward attenuates incubation of drug craving. The extent to which this effect generalises to rats trained to self-administer alcohol is not known. In this study we aimed to test the effect of social reward on choice for alcohol in male and female rats. We first validated social reward self-administration in both male and female Long-Evans rats, and found that 60 s access to a social partner of the same sex can serve as an operant reinforcer. Next we trained rats to self-administer both social reward and alcohol (20% ethanol in water), and then used discrete choice trial based tests to determine whether there is a choice preference for alcohol or social reward. Our main finding is that both male and female rats showed persistent choice for alcohol over social reward, with only minor differences between the sexes. We also show that choice for alcohol could be reduced via increased response requirement for alcohol, pre-choice alcohol exposure, and also decreasing the alcohol percentage. This study shows that preference for social rewards over drugs may not generalise to rats self-administering alcohol, and we describe several conditions where choice for social reward can be developed. This study highlights the important contribution of social factors to alcohol abuse, and future studies can investigate the neurobiology underlying a shift in preference from alcohol to social rewards.

Humor and Hunger Affect the Response Toward Food Cues.

The omnipresence of food cues in everyday life has been linked to troubled eating behavior and rising rates of obesity. While extended research has been conducted on the effects of negative emotions and stress on food consumption, very little is known about how positive emotions affect eating and particularly attention toward food cues. In the present study, we investigated whether humor impacts attentional bias toward food and whether it will affect preferences for healthy and unhealthy food items, depending on the hunger state. To do so, a group of randomly assigned participants watched funny video clips (humor group, N = 46) or neutral ones (control group, N = 49). Afterwards, they performed a modified Posner cueing task with low or high caloric food images serving as cues. We found a significant group × hunger interaction. Compared to the control group, the humor group responded more slowly to food cues when hungry, whereas the opposite was true when participants were satiated. Additionally, our results suggest that hunger possibly directs attention away from healthy food cues and toward unhealthy ones. No group differences were found with respect to food preferences and engagement and disengagement of attention. We discuss the potential of humor in counteracting aversive consequences of hunger on attention allocation toward food. We propose an underlying mechanism involving a combined reduction in cortisol levels and a decrease in activation of the reward system. However, given the novelty of the findings, further research is warranted, both to replicate the results as well as to investigate the suggested underlying processes.