The Role of the Gut‐Brain Axis in the Capacity for Learning in Zebrafish

Abstract

Starved (low calorie) and overfed (high calorie) diets are common in food insecure areas and can shift gut microbiota diversity. While there is increasing evidence linking the gut microbiota composition to psychiatric disorders including anxiety and depression, little is known regarding the impact gut microbes have on learning behavior and capacity. Current literature supports that alterations in intestinal microbiota diversity and richness can influence serotonergic and dopaminergic neurotransmission. The aim of this study is to examine the influence of gut‐brain axis on learning capacity. We hypothesize that a decrease in microbial diversity and abundance will negatively impact learning in zebrafish. Fish were grouped and fed a control diet, a starved low caloric diet and an overfed high caloric diet. Afterwards microbial DNA and RNA from zebrafish brain tissue was isolated. Bacterial abundance was quantified with primers designed against 16s ribosomal RNA. Dopamine and serotonin receptor expression was examined using TaqMan primer probes. Overfed fish exhibited a significant increase weight relative to starved fish, in addition starved fish displayed a 7.0 mg decrease in weight (p<.001, n=5). Both overfed and starved fish exhibited a decrease in intestinal microbial abundance. Associative learning was assessed using a plus‐maze protocol. Interestingly we observed modest, though not significant increases in learning in the starved fish relative to overfed and control fish. Coinciding with this data, overfed fish showed no significant changes in serotonin or dopamine receptor gene expression compared to control diets, however starved diets illustrated an increasing trend in serotonin receptor expression and a significant increase in dopamine D1 receptor expression (p<.04, n=11). These results indicate that starved and overfed diets decrease gut microbial abundance and may influence learning capacity through the gut‐brain axis in starved fish.Support or Funding InformationElon University