Antibiotics‐induced modulation of large intestinal microbiota altered aromatic amino acid profile and expression of neurotransmitters in the hypothalamus of piglets

Abstract

The evidence of gut microbiota-mediated modulation of brain function has been widely recognized from studies using germ-free rodents or animals with oral antibiotic-induced microbiota depletion. Since the large intestine harbors greater numbers and more diverse of microbes than in the small intestine, large intestinal microbiota may play a crucial role in the modulation of brain function. In this study, a large intestinal microbiota-targeted strategy was used to investigate the impact of large intestinal microbiota on brain function. Twelve piglets (12.08 ± 0.28 kg) fitted with a T-cannula at the distal ileum were fed a standard diet and randomly assigned to two groups (n = 6) for ileal infusion of either saline or antibiotics. After 25 days of infusion, ileal and fecal microbiota, serum amino acids and neurotransmitters, and hypothalamic transcriptomics were analyzed. While the antibiotic infusion did not change the proximal ileal microbial composition, it markedly altered the fecal microbial composition and increased aromatic amino acid (AAAs) metabolism (p < 0.05), suggesting the infusion specifically targeted large intestinal microbes. Concentrations of AAAs were likewise decreased in the blood and hypothalamus (p < 0.05) by antibiotic infusion. Antibiotic infusion further decreased concentrations of hypothalamic 5-hydroxytryptamine (5-HT) and dopamine, in line with AAAs being their precursors. An up-regulation in gene expressions of neurotransmitter transporters and synthetases was observed (q < 0.001). In conclusion, the distalileal-antibiotic infusion altered neurotransmitter expression in the porcine hypothalamus and this effect occurred simultaneously with changes in both the large intestinal microbiota, and AAAs in the large intestine, blood and hypothalamus. These findings indirectly indicate that large intestinal microbiota affects hypothalamic neurotransmitter expressions. Read the Editorial Highlight for this article on page 208.

Increasing carbohydrate availability in the hindgut promotes hypothalamic neurotransmitter synthesis: aromatic amino acids linking the microbiota–brain axis

“…In the present study, in order to investigate the impact of increasing carbohydrate availability and specifically promoting microbial fermentation in the hindgut, a cannulated piglet model was chosen, which allows to easily manipulate gut microbiota at specific intestinal segments (Gao et al . ). To better understand the role of circulating AAAs in the gut microbiota–brain axis, single AAAs were i.p .…”

“…Findings from the present study and our previous study (Gao et al . ) within piglets inferred that hindgut microbiota may affect hypothalamic neurochemistry by modulating AAA availability in circulation. To verify the potential role of circulating AAAs along the hindgut microbiota–hypothalamus axis, single AAAs were i.p .…”

“…In our previous study, with cannulated piglet model, antibiotics were infused into the ileal terminal to specifically target the hindgut microbiota and revealed for the first time that the alterations of hindgut microbiota are associated with the changes in hypothalamic neurochemistry (Gao et al . ). Alterations of hindgut microbiota decreased AAA concentrations along the gut–brain axis, as well as levels of AAA‐derived neurotransmitters (5‐HT and dopamine) and BDNF in the porcine hypothalamus (Gao et al .…”

“…Alterations of hindgut microbiota decreased AAA concentrations along the gut–brain axis, as well as levels of AAA‐derived neurotransmitters (5‐HT and dopamine) and BDNF in the porcine hypothalamus (Gao et al . ).…”

“…A cannulated piglet model, which allows to easily manipulate the microbiota at specific intestinal segments (Gao et al . ), was chosen to increase carbohydrate availability by cecal corn starch infusion to specifically promote microbial fermentation in the hindgut, and the alterations in the AAA profile and neurochemistry were investigated. Furthermore, to test whether an elevation in circulating AAA levels has neuromodulatory effects, single AAA treatment of mice and in vitro neuronal cells were conducted, aiming to gain mechanistic insights toward the potential role of AAAs along the gut microbiota−brain axis.…”