The microbiota-gut-brain axis is a modern concept with wide and physiologically important effects.
The aim of the study was to investigate if an orally given short chain fatty acid (SCFA), butyrate,
stimulates the formation and release of serotonin and dopamine in an in vivo rat model. The effect of
butyrate was investigated in the entire gastrointestinal tract since previous studies have mainly
focused on the colon. A total of seven male Wistar rats (270-300 g) had free access to a 40 mM
butyrate solution as the only drink for 10 days while another seven rats had access only to tap water
(control group). Urine samples were collected in metabolic cages for 24 h twice during the
experiment, once before administration of butyrate and once after 9 days. A section of 5 mm was
isolated from the middle of the stomach, duodenum, jejunum, ileum and colon. The sections were
homogenized, and the levels of serotonin were assayed using a commercial ELISA kit. The excreted
amounts of 5-HIAA and HVA in the urine were assayed using commercial ELISA kits as indicators for
serotonin and dopamine respectively. This study showed that butyrate tends to increase duodenal
tissue levels of serotonin and decrease serotonin concentrations in the ileum and colon. Butyrate did
not affect urinary concentrations of 5-HIAA but appeared to increase the urinary excretion of HVA
after 10 days. This finding is important due to the scarce number of studies investigating the effect of
butyrate on dopamine. The study suggests that butyrate may influence neurotransmitter
concentrations in the gastrointestinal tract and probably in the whole organism. In the future, this
might be of importance in understanding and preventing disorders related to the microbiota-gut-brain
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