Amazing stuff! I am not sure this study resolved the chicken and egg issue or what came first. Did the microbiome influence the temperament or vice versa.
"... a new preprint, may be differences in their microbiomes.
Previous studies have drawn connections between microbiome composition and certain temperament traits.
But it’s hard to tell the chicken from the egg: Do kids who behave certain ways end up with a specific mix of microbes, or do some microbes influence the way kids behave? ...
They gathered four exuberant 2.5-year-old toddlers and four more inhibited ones. ... The team obtained fecal samples from all the toddlers, then prepared a bunch of rats for a poo transfusion by essentially rinsing the microbes from their bowels before giving them a filtered stool sample or a sham control, followed by booster inoculations 2 and 3 days later.
Rats that received exuberant toddler poo were more exploratory in standard lab tests than both the rats that received samples from the inhibited kids and the control rats.
Intriguingly, although the rats that received the inhibited kids’ stools didn’t show significant behavioral differences from the controls, a part of their brains showed reduced dopamine signaling, which could indicate that they felt less “reward” from joyful activities. ..."
From the abstract:
"Background
Behavioural phenotypes have previously been transferred via faecal microbiota transplantation (FMT) from patients with psychiatric disorders to rodents. Studies indicate that the gut microbiota composition may be linked to certain temperament traits, defined as biologically-based differences in emotional reactivity and self-regulation. Here, we aimed to determine if the gut microbiota plays a role in temperament using an FMT approach. We focused on the temperament traits of exuberance, defined as positive reactivity, decreased behavioural inhibition, and high behavioural approach tendencies.
Methods
Faeces from 2.5-year-old toddlers from FinnBrain Birth Cohort Study with high exuberance/approach or high behavioural inhibition in the LabTAB bubbles-episode was transferred to juvenile male Sprague Dawley rats (age 22/23 days). Behaviour of the rat recipients (n=53) was assessed using the novel non-social arena, novel social arena, hole board test for exploratory behaviour, social approach-avoidance test, and forced swim test. The faecal pellets collected from the rodents were analyzed with 16s rRNA sequencing and faecal samples from the sample of toddlers (which included the donors, n=176) were analysed using short-read metagenomic sequencing. The striatum and prefrontal cortex from the rodents’ brains were analysed post-mortem using RNAseq.
Results
Microbiome from toddlers with high exuberance traits induced increased exploratory behaviour compared to vehicle-controls and rats receiving faeces from inhibited toddlers.
Locomotor activity, social, and depressive-like behaviour remained unaffected. We noted a downregulation of the dopamine synapse pathway within the striatum of the rats that received faeces from the inhibited trait donors compared with vehicle-controls. Faecal microbiota of rats receiving faeces from the same donor resembled more each other than rats from a different cage. Clostridium species AM29 11AC in toddler microbiome was positively related to exuberance, but there were no cross-sectional associations between faecal metabolites in the human sample.
Conclusions
FMT from exuberant toddlers lead to altered exploratory-related behaviour in rats."
Faecal transplantation from exuberant toddlers increases exploratory behaviour in rats (preprint, open access)
Figure 1. Schematic of the animal experiment timeline.
Figure 3. Pathway analysis of differentially expressed genes in striatum in recipients of inhibited toddler’s faeces vs controls were not statistically significant.
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