Glutamatergic Gene Expression Mediates the Relationship between Gut Bacteria and Recognition Memory in Context of Milk Oligosaccharide Intake

Author(s):
Jonas Hauser
Stephen A. Fleming
Jian Yan
Sylviane Metairon
Pascal Steiner
Sharon M. Donovan
Ryan N. Dilger

Objectives and Study:

Modulation of the gut microbiome via prebiotics or probiotics can improve memory or reduce anxiety. The mechanisms by which pre- and probiotics act are largely undiscovered. We have shown that oligosaccharides impact recognition memory in
both an oligosaccharide- and memory type-specific manner. Herein, a sub-groups mediation analysis was performed to identify variables mediating the relationship between colonic bacterial genera and recognition memory in context of oligosaccharide
intake in young pigs.

Methods:

Male pigs (n=70) were artificially reared from postnatal days 2-33 and provided milk replacers analyzed to contain: 0 g/L oligosaccharides (control [CON]); 5.8 g/L bovine milk oligosaccharides (BMOS); 1.2 g/L human milk oligosaccharides (HMO, 0.8 g/L of 2’fucosyllactose [2’FL] + 0.4 g/L of Lacto-N- neotetraose [LNnT]); BMOS and HMO (5.8 g/L BMOS + 1.0 g/L 2’FL + 0.5 g/L LNnT); 3.6 g/L oligofructose (OF); or 3.4 g/L OF + 1.1 g/L 2’FL (OF + 2’FL). All groups underwent magnetic resonance imaging (MRI) and
the novel object recognition task, mRNA expression from hippocampus were analyzed, and colonic samples were collected for 16S sequencing. Using R, Ordinary Least Squares regression co effcients were constructed using the “stats” package. Mediation
analyses were conducted with the package “Mediation”, with a bootstrap sample size of 2000 with 95% confidence interval estimates constructed using the percentile method. Predictor variables included microbial genera from colonic and fecal samples. Mediating variables included gene expression, MRI, and behavioral variables. The predicted variable was the recognition index from either a short- or a long- delay. All mediations were performed on each diet group by using a sub-group analysis.

Results:

Numerous bacterial genera in both the colon and feces were related to short- and/or long-term memory. Mediating variables frequently included GABA- and glutamatergic hippocampal gene expression. Other mediating variables included genes related to
myelination, transcription factors, brain volume, and exploratory behavior. Importantly, these mediating variables differed by diets, with pigs fed HMO demonstrating a significant number of glutamatergic genes as mediators of short-term memory, and
myelination related genes mediated long-term memory in pigs fed BMOS.

Conclusion:

Mediation analysis identified multiple pathways between the gut and brain, with a focus on genes related to excitatory/inhibitory neurotransmission. Emerging research suggests that multiple neurotransmitter pathways regulate the relationship between the gut microbiome and brain development, this research highlights the specificity of these systems to the type of oligosaccharide consumed in early life.