Piglets fed an infant formula containing the prebiotics polydextrose (PDX) and galactooligosaccharide (GOS) performed better in the novel object recognition (NOR) test. The supplemented pigs also demonstrated more exploratory behaviour than controls, found the scientists from the University of Illinois, Urbana.
The novel object recognition (NOR) test is an indicator of recognition memory, and is an improvement on the maze tests used in rodents studies. Preference for new objects indicates curiosity, a characteristic of healthy brain development in terms of learning and memory, the scientists explained.
“Our study demonstrated that PDX/GOS elicited a notable influence on recognition memory and exploratory behaviour. We chose to use the NOR task in this study as it is a novelty preference-based task, which is a widely used paradigm for assessment of recognition memory in infants,” said lead researcher Professor Ryan Dilger.
The researchers decided to use piglets for this study as they show high levels of similarity to humans in terms of digestive systems, nutritional requirements and brain development.
The findings may thus in future be helpful in designing interventions to boost learning and memory skills in human infants.
Changes in gut bacteria metabolites
The scientists also found that the prebiotics reduced levels of volatile fatty acids (VFAs) (metabolites of gut bacteria) in the colon, blood and brain.
"When we provide prebiotics in formula, our results confirm that we can not only benefit gut health, which is known, but we can also influence brain development," said lead researcher Professor Ryan Dilger. "We can actually change the way piglets learn and remember by influencing bacteria in the colon."
"VFAs are a global indicator for whether prebiotics had an effect on the overall population of bacteria. For example, we might want to see an increase in Lactobacillus and other beneficial bacteria that produce butyrate," he explained.
The researchers were surprised to find that the prebiotics lowered the level of hippocampal serotonin in the supplemented pigs.
"When you hear less serotonin, there's an immediate reaction to say: 'Well, that's bad,'" said lead author Stephen Fleming. However, the researchers found no increase in anxiety levels in the prebiotic-fed pigs when given a stress test. The researchers suggested that the lower serotonin might be due to the prebiotics altering the level of tryptophan (a precursor of the neurotransmitter), but emphasised further work was need to establish the mechanism.
They also found a lack of association between levels of VFAs (which have been proven to reach the brain), and the behavioural test results.
"We found that, yes, VFAs are absorbed in the blood of pigs that were fed PDX/GOS. And, yes, they do get into the brain," Fleming explains. "But when we looked at the relationship between these VFAs and the results of our behaviour tests, there did not appear to be a clear connection."
Further work is therefore needed to establish the effects of these metabolites on mood and behaviour, suggested the researchers.
Source: Nutritional Neuroscience
Published online. DOI: 10.1080/1028415X.2017.1415280
“Dietary polydextrose and galactooligosaccharide increase exploratory behavior, improve recognition memory, and alter neurochemistry in the young pig”
Authors: Stephen A. Fleming, Supida Monaikul, Alexander J. Patsavas, Rosaline V. Waworuntu, Brian M. Berg & Ryan N. Dilger