A Study On The Effect And Mechanism Of Lactic Acid Bacteria In Enhancing The Host's Learning And Memory

Learning and memory are two important processes in cognitive ability.Learning refers to the acquisition of information,and memory refers to the storage of information.At present,many studies have shown that there is a correlation between gut microbiota and the host's learning and memory ability.Adding lactic acid bacteria(Lactobacillus,Bifidobacterium,etc.)to the diet can improve the host's learning and memory,but the underlying mechanism remains unclear.Therefore,a research model was established in this study to examine the relationship between the gut microbiota and learning and memory by using the model animal bumblebee(Bombus terrestris),aiming to study the effect of specific lactic acid bacteria's dietary intervention on the host's learning and memory,and to explore the mechanism with metabolomics analyses from the perspective of lactic acid bacteria affecting the host metabolism.The study will lay a foundation for the development of probiotic products based on the lactic acid bacteria.The bumblebee as the model animal was used in this study.Firstly,a research model to study the learning and memory was established,based on their excellent visual learning and memory abilities and simple gut microbiota composition.This model was successfully applied to verify the effect of lactic acid bacteria BB1(Lactobacillus sp.Ap61578)on the host's learning and memory.The experimental results showed that the long-term memory of the experimental animals in the lactic acid bacteria intervention group(n = 15)was significantly higher than that of the control group(n = 15),and the learning speed tended to increase.Secondly,the metabolite profiles in the hindguts,hemolymph and brain of experimental animals were analyzed by LC-MS/MS system.The results showed that 102,122 and 19 metabolites were found to be different in the hindgut,hemolymph,and brain tissue of experimental animals between the lactic acid bacteria intervention and control groups,respectively.Lactic acid bacteria intervention altered metabolites were mainly enriched in the amino acid metabolism pathways(such as D-glutamine and D-glutamate metabolism,lysine biosynthesis,lysine degradation,arginine biosynthesis,glycine,serine and threonine metabolism,aminoacyl t RNA biosynthesis,amino acid biosynthesis)in the host's hindguts,lipid metabolism pathways(such as glycerophospholipid metabolism,?-linolenic acid metabolism,linoleic acid metabolism,arachidonic acid metabolism,fat digestion and absorption,glycerolipid metabolism)in the host's hemolymph and brains,and some signaling pathways(such as Gn RH signaling pathway,phosphatidylinositol signaling system,c AMP signaling pathway,phospholipase D signaling pathway)in the host's brains.Finally,the concentration of 21 free amino acids in experimental animals' hindguts,hemolymph and brains were analyzed by the HPLC system.The results showed that compared with the control group,the four free non-essential amino acids(serine,histidine,glutamine and glycine)were significantly reduced in the hindguts,and the concentration of most free essential amino acids,non-essential amino acids and branched-chain amino acids were significantly reduced in the hemolymph and brains of the lactic acid bacteria intervention group.Among them,the concentration of serine and glutamine in the hindguts,hemolymph,and brains are significantly reduced.While heat-killed lactic acid bacteria hardly caused the above changes.Based on the untargeted metabolomics and free amino acid analyses results,lactic acid bacteria may improve the host's memory ability by causing changes in brain signaling pathways via affecting the host amino acid metabolism,synthesis of neurotransmitters,lipid metabolism,and conversion of amino acids to lipids.The molecular mechanism needs to be validated by further research.