Memory improvement in senile rats after prebiotic and probiotic supplementation is not induced by GLP-1

Abstract
Introduction: The mechanism underlying the memory improvement induced by prebiotic and probiotic supplementation remains unclear. Glucagon-like peptide type 1 (GLP-1) could play an important role since it is induced by prebiotics and enhances memory and learning. Aims: We correlated the levels of GLP-1 with spatial memory in senile animals to determine its role in memory improvement after prebiotic and probiotic supplementation. Methods: Senile rats were randomly assigned to four groups: (1) water (control); (2) Enterococcus faecium (probiotic); (3) agave inulin (prebiotic); and (4) E. faecium + agave inulin (symbiotic). Each supplement was administered by an orogastric cannula for 5 weeks. In the fifth week, spatial memory was assessed using the Morris Water Maze test (MWM). We extracted the hippocampus, intestine, and serum. GLP-1 levels were quantified by enzyme-linked immunosorbent assay. Results: A significant decrease in escape latency time in the MWM was observed in all groups treated with supplements. The symbiotic group achieved the highest reduction (15.13 s ± 6.40) (p < 0.01). We did not find a significant increase in GLP-1 levels nor a direct correlation of its levels with spatial memory improvement (p > 0.05). Conclusion: Prebiotic and probiotic supplementation improved spatial memory in senile animals. However, this beneficial effect did not correlate with GLP-1 levels.