Effects of combined palmitoylethanolamide and probiotics on behavior and hippocampal and colonic gene expression in 12-month-old mice exposed to chronic stress

Aims To evaluate the effects of combined palmitoylethanolamide (PEA) and three probiotics ( Lactobacillus rhamnosus LA801, Lactobacillus helveticus LA102 and Bifidobacterium longum LA101) in middle-aged mice exposed to chronic unpredictable mild stress (CUMS), a model that reflects the transitional stages of aging associated with late-life depression. Methods Twelve-month-old male C57BL/6J mice received a daily supplementation of PEA (5 mg/kg) and probiotic strains (2 × 10 9 CFU in total) or vehicle for 10 weeks, starting 7 days before the initiation of an 8-week CUMS protocol. Behavioral tests were conducted after CUMS protocol. Underlying mechanisms were investigated by analyzing the expression of genes in the colon and hippocampus at study endpoint, in mice that were then 14.5 months old. Results PEA and probiotic supplementation significantly reduced specific CUMS-induced anxiety-like behaviors and increased locomotion in comparison with CUMS-exposed control group. Results suggest a more moderate CUMS-induced increase in corticosterone levels and showed hippocampal Nr3c1 upregulation, a key mediator of glucocorticoid signaling. In the hippocampus, supplementation markedly decreased Il6 expression, increased glial-associated markers expression ( Gfap , Iba1 ) and promoted genes involved in plasticity and neurogenesis ( Bdnf , Syn1 and Syp ). In addition, supplementation modulated monaminergic gene expression. At the colonic level, supplementation increased Ocln and Il10 expression while reducing Il6 expression. Conclusion Although the PEA and probiotic combination produced limited behavioral improvements in middle-aged mice exposed to chronic stress, it was associated with coordinated transcriptomic changes in both peripheral and central tissues. The modulation of pathways related to inflammation, pro-resolving responses, neuroplasticity, and neurotransmission provides mechanistic support for further investigation of this intervention as a candidate approach to counteract alterations associated with chronic stress and late-life depression.