Probiotics decrease depressive behaviors induced by constipation via activating the AKT signaling pathway

Chronic constipation is often accompanied by emotional disorders such as depression and anxiety. The aim of this study was to determine whether administration of a multispecies probiotic can decrease depressive behaviors through the gut-brain axis and identify any underlying mechanisms. A mouse model of constipation induced by loperamide (5 mg·kg^-1,i.p.) was used. For that purpose, 36 ICR male mice were divided into three groups: control, constipation and probiotic groups. The probiotic group received treatment with a probiotic once per day for 14 days via a gavage. All other groups were given an equal volume of normal saline. The fecal parameters and intestinal transit ratio were recorded. The forced swimming test and tail suspension test were used to detect changes in depressive behaviors. Total superoxide dismutase (T-SOD) activity and malondialdehyde (MDA) levels were measured by assay kits. We also detected neuronal survival, as well as phosphorylated Ser/Thr protein kinase (p-AKT), Bcl-2, Bcl-2 associated X protein (Bax) and cleaved caspase-3 levels in the hippocampus. The results showed that administration of a probiotic could ameliorate depressive behaviors and relieve neuronal cell injury in the hippocampal CA3 regions. Moreover, probiotic treatment decreased MDA levels and increased SOD activity. Furthermore, probiotic administration increased p-AKT and Bcl-2 levels in the hippocampus of the constipated mice, while decreasing the concentrations of Bax and cleaved caspase-3, so as to inhibit the neural apoptosis. In the present study, we confirm that probiotics can alleviate depression induced by constipation through protecting neuronal health via activation of the AKT signaling pathway.