| Summary: | 碩士 === 國立陽明大學 === 解剖學及細胞生物學研究所 === 106 === Gut microbiota plays a role in maintaining the dynamic metabolic and ecological balance of the digestive tracts. In recent years, it has been discovered that gut microbiota can modulate brain functions via the gut–brain axis, therefore affecting emotions and behaviors. In the past, many studies have shown that reduction of adult neurogenesis in the hippocampus and dysfunction of the orexin system in hypothalamus might be involved in the pathophysiology leading to depression. In the present study, we used male Sprague-Dawley rats and inescapable footshock stress followed by avoidance tests to classify animals displaying no learned helplessness (NoLH) and learned helplessness (LH) behaviors to simulate helplessness symptom in depression patients. In addition, Lactobacillus plantarum PS128 was orally administered to the rats (1x1010 CFU/Day) for 4 weeks. Then we observed the behavioral changes in the sucrose preference test and the elevated plus maze (EPM) test. In order to understand the pathways between PS128 and helplessness behaviors, we investigated neurogenesis in the hippocampus as well as the activation of orexin neurons (OX-A & OX-B), amygdala, and vagus nerve after stress stimulation. Furthermore, the concentration of serum OX-A and corticosterone were examined. We found that LH rats had reduced neurogenesis in the hippocampus. Moreover, LH rats showed reduced activation of OX-A neurons in the hypothalamus and had lower concentration of serum OX-A, but showed increased activation of OX-B neurons and the amygdala compared to those of NoLH rats. These findings suggested that reduced hippocampal neurogenesis, over-activated amygdala, and distinct orexin expression could be associated with learned helplessness behaviors. We also found that PS128 ingestion decreased the locomotor activity of the rats during EPM test. Additionally, PS128 had an impact on anhedonia and the activation of orexin neurons. But we still need more studies to confirm whether PS128 can improve helpless behavior and how it functions through the gut-brain axis.
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