Abstract
Capsaicin (CAP) is an active ingredient in chili pepper that is frequently consumed. It exerts various pharmacological activities, and also has potential effects on mental illness. However, its mechanism of antidepressant effects is still unclear. Based on the emerging perspective of the gut-brain axis, we investigated the effects of dietary CAP on gut microbes in mice with depression-like behaviors induced by lipopolysaccharide (LPS). C57BL/6J male mice (four weeks old) were given specific feed (standard laboratory chow or laboratory chow plus 0.005% CAP) for 4 months. During the last five days, LPS (0.052/0.104/0.208/0.415/0.83 mg/kg, 5-day) was injected intraperitoneally to induce depression. Behavioral indicators and serum parameters were measured, and gut microbiota were identified by sequencing analysis of the 16S gene. This study showed that dietary CAP improved depressive-like behavior (sucrose preference test, forced swimming test, tail suspension test) and levels of 5-HT and TNF-α in serum of LPS-induced mice with depression-like behaviors. In addition, CAP could recover abnormal changes in depression-related microbiota. Especially at the genus level, CAP enhanced the variations in relative abundance of certain pivotal microorganisms like Ruminococcus, Prevotella, Allobaculum, Sutterella, and Oscillospira. Correlation analysis revealed changes in microbiota composition that was closely related to depressive behavior, 5-HT and TNF-α levels. These results suggested that dietary CAP can regulate the structure and number of gut microbiota and play a major role in the prevention of depression.
Highlights
Depression is an emotional dysfunction caused by abnormalities in the individual’s genetic system or by changes in the environment (Hecke et al, 2017; Bleys et al, 2018)
There are clinical studies showing that the structure of gut microbiota in major depressive disorder (MDD) patients has altered observably, and that bacterial abundance is affected by depression, showing some degree of decline (Chen et al, 2018)
In the open field test, the number of crossings and rearings in the LPS group were lower than those in the Control group (CON) group (P < 0.01) (Figure 2B), and these values were effectively improved in the Capsaicin diet + lipopolysaccharide-treated group (CAP+LPS) group (P < 0.05) (Figure 2C)
Summary
Depression is an emotional dysfunction caused by abnormalities in the individual’s genetic system or by changes in the environment (Hecke et al, 2017; Bleys et al, 2018). It manifests as depressed mood, slow thinking, impaired cognitive function, negative and pessimistic thoughts, and even suicidal tendencies. There are clinical studies showing that the structure of gut microbiota in MDD patients has altered observably, and that bacterial abundance is affected by depression, showing some degree of decline (Chen et al, 2018). The stability of gut microbiota is greatly affected by diet style, and diet can alter the amount and structure of gut microbes, which in turn affects mood and brain activity (Paola et al, 2010; Giada et al, 2017)
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