AIM:To investigate the distribution and expressionof C-type natriuretic peptide(CNP)/natriuretic peptide receptor B(NPR-B) in the rectum of a rodent depression model and the interventional effect of Xiaoyaosan(XYS).METHODS:Male rats(n = 45) of clean grade(200 ± 20 g) were divided into five groups after one week of adaptive feeding:primary control,depression model,low dose XYS,middle dose XYS,and high dose XYS.The animal experiment continued for 3 wk.Primary controls were fed normally ad libitum.The rats of all other groups were raised in solitary and exposed to classic chronic mild unpredictable stimulation each day.XYS groups were perfused intragastrically with low dose,middle dose,and high dose XYS one hour before stimulation.Primary control and depression model groups were perfused intragastrically with normal saline under similar conditions as the XYS groups.Three weeks later,all rats were sacrificed,and the expression levels of CNP and NPR-B in rectum tissues were analyzed by immunohistochemistry,real-time polymerase chain reaction,and Western blotting.RESULTS:CNP and NPR-B were both expressed in the rectum tissues of all rats.However,the expression levels of CNP and NPR-B at both gene and protein levels in the depression model group were significantly higher when compared to the primary control group(n = 9; P < 0.01).XYS intervention markedly inhibited the expression levels of CNP and NPR-B in depressed rats.The expression levels of CNP and NPR-B in the high dose XYS group did not significantly differ from the expression levels in the primary control group.Additionally,the high and middle dose XYS groups(but not the low dose group) significantly exhibited lower CNP and NPR-B expression levels in the rectum tissues of the respectively treated rats compared to the untreated depression model cohort(n = 9; P < 0.01).CONCLUSION:The CNP/NPR-B pathway is upregulated in the rectum of depressed rats and may be one mechanism for depression-associated digestive disorders.XYS antagonizes this pathway at least partially. AIM: To investigate the distribution and expression of C-type natriuretic peptide (CNP) / natriuretic peptide receptor B (NPR-B) in the rectum of a rodent depression model and the interventional effect of Xiaoyaosan (XYS). METHODS: Male rats = 45) of clean grade (200 ± 20 g) were divided into five groups after one week of adaptive feeding: primary control, depression model, low dose XYS, middle dose XYS, and high dose XYS. Animal experiment continued for 3 wk . Primary controls were fed normally ad libitum. The rats of all other groups were raised in solitary and exposed to classic chronic mild unpredictable stimulation. Each cycle. XYS groups were perfused intragastrically with low dose, middle dose, and high dose XYS one hour before stimulation . Primary control and depression model groups were perfused intragastrically with normal saline under similar conditions as the XYS groups. Week weeks later, all rats were sacrificed, and the expression levels of CNP and NPR-B in rectum tissues analyzed by imm Both uncohistochemistry, real-time polymerase chain reaction, and Western blotting .RESULTS: CNP and NPR-B were both expressed in the rectum tissues of all rats. However, the expression levels of CNP and NPR-B at both gene and protein levels in the depression model group were significantly higher when compared to the primary control group (n = 9; P <0.01) .XYS intervention markedly inhibited the expression levels of CNP and NPR-B in depressed rats. The expression levels of CNP and NPR-B in the high dose XYS group did not significantly differ from the expression levels in the primary control group. Additionally, the high and middle dose XYS groups (but not the low dose group) significantly exhibited lower CNP and NPR-B expression levels in the rectum tissues of the treated rats compared to the untreated depression model cohort (n = 9; P <0.01) .CONCLUSION: The CNP / NPR-B pathway is upregulated in the rectum of depressed rats and may be one mechanism for depression- associated digestive disorders s.XYS antagonizes this pathway at least partially.