Our results showed that the expression of GDNF in the constipation group was significantly lower than that in the normal group (P < 0.05) and L. sakei treatment significantly increased the expression of GDNF. The expression of GDNF in both the ST and the synbiotic group was increased but did not reach a significant difference compared with the constipation group (Figure 2E). Here, GDNF is linked to constipation disorder.