POMC and major depressive disorder: To further explore the correlation between the gut microbiota (significantly different microbiota at the genus level) and depression-related behavioural indices (OFT, SPT, TST, and FST), depression-related hormones (ACTH and CORT), serum inflammatory factors (IL-1β and TNF-α), and BDNF, a heatmap of Spearman’s correlation analysis was generated (R and P value was showed in Additional file: Table.