Study explains why a moody gut often accompanies depression

Mice with a genetic mutation linked to severe depression had impaired ability for neurons in the gut and brain to create serotonin. The reduction of serotonin in the gut led to a deterioration in the gut's lining, slowing the movement of contents through the GI tract and resulting in constipation. However, treatment with 5-HTP increased neurogenesis in the gut, restoring normal function.