Hormones and neurotransmitters like serotonin and dopamine are all present in the gut. My theory is... if the gut is inflamed, the signals, or even the existence of these things is greatly compromised. We know hormones are excreted in feces. I would think that in a state of inflammation that the turnover rate of these hormones and neurotransmitters would have to increase until a state of depletion was reached. I read a study of a tricyclic antidepressant helping with inflammation. Just a theory.