Q:  Is it true that when your stomach is upset it affects your serotonin levels which affects your depression, (mental state of mind)? Is serotonin produce in your stomach also?
 

Dear Carol -- 
Serotonin, you're right, is a very common transmitter in the gastrointestinal tract -- not produced in the stomach, but by the nerve cells which regulate the stomach and much of the rest of the gut.  But is it true that when your stomach is upset, this affects serotonin somehow? 

More likely it's the other way around, but first we'd have to decide what we mean by the stomach being "upset".  For the moment, let me assume that this means some sort of pain in your abdomen (you might also have meant nausea, or pain more specifically confined to the region of the stomach). There are many possible causes of such pain, but one of the most common, and one that travels very frequently with complex mood problems, is called "irritable bowel syndrome", or IBS for short. 

IBS is an example of a condition that worsens when mood symptoms worsen, and improves when mood symptoms improve.  So in this case, it's more like the brain gets better first, then the stomach, if you will -- rather than the other way around.  But just what role serotonin plays in this drama is still pretty unclear: even in the brain it's not exactly clear, although there is more information on this in the last 5 years (described on my website in the section on the Brain Chemistry of Depression -- Part Two).  As for what and how serotonin is acting on the gut in IBS, I haven't looked at that research in quite a while, but I  think that story is equally complicated.  

The bottom line: yes, you're right, there is a complex interplay between the gut and the brain. In some respects, they act as though they're connected -- which of course they are, both chemically and through nerve cell connections.  Exactly how that interplay goes, though; and what role serotonin is playing; is still not very clear. 

Dr. Phelps

Published March, 2006