I have to get to sleep, but yes, most forms of depression and other mental disorders are caused by chemical imbalances.
Several things can trigger such imbalances, stress is one huge trigger. Lack of sleep another one. Hormone shifts.
Answer to your post I would definately say "yes", when I was in college we read many things in regards to neurotransmitters and what type of meds work and do not on certain neurotransmitters. I best stop here, my eyes are getting weary, but there are many books and internet info that best explain this, some great info can be found in some of the books I mentioned in my forum for Bipolar Disorder. The books are not all just limited to Bipolar Disorder, they also have info about other things like this.
Hope I helped answer your question.
Please take care now,

DE