Hmmm, a bit of a loaded question friedzucchini. It is believe that the hormones (chemical balances) in our brains do control thoughts and moods. When someone enters a negative environment, it can upset their hormones. I would be surprised if someone left prison and was completely normal and happy two weeks later. So, to cut to the point 1.Yes 2.Yes 3.No 4.Yes (possibly). People are certainly given antidepressants while in jail, if asked for, for a reason. If someone's feeling depressed, they believe that neurons aren't producing enough, accepting enough, or returning enough of these chemical messengers (hormones like serotonin, dopamine etc). Instantly leaving prison wouldn't make these instantly return to their natural state. Antidepressants can help get things normal until the circumstances are better and the person can titrate off the medications.
The reason I am so interested in this hypothetical series of questions is that I have bipolar depression, something there is no history in any of my extended family. When I was 3 years old, I fell head first from a bunk bed and was in a coma for around half a day. There is a possibility that this damaged my brain and has caused my mental illness. No way of me knowing at this point. The video I've linked below helps describe some of the ways that the brain affects moods and mental health. It is around 15 minutes long and shows some profound information about mental illness and disorders. It's around 15 minutes long.
The most important lesson from 83,000 brain scans | Daniel Amen
https://www.youtube.com/watch?v=esPRsT-lmw8