What does depression do to brain chemistry

In people with MDD, however, the long-term exposure to increased cortisol levels can slow the production of new neurons and cause the neurons in the hippocampus to shrink. This can lead to memory problems. The prefrontal cortex is located in the very front of the brain

The cause of depression is unknown, however depression can be related to an imbalance of natural chemicals between nerve cells in the brain which is what it has to do with brain chemistry.