What are the neurobiological factors related to depression? While it is agreed that neurotransmitters aren't the primary "cause" of depression, what other factors are a part of this mental illness that focus on the neurobiological aspects of it?
You can look into the research being done with ketamine as an amazingly fast antidepressant, even for those with severe treatment resistant depression. Other than that, they now think decreased neurogenesis and synaptogenesis are the more direct and important links to depression. There is also some early research into the links between depression and the immune system, as well as people's microbiomes.