Did those studies show a causal direction of depression causing neural destruction? My current notion is that the causality is reversed - chronic oxidative stress and neuroinflammation cause physical damage to the brain, which results in depression-like symptoms (e.g. low mood, poor memory, loss of motivation etc.). If this turns out to be correct, then there is a clear physiological cause of depression which can be cured through neuro anti-inflammatory and antioxidant medication.