Central monoamine deficiency in depressions: causative of secondary phenomenon?

There are indications for a functional deficiency of 5-HT and DA in certain kinds of depression. The question arises if these biochemical disturbances are primary or secondary, whether they contribute to the pathogenesis of the depression or whether they result from it. From research with MA precursors we drew the tentative conclusion that they are presumabely primary and interrelated with the depression in a causal and/or predisposing way.