NPY and major depressive disorder: In the same study, neuropeptide-y/CRF ratios were significantly lower in the maternal separation groups and the effect was dose dependent, such that more maternal separation was associated with lower ratios (Husum and Mathe, 2002); greater neuropeptide-y has been seen as protective in depression-like behavior in rats (Stogner and Holmes, 2000), therefore a lower ratio represents a concern for increased rates of depression-like behavior in the presence of ELS.