SHH and major depressive disorder: Yao et al. (2016) investigated the role of Shh in electroconvulsive (ECT) therapy in rats. ECT is often used in treatment-resistant depression and severe cases of depression. ECT induced the proliferation of hippocampal neural progenitor cells in rats, and blockade of Shh signaling with cyclopamine completely inhibited ECT-induced neural progenitor cell proliferation (Yao et al., 2016). However, it is yet to be investigated how Shh signaling mechanisms induce depression-like behaviors.