MAPK8 and depressive symptom measurement: Ghrelin/GHS-R1a was reported to engage in multiple cell signaling pathways participating in the neuronal modulation of stress response and depression (Duman and Voleti, 2012), which include ERK1/2, p38MAPK, c-Jun-N-terminal kinase/stress-activated protein kinase (JNK/SAPK), Akt, CREB, and etc. We then checked the activities of those signaling pathways in the hippocampus of Ghsr+/+ mice and Ghsr-/- mice, both at baseline state and after CSDS exposure.