During the initial stage after trauma, elevated cortisol triggers the activation of NMDA receptors through NMDA-extracellular signal-regulated kinase (ERK) and mitogen and stress-activated kinase (MSK) (NMDA-ERK-MSK), and the glucocorticoid receptor (GR) pathways resulting in the formation of recurring memories, which is one of the phenotypes of PTSD (Fig. 3) (Reul and Nutt 2008). Here, SIK1 is linked to post-traumatic stress disorder.