While it is not clear if these changes contribute to the behavioral outcome after stress or to the pathophysiology of PTSD, it is well established that NGF-TrkA signaling has a role in neuroplasticity and cognitive flexibility [16, 17] and plays a critical role in establishing the septo-hippocampal circuitries that affect hippocampus-dependent contextual fear encoding [13–15]. This evidence concerns the gene NGF and post-traumatic stress disorder.