Studies by NIMH grantee Rita Valentino PhD: Women are twice as vulnerable as men to many stress-related disorders, such as depression and PTSD. Corticotropin releasing factor (CRF), which acts as both a hormone and a neurotransmitter, appears to be a key player. Researchers used antibodies and an electron microscope to see how the CRF receptor responds in the brains of male versus female rats — both unstressed and after exposure to a stressful swim. In the male brain under stress, many of the hormone's receptors retreated into the cell, making the brain less stress reactive. Even in the absence of any stress, the researchers found the female stress signaling system to be more sensitive from the start.