This application addresses broad Challenge Area (01) Behavior, Behavioral Change, and Prevention and specific Challenge Topic 03-MH-101* Biomarkers in mental disorders. The major hypothesis is that post-traumatic stress disorder (PTSD) leads to a reduction in the ability to respond to safety signals. For example, central to the clinical problem of PTSD, which has a ~90% comorbidity with major depressive disorder in patients who had early life stress, is the inability of these patients to inhibit their fear to stimuli reminiscent of their traumatic experience, even in safe conditions. In fact, we now have evidence that the inability to inhibit fear may be a unique biomarker of PTSD. Thus the sound of a car back firing or the smell of sulfur can lead to an intense fear reaction in Viet Nam veterans many years after combat, even in the safety of their own home. Despite substantial anecdotal evidence in support of this hypothesis, direct tests in humans or animals, using well-controlled behavioral paradigms, have been limited. We have now developed in rats, rhesus monkeys and humans an objective measure of safety signal learning and expression using identical paradigms and the acoustic startle reflex in all species. Three cues are used in the form AX+/BX-, where cues A and X in compound (e.g. a light and air blowing from a quiet fan) are paired with an aversive event (+), and a new cue B (e.g. a tone) and the same cue X signal no aversive event (-). Cue A becomes excitatory as the subject learns that A and X presented together predict the US. Cue B becomes inhibitory because B presented with X predicts "safety" from the US. In a critical subsequent transfer test trial, presentation of A and B together (AB) results in a reduced fear response compared with the response to A. In three independent studies PTSD patients sometimes could discriminate AX from BX while others could not. However, in all three studies PTSD patients did not inhibit fear to A on AB test trials. Because PTSD has high comorbidity with early life stress and major depression other studies in our group have now shown that patients with early life stress only or major depression only have normal safety signal learning and only patients with PTSD or PTSD with depression fail in show safety signal learning or expression. Thus, we believe we have an objective way to measure a major biomarker of PTSD. In a prior grant we tested 6 young adult rhesus monkeys, 3 with typical social and mother-infant interactions (controls) and 3 separated from their mothers for variable periods of time each day when they were infants (maternally-separated). 3 control and 1 maternally-separated showed successful AX+, BX- discrimination and all of them had less startle in the presence of AB, vs. A. The other two monkeys, both maternally separated, were never able to discriminate between A+ and B- because they continued to be fearful of both A and B (i.e. no safety signal learning following early life stress). The one maternally separated monkey that learned very well suggests resilience to early life stress in this animal. Currently we are testing the second cohort of 6 monkeys which should be completed in the next 2 months so we will have 12 monkeys in total, 6 control and 6 maternally-separated. As part of a long standing ongoing program at the Yerkes National Primate Center studying the effects of early life stress in rhesus monkeys, a great deal of data on another 36 animals in addition to the 12 we will have tested has been carried out. This includes neuroendrocrine, behavioral, autonomic, neuroimaging and genetic data, as well as banked DNA from all the animals available for further genotyping. We believe this is a tremendous resource that should not be wasted. If we cannot pay the per diems on these animals they will have to be released and we will no longer have access to them. Hence, we propose to finish testing these 36 additional monkeys so that our final sample will be 48 monkeys. This will allow a thorough analysis of how early life stress affects safety signal learning, autonomic, neuroimaging and neuroendrocrine functioning and whether some of these effects can be associated with various genetic variants. It may also detect monkeys that are resilient to early life stress so the measures already collected on them can be correlated with this behavioral measure of resilience. This is a "shovel ready" project. By hiring two new, full time technicians devoted entirely to this project we can get this work done in 2 years and believe it will be money well spent by NIMH. PUBLIC HEALTH RELEVANCE: The major hypothesis is that post-traumatic stress disorder (PTSD) leads to a reduction in the ability to respond to safety signals. We have evidence for this in humans using an objective test of fear inhibition. In this grant we want to evaluate whether early life stress in rhesus monkeys will associated with this deficit using the same objective measure of fear inhibition we also have developed in monkeys. If so would provide the first model of PTSD in rhesus monkeys.