Heightened muscle tension and diurnal hyper-vigilance following exposure to a social defeat-conditioned odor cue in rats

Patients with post-traumatic stress disorder (PTSD) exhibit exaggerated daytime muscle tension as well as nocturnal sleep disturbances. Yet, these physiological and behavioral features of the disorder are little studied in animal models of PTSD. Accordingly, the present studies were designed to assess alterations in muscle tension and diurnal hyper-vigilance resulting from exposure to a social defeat stressor paired with an olfactory stimulus, which was then used as a reminder of stressor exposure. In the first series of experiments, rats presented with an olfactory cue paired previously with a single social defeat exhibited a significant increase in muscle tension 4 weeks following defeat. In the second series of experiments, an olfactory cue paired previously with a single social defeat induced a significant increase in locomotor activity among quiescent rats 4 weeks following stressor exposure. The present results thus support the a priori hypotheses that novel physiological and behavioral hallmarks of PTSD can be documented in an animal model of the disorder and that the present overt signs of reactive hyper-vigilance can be triggered by reintroduction of an olfactory stimulus present at the time of initial trauma exposure.