Heightened Muscle Tension in Rodent Model of PTSD

Abstract

Individuals suffering from posttraumatic stress disorder (PTSD) exhibit exaggerated daytime facial muscle tension when exposed to trauma reminder cues. The objective of the present chapter is to characterize an analogous animal model of muscular tension resulting from acute stressor exposure as well as reminders of prior stressor exposure. In a series of experiments, rodents exposed to a threatening stimulus exhibited a 15 % increase in skeletal muscle tension measured electromyographically via subcutaneously implanted electrodes. Moreover, rodents exposed to an olfactory cue paired previously with a hostile social defeat interaction exhibited a 400 % increase in muscle tension that endured for weeks following initial stressor exposure. Evidence supporting the sympathomimetic nature of exagger- ated muscle tension was provided by the ability of ephedrine administration to mimic stressor-induced muscle tension hyperreactivity over both the short and long terms. Efficacy of a competitive inhibitor of sympathetic activation in normalizing muscle hypertension suggests a possible avenue of therapeutic efficacy to explore in future studies. The present findings thus support the a priori hypotheses that a novel physiological hallmark of PTSD can be documented in an animal model of the disorder and that the present overt signs of latent muscular hyperarousal can be triggered by reintroduction of reminder stimuli present at the time of initial trauma exposure.