Chewing ameliorates stress-induced enhancement of anxiety behaviours in an animal model of post-traumatic stress disorder

Post-Traumatic Stress Disorder (PTSD) is a stress-related mental disorder caused by traumatic experience, with symptoms such as intrusive memories, hyperarousal, and avoidance, which endure for years. Single-Prolonged Stress (SPS) is an animal model proposed for PTSD. Rats exposed to SPS showed enhanced Hypothalamic-Pituitary-Adrenal (HPA) axis inhibition, which has been reliably reproduced in PTSD patients, and increased Glucocorticoid Receptor (GR) expression in the hippocampus. We aimed to elucidate whether chewing improved stress-induced fear responses and anxiety behaviours along with ameliorating feedback inhibition of HPA responses. SPS rats were subjected to restraint stress by immobilization for 2 h before forced swimming and ether anaesthesia exposure. SPS with chewing (SC) group were allowed to chew on a wooden stick during the latter half of the immobilization period, whereas the stress without chewing (ST) group were not allowed to do so. Fear response and anxiety behaviour were significantly increased in the ST group compared with the SC group. Further, we found significantly reduced field Excitatory Postsynaptic Potentials (EPSPs) in the CA1 region of the hippocampus in the ST group compared with control and SC groups. The results suggest that chewing is a behavioural mechanism to cope with PTSD.