Evaluation of the Circadian Rhythm Neuropeptides and Hippocampus in Rat Model of Posttraumatic Stress

Abstract

ABSTRACT We investigated hippocampus weight and the levels of circadian rhythm-related neuropeptides; Somatostatin (SST), Vasoactive Intestinal Peptide (VIP), Neuropeptide Y (NPY), Melatonin (MLT), and Corticotrophin Releasing Hormone (CRH) in plasma (p) and hippocampus tissue (h) of rats with posttraumatic stress (PTS) symptoms. Thirty four healthy Spraque-Dawley rats were randomly divided into control and PTS groups. Single prolonged stress (SPS) model was used to mimic PTS. Elevated Plus Maze Test (EPMT) was used to assess anxiogenic behavior. Rats were sacrificed under anesthesia and hippocampus weight, SST, NPY, CRH, MLT, and VIP levels were measured by the Enzyme-Linked-Immuno-Sorbent-Assay method. Hippocampus weights in the PTS group were significantly lower compared to controls. NPYh and MLTh levels were significantly higher in the PTS group. NPYh and MLTh and MLTp were significantly higher in the PTS. CRH, VIP, and SST levels in hippocampus tissue and CRH, NPY, VIP, and SST in plasma did not differ between groups. A positive correlation was found between MLTh and VIPh tissue levels. There was a positive correlation between NPYh and VIPh levels, and a high degree of positive correlation between NPYp and VIPp levels. As far as we know, this is the first study in which 5 neuropeptides’ hippocampus tissue and plasma levels were evaluated together in a PTSD model. Hippocampus weights may tend to decrease in PTS. Especially, NPY and MLT from circadian rhythm neuropeptides play an important role in PTS etiology. After the 7th day of trauma exposure, the hippocampal NPY and MLT levels may increase as a stress-adaptive mechanism in PTS.