Hypocampal circadian rhythm neuropeptide levels in A rat model of posttraumatic stress disorder

Objective: We aimed investigate the levels of circadian rhythm neuropeptids; Somatostatin (SST), Vasoactive Intestinal Peptide (VIP), Neuropeptide Y (NPY), Melatonin (MLT) and Corticotrophin Releasing Hormone (CRH) in plasma samples and brain hippocampus tissue of rats with PTSD model. Methods: A total of 34 healthy Spraque Dawley rats randomly divided into a normal sham group and PTSD groups. Single‐prolonged stress (SPS) model used to mimic PTSD in rats. Elevated Plus Maze Test was used to assess PTSD-associated anxiogenic behavior for both groups. Rats were sacrificed under anesthesia and then SST, NPY, CRH, MLT, VIP levels were measured by ELISA (Enzyme-Linked-ImmunoSorbent-Assay) method from plasma and hippocampus tissue samples. Results: In the elevated plus maze experiment, the number of entries in the open arms (p = 0.050) and the total time spent in the open arms (p = 0.031) were found to be significantly lower in the PTSD group compared to the control group. It was found that the values of NPY and MLT in hippocampus tissue were significantly higher in the PTSD group rats compared to the sham group (p = 0.020 *, p = 0.043 *), and serum levels of MLT were higher in the PTSD group compared to the sham group (p = 0.008 *). Conclusions: As far as we know, this is the first study in literature in which 5 neuropeptides' hippocampus tissue and serum levels that associated with circadian rhythm were evaluated together in the PTSD model. The predominance of tissue levels of neuropeptide hormones NPY and MLT indicates that they play a role in PTSD etiology. Considering the mechanism of these results, the hippocampus NPY and MLT levels may increase as a result of an adaptive mechanism against stress, since the results were sacrificed after the 7th day. In further studies, re-evaluation of hormone levels with more rats and experiments to be performed at different time intervals will be a guide for better understanding. Key words: Post-traumatic stress disorder, Hippocampus, neuropeptides, Neuropeptide Y, Melatonin