Is maternal deprivation a risk factor for post traumatic stress disorder induced by underwater stress in Wistar male and female rats: participation of neuropeptide Y

Abstract

Posttraumatic stress disorder (PTSD) is a mental disorder caused by a traumatic event and PTSD patients present behavioural, neurochemical and psychobiologic symptoms leading to major consequences in daily life functioning. It is often associated with depression and anxiety and dysregulated cortisol stress response. Moreover, reduced neuropeptide Y (NPY) levels in plasma and cerebrospinal fluid has been reported, suggesting that this neuropeptide plays an important role in PTSD. However, transversal studies in humans do not allow the establishment of whether reduction of this resilience factor is a biomarker of vulnerability to PTSD or a consequence of the traumatic event. Although a myriad of risk factors is known to increase the probability to this disorder, early childhood adversity is one of the key vulnerability factors. We will, therefore, make use of a rat model of early life adversity, to induce vulnerability and expose these rats to a traumatic event later in life. Maternal deprivation for 24 h (DEP) is a model of extreme neglect. Findings from our group indicate that DEP on postnatal day (PND) 3 (DEP3), results in more severe consequences than DEP on PND 11 (DEP11). In both ages, however, DEP reduces the expression of NPY, with greater impact on the dorsal hippocampus of DEP3 than DEP11 adolescents. In the proposed research we want to assess whether mild and severe early life adversity-induced impairment of NPY system represents a risk factor for the development of PTSD-like behaviours and co-morbidities. To do so, we will expose rat pups to DEP at 3 or 11 days and as young adults, to the underwater trauma (UWT). Three experiments will be carried out to investigate the involvement of the NPY system with PTSD: Experiment 1: Explore how DEP, associated or not with UWT impacts PTSD-related emotional behaviours, the activity of NPY neurons and expression of the Y1-type receptor. Wistar rats of both sexes will remain with their mothers (CTL) or submitted to DEP3 or 11 DEP11. On PND 60, they will either be submitted to the underwater trauma (UWT+) protocol or not (UWT-), generating 6 groups. On PNDs 59 and 88, the animals will be tested in the sucrose splash test to establish basal and post-trauma hedonia, respectively. On PND 90, they will be assessed in the elevated plus maze (EPM) and the open arm exploration will be taken as an anxiety index and immobility as an index of fear. The performance of each rat will be compared to CTL-UWT(-) group, and those showing impaired performance in at least 70% of the behavioural parameters will be classified as 'vulnerable', whereas the others will be classified as 'resilient'. Immunoreactivity of NPY+Fos and Y1 receptor will be compared between these sub-populations. Experiment 2: Dose-response curve of NPY will be determine in 60 day-old Wistar male rats, treated for 3 consecutive days after exposure to UWT or not and tested in the EPM. Thirty min after the EPM plasma samples will be used to determine corticosterone (CORT) plasma levels. Experiment 3: Potential of NPY to prevent the development of PTSD-like behaviours in male and female rats submitted to DEP and/or UWT. Animals will be tested exactly like in Experiment 1. Thirty min after the EPM, animals will be blood sampled for determination of CORT plasma levels. The results of this proposal will provide proof of concept of the role of NPY in the vulnerability or resilience to PTSD and may give support for proposition of new therapeutic strategies for PTSD. The present proposal was conceived from a collaboration supported by SPRINT Program of FAPESP (Grant # 17-50378-0) between Profs. Deborah Suchecki, in the Department of Psychobiology of UNIFESP and Gal Richter-Levin, in the Department of Neurobiology of Haifa University, in Israel. (AU)