Evaluation of Molecular Biomarkers in an Adolescent Chronic Restraint Stress Model of Depression
Authors: Graham Martha , Hibicke Meghan , Hayslett Renee 
Published: November 2023

Background

Chronic stress during sensitive developmental periods has been shown to be a risk factor for Major Depressive Disorder (MDD), a mood disorder that disproportionately affects women. In order to develop an animal model of MDD that addresses the impact of chronic stress during these periods, our lab modified previously published methods of adolescent chronic restraint stress (aCRS). Additionally, we sought to evaluate potential biomarkers of MDD in our aCRS model.

Methods

Female Sprague‐Dawley rats were divided into 3 treatment groups: non‐restrained saline (NRSAL; n=5), restrained saline (RSAL; n=6), and restrained desipramine (RDES; n=5). Animals aged post‐natal day 35 (±1) were restrained daily for one hour for 14 days, while age‐matched control animals were housed in a separate room. The restraint period was followed by a seven‐day recovery period and then daily subcutaneous injections of saline or desipramine (5 mg/kg) for 14 days. The day after the last injection, depressive‐like behaviors were assessed with the forced swim test (FST). Locomotor activity was also assessed. Animals were sacrificed immediately following behavioral testing via decapitation. Trunk blood was collected and the frontal cortex (FCX) and hippocampus (HIP) brain regions were dissected for evaluation of biomarkers. Western blot (WB) analysis of extracellular receptor kinase (ERK) and phosphorylated ERK (pERK) levels in the brain regions was performed. Additional WB analysis of C‐reactive protein (CRP) levels in serum was also conducted. Malondialdehyde (MDA) levels in brain and serum were evaluated via a thiobarbituric acid reactive substances assay.

Results

RSAL animals displayed significantly elevated depressive‐like behaviors compared to NRSAL animals, as indicated by immobility during the FST. Treatment with desipramine significantly reduced immobility in the FST compared to RSAL. There were no significant differences among the treatment groups in ERK and pERK levels in both of the brain regions examined. However, there were significantly higher levels of pERK expression in HIP compared to FCX in RDES. No significant differences in CRP expression were found. There were no significant differences among the treatment groups in MDA levels in HIP, FCX, or serum. Interestingly, there were significantly higher levels of MDA in FCX compared to both HIP and serum in RDES.

Conclusions

aCRS induces depressive‐like behavior in female rats that persists into adulthood and is ameliorated by desipramine, as observed in the FST. The differences in pERK levels in HIP compared to FCX in RDES suggest that desipramine may have region‐specific effects in this model. The regional differences in MDA levels only in RDES suggest that desipramine may influence mechanisms of oxidative stress in aCRS. Additionally, the lack of significant differences in MDA levels among treatment groups may be due to the length of the antidepressant treatment period. The lack of significant differences in CRP expression indicate that systemic inflammation may not play a major role in depressive‐like behaviors induced by aCRS. In this study, we have shown that aCRS is a robust animal model of depression that can be utilized to evaluate potential molecular biomarkers of MDD.

Support or Funding Information

Mercer University College of Pharmacy