Validation of chronic restraint stress model in rats for the study of depression using longitudinal multimodal MR imaging

Prior research suggests that the neurobiological underpinnings of depression include disruptions in functional connectivity, neurometabolite levels, and hippocampal volume. This study examined the validity of a chronic restraint stress (CRS) paradigm in male Sprague Dawley rats for the study of depression using longitudinal behavioural tests and multiple 9.4 T MRI modalities (resting-state functional MRI, proton magnetic resonance spectroscopy, and volumetric studies). In the CRS protocol, rats were placed in individual transparent tubes for 2.5 h daily over 13 days. Elevated plus-maze test (EPM) and forced swim test (FST) confirmed the presence of anxiety-like and depression-like behaviours respectively post-restraint. Brain changes were also detected by MR. The rs-fMRI data revealed hypoconnectivity within the salience and interoceptive networks and hyperconnectivity of several brain regions to the cingulate cortex. The 1H-MRS data revealed decreased sensorimotor cortical glutamate, glutamine and combined glutamate-glutamine levels. Volumetric analysis of T2-weighted images revealed decreased hippocampal volume, which was also correlated with salience network connectivity. Depression-like behaviours were correlated with salience and interoceptive network connectivity, glutamate and combined glutamate-glutamine levels and hippocampal volume. Anxiety-like behaviours were correlated with both hippocampus connectivity and interoceptive network connectivity. The present findings identify significant changes in brain connectivity, neurometabolites and structure that are correlated with abnormal behaviour in CRS rats. Importantly, these changes parallel those found in human depression, suggesting that the CRS rodent model has utility for translational studies and novel intervention development for depression.