Analysis of the molecular and behavioral effects of acute social isolation on rats

Abstract

The mechanism underlying depression, anxiety, and stress-related psychiatric disorders is far from understood. The utilization of animal models of anxiety and stress can improve our knowledge of the pathology of these disorders as well as aiding in the identification of pharmacological therapeutic targets. The involvement of inflammation in the pathology of stress-related disorders is widely acknowledged. This study was therefore undertaken to assess depressive and anxiety-like behavior as well as neuroinflammation in acute-isolated rats. The study design comprised two main groups:1) rats in acute isolation (one rat per cage) and 2) standard housing (two rats per cage). Within ten days of acute isolation, we carried behavioral tests including Sucrose Neophobia (SNP), Sucrose Preference Test (SPT), Open field (OPF), and a Forced swim test (FST). In a separate set of experiments, we examined the molecular changes after five days of isolations, we examined the mRNA expression of Toll-like receptors (TLRs) and inflammatory markers in the hippocampal brain region. We found that acute social isolation did not have profound functional effects and the behavioral analysis revealed similarities between the isolated and standard housed rats. However, the molecular studies showed a significant increase in TLRs. An increase in Interleukin 6 (IL-6) and Tumor necrosis factor-alpha (TNF-alpha) was observed in the hippocampus of isolated rats but not the control rats. The results suggest that acute environmental isolation does not significantly affect depressive and anxiety-like behavior but does contribute to upregulations in neuroinflammatory responses. This indicates the initiation of neuronal insults following exposure to short-term isolation.

Keywords: Anxiety-like behavior; Depression; Neuroinflammation; Social isolation; Toll-like receptors.