Disrupting monotony during social isolation stress prevents early development of anxiety and depression like traits in male rats

Abstract

Background: Although there have been several reports on social isolation induced mood alterations, the independent contribution of monotonous environment in mediating mood alterations has been less studied. In view of the above, the present study is aimed at investigating the relative contribution of monotony towards mood alterations during isolation stress. Monotony was induced in a specially designed isolation chamber in male Sprague-Dawley rats in the presence or absence of isolation by housing animals singly (SH) or in pairs (PH). Novel objects were introduced to disrupt monotony in singly housed animals (SHNO) or paired housed animals (PHNO). Behavioural alterations were assessed using Open field test (OFT), Elevated Plus Maze (EPM) and Forced Swim Test (FST). Neuro-morphological changes in the CA3 region of hippocampus were studied by cresyl violet and golgi-cox staining. Hippocampal serotonin and 5-hydroxy indole acetic acid (5-HIAA) levels were estimated along with the expression of phospho-insulin like growth factor-1 receptor (pIGF-1R) and phospho cyclic AMP response-element binding protein (pCREB). Serotonin was depleted by administering Para-chlorophenylalanine (PCPA) to a separate PH group (PHPCPA), PHNO group (PHNOPCPA) and SHNO group (SHNOPCPA) to determine the role of serotonin in mediating monotony induced emotional mal-adaptations. Results: The results showed anxiety and depression like traits in both PH and SH groups during behavioural test such as OFT, EPM and FST. Pyknosis along with decrease in apical dendritic arborization was observed in the CA3 region of SH group along with decrease in serotonin and reduced expression of pIGF-1R and pCREB. Disrupting monotony through intervention of novel objects in PHNO and SHNO groups ameliorated anxiety and depression like traits and augmented pIGF-1R along with increase in serotonin level. Depletion of hippocampal serotonin level by PCPA administration in PHNOPCPA and SHNOPCPA groups on the other hand resulted in altered mood state despite disruption of monotony by novel objects intervention. Conclusion: The findings of our study suggest that monotonous environment independently contributes to impairment in mood state and disrupting monotony by intervention of novel objects during social isolation prevents mood disorders and emotional maladaptation through up regulation of hippocampal pIGF-1R and increase in serotonin.