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Abstract
BackgroundAlthough 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.ResultsThe 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.ConclusionThe 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.
Highlights
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
The SHNOPCPA group on the other hand, registered significant decline in distance travelled in central zone (F6,65 = 228.2, P < 0.01) (Figure 1v), time spent in central zone (F6,65 = 288.4, P < 0.01) (Figure 1iv) and central zone crossing (F6,65 = 104.6, P < 0.01) (Figure 1vi) along with concomitant increase in distance travelled in peripheral zone (F6,65 = 236.8, P < 0.01) (Figure 1iii) and time spent in peripheral zone (F6,65 = 63.51, P < 0.01) (Figure 1ii) as compared to Paired housed rats with novel objects intervention (PHNO) group
SHNO group, on the other hand, registered significant enhancement in the time spent in central zone (Figure 1iv) and frequency of central zone crossing (Figure 1vi) along with decrease in the time spent in peripheral zone when compared to Singly housed isolated rat (SH) group (Figure 1vi)
Summary
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. Isolation rearing of rats leads to long term effects on mood behaviour, neuromorphology and neurotransmitters functions [5,6,7] Most of these experiments on rats involved housing animals in individual cages from the first day of weaning for a minimum period of 21 days [8] and there are few reports focusing on adult social isolation after social rearing. Diversion in attention during social isolation on the other hand, has been reported to lower stress responsive hormones in singly housed male and female rats [9]. None of these studies addressed a basic question as to whether the mood alterations were due to monotony or due to lack of interaction with conspecifics through physical, visual, auditory or pheromonal stimuli
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