The Effects of Social Isolation in Standard and Enriched Physical Environments on the Adult Emotional Behavior of Rats Administered With MK-801 During the Early Developmental Stage

Abstract

Objective: The present study was aimed at the investigation of the effects of chronic N-methyl-D-aspartate (NMDA) receptor blockade applied during the late stage of brain maturation (days 20-30 after birth) and physical environment on affective behaviors during adulthood in socially isolated rats.

Methods: In order to establish a social isolation model, the experimental animals were kept in individual cages, starting from 21 days of age till adulthood. The socially isolated rats, which were reared under standard and enriched environmental conditions, were administered with MK-801 (between days 20-30 after birth for a period of 10 days at a dose of 0.25 mg/kg body weight, twice a day, by subcutaneous route). As from 3 months of age, the behavior of the adult rats was assessed using the open-field test, light-dark preference test and the elevated plus-maze test.

Results: In the open-field test, it was observed that the frequency of rearing, considered as exploratory behavior, has increased significantly in the group administered with physiological saline and isolated under enriched physical environmental conditions compared to the group isolated under standard physical environmental conditions (p<0.01). In the elevated plus-maze test, the duration of the period the animals remained in the open arm has shortened in the group, which was administered with physiological saline and isolated under enriched physical environmental conditions in comparison to the animals exposed to standard physical environmental conditions (p<0.01). Compared to the group given physiological saline, in the group administered with MK-801 and reared in a standard physical environment, a significant decrease was observed in the same parameter (p<0,05).

Conclusion: In conclusion, growth under enriched physical environmental conditions provides protection against both adulthood anxieties arising from NMDA receptor hypofunction in early childhood and emotional and behavioral abnormalities related to novel stimuli. (Archives of Neuropsychiatry 2012; 49: 248-254)