Background and Aim: Environmental enrichment (EE) has been shown as an effective positive intervention for cognitive development in both animals and human. Some evidence shows that sudden excessive environmental enrichment makes cause sensory overloading and in turn neural or cognitive deficiencies. The role of brain derived neurotrophic factor (BDNF) protein in mediating the effects of environmental enrichment by affecting brain plasticity has been suggested as one of the possible involved mechanisms. Methods For the propos of the study twenty male rats were divided into two groups of control and environmental enrichment (n=۱۰ in each group). So that on PND۲۱, immediately after weaning, the rats in the EE group were moved to a larger cage with different objects and equipment to facilitate play and motor activity, until the adolescent age (PND۴۲-۵۶). In control group rats were reared in normal condition. At adolescence, three-chamber test, marble burying and open- field tests were taken from both groups. For the behavioral tests, rats were transferred to the test room one hour before starting the tests. All tests were performed in one day (۸am-۳pm) at ۲۰ lux. Plasma BDNF levels were measured by ELISA. Results: The aim of the current study is to explore any possible effect of the sudden and excessive exposure to enriched environment on the plasma BDNF level as well as behavior level, including social behaviors, repetitive behaviors, anxiety and motor behaviors. Conclusion: Sudden exposure to an enriched environment in adolescence resulted in a significant increase in anxiety behavior (p<۰.۰۵) and a significant decrease in the tendency for social interaction (p<۰.۰۵. Repetitive behaviors and motor behavior showed no significant difference between the two groups (p>۰.۰۵). The plasma BDNF level was significantly increased in the EE group compared to the control group. The different effects of EE on rodents can be related to various factors such as age, length of period and laboratory differences. The decline in social behavior may also be due to over-involvement of the animals with objects rather than social interaction with each other which may be resulted in more exploratory behavior. Also, the sudden change of environment in adolescence may be a reason for anxiety in this group. Increased plasma BDNF levels indicate its possible role in these behavioral observations, however, these results in line with some previous reports shows the need for further studies to find unanswered questions in this area.
