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Int J Appl Basic Med Res. 2018 Oct-Dec;8(4):231-236. doi: 10.4103/ijabmr.IJABMR_379_17.

Exposure to Enriched Environment Restores Altered Passive Avoidance Learning and Ameliorates Hippocampal Injury in Male Albino Wistar Rats Subjected to Chronic Restraint Stress.

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Department of Basic Sciences, College of Science and Health Professions, King Saud Bin Abdulaziz University for Health Sciences, Jeddah, Saudi Arabia.
Department of Physiology, RAK College of Medical Sciences, RAK Medical and Health Sciences University, Ras Al Khaimah, UAE.
Department of Anatomy, Melaka Manipal Medical College Manipal Academy of Higher Education, Karnataka, India.



The aim of the study was to investigate the effects of exposure to enriched environment (EE) on passive avoidance learning and hippocampal cellular morphology in rats exposed to chronic restraint stress.

Materials and Methods:

Adult male albino Wistar rats were assigned into the following groups: normal control (NC) remained undisturbed in their home cages; stressed group (S) subjected to restrained stress (6 h/day) followed by housing in standard housing for 21 days; And stressed + EE (S + EE) subjected to restrained stress followed by housing in EE for 21 days. On 22nd day, six animals from each of the three groups were exposed to passive avoidance test. The remaining animals were sacrificed. Hippocampus was isolated and processed for cellular morphology using cresyl violet staining.

Statistical Analysis Used:

Data were analyzed using one-way analysis of variance followed by Tukey's multiple comparison test (post hoc).


Stressed rats exposed to EE showed significant improvement in passive avoidance learning test compared to NC. Quantification of the surviving neurons in the hippocampal subfields and their cellular morphology revealed significant neuroprotection in S + EE in cornu ammonis-2 (CA2) neurons and CA3 hippocampal neurons. No significant changes were found in CA1 hippocampal subfield.


The outcome of this study makes us to think the possibilities of adopting EE as an alternative strategy in brain diseases where there is chronic stress and to minimize the impairment in learning and memory.


Chronic-restraint stress; cresyl violet staining; enriched environment; hippocampus; passive avoidance test

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