Effect of environmental enrichment on thyroid hormone and thyroid hormone receptor in chronic cerebral hypoperfusion rats

Abstract

Objective To observe the changes of learning and memory, thyroid hormone and thyroid hormone receptor in chronic cerebral hypoperfusion in rats, as well as the effects of enriched environment. Methods The rats were randomly divided into 4 groups: sham+standard environment group (sham+SE), 2-VO+standard environment group (2-VO+SE), sham+enriched environment group (sham+EE) and 2-VO+enriched environment group (2-VO+EE). Morris water maze, radioimmunoassay, immunohistochemistry and Western blotting methods were used to detect changes in learning and memory in rats, serum thyroid hormone levels and hippocampus thyroid hormone receptors levels. Results Morris water maze showed that compared to the control group, the 2-VO+SE rats took more time to find the platform in day 2, 4 and 5, the difference was significant (t=2.67, 2.67 and 3.18; P<0.05, P<0.05 and P<0.01, respectively); and which could be restored by enriched environment in day 4 and 5 (t=4.08 and 3.55, both P<0.01). The time spent in the target quadrant in 2-VO+SE rats was significantly shorter than the sham group (t=3.33，P<0.05); and which could be restored by enriched environment (t=4.46，P<0.01). Radioimmunoassay test showed serum T3 levels had a decreased trends in 2-VO+SE rats compared the control; and which could be restored by enriched environment (t=3.62，P<0.01). Immunohistochemistry showed that compared to the sham group, the thyroid hormone receptor α1 in hippocampus CA1 and DG areas was significantly lower in 2-VO+SE rats (t=3.18 and 3.20，both P<0.05); and which could be restored by enriched environment (t=3.93 and 4.12，both P<0.01). Western blotting results indicated that compared to the sham group, the hippocampus TRα1 was significantly lower in 2-VO+SE rats (t=4.35，P<0.05); and which could be restored by enriched environment (t=6.20，P<0.01). Conclusion Chronic cerebral hypoperfusion can damage the hippocampus-related learning and memory, and which can be restored by enriched environment; serum T3 and hippocampus TRα1 may be involved in the restorations of enriched environment. Key words: Dementia; vascular; Environment; Memory; Thyroid hormones; Receptors; thyroid hormone