Effects of thyroid hormone levels on spatial learning and memory in rats

Abstract

Objective To assess the effect of thyroid hormone levels on spatial memory in Wistar rats. Methods Healthy 8-week-old Wistar rats [N=30, approximately (200±20) g, after 1 week of adaptive feeding] were used in this study. The rats were randomly and equally divided into a control group, a hypothyroidism group and a hyperthyroidism group. Normal Wistar rats underwent bilateral thyroidectomy to establish a hypothyroidism model. Hypothyroidism was established 28 days after operation. Normal Wistar rats were injected subcutaneously with thyroxine 20 µg/100 g body weight each day for 28 days to establish a hyperthyroidism model. The Morris water maze test (including navigation and space exploration experiments) was performed on the three groups of rats after the establishment of the models to observe their difference in spatial learning and memory ability. Results Compared with control group rats, the escape latency was significantly prolonged in the navigation experiment and the space exploration ability decreased significantly in the hypothyroidism group and hyperthyroidism group, which manifested as statistically significant extended distance and time in the target quadrant and reduced number of passes through the target (P<0.05 for all). Conclusion Hypothyroidism or hyperthyroidism can lead to a decrease of spatial memory in Wistar rats. Key words: Thyroid hormone; Hyperthyroidism; Hypothyroidism; Cognitive function; Spatial memory