Treatment by Vitamin D Reversed the Adverse Effects of Hypothyroidism on Learning and Memory in Juvenile Rats: Protection Against Acetylcholinesterase Activity and Brain Tissue Oxidative Damage.

Abstract

Apart from a role as a key regulator of calcium/phosphate homeostasis, vitamin D (Vit D) is suggested to be a potential player in nervous system growth and function. This study aimed to assess the impacts of Vit D administration against memory impairment, oxidative damage and acetylcholinesterase (AchE) overactivity caused by hypothyroidism in juvenile rats. The animals were randomly grouped as: 1) Control; 2) Hypothyroid; 3) Hypothyroid-Vit D 100 and 4) Hypothyroid-Vit D 500. Propylthiouracil (PTU) was added to their drinking water (0.05%) for 6 weeks and Vit D (100 or 500 IU/kg) treatment was daily performed by gavage. Morris water maze (MWM) and passive avoidance (PA) tests were performed. The brains were removed under deep anesthesia, then the hippocampal and cortical tissues were separated to assess biochemical parameters. Hypothyroidism was significantly associated with learning and memory impairment in MWM and PA tests. Hypothyroidism also elevated acetylcholinesterase (AChE) activity and malondialdehyde (MDA) content, while it reduced thiol content and superoxide dismutase (SOD) activity in the brain. Treatment with Vit D recovered hypothyroidism-induced cognitive impairment and improved memory performance in MWM and PA tasks. On the other hand, Vit D alleviated AChE activity and MDA level, whereas increased SOD activity and thiol content in the hippocampal and cortical tissues. In conclusion, these outcomes suggest that oral consumption of Vit D may play a protective role against memory dysfunction caused by hypothyroidism by inhibiting AChE activity and oxidative stress in the brain.