Concentration of hippocampal ACh from Hypo, T4, DON, T4+DON and C groups (n=10–12). Homogenates were extracted from the hippocampus of each rat. Hypothyroidism induced a significant decrease in ACh content in the hippocampus, and the DON (0.005%), T4 (6 μg/100 g body weight) or combined treatment (T4+DON) restored the Ach levels to the control value. Data shown are the mean ± SEM of three independent experiments. C, control group; Hypo, hypothyroid group; DON, hypothyroid rats treated with 0.005% (w/v) DON; T4, hypothyroid rats treated with 6 μg T4/100 g BW; T4+DON, hypothyroid rats treated with 6 μg T4/100 g BW beside adding 0.005% (w/v) DON to the drinking water. *P<0.05, vs C. ACh, acetylcholine; T4, thyroxine; DON, donepezil; Prot, hippocampus protein; SEM, standard error of the mean; w/v, weight/volume.