The effect of triiodothyronine on the hippocampal long-term potentiation in an animal model of the Alzheimer's disease: The role of BDNF and reelin

Converging evidence, propose a close relation between thyroid function and Alzheimer’s disease (AD). We have assessed the effect of subcutaneous and intrahippocampal administrations of triiodothyronine (T3) on the electrophysiological activity (hippocampal long-term potentiation (LTP)), the levels of thyroid hormones (THs) and TSH, the protein expression of BDNF and reelin as well as histological changes in the hippocampus of AD rats. Beta-amyloid (Aβ) plus ibotenic acid (Ibo) were injected intrahippocampally and rats were treated with T3 or saline. The hippocampal levels of THs and the protein expression are measured by ELISA kits and Western blotting method respectively. Results have been shown that T3 (S.C., and I. H), significantly reversed the amplitude and the slope impairment of the DG neurons, induced by Aβ. The hippocampal levels of THs, TSH and two protein expression were significantly decreased (p < 0.001) in AD animals and increased significantly in AD rats that have received T3 (S. C and I. H) (p < 0.01). Formation of amyloid plaques was declined in AD rats treated with T3. In conclusion, both S.C., and I.H. injections of T3 is effective in preventing the disruption of synaptic plasticity induced by Aβ. This positive effect of T3 may be mediated through a regulation of proteins expression and the hippocampal level of THs. The best effect was observed in I.H. microinjection of T3.