ABSTRACT
BACKGROUND: Multiple sclerosis (MS) is a demyelinating disease of the central nervous system which has no any known definitive treatment. Studies have shown that thyroid hormones (THs) in addition to their roles in the development of the nervous system and the production of myelin have important roles in the adult's brain function. Since the only way to treat MS is the restoration of myelin, the aim of this study was to evaluate the effects of levothyroxine on visual evoked potential (VEP) impairment following local injections of lysolecithin into the rat optic chiasm. METHODS: To induce demyelination, lysolecithin was injected into the optic chiasm of male Wistar rats. VEP recording was used to evaluate demyelination and remyelination before and 10, 17, and 24 days after the lysolecithin injection. The rats received an intraperitoneal injection of levothyroxine with doses 20, 50, and 100 µg/kg in different experimental groups. RESULTS: VEP latency and amplitude showed demyelination at 10 and 17 days after an induced lesion in MS group which was reversed at day 24. Levothyroxine prevented these impairments, especially in high doses. CONCLUSIONS: According to the results, lysolecithin-induced demyelination at optic chiasm and VEP impairments can be restored by administration of levothyroxine. Therefore, THs probably have positive effects in demyelinating diseases.
ABSTRACT
BACKGROUND: There is an increase in inflammatory and a reduction in anti-inflammatory cytokines in multiple sclerosis (MS). Considering the role of thyroid hormones in the development and regulation of both neural and immune systems, the aim of this study was to evaluate the effects of levothyroxine on serum concentrations of interleukin-10 (IL-10) and interferon gamma (IFN-γ) in animal models of MS. MATERIALS AND METHODS: To induce demyelination in male Wistar rats, lysolecithin was injected into the optic chiasm. Then levothyroxine was injected intraperitoneally (20, 50, and 100 µg/kg) for 21 days. Serum levels of cytokines were measured by enzyme-linked immunosorbent assay at 7, 14, and 21 days after that. RESULTS: The results showed that injection of lysolecithin to the optic chiasm only increased serum concentrations of IL-10 compared to the sham group (P < 0.05) at 7th day, but this increase was prevented by all doses of levothyroxine. IFN-γ was decreased significantly (P < 0.001) 21 days after. Comparing to the sham group at all sampling time and with respect to the MS group at the days 7 and 21, levothyroxine decreased serum concentrations of IFN-γ significantly. CONCLUSION: The results showed that thyroid hormones probably could produce protective effects against induced demyelination through affecting immune responses.