Protective effect of melatonin on learning and memory impairment and hippocampal dysfunction in rats induced by high-fructose corn syrup

Objective(s): We investigated the harmful effects of high fructose corn syrup (HFCS) on learning and memory in the hippocampus and the ameliorative effects of melatonin (Mel). Materials and Methods: Thirty-six adult male Sprague Dawley rats were divided into three groups: Group I, control; Group II, HFCS; and Group III, HFCS+Mel. HFCS form F۵۵ was prepared as a ۲۰% fructose syrup solution. Rats in HFCS and HFCS+Mel groups were given drinking water for ۱۰ weeks. Rats in the HFCS+Mel group have been given ۱۰ mg/kg/day melatonin orally for the ۶ weeks, in addition to HFCS ۵۵. The Morris water maze (MWM) test was applied to all animals for ۵ days to determine their learning and memory levels. After decapitation, one-half of the hippocampus samples were collected for western blot analysis, and another half of the tissues were collected for histopathological and immunohistochemical analyses. Results: In the HFCS group, there was a significant difference between the time to find the platform in the MWM test and time spent in the quadrant between days ۱ and ۵ (P=۰.۰۳۷ and P=۰.۰۰۱, respectively). In addition, a decreased level of MT۱A receptor, TNF-α, iNOS, osteopontin (OPN), and interleukin-۶ (IL-۶) expressions were significantly increased in the HFCS group. Melatonin treatment reversed MT۱A receptor levels and TNF-α, iNOS, OPN, and IL-۶ expressions. During the histopathological examination, increased neuronal degenerations were observed in the HFCS group. Melatonin ameliorated these changes.Conclusion: Consumption of HFCS caused deterioration of learning and memory in adult rats. We suggest that melatonin is effective against learning and memory disorders.