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Effects of walnuts (Juglans regia) on learning and memory functions.

Walnut has been regarded as a health food that is delicious and nutritious. Both preventive and therapeutic effects of walnut are well documented. Walnuts are rich in omega-3 fatty acids that are reported to have beneficial effects on brain function. The present work was designed to evaluate the effects of walnuts on learning and memory in male rats. The effect of oral intake of walnut was also monitored on food intake. Walnut was given orally to rats for a period of 28 days. Memory function in rats was assessed by elevated plus maze (EPM) and radial arm maze (RAM). A significant improvement in learning and memory of walnut treated rats compared to controls was observed. Walnut treated rats also exhibited a significant decrease in food intake while the change in growth rate (in terms of percentage) remained comparable between the two groups. Analysis of brain monoamines exhibited enhanced serotonergic levels in rat brain following oral intake of walnuts. The findings suggest that walnut may exert its hypophagic and nootropic actions via an enhancement of brain 5-HT metabolism.

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Walnut diet reduces accumulation of polyubiquitinated proteins and inflammation in the brain of aged rats

An increase in the aggregation of misfolded/damaged polyubiquitinated proteins has been the hallmark of many age-related neurodegenerative diseases. The accumulation of these potentially toxic proteins in brain increases with age, in part due to increased oxidative and inflammatory stresses. Walnuts, rich in omega fatty acids, have been shown to improve memory, cognition and neuronal effects related to oxidative stress (OS) and inflammation (INF) in animals and human trials. The current study found that feeding 19-month-old rats with a 6% or 9% walnut diet significantly reduced the aggregation of polyubiquitinated proteins and activated autophagy, a neuronal housekeeping function, in the striatum and hippocampus. Walnut-fed animals exhibited up-regulation of autophagy through inhibiting phosphorylation of mTOR, up-regulating ATG7 and Beclin 1, and turnover of MAP1BLC3 proteins. The clearance of polyubiquitinated protein aggregates such as p62/SQSTM1 was more profound in hippocampus, a critical region in the brain involved in memory and cognitive performance, than striatum. The clearance of ubiquitinated aggregates was in tandem with significant reductions in OS/INF, as indicated by the levels of P38-MAP kinase and phosphorylations of nuclear factor kappa B and cyclic AMP response element binding protein. The results demonstrate the effectiveness of a walnut-supplemented diet in activating the autophagy function in brain beyond its traditionally known antioxidant and anti-inflammatory benefits.