Dose-Dependent Effects of Walnuts on Motor and Cognitive Function in Aged Rats

Authors: Willis, Lauren; Shukitt-Hale, Barbara; Cheng, Vivian; Joseph, James

Submitted to: British Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2008
Publication Date: 4/13/2009
Citation: Willis, L., Shukitt Hale, B., Cheng, V., Joseph, J.A. 2009. Dose-Dependent Effects of Walnuts on Motor and Cognitive Function in Aged Rats. British Journal of Nutrition. 101:1140-1144.

Interpretive Summary: Aged rats show deficits in performance on physical and cognitive tasks that require the use of spatial learning and memory. Previously, we have shown that these deficits can be reversed by the polyphenolics in fruits and vegetables. Walnuts, which contain omega-3 fatty acids, are a dietary source of polyphenols and antioxidants. Thus, the present study examined three diets with varying amounts of walnut supplementation to determine if they have similar beneficial properties on brain aging as has been seen previously with fruit or vegetable supplementation. Old rats were fed either a diet not containing walnut or a diet with 2%, 6%, or 9% walnut added for 8 weeks prior to physical and cognitive testing. Results for the motor testing showed that the 2% walnut diet improved performance on a certain test, while the 6% walnut diet improved performance on a different test. However, the highest diet of 9% walnut did not improve performance, and on one test actually impaired performance. All of the walnut diets improved short-term memory in the cognitive task. These findings show for the first time that dietary walnut supplementation can improve cognitive and motor performance in aged rats.

Technical Abstract: Aged rats show decrements in performance on motor and cognitive tasks that require the use of spatial learning and memory. Previously we have shown that these deficits can be reversed by the polyphenolics in fruits and vegetables. Walnuts, which contain the omega-3 fatty acids alpha-linolenic acid (ALA) and linoleic acid (LA), are a dietary source of polyphenols, antioxidants, and lipids. Thus, the present study examined three different doses of a walnut-supplemented diet to determine if they have similar beneficial properties on brain aging as has been seen previously with fruit or vegetable supplementation. Old (19 mo) Fischer 344 (F344) rats were fed a control, 2%, 6%, or 9% walnut diet for 8 weeks prior to motor and cognitive testing. Results for the motor testing showed that the 2% walnut diet improved performance on rod walking, while the 6% walnut diet improved performance on the medium plank walk; the higher dose of 9% walnut diet did not improve psychomotor performance and on the large plank actually impaired performance. All of the walnut diets improved working memory in the Morris water maze, although the 9% diet showed impaired reference memory. These findings show for the first time that dietary walnut supplementation can improve cognitive and motor performance in aged rats.