When vitamin A is added back to their diets, the impairment is reversed. At 15 weeks of age, the responses of vitamin A-deprived mice are reduced to about 50 percent normal. Adding vitamin A back to the diet for as little as two days restores brain responses to normal levels. Normal function was also restored when isolated hippocampus tissue from the mice was bathed in vitamin A, indicating that the nutrient functions in the hippocampus directly, not in other parts of the brain that might influence the important learning region. The current work builds on earlier studies from Evans' laboratory, in which researchers found that mice born without receptors for vitamin A in the hippocampus lacked LTP ability and performed under par in standardized learning tests.
Receptors are molecules within brain cells that detect and respond to the vitamin.
Now we've shown that removing vitamin A from fully-developed animals impairs learning pathways, and equally important, the effects are reversible. Salk co-authors include Dinah Misner, Yasushi Shimizu, Luigi De Luca and Professor Charles Stevens. Evans and Stevens are Howard Hughes Medical Institute investigators. The Salk Institute for Biological Studies, located in La Jolla, Calif., is an independent nonprofit institution dedicated to fundamental discoveries in the life sciences, the improvement of human health and conditions, and the training of future generations of researchers. The Institute was founded in 1960 by Jonas Salk, M.D., with a gift of land from the City of San Diego and the financial support of the March of Dimes Birth Defects Foundation.