Relationship between brain zinc and transient learning impairment of adult rats fed zinc-deficient diet

The relationship between brain zinc and learning behavior was studied based on the data of 65Zn localization in the hippocampal formation. Learning behavior, tested by passive avoidance performance, of 6-week-old rats improved significantly compared to that of 4-week-old rats and it was maintained at 20 weeks of age. When 8-week-old rats were fed zinc-deficient diet for 4 weeks, the learning behavior was significantly impaired. However, it was recovered to almost normal level by feeding with control (zinc-adequate) diet for 5 weeks. These results demonstrate that a proper zinc supply to the brain is necessary for improvement and maintenance of learning ability. Although an appreciable decrease in brain zinc was not observed in the rats fed zinc-deficient diet for 4 weeks, significant decrease of hippocampal zinc was observed in rats fed zinc-deficient diet for 12 weeks. Moreover, synaptosomal zinc in the hippocampal formation and cerebral cortex was significantly decreased by the 12 weeks of zinc deprivation. These results suggest that the decrease of vesicular zinc in the hippocampal formation and cerebral cortex is involved in the transient learning impairment of adults rats.