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

The relationship between brain zinc and learning behavior was studied based on the data of Zn-65 localization in the hippocampal formation. Learning b ehavior, tested by passive avoidance performance, of 6-week-old rats improv ed 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 r ecovered to almost normal level by feeding with control (zinc-adequate) die t for 5 weeks. These results demonstrate that a proper zinc supply to the b rain is necessary for improvement and maintenance of learning ability. Alth ough 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, synapt osomal zinc in the hippocampal formation and cerebral cortex was significan tly decreased by the 12 weeks of zinc deprivation. These results suggest th at the decrease of vesicular zinc in the hippocampal formation and cerebral cortex is involved in the transient learning impairment of adults rats. (C ) 2000 Elsevier Science B.V. All rights reserved.