Effects of dietary zinc-deprivation and pair-feeding on water maze performance and protein expression in young male rats
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Zinc deprivation in young rats has been shown to negatively affect short-term memory in a water maze. This study explores further the behavioral performance of rats in the maze. A revised short-term memory testing procedure was used and no short-term memory deficit was observed in zinc-deprived rats. This observation was different from previous results and may lie in differences in the methodological approach used for determining the short-term memory. Long-term memory and learning ability were also measured. No dietary effects on long-term memory were found, but the pair-fed rats exhibited less effective learning in the consecutive and reversal-learning tests compared with the control group. Both the pair-fed and zinc-deprived animals exhibited thigmotaxic (wall-hugging) behavior in the learning test but to different degrees. Thigmotaxic behavior in the zinc-deprived rats was less severe than that of the pair-fed rats. The stress response of these rats before and after the swim tests indicated that the zinc-deprived and pair-fed rats were stressed by the dietary treatment. However, the stress level of pair-fed rats was elevated earlier than the zinc-deprived group. The stress responses in these rats may contribute to their anxiety-related thigmotaxic behavior, but may not be the only cause of the behavioral differences. Neurological changes in the cerebellum and the cholinergic systems may also be involved. Interestingly, the learning deficits observed in consecutive swim tests were not obvious in the learning tests with probing test insertions, suggesting that the consecutive swim test is a more sensitive measure of learning performance. Differential protein expression in the hippocampal region of these rats was determined using two-dimensional gel electrophoresis. The changes in protein profiles suggest that zinc deprivation and pair feeding affect protein expression differently. Twenty differentially expressed protein spots were tentatively identified using the program TagIdent and the SWISS-PROT database. The results indicate that dietary treatment affects the expression of a wide range of proteins.