Age-dependent influence of dietary zinc restriction on short-term memory in male rats

Zinc is an essential micro-nutrient involved in numerous physiological func tions. The high content of zinc in the hippocampus, coupled with the integr al involvement of the hippocampus in memory, strongly implicates zinc in me mory processing. The hypothesis of the current study was that dietary zinc restriction influenced short-term memory in postweaned rats, and this influ ence was age-dependent. Male rats (43 days to 18 months old) were divided i nto five experimental groups based on age, and fed zinc-adequate (zinc at 2 0 mg/kg as zinc chloride) or zinc-deficient (zinc less than 1-2 mg/kg) diet s for a minimum of 3 weeks. Short-term memory was assessed using the distal -cue version of the Morris water maze (MWM). All rats fed the zinc-restrict ed diet exhibited cyclic anorexia, decreased weight gain, and significantly lower liver and femur zinc concentrations compared to age-matched controls . Further, whole brain, hippocampal, and cerebral wet weights were signific antly reduced in the zinc-restricted treatment groups of all the age groups . Only zinc-restricted rats that were less than 62 days of age at the start of zinc restriction demonstrated significantly prolonged escape latencies in the water maze, indicating deficits in short-term memory. Regression ana lyses confirmed that the short-term memory deficits were correlated with si gnificantly lower hippocampal and cerebral zinc concentrations compared to age-matched control and pair-fed rats. These results emphasize the signific ance of a critical age of influence for dietary zinc in memory processing, and the importance of considering age when studying zinc nutriture and CNS function. (C) 2001 Elsevier Science Inc. All rights reserved.