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

Zinc is an essential micro-nutrient involved in numerous physiological functions. The high content of zinc in the hippocampus, coupled with the integral involvement of the hippocampus in memory, strongly implicates zinc in memory processing. The hypothesis of the current study was that dietary zinc restriction influenced short-term memory in postweaned rats, and this influence was age-dependent. Male rats (43 days to 18 months old) were divided into five experimental groups based on age, and fed zinc-adequate (zinc at 20 mg/kg as zinc chloride) or zinc-deficient (zinc less than 1-2 mg/kg) diets 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-restricted 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 significantly 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 analyses confirmed that the short-term memory deficits were correlated with significantly lower hippocampal and cerebral zinc concentrations compared to age-matched control and pair-fed rats. These results emphasize the significance 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.