Experimental protocol.

<p>Effects of 4 months of vitamin A supplementation started at mid-age on spatial memory, hippocampal neurogenesis and retinoid status in rats. The weaned rats and half of the middle-aged rats were fed with a control diet containing 5 IU retinol/g during 4 months (control condition): they are referred to as the 5-month-old young rats and the 17-month-old aged rats, respectively. The second half of the middle-aged group received the vitamin A-enriched diet (45 IU retinol/g) for the same duration : they are referred to as the 17-month-old enriched-aged rats.