Hippocampal cell genesis does not correlate with spatial learning ability in aged rats

Aging in rodents is known to lead to deficits in spatial learning and memory, including decreased performance on the Morris water maze. Recent attention has focused on the possible role of adult hippocampal neurogenesis in regulating spatial learning and memory. Therefore, in this study, we have examined levels of hippocampal cell proliferation in relation to water maze performance in aged and young male Fischer 344 rats. Aged rats (24 months old) were divided into aged-unimpaired and aged-impaired groups based on comparison with performance of young animals. Animals received five daily injections of the thymidine-analog bromodeoxyuridine (BrdU) and were killed 1 week later. Total numbers of BrdU-labeled cells were quantified in the hippocampal dentate gyrus and hilus and were related to behavioral performance. Whereas aging was associated with a significant reduction in the number of BrdU-labeled cells, behavioral impairment with aging was not associated with a further reduction in BrdU labeling. In the context of aging, these finding do not support a direct relationship of adult hippocampal neurogenesis with learning and memory capability.