Maternal care influences neuronal survival in the hippocampus of the rat

Maternal care during the first week of postnatal life influences hippocampal development and function (Liu et al., 2000; Nature Neurosci., 3, 799-806). Offspring reared by mothers who exhibit increased levels of pup licking/grooming (LG) show increased hippocampal synaptic density and enhanced spatial learning and memory. Using 5-bromo-2'-deoxyuridine (BrdU), a thymidine analogue incorporated into cells during DNA synthesis, we examined the effects of early maternal care on hippocampal cell proliferation and neuronal survival in the rat. Twenty-four hours following injection on day 7 of life (P7) there were no differences in BrdU labelling in the offspring of high- compared with low-LG mothers, suggesting no maternal effect on the rate of proliferation at this age. However, 14 and 83 days following injection (P21 and P90), the offspring of high-LG mothers had significantly more surviving BrdU-labelled cells and BrdU-NeuN+-colabelled neurons in the dentate gyrus subgranular zone and granule cell layer. At P21, the offspring of high-LG mothers showed increased protein expression of basic fibroblast growth factor and significantly decreased levels of pyknosis. These findings suggest an influence of maternal care on neuronal survival in the hippocampus. Conversely, at the same time point there was a significantly higher level of hippocampal glial fibrillary acidic protein expression in the offspring of low-LG mothers. These findings emphasize the importance of early maternal care for hippocampal development.