[Preweaning exposure to enriched environment induces hippocampal neurogenesis: experiment with rats]

To explore the effects of preweaning exposure to enriched environment on hippocampal neurogenesis and the underlying mechanisms.

Thirty-six 10-day-old SD rats were randomly divided into the 2 equal groups: control group and enriched environment group (EE group. From the age of 10 days to 24 days the rats received intraperitoneal injection of bromodeoxyuridine (BrdU) 50 mg/kg every other day to label the newly proliferated cells in vivo, and the rats in EE group were daily exposed to enriched environment for 20 minutes. Six rats of each group were sacrificed whren they were 24 days of age. Nuclear protein of the hippocampus was extracted to undergo Western blotting to detect the levels of calmodulin and phosphorylated CREB (cAMP response element binding). Other rats were sacrificed at the age of 63 days. Coronal cryostat sections of brain were cut. Sections at the level 3.6 mm posterior to the bregma were obtained and stained with methyl aniline blue and the number of cells in the hippocampal dentate gurus (DG) of the right hemisphere were counted using x 400 microscope. BrdU immunohistochemistry and double immunofluorescence labeling with BrdU/NeuN or BrdU/GFAP were done, and the numbers of BrdU-labeled cells and ratios of neurons and astrocytes differentiated from BrdU-labeled cells were calculated.

The levels of calmodulin and phosphorylated CREB in the hippocampal nuclear extract of the EE group were 0.065 +/- 0.035 and 0.485 +/- 0.007 respectively, both significantly higher than those of the control group (0.245 +/- 0.035 and 0.220 +/- 0.014 respectively, P = 0.01 and P = 0.002). The number of cells in the DG area of right hippocampus 3.6 mm posterior to bregma of the EE group was 1580 +/- 72, significantly higher than that of the control rats (1375 +/- 62, t = -7.461, P < 0.01). The number of BrdU labeled cells of the EE group was 5363 +/- 487, significantly higher than that of the control group (2984 +/- 318, t = -14.177, P < 0.01). The ratio of neurons of the EE group was 85.0% +/- 2.8%, significantly higher than that of the control group (80.2% +/- 2.8%, t = -4.166, P < 0.01). The differentiation rate of astrocytes of the EE group was 4.0% +/- 0.5%, significantly higher than that of the control group (2.6% +/- 0.6%, t = -6.493, P < 0.01).

Preweaning exposure to enriched environment can induce neurogenesis. The underlying mechanism may be that enriched environment induces the activation of calmodulin and CREB in hippocampus.