Total number of astrocytes in the molecular layer of the dentate gyrus of rats at different ages.

To estimate the total number of glial fibrillary acidic protein (GFAP)-positive astrocytes and the volume of GFAP-positive structures in the left molecular layer of the dentate gyrus by unbiased methods to provide reference values for neurotoxicologic model studies.The number of astrocytes was estimated by the optical fractionator, and the volume of GFAP-positive structures was estimated by the Cavalieri principle in male Wistar rats at 3, 13 and 25 months of age.The number of astrocytes was statistically significantly increased in the oldest age group (111.000 +/- 11.000 [mean +/- SD]) as compared to the youngest group (88.000 +/- 15.000). The value for 13-month-old rats was intermediate (103.000 +/- 14.000). The GFAP volume per astrocyte was statistically significantly reduced in the oldest age group (441 +/- 103 microns 3) as compared to the youngest one (673 +/- 146). The GFAP volume per astrocyte of 13-month-old rats was intermediate (629 +/- 245).There is a slight increase in the number of astrocytes with age and a slight decrease in GFAP volume per astrocyte with age. Stereology combined with immunohistochemistry is a strong tool for estimation of the total number of accurately identified cells in different brain regions.