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

OBJECTIVE: 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 gyras by unbiased methods to provide reference values for neurotoxicologic model studies. STUDY DESIGN: 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. RESULTS: 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 μm3) as compared to the youngest one (673 ± 146). The GFAP volume per astrocyte of 13-month-old rats was intermediate (629 ± 245). CONCLUSION: 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.