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 pro tein (GFAP)-positive astrocytes and the volume of GFAP-positive struct ures in the left molecular layer of the dentate gyrus by unbiased meth ods to provide reference values for neurotoxicologic model studies. ST UDY DESIGN: The number of astrocytes was estimated by the optical frac tionator, and the volume of GFAP-positive structures teas estimated by the Cavalieri principle in male Wistar vats at 3, 13 and 25 months of age. RESULTS: The number of astrocytes was statistically significantl y 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 volu me per astrocyte teas statistically significantly reduced in the oldes t age group (441 +/- 103 mu m(3)) as compared to the youngest one (673 +/- 146). The GFAP volume per astrocyte of 13-month-old rats was inte rmediate (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 It strong tool for estimation of the total number of accurately identi fied cells in different brain regions.