Stereological estimation of total microglia number in mouse hippocampus

Microglia are brain cells of considerable interest because of their role in CNS inflammatory responses and strong association with neuritic plaques in Alzheimer's disease (AD). In the present study, immunocytochemistry was co mbined with unbiased stereology to estimate the mean total number of microg lia in dentate gyrus and CA1 regions of the mouse hippocampus. Systematic-u niform-random (SUR) sections were cut through the hippocampal formation of male C57BL/6J mice (n = 7, 4-5 months) and immunostained with Mac-1, an ant ibody to the complement subunit 3 receptor (CR3). The total number of Mac-1 immunopositive cells was determined using the optical fractionator method. The mean total number of microglia in the mouse dentate gyrus was estimate d to be 20300 (CV = 0.21) with a mean coefficient of error (CE)= 0.09. The mean total number of microglia in the mouse CA1 was estimated to be 43200 ( CV = 0.24) with a CE = 0.11. Comparison of total number estimates, derived from fraction- or volume-based methods, supported stereological theory rega rding the equivalence of the two techniques. The time required to determine total microglia number in both hippocampal sub-regions was approximate to 6 h per mouse from stained sections. The combination of immunocytochemistry and stereology provides a reliable means to assess microglia number that c an easily be adopted for studies of transgenic and lesion-based models of a ging and neurodegenerative diseases. (C) 1998 Elsevier Science B.V. All rig hts reserved.