Proliferation of microglia and astrocytes in the dentate gyrus following entorhinal cortex lesion: a quantitative bromodeoxyuridine-labelling study

Entorhinal cortex lesion of adult rats induces glial activation and prolife ration in the deafferented dentate molecular layer. Double-labelling immuno cytochemistry for the astrocyte-specific antigen glial fibrillary acidic pr otein or the microglial cell marker Griffonia simplicifolia isolectin B-4 w ith bromodeoxyuridine detection revealed that microglia counts and the prol iferation rate in the ipsilateral dentate gyrus reached a maximum in the mo lecular layer at 3 days post-lesion (dpl) and returned to control levels by 30 dpl. Astrocyte counts in the ipsilateral dentate gyrus peaked at 30 dpl , with maximum proliferation at 7 dpl. At 100 dpl the astrocyte count had r everted to control levels. Glial proliferation was not restricted to the ip silateral molecular layer but also occurred to some degree in the granule c ell layer and the contralateral dentate gyrus. Thus entorhinal cortex lesio n induces a rapid microglia reaction and longlasting astrocyte activation i n the deafferented termination zone of the perforant path. We conclude that glial proliferation after entorhinal cortex lesion follows a complex tempo ral and spatial pattern that coincides with processes of neuronal and axona l reorganization.