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 proliferation in the deafferented dentate molecular layer. Double-labelling immunocytochemistry for the astrocyte-specific antigen glial fibrillary acidic protein or the microglial cell marker Griffonia simplicifolia isolectin B4 with bromodeoxyuridine detection revealed that microglia counts and the proliferation rate in the ipsilateral dentate gyrus reached a maximum in the molecular 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 reverted to control levels. Glial proliferation was not restricted to the ipsilateral molecular layer but also occurred to some degree in the granule cell layer and the contralateral dentate gyrus. Thus entorhinal cortex lesion induces a rapid microglia reaction and long-lasting astrocyte activation in the deafferented termination zone of the perforant path. We conclude that glial proliferation after entorhinal cortex lesion follows a complex temporal and spatial pattern that coincides with processes of neuronal and axonal reorganization.