Induction of P-glycoprotein expression in astrocytes following intracerebroventricular kainate injections

The expression of P-glycoprotein (PGP) was studied by immunocytochemistry and light and electron microscopy, in normal rats and after intracerebroventricular kainate injections. Two antibodies to PGP, mdr (Ab-l) and c-219, were used. As in previous studies (Thiebault et al, and Jette et al.), labelled capillaries were observed in normal rats. Kainate injections resulted in death of pyramidal neurons in the hippocampus, and a proliferation of glial cells in the affected cornu ammonis fields. An increase in PGP expression was observed in reactive astrocytes as early as 1 day postinjection. Immunoreactivity peaked at 2 weeks postinjection, but was still visible as late as 10 weeks postinjection. Similar results were observed using the two antibodies. Double immunolabelling and confocal microscopy also showed that PGP was colocalised with GFAP, a marker for astrocytes. The expression of PGP in astrocytes was confirmed by electron microscopy, which showed immunoreaction product in cells containing dense bundles of glial filaments and features of reactive astrocytes. The increased PGP expression in reactive astrocytes could be part of a cellular stress response program in these cells.