Upregulation of phospholipase D in astrocytes in response to transient forebrain ischemia

Previous in vitro studies using cell cultures or brain slices have demonstr ated that phospholipase D (PLD) in the nervous system is involved in the si gnaling mechanism in response to a variety of agonists. However, little is known about the pathophysiological role of PLD-mediated signaling in the ad ult brain. We examined the changes in the expression of a PLD isozyme, PLD1 , in the adult rat hippocampus, using immunological approaches and an assay for PLD activity after transient forebrain ischemia (four-vessel occlusion model) that results in the selective delayed death of CA1 pyramidal cells and induces reactive astrocytes in the CA1 subfield. In the control hippoca mpus, PLD1 the level of immunoreactivity was very low. After ischemia, in p arallel with the results of Western blot analysis and the PLD activity assa y, immunohistochemical analysis of PLD1 demonstrated that the immunoreactiv e proteins peaked at 7-14 days and were most prominent in the CA1 and the d entate hilar region. The temporal and spatial patterns of immunoreactivity off both PLD1 and glial fibrillary acidic protein (GFAP) were very similar, indicating that reactive astrocytes express PLD1, confirmed by double stai ning for PLD1 and GFAP. These results demonstrate that reactive astrocytes upregulate PLD in vivo after injury in the adult rat hippocampus. (C) 2000 Wiley-Liss, Inc.