Previous in vitro studies using cell cultures or brain slices have demonstrated that
phospholipase D (
PLD) in the nervous system is involved in the signaling mechanism in response to a variety of agonists. However, little is known about the pathophysiological role of
PLD-mediated signaling in the adult 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 hippocampus, PLD1 the level of immunoreactivity was very low. After
ischemia, in parallel with the results of Western blot analysis and the
PLD activity assay, immunohistochemical analysis of PLD1 demonstrated that the immunoreactive
proteins peaked at 7-14 days and were most prominent in the CA1 and the dentate hilar region. The temporal and spatial patterns of immunoreactivity of both PLD1 and
glial fibrillary acidic protein (GFAP) were very similar, indicating that reactive astrocytes express PLD1, confirmed by double staining for PLD1 and GFAP. These results demonstrate that reactive astrocytes upregulate
PLD in vivo after injury in the adult rat hippocampus.