Active neuronal-glial interaction is important in the maintenance of brain
homeostasis and is vital for neuronal survival following brain injury. The
time course of post-ischemic astroglial dysfunction and neuronal death was
studied in the spontaneously hypertensive rat (SHR) brain following permane
nt middle cerebral artery occlusion (MCAO). In situ hybridization with S-35
-labeled riboprobes for GFAP and GLUT3 was used to monitor mRNA expression
in glia and neurons. Astrocytic proteins GFAP, vimentin, S100, Glutathione-
S-Transferase Y-b (GST Y-b) and neuronal protein TG2 were detected by immun
ofluorescence. Cells were co-stained with in situ end labeling (ISEL) to de
tect DNA fragmentation, a hallmark of cell death. GFAP mRNA expression decl
ined rapidly in the ischemic region of the cortex and was almost absent by
12 h. Immunohistochemical studies revealed a parallel decline in the corres
ponding protein: a reduction in GFAP staining was apparent in the infarct a
fter 3 h and by 24 h, there was essentially no remaining GFAP. Three other
glial proteins (vimentin, S100 and GST Y-b) disappeared from infarct over a
similar time course. A few ISEL positive cells were observed in the infarc
t at 6 h, but maximal detection was not seen until 24-48 h. Most of the ISE
L-positive cells were neurons, identified by co-staining with the neuronal
marker TG2. Few cells expressing GFAP or other glial markers were positive
at any time point. Neuronal GLUT3 mRNA declined more slowly than GFAP mRNA
in the ischemic core and disappeared during the period of neuronal death. C
oncurrent with the loss of GFAP mRNA and protein expression in the infarct,
there was a rapid rise in GFAP mRNA in the peri-infarct region of ipsilate
ral hemisphere and proximal region of the contralateral hemisphere. This wa
s followed by the enhanced GFAP protein expression characteristic of reacti
ve astrocytes, but over a significantly slower time course. These studies s
how that MCAO leads to a rapid decline of GFAP mRNA and glial proteins, whi
ch appears to precede the decline in neuronal mRNA and neuronal death withi
n the infarct. Early astroglial dysfunction may play a critical role in det
ermining the outcome of acute hypoxic-ischemic injury by compromising neuro
nal-glial interactions. (C) 1999 Elsevier Science B.V. All rights reserved.