Transient increase in endogenous basic fibroblast growth factor in neurons of ischemic rat brains

An antiserum against basic fibroblast growth factor (bFGF) was shown to recognize an 18-kDa protein (possibly bFGF) in crude neocortical extracts by immunoblot and used to investigate the changes of bFGF immunoreactivity in neurons and astrocytes of the cerebral cortex of rats 1-21 days after unilateral occlusion of the middle cerebral artery (MCA). The mildly ischemic neocortex exhibited no signs of cell loss or degeneration in Nissl-stained sections 1-14 days after MCA occlusion, but it contained pyramidal cell bodies and processes with more intense bFGF immunoreactivity than did the control neocortex. bFGF immunoreactivity in the ischemic hemisphere gradually declined in intensity and by 21 days after MCA occlusion, it had reached the control level. On the other hand, there were many bFGF immunoreactive astrocytes in the primary olfactory cortex on the side of infarction. These findings suggest that MCA occlusion causes an increase in bFGF content not only in astrocytes but also in neurons, depending on the severity of the ischemic insult in individual cortical regions. The transient augmentation of bFGF expression or accumulation in mildly ischemic pyramidal neurons but not in astrocytes is in line with previous studies suggesting the neurotrophism of exogenously applied bFGF.