PHOTOCHEMICALLY INDUCED FOCAL CEREBRAL-ISCHEMIA IN RAT - TIME-DEPENDENT AND GLOBAL INCREASE IN EXPRESSION OF BASIC FIBROBLAST GROWTH-FACTORMESSENGER-RNA

Induction of basic fibroblast growth factor (bFGF) mRNA expression was studied in a Rose bengal induced focal cerebral ischemia during a tim e course of 2, 4, 24, 72 h and 7 days. Focal cerebral ischemia induced by Rose bengal resulted in a global upregulation in bFGF gene express ion at the 24 h time-interval. This upregulation in bFGF gene expressi on was due to an upregulation in glial bFGF expression in most of the areas studied as seen by means of non-radioactive in situ hybridizatio n in combination with immunocytochemistry for glial fibrillary acidic protein. However, in the piriform cortex a putative neuronal upregulat ion of bFGF could be detected by combination of non-radioactive in sit u hybridization, immunohistochemistry for glial fibrillary acidic prot ein and nuclear staining with Neutral red. Semiquantitative data conce rning bFGF mRNA expression were obtained by use of computer-assisted m icrodensitometry and revealed substantial increases in bFGF mRNA expre ssion in the cingulate cortex, the neostriatum, a 1 mm marginal zone c lose to the external capsule and the olfactory tubercle at bregma leve ls 1 to 2 mm rostral to the lesion. No changes in bFGF gene expression were seen in field CA1 of Ammon's horn on the lesioned side and in de ntate gyrus at bregma levels between - 2.12 to - 3.30 mm. We observed significant changes in bFGF upregulation in the caudate putamen, the p iriform cortex and the amygdaloid region and the frontoparietal cortex at bregma levels - 2.12 to - 3.30 mm. These data indicate that photoc hemically induced focal cerebral ischemia leads to an early and global response in bFGF gene expression, which is due to an upregulation mai nly in astrocytes. The observed widespread upregulation of the bFGF ge ne transcription rostral and caudal to the lesion is suggested to be d ue in part to neuronal glutaminergic connections between the areas inv estigated and in part due to increases in extracellular fluid signals (volume transmission).