DIFFERENTIAL REGULATION OF C-FOS EXPRESSION AFTER CORTICAL BRAIN INJURY DURING DEVELOPMENT

Unilateral cortical brain injury is accompanied by widespread expressi on of c-fos protein(s) throughout the wounded cortex, including areas far from the lesion site. Here we report that this phenomenon is diffe rentially regulated during development. At postnatal day (PD) 10 or 15 , when rats were sacrificed 1.5 h after a mechanical cortical injury, they did not show an increase in c-fos immunoreactivity far from the w ound, despite the fact that some of these animals (PD 15) displayed a positive response close to the lesion. At PD 22, the same injury induc ed an increase in c-fos-immunoreactive nuclei in the piriform cortex i psilateral, but not contralateral, to the lesion. This pattern was mai ntained up to at least PD 360. Similarly, the presence of c-fos-immuno reactive cells was observed in the ipsilateral cingulate cortex in ani mals 22 days old and older. The pattern of c-fos expression in adult a nimals after mechanical damage was compared with other models of focal brain injury: application of potassium to the cortical surface and de vascularization. Though all models generated c-fos expression far from the lesion site, potassium application resulted in higher numbers of c-fos-positive cells, particularly in the cingulate cortex. This study shows that c-fos expression after cortical brain injury is regulated differently during development, and that dissimilar models of cortical injury induce qualitatively similar responses although c-fos-like pro tein expression differs quantitatively.