Expression of cell cycle proteins (cyclin D1 and cdk4) after controlled cortical impact in rat brain

We measured the expression of Cyclin D1 and its kinase cdk4, 48 h after induction of cortical contusion in the rat. Brain from rats (n = 6) subjected to controlled cortical impact injury and sham-operated (n = 3) and normal (n = 2) rats were processed for dual label immunohistochemical study to identify cellular expression of these cell cycle proteins. Antibodies against neurofilaments 68 and 200 and glial fibrillary acidic protein were employed to identify neurons and astrocytes, respectively, whereas microglia were identified using histochemical detection of IB4-isolectin. Double staining for DNA fragmentation detection, using terminal deoxynucleotdyl transferase mediated biotinylated deoxyuridine triphosphate nick end 3 'OH labeling (TUNEL) and antibodies for expression of Cyclin D1 and cdk4 was also performed. Cyclin D1 and cdk4 were selectively expressed in morphologically intact or injured neurons throughout the rat brain. Apoptotic cells were not immunoreactive to Cyclin D1 and cdk4. The selective expression of cell cycle proteins observed in nonapoptotic postmitotic neurons suggests a role for these proteins in the survival of cells after cortical contusion.