Characterization of cell proliferation in the adult dentate under normal conditions and after kainate induced seizures using ribonucleotide reductase and BrdU.

Ribonucleotide reductase (RNR), an enzyme for DNA synthesis, was recently used as a marker of proliferating cells in the dentate gyrus and subventricular zone in normal adult mammalian brains. However, the duration of RNR expression in normal adult brain and the expression pattern of RNR in the adult dentate gyrus following brain injury have not been explored. In this study, we examined the duration of the RNR expression in newborn cells in the normal adult rat brain by analysis of RNR and BrdU double-labeled specimens at different time intervals after BrdU application. Secondly, we induced, in adult rats, seizures by kainic acid and investigated the changes in expression of RNR following seizures, and characterized the phenotype of RNR-positive cells using a variety of other markers. Our results revealed that RNR was detectable in proliferating cells from 2 h to at least 1 day. At 7 and 28 days after seizures, there was a fivefold increase in number of clusters of RNR-positive cells in the dentate gyrus, and a doubling of the number of BrdU-labeled cells in each cluster. Proliferating astrocytes and neuronal precursors were recognized in each RNR-positive cell cluster, and both types increased in number after seizures. Colocalization of RNR and activated caspase-3 was observed at 7 days, indicating that proliferating cells were susceptible to status epilepticus induced damage. RNR immunohistochemistry provides a useful approach in experiments investigating a change in cell proliferation, revealing the location, number, morphology and fate of newly formed cells after, e.g., brain injury.