Patterns of Apoptosis and Autophagy Activation After Hydroxyurea Exposure in the Rat Cerebellar External Granular Layer: an Immunoperoxidase and Ultrastructural Analysis.

The time courses of apoptosis and autophagy activation were investigated in neuroblasts of the cerebellar external granular layer (EGL) following the treatment with a single dose (2 mg/g) of hydroxyurea (HU), a cytotoxic agent. The rats were examined at postnatal day 9 and sacrificed at appropriate times ranging from 10 to 60 h after drug administration. We used the Feulgen method, the TUNEL assay, immunohistochemistry for active caspase-3, and LC3B and p62/SQSTM1 immunoperoxidase procedures. The resulting data indicated that the administration of HU leads to the activation of apoptotic cellular events that began to increase 10 h after HU exposure, peaked at 30 h, and decrease thereafter. It also showed that apoptosis was followed by autophagy activation. Interestingly, LC3B and p62/SQSTM1-stained cells, as well as mitotic cells, started to appear 20 h after the HU injection and their counts increased until 40 h. Afterwards, the values remained stable. The current results highlight an important role of the apoptotic and autophagic processes in the EGL after HU administration. Moreover, they provide a clue for studying the mechanism of chemoresistance triggered by proliferating cells exposed to anticancer agents.