Busulfan-induced pathological changes of the cerebellar development in infant rats

Busulfan, an antineoplastic bifunctional-alkylating agent, is known to induce developmental anomalies and fetal neurotoxicity. We previously reported that busulfan induced p53-dependent neural progenitor cell apoptosis in fetal rat brain (Ohira et al., 2012). The present study was carried out to clarify the characteristics and sequence of busulfan-induced pathological changes in infant rat brain. Six-day-old male infant rats were treated with 10, 20, 30 or 50 mg/kg of busulfan, and their brains were examined at 1, 2, 4, 7, and 14 days after treatment (DAT). As a result, histopathological changes were selectively detected in the external granular layer (EGL), deep cerebellar nuclei (DCN) and cerebellar white matter (CWM) in the cerebellum with dose-dependent severity but not in the cerebrum. In the normal infant rat cerebellum, granular cells in the EGL were proliferating and moving to the internal granular layer during the normal developmental process. In the EGL of the busulfan group, apoptotic granular cells increased at 2 DAT simultaneously with increased numbers of p53- and p21-positive cells while mitotic granular cells decreased, suggesting an occurrence of p53-related apoptosis and depression of proliferative activity in granular cells. In the DCN, apoptotic glial cells increased at 2 DAT and glial cells showing abnormal mitosis increased at 4 DAT. In the CWN, edematous change accompanying a few apoptotic cells was found in the CWN, especially in the parafolliculus (PFL), from 2 to 7 DAT. The present study demonstrated for the first time the characteristics and sequence of busulfan-induced pathological changes in infant rat cerebellum.