Ionizing radiation can significantly affect brain function in children and young adults, particularly in the hippocampus where neurogenic niches are located. Injury to normal tissue is a major concern when whole-brain irradiation (WBI) is used to treat central nervous system (CNS) tumors, and the pathogenesis of this injury remains poorly understood. We assessed the expression of selected neurotrophins (NTs) and NT receptors (NTRs) in brains of young mice after a single 10 Gy gamma-ray exposure using morphological and molecular analyses [qRT-PCR, Western blot, immunohistochemistry (IHC)] to evaluate WBI-induced injury in its acute phase. Activity of the NT–NTR axes was examined by analysis of ERK and Akt phosphorylation. Using Nissl staining of hippocampus slices to visualize morphological changes, and TUNEL assay and active caspase-3 detection to assess apoptotic cell death, we found evidence of apoptosis and degenerative changes in hippocampal tissue after WBI. Shortly after WBI, we also observed significant overexpression of several NTs (BDNF, NT-3, NGF and GDNF) and NTRs (TrkA, TrkB, TrkC, GFRα-1, and p75NTR) compared to control animals. The upregulated NT and NTR proteins, in part, originated from two analyzed neurogenic areas: the subgranular zone of the hippocampal dentate gyrus and the subventricular zone, as confirmed by IHC. Finally, components of intracellular signaling pathways, including Akt and MAPK, were activated in acute phase after WBI. Given the role of NTs in diverse biological mechanisms, including maintenance and growth of neurons in the adult brain, our findings of altered expression of neurotrophins and their receptors in brain tissue shortly after irradiation suggest that these molecules play a vital role in the pathophysiology of the acute phase of WBI-induced injury.
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Vol. 186 • No. 5