Differential expression of doublecortin and microglial markers in the rat brain following fractionated irradiation.

Ionizing radiation induces altered brain tissue homeostasis and can lead to morphological and functional deficits. In this study, adult male Wistar rats received whole-body exposure with fractionated doses of gamma rays (a total dose of 5 Gy) and were investigated 30 and 60 days later. Immunohistochemistry and confocal microscopy were used to determine proliferation rate of cells residing or derived from the forebrain anterior subventricular zone (SVZa) and microglia distributed along and/or adjacent to subventricular zone-olfactory bulb axis. Cell counting was performed in four anatomical parts along the well-defined pathway, known as the rostral migratory stream (RMS) represented by the SVZa, vertical arm, elbow and horizontal arm of the RMS. Different spatiotemporal distribution pattern of cell proliferation was seen up to 60 days after irradiation through the migratory pathway. A population of neuroblasts underwent less evident changes up to 60 days after treatment. Fractionated exposure led to decline or loss of resting as well as reactive forms of microglia until 60 days after irradiation. Results showed that altered expression of the SVZa derived cells and ultimative decrease of microglia may contribute to development of radiation-induced late effects.