REPAIR CAPACITY OF ADULT-RAT GLIAL PROGENITOR CELLS DETERMINED BY AN INVITRO CLONOGENIC-ASSAY AFTER INVITRO OR INVIVO FRACTIONATED-IRRADIATION

Demyelination is one of the pathological conditions identified as a la te response of the central nervous system (CNS) to irradiation. We hav e proposed that radiation-induced depletion of glial stem cells, which are the source of myelinating cells in the CNS, would lead to a lack of replacement of senescent or otherwise damaged oligodendrocytes. Thi s impaired process of cell renewal would result in a decline of oligod endrocytes, i.e. demyelination. In the present study the repair capaci ty of glial stem cells was investigated and compared with the repair c apacity of the CNS in vivo using functional endpoints. For this purpos e, glial stem cells, derived from the adult rat optic nerve, were subj ected to fractionated irradiation in vivo and in vitro and their survi val was quantified with an in vitro clonogenic assay. The data were an alysed by three different methods, all based on the LQ-model (single d ose survival curve; 'beta(RR)', 'F(e)-plot'). The resulting value of t he beta-parameter of adult glial stem cells is consistent with values obtained for functional endpoints after irradiation of the CNS in vivo . The alpha/beta-ratio (4.9-7.3Gy) of adult glial stem cells, however, is higher than the alpha/beta-ratio (approximately 2Gy) obtained for CNS in vivo and is closer to that of an acute responding tissue.