Identification of living oligodendrocyte developmental stages by fractal analysis of cell morphology

The Mandelbrot's fractal dimension (D), a measure of shape complexity, has been used to quantify the complex morphology of living cells. Previous stud ies on glial cells have shown that as cells increase in morphological compl exity, their "D" value increases, suggesting that "D" could be used to esti mate their stage of differentiation. In the present study the box-counting method was used to calculate the "D" values of rat cerebellar oligodendrocy tes during their differentiation in primary culture. These values were corr elated with the immunoreactivity of cells to antigenic markers commonly use d for assessing their stages of differentiation: A2B5, O4 and anti-galactoc erebroside (Gal-C). Our results show that changes of the fractal dimension during differentiation follow the well known pattern of markers expression by these cells. These results demonstrate that A2B5-, O4-, and Gal-C-expres sing oligodendrocytes can be confidently estimated from their respective fr actal dimension values. Based on this immunocytochemical calibration, the c alculation of "D" allows an easy and fast determination of the developmenta l stage of living (unstained) oligodendrocytes before the study of their ph ysiological characteristics. Using this method we precisely identified livi ng oligodendrocyte progenitors and early pro-oligodendrocytes expressing vo ltage-activated sodium currents that is a common characteristic of these tw o immature developmental stages. (C) 2001 Wiley-hiss, Inc.