COMPARATIVE FRACTAL ANALYSIS OF CULTURED GLIA DERIVED FROM OPTIC-NERVE AND BRAIN DEMONSTRATE DIFFERENT RATES OF MORPHOLOGICAL-DIFFERENTIATION

O-2A progenitor cells derived from neonatal rat cerebral hemispheres o r optic nerves, were induced to differentiate in culture into either o ligodendrocytes or type 2 astrocytes. The fractal dimensions, a measur e of morphological complexity, of the differentiating glial cells were measured over time. Analysis of the changes in fractal dimension (D) with respect to time revealed specific rates of growth for each glial phenotype and a specific final D. The time course of these changes is well fit by a simple mathematical model. While brain-derived oligodend rocytes matured faster than the astrocytes, they ultimately attained c omparable levels of complexity, with similar maximum fractal dimension s. Oligodendrocytes from nerve also matured faster than nerve derived astrocytes, in contrast, however, they attained a greater morphologica l complexity than nerve astrocytes. While the brain-derived oligodendr ocytes showed a faster rate of maturation than their optic nerve count erparts, astrocytes from both regions had similar rates of morphologic al differentiation. Self-similarity, a defining property of fractal ob jects was investigated, by determining the fractal dimension of cells over a range of magnifications. The calculated fractal dimension remai ned constant over a 10-fold range in optical magnification, illustrati ng that cultured glial cells exhibit this important characteristic of fractal objects. In addition, we analyzed the branching patterns of gl ial processes by the Sholl method and found that the results were not as interpretable or meaningful as those of fractal analysis.