The effects of exogenously applied hormones on glial cell maturation of telencephalic song motor centers, midbrain and cerebellar structures was studied in juvenile male zebra finches. Testosterone was administered and the development of oligodendrocytes was studied using immunochemistry and computer aided image analysis on silver impregnated brain sections. A testosterone induced acceleration of oligodendrocyte maturation could be detected in several brain areas by using the monoclonal antibody O 10 recognizing an oligodendrocyte-specific cell surface antigen and by the silver impregnation for myelin. The increase in myelin density was higher in the testosterone treated animals than in the control animals in the forebrain and in the cerebellum, whereas two regions in the midbrain showed no difference between treated and controls.
