EXOGENOUS TESTOSTERONE DIFFERENTIALLY AFFECTS MYELINATION AND NEURON SOMA SIZES IN THE BRAIN OF CANARIES

WE assessed the temporal and functional relationship of myelin maturat ion and of neuronal development in the telencephalic song motor centre s of the canary at different developmental stages. Brain differentiati on was modulated by exogenous testosterone, its effects on song qualit y were also monitored. Myelin maturation was studied by using computer aided analysis of silver impregnated brain sections, whereas the diff erentiation of neurones was determined by measuring neuronal soma size s. At an early developmental stage, testosterone triggers growth of ne urones but does not affect myelination. At a later developmental stage , both neurone soma sizes and myelination are enhanced by testosterone .