Action of steroid hormones on growth and differentiation of CNS and spinal cord organotypic cultures.

During the prenatal period, gonadal steroid environment induces dramatic sexually dimorphic changes in the nervous system. We have used in vitro methods to study the mechanism and timing of hormonal influences on neuronal sprouting and myelination during the prenatal period. Organotypic cultures of hypothalamus and lumbar spinal cord (SC) slices from rat fetuses were grown on plasma clot or in hyaluronic acid and exposed to estrogen (17 beta estradiol) and testosterone (T) during cultivation. Both steroid hormones were active: 17 beta estradiol enhanced sprouting of hypothalamic neuronal fibers and increased the amount of synapses. In SC cultures T induced regeneration of thick nerve processes and an early onset of myelination, mainly of peripheral myelin.