In vivo evidences of early neurosteroid synthesis in the developing rat central nervous system and placenta.

The aim of the present study was to determine the developmental pattern of progesterone metabolism in rat brain and spinal cord from embryonic day 13 (E13) to the perinatal period. A marked decrease in the 5alpha-reduction of progesterone in brain cortex was observed between E13 and postnatal day 5 (P5). Isopregnanolone was the predominant isomer in E13 in both cortex and spinal cord and its synthesis diminished gradually, while the concentration of allopregnanolone did not change significantly during development. The placental tissue was able to synthesize the 3alpha and 3beta isomers in E13, E16 and E19 embryos with allopregnanolone being the major metabolite in all the samples. We conclude that embryonic central nervous system tissues are able to synthesize neurosteroids at least from stage E13 and that they are developmentally regulated.