The 5 α-reductase in the central nervous system: expression and modes of control

The present paper will summarize two important aspects of the interactions between steroids and the brain, which have recently been studied in the authors' laboratory. In particular the paper will consider data on: (1) the significance of the two isoforms of the 5 α-R during brain ontogenesis and development, and (2) the cross-talk between glial and neuronal elements, particularly in relation to the metabolism of sex hormones. (1) The data obtained have shown that the 5 α-R type 1 enzyme is constitutively expressed in the rat CNS at all stages of brain development. Moreover, the expression of the 5 α-R type 1 is similar in males and in females, and does not appear to be controlled by androgens. The gene expression of the 5 α-R type 2 is totally different. This isoform appears to be expressed in the rat brain almost exclusively in the late fetal/early post-natal life and is controlled by testosterone. (2) The present data show that two cell lines derived respectively from a rat glioma (C6 cell line) and from a human astrocytoma (1321N1 cell line) are able to convert testosterone and progesterone into their corresponding 5 α-reduced metabolites dihydrotestosterone and dihydroprogesterone. The possibility that secretory products of normal and tumoral brain cells might be able to influence steroid metabolism occurring in the two glial cell lines previously mentioned has been considered.