ABSTRACT
The intriguing observation that steroids could be synthesized in the brain came initially from experiments performed in the 1980’s by Baulieu and colleagues who found that steroids such as pregnenolone, DHEA and their sulfate and lipoidal esters were present in higher concentrations in tissue from the nervous system (brain and peripheral nerve) than in the plasma. While these compounds could be due to peripheral synthesis and then sequestration in the brain, Baulieu and colleagues found that the steroids remained in the nervous system long after gonadectomy or adrenalectomy (Corpechot et al., 1981, 1983), suggesting that steroids might either be synthesized de novo in the CNS and PNS or might accumulate in those structures. Such steroids were named “neurosteroids” to refer to their unusual origin and to differentiate them from steroids derived from more classical steroidogenic organs such as gonads, adrenals and placentae. How were these steroids synthesized? To test whether steroids were actually made in the brain or if they accumulated specifically in tissue from the nervous system, several laboratories, including our laboratory, determined directly if enzymes known to be involved in steroidogenesis adrenals, gonads and placentae could be responsible for neurosteroids synthesis. These results have established unequivocally that the enzymes found in classic steroidogenic tissues are indeed found in the nervous system (reviewed in MensahNyagan et al., 1999; Compagnone and Mellon, 2000).
