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Dehydroepiandrosterone (DHEA) and its sulfate derivative (DHEAS) are the most abundant steroids produced by the human adrenal, but no receptors have been identified for these steroids, and no function for them has been established, other than as precursors for sex steroid synthesis. DHEA and DHEAS are found in brains from many species, and we have shown that enzymes crucial for their synthesis, especially P450c17 (17␣-hydroxylase͞c17,20 lyase), are expressed in a developmentally regulated, region-specific fashion in the developing rodent brain. One region of embryonic expression of P450c17, the neocortical subplate, has been postulated to play a role in guiding cortical projections to their appropriate targets. We therefore determined if products of P450c17 activity, DHEA and DHEAS, regulated the motility and͞or growth of neocortical neurons. In primary cultures of mouse embryonic neocortical neurons, DHEA increased the length of neurites containing the axonal marker Tau-1, and the incidence of varicosities and basket-like process formations in a dose-dependent fashion. These effects could be seen at concentrations normally found in the brain. By contrast, DHEAS had no effect on Tau-1 axonal neurites but increased the length of neurites containing the dendritic marker microtubule-associated protein-2. DHEA rapidly increased free intracellular calcium via activation of Nmethyl-D-aspartate (NMDA) receptors. These studies provide evidence of mechanisms by which DHEA and DHEAS exert biological actions, show that they have specific functions other than as sex steroid precursors, mediate their effects via nonclassic steroid hormone receptors, and suggest that their developmentally regulated synthesis in vivo may play crucial and different roles in organizing the neocortex.Neurosteroids including pregnenolone, allopregnanolone, dehydroepiandrosterone (DHEA), and their sulfated and lipoidal fatty acid ester derivatives are synthesized in the nervous system from cholesterol (1, 2). The same steroidogenic enzymes are found in the nervous system and in the classical steroidogenic tissues (3-9) although their extremely low level of expression in the brain and peripheral nervous system delayed their identification. DHEA and its sulfated derivative (DHEAS) and lipoidal fatty acid ester derivatives are abundant (10 Ϫ8 to 10 Ϫ7 M) in rodent, rabbit, monkey, dog, and human brains (10-14) but expression of P450c17, the sole enzyme having the 17␣ hydroxylase and c17,20 lyase activities needed for DHEA synthesis (15-17) only recently was identified in the fetal but not adult rodent brain (7). Some neurosteroids, such as allopregnanolone and pregnenolone, act through ␥-aminobutyric acid (GABA) A (18-20) receptors while the neurosteroid pregnenolone sulfate may act through NMDA receptors (21, 22) rather than through classical nuclear steroid hormone receptors. Using these neurotransmitter receptors, allopregnanolone elicits anxiolytic, anticonvulsant activity (23, 24). Pregnenolone sulfate, DHEA and DHEAS enhance memory in mi...

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Neurosteroids are steroids that are synthesized de novo in the brain and include some classical (adrenal and gonadal steroids) and some unique brain-specific steroids. Neurosteroids are thought to mediate their action through ion gated channel receptors such as gamma-aminobutyric acid(A) and N-methyl-D-aspartate rather than through classical nuclear steroid hormone receptors. Some enzymes involved in neurosteroidogenesis have been identified as those found in steroidogenic tissues, and some may be unique to the brain. We previously demonstrated that the messenger RNAs (mRNA) for the cholesterol side-chain cleavage enzyme, cytochrome P450scc, and one form of 11 beta-hydroxylase, cytochrome P450c11 beta, are regionally expressed in the adult rat brain. However, cytochrome P450c17, which has 17-hydroxylase and 17,20-lyase activity and is thought to be required for the synthesis of dehydroepiandrosterone, was not detected in any region of the rat brain, even though dehydroepiandrosterone is one of the most abundant neuroactive steroids. We now demonstrate that P450c17 is expressed in the nervous system of the developing rodent embryo. By ribonuclease protection assays, P450c17 mRNA was found in the trunk but not in the head of rat embryos but reverse transcriptase-polymerase chain reaction analysis showed expression of P450c17 mRNA in the head of E15.5 to E19.5 rat embryos. Immunocytochemically detectable P450c17 protein was expressed in the nervous system as early as embryonic day E10.5 in the mouse, mainly in tissue derived from the neural crest. Neuronal cell bodies as well as fibers staining for P450c17 were observed in the central and peripheral nervous systems. The sites of P450c17 expression in the peripheral nervous system suggest it may be involved in a wide variety of sensory-motor functions. In the central nervous system, cell bodies expressing P450c17 are found in the hind brain, in mesencephalic nuclei, and in a region in the location of the locus coeruleus, but in cells distinct from those expressing the dopamine-beta-hydroxylase. Furthermore, its particular location and temporal expression in axons reaching the cortical areas suggest it is a marker for the axonal growth in this region, and that its neurosteroid product may be a signal for targeting cortical axons during embryogenesis.