Steroidogenic enzymes in the brain: morphological aspects.

It is now well documented that brain tissue is capable of synthesizing de novo bioactive steroids, named neurosteroids, which are involved in the regulation of various functions in the brain, including behavioral, neuroendocrine and metabolic processes. In this chapter, we have summarized the current knowledge about the expression of enzymes involved in the biosynthesis and metabolism of steroids in the brain with special emphasis on the morphological localization of those enzymes. The results obtained following use of immunocytochemistry and/or in situ hybridization indicate that the enzymes are expressed in both neurons and glial cells distributed throughout the brain with some species-related variations. As observed at the electron microscopic level, the enzymes localized in the neurons or glial cells are not associated with any specific organelles, being distributed throughout the cytoplasm. Since usually one nerve cell expresses only one enzyme, it might be suggested that the neuroactive steroid synthesis that requires the action of several enzymes involves the intervention of several cells (neurons and/or glial cells). More work is required to fully establish the migration of precursors and active steroids in the brain.