**2.9 The brain is an endocrine organ and can produce androgens**

These enzymes as well as others are critical for *de novo* production of androgens in the brain (termed "neurosteroidogenesis) from precursors, such as cholesterol, pregnanolone, and progesterone. The biosynthetic pathway for neurosteroid production involves many recognized factors, including the 18kDA translocator protein (see **Figure 7**): TSPO, a.k.a. peripheral-type benzodiazepine receptor), the steroidogenic acute regulatory (StAR) protein, cytochrome P450-dependent C27 side chain cleavage enzymes (P450scc), 3β-hydroxysteroid dehydrogenase (3β-HSD),

#### **Figure 6.**

*Metabolic pathways for formation of testosterone and its metabolites in the brain, figure provided by and modified from colleague Marco Bortelatto.*

*Androgens' Effects across the Lifespan in Men and Animal Models DOI: http://dx.doi.org/10.5772/intechopen.96707*

5α-reductase, and 3α-HSD. TSPO and StAR have actions to transport cholesterol (a requisite precursor for all steroids) into the mitochondria. In the mitochondria, cholesterol is oxidized by P450scc to form pregnanolone, which is then metabolized by 3β-HSD to progesterone. Progesterone can then be metabolized to form T. A pathway to form 3α-diol from T involves sequential actions of 5α-reductase (an irreversible action that forms DHT) and then 3α-hydroxysteroid 3α-HSD. Most recently, we have been investigating the pregnane xenobiotic receptor (PXR) as a novel target for neurosteroid production [8].
