Description
Steroids and neurosteroids are synthesized from cholesterol, the basic building block of all steroid hormones.
While the classic steroids are produced in tissues like adrenal gland, gonads or placenta, the synthesis of neurosteroids takes place in the central and peripheral nervous system. In the 1980s, Baulieu et al. demonstrated that several steroids, such as dehydropiandrosterone and pregnenolone, are synthesized de novo in the central nervous system and present in higher concentrations in the brain than in the blood. These steroids are universally referred as neurosteroids and are differently distributed in the brain and the pituitary gland. Neurosteroids are formed from cholesterol via pregnenolone and progesterone. Pregnenolone and progesterone are precursors not only of the synthesis of gluco- and mineralcorticoids in the adrenal gland and of the sexual hormones in the gonads or placenta, but also of neurosteroids in the central nervous system.
Due to their lipophilicity, most of the free steroids can easily pass the blood-brain barrier. A number of steroids are conjugated as sulfate or fatty acid esters and occur in concentrations much higher than these of the free steroids. In contrast to the free steroids, they cannot pass through the blood-brain barrier and represent the active forms involved in the control of various physiological and pathophysiological processes.