Phylogenetic Distribution of Aromatase and Other Androgen-Converting Enzymes in the Central Nervous System*

Abstract

Metabolism of [3H]androstenedione was studied in brain tissue homogenates of opossum, bird, snake, sea turtle, urodele amphibian, teleost, shark, skate, hagfish, and lobster. Estrone, 17 beta-estradiol, or 17 alpha-estradiol was formed by central neural tissues of all species, with the exception of the opossum, hagfish, and lobster. Aromatase activity was concentrated in the forebrain, although some estrogen was synthesized by mid- or hindbrain homogenates of two lower vertebrates (teleost and skate) and the newly hatched chick. 5 alpha-Androstanedione (5 alpha-androstane-3,17-dione) or 5 alpha-dihydrotestosterone were products of metabolism in several nonmammalian vertebrates and in the invertebrate central nervous system also. 5 alpha-Reductase was found in all major brain divisions. These and previously reported comparative studies indicate that the ability to aromatize and otherwise transform androgen substrates is a primitive characteristic of the brain that has been widely conserved phylogenetically.

Insights into Rapid Modulation of Neuroplasticity by Brain Estrogens

“…Aromatase enzyme activity has been described in several brain regions and cell types in vertebrate brains ranging from fish to humans (Naftolin et al, 1971a,b;Callard et al, 1978;MacLusky et al, 1986). Changes in aromatase activity can occur in a matter of minutes.…”

Subcellular compartmentalization of aromatase is sexually dimorphic in the adult zebra finch brain

“…In males of many species, aromatase is expressed at specific neural loci such as the diencephalic preoptic area (POA), ventromedial nucleus (VMN), and tuberal hypothalamus (Tu). Aromatization in the brain results in locally elevated levels of E critical in the organization and activation of male-specific copulatory and aggressive behaviors (Callard et al, 1978;Lephart, 1996;Schlinger, 1997).…”

Aromatase activity in the ovary and brain of the eastern mosquitofish (Gambusia holbrooki) exposed to paper mill effluent.

“…Aromatase converts (the androgens) androstenedione or testosterone to the estrogens estrone or 17β-estradiol (E 2 ), respectively (27). This enzyme has been identified in the gonad, liver, brain, and various peripheral tissues, such as fat cells in mammals, as well as in the gonad and brain of all other vertebrates including fishes and the cephalochordate, amphioxus (27)(28)(29). At least two forms of aromatase have been reported in mammals and fishes, with gonadal and brain forms coded for on two separate genes (30)(31)(32).…”