Aromatase and 5α-reductase in the teleost brain, spinal cord, and pituitary gland

The distribution of aromatase and 5α-reductase was investigated in the brain, spinal cord, and pituitary of adult goldfish ( Carassius auratus) and toadfish ( Opsanus tau) of both sexes. Tissue homogenates were incubated with [ 3H]androstenedione in the presence of an NADPH-generating system and, following validation of assay conditions, radiolabeled products (estradiol, estrone, 5α-androstanedione), were measured as an index of enzyme activity. Neuroendocrine tissue of both species produced exceptionally large amounts of estrogen, thus confirming previously observed differences between teleosts and other vertebrates. By contrast, 5α-reductase levels resembled the vertebrate norm. In general, aromatase was concentrated in the pituitary and various forebrain regions, especially the hypothalamus/preoptic area; however, estrogen yields from the medulla and anterior spinal cord of toadfish were high compared to adjacent midbrain, hindbrain, and cord regions. This same neural region in toadfish, but not in goldfish, is known to control a sex dimorphic behavior, the courtship boatwhistle. In contrast to aromatase, 5α-reductase was more uniformly distributed throughout the brain, although somewhat higher activity was obtained in the pituitary. High levels of aromatase in the neuroendocrine tissues of teleosts recommend them as animal models for further studying the enzyme, its regulation, and its role in governing androgen-dependent responses in central targets.