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Widespread Capacity for Steroid Synthesis in the Avian Brain and Song System

University of California, Los Angeles (S.E.L., B.A.S.), Los Angeles, California 90095-1606; and Michigan State University (D.A.M., J.W.), East Lansing, Michigan 48824

Address all correspondence and requests for reprints to: Sarah E. London, Institute for Genomic Biology, 2610 Beckman Institute, 405 North Mathews, Urbana, Illinois 61801. E-mail: slondon{at}igb.uiuc.edu; or Barney A. Schlinger, Department of Physiological Science, University of California, Los Angeles, 621 Charles Young Drive South, P.O. Box 951606, Los Angeles, California 90095-1606.

Steroids exert powerful effects on the brains and behavior of many species, but measures and manipulations of endocrine physiology in songbirds often reveal unexplained connections between steroids and the brain. The zebra finch song system, a sensorimotor neural circuit sensitive to steroids throughout life, organizes and functions largely in apparent independence from gonadally derived steroids. We tested the hypothesis that the zebra finch brain has the capacity for de novo steroidogenesis and that neurally synthesized steroids, neurosteroids, may impact the song system. Using multiple techniques, we demonstrate that the steroidogenic acute regulatory protein (StAR), cytochrome P450 side-chain cleavage (CYP11A1), and 3ß-hydroxysteroid dehydrogenase/5-4 isomerase, the first three factors in the steroidogenic pathway, are expressed in both developing and adult zebra finch brain. Detailed expression mapping at posthatch d 20 (P20) and adult reveals widespread area-specific expression and coexpression patterns for steroidogenic acute regulatory protein, CYP11A1, and 3ß-hydroxysteroid dehydrogenase/5-4 isomerase, which suggest neurosteroids may modulate multiple brain functions, including sensory and motor systems. Notably, whereas expression of other steroidogenic genes such as aromatase has been essentially absent from the song system, each of the major song nuclei express at least a subset of steroidogenic genes described here, establishing the song system as a potential steroidogenic circuit.

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