Expression of 5α- and 5β-reductase in spinal cord and muscle of birds with different courtship repertoires.
BACKGROUND
Through the actions of one or more isoforms of the enzyme 5α-reductase in many male reproductive tissues, circulating testosterone (T) undergoes metabolic conversion into 5α-dihydrotestosterone (DHT), which binds to and activates androgen receptors (AR) with greater potency than T. In birds, T is also subject to local inactivation into 5β-DHT by the enzyme 5β-reductase. Male golden-collared manakins perform an androgen-dependent and physically elaborate courtship display, and these birds express androgen receptors in skeletal muscles and spinal cord at levels far greater than those expressed in species with more limited courtship routines, including male zebra finches. To determine if local T metabolism facilitates or impedes activation of male manakin courtship, we examined expression of two isoforms of 5α-reductase, as well as 5β-reductase, in forelimb muscles and spinal cords of males and females of the two aforementioned species.


RESULTS
We found that all enzymes were expressed in all tissues, with patterns that partially predict a functional role for 5α-reductase in these birds, especially in both muscle and spinal cord of male manakins. Moreover, we found that 5β-reductase was markedly different between species, with far lower levels in golden-collared manakins, compared to zebra finches. Thus, modification to neuromuscular deactivation of T may also play a functional role in adaptive behavioral modulation.


CONCLUSIONS
Given that such a role for 5α-reductase in androgen-sensitive mammalian skeletal muscle is in dispute, our data suggest that, in birds, local metabolism may play a key role in providing active androgenic substrates to peripheral neuromuscular systems. Similarly, we provide the first evidence that 5β-reductase is expressed broadly through an organism and may be an important factor that regulates androgenic modulation of neuromuscular functioning.
Department of Biology, Wake Forest University, 228 Winston Hall, Winston-Salem, NC 27109 USA ; Center for Molecular Communication and Signaling, Wake Forest University, Winston-Salem, USA.
Matthew J
MJ
Fuxjager
Department of Biology, Wake Forest University, 228 Winston Hall, Winston-Salem, NC 27109 USA.
Eric R
ER
Schuppe
Department of Integrative Biology and Physiology, University of California, Los Angeles, USA.
John
J
Hoang
Department of Integrative Biology and Physiology, University of California, Los Angeles, USA.
Jennifer
J
Chew
Department of Integrative Biology and Physiology, University of California, Los Angeles, USA.
Mital
M
Shah
Department of Integrative Biology and Physiology, University of California, Los Angeles, USA ; Laboratory of Neuroendocrinology, Brain Research Institute, University of California, Los Angeles, USA ; Department of Ecology and Evolutionary Biology, University of California, Los Angeles, USA ; Smithsonian Tropical Research Institute, Balboa, Ancon, Republic of Panama.
Barney A
BA
Schlinger
Androgens; Courtship behavior; Elaborate displays; Hormones; Manakins; Neuromuscular system; Reproduction; Skeletal muscles; Testosterone androgen receptor; Tropical birds