Conversion of Testosterone to Estradiol May Not
Be Necessary for the Expression of Mating
Behavior in Male Syrian Hamsters
( Mesocricetus auratus )
Timothy T. Cooper,* Andrew N. Clancy,² Mary Karom,*
Tim O. Moore,*
,
‡ and H. Elliott Albers*
*Laboratory of Neuroendocrinology and Behavior, Departments of Biology and of Psychology,
Georgia State University, Atlanta, Georgia 30303; †Department of Biology, Georgia State
University, Atlanta, Georgia 30302, and Department of Psychiatry and Behavioral Sciences,
Emory University School of Medicine, Emory West Campus, 1256 Briarcliff Road, Atlanta,
Georgia 30306; and ‡Neuroscience Institute, Morehouse School of Medicine, and Department
of Psychology, Clark Atlanta University, Atlanta, Georgia 30310
Received May 6, 1999; revised February 16, 2000; accepted February 29, 2000
Male sexual behavior is mediated in part by androgens,
but in several species, mating is also influenced by es-
tradiol formed locally in the brain by the aromatization of
testosterone. The role of testosterone aromatization in
the copulatory behavior of male Syrian hamsters is un-
clear because prior studies are equivocal. Therefore, the
present study tested whether blocking the conversion of
testosterone to estradiol would inhibit male hamster
sexual behavior. Chronic systemic administration of the
nonsteroidal aromatase inhibitor Fadrozole (2.0 mg/kg/
day) for 5 or 8 weeks did not significantly increase mount
latency or reduce mount frequency, intromission fre-
quency, ejaculation frequency, or anogenital investiga-
tion relative to levels shown by surgical controls. How-
ever, Fadrozole effectively inhibited aromatase activity,
as evidenced by the suppression of estrogen-dependent
progesterone receptor immunoreactivity in the male
hamster brain. The JZB39 anti-progesterone receptor
antibody labeled significantly more neurons in brains of
sham-treated hamsters than in brains of Fadrozole-
treated hamsters. These data suggest that aromatiza-
tion of testosterone to estradiol is not necessary for
normal mating behavior in Syrian hamsters. © 2000
Academic Press
Key Words: aromatization; sexual behavior; Me-
socricetus auratus; testosterone; estradiol.
Testicular hormones are important in the display of
male sexual behavior in many mammalian species, in-
cluding Syrian hamsters. Castration significantly re-
duces and exogenous testosterone (T) fully restores mat-
ing behaviors in many rodent species (Beach, 1945;
Beach and Pauker, 1949; Whalen and Luttge, 1971) and
in nonhuman primates (Michael and Wilson, 1974). Tes-
tosterone can be metabolized into either the nonaroma-
tizable androgen dihydrotestosterone (DHT) by the en-
zyme 5 reductase or into estradiol (E
2
) by an enzymatic
process termed aromatization. Hormone replacement
studies have suggested that supraphysiological doses of
either DHT or E
2
alone can facilitate certain aspects of
male sexual behavior (Tiefer, 1970; Alsum and Goy,
1974; Michael and Wilson, 1974; Whalen and DeBold,
1974), but complete restoration can be achieved by com-
bined treatment with physiological levels of DHT and E
2
(Baum and Vreeburg, 1973; Larsson, Sodersten, and
Beyer, 1973) or T alone (Yahr, 1979; McGinnis and Drei-
fuss, 1989).
Androgens appear to be the primary gonadal hor-
mone controlling sexual behavior in some species. For
example, systemic administration of DHT, but not E
2
,
elicits the full expression of mating behavior in guinea
pigs (Alsum and Goy, 1974). In contrast, sexual behav-
ior in other species may be influenced by E
2
formed
from the aromatization of T in the brain. Several stud-
ies provide support for the aromatization hypothesis,
which specifies that androgens must be converted to
estrogens for the activation of male sexual behavior.
Dihydrotestosterone given systemically did not facili-
tate sexual behavior in male rats (McDonald, Beyer,
Hormones and Behavior 37, 237–245 (2000)
doi:10.1006/hbeh.2000.1579, available online at http://www.idealibrary.com on
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