The Journal of Neuroscience, February 1, 2001, 21(3):1062-1066
Neuronal Size in the Spinal Nucleus of the Bulbocavernosus:
Direct Modulation by Androgen in Rats with Mosaic Androgen
Insensitivity
Neil V.
Watson1,
Louise M.
Freeman2, and
S.
Marc
Breedlove3
1 Department of Psychology, Simon Fraser University,
Burnaby, British Columbia, V5A 1S6 Canada, 2 Mary Baldwin
College, Staunton, Virginia 24401, and 3 Department of
Psychology, University of California, Berkeley, California 94720
The motoneurons of the spinal nucleus of the bulbocavernosus (SNB)
and its target muscles, the bulbocavernosus and levator ani, form a
sexually dimorphic circuit that is developmentally dependent on
androgen exposure and exhibits numerous structural and functional
changes in response to androgen exposure in adulthood. Castration of
male adult rats causes shrinkage of SNB somata, and testosterone
replacement reverses this effect, but the site at which androgen is
acting to cause this change is undetermined. We exploited the
X-chromosome residency of the androgen receptor (AR) gene to generate
androgenized female rats that were heterozygous for the testicular
feminization mutant (tfm) AR mutation and that, as a
consequence of ontogenetic random X-inactivation, expressed a blend of
androgen-sensitive wild-type cells and tfm-affected androgen-insensitive cells in the SNB. Chronic testosterone treatment of adult mosaics increased soma sizes only in androgen-competent wild-type SNB cells. The size of tfm-affected SNB somata
in the same animals did not differ from the size of either the
wild-type or tfm-affected SNB neurons in control mosaics
that did not receive androgen treatment in adulthood. Because the
muscle targets of the SNB are known to be uniformly androgen-sensitive
in tfm mosaics, this mosaic analysis provides
unambiguous evidence that androgenic effects on motoneuron soma size
are mediated locally in the SNB. It is possible that the neuronal AR
plays a permissive role in coordinating the actions of androgen.
Key words:
mosaic; androgen; spinal nucleus of the bulbocavernosus; tfm mutation; soma size; steroid receptors
Copyright © 2001 Society for Neuroscience 0270-6474/01/2131062-05$05.00/0
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