Volume 16, Number 21,
Issue of November 1, 1996
pp. 6625-6633
Copyright ©1996 Society for Neuroscience
Trophic Effects of Androgen: Receptor Expression and the Survival
of Laryngeal Motor Neurons after Axotomy
Received May 14, 1996; revised July 30, 1996; accepted Aug. 6, 1996.
Julio Pérez and
Darcy B. Kelley
Department of Biological Sciences, Columbia University, New York,
New York 10027
To determine whether changes in androgen receptor (AR) expression
are associated with trophic actions of androgens, we have examined the
laryngeal motor nucleus (N. IX-X) of Xenopus laevis 1 and 5 months after section of the laryngeal nerve. In situ
hybridization was used to recognize cells expressing mRNA for
the Xenopus AR and bromodeoxyuridine to assess cell
proliferation. In addition, the total number of cells was determined in
untreated and dihydrotestosterone (DHT)-treated animals after 5 months
of axotomy. After 1 month of axotomy, the number of AR mRNA-expressing
cells in N. IX-X is 1.8-fold higher than in the intact side. Androgen
upregulates expression of AR mRNA in N. IX-X on both the intact and
the axotomized sides, suggesting that the increase is independent of
contact with muscle. Neither the axotomy- nor the androgen-induced
increase in number of cells expressing AR mRNA is attributable to cell
proliferation. Five months after axotomy, both the total number of
cells and the number of AR mRNA-expressing cells are severely
decreased in the axotomized N. IX-X. DHT treatment mitigates the cell
loss in N. IX-X induced by prolonged axotomy; the effect includes
maintenance of AR mRNA-expressing cells. Gonadally intact males have
more cells in the axotomized N. IX-X than castrated animals,
suggesting that androgen acts at physiological levels as a trophic
hormone. Axotomy-induced upregulation of AR expression may facilitate
the trophic actions of androgens.
Key words:
trophic factor;
dihydrotestosterone;
axotomy;
androgen receptor mRNA expression;
motor neurons