Trophic effects of androgen: Receptor expression and the survival of laryngeal motor neurons after axotomy

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-inducedincrease 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.