November 1, 1996;
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-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.
[+] show captions
References [+] :
Figure 1. Cell death in N. IX–X after 5 months of axotomy. A, Cresyl
violet-stained cells in the intact N. IX–X of a non-gonadectomized male.
B, In the axotomized N. IX–X, swollen (arrowheads) and pyknotic cells
(arrow) are changes associated with prolonged axotomy. Scale bar, 50 mm.
Figure 2. Total number of cells in N. IX–X 5 months after axotomy. A,
Neuronal survival in N. IX–X of females and males 5 months after
axotomy with or without DHT treatment (mean 6 SEM; n 5 4 animals/
group). Significantly (*p , 0.05) more cells were found in the axotomized
N. IX–X of DHT-treated animals than in untreated gonadectomized
animals. B, Number of cells (mean 6 SEM; n 5 4 animals/group) in the
intact (white) and axotomized (black) N. IX–X of untreated and DHTtreated
animals. In all groups, the number of cells in the axotomized N.
IX–X was significantly smaller than in the intact side (*p , 0.05, **p ,
0.01). C, Significantly more cells survived in the axotomized N. IX–X of
non-gonadectomized males and DHT-treated males than in untreated
gonadectomized males ( p , 0.05; n 5 4 animals/group).
Figure 3. In situ hybridization signals with the AR probe in the brainstem
of X. laevis 1 month after nerve section. A, Increases in in situ hybridization
signals were found in the axotomized (a) N. IX–X as compared to the
intact side (i). The intensity of hydridization in cells of the adjacent
reticular formation (Re) or motor neurons of the spinal cord (SC) does not
change after axotomy. The horizontal section at the level of the brainstem
shows the root of the IX–X nerve (IX-Xn). B, A higher magnification of in
situ hybridization signals in the axotomized N. IX–X of an untreated
animal. Cells with unstained nucleus and cytoplasmic labeling (V) were
counted, whereas cytoplasmic profiles were not (*). C, No hybridization
was observed with sense probe. The horizontal section at the level of the
brainstem and spinal cord (SC) shows the root of the IX–X nerve (IX-Xn).
Scale bars: A, C, 180 mm; B, 25 mm.
Figure 4. Number of AR mRNA-expressing cells (mean 6 SEM; n 5
number of animals within histogram bars) in the intact (white) and axotomized
(black) N. IX–X of untreated and DHT-treated animals 1 month
after axotomy. Asterisks indicate significant differences between intact and
axotomized sides (*p , 0.05, **p , 0.01). Brackets with significance
information show differences between untreated and DHT-treated
groups. In untreated animals, more AR mRNA-expressing cells were
found in the axotomized side than in the intact side. The number of AR
mRNA-expressing cells was significantly higher in both intact and axotomized
sides of DHT-treated juveniles than the respective sides of untreated
juveniles. The number of AR mRNA-expressing cells in the intact
side of DHT-treated males was significantly higher than in untreated
Figure 5. Cell proliferation in the CNS of juvenile frogs. A, Bromodeoxyuridine labeling was found in cells of the ependymal layer of the lateral ventricle (LV)
within the telencephalon and in cells in the ventral striatum (vSt) and septum (Sep; arrowheads). 3V, Third ventricle. B, A higher magnification of
bromodeoxyuride-labeled cell nuclei in the ventral striatum. C, In the same animals, after DHT treatment for 1 month, N. IX–X was back-labeled with HRP
(arrow). D, A higher magnification of C shows no bromodeoxyuridine labeling in HRP-back-labeled motor neurons of N. IX–X. Scale bars: A, C, 140 mm; B,
10 mm; D, 10.7 mm.
Figure 6. Hybridization of the AR probe to cells in the brainstem of an
untreated male (A) and a DHT-treated male (B) 5 months after axotomy.
In untreated animals, fewer AR mRNA-expressing cells were present in
the axotomized N. IX–X (a) than in the intact side (i). DHT-treated
animals had significantly more AR mRNA-expressing cells in the axotomized
side than did untreated animals. Scale bar, 75 mm.
Figure 7. AR mRNA-expressing cells 5 months after axotomy. A, DHT treatment resulted in significantly more AR mRNA-expressing cells in the
axotomized N. IX–X than were seen in untreated animals (mean 6 SEM; n 5 3 animals/group). B, Number of AR mRNA-expressing cells in N. IX–X
of untreated and DHT-treated animals (mean 6 SEM; n 5 3 animals/group). Asterisks represent significant differences between intact and axotomized
sides (*p , 0.05; **p , 0.01). Axotomy for 5 months caused significant decrease in number of AR mRNA-expressing cells in the axotomized N. IX–X
of untreated males and females and DHT-treated males.
Estimation of nuclear population from microtome sections.