Journal of Neuroscience, Vol 10, 935-946, Copyright © 1990 by Society for Neuroscience
Androgen regulation of dendritic growth and retraction in the development of a sexually dimorphic spinal nucleus
LA Goldstein, EM Kurz and DR Sengelaub
Program in Neural Science, Indiana University, Bloomington 47405.
The spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic
group of motoneurons whose development and maintenance are under androgenic
control. Exposure to androgens early in development permanently alters SNB
motoneuron number and soma size; in adulthood, androgens regulate dendritic
and synaptic architecture. The present set of experiments investigates the
influence of androgens on the development of SNB dendritic morphology. In
normal males, SNB dendritic growth is biphasic, reaching exuberant lengths
by the fourth postnatal week and then retracting to adult lengths by 7
weeks of age. This dendritic growth is androgen dependent--males castrated
on postnatal day (P) 7 and given daily injections of testosterone
propionate (TP) had exuberant dendritic lengths similar to those of normal
males; dendritic length in oil-treated males remained at P7 levels. The
early exuberant dendritic length was retained in TP-treated males through
P49. The retraction of SNB dendrites after P28 is also influenced by
androgens. Males castrated at P28 and given testosterone implants retained
exuberant dendritic length at P49; blank-implanted males had significantly
shorter dendritic lengths by P70. These results suggest that androgens are
necessary for the early exuberant growth of SNB dendrites. Furthermore, the
subsequent retraction of SNB dendrites may be halted when testosterone
titers reach a critical level during puberty, stabilizing their adult
length.