Aromatase inhibition reduces dendritic growth in a sexually dimorphic rat spinal nucleus

The rat lumbar spinal cord contains the steroid-sensitive spinal nucleus of the bulbocavernosus (SNB), whose motoneurons innervate perineal muscles in volved in copulatory reflexes. In normal males, SNB motoneuron dendrites gr ow exuberantly through postnatal (P) day 28, This growth is steroid depende nt: Dendrites fail to grow in males castrated at P7, but grow normally in c astrates treated with testosterone or its metabolites, dihydrotestosterone combined with estrogen, Treatment with either metabolite alone supports den dritic growth, but not to the level of testosterone-treated or intact males . In this study, we tested the hypothesis that aromatization of androgens t o estrogens was involved in the masculine development of SNB dendrites, Mot oneuron morphology was assessed in normal males and males treated daily (P7 -28) with fadrozole, a potent aromatase inhibitor (0.25 mg/kg, subcutaneous ly) or saline vehicle (n = 4-6/group). SNB motoneurons were retrogradely la beled,vith cholera toxin-horseradish peroxidase at P28 (when dendritic leng th is normally maximal) and reconstructed in three dimensions. Comparable l abeling was seen across groups; it was equivalent in both the rostrocaudal and radial extents. However, dendritic lengths in fadrozole-treated males w ere significantly below those of intact or saline-treated males. Neither SN B somata size nor target muscle weight differed across groups. These result s suggest that aromatization of androgens to estrogens is necessary for dev elopment of masculine SNB dendritic morphology. (C) 1999 John Wiley & Sons, Inc.