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Development of a sexually dimorphic neuromuscular system in male rats after spinal transection: Morphologic changes and implications for estrogen sites of action
Author(s) -
Hebbeler Sara L.,
Sengelaub Dale R.
Publication year - 2003
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.10911
Subject(s) - biology , spinal cord , sexual dimorphism , lumbar spinal cord , bulbocavernosus reflex , endocrinology , estrogen , medicine , central nervous system , period (music) , neuroscience , acoustics , physics
Abstract The lumbar spinal cord of rats contains the sexually dimorphic, steroid‐sensitive spinal nucleus of the bulbocavernosus (SNB). In male rats, SNB motoneurons exhibit a biphasic pattern of dendritic growth, having an initial period of exuberant growth followed by a period of retraction to mature lengths by 7 weeks of age. This growth is steroid dependent: dendrites fail to grow after castration, but growth is supported in castrates treated with estradiol. In this experiment, we examined whether supraspinal afferent input by means of descending spinal tracts to the SNB was involved in the normal postnatal development of SNB motoneurons, and whether the effect of estradiol on SNB dendritic growth could be explained by an indirect action of estradiol on supraspinal afferents. Motoneuron morphology was assessed in normal males, early‐ or late‐postnatally transected males, castrated males left untreated or treated with estradiol, and transected castrates treated with estradiol. SNB motoneurons were retrogradely labeled with cholera toxin–horseradish peroxidase during both the growth and retraction phases of dendritic development and reconstructed in three dimensions. The removal of supraspinal afferents resulted in extremely local effects within the developing SNB arbor, as well as transient alterations in somal growth. Furthermore, spinal transection did not block the trophic effect of estradiol on supporting SNB dendritic growth, indicating that estrogens do not act by means of supraspinal input to support SNB motoneuron development. J. Comp. Neurol. 467:80–96, 2003. © 2003 Wiley‐Liss, Inc.