Estrogenic support of motoneuron dendritic growth via the neuromuscular periphery in a sexually dimorphic motor system.

Full Abstract

The lumbar spinal cord of rats contains the sexually dimorphic, steroid-sensitive spinal nucleus of the bulbocavernosus (SNB). In males, the growth of SNB dendrites is steroid-dependent:
dendrites fail to grow after castration, but grow in castrates treated with androgens or estrogens. Blocking estradiol synthesis or estrogen receptors in gonadally intact males attenuates SNB dendritic growth, suggesting that estrogens are required and must be able to act at their receptors to support normal masculine dendritic growth. However, SNB motoneurons do not accumulate estrogens, suggesting that estrogens act indirectly to support SNB dendritic growth. In this experiment, we examined whether local estrogen action in the neuromuscular periphery was involved in the postnatal development of SNB motoneurons. Motoneuron morphology was assessed in gonadally intact and castrated males. Gonadally intact males were left untreated or given either blank or tamoxifen implants sutured to the target musculature, or tamoxifen interscapular implants. Castrated males were left untreated or were given estradiol by muscle or interscapular implants or systemic injection during the period of SNB dendritic growth. At postnatal day 28, when SNB dendritic length is normally maximal, SNB motoneurons were retrogradely labeled with cholera toxin-HRP and reconstructed in three dimensions. While interscapular tamoxifen implants were ineffective, blocking estrogen receptors at the target musculature resulted in attenuation of SNB dendritic growth. In contrast, while interscapular implants of estradiol were ineffective, local treatment with estradiol at the target musculature in castrated males resulted in masculinization of dendritic growth. Thus, estrogens may act by an indirect action in the neuromuscular periphery to support SNB dendritic growth.

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Author information

Author/s: Nowacek, Ari S (AS); Sengelaub, Dale R (DR);

Affiliation: Department of Psychological and Brain Sciences, Indiana University, Bloomington, 47405, USA.

Grants: HD35315 (Agency:NICHD NIH HHS)

Journal and publication information

Publication Type: Journal Article; Research Support, N.I.H., Extramural

Journal: Journal of neurobiology (J Neurobiol), published in United States. (Language: eng)

Reference: 2006-Aug; vol 66 (issue 9) : pp 962-76

Dates: Created 2006/08/21; Completed 2006/09/28; Revised 2007/11/14;

PMID: 16779828, status: MEDLINE (last retrieval date: 12/26/2008)

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Animals
Dendrites - drug effects; ultrastructure
Estrogens - physiology
Female
Male
Motor Neurons - cytology; drug effects
Muscle, Skeletal - anatomy & histology; drug effects

Neuromuscular Junction - physiology
Organ Size
Rats
Rats, Sprague-Dawley
Sex Characteristics
Sexual Maturation
Tamoxifen - pharmacology

Associated Chemicals: Estrogens (0) ; Tamoxifen (10540-29-1)

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