Document Detail

Evidence that thyroid hormones act in the ventromedial preoptic area and the premammillary region of the brain to allow the termination of the breeding season in the ewe.
MedLine Citation:
PMID:  12810544     Owner:  NLM     Status:  MEDLINE    
Thyroid hormones are permissive for various species to enter seasonal anestrus. In the ewe they act centrally to permit the onset of potent estradiol-negative feedback responsible for anestrus, but the specific sites of action are unknown. Therefore, we tested whether T(4) replacement via chronic microimplants in any of five brain areas could reverse the reproductive effects of thyroidectomy. Diffusion of (125)I-T(4) from the microimplant was largely (>98%) limited to a 1.2-mm radius. A marked decline in LH concentration in ovariectomized, estradiol-treated ewes was used as an index for anestrus. In experiment 1, all thyroidectomized (THX) ewes with microimplants in the medial preoptic area, A15 area, and medial basal hypothalamus failed to enter anestrus; instead, LH levels remained elevated, similar to those in untreated THX controls. In ventromedial preoptic area (vmPOA)-microimplanted ewes, only the two animals with the most caudal microimplants entered anestrus, as did thyroid-intact controls and THX ewes receiving icv or sc T(4) replacement. In experiment 2, all vmPOA-treated ewes with similar placements to those effective in experiment 1 along with all ewes microimplanted in the premammillary region entered neuroendocrine anestrus. Thus, the premammillary region and vmPOA are brain sites in which thyroid hormones act to permit the onset of seasonal anestrus.
Greg M Anderson; Steven L Hardy; Miroslav Valent; Heather J Billings; John M Connors; Robert L Goodman
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Endocrinology     Volume:  144     ISSN:  0013-7227     ISO Abbreviation:  Endocrinology     Publication Date:  2003 Jul 
Date Detail:
Created Date:  2003-06-17     Completed Date:  2003-07-22     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  0375040     Medline TA:  Endocrinology     Country:  United States    
Other Details:
Languages:  eng     Pagination:  2892-901     Citation Subset:  AIM; IM    
Department of Physiology and Pharmacology, West Virginia University, Health Sciences Center North, Medical Center Drive, Morgantown, WV 26506, USA.
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MeSH Terms
Anestrus / drug effects*,  physiology*
Drug Implants
Hypothalamus, Middle / drug effects,  physiology*
Preoptic Area / drug effects,  physiology*
Reproduction / physiology
Thyroid Gland / physiology
Thyroxine / blood,  cerebrospinal fluid,  pharmacology*
Grant Support
Reg. No./Substance:
0/Drug Implants; 7488-70-2/Thyroxine

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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