Document Detail


The thyroid and photoperiodic control of seasonal reproduction in American tree sparrows (Spizella arborea).
MedLine Citation:
PMID:  8151015     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
To explore the role of the thyroid gland in the control of seasonal reproduction in obligately photoperiodic American tree sparrows (Spizella arborea), the effects of (1) thyroxine administered in drinking water to thyroid-intact photosensitive or photorefractory birds, and (2) radiothyroidectomy before and after photostimulation and during photorefractoriness were examined. Chronic administration of pharmacological doses of thyroxine induced testicular growth and usually regression in initially photosensitive birds held on short or intermediate daylengths. Some thyroxine-treated birds with regressed testes were absolutely photorefractory, but most remained photosensitive. Exogenous thyroxine never induced testicular growth in photorefractory birds moved to short days, though it often impeded, and sometimes even blocked, the recovery of photosensitivity. Although circumstantial, these effects of exogenous thyroxine are consistent with an hypothesis that assigns to thyroid hormones two roles--one stimulatory and the other inhibitory--in the control of seasonal reproduction. Radiothyroidectomy before photostimulation inhibited (but did not prevent) photoinduced testicular growth, blocked spontaneous testicular regression, suppressed molt, and prevented photorefractoriness. Moreover, as demonstrated by testicular growth after thyroxine replacement therapy, radiothyroidectomy during photorefractoriness later restored photosensitivity despite continued photostimulation. Thus, euthyroidism is an essential condition for maximizing (but not for initiating) photoinduced testicular growth and for triggering and maintaining photorefractoriness in photostimulated tree sparrows. However, when performed early during photostimulation, radiothyroidectomy neither immediately induced nor later blocked spontaneous testicular regression. Thus, endogenous thyroid hormones and long days may interact during a critical period to program a sequence of physiological events that plays out as photorefractoriness in chronically photostimulated birds. Such an organizational event cannot be permanent, for seasonal reproduction is episodic and its control mechanism necessarily cyclic. Because thyroidectomy simulated the well-known restorative effect of short days (and exogenous thyroxine impeded it), short days may dissipate photorefractoriness by creating a milieu wherein thyroid hormones are deficient or inactive.
Authors:
F E Wilson; B D Reinert
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology     Volume:  163     ISSN:  0174-1578     ISO Abbreviation:  J. Comp. Physiol. B, Biochem. Syst. Environ. Physiol.     Publication Date:  1993  
Date Detail:
Created Date:  1994-05-06     Completed Date:  1994-05-06     Revised Date:  2009-06-08    
Medline Journal Info:
Nlm Unique ID:  8413200     Medline TA:  J Comp Physiol B     Country:  GERMANY    
Other Details:
Languages:  eng     Pagination:  563-73     Citation Subset:  IM    
Affiliation:
Division of Biology, Kansas State University, Manhattan 66506-4901.
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MeSH Terms
Descriptor/Qualifier:
Animals
Birds / physiology*
Male
Photoperiod
Reproduction / drug effects,  physiology*
Seasons
Testis / drug effects,  growth & development
Thyroid Gland / physiology*
Thyroidectomy
Thyroxine / pharmacology,  physiology
Chemical
Reg. No./Substance:
7488-70-2/Thyroxine

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


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