Thyroxine treatment prevents the development of photosensitivity in european starlings (Sturnus vulgaris)

Boulakoud, Mohamed Salah; Ivings, W. E.; Goldsmith, Arthur R.

doi:10.1007/bf00257906

Cited by 4 publications

(1 citation statement)

References 17 publications

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“…In this regard the thyroid gland appears to have a specific influence on the regulation of the transition from the breeding to the nonbreeding season. For example, thyroidectomy of certain species of birds can prevent seasonal gonadal regression; thyroxine replacement allows gonadal changes to resume; and injection of large doses of thyroxine can shorten the breeding season [12,16,19,20,23]. Similar reproductive responses have been reported in sheep, in which thyroidectomy maintains ewes in a reproductively active state [13][14] and replacement of physiological doses of thyroxine allows a normally timed transition to anestrus after removal of the thyroid gland [17].…”

Section: Discussionmentioning

confidence: 72%

Effect of Exogenous Thyroxine on Timing of Seasonal Reproductive Transitions in Ewes1

O'Callaghan

Wendling

Karsch

et al. 1993

Biology of Reproduction

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The thyroid gland is necessary for the transition from the breeding season to anestrus in the ewe, but the importance of seasonal changes in thyroxine in this process is not known. The objective of this experiment was to determine the effects of exogenous thyroxine during the breeding season on the time of the transition to anestrus and on the onset of the subsequent breeding season in ewes maintained on natural photoperiod. Cyclic Galway ewes were blocked on the basis of body weight and randomly allocated to the following groups: 1) untreated controls (n = 11), 2) placebo-injected controls (n = 9), and 3) ewes injected daily with thyroxine from the middle of the breeding season until the onset of anestrus (n = 10). Reproductive state was assessed from serum progesterone concentrations determined twice weekly until the breeding season had ended in placebo-injected controls, and until the onset of the subsequent breeding season in untreated and thyroxine-injected ewes. The mean (+/- SEM) date of onset of anestrus did not differ between untreated ewes (April 19 +/- 9 days) and placebo-injected controls (April 15 +/- 9 days; p > 0.05), but occurred earlier in ewes injected with thyroxine (February 28 +/- 6 days; p < 0.001). Thyroxine treatment during the breeding season, however, did not affect the onset of the subsequent breeding season. These data indicate that supplementary thyroxine during the breeding season can advance anestrus and thus shorten the duration of the breeding season.(ABSTRACT TRUNCATED AT 250 WORDS)

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Section: Discussionmentioning

confidence: 72%

Effect of Exogenous Thyroxine on Timing of Seasonal Reproductive Transitions in Ewes1

O'Callaghan

Wendling

Karsch

et al. 1993

Biology of Reproduction

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The thyroid and photoperiodic control of seasonal reproduction in American tree sparrows (Spizella arborea)

Wilson

Reinert

1993

J Comp Physiol B

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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.

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Neuroendocrine Mechanisms Regulating Reproductive Cycles and Reproductive Behavior in Birds

Ball

Balthazart

2002

Hormones, Brain and Behavior

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Thyroxine treatment prevents the development of photosensitivity in european starlings (Sturnus vulgaris)

Cited by 4 publications

References 17 publications

Effect of Exogenous Thyroxine on Timing of Seasonal Reproductive Transitions in Ewes1

Effect of Exogenous Thyroxine on Timing of Seasonal Reproductive Transitions in Ewes1

The thyroid and photoperiodic control of seasonal reproduction in American tree sparrows (Spizella arborea)

Neuroendocrine Mechanisms Regulating Reproductive Cycles and Reproductive Behavior in Birds

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