Effects of thyroxine (T4) or triiodothyronine (T3) replacement therapy on the programming of seasonal reproduction and postnuptial molt in thyroidectomized male American tree sparrows (Spizella arborea) exposed to long days

Reinert, Bryan D.; Wilson, Fred E.

doi:10.1002/(sici)1097-010x(19971101)279:4<367::aid-jez6>3.0.co;2-m

Cited by 22 publications

(12 citation statements)

References 41 publications

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“…In tropical and subtropical birds the picture is more complex, with thyroidectomy resulting in a wide variety of responses in different species. A number of studies that have manipulated brain thyroid hormones in relation to photoperiod in American tree sparrows have addressed many of the interactions of T 4 , T 3 , and photoperiod on the programming of seasonal reproduction, photorefractoriness, and postnuptial molt using a variety of experimental paradigms including intracerebroventricular injections of T 4 and T 3 (e.g., Reinert and Wilson, 1997;Reinert, 1998, 2000). The brain injection studies suggest that T 4 is more important than T 3 in its effects on the brain/HPT axis in the interaction of photoperiod and reproduction.…”

Section: Gonadal Developmentmentioning

confidence: 99%

The Hypothalamic-Pituitary-Thyroid (HPT) Axis in Birds and Its Role in Bird Development and Reproduction

McNabb

2007

Critical Reviews in Toxicology

185

163

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This article reviews thyroid function and its hypothalamic-pituitary-thyroid (HPT) axis control in birds with emphasis on the similarities and differences in thyroid function compared to mammals and other vertebrate classes. Thyroid hormones are important in metabolism and the thermogenesis required for homeothermy in birds, as in mammals, the other homeothermic class of vertebrates. Thyroid hormones play important roles in development and growth in birds, as is the case for all vertebrate classes. The developmental effects of thyroid hormones in birds are presented in the context of differences in precocial and altricial patterns of development and growth with emphasis on oviparous development. The sections on thyroid hormone actions include discussion of effects on the development of a number of tissue types as well as on seasonal organismal processes and interactions of the thyroid axis with reproduction. The current picture of how environmental chemicals may disrupt avian thyroid function is relatively limited and is presented in the context of the assessment endpoints that have been used to date. These endpoints are categorized as thyroid and HPT axis endpoints versus target organ endpoints. The final section discusses two recommended assay protocols, the avian two-generation toxicity assay and the avian one-generation assay, and whether these protocols can evaluate thyroid disruption in birds.

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Section: Gonadal Developmentmentioning

confidence: 99%

The Hypothalamic-Pituitary-Thyroid (HPT) Axis in Birds and Its Role in Bird Development and Reproduction

McNabb

2007

Critical Reviews in Toxicology

185

163

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“…This is of particular importance in nestlings that experience rapid cellular differentiation and development. Thyroxine is also important for proper feather growth, coloration, and molting (Oglesbee, 1992;Harms et al, 1994) as well as reproductive timing (Pant and ChandolaSaklani, 1995;Reinhert and Wilson, 1997). The mechanisms responsible for the observed changes in thyroid physiology are unresolved.…”

Section: Discussionmentioning

confidence: 99%

Thyroid Function in Nestling Tree Swallows and Eastern Bluebirds Exposed to Non-Persistent Pesticides and p, p?-DDE in Apple Orchards of Southern Ontario, Canada

Mayne

Bishop²,

Martin³

et al. 2005

Ecotoxicology

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This study examined the associated effects of pesticides and persistent residues of p,p'-DDE on thyroid function in 16-day-old tree swallows (Tachycineta bicolor) and 12-day-old eastern bluebirds (Sialia sialis). Apple orchards sprayed with pesticides in current use and reference sites were chosen for study in southern Ontario, Canada, during 2000-2001. We assessed thyroid hormone concentrations (plasma and muscle thyroxine [T4], and triiodothyronine [T3]) and the response to a challenge with thyroid stimulating hormone (TSH) as well as parameters of thyroid histology. Individual nests were exposed to as many as seven individual pesticide applications and up to five pesticide mixtures. Concentrations of p,p'-DDE in eggs from both species were highest in orchard sites, and ranged from 0.05 to 5.44 mg/kg wet weight for tree swallows, and from 0.17 to 95.4 mg/kg for eastern bluebirds. In 2000, tree swallows from sprayed orchards had elevated plasma T4 concentrations, and thyroid glands with collapsed follicles, hypertrophic epithelia, and higher follicular epithelial cells relative to chicks from reference sites. Plasma T4 concentration was positively correlated with the total number of pesticide mixtures applied during egg incubation through chick rearing. In 2001, basal plasma T3 concentration in tree swallow chicks did not differ between orchard and reference sites, though there were differences among orchards; T3 was positively correlated with total number of individual sprays applied during egg incubation through chick rearing. Tree swallows challenged with TSH showed no significant difference in thyroid hormone concentration or follicular epithelial cell height between exposure groups; however, a significantly greater proportion of chicks from reference sites were found to have thyroids with focal or diffuse hypertrophic epithelia relative to orchard chicks. In 2001, bluebirds from sprayed orchards had significantly higher T3 concentrations in response to TSH challenge; this response was positively correlated with the total number of pesticides applied during egg incubation through chick rearing.

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“…Alternatively, the protracted long-day requirement may indicate that our model merely requires refinement. Thus, long days may have two effects on the vernal component of seasonality: an early, interactive programming effect (with THs or a TH-dependent metabolite or ligand) [12,[14][15][16][17][18]26] and a later, independent permissive effect (current study), which creates a milieu appropriate for full expression of programmed testicular growth. Our assigning a postprogramming permissive role to long days corroborates the conclusion of Harris and Turek [27], namely, that after the testes of thyroid-intact white-throated sparrows have grown to a functional size (cf.…”

Section: Discussionmentioning

confidence: 99%

“…Our studies on obligately photoperiodic American tree sparrows (Spizella arborea) lead us to conclude that THs and long days interact to program males for the vernal component of seasonality, as well as the autumnal component [12,[14][15][16][17][18]. By performing thyroidectomy (THX) before, at, or after the onset of photostimulation, we have demonstrated that programming for testicular growth occurs during the first week of photostimulation [16,18] and is independent of programming for photorefractoriness and postnuptial molt, which occurs between Weeks 1 and 3 [15,16,18].…”

Section: Introductionmentioning

confidence: 99%

“…These results provide strong support for the concept that vernal and autumnal events are independently controlled [1]. Furthermore, we have shown that thyroxine (T 4 ), administered s.c. to thyroidectomized male tree sparrows either as a one-time injection (100 ,ug) on the first day of photostimulation [12] or as 14 daily injections (1 or 10 Rg each) during the first 2 wk of photostimulation [17], later restores all three components of seasonality in the proper sequence. These findings, generated against a backdrop of protracted long-day stimulation, argue against a permissive role for T 4 (i.e., an essential, nonregulatory presence [9,19]) in the control of seasonality, a role that others [9,10,20,21] have suggested.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Withdrawing Long Days from Male American Tree Sparrows (Spizella Arborea): Implications for Understanding Thyroid-Dependent Programming of Seasonal Reproduction and Postnuptial Molt1

Wilson

Reinert²

1998

Biology of Reproduction

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In previous studies, we withdrew thyroid hormones by thyroidectomy before, at, or after the onset of photostimulation and showed that male American tree sparrows (Spizella arborea) are programmed for seasonal reproduction and postnuptial molt by or before Week 3 on long days. In this corollary study, we withdrew long days before or after the control circuits had been programmed. After 1 day to 4 wk on long days, groups of thyroid-intact males were returned to short days until Week 7, when they were moved to constant light and evaluated for photosensitivity or photorefractoriness and postnuptial molt. Long-day controls held 7 wk on long days showed robust testicular growth through Week 6 and then spontaneous testicular regression. Testes of short-day controls and of males photostimulated for 1 day remained small. In all other groups, photostimulation induced testicular growth, which gave way to regression during exposure to short days. Long-day controls tested photorefractory at Week 7 and initiated molt by Week 10. All other groups tested photosensitive and did not molt. Our demonstration that long days are required for expression of seasonal reproduction and postnuptial molt in thyroid-intact male tree sparrows previously programmed for these events suggests that long days create a milieu that is permissive for expression.

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Effects of thyroxine (T4) or triiodothyronine (T3) replacement therapy on the programming of seasonal reproduction and postnuptial molt in thyroidectomized male American tree sparrows (Spizella arborea) exposed to long days

Cited by 22 publications

References 41 publications

The Hypothalamic-Pituitary-Thyroid (HPT) Axis in Birds and Its Role in Bird Development and Reproduction

The Hypothalamic-Pituitary-Thyroid (HPT) Axis in Birds and Its Role in Bird Development and Reproduction

Thyroid Function in Nestling Tree Swallows and Eastern Bluebirds Exposed to Non-Persistent Pesticides and p, p?-DDE in Apple Orchards of Southern Ontario, Canada

Effect of Withdrawing Long Days from Male American Tree Sparrows (Spizella Arborea): Implications for Understanding Thyroid-Dependent Programming of Seasonal Reproduction and Postnuptial Molt1

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