Lack of gonadotrophin-releasing hormone (GnRH) neuron response to decreasing photoperiod in thyroidectomized male starlings (Sturnus vulgaris)

Bentley, G.; Dawson, Alistair; Goldsmith, Arthur R.

doi:10.1002/1097-010x(20000615)287:1<74::aid-jez9>3.0.co;2-r

Cited by 17 publications

(6 citation statements)

References 18 publications

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“…Both types of changes are dependent on gonadal steroids and can be driven by changing the steroid milieu (9,10). Within the GnRH system of some bird species, changes in neuronal morphology and gene expression have also been reported (11)(12)(13)(14)(15). However, whether these changes in the avian GnRH system also reflect an underlying change in neuronal connectivity, glial associations, or other mechanisms is not clear.…”

Section: Y Early Cycles Of Fertility and Infertility In Sheep Andmentioning

confidence: 99%

Seasonal Plasticity within the Gonadotropin-Releasing Hormone (GnRH) System of the Ewe: Changes in Identified GnRH Inputs and Glial Association

et al. 2003

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The annual reproductive cycle in sheep may reflect a functional remodeling within the GnRH system. Specifically, changes in total synaptic input and association with the polysialylated form of neural cell adhesion molecule have been observed. Whether seasonal changes in a specific subset(s) of GnRH inputs occur or whether glial cells specifically play a role in this remodeling is not clear. We therefore examined GnRH neurons of breeding season (BS) and nonbreeding season (anestrus) ewes and tested the hypotheses that specific (i.e. gamma-aminobutyric acid, catecholamine, neuropeptide Y, or beta-endorphin) inputs to GnRH neurons change seasonally, and concomitant with any changes in neural inputs is a change in glial apposition. Using triple-label immunofluorescent visualization of GnRH, glial acidic fibrillary protein and neuromodulator/neural terminal markers combined with confocal microscopy and optical sectioning techniques, we confirmed that total numbers of neural inputs to GnRH neurons vary with season and demonstrated that specific inputs contribute to these overall changes. Specifically, neuropeptide Y and gamma-aminobutyric acid inputs to GnRH neurons increased during BS and beta-endorphin inputs were greater during either anestrus (GnRH somas) or BS (GnRH dendrites). Associated with the changes in GnRH inputs were seasonal changes in glial apposition, glial acidic fibrillary protein density, and the thickness of glial fibrils. These findings are interpreted to suggest an increase in net stimulatory inputs to GnRH neurons during the BS contributes to the seasonal changes in GnRH neurosecretion and that this increased innervation is perhaps stabilized by glial processes.

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Section: Y Early Cycles Of Fertility and Infertility In Sheep Andmentioning

confidence: 99%

Seasonal Plasticity within the Gonadotropin-Releasing Hormone (GnRH) System of the Ewe: Changes in Identified GnRH Inputs and Glial Association

et al. 2003

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“…For example, iopanoic acid both inhibits thyroid hormone release from the thyroid gland but also the conversion of T4 to T3 by inhibiting DIO2, but it is less practical for long term treatment strategies (Pant and Chandola-Saklani 1993). In the past both surgical and radioactive thyroidectomy have been applied to study the effects of thyroid hormones on seasonal reproduction (Dawson, Goldsmith et al 1986, Bentley, Dawson et al 2000. Analogous to experiments examining the local effects of testosterone by local androgen receptor inhibition (Alward, Balthazart et al 2017), thyroid hormone antagonists and thyroid hormone receptor modulators have been developed and could be injected locally within specific song nuclei, to investigate their role in song behavior (Lim, Nguyen et al 2002, Yoshihara and Scanlan 2003, Raparti, Jain et al 2013.…”

Section: Future Perspectivesmentioning

confidence: 99%

“…Thyroid hormone levels change seasonally and are known to play a role in reproductive maturation and maintaining the photorefractory state in seasonally breeding birds (Bentley, Goldsmith et al 1997, Bentley, Dawson et al 2000. They closely interact with the hypothalamus-pituitary-gonadal (HPG) axis.…”

Section: Introductionmentioning

confidence: 99%

Unravelling the role of thyroid hormones in seasonal neuroplasticity in European Starlings (Sturnus vulgaris)

Orije

Raymaekers

Majumadar

et al. 2021

Preprint

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Thyroid hormones clearly play a role in the seasonal regulation of reproduction, but any role they might play in song behavior and the associated seasonal neuroplasticity in songbirds remains to be elucidated. To pursue this question, we first established seasonal patterns in the expression of thyroid hormone regulating genes in male European starlings employing in situ hybridization methods. Thyroid hormone transporter LAT1 expression in the song nucleus HVC was elevated during the photosensitive phase, pointing towards an active role of thyroid hormones during this window of possible neuroplasticity. In contrast, DIO3 expression was high in HVC during the photostimulated phase, limiting the possible effect of thyroid hormones to maintain song stability during the breeding season. Next, we studied the effect of hypothyroidism on song behavior and neuroplasticity using in vivo MRI. Hypothyroidism inhibited the photostimulation-induced increase in testosterone, confirming the role of thyroid hormones in activating the hypothalamic-pituitary-gonadal (HPG) axis. Surprisingly, apart from the myelination of several tracts during the photostimulated phase, most neuroplasticity related to song production was unaffected by hypothyroidism. Remarkably, T3 plasma concentrations were negatively correlated to the microstructural changes in several song control nuclei. Potentially, a global reduction of circulating thyroid hormones during the photosensitive period is necessary to lift the brake imposed by the photorefractory period, whereas local fine-tuning of thyroid hormone concentrations through LAT1 could activate underlying neuroplasticity mechanisms. Given the complexity of thyroid hormone effects, this study is a steppingstone to disentangle the influence of thyroid hormones on seasonal neuroplasticity.

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“…Central administration of thyroid hormones to thyroidectomized tree sparrows restores all of the photoperiodic responses, with the effects of T 4 being more potent than triiodothyronine, T 3 (Wilson and Reinert, 2000). Chronic thyroidectomy appears to render starlings “photoperiodically blind,” because the GnRH response to an increase or a decrease in photoperiod is greatly attenuated (Bentley et al, 2000a), although less chronically thyroidectomized starlings still exhibit a robust long day photoperiodic response (Bentley et al, 1997). In house sparrows, the effects of thyroidectomy are very different.…”

Section: Regulation Of Gnrh and Gnrh-rmentioning

confidence: 99%

Neuroendocrine regulation of gonadotropin secretion in seasonally breeding birds

Ubuka¹,

Bentley²,

Tsutsui³

2013

Front. Neurosci.

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Seasonally breeding birds detect environmental signals, such as light, temperature, food availability, and presence of mates to time reproduction. Hypothalamic neurons integrate external and internal signals, and regulate reproduction by releasing neurohormones to the pituitary gland. The pituitary gland synthesizes and releases gonadotropins which in turn act on the gonads to stimulate gametogenesis and sex steroid secretion. Accordingly, how gonadotropin secretion is controlled by the hypothalamus is key to our understanding of the mechanisms of seasonal reproduction. A hypothalamic neuropeptide, gonadotropin-releasing hormone (GnRH), activates reproduction by stimulating gonadotropin synthesis and release. Another hypothalamic neuropeptide, gonadotropin-inhibitory hormone (GnIH), inhibits gonadotropin synthesis and release directly by acting on the pituitary gland or indirectly by decreasing the activity of GnRH neurons. Therefore, the next step to understand seasonal reproduction is to investigate how the activities of GnRH and GnIH neurons in the hypothalamus and their receptors in the pituitary gland are regulated by external and internal signals. It is possible that locally-produced triiodothyronine resulting from the action of type 2 iodothyronine deiodinase on thyroxine stimulates the release of gonadotropins, perhaps by action on GnRH neurons. The function of GnRH neurons is also regulated by transcription of the GnRH gene. Melatonin, a nocturnal hormone, stimulates the synthesis and release of GnIH and GnIH may therefore regulate a daily rhythm of gonadotropin secretion. GnIH may also temporally suppress gonadotropin secretion when environmental conditions are unfavorable. Environmental and social milieus fluctuate seasonally in the wild. Accordingly, complex interactions of various neuronal and hormonal systems need to be considered if we are to understand the mechanisms underlying seasonal reproduction.

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Lack of gonadotrophin-releasing hormone (GnRH) neuron response to decreasing photoperiod in thyroidectomized male starlings (Sturnus vulgaris)

Cited by 17 publications

References 18 publications

Seasonal Plasticity within the Gonadotropin-Releasing Hormone (GnRH) System of the Ewe: Changes in Identified GnRH Inputs and Glial Association

Seasonal Plasticity within the Gonadotropin-Releasing Hormone (GnRH) System of the Ewe: Changes in Identified GnRH Inputs and Glial Association

Unravelling the role of thyroid hormones in seasonal neuroplasticity in European Starlings (Sturnus vulgaris)

Neuroendocrine regulation of gonadotropin secretion in seasonally breeding birds

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