The GnRH System of Seasonal Breeders: Anatomy and Plasticity

@article{Lehman1997TheGS,
  title={The GnRH System of Seasonal Breeders: Anatomy and Plasticity},
  author={Michael N Lehman and Robert L Goodman and Fred J. Karsch and Gary L. Jackson and Sandra J. Berriman and Heiko T. Jansen},
  journal={Brain Research Bulletin},
  year={1997},
  volume={44},
  pages={445-457}
}
Neuronal plasticity and seasonal reproduction in sheep
TLDR
Evidence for structural changes in the circuitry responsible for seasonal inhibition of GnRH secretion in sheep is reviewed and preliminary data suggesting a role for neurotrophins and neurotrophin receptors as an early mechanistic step in the plasticity that accompanies seasonal reproductive transitions in sheep are presented.
Seasonal plasticity within the gonadotropin-releasing hormone (GnRH) system of the ewe: changes in identified GnRH inputs and glial association.
TLDR
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.
Neuroanatomical plasticity in the gonadotropin‐releasing hormone system of the ewe: Seasonal variation in glutamatergic and γ‐aminobutyric acidergic afferents
TLDR
A dynamic seasonal reorganization of identified inputs onto Gn RH neurons is revealed and lends additional support to the overall hypothesis that seasonal modulation of GnRH neurons involves glutamatergic and GABAergic neural plasticity.
Information theory and the neuropeptidergic regulation of seasonal reproduction in mammals and birds
TLDR
The constancy/contingency model of predictability is applied to investigate how GnRH1 and Kiss1 integrate different environmental cues to regulate reproduction and shows that variation in Gn RH1 from a highly seasonal avian species exhibits a predictive change that is primarily based on contingency information.
Melatonin and the seasonal control of reproduction.
TLDR
Although melatonin binding sites are preferentially localised in the pars tuberalis of the adenohypophysis, the hypothalamus contains the physiological target sites of melatonin for its action on reproduction and appears to involve a complex neural circuit of interneurons that includes at least dopaminergic, serotoninergic and excitatory aminoacidergic neurons.
KiSS‐1: A Likely Candidate for the Photoperiodic Control of Reproduction in Seasonal Breeders
TLDR
Recent data indicate that the product of the KiSS‐1 gene is a potent stimulator of the hypothalamic‐pituitary‐gonadal axis and may play a central role in the neuroendocrine regulation of gonadotropin secretion, and arguments that KiSS-1 could take part in the seasonal control of reproduction are presented.
Kisspeptin: A key link to seasonal breeding
TLDR
It is proposed that the photoperiod, via melatonin, modulates KiSS-1 neurons to drive the reproductive axis.
The Regulation of Seasonal Reproduction by RFamide Peptides
TLDR
It is suggested that the phenomenon of nonresponsiveness and phenotypic variation in reproductive photoresponse may result, at least in part, from variation in the morphological features and seasonal response of the RFRP system.
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References

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Evidence for seasonal plasticity in the gonadotropin-releasing hormone (GnRH) system of the ewe: changes in synaptic inputs onto GnRH neurons.
TLDR
It was found that preoptic GnRH neurons in breeding season ewes received more than twice the mean number of synaptic inputs per unit of plasma membrane as Gn RH neurons in anestrous animals, and significant seasonal differences were seen in both axodendritic and axosomatic inputs.
Effects of gonadal steroids on the ultrastructure of GnRH neurons in the rhesus monkey: synaptic input and glial apposition.
TLDR
Investigation of the ultrastructure of GnRH neurons in the preoptic area and medial basal hypothalamus of rhesus monkeys provided strong evidence that alterations in the gonadal steroid milieu can produce morphological changes in the GnRH neuron and its immediate environment in the primate.
Role of the thyroid gland in seasonal reproduction. III. Thyroidectomy blocks seasonal suppression of gonadotropin-releasing hormone secretion in sheep.
TLDR
The finding that pulsatile secretion of GnRH is elevated in THX ewes that fail to make the transition to anestrus supports the hypothesis that the thyroid gland is required for the endogenously generated switch in function of the GnRH neurosecretory system that leads to the end of the breeding season of the ewe.
Identification and distribution of neuroendocrine gonadotropin-releasing hormone neurons in the ewe.
TLDR
The hypothesis that in the ewe, GnRH neurons projecting to the ME are localized to specific regions is not supported, and it is postulated that GnRH release into the hypophyseal portal system reflects the output of Gn RH neurons located in multiple areas.
Seasonal changes of gonadotropin-releasing hormone secretion in the ewe.
TLDR
The pattern of GnRH secretion into pituitary portal blood was examined in ewes during both the breeding and anestrous seasons, with a focus on determining whether the absence of ovulation during the nonbreeding season is associated with the lack of a sustained increase in pulsatile GnRH release.
Expression of Fos-like proteins in gonadotropin-releasing hormone neurons of Syrian hamsters: effects of estrous cycles and metabolic fuels.
TLDR
The results of these experiments suggest that in Syrian hamsters, there are separate populations of GnRH-IR neurons associated with pulsatile and surge modes of LH secretion, and provides strong support for the hypothesis that nutritional infertility is due in part to decreased GnRH secretion.
Seasonal breeding: nature's contraceptive.
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TLDR
It is established that systemic administration of estradiol benzoate elevates levels of nuclear estrogen receptor concentrations and results in the appearance of cytosolic progestin receptor the binding characteristics of which are comparable with that reported in rats and guinea pigs.
Role of the thyroid gland in seasonal reproduction. II. Thyroxine allows a season-specific suppression of gonadotropin secretion in sheep.
TLDR
The concept that the thyroid gland plays a fundamental role in seasonal reproduction in the ewe is supported for an endogenously generated change in the neuroendocrine axis that leads to an intensified E negative feedback and an end to the breeding season.
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