Seasonal Variation in Long-Day Stimulation of Prolactin Secretion in Ewes1

Sweeney, T.; Kelly, Gregory; O'Callaghan, D.

doi:10.1095/biolreprod60.1.128

Cited by 11 publications

(5 citation statements)

References 23 publications

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“…PRL displays a seasonal pattern of secretion, with higher levels during spring and summer and a rapid increase or decrease upon acute exposure to longer or shorter daylengths, respectively . Photoperiodic history also affects the long‐day response of PRL secretion in ewes . In sheep, gonadotrophic (LH/FSH) and lactotrophic axes (PRL) display opposite responses to daylength, which are driven by two distinct neuroendocrine axes: the gonadotrophic axis uses the retrograde TSH/DIO2/T3 axis, whereas the lactotrophic axis relies on anterograde signalling from the PT to the pars distalis, independently of T3 (in both rams and ewes), via one or several endocrine factors (known as tuberalin[s]), for which the identity remains unclear .…”

Section: Discussionmentioning

confidence: 99%

Discontinuity in the molecular neuroendocrine response to increasing daylengths in Ile‐de‐France ewes: Is transient Dio2 induction a key feature of circannual timing?

Dardente

Lomet

Chesneau

et al. 2019

J Neuroendocrinology

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In mammals, melatonin is responsible for the synchronisation of seasonal cycles to the solar year. Melatonin is secreted by the pineal gland with a profile reflecting the duration of the night and acts via the pituitary pars tuberalis (PT), which in turn modulates hypothalamic thyroid hormone status via seasonal changes in the production of locally-acting thyrotrophin. Recently, we demonstrated that, in the Soay sheep, photoperiodic induction of Tshb expression and consequent downstream hypothalamic changes occur over a narrow range of photoperiods between 12 and 14 hours in duration. In the present study, we aimed to extend our molecular characterisation of this pathway, based on transcriptomic analysis of photoperiodic changes in the pituitary and hypothalamus of ovariectomised, oestradiol-implanted Ile-de-France ewes. We demonstrate that photoperiodic treatments applied before the winter solstice elicit two distinctive modes of accelerated reproductive switch off compared to ewes held on a simulated natural photoperiod, with shut-down occurring markedly faster on photoperiods of 13 hours or more than on photoperiods of 12 hours and less. This pattern of response was reflected in gene expression profiles of photoperiodically sensitive markers, both in the PT (Tshb, Fam150b, Vmo1, Ezh2 and Suv39H2) and in tanycytes (Tmem252 and Dct). Unexpectedly, the expression of Dio2 in tanycytes did not show any noticeable increase in expression with lengthening photoperiods. Finally, the expression of Kiss1, the key activator of gonadotrophin-releasing hormone release, was proportionately decreased by lengthening photoperiods, in a pattern that correlated strongly with gonadotrophin suppression. These data show that stepwise increases in photoperiod lead to graded molecular responses at the level of the PT, a progressive suppression of Kiss1 in the hypothalamic arcuate nucleus and luteinising hormone/ follicle-stimulating hormone release by the pituitary, despite apparently unchanged Dio2 expression in tanycytes. We hypothesise that this apparent discontinuity in the seasonal neuroendocrine response illustrates the transient nature of the thyroid hormone-mediated response to long days in the control of circannual timing.

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Section: Discussionmentioning

confidence: 99%

Discontinuity in the molecular neuroendocrine response to increasing daylengths in Ile‐de‐France ewes: Is transient Dio2 induction a key feature of circannual timing?

Dardente

Lomet

Chesneau

et al. 2019

J Neuroendocrinology

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“…In sheep, seasonal changes in secretion of MLT which are determined by the biological clock represent a signal in the annual reproductive cycle (Sweeney et al 1999). The endocrine mechanism of entering and maintenance of lactation has not been fully understood.…”

Section: Discussionmentioning

confidence: 99%

The effect of the diversified signal of melatonin on milk yields in seasonally breeding sheep

et al. 2013

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Abstract. Previous studies demonstrated that milk yields in sheep displaying strong seasonal sexual activity depend on the day length. The objective of the studies was to determine whether the introduction of melatonin in high pregnancy affects milk secretion in seasonally sheep. The studies were carried out on 60 Polish Longwool sheep. Sheep were allocated to three groups: Group I (n = 20 – the control group, lambed in February), Group II (n = 20 – a group of sheep lambed in June and kept under natural day-length conditions), Group III (n = 20 – a group of sheep with melatonin implants injected six weeks before lambing, sheep lambed in June). Lambs were reared with mothers up to 56th day of their life. When lambs were weaned, ewes were milked mechanically twice a day up to the dry period. Once a month collective milk samples were drawn from six sheep from each group in order to determine the concentration of melatonin. Milk yields were subjected to individual checks every 10 days. The studies demonstrated that sheep lambed in February (Group I) displayed the highest milk yields in the milking period (37.8 ± 8.1 l). The milk performance of the two other groups was lower and amounted to 30.2 ± 9.4 litres in case of sheep lambed in June and to 29.2 ± 7.6 litres in sheep with melatonin implants. The introduction of melatonin signal to produce a short-day condition in state of high pregnancy in ewes caused a drop of milk yields both in the period of lambs raising and during milking.

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“…It may be an expression of the circannual clock or some kind of memory for photoperiodic history. Indeed, it has been shown both in a long-day breeder, the Djungarian hamster, and in a short-day breeder, the sheep, that a certain duration of the melatonin signal or photoperiod is not critical for the timing of reproductive functions, but the relative duration of the preceding photoperiod (or melatonin signal) determines the responses (Hoffmann et al, 1986;Robinson and Karsch, 1987;Sweeney et al, 1997Sweeney et al, , 1999.…”

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confidence: 99%

Seasonal Variation in Endogenous Serum Melatonin Profiles in Goats: A Difference between Spring and Fall?

Alila-Johansson

Eriksson²,

Soveri

et al. 2001

J Biol Rhythms

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The pineal hormone melatonin serves as a signal of day length in the regulation of annual rhythms of physiological functions and behavior. The duration of high melatonin levels in body fluids is proportional to the duration of the dark period of the day. Due to the direct suppression of melatonin by light, the overt melatonin rhythm may differ from the endogenous rhythm driven by the hypothalamic circadian clock. The aim of this study was to find out possible differences between the overt and endogenous melatonin rhythms in goats during the course of a year. Seven Finnish landrace goats (nonlactating females) were kept under artificial lighting that approximately simulated the annual changes of day length at 60 degrees N. Blood samples for melatonin measurements by radioimmunoassay were collected at 2-h intervals during six seasons: winter (light:dark 6:18 h), early spring (10:14), late spring (14:10), summer (18:6), early fall (14:10), and late fall (10:14). Melatonin profiles were determined for 2 consecutive days, first in light-dark (LD) conditions and then in continuous darkness (DD). In LD conditions, the profiles matched the dark period with one exception: In winter, the mean peak duration was significantly shorter than the scotoperiod. In DD conditions, two types of endogenous melatonin patterns were found: a "winter pattern" (peak duration 13-15 h) in winter, early spring, early fall, and late fall, and a "summer pattern" (duration about 11 h) in late spring and summer. Thus, in equal habitual LD conditions in late spring and early fall (LD 14:10), the endogenous melatonin rhythms were not quite similar: The pattern in late spring resembled that in summer, and the pattern in early fall that in winter. These results suggest that, in addition to the light-adjusted overt melatonin rhythm, the endogenous rhythm of melatonin secretion varies during the course of a year.

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Seasonal Variation in Long-Day Stimulation of Prolactin Secretion in Ewes1

Cited by 11 publications

References 23 publications

Discontinuity in the molecular neuroendocrine response to increasing daylengths in Ile‐de‐France ewes: Is transient Dio2 induction a key feature of circannual timing?

Discontinuity in the molecular neuroendocrine response to increasing daylengths in Ile‐de‐France ewes: Is transient Dio2 induction a key feature of circannual timing?

The effect of the diversified signal of melatonin on milk yields in seasonally breeding sheep

Seasonal Variation in Endogenous Serum Melatonin Profiles in Goats: A Difference between Spring and Fall?

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