Plasma melatonin profiles of Romney Marsh sheep in natural photoperiod and in acutely extended darkness

Matthews, Colin D.; Seamark, R.F.; Guerin, Michael V.

doi:10.1530/jrf.0.0950869

Cited by 21 publications

(21 citation statements)

References 24 publications

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“…In a previous study (Matthews et al, 1992), when animals in the natural photoperiod were sampled under acutely extended darkness, melatonin secretion demonstrated a rather stable phase and duration from the winter to the summer solstice. In the present study, for the control group, the onset and the offset of melatonin secretion sampled under acutely extended darkness occurred prior to dusk and after dawn, respectively, under conditions of decreasing night length.…”

Section: Methodsmentioning

confidence: 78%

“…Using this knowledge, we sampled melatonin in the Romney Marsh ewe (held under natural conditions throughout the year) after acutely extending darkness to avoid any masking effects of natural light and reported a pattern of melatonin secretion different from that normally found under natural environmental conditions (Matthews et al, 1992). During the spring/summer period, natural light at dusk appeared to suppress the melatonin signal; thus natural light coincides with a critical interval when the onset of melatonin secretion would normally be present under dim light conditions, the timing of which is regulated by the SCN.…”

Section: Introductionmentioning

confidence: 99%

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Is a Critical Interval of the Circadian Pacemaker at Dusk Responsive to Light and Melatonin Responsible for the Timing of Estrus in the Romney Marsh Ewe?

1995

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Two experiments, using Romney Marsh ewes, tested for the existence and role of a critical interval of the circadian pacemaker located near dusk that may be integrally involved in the precise timing of the breeding season. Groups of Romney Marsh ewes (n = 6) were provided with exogenous melatonin by injection at dusk (Experiment 1) or by infusion at dawn or subjected to extended darkness at dawn (Experiment 2) from the winter to the summer solstice before being exposed to natural photoperiod at latitude 35 degrees S. Other than the experimental protocols, all animals were held in natural photoperiod. The onset of the breeding season (defined as cyclic ovarian activity as indicated by plasma progesterone monitoring) was normal in those animals treated with morning melatonin but was delayed in those animals treated with melatonin at dusk or extended darkness at dawn compared to controls in natural photoperiod (p < .01). Exogenous melatonin at dusk was associated with a phase advance of the onset of the circadian pacemaker (as measured by endogenous melatonin in acutely extended darkness); additional darkness at dawn was associated with a phase delay of both the onset and the offset of the circadian pacemaker. Exogenous morning melatonin did not change the phase of the circadian pacemaker relative to the controls. The results are consistent with an external coincidence model of seasonal breeding in which a critical interval of the circadian pacemaker requires exposure to light during spring/summer to time estrus correctly. The proposed critical interval appears to be located near dusk in this model and is phase locked to the circadian pacemaker. The effect of the exogenous melatonin on the timing of the breeding season is similar to darkness when administered at dusk but is not equivalent to darkness at dawn. The timing of anestrus was not affected by any of the experimental treatments and may reflect a common response to an environmental influence.

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Section: Methodsmentioning

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Is a Critical Interval of the Circadian Pacemaker at Dusk Responsive to Light and Melatonin Responsible for the Timing of Estrus in the Romney Marsh Ewe?

1995

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“…We have presented evidence that the usual reported pattern of endogenous melatonin in the Romney Marsh sheep, namely closely linked to the duration of darkness, is not fully representative of the SCN signal (Matthews et al, 1992), the pattern reflecting only a masked or gated version (by natural photoperiod) of the circadian pacemaker. Measurements of melatonin under conditions of acutely extended darkness (to avoid entrainment effects) suggest that there is a critical circadian time, particularly during the spring/summer, when the natural light of dusk gates the full expression of the melatonin rhythm.…”

Section: Introductionmentioning

confidence: 90%

Alterations of Estrous Activity in the Ewe by Circadian-Based Manipulation of the Endogenous Pacemaker

Guerin¹,

Matthews

1998

J Biol Rhythms

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The timing of reproductive activity in the seasonal breeding Romney Marsh ewe depends on the measurement of photoperiodic time. In this experiment, artificial light and dark signals are provided in a measured sequence at an inappropriate time of year to induce breeding out of phase with environmental photoperiod. The endogenous circadian responses and reproductive effects are documented. One group (Group A, control) of 6 Romney Marsh ewes was held in natural photoperiod throughout the experiment. For 8 weeks centered about the winter solstice (Stage 1), an additional 18 animals (Groups B, C, and D) were exposed to an artificial earlier dawn. Measurements of endogenous melatonin performed under acutely extended darkness confirmed a phase advance of the endogenous circadian pacemaker of the suprachiasmatic nucleus compared to control animals. In Stage 2, to the summer solstice (21 December), Group B animals were returned to natural photoperiod, Group C animals were subjected to an earlier artificial dusk, and Group D animals were subjected to an artificial delayed dawn. Melatonin measurements during Stage 2 confirmed that onset and offset times for Group C were earlier and that onset and offset times for Group D were delayed compared to corresponding times for Group B animals. Ovarian activity was monitored throughout. During Stage 2, Groups C and D commenced reproductive activity in mid-spring, and this continued until the experimental conditions changed. Groups A and B commenced reproductive activity at the normal timing in the subsequent autumn. Although not exclusive, these results are consistent with a coincidence model to explain the timing of seasonal breeding in this species with a dusk-located phase of the endogenous pacemaker sensitive to both light and melatonin. The temporal relationship between circadian alterations and the environmental photoperiod warrants further investigation as an explanation for seasonal breeding.

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“…In one study there was evidence that grooming and aggression were modified by post-surgical analgesia and could indicate pain (Pollard et al, 1992a), suggesting that behaviour could be used to compare the degree of pain following velvet removal using different methods of analgesia. Studies that have used electrical stimulation to test the reappearance of sensitivity in the antler following administration of lignocaine indicate that the duration of analgesia lasts from 88 to 120 min (Bartels et al, 2001;Matthews et al, 1992a). If this is the case, then behavioural signs of pain may be expected to appear in lignocaine treated animals after this time.…”

Section: Introductionmentioning

confidence: 99%

Behaviour of red deer following antler removal with two methods of analgesia

Webster

Matthews

2006

Livestock Science

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Plasma melatonin profiles of Romney Marsh sheep in natural photoperiod and in acutely extended darkness

Abstract: Summary. Plasma

Cited by 21 publications

References 24 publications

Is a Critical Interval of the Circadian Pacemaker at Dusk Responsive to Light and Melatonin Responsible for the Timing of Estrus in the Romney Marsh Ewe?

Is a Critical Interval of the Circadian Pacemaker at Dusk Responsive to Light and Melatonin Responsible for the Timing of Estrus in the Romney Marsh Ewe?

Alterations of Estrous Activity in the Ewe by Circadian-Based Manipulation of the Endogenous Pacemaker

Behaviour of red deer following antler removal with two methods of analgesia

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