Photoperiodic Responses Differ among Inbred Strains of Golden Hamsters (Mesocricetus Auratus)1

Vitaterna, Martha Hotz; Turek, Fred W.

doi:10.1095/biolreprod49.3.496

Cited by 20 publications

(8 citation statements)

References 24 publications

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“…The mutation might also have affected the gonadal response by altering gonadal sensitivity to pituitary hormones, or photoperiodic effects on FSH levels might be critical in determining testicular mass [31]. Additionally, strain differences between the wild-type Wrights and Charles River taus may have contributed to the differences observed between genotypes: different strains of normal inbred laboratory hamsters are reported to exhibit different rates of response to photoperiod, although these were apparently not attributable to genetic differences in circadian rhythmicity [32]. Nevertheless, it remains a possibility that had the study continued for one or two more weeks, the subtle differences observed between the two genotypes in response to the 6.67-h infusion of melatonin may not have been significant.…”

Section: Discussionmentioning

confidence: 99%

Gonadal Responses of the Male Tau Mutant Syrian Hamster to Short-Day-Like Programmed Infusions of Melatonin1

Stirland

Grosse

Loudon

et al. 1995

Biology of Reproduction

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Changes in the duration of the nocturnal peak of the circadian rhythm of melatonin secretion by the pineal gland mediate pohotoperiodic control of reproductive cycles in mammals. The present study examined whether the tau mutation of the circadian clock of the Syrian hamster altered the ability of the animals to exhibit photoperiodic, gonadal responses to timed infusions of exogenous melatonin. Pinealectomized tau mutant and wild-type hamsters received s.c. infusions of vehicle or melatonin solution (50 ng/h) for either 8 h or 6.67 h (i.e., 83% of 8 h, a reduction by the same proportion as circadian period is shortened by the mutation, 20 h vs. 24 h) once every 20 h for 6 wk. Testicular weight and serum levels of LH and prolactin were measured to assess the effects of the infusions on the reproductive axis. Both genotypes exhibited significant gonadal regression to the 8 h and 6.67 h melatonin signals, versus saline controls, although in taus the magnitude of the response to 6.67 h melatonin was significantly greater and more consistent than in wild-types. Compared to saline-infused hamsters, animals that received infusions of melatonin of either duration showed significantly reduced serum levels of LH and prolactin. There was no significant difference between the two genotypes in the observed endocrine responses to melatonin infusions. These preliminary data demonstrate that tau mutant hamsters can respond to programmed systemic infusions of melatonin in a manner comparable to that observed in wild-type hamsters, and therefore, that the tau mutation of the circadian clock has not impaired the ability of the hamster to measure photoperiodic time, as represented by melatonin.

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Section: Discussionmentioning

confidence: 99%

Gonadal Responses of the Male Tau Mutant Syrian Hamster to Short-Day-Like Programmed Infusions of Melatonin1

Stirland

Grosse

Loudon

et al. 1995

Biology of Reproduction

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“…However, the pineal produces melatonin also under LD and there is evidence that the target tissues are indeed quite able to decode the melatonin message (193,195). More importantly, the difference between a constantly active gonadotroph axis and a permanently inactive one is only a matter of minutes, as demonstrated by experiments aimed at the identification of the critical PP, which is of 12.5 h (197–199). This appears to hardly be compatible with the desensitisation hypothesis.…”

Section: The Seasonal Reproductive Cycles Of the Golden Hamster And Smentioning

confidence: 99%

Melatonin‐Dependent Timing of Seasonal Reproduction by the Pars Tuberalis: Pivotal Roles for Long Daylengths and Thyroid Hormones

Dardente

2012

J Neuroendocrinology

111

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Most mammals living at temperate latitudes exhibit marked seasonal variations in reproduction. In long‐lived species, it is assumed that timely physiological alternations between a breeding season and a period of sexual rest depend upon the ability of day length (photoperiod) to synchronise an endogenous timing mechanism called the circannual clock. The sheep has been extensively used to characterise the time‐measurement mechanisms of seasonal reproduction. Melatonin, secreted only during the night, acts as the endocrine transducer of the photoperiodic message. The present review is concerned with the endocrine mechanisms of seasonal reproduction in sheep and the evidence that long day length and thyroid hormones are mandatory to their proper timing. Recent evidence for a circadian‐based molecular mechanism within the pars tuberalis of the pituitary, which ties the short duration melatonin signal reflecting long day length to the hypothalamic increase of triiodothyronine (T3) through a thyroid‐stimulating hormone/deiodinase2 paracrine mechanism is presented and evaluated in this context. A parallel is also drawn with the golden hamster, a long‐day breeder, aiming to demonstrate that features of seasonality appear to be phylogenetically conserved. Finally, potential mechanisms of T3 action within the hypothalamus/median eminence in relationship to seasonal timing are examined.

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“…Long photoperiods result in an increase in pituitary gonadotrophin secretion and activation of the gonads (Elliott 1976;Stetson & Tate-Ostro¡ 1981;Hastings et al 1989;Vitaterna & Turek 1993). In contrast, short photoperiods or continuous darkness (DD) initially causes the suppression of gonadotrophins and prolactin, and gonadal atrophy (Gaston & Menaker 1967;Berndtson & Desjardins 1974;Steger et al 1982;Vitaterna & Turek 1993;Stirland et al 1996a). However, after approximately 10^12 weeks, photo-inhibited animals undergo spontaneous recrudescence of the neuroendocrine axis and gonadal regrowth occurs, even during photoperiods which initially caused reproductive suppression (Stetson et al 1977;Turek & Campbell 1979;Reiter 1980).…”

Section: Introductionmentioning

confidence: 99%

“…During such cycles, tau mutants are unable to undergo gonadal regression in response to short photoperiods, even as short as 1 h of light per 24 h (1L:23D; Menaker & Re¢netti 1993). For wild-type hamsters, the equivalent photoperiod at which gonadal regression occurs is approximately 12L:12D or less (Elliott 1976;Hastings et al 1989;Vitaterna & Turek 1993;Stirland et al 1996a). In contrast, tau mutants kept on 20-h L:D cycles exhibit a normal photoperiodic response, undergoing full testicular regression at photoperiods of 10L:10D or less (Stirland et al 1996a).…”

Section: Introductionmentioning

confidence: 99%

Effects of a circadian mutation on seasonality in Syrian hamsters (Mesocricetus auratus)

Loudon

Ihara

Menaker

1998

Proc. R. Soc. Lond. B

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In Syrian hamsters, exposure to short photoperiods or constant darkness induces a decrease in gonadotrophin secretion and gonadal regression. After 10-12 weeks, animals undergo spontaneous gonadal reactivation, gonadotrophin concentrations rise, and in males, testes size increases and spermatogenesis resumes. The tau mutation shortens the period of circadian wheel-running activity by 4 h in the homozygote. Here, we examine the impact of this mutation on the reproductive response to photoperiod change. Seventeen adult tau mutant and nine adult wild-type males were housed in complete darkness for 25 weeks and testes size determined at weekly intervals. Gonadal regression and subsequent recrudescence occurred in both groups of animals. Regression occurred more rapidly in tau mutants, with a nadir significantly earlier than wild-types but after a similar number of circadian cycles. Rates of testicular recrudescence were similar in both groups. Our data suggest that an acceleration of the circadian period increases the rate of reproductive inhibition in animals exposed to inhibitory photoperiods. Once initiated, the rate of spontaneous reactivation may be independent of the circadian axis.

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Photoperiodic Responses Differ among Inbred Strains of Golden Hamsters (Mesocricetus Auratus)1

Cited by 20 publications

References 24 publications

Gonadal Responses of the Male Tau Mutant Syrian Hamster to Short-Day-Like Programmed Infusions of Melatonin1

Gonadal Responses of the Male Tau Mutant Syrian Hamster to Short-Day-Like Programmed Infusions of Melatonin1

Melatonin‐Dependent Timing of Seasonal Reproduction by the Pars Tuberalis: Pivotal Roles for Long Daylengths and Thyroid Hormones

Effects of a circadian mutation on seasonality in Syrian hamsters (Mesocricetus auratus)

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