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

Stirland, J. A.; Grosse, J.; Loudon, A. S. I.; Hastings, Michael H.; Maywood, Elizabeth S.

doi:10.1095/biolreprod53.2.361

Cited by 17 publications

(13 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Brains were collected from short-day hamsters after 3 weeks ( n = 5) or 8 weeks ( n = 15) of photoperiod exposure. Short-term photo-period exposure (i.e., 3 weeks) was used to separate the effects of photoperiod from hormonal status; these animals are acclimated to short day lengths but have not undergone alterations in the reproductive axis, and have testosterone profiles equivalent to long-day animals (Stirland et al, 1995, 1996). Animals responsive to short days display fully regressed gonads and basal sex steroids by 8 weeks in photoperiod.…”

Section: Methodsmentioning

confidence: 99%

Photoperiod and Reproductive Condition Are Associated with Changes in RFamide-Related Peptide (RFRP) Expression in Syrian Hamsters (Mesocricetus auratus)

et al. 2010

View full text Add to dashboard Cite

To conserve scarce energetic resources during winter, seasonal breeders inhibit reproduction and other nonessential behavioral and physiological processes. Reproductive cessation is initiated in response to declining day lengths, a stimulus represented centrally as a long-duration melatonin signal. The melatonin signal is not decoded by the reproductive axis directly, but by an unidentified neurochemical system upstream of gonadotropin-releasing hormone (GnRH). The dorsomedial nucleus of the hypothalamus (DMH) has been implicated in seasonal changes in reproductive function in Syrian hamsters (Mesocricetus auratus), although the specific-cell phenotype decoding photoperiodic information remains unknown. RFamide-related peptide (RFRP; the mammalian homolog of the gonadotropin-inhibitory hormone (GnIH) gene identified in birds) has emerged as a potent inhibitory regulator of the reproductive axis and, significantly, its expression is localized to cell bodies of the DMH in rodents. In the present study, the authors explored the relationship between RFRP expression, photoperiod exposure, and reproductive condition/hormonal status. In male hamsters that respond to short days with reproductive inhibition, RFRP-ir and mRNA expression are markedly reduced relative to long-day animals. Replacement of testosterone in short-day animals did not affect this response, suggesting that alterations in RFRP expression are not a result of changing sex steroid concentrations. A subset of the hamster population that ignores day length cues and remains reproductively competent in short days (nonresponders) exhibits RFRP-ir expression comparable to long-day hamsters. Analysis of cell body and fiber density suggests a potential interplay between peptide production and release rate in differentially regulating the reproductive axis during early and late stages of reproductive regression. Together, the present findings indicate that photoperiod-induced suppression of reproduction is associated with changes in RFRP and mRNA expression, providing opportunity for further exploration on the role that RFRP plays in this process.

show abstract

Section: Methodsmentioning

confidence: 99%

Photoperiod and Reproductive Condition Are Associated with Changes in RFamide-Related Peptide (RFRP) Expression in Syrian Hamsters (Mesocricetus auratus)

et al. 2010

View full text Add to dashboard Cite

show abstract

“…This 4 h shift in the range of effective melatonin frequencies from that of wild-type hamsters correlates well with the shortened circadian period of the tau mutant. Tau mutant hamsters also have shorter critical day lengths and more robust short-day responses to an intermediate duration melatonin infusion (6.67 h) than do wild-type hamsters; this circadian mutation does affect the threshold duration of day length and melatonin required for short-day responses (Stirland et al 1995;Shimomura et al 1997). Perhaps decoding the melatonin signal, while not using a circadian mechanism, must resonate temporally with underlying daily physiological processes that are regulated by the circadian system.…”

Section: On the Location Of Interval Timers And Circannual Clocksmentioning

confidence: 99%

Tracking the seasons: the internal calendars of vertebrates

Paul

Zucker

Schwartz

2007

Phil. Trans. R. Soc. B

175

152

View full text Add to dashboard Cite

Animals have evolved many season-specific behavioural and physiological adaptations that allow them to both cope with and exploit the cyclic annual environment. Two classes of endogenous annual timekeeping mechanisms enable animals to track, anticipate and prepare for the seasons: a timer that measures an interval of several months and a clock that oscillates with a period of approximately a year. Here, we discuss the basic properties and biological substrates of these timekeeping mechanisms, as well as their reliance on, and encoding of environmental cues to accurately time seasonal events. While the separate classification of interval timers and circannual clocks has elucidated important differences in their underlying properties, comparative physiological investigations, especially those regarding seasonal prolactin secretions, hint at the possibility of common substrates.Keywords: seasonality; photoperiodism; circannual; interval timers While the Earth remaineth, seedtime and harvest, and cold and heat, and summer and winter, and day and night shall not cease.Genesis 8: 22, King James Version (1611) As the Earth makes its yearly orbit around the Sun, the planet's 23.58 axial tilt leads to the cyclical environmental changes that we call the seasons. Recurrent challenges to the survival of organisms and their offspring arise with the dawning of each new season, and animals have evolved seasonally induced changes in phenotype that adapt them to these predictable events. For example, in many temperate environments, winter is generally characterized by severe decreases in ambient temperature and food availability, leading to increased energetic demands at a time when resources are diminished. Because energy requirements of female mammals typically increase markedly during lactation (Bronson 1989) and newly weaned offspring are particularly vulnerable to environmental perturbations (Hill 1992), raising offspring during this time of year is often futile. Thus, many temperate species have evolved winter-specific behaviours and physiology to conserve energy (e.g. hibernation, a more insulative pelage, huddling) or provide for escape (e.g. migration). Many species also increase the chances of offspring survival by timing their mating behaviours so that parturition occurs during energetically favourable times of year.

show abstract

“…To test whether the tau mutation has altered the definition of what constitutes a long-duration (short-night) melatonin signal or how the mutation may impair interpretation of melatonin signals of differing frequencies, we exposed pinealectomized tau and wild-type hamsters to programmed melatonin infusions every 20 hours of 8-hour duration (which are known to be inhibitory in this species) or signals of 20% shorter duration (6.7 hour), reduced by the same proportion by which the circadian period is shortened (Stirland et al 1995), measuring testicular regression, serum LH, and prolactin as an end point. Both genotypes exhibited a short-day-like response, but in taus, the magnitude of response to the short-duration 6.7-hour signal was greater, with significantly reduced testis size and lowered LH levels.…”

Section: Seasonal and Photoperiodic Time Measurementmentioning

confidence: 99%

The Biology of the Circadian Ck1εtauMutation in Mice and Syrian Hamsters: A Tale of Two Species

Loudon¹,

Meng²,

Maywood³

et al. 2007

Cold Spring Harbor Symposia on Quantitative Biology

View full text Add to dashboard Cite

INTRODUCTIONThe past decade has witnessed spectacular advances in our understanding of the genetic basis of circadian timing in mammals. The circadian pacemakers within the suprachiasmatic nucleus (SCN) of the hypothalamus provide a crucial function in conducting a circadian repertoire throughout the body, acting on peripheral oscillators in all major body organs and tissues, with profound effects on general systemic physiology (Reppert and Weaver 2002;Hastings et al. 2003;Lowrey and Takahashi 2004;Saper et al. 2005). In both brain and periphery, the molecular clockwork operates as a series of interlocked autoregulatory feedback loops in which CLOCK:BMAL1 heterodimers bind to E-box DNA sequences contained within genes encoding transcriptional repressors PER and CRY. Following their accumulation in the cytoplasm, PER:CRY complexes translocate to the nucleus after a delay of several hours and repress the activity of constitutively bound CLOCK:BMAL1 complexes. These inhibitory complexes are then degraded following a further delay, and the consequent derepression of CLOCK:BMAL1 activity initiates the next circadian cycle of Per and Cry transcription.We have now come to recognize the all-pervasive nature of circadian timing in biology, and the next challenge is to unravel the mechanisms and pathways involved in mediating the effects of the clocks on physiology and metabolism. The general prevalence of many diseases is also marked by a strong circadian component in morbidity, and circadian mutants are often characterized by unexpected side effects in a wide range of pathologies, including malignancy and metabolic and cardiovascular defects. Mutations in various elements of this core molecular clock have been described, many of which result in either arrhythmia or alteration in period of rest/activity and sleep cycles. Genetically mediated desynchronization of central pacemaker function is also strongly implicated as the primary causal mechanism of familial advanced sleep phase syndrome (FASPS), and unraveling the complexities of how circadian mutations act on both central and peripheral pacemakers will reveal important new insight into both the normal regulation of sleep and the pathologies associated with sleep disruption.As in many areas of biology, much of our recent understanding has come from the use of genetically modified mice, allowing studies of incredible sophistication in a species that has an "amenable" genome. Many of the chapters in this volume are devoted to a detailed exposition of the molecular regulation of circadian timing and the impact of clocks on both normal physiology and disease processes. Here, we describe the biology of the first bona fide circadian mutation ever discovered in a mammal, the tau mutation of the Syrian hamster. We explore the impact that this timing mutation has on both the daily and seasonal biology of this species and then describe the same mutation in genetically modified mice. Here, we are able to use the power of mouse genetics to demonstrate some unexpected features of t...

show abstract

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

Cited by 17 publications

References 28 publications

Photoperiod and Reproductive Condition Are Associated with Changes in RFamide-Related Peptide (RFRP) Expression in Syrian Hamsters (Mesocricetus auratus)

Photoperiod and Reproductive Condition Are Associated with Changes in RFamide-Related Peptide (RFRP) Expression in Syrian Hamsters (Mesocricetus auratus)

Tracking the seasons: the internal calendars of vertebrates

The Biology of the Circadian Ck1εtauMutation in Mice and Syrian Hamsters: A Tale of Two Species

Contact Info

Product

Resources

About