Characterizing a Mammalian Circannual Pacemaker

  title={Characterizing a Mammalian Circannual Pacemaker},
  author={Gerald Lincoln and Iain J Clarke and Roelof A. Hut and David G. Hazlerigg},
  pages={1941 - 1944}
Many species express endogenous cycles in physiology and behavior that allow anticipation of the seasons. The anatomical and cellular bases of these circannual rhythms have not been defined. Here, we provide strong evidence using an in vivo Soay sheep model that the circannual regulation of prolactin secretion, and its associated biology, derive from a pituitary-based timing mechanism. Circannual rhythm generation is seen as the product of the interaction between melatonin-regulated timer cells… 

A Physiological Model of a Circannual Oscillator

A physiological model of a circannual rhythm generator centered in the pituitary gland based on the interaction between melatonin-responsive cells in the pars tuberalis that act to decode photoperiod, and lactotroph cells of the adjacent pars distalis that secrete prolactin is presented.

Mammalian circannual pacemakers.

It is proposed that circannual timing involves mechanisms that are integral to the ontogenetic life-history programme where annual transitions are generated by cell birth, death and tissue regeneration throughout the life cycle--the histogenesis hypothesis.

Stem Cell Regulation of Circannual Rhythms

This chapter conjecture that all three mechanisms can contribute to the generation of the seasonal phenotype in complex organisms, different for each species, and that an evolutionally conserved, cell-autonomous mechanism may be expressed in stem cells to act as a pacemaker for circannual timing.

Circannual rhythms in birds

The present review outlines the basics ofcircannual rhythms, its interaction with environmental factors, differences between the two mechanisms that regulate seasonal responses in organisms i.e. photoperiodism and circannual rhythm, and also presents some experiments which have demonstrated circann annual rhythm in reproduction, migration and molt behaviour of birds.

Circannual prolactin rhythms: calendar-like timer revealed in the pituitary gland

  • M. Duncan
  • Biology, Medicine
    Trends in Endocrinology & Metabolism
  • 2007

Circadian Timekeeping and Multiple Timescale Neuroendocrine Rhythms

The recent evidence suggesting that the circadian clock genes that pace the authors' daily rhythms may also contribute to the regulation of pituitary pulsatility, even in the non 24‐h range is summarized.

A riot of rhythms: neuronal and glial circadian oscillators in the mediobasal hypothalamus

These results provide the first single cell resolution of endogenous circadian rhythms in clock gene expression in any intact tissue outside the SCN, reveal the cellular basis for tissue level damping in extra-SCN oscillators and demonstrate that an oscillator in the ME/PT is responsive to changes in metabolism.

Epigenetic Mechanisms Regulating Circannual Rhythms

A Dual Compartmentalization Model is proposed in which the first compartment is composed of stem/primordial cells and provides the initiation signal for the circannual cycle, and the second compartment is formed of differentiated cells that propagate and amplify the circANNual cycle.

Hypothesis: cyclical histogenesis is the basis of circannual timing.

The authors propose that circannual rhythm generation depends on tissue-autonomous, reiterated cycles of cell division, functional differentiation, and cell death, and see the feedback control influencing localized stem cell niches as crucial to this cyclical histogenesis hypothesis.



Evidence for an endogenous per1‐ and ICER‐independent seasonal timer in the hamster pituitary gland

The PT is identified as a key anatomical structure involved in endogenous seasonal timing mechanisms, which breaks from prevailing day length‐induced gene expression, and is associated with prolactin secretion in refractory Syrian hamsters.

Circannual Alterations in the Circadian Rhythm of Melatonin Secretion

Evidence is provided for a circannual change in the circadian rhythm of melatonin secretion that may serve as a "functional" change in daylength, and thereby may influence the expression of thecircannual reproductive rhythm of sheep held in a fixed photoperiod for an extended time.

Biology of Mammalian Photoperiodism and the Critical Role of the Pineal Gland and Melatonin

Indoleamine at the level of the central nervous system is a modulation of GnRH secretion but it does not act directly on GnRH neurones; rather, its action involves a complex neural circuit of interneurones that includes at least dopaminergic, serotoninergic and aminoacidergic neurones.

Circannual Rhythms Mammals

Seasonal rhythms are evident at all levels of biological organization: mammals anticipate and take advantage of predictable changes in the external environment imposed by the 12-month geophysical cycle.

Photorefractoriness in mammals: dissociating a seasonal timer from the circadian-based photoperiod response.

The generation of long-term endocrine cycles depends on the interaction between a circadian-based, melatonin-dependenttimer that drives the initial photoperiodic response and a non-circadian-based timer that drives circannual rhythmicity in long-lived species.

Circannual Rhythms of Ground Squirrels: A Test of the Frequency Demultiplication Hypothesis

The periods of the circannual body mass and estrous cycles of golden-mantled ground squirrels with circadian locomotor activity rhythms entrained to 23-, 24-, or 25-hr days were determined.

Rhythms in clock proteins in the mouse pars tuberalis depend on MT1 melatonin receptor signalling

Results show that melatonin, acting through the MT1, determines availability of the circadian proteins mPER1, mPER2 and mCRY1 and thus plays a crucial role in regulating rhythmicity in PT cells.

Photoperiodic synchronization of a circannual reproductive rhythm in sheep: identification of season-specific time cues.

The results support the concept that there is a seasonal specificity with regard to the photoperiodic cues that synchronize the circannual rhythm of reproductive neuroendocrine activity in the ewe.

Pulses of prolactin promoter activity depend on a noncanonical E-box that can bind the circadian proteins CLOCK and BMAL1.

It is demonstrated that PRL-GE pulses are dependent on a specific E-box binding site in the PRL promoter and the indication that CLOCK/BMAL1 can bind to this site suggests that these circadian proteins, either alone or in conjunction with other factors, may regulate intermittentPRL promoter activity in mammotropes, perhaps by acting as a temporal switch for the on/off expression of PRL.