scholarly journals Physiology of Circadian Entrainment

2010 ◽  
Vol 90 (3) ◽  
pp. 1063-1102 ◽  
Author(s):  
Diego A. Golombek ◽  
Ruth E. Rosenstein
Keyword(s):  
Circadian Rhythms ◽  
Clock Gene ◽  
Retinal Diseases ◽  
Suprachiasmatic Nuclei ◽  
Circadian Variations ◽  
Dark Cycle ◽  
Clock Gene Expression ◽  
Biological Oscillators ◽  
Pituitary Adenylate Cyclase ◽  
Neurotransmitter Glutamate

Mammalian circadian rhythms are controlled by endogenous biological oscillators, including a master clock located in the hypothalamic suprachiasmatic nuclei (SCN). Since the period of this oscillation is of ∼24 h, to keep synchrony with the environment, circadian rhythms need to be entrained daily by means of Zeitgeber (“time giver”) signals, such as the light-dark cycle. Recent advances in the neurophysiology and molecular biology of circadian rhythmicity allow a better understanding of synchronization. In this review we cover several aspects of the mechanisms for photic entrainment of mammalian circadian rhythms, including retinal sensitivity to light by means of novel photopigments as well as circadian variations in the retina that contribute to the regulation of retinal physiology. Downstream from the retina, we examine retinohypothalamic communication through neurotransmitter (glutamate, aspartate, pituitary adenylate cyclase-activating polypeptide) interaction with SCN receptors and the resulting signal transduction pathways in suprachiasmatic neurons, as well as putative neuron-glia interactions. Finally, we describe and analyze clock gene expression and its importance in entrainment mechanisms, as well as circadian disorders or retinal diseases related to entrainment deficits, including experimental and clinical treatments.

scholarly journals Clock Gene Expression in Adult Primate Suprachiasmatic Nuclei and Adrenal: Is the Adrenal a Peripheral Clock Responsive to Melatonin?

Endocrinology ◽  
2008 ◽  
Vol 149 (4) ◽  
pp. 1454-1461 ◽  
Author(s):  
F. J. Valenzuela ◽  
C. Torres-Farfan ◽  
H. G. Richter ◽  
N. Mendez ◽  
C. Campino ◽  
...  
Keyword(s):  
Adrenal Gland ◽  
Clock Gene ◽  
Clock Genes ◽  
Phase Relationship ◽  
Suprachiasmatic Nuclei ◽  
Rhythmic Expression ◽  
Peripheral Oscillators ◽  
Clock Gene Expression ◽  
Timing System ◽  
Circadian Timing System

The circadian production of glucocorticoids involves the concerted action of several factors that eventually allow an adequate adaptation to the environment. Circadian rhythms are controlled by the circadian timing system that comprises peripheral oscillators and a central rhythm generator located in the suprachiasmatic nucleus (SCN) of the hypothalamus, driven by the self-regulatory interaction of a set of proteins encoded by genes named clock genes. Here we describe the phase relationship between the SCN and adrenal gland for the expression of selected core clock transcripts (Per-2, Bmal-1) in the adult capuchin monkey, a New World, diurnal nonhuman primate. In the SCN we found a higher expression of Bmal-1 during the h of darkness (2000–0200 h) and Per-2 during daytime h (1400 h). The adrenal gland expressed clock genes in oscillatory fashion, with higher values for Bmal-1 during the day (1400–2000 h), whereas Per-2 was higher at nighttime (about 0200 h), resulting in a 9- to 12-h antiphase pattern. In the adrenal gland, the oscillation of clock genes was accompanied by rhythmic expression of a functional output, the steroidogenic enzyme 3β-hydroxysteroid dehydrogenase. Furthermore, we show that adrenal explants maintained oscillatory expression of Per-2 and Bmal-1 for at least 36 h in culture. The acrophase of both transcripts, but not its overall expression along the incubation, was blunted by 100 nm melatonin. Altogether, these results demonstrate oscillation of clock genes in the SCN and adrenal gland of a diurnal primate and support an oscillation of clock genes in the adrenal gland that may be modulated by the neurohormone melatonin.

scholarly journals Neuron-specific knockouts indicate the importance of network communication to Drosophila rhythmicity

2019 ◽  
Author(s):  
M Schlichting ◽  
MM Diaz ◽  
J Xin ◽  
M Rosbash
Keyword(s):  
Gene Expression ◽  
Circadian Rhythms ◽  
Intercellular Communication ◽  
Clock Gene ◽  
Feedback Loops ◽  
Neuronal Firing ◽  
Network Communication ◽  
Constant Darkness ◽  
Circadian Period ◽  
Clock Gene Expression

AbstractAnimal circadian rhythms persist in constant darkness and are driven by intracellular transcription-translation feedback loops. Although these cellular oscillators communicate, isolated mammalian cellular clocks continue to tick away in darkness without intercellular communication. To investigate these issues in Drosophila, we assayed behavior as well as molecular rhythms within individual brain clock neurons while blocking communication within the ca. 150 neuron clock network. We also generated CRISPR-mediated neuron-specific circadian clock knockouts. The results point to two key clock neuron groups: loss of the clock within both regions but neither one alone has a strong behavioral phenotype in darkness; communication between these regions also contributes to circadian period determination. Under these dark conditions, the clock within one region persists without network communication. The clock within the famous PDF-expressing s-LNv neurons however was strongly dependent on network communication, likely because clock gene expression within these vulnerable sLNvs depends on neuronal firing or light.

The neural circadian system of mammals

2011 ◽  
Vol 49 ◽  
pp. 1-17 ◽  
Author(s):  
Hugh D. Piggins ◽  
Clare Guilding
Keyword(s):  
Circadian Rhythms ◽  
Circadian System ◽  
Daily Activities ◽  
Suprachiasmatic Nuclei ◽  
Dark Cycle ◽  
Environmental Light ◽  
Endogenous Clock ◽  
Central Clock

Humans and other mammals exhibit a remarkable array of cyclical changes in physiology and behaviour. These are often synchronized to the changing environmental light–dark cycle and persist in constant conditions. Such circadian rhythms are controlled by an endogenous clock, located in the suprachiasmatic nuclei of the hypothalamus. This structure and its cells have unique properties, and some of these are reviewed to highlight how this central clock controls and sculpts our daily activities.

Endogenous clock gene expression in the suprachiasmatic nuclei of previsual newborn rabbits is entrained by nursing

2009 ◽  
Vol 69 (1) ◽  
pp. 47-59 ◽  
Author(s):  
Ivette Caldelas ◽  
Belén González ◽  
Rodrigo Montúfar-Chaveznava ◽  
Robyn Hudson
Keyword(s):  
Gene Expression ◽  
Clock Gene ◽  
Suprachiasmatic Nuclei ◽  
Clock Gene Expression ◽  
Endogenous Clock
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