A riot of rhythms: neuronal and glial circadian oscillators in the mediobasal hypothalamus.
BACKGROUND
In mammals, the synchronized activity of cell autonomous clocks in the suprachiasmatic nuclei (SCN) enables this structure to function as the master circadian clock, coordinating daily rhythms in physiology and behavior. However, the dominance of this clock has been challenged by the observations that metabolic duress can over-ride SCN controlled rhythms, and that clock genes are expressed in many brain areas, including those implicated in the regulation of appetite and feeding. The recent development of mice in which clock gene/protein activity is reported by bioluminescent constructs (luciferase or luc) now enables us to track molecular oscillations in numerous tissues ex vivo. Consequently we determined both clock activities and responsiveness to metabolic perturbations of cells and tissues within the mediobasal hypothalamus (MBH), a site pivotal for optimal internal homeostatic regulation.


RESULTS
Here we demonstrate endogenous circadian rhythms of PER2::LUC expression in discrete subdivisions of the arcuate (Arc) and dorsomedial nuclei (DMH). Rhythms resolved to single cells did not maintain long-term synchrony with one-another, leading to a damping of oscillations at both cell and tissue levels. Complementary electrophysiology recordings revealed rhythms in neuronal activity in the Arc and DMH. Further, PER2::LUC rhythms were detected in the ependymal layer of the third ventricle and in the median eminence/pars tuberalis (ME/PT). A high-fat diet had no effect on the molecular oscillations in the MBH, whereas food deprivation resulted in an altered phase in the ME/PT.


CONCLUSIONS
Our 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.
Guilding
Clare
C
Faculty of Life Sciences, University of Manchester, Manchester, UK. clare.guilding@manchester.ac.uk
Hughes
Alun T L
AT
Brown
Timothy M
TM
Namvar
Sara
S
Piggins
Hugh D
HD
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000187:drug effects / Q000502:physiology; D001683:Biological Clocks / Q000187:drug effects / Q000502:physiology*; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology*; D005576:Colforsin / Q000494:pharmacology; D004041:Dietary Fats / Q000008:administration & dosage / Q000494:pharmacology; D005247:Feeding Behavior / Q000187:drug effects; D005508:Food Deprivation; D007031:Hypothalamus / Q000187:drug effects / Q000502:physiology*; D008156:Luciferases / Q000378:metabolism; D008163:Luminescent Measurements; D008297:Male; D008473:Median Eminence / Q000187:drug effects / Q000502:physiology; D051379:Mice; D009457:Neuroglia / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009928:Organ Specificity / Q000187:drug effects; D056950:Period Circadian Proteins / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism; D013493:Suprachiasmatic Nucleus / Q000187:drug effects / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology
D004041:Dietary Fats; C513312:Per2 protein, mouse; D056950:Period Circadian Proteins; D015222:Sodium Channels; D005576:Colforsin; D013779:Tetrodotoxin; D008156:Luciferases