bims-ciryme Biomed News
on Circadian Rhythms and Metabolism
Issue of 2019‒02‒03
two papers selected by
Gabriela Da Silva Xavier
University of Birmingham

  1. Nat Commun. 2019 Feb 01. 10(1): 550
      The clockwork of plant circadian oscillators has been resolved through investigations in Arabidopsis thaliana. The circadian oscillator is an important regulator of much of plant physiology, though many of the mechanisms are unclear. New findings demonstrate that the oscillator adjusts phase and period in response to abiotic and biotic signals, providing insight in to how the plant circadian oscillator integrates with the biology of the cell and entrains to light, dark and temperature cycles. We propose that the plant circadian oscillator is dynamically plastic, in constant adjustment, rather than being an isolated clock impervious to cellular events.
  2. Endocrinology. 2019 Jan 22.
      The hypothalamo-pituitary-adrenal (HPA) axis involves timed signaling between the hypothalamus, pituitary, adrenal glands and back to the brain, causing an inherently oscillating system. Corticosteroids like corticosterone (CORT) are secreted in a circadian rhythm, characterized by low and high levels respectively at the start of the inactive and active phase. The circadian rhythm overarches ultradian CORT pulses, with an approximate 1-hour interpulse intervals. We examined the physiological relevance of pulsatile CORT exposure for neurons of the basolateral amygdala (BLA), an area important for fear learning. We first applied four pulses of equal, high CORT concentration and measured the frequency of miniature excitatory postsynaptic currents (mEPSC) -reflecting spontaneous glutamate signaling. The results, extending earlier studies, show that BLA neurons respond differently to each pulse, showing 'meta-plasticity'. Next we mimicked the progression of the inactive and active phase by four CORT pulses of increasing or decreasing concentration respectively. CORT pulses of increasing concentration were necessary and sufficient to gradually increase baseline (between-pulse) mEPSC frequency during the mimicked inactive phase while the opposite was seen with decreasing CORT levels during the mimicked active phase. To study the relevance of changed glutamate transmission for behavior, mice were tested in tone-cued fear conditioning during the active or inactive phase. Animals tested at the inactive compared to active phase showed efficient fear learning; this was also observed when animals tested during the active phase were treated with the CORT synthesis blocker metyrapone. This suggests that natural CORT rhythms influence electrical activity in the BLA, possibly contributing to altered behavioral function.