Central versus peripheral regulation of thyroidal status in a teleost fish, Sciaenops ocellatus: evidence for a free-running circadian rhythm of T4 secretion

Membrane properties of whole cells of Gonyaulax polyedra were measured by fluorescence polarization. Circadian changes of fluorescence polarization exist in exponentially growing cultures. They show an amplitude larger than that of stationary cultures, indicating that a part of the change is due to or amplified by an ongoing cell cycle. Measurements of parameters of the circadian glow rhythm were analyzed for possible correlation with the membrane data. Considerable differences (Q10 = 2.5-3.0) in fluorescence polarization were found in cultures kept at different temperatures ranging from 15 to 27.5 degrees C. The free-running period length at different temperatures, on the other hand, differed only slightly (Q10 = 0.9-1.1). Stationary cultures showed higher fluorescence polarization compared with growing cultures, whereas the free-running period lengths did not differ in cultures of various densities and growth rates. Temperature steps of different sign changed the fluorescence polarization slightly in different directions. The phase shift of 4-h pulses (-5, -9, +7 degrees C) resulted in maximal phase advances of 4, 6, and 2 h, respectively. The phasing of the phase-response curves was identical in all these experiments, a finding not to be expected if the pulses act via the measured membrane properties. Pulses of drugs that change the fluorescence polarization (e.g., chlorpromazine and lidocaine) did not or only slightly phase-shift the circadian rhythm.

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A geophysical note on man's free‐running circadian rhythm

Journal of Interdisiplinary Cycle Research ◽

10.1080/09291018609359903 ◽

1986 ◽

Vol 17 (2) ◽

pp. 113-119 ◽

Cited By ~ 2

Author(s):

Frank Heynick

Keyword(s):

Circadian Rhythm ◽

Free Running

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A free-running bimodal circadian rhythm in the tsetse fly Glossina longipennis

Journal of Insect Physiology ◽

10.1016/0022-1910(94)90112-0 ◽

1994 ◽

Vol 40 (1) ◽

pp. 63-67 ◽

Cited By ~ 6

Author(s):

Charles Kyorku ◽

John Brady

Keyword(s):

Circadian Rhythm ◽

Tsetse Fly ◽

Free Running

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Effects of aging on entrainment and rate of resynchronization of circadian locomotor activity

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1992.263.5.r1099 ◽

1992 ◽

Vol 263 (5) ◽

pp. R1099-R1103 ◽

Cited By ~ 7

Author(s):

P. C. Zee ◽

R. S. Rosenberg ◽

F. W. Turek

Keyword(s):

Circadian Rhythm ◽

Locomotor Activity ◽

Activity Rhythm ◽

Phase Advance ◽

Middle Aged ◽

Age Related ◽

Free Running ◽

Effects Of Aging ◽

Free Running Period ◽

Related Phase

The phase angle of entrainment of the circadian rhythm of the locomotor activity rhythm to a light-dark (LD) cycle was examined in young (2-5 mo old) and middle-aged (13-16 mo old) hamsters. An age-related phase advance in the onset of locomotor activity relative to lights off was seen during stable entrainment to a 14:10-h LD cycle. In addition, the effects of age on the rate of reentrainment of the circadian rhythm of locomotor activity were examined by subjecting young and middle-aged hamsters to either an 8-h advance or delay shift of the LD cycle. Middle-aged hamsters resynchronized more rapidly after a phase advance of the LD cycle than did young hamsters, whereas young hamsters were able to phase delay more rapidly than middle-aged hamsters. The age-related phase advance of activity onset under entrained conditions, and the alteration of responses in middle-aged hamsters reentraining to a phase-shifted LD cycle, may be due to the shortening of the free-running period of the circadian rhythm of locomotor activity with advancing age that has previously been observed in this species.

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Cortisol-mediated synchrinization of circadian rhythm in urinary potassium excretion

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1977.233.5.r230 ◽

1977 ◽

Vol 233 (5) ◽

pp. R230-R238 ◽

Cited By ~ 2

Author(s):

M. C. Moore-ede ◽

W. S. Schmelzer ◽

D. A. Kass ◽

J. A. Herd

Keyword(s):

Circadian Rhythm ◽

Saimiri Sciureus ◽

Potassium Excretion ◽

Dark Cycle ◽

Urinary Potassium ◽

Timing System ◽

Daily Dose ◽

Circadian Timing System ◽

Free Running ◽

Renal Potassium Excretion

Conscious chair-acclimatized squirrel monkeys (Saimiri sciureus) studied with lights on (600 lx) from 0800 to 2000 h daily (LD 12:12) display a prominent circadian rhythm in renal potassium excretion. The characteristics of this rhythm were reproduced in adrenalectomized monkeys by infusing 5 mg cortisol and 0.001 mg aldosterone, or 5 mg cortisol alone, between 0800 and 0900 h daily. When the timing of cortisol adminisration (with or without aldosterone) was phase-delayed by 8 h, the urinary potassium rhythm resynchronized by 80% of the cortisol phase shift, but only after a transient response lasting 3–4 days. With the same daily dose of adrenal steroids given as a continuous infusion throughout each 24 h, urinary potassium excretion showed free-running oscillations no longer synchronized to the light-dark cycle. These results indicate that the cirdacian rhythm of plasma cortisol concentration acts as an internal mediator in the circadian timing system, synchronizing a potentially autonomous oscillation in renal potassium excretion to environmental time cues and to other circadian rhythms within the animal.

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