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M C Moore-Ede

Publications and source records attributed to M C Moore-Ede.

At least 55 records · Page 3Linked to original sources
PubMed1983

The circadian timing system in mammals: two pacemakers preside over many secondary oscillators.

There is considerable evidence to indicate that circadian timekeeping in mammals is accomplished by a multioscillator system. Circadian rhythms in physiological variables may under certain circumstances adopt different periodicities within the same animal, and many mammalian tissues have been shown capable of generating persisting circadian rhythms in vitro. However, as yet only one circadian pacemaker has been identified unequivocally: the suprachiasmatic nuclei (SCN) in the anterior hypothalamus. This paper presents evidence that mammals possess another major circadian pacemaking system that is normally coupled to the SCN but that can function independently. Each of these major pacemakers presides over a considerable number of secondary oscillators located in diverse tissues.

Animals↗
PubMed1982

Three-dimensional structure of the mammalian suprachiasmatic nuclei: a comparative study of five species.

The suprachiasmatic nuclei from five mammalian species (rat, hamster, cat, rhesus, and squirrel monkey) were reconstructed in three-dimensions by use of computer graphics and conventional histological techniques. The gross nuclear structures of the suprachiasmatic nuclei have complex three-dimensional geometries in every plane of orientation, and between the five species there are marked differences in the three-dimensional morphology of the suprachiasmatic nuclei. These dimensionally accurate reconstructions are discussed in relation to previous data suggesting morphological and/or functional specialization within specific regions of the suprachiasmatic nuclei.

Animals↗
PubMed1982

Entrainment and masking of circadian drinking rhythms in primates: influence of light intensity.

The entrained drinking rhythms of squirrel monkeys were studied during exposure to 24 hr illumination cycles of three different intensities (60:0, 66:6, 76:16 lux). Increasing the intensity of ambient illumination significantly delayed the offset of drinking but had no effect on either the onset or the total amount of daily drinking behavior. Comparison of drinking behavior under an alternating schedule of LD 66:6 lux and constant light of 6 lux indicated that the twice daily light transitions consistently altered the temporal distribution of drinking behavior. The daily timing of squirrel monkey drinking behavior thus, depends not only o the mechanisms of circadian entrainment to the LD cycle, but also on the ability of the LD cycle to directly influence, or "mask" behavior.

Animals↗
PubMed1982

Circadian entrainment of the squirrel monkey by extreme photoperiods: interactions between the phasic and tonic effects of light.

To examine the role that the phasic and tonic aspects of the light-dark (LD) cycle play in entraining the circadian timing system of primates, squirrel monkeys (Saimiri sciureus) were exposed to 24 hr LD cycles in which the light duration (photoperiod) was varied from 1 sec to 23 hr. The monkeys were maintained in isolation and the circadian rhythm of drinking was monitored. The photoperiod was first gradually shortened until constant darkness was reached. Even in extremely short photoperiods of only one second of light per day, the drinking rhythm remained synchronized to the 24 hr period of the LD cycle. In the second set of experiments, the photoperiod was gradually lengthened until constant light was achieved. The drinking rhythm of all monkeys was synchronized by 21 hr photoperiods (LD 21:3), but free-ran in 23 hr photoperiods (LD 23:1) which provided a 1 hr dark pulse each day. The tonic effects of light may contribute to the difference between the ability to entrain to short versus long photoperiods. In constant darkness the free-running period was close to 24 hr, thus reducing the phase-resetting necessary to achieve entrainment to a 24 hr period by short light pulses. However, in constant light or in the long photoperiods which did not entrain (LD 23:1) the free-running period of the drinking rhythm was greater than 25 hr, thus requiring a much larger daily phase shift to achieve entrainment to a 24 hr period.

Animals↗
PubMed1982

Mathematical model of the human circadian system with two interacting oscillators.

Human subjects during extended isolation from environmental time cues show complex variations in timing and duration of sleep with a progressive pattern, which eventually results in rest-activity and body temperature rhythms having different average periods. We present a model where temperature and rest-activity are each governed by an oscillator of the van der Pol type, denoted x and y, respectively. The oscillators affect one another through "velocity" type coupling, the effect of x on y being about four times greater than y on x. Periodic zeitgeber, z, is modeled as forcing only on y. We find that the entire pattern sequence can be realistically reproduced by causing only the intrinsic period of the y oscillator to increase while that of x remains stable. Desynchronization between x and y is the result of the intrinsic periods of the two oscillators becoming so disparate that the coupling is no longer able to enforce synchrony. Prior to desynchronization both human subjects and our model exhibit "phase trapping" wherein the relative phase of x and y is slowly modulated although the average x and y periods match. The model phase relations between temperature and both the timing and duration of sleep are, throughout, in good agreement with entrained and free-running human data. Most importantly, the model shows that the dramatic change in the length of the rest-activity cycle when desynchronization occurs is actually due to a relatively small variation in the governing variable, y.

Body Temperature↗
PubMed1982

Renal responses to prolonged central volume expansion in conscious primates.

Urinary and hormonal responses to prolonged central vascular volume expansion induced by 4 days of continuous lower body positive air pressure (LBPP) were examined in conscious, chair-acclimatized squirrel monkeys. The initial 12 h of exposure to LBPP (20 mmHg) induced a marked natriuresis, diuresis, kaliuresis, and decrease in urine osmolality. During the subsequent 4 days of LBPP stimulation, the acute natriuresis gradually declined by 75%, whereas potassium excretion completely returned to control rates after 24 h. In contrast, the diuresis and decrease in osmolality persisted, although there were significant circadian variations in urine flow (as well as sodium and potassium excretion) produced by a marked nocturnal suppression of renal responses to LBPP. Plasma aldosterone and potassium concentration both decreased acutely following LBPP initiation; however, aldosterone levels subsequently returned to normal range during continued LBPP exposure, whereas plasma potassium remained low until the pressure stimulus was terminated. These results indicated that prolonged central volume expansion induced both a sustained natriuresis and diuresis; however, chronic adaptation limited net fluid and electrolyte losses through the first 24 h of LBPP exposure. The loss of potassium appeared to be a consequence of the initial diuresis and natriuresis induced by LBPP, rather than being directly mediated by aldosterone.

Air Pressure↗
PubMed1981

Gradual decay of circadian drinking organization following lesions of the suprachiasmatic nuclei in primates.

The circadian organization of squirrel monkey drinking behavior was examined in constant illumination following lesions which totally destroyed the suprachiasmatic nuclei. Although these lesions eventually led to a severe disruption in the temporal organization of drinking behavior, a statistically significant circadian pattern of drinking was observed in each monkey for at least 4-6 weeks after lesioning.

Animals↗
PubMed1981

Chronotherapy: resetting the circadian clocks of patients with delayed sleep phase insomnia.

We report here the development of a brief drug-free rescheduling treatment ("chronotherapy") for Delayed Sleep Phase (DSP) insomnia, a syndrome characterized by sleep-onset insomnia with difficulty in morning awakening. We postulated that patients with DSP insomnia had an inadequate capacity to achieve phase advance shifts of the circadian pacemaker which times the sleep-wake cycle. Chronotherapy was therefore designed to reset these patients' biological clocks by the phase delay route. This single 5-6 day treatment was tested in 5 patients with a 4-15 year history of DSP insomnia. All 5 patients reported a lasting resolution of their symptoms substantiated by systematic long-term self-reports and objective polygraphic recording before and after treatment (average follow-up of 260 days; range, 42-910 days). The average sleep onset advanced from 4:50 a.m. before treatment to 12:20 a.m. afterwards, and wake times advanced from 1:00 p.m. to 755 a.m. (for both, p less than 0.001), with no reduction in sleep efficiency. As a result, all 5 patients were able to end their chronic dependence on hypnotic medications.

Adult↗
PubMed1981

Circadian rhythm of body temperature persists after suprachiasmatic lesions in the squirrel monkey.

Squirrel monkeys (Saimiri sciureus) demonstrate prominent circadian (approx 24 h) rhythms in many behavioral and physiological variables including drinking and body temperature. Both of these rhythms can be entrained by a 24-h light-dark cycle (LD 12:12) but will free-run with an endogenous period in a constantly illuminated (LL:600 lx) environment free of time cues. After radio-frequency lesions were placed stereotaxically in the suprachiasmatic nuclei (SCN) of five monkeys, the circadian rhythm of drinking behavior was disrupted when the monkeys were maintained in LL. However, the circadian rhythm in core body temperature in these animals persisted in LL with a significant circadian spectral component following destruction of the SCN. The SCN thus appear to be of fundamental importance for regulating the circadian organization of drinking; however, an oscillator located elsewhere in the squirrel monkey is capable of generating the core body temperature rhythm.

Acclimatization↗
PubMed1980

Human sleep: its duration and organization depend on its circadian phase.

Two- to threefold variations in sleep length were observed in 12 subjects living on self-selected schedules in an environment free of time cues. The duration of polygraphically recorded sleep episodes was highly correlated with the circadian phase of the body temperature rhythm at bedtime and not with the length of prior wakefulness. Furthermore, the rate of REM (rapid eye movement) sleep accumulation , REM latency, bedtime selection, and self-rated alertness assessments were also correlated with the body temperature rhythm.

Adult↗
PubMed1980

Three dimensional structure of the suprachiasmatic nuclei in the diurnal squirrel monkey (Saimiri sciureus).

In the squirrel monkey the suprachiasmatic nuclei (SCN) play a major role in the neural control of circadian physiology. Functional specificity within these nuclei has been suggested by the finding that subtotal lesions destroying only the posterior portion of the SCN altered the saliency of certain external stimuli as zeitgebers. Computer assisted histological analyses of the three dimensional (3-D) morphology of the SCN reveal a concomitant heterogeneity of structure between the rostral versus the caudal poles of these nuclei. The results are discussed in terms of a hypothesized specificity of function within the SCN.

Animals↗
PubMed1980

Suprachiasmatic region of the human hypothalamus: homolog to the primate circadian pacemaker?

The suprachiasmatic nuclei (SCN) of the hypothalamus in mammals, including nonhuman primates, contain a key pacemaker of the circadian timing system. Examination of the histology of the anterior hypothalamus in human fetal, child, and adult brains indicates that there is a cluster of neurons which may be homologous to SCN. These neurons are more diffusely organized and laterally placed in human brains than is the SCN of nonhuman primates.

Adolescent↗