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M C Moore-Ede

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

At least 37 records · Page 2Linked to original sources
PubMed1985

Effectiveness of cyclic intragastric feeding as a circadian zeitgeber in the squirrel monkey.

To investigate the mechanism of circadian synchronization by oral food consumption, we tested the effectiveness of cyclic intragastric feeding in synchronizing squirrel monkeys to a 24-hour schedule. Five monkeys were prepared with intragastric catheters and were studied free-ranging within a cage in an environmentally controlled chamber with continuous monitoring of body temperature (every 15 min) and locomotor activity (every 30 min). A balanced mixture of dextrose, amino acids, fat emulsion, vitamins and minerals was infused from 0800-2000 every day via the gastrostomy, first during a 12-hour light and 12-hour dark cycle (lights on 0800-2000 hours), and then subsequently in constant illumination. Serial phase analysis was performed by computing cycle-by-cycle acrophases of best-fitting sinusoids. One animal was synchronized by the feeding regimen while four others exhibited relative coordination. We conclude from these results that the timing of intragastic feeding may have only a weak synchronizing effect on primate circadian rhythms and that pre-gastric cues associated with oral food ingestion contribute to entrainment by feeding schedules.

Animals↗
PubMed1985

Sleep-wake stages during the subjective night of the squirrel monkey.

The study of the circadian sleep-wake cycle is beset by unique technical challenges. Continuous polygraphic recordings are necessary to characterize circadian phenomena; however, the traditional method of recording sleep at high (15 mm/sec) chart speed is impractical for continuous animal studies that may last several weeks at a stretch. A system to determine four sleep-wake stages (awake, transitional, non-REM, REM) from low chart speed (1.5 mm/sec) recordings was developed and validated by direct behavioral observation using four adult male squirrel monkeys prepared for chronic recording of EEG, EOG and EMG. The polygraphic stages "transitional," non-REM and REM were highly correlated with behavioral observations of sleep, although individual sleep stages could not be resolved by behavioral parameters alone.

Animals↗
PubMed1985

Medical implications of shift-work.

The circadian pacemakers, which time the approximately 24-hour rhythms in sleep and wakefulness, neuroendocrine, thermoregulatory, and other body functions, resynchronize only slowly after an abrupt phase shift in environmental time cues. While the symptoms of jet-lag are transient, the kinds of repeated shifts over a number of years experienced by shift-workers on rotating schedules induce sleep-wake disorders, gastrointestinal pathology, and an increased risk of cardiovascular disease. There is significant interindividual variation in the ability to adapt and also a deterioration with age. Evidence is accumulating that poor adapters present with a Shift Maladaption Syndrome with characteristic pathological manifestations.

Adaptation, Physiological↗
PubMed1985

Circadian rhythms of sleep and wakefulness in mice: analysis using long-term automated recording of sleep.

Circadian rhythms of wheel-running activity and polygraphically defined wakefulness, rapid-eye-movement (REM) sleep and non-REM (NREM) sleep were continuously observed in ten mice (Mus musculus) under both alternating light-dark (LD 12:12) and continuous darkness (DD) conditions. Sleep-wake state was determined automatically using a computer-based method that allowed continuous recordings of from 60 to 280 days in duration. The sleep-wake state percentages (of the circadian cycle) thus obtained were in substantial agreement with other estimates for this or similar strains and showed no significant difference between LD 12:12 (wake 54.3%, NREM sleep 38.1%, REM sleep 7.6%) and DD (wake 53.1%, NREM sleep 39.9%, REM sleep 7.0%) conditions. All 10 mice exhibited clear circadian rhythms in each of the three states and wheel-running activity under both lighting conditions for the entire duration of observation. Probability functions, computed using stationary sections of data from all 10 mice, showed distinct waveforms for all three states and wheel running. These waveforms were remarkably similar under entrained and free-running conditions. This documentation of sustained circadian rhythmicity in sleep-wake state throughout observations of unprecedented length contradicts the currently common assertion that circadian control of sleep state is weaker than that of activity.

Animals↗
PubMed1985

Circadian sleep-wake cycle organization in squirrel monkeys.

To investigate the relationship between circadian rhythms of body temperature and sleep-wake stages, four squirrel monkeys were prepared for unrestrained monitoring of temperature, locomotor activity, electroencephalogram, electroculogram, and electromyogram. Continuous records for each animal were made for several 12-h light-dark (LD) cycles and then after a few days in constant illumination (LL). All animals maintained consolidated sleep-wake cycles and had a longer circadian period (mean 24.7 h) in LL than in LD (mean 24.1 h). The increased period reflected greater time per circadian cycle spent awake in LL (mean 14.0 h) than in LD (mean 12.8 h). Total night NREM sleep was less in LL (mean 6.5 h) than in LD (mean 8.2 h). Sleep onset occurred at later phases in LL (187 +/- 6 degrees) than in LD (170 +/- 2 degrees). Because the circadian phase measure of NREM sleep was unchanged between LD and LL conditions, the difference in sleep onsets reflected balanced changes in NREM circadian waveforms. Wake-up phases were the same in both conditions (mean 342 degrees). In summary, during free run squirrel monkeys maintain a stable consolidated circadian sleep-wake cycle with a period greater than 24 h, but they exhibit only minimal internal phase restructuring.

Animals↗
PubMed1985

Forced internal desynchronization between circadian temperature and activity rhythms in squirrel monkeys.

In an attempt to force internal desynchronization between the rest-activity rhythm and the body temperature rhythm of the squirrel monkey (Saimiri sciureus), five animals were studied in a 14:14 light-dark cycle. In four animals a 28-h spectral component was found to predominate in the rest-activity rhythm, whereas an unentrained circadian component (tau = 25.9 +/- 0.4 h) predominated in the body temperature rhythm. Plots of the cycle-by-cycle acrophases of the two rhythms confirm that they desynchronize, due to the failure of the temperature rhythm to entrain to the light-dark cycle. These data from intact animals provide further support for the hypothesis that the squirrel monkey circadian timing system has at least two pacemakers. A rhythm for which the supra-chiasmatic nuclei (SCN) have previously been shown to be essential (rest-activity) simultaneously exhibited a different period from a rhythm (body temperature) that has been shown to persist after destruction of the SCN.

Animals↗
PubMed1984

Neurospora circadian rhythms in space: a reexamination of the endogenous-exogenous question.

To test the functioning of circadian rhythms removed from periodicities of the earth's 24-hour rotation, the conidiation rhythm of the fungus Neurospora crassa was monitored in constant darkness during spaceflight. The free-running period of the rhythm was the same in space as on the earth, but there was a marked reduction in the clarity of the rhythm, and apparent arrhythmicity in some tubes. At the current stage of analysis of our results there is insufficient evidence to determine whether the effect seen in space was related to removal from 24-hour periodicities and whether the circadian timekeeping mechanism, or merely its expression, was affected.

Biological Clocks↗
PubMed1984

Role of the suprachiasmatic nuclei in the circadian timing system of the squirrel monkey. I. The generation of rhythmicity.

The circadian organization of squirrel monkey (Saimiri sciureus) drinking behavior was evaluated before and after the placement of radiofrequency lesions which completely destroyed the suprachiasmatic nuclei (SCN) in 4 monkeys and partially ablated the SCN in another 4 animals. In continuous illumination (LL: 600 lux) prior to surgery, each monkey had a precise free-running circadian rhythm of drinking behavior with a period of 25.31 +/- 0.21 h (means +/- S.E.M.). By 4-6 weeks following the lesions, the temporal organization of drinking behavior had become disrupted, but a statistically significant free-running circadian rhythm was still detectable by time series analyses. Subsequently, the circadian organization of drinking behavior in 7 out of 8 monkeys gradually decayed with either no statistically significant rhythmicity or only weak circadian and/or ultradian rhythmicity detected by time series analyses by 10-92 weeks post-lesion. The remaining animal which maintained a statistically reliable free-running rhythm in drinking behavior received the least damage (less than 50%) to the SCN. Despite the major alterations in the temporal patterning of behavior, the overall amount of drinking behavior per 24 h was unchanged. The SCN are thus essential for maintaining the circadian organization of squirrel monkey drinking behavior. However, the existence of residual circadian rhythmicity following SCN lesions and the gradual decay of circadian organization thereafter suggest that the SCN may coordinate the activity of circadian oscillators which lie outside its borders.

Animals↗
PubMed1984

Role of the suprachiasmatic nuclei in the circadian timing system of the squirrel monkey. II. Light-dark cycle entrainment.

The role of the suprachiasmatic nuclei (SCN) in light-dark (LD) cycle entrainment in the squirrel monkey (Saimiri sciureus) was evaluated by continuously monitoring core body temperature and drinking behavior in both intact and SCN-lesioned animals exposed to different LD conditions. In a 24-h LD cycle with 12 h of light per day (LD 12:12), both intact and SCN-lesioned monkeys had a prominent rhythm in body temperature with an acrophase 6.51 +/- 0.36 h (intact) or 5.12 +/- 0.42 h (SCN-lesioned) after light onset. In a 23-h LD cycle composed of 1 hr of light and 22 h of dark (LD 1:22), the temperature rhythm in both intact and SCN-lesioned monkeys became synchronized with the 23-h period of the LD cycle. Studies examining the effects of LD cycle exposure on the temporal pattern of drinking behavior indicated that both intact and SCN-lesioned monkeys confined their drinking to the daily period of light. Each monkey was subsequently exposed to an LD cycle with 6 h of bright light and 18 h of darkness or dim background illumination (i.e. 60:0, 66:6 and 76:16 lux cycles). In intact monkeys systematic increases in the average intensity of the daily LD cycle produced corresponding delays in the phase of the daily offset of drinking behavior but did not alter the basic 24-h rhythmicity in the behavior. In contrast, increasing the intensity of the 24-h LD cycle in SCN-lesioned monkeys produced no delay in the daily termination of drinking, but instead produced a disintegration in the 24-h rhythm of drinking behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Simulating the action of zeitgebers on a coupled two-oscillator model of the human circadian system.

Our two-oscillator model was originally designed to describe the circadian rhythms of human subjects maintained in temporal isolation. The performance of this model in response to simulated environmental synchronizing cycles (zeitgebers) is examined here. Six distinct types of synchronization are demonstrated between the x oscillator (postulated to regulate the core temperature rhythm), the y oscillator (postulated to regulate the rest-activity rhythm), and z (the zeitgeber). Four types of synchronization are identifiable, if we consider only the periods of the three oscillators. Both x and y may be synchronized by z; either may synchronize with z while the other exhibits a different period; or x, y, and z may each show different periods. Two further classes of synchronization are discernible when phase criteria are taken into account. When either x or y is on the verge of desynchronizing from the other two oscillators, it undergoes periodic phase modulations while retaining the common overall period. The type of synchronization observed depends on the periods of x, y, and z and on the strength of the z drive. The effects of modifying each of these parameters have been systematically investigated by simulation, and model performance is summarized in terms of range of entrainment "maps." These constitute extensive sets of predictions about expected patterns of entrainment of the core temperature and rest-activity rhythms of human subjects exposed to various environmental zeitgebers. Experimental data are available against which model predictions can be tested.

Body Temperature↗
PubMed1984

Modeling the action of zeitgebers on the human circadian system: comparisons of simulations and data.

In our two-oscillator model for the human circadian timing system, the effect of an environmental synchronizing cycle (zeitgeber) is determined by the periods of the two oscillators and of the zeitgeber and by the zeitgeber strength. The oscillators x and y are postulated to regulate the core temperature and rest-activity rhythms, respectively. From published examples of experiments in which human subjects were exposed to artificial zeitgebers, it is possible to derive estimates of the periods of the core temperature and/or the rest-activity rhythms and the zeitgeber. Two strengths of zeitgeber input to the model that correspond to two of the common zeitgeber regimes used in human entrainment studies have now been elucidated. Thus specific model simulations can be generated for each of the available examples of entrainment of human subjects by artificial zeitgebers. Such simulations indicate that the model can reproduce, with remarkable subtlety, the types of full and partial entrainment observed experimentally. The model is thus demonstrated to accommodate the period and phase control of endogenous rhythms by environmental zeitgebers, which is a crucial functional attribute of circadian timing systems.

Activity Cycles↗
PubMed1984

Effects of a muramyl dipeptide on the temperature and sleep-wake cycles of the squirrel monkey.

The circadian sleep-wake and body temperature cycles of squirrel monkeys were monitored continuously in an environment free of time cues before and after a 50-nmol injection of a synthetic muramyl dipeptide (MDP) either 1 h after wake-up time (subjective day) or just before sleep time (subjective night). At both phases decreases in percent time awake (relative to saline controls) were observed. After administration of MDP early in the subjective day, the animals exhibited alert wakefulness only 47.4% of the daytime, compared with a mean 86.7% of daytime after a saline control injection. The transitional stage was significantly elevated from 6.2 to 28.7% of time after MDP. Nonrapid-eye-movement (REM) sleep was elevated in four of five animals, but in the fifth animal, which had the least consolidated base-line sleep-wake pattern, a small decrease in non-REM sleep was seen. Regression analysis demonstrated a significant (P less than 0.01) relationship between the degree of sleep-wake consolidation and the effect of MDP on non-REM sleep. Normal sleep behaviors and spontaneous arousals were observed. MDP given at the circadian nighttime of two animals resulted in sleep and transitional episodes occupying 84% of the subjective night vs. 73% of time asleep after control injection. Again, these were mostly transitional and non-REM sleep stages, and they persisted 4-5 h into the predicted circadian daytime. REM sleep appeared to be suppressed in the early hours after injection at either time of day.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1984

Sex differences in circadian control of LH secretion.

Sex differences in the hourly values of serum LH were examined in male and female Syrian hamsters exposed to either long photoperiods (14 h light: 10 darkness; 14L: 10D) or short photoperiods (6L: 18D). In long photoperiods, females exhibited a pro-oestrous surge of LH in response to high levels of circulating oestradiol (1047.36 +/- 90.68 pmol/l), while LH values in male hamsters remained essentially constant. In females housed in short photoperiods oestradiol levels were reduced by fivefold; however, a discrete surge in serum LH, similar to that seen at pro-oestrus in females exposed to long photoperiods, was observed. Although exposure to a short photoperiod eliminates the requirement of a positive feedback of oestrogen for the expression of an afternoon surge in LH, male hamsters housed in short photoperiods showed no indication of an afternoon surge in serum LH. These observations indicate that sex differences in the neural control of LH release are not the result of sex differences in oestrogen sensitivity or responsiveness.

Animals↗
PubMed1983

In vivo metabolic activity of the suprachiasmatic nuclei: a comparative study.

In vivo glucose utilization was measured in the suprachiasmatic nuclei (SCN) of the rat, monkey, and cat using the 14C-labeled deoxyglucose technique. SCN metabolic activity in all species was endogenously rhythmic with high levels during the subjective daylight portion of the 24 h day. Such phase conservation across night-, day-, and randomly-active species is in agreement with formal analyses of the properties of entrainable circadian oscillators, and our data suggest that the biochemical processes which underlie the activity of this circadian clock are similar in mammals with differing patterns of expressed circadian rhythmicity.

Animals↗
PubMed1983

Auditory entrainment of primate drinking rhythms following partial suprachiasmatic nuclei lesions.

In the absence of other environmental cycles, daily variations in auditory stimuli are normally not capable of entraining the circadian rhythms of drinking behavior in the squirrel monkey (Saimiri sciureus). However, the drinking rhythm appears to become entrainable by previously ineffective auditory cues after lesions are placed which destroy only the caudal portion of the hypothalamic suprachiasmatic nuclei. The results suggest specificity of function within the SCN and an increased influence of auditory stimuli in animals with impaired SCN function.

Acoustic Stimulation↗
PubMed1983

Light-dark masking of circadian temperature and activity rhythms in squirrel monkeys.

In addition to the synchronizing effects of light-dark cycles on the circadian timing system, light per se can have a direct masking effect on the rhythmic variables monitored as indicators of the circadian system. To evaluate the masking action of light on the rest-activity and body temperature rhythms of squirrel monkeys (Saimiri sciureus), animals were exposed to cycles of 2 h of light alternating with 2 h of darkness (LD 2:2). There was evidence of phase-dependent masking responses in both rhythms, with the light-induced elevation of activity levels and temperature greatest around the times of the circadian maxima of the respective rhythms. The temporal distribution of activity was more strongly affected by the masking action of the 2:2 cycle than was the temporal pattern of temperature variation. The increase in activity observed during lights on was evidently a major factor contributing to the corresponding increase in temperature.

Animals↗