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R Refinetti

Publications and source records attributed to R Refinetti.

At least 37 records · Page 2Linked to original sources
PubMed1995

Effects of hypothalamic lesions on the body temperature rhythm of the golden hamster.

The effects of electrolytic and neurotoxic lesions of the suprachiasmatic nucleus (SCN) and preoptic area (POA) of the anterior hypothalamus were studied by temperature telemetry in the golden hamster (Mesocricetus auratus) examined under two ambient temperature conditions: 24 degrees C and 6 degrees C. Although attempted lesions with microinjections of ibotenic acid proved unsuccessful, electrolytic lesions of the SCN eliminated the circadian rhythm of body temperature (CRT), indicating an active role of this nucleus in the establishment of the CRT. Electrolytic lesions of the POA, but not of the SCN, resulted in an increased amplitude of the CRT at both 24 degrees C and 6 degrees C, with the lower ambient temperature enhancing this amplitude change to a greater extent. These results suggest that the POA and the SCN are independently responsible for the homeostatic and circadian regulation of body temperature, respectively. The increased amplitude of the CRT after POA lesions raises the possibility that the thermoregulatory system may oppose rather than defend the circadian control of body temperature in normal animals, which is consistent with several recent behavioral findings.

Animals↗
PubMed1995

Body temperature and behaviour of golden hamsters (Mesocricetus auratus) and ground squirrels (Spermophilus tridecemlineatus) in a thermal gradient.

Golden hamsters and thirteen-lined ground squirrels were maintained individually in a thermal gradient (14 degrees C to 33 degrees C) for several weeks under a 14L:10D light-dark cycle. Animals of both species showed robust daily rhythms of body temperature and locomotor activity with acrophases consistent with the habits of the species (diurnal acrophases in the diurnal squirrels and nocturnal acrophases in the nocturnal hamsters). Hamsters showed a robust daily rhythm of temperature selection 180 degrees out of phase with the rhythms of body temperature and locomotor activity. Squirrels did not show a daily rhythm of temperature selection. These results raise the hypothesis that a daily rhythm of temperature selection is exhibited by nocturnal but not by diurnal endotherms.

Analysis of Variance↗
PubMed1995

Effects of suprachiasmatic lesions on temperature regulation in the golden hamster.

The body temperature of individually housed golden hamsters was studied by telemetry. Elimination of circadian rhythmicity by electrolytic lesions of the suprachiasmatic nuclei of the hypothalamus (SCN) did not affect the mean level of body temperature of animals maintained at 22, 12, or 6 degrees C. The range of variation of body temperature around the mean level was also found not to differ from that of intact animals that had the circadian component filtered out by a subtractive moving-averages procedure. These results indicate that the SCN plays no role in the homeostatic control of body temperature. The role of the SCN seems to be limited to the generation of circadian rhythmicity that is superimposed on the homeostatic process of temperature regulation.

Animals↗
PubMed1995

Rhythms of temperature selection and body temperature are out of phase in the golden hamster.

Body temperature, locomotor activity, and thermoregulatory behavior of freely moving golden hamsters maintained in a spatial thermocline were measured over several weeks. The thermoregulatory behavior of temperature selection exhibited a robust daily rhythm 180 degrees out of phase with the rhythms of body temperature and locomotor activity. However, the parameters of the body temperature rhythm (rhythmicity, mean level, and amplitude) were not significantly affected by the thermoregulatory behavior. Although the observed phase difference between the rhythms of temperature selection and body temperature might suggest that thermoregulatory behavior is modulated to oppose (rather than to defend) the rhythm of body temperature, the absence of effect of temperature selection on the parameters of the body temperature rhythm fails to reveal the physiological significance of such opposition. Further studies are necessary to establish the physiological significance of the rhythm of temperature selection.

Animals↗
PubMed1994

Complete suprachiasmatic lesions eliminate circadian rhythmicity of body temperature and locomotor activity in golden hamsters.

The effects of suprachiasmatic and control lesions on the circadian rhythms of locomotor activity and body temperature were studied in golden hamsters (Mesocricetus auratus) maintained in constant light as well as constant darkness. Large suprachiasmatic lesions, but not control lesions, eliminated circadian rhythmicity in locomotor activity as well as in body temperature. Analysis of the "robustness" of the rhythms of locomotor activity and body temperature in unlesioned and lesioned animals suggests that, because body temperature rhythmicity is more robust than locomotor rhythmicity, lesions that spare a small number of suprachiasmatic cells might abolish the latter but not the former. Our results do not support the hypothesis that the body temperature rhythm is controlled by a circadian pacemaker distinct from the main pacemaker located in the suprachiasmatic nuclei.

Animals↗
PubMed1994

Contribution of locomotor activity to the generation of the daily rhythm of body temperature in golden hamsters.

The locomotor activity and body temperature of 40 golden hamsters maintained under a 14L:10D light:dark cycle were studied by telemetry. Body temperature was found to be highly correlated with activity. On average, an increase from 0 to 200 units of activity was associated with a 0.7 degrees C increase in body temperature. However, body temperature during the dark phase of the light:dark cycle was 0.3 degrees C higher than during the light phase, irrespective of the activity level. These results indicate that, although activity can affect body temperature, the increase in activity during the dark phase is not the cause of the temperature rhythm. At least 30% of the total daily variation in body temperature is independent of variations in the activity level.

Animals↗
PubMed1993

A functional model of the mammalian circadian pacemaker.

This paper describes a general model of the mammalian circadian pacemaker with specific parameters for golden hamsters. The model successfully simulates free-runs in constant darkness and constant light, phase shifts induced by light pulses and entrainment and relative coordination under light-dark cycles. It also accounts for the recent findings that the amplitude of the phase response curve to light pulses is dependent on the free-running period of the animal and on the previous history of photic stimulation. Effects of non-photic stimuli on the circadian pacemaker are discussed.

Adaptation, Physiological↗
PubMed1993

Laboratory instrumentation and computing: comparison of six methods for the determination of the period of circadian rhythms.

Data sets with known periodicity were used to compare the accuracy and noise tolerance of six methods of circadian period analysis: Fourier analysis, autocorrelation, Enright's (chi-square) periodogram, linear regression of onsets, interonset averaging, and acrophase counting. All methods except acrophase counting accurately detected the period of rhythms with pure waveform (cosine and square wave), whereas Fourier analysis and Enright's periodogram were superior to the other methods in the analysis of more complex waveforms (which more closely resemble actual circadian rhythms). The sensitivity of all methods was reduced by the insertion of random noise into the original data sets, but the methods of autocorrelation and Enright's periodogram were more tolerant of low signal-to-noise ratios than the remaining methods. Although particular situations may require particular methods, the results suggest that Enright's periodogram is the best choice as a general method for the determination of the period of circadian rhythms.

Animals↗
PubMed1993

Effects of imipramine on circadian rhythms in the golden hamster.

The effects of the antidepressant imipramine on circadian organization were studied in wild-type and tau-mutant golden hamsters. Chronic imipramine treatment in doses ranging from 0-50 mg kg-1.day-1 depressed general activity and body temperature and caused a reduction in body weight but had no significant effect on circadian organization. Imipramine treatment did not affect the rate of reentrainment after a 6-h advance in the light-dark cycle, did not alter the advanced-phase angle of entrainment of tau-mutant hamsters, did not affect the free-running period of wild type hamsters, and did not alter the phase-response curve to light pulses. Because imipramine, a clinically effective antidepressant, did not have any measurable effect on the circadian system in these experiments, our results do not provide support for the hypothesis that the antidepressant action of imipramine is mediated by alterations in the circadian system.

Animals↗
PubMed1993

Independence of heart rate and circadian period in the golden hamster.

Cardiac contractions are under the influence of at least two processes of biological timing, one responsible for the mean level of heart rate (oscillations with a frequency of up to several hundred per minute) and another responsible for the circadian rhythm of heart rate (oscillations with a frequency of one per 24 h). To investigate whether the mean level of heart rate is proportional to the frequency of circadian oscillation, we compared the heart rates of normal golden hamsters (circadian period approximately 24 h) and tau-mutant hamsters (circadian period approximately 20 h). Neither in anesthetized preparations nor in freely moving animals was there a difference in heart rate between the two groups despite the 20% difference in circadian period. Thus the mean level of heart rate seems to be independent of the circadian period. It is likely that the tau gene, which affects the frequency of the circadian pacemaker, has no effect on the intrinsic frequency of the cardiac pacemaker. In vitro studies of isolated hearts or myocardial cell cultures are necessary to confirm this inference.

Animals↗
PubMed1992

Body temperature rhythm of the tree shrew, Tupaia belangeri.

The circadian rhythm of body temperature of the tree shrew Tupaia belangeri was studied by telemetry. The amplitude of the daily (or circadian) variation was found to be much larger than that of most endotherms (amplitude approximately 5 degrees C) and the bimodal shape of the rhythm differed from the cosine waveform that characterizes the temperature rhythms of most other species. In free-running conditions, as well as in the entrained state, the temperature rhythm remained synchronized to the rhythm of locomotor activity.

Animals↗
PubMed1992

Social stimuli fail to act as entraining agents of circadian rhythms in the golden hamster.

The ability of social stimuli to act as entraining agents of circadian rhythms was investigated in golden hamsters (Mesocricetus auratus). In a first experiment, pairs of male hamsters (one of them enucleated and the other intact) were maintained under a ligh-dark (LD) cycle with a period of 23.3 h. Running-wheel activity was recorded to determine the effect of social interaction on the free-running circadian rhythm of activity. In several pairs, general activity and body temperature were also recorded. In all pairs the intact animals entrained to the LD cycle, whereas the activity rhythms of the enucleated animals free-ran with periods of approximately 24 h and showed no apparent sign of synchronization or relative coordination with the other member of the pair. In a second experiment, male hamsters maintained in constant darkness received pulses of social interaction, which have been reported to induce phase shifts of the activity rhythm. Consistent phase shifts in the running-wheel activity rhythm were not induced by the social pulses in our experiment. These results suggest strongly that social stimuli are not effective entraining agents of circadian rhythms in the golden hamster.

Animals↗
PubMed1992

Non-parametric procedures for the determination of phase markers of circadian rhythms.

The accurate determination of phase markers is an essential procedure in the analysis of the temporal organization of circadian rhythms. The method of cosinor analysis, a parametric procedure, has been often used to determine the time at which the peak of a rhythm (the "acrophase") occurs. To avoid several difficulties associated with the use of parametric procedures, two non-parametric procedures are described in this paper. One of them is based on the onset times of dichotomous (and, by derivation, of fully numerical) variables. The other one is based on the acrophase of data previously smoothed by the method of moving averages. These two procedures are very easy to conduct, do not make assumptions about the distribution of the data (except that there is indeed a daily or circadian rhythm), and do not require stationary rhythms. They constitute a powerful alternative to the use of cosinor analysis.

Algorithms↗
PubMed1992

The circadian rhythm of body temperature.

This paper reviews the literature on the circadian rhythm of body temperature (CRT). The review starts with a brief discussion of methodological procedures followed by the description of known patterns of oscillation in body temperature, including ultradian and infradian rhythms. Special sections are devoted to issues of species differences, development and aging, and the relationships between the CRT and the circadian rhythm of locomotor activity, between the CRT and the thermoregulatory system, and between the CRT and states of disease. A section on the nervous control of the CRT is followed by summary and conclusions.

Animals↗
PubMed1992

Evidence for separate control of estrous and circadian periodicity in the golden hamster.

To study the relationship between estrous and circadian periodicity, we investigated the period of the estrous cycle in two types of female golden hamsters: normals (circadian period approximately 24 h) and tau mutants (circadian period approximately 20 h). Records of running wheel activity, general locomotor activity, body temperature, vaginal secretion, and sexual receptivity of hamsters kept under constant lighting conditions indicated an estrous period of approximately 96 h for both groups of animals. The fact that animals with different circadian periods have the same estrous period suggests the existence of separate mechanisms in the control of circadian and estrous periodicity. Circadian periodicity is determined by a pacemaker located in the suprachiasmatic nuclei, whereas estrous periodicity is determined by positive and negative feedback loops involving the hypothalamus, pituitary, and gonads. Coupling of the two mechanisms takes place under at least some conditions, but additional research is necessary to elucidate the mechanisms by which this is accomplished.

Animals↗
PubMed1991

Use of chi square periodogram in the analysis of estrous rhythmicity.

The usefulness of the chi square periodogram procedure for the analysis of estrous rhythmicity was investigated. Sokolove-Bushell's Q statistic was found to have a chi square distribution at the small degrees of freedom involved in estrous rhythmicity in rodents (i.e., rhythmicity with periods of 2-7 days). Consequently, the significance of the peaks in the periodogram can be effectively evaluated. The effects of multiple-period rhythmicity and of random noise added to periodical data were also investigated. Overall, the analysis of simulated as well as empirical data indicated that the chi square periodogram is an excellent tool for the evaluation of estrous rhythmicity.

Animals↗
PubMed1991

An extremely simple procedure for the analysis of circadian and estrous periodicity.

A method for the analysis of circadian and estrous periodicity based on immediate visual inspection of the data is described. The method involves the calculation of two statistics, P (the period of the oscillations in the data) and h (an index of homogeneity of P). The sampling distribution of both statistics is examined and critical values for significance tests are presented. A computational algorithm for use with large data sets is also presented. The method is intended to be not a substitute for traditional methods of time series analysis but an alternative strategy to be used in cases where a rapid and simple determination of periodicity is desired.

Algorithms↗