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R Refinetti

Publications and source records attributed to R Refinetti.

At least 19 recordsLinked to original sources
PubMed2007

Annual rhythmicity and maturation of physiological parameters in goats.

This study was conducted to investigate seasonal rhythmicity and maturation of physiological parameters in goats. Five kids (Capra hircus, Maltese breed) were studied for 24 months, starting at 5 months of age. Rectal temperature and various blood-borne substances (melatonin, cholesterol, urea, total bilirubin, albumin, glucose, calcium, magnesium, phosphate, and sodium) were measured once a month at dawn and dusk. Serum bilirubin concentration exhibited statistically significant 12-month rhythmicity, and melatonin concentration exhibited 6-month rhythmicity. Changes in the dusk-to-dawn difference in rectal temperature during the course of the study provided suggestive evidence that the circadian rhythm of body temperature in goats is not fully developed until the end of the second year of life. The results documented also maturational changes in cholesterol production and blood glucose regulation.

Animals↗
PubMed2006

Absence of circadian and photoperiodic conservation of energy expenditure in three rodent species.

According to a traditional homeostatic view, living beings spend metabolic energy at a constant rate, just like a light bulb spends electrical energy, so that energy expenditure can be expressed in units of watts. However, research conducted during the last half-century has evinced pronounced circadian variation in physiological processes, not only demonstrating circadian rhythmicity in energy expenditure but also raising the hypothesis that energy expenditure may be regulated on a daily (circadian) basis rather than on a constant-rate (homeostatic) basis. In the present study, the hypothesis of circadian (and photoperiodic) conservation of energy expenditure was tested in three rodent species: domestic mice, Nile grass rats, and Syrian hamsters. Two correlates of energy expenditure (running-wheel activity and food intake) and a classic index (oxygen consumption) were used. Changes in energy expenditure were studied in animals maintained under light-dark cycles (LDs) with periods shorter or longer than 24 h as well as in animals maintained under 24-h LDs with short and long photophases. In none of the conditions in any of the species was evidence found in support of the hypothesis of circadian (or photoperiodic) conservation of energy expenditure. Energy expenditure was generally conserved on a homeostatic basis.

Animals↗
PubMed2006

Variability of diurnality in laboratory rodents.

The locomotor activity rhythms of domestic mice, laboratory rats, Syrian hamsters, Siberian hamsters, Mongolian gerbils, degus, and Nile grass rats were compared. Running-wheel activity was monitored under a light-dark cycle with 12 h of light and 12 h of darkness per day. Nile grass rats were found to be reliably diurnal, whereas laboratory rats, Siberian hamsters, domestic mice, and Syrian hamsters were reliably nocturnal. Both diurnal and nocturnal subgroups were observed in Mongolian gerbils and degus. A downward gradient of diurnality was observed from Mongolian gerbils classified as diurnal, degus classified as diurnal, gerbils classified as nocturnal, and degus classified as nocturnal. Nocturnal degus remained nocturnal when tested with an infrared motion detector without running wheels. Thus, although the diurnal-nocturnal dichotomy could be applied to some of the species, it was not appropriate for others. The dichotomy may reflect researchers' needs for systematization more than a natural distinction between species. Through mechanisms as yet poorly understood, the balance between entraining and masking processes seems to generate a gradient of temporal niches that runs from predominantly diurnal species to predominantly nocturnal species with many chronotypes in between, including species that exhibit wide intra-species gradients of temporal niche.

Analysis of Variance↗
PubMed2005

Temporal relationships of 21 physiological variables in horse and sheep.

Daily or circadian oscillation has been documented in a variety of physiological and behavioral processes. Although individual variables have been studied in great detail, very few studies have been conducted on the temporal relationships between the rhythms of different variables. It is not known whether the circadian pacemaker generates each and every rhythm individually or whether most rhythms are simply derived from a few clock-controlled rhythms. As a first step in elucidating this issue, 21 physiological variables were recorded simultaneously in horse and sheep. The results indicated that, in both species, different variables exhibit different degrees of daily rhythmicity and reach their daily peaks at different times of the day. The variables exhibiting strongest rhythmicity were locomotor activity, rectal temperature, and plasma concentrations of melatonin and glucose. Comparison of rhythmicity and acrophase in the various rhythms allowed inferences to be made about mechanisms of causation.

Animals↗
PubMed2005

Daily rhythms of blood pressure, heart rate, and body temperature in fed and fasted male dogs.

Daily or circadian rhythmicity in physiological processes has been described in a large number of species of birds and mammals. However, in dogs, most studies have either failed to detect rhythmicity or have found that rhythmicity reflects merely an acute exogenous effect of feeding rather than an autonomous rhythmic process. In the present study, we investigated the rhythmicity of body temperature, blood pressure, and heart rate in dogs fed daily as well as in dogs deprived of food for 60 h. Our results document clear rhythmicity in all three parameters and demonstrate that the rhythmicity is independent of the feeding schedule. The failure of various previous investigations to document daily rhythmicity in dogs is probably due to lack of experimental rigour rather than to weakness of daily rhythmicity in dogs.

Animals↗
PubMed2003

Daily rhythmicity of body temperature in the dog.

Research over the past 50 years has demonstrated the existence of circadian or daily rhythmicity in the body core temperature of a large number of mammalian species. However, previous studies have failed to identify daily rhythmicity of body temperature in dogs. We report here the successful recording of daily rhythms of rectal temperature in female Beagle dogs. The low robustness of the rhythms (41% of maximal robustness) and the small range of excursion (0.5 degrees C) are probably responsible for previous failures in detecting rhythmicity in dogs.

Animals↗
PubMed1999

Relationship between the daily rhythms of locomotor activity and body temperature in eight mammalian species.

The relationship between the daily rhythms of locomotor activity and body temperature was studied by telemetry in four nocturnal and four diurnal mammalian species. The results showed that the two rhythms are very closely synchronized, as they 1) ascend past the daily mean at the same time, 2) reach the daily acrophase at the same time, and 3) are best correlated at time lags approaching zero. The rhythms of nocturnal animals crossed the daily mean at the transition between the light and dark phases of the light-dark cycle and reached their acrophases during the dark phase, whereas the rhythms of diurnal animals crossed the daily mean at the transition between the dark and light phases and reached their acrophases during the light phase. Despite the close synchrony of the two rhythms, the results indicate that the temperature rhythm is not a byproduct of the activity rhythm, as body temperature during the active phase of the daily cycle was higher than body temperature during the inactive phase in all species irrespective of the activity level prevailing during each phase.

Animals↗
PubMed1998

Body temperature and behavior of tree shrews and flying squirrels in a thermal gradient.

The daily rhythms of body temperature, temperature selection, and locomotor activity of tree shrews and flying squirrels were studied in a thermal gradient. In accordance with previous observations in other mammalian species, the rhythm of temperature selection was found to be 180 degrees out of phase with the body temperature rhythm in both species. Comparison of the amplitude of the body temperature rhythm in the presence and absence of the ambient temperature gradient indicated that behavioral temperature selection reduces the amplitude of the body temperature rhythm. This provides support for the hypothesis that the homeostatic control of body temperature opposes-rather than facilitates-the circadian oscillation in body temperature.

Animals↗
PubMed1998

Homeostatic and circadian control of body temperature in the fat-tailed gerbil.

The interplay of homeostasis and circadian rhythmicity in the control of body temperature was studied in the fat-tailed gerbil (Pachyuromys duprasi). In a first study, the body temperature rhythm of 8 gerbils maintained at 24 degrees C under a 14L:10D light-dark cycle was studied by telemetry. Data from 9 other species of small mammals were also obtained for comparison. The gerbils were found to exhibit a robust rhythm of body temperature (the most robust of the 10 species) with a high plateau during the dark phase of the light-dark cycle and a low plateau during the light phase. In a second experiment, 5 gerbils were allowed to select the temperature of their environment by moving along a thermal gradient. The animals consistently selected higher ambient temperatures during the light phase of the light-dark cycle (when their body temperature was at the low plateau). In a third experiment, the metabolic response of 8 gerbils to an acute cold exposure was determined by indirect calorimetry. Greater cold-induced thermogenesis was observed during the light phase. The fact that the animals selected higher ambient temperatures and displayed greater cold-induced thermogenesis when their body temperature was lower contradicts the hypothesis that the body temperature rhythm is caused by a rhythmic oscillation of the thermoregulatory set point.

Animals↗
PubMed1998

Influence of early environment on the circadian period of the tau-mutant hamster.

The role of the period of the environmental cycle during gestation and infancy on the circadian period of adult hamsters was studied. Tau-mutant hamsters of all three genotypes (+/+, 24-h circadian period; +/tau, 22-h period; tau/tau, 20-h period) were conceived and raised under either a 20-h light-dark cycle or a 24-h cycle. The circadian period in constant darkness was determined at 2 months of age by inspection of records of running-wheel activity. Differences in circadian period of up to 1.2 h were observed. However, changes of the same magnitude were also observed in animals conceived and raised under a 24-h cycle and exposed to a 20-h cycle at 8 months of age. Therefore, it is concluded that the aftereffects of entrainment can account for the apparent influence of the early environment. The free-running period of the circadian pacemaker seems to be under complete genetic control and not to be influenced by the period of the environmental cycle under which the animal is raised.

Animals↗
PubMed1997

Is energy expenditure in the hamster primarily under homeostatic or circadian control?

1. In order to discriminate between homeostatic and circadian control of energy expenditure, this paper considers whether a shorter circadian cycle will produce a proportional reduction in energy expenditure (so that expenditure per unit time is conserved) or alternatively whether energy expenditure will be compressed into the shorter cycle (so that energy expenditure per cycle is conserved). To answer this question, we measured energy expenditure in tau mutant hamsters (whose free-running circadian period has been reduced to about 20 h by a single gene mutation) and wild-type hamsters (whose free-running circadian period is about 24 h). 2. In one experiment, the circadian rhythm of running-wheel activity of tau mutant hamsters was compared with that of wild-type hamsters. The rate of running was not affected by the mutation and, consequently, the total amount of activity per cycle was significantly less in mutants than in wild-type hamsters, whereas the total amount of activity per unit time was nearly the same. 3. In a second experiment, we measured energy expenditure by indirect calorimetry. Metabolic rate was not affected by the mutation and, consequently, the total amount of energy expended per cycle was significantly less in mutants than in wild-type hamsters but equivalent per unit time. 4. Because the amount of energy expenditure and locomotor activity was found to be proportional to the circadian cycle, we conclude that expenditure per unit time-rather than expenditure per circadian cycle-is conserved in the mutant animals. Therefore, we infer that energy expenditure in hamsters is primarily under homeostatic, not circadian, control. Further research is necessary to determine whether this inference can be applied to other species.

Animals↗
PubMed1997

Circadian rhythm of temperature selection in a nocturnal lizard.

We recorded body temperature and locomotor activity of Tokay geckos (Gekko gecko) with free access to a heat source under a 14:10 light-dark cycle and in constant darkness. Under the light-dark cycle, the lizards selected higher temperatures during the light phase, when locomotor activity was less intense. Rhythmicity in temperature selection was transiently disrupted but later resumed when the animals were placed in constant darkness. These results demonstrate the existence of a circadian rhythm of temperature selection in nocturnal ectotherms and extend previous findings of a temporal mismatch between the rhythms of locomotor activity and temperature selection in nocturnal rodents.

Animals↗
PubMed1997

Philosophy of science and physiology education.

Since the mid-1960s, philosophy of science [particularly that derived from Kuhn's work (The Structure of Scientific Revolutions, Chicago: University of Chicago Press, 1962)] has become an informal part of the education of scientists worldwide, including physiologists. However, recent postmodernist developments have enraged a number of scientists, who would like to sever any ties with philosophy of science. The author contends that the perceived conflict is due mainly to a misunderstanding of the implications of constructivist assertions and partially to flawed reasoning in a few constructivist approaches. There is no fundamental conflict that would justify the elimination of philosophy of science from science education.

Philosophy↗
PubMed1996

Comparison of the body temperature rhythms of diurnal and nocturnal rodents.

The daily rhythm of body temperature of six rodent species, three of them nocturnal (Rattus norvegicus, Mesocricetus auratus, and Meriones unguiculatus) and three diurnal (Octodon degus, Spermophilus tridecemlineatus, and S. richardsoni), was studied by telemetry under a 14L:10D light-dark cycle. Significant interspecies differences were found in the mean level (range: 36.0-37.4 degrees C), amplitude (range: 2.1 degrees-4.3 degrees C), robustness (range: 115-185 Qp), and acrophase (range: 8.5-16.0 hr) of the temperature rhythm. In addition, a positive correlation (r = 0.79) was found between body mass and robustness of the rhythm across species. However, the only consistent difference between the diurnal and nocturnal species was the acrophase, which occurred during the day in the diurnal species (range: 8.5-11.5 hr) and during the night in the nocturnal species (range: 13.5-16.0 hr).

Animals↗
PubMed1996

Rhythms of body temperature and temperature selection are out of phase in a diurnal rodent, Octodon degus.

Individual Chilean degus (Octodon degus) were maintained in a thermal gradient (14 degrees C to 33 degrees C) for two or more weeks under a 14L:10D light-dark cycle. All animals showed robust daily rhythms of body temperature and locomotor activity consistent with the diurnal habits of the species. They also showed a robust daily rhythm of temperature selection 180 degrees out of phase with the rhythms of body temperature and locomotor activity. These results in a diurnal species extend previous findings of a 180 degrees phase difference between the rhythms of body temperature and temperature selection in nocturnal rodents. The asynchrony between these two rhythms implies an opposition between the circadian system (responsible for the generation of the body temperature rhythm) and the homeostatic system (responsible for the behavioral response of temperature selection that opposes the body temperature rhythm.

Animals↗