1. Rhythmic oscillations in the environment range in period from a few femtoseconds to tens of thousands of years. Of all the environmental rhythms on Earth, only those in four temporal domains have been shown to have specific effects on endogenous rhythms of individual organisms: tidal, daily, lunar, and annual rhythms.

2. Circadian rhythms are biological rhythms with durations of approximately 24 hours. More exactly, 24-hour rhythms that are induced by environmental factors are called daily rhythms. A daily rhythm that is endogenously generated but is modulated by 24-hour environmental cycles is called a circadian rhythm. Many behavioral and autonomic processes of individual organisms exhibit daily and/or circadian rhythmicity.

3. Ultradian rhythms are biological rhythms with durations shorter than circadian rhythms (i.e., shorter than approximately 19 hours). They include cardiac, respiratory, neuroendocrine, gastrointestinal, tidal, and other rhythms. Although many ultradian rhythms are endogenously generated by some sort of pacemaker, only tidal rhythms are regularly synchronized to environmental cycles.

4. Infradian rhythms are biological rhythms with durations longer than circadian rhythms (i.e., longer than approximately 28 hours). They include estrous, weekly, lunar, annual, and other rhythms. Although many infradian rhythms are endogenously generated by some sort of pacemaker, only lunar and annual rhythms can be fully synchronized to environmental cycles with periods similar to the endogenous periods.

5. Annual rhythms constitute a particularly ubiquitous class of infradian rhythms. Physiological parameters that exhibit annual rhythmicity include body mass, cold-induced thermogenesis, food intake, heterothermy, melatonin secretion, pelage molting, and reproductive capacity. Many, but not all, annual rhythms are endogenously generated and can be synchronized to annual environmental cycles. These particular rhythms are called circannual rhythms.

The main line of research in our lab since 1990 has been the study of biological rhythms (especially, although not exclusively, circadian rhythms). Physiological and behavioral processes are studied at the organismal level. The following are some of our research articles on biological rhythms:

Refinetti, R., Earle, G., and Kenagy, G. J. (2019). Exploring determinants of behavioral chronotype in a diurnal-rodent model of human physiology. Physiology and Behavior 199: 146-153.

Refinetti, R. (2017). Western diet affects the murine circadian system possibly through the gastrointestinal microbiota. Biological Rhythm Research 48: 287-296.

Wassmer, T. and Refinetti, R. (2016). Daily activity and nest occupation patterns of arboreal fox squirrels (Sciurus niger) throughout the year. PLoS One 11: e0151249.

Refinetti, R. (2014). Relationship between circadian period and body size in the tau-mutant golden hamster. Canadian Journal of Physiology and Pharmacology 92: 27-33.

Refinetti, R. (2010). Entrainment of circadian rhythm by ambient temperature cycles in mice. Journal of Biological Rhythms 25: 247-256.

Piccione, G., Fazio, F., Caola, G., and Refinetti, R. (2008). Daily rhythmicity in nutrient content of asinine milk. Livestock Science 116: 323-327.

Refinetti, R. (2007). Absence of circadian and photoperiodic conservation of energy expenditure in three rodent species. Journal of Comparative Physiology B 177: 309-318.

Refinetti, R. (2006). Variability of diurnality in laboratory rodents. Journal of Comparative Physiology A 192: 701-714.

Refinetti, R. (2005). Time for sex: nycthemeral distribution of human sexual behavior. Journal of Circadian Rhythms 3: 4.

Piccione, G., Caola, G., and Refinetti, R. (2005). Daily rhythms of blood pressure, heart rate, and body temperature in fed and fasted male dogs. Journal of Veterinary Medicine A 52: 377-381.

Refinetti, R. (2004). Daily activity patterns of a nocturnal and a diurnal rodent in a semi-natural environment. Physiology and Behavior 82: 285-294.

Refinetti, R. (2004). Parameters of photic resetting of the circadian system of a diurnal rodent, the Nile grass rat. Acta Scientiae Veterinariae 32: 1-6.

Refinetti, R. (2003). Effects of prolonged exposure to darkness on circadian photic responsiveness in the mouse. Chronobiology International 20: 417-440.

Piccione, G., Caola, G., and Refinetti, R. (2003). Circadian rhythms of body temperature and liver function in fed and food-deprived goats. Comparative Biochemistry and Physiology A 134: 563-572.

Piccione, G., Caola, G., and Refinetti, R. (2002). Circadian modulation of starvation-induced hypothermia in sheep and goats. Chronobiology International 19: 531-541.

Refinetti, R. (2001). Dark adaptation in the circadian system of the mouse. Physiology and Behavior 74: 101-107.

Refinetti, R. (2000). Circadian rhythm of locomotor activity in the pill bug, Armadillidium vulgare (Isopoda). Crustaceana 73: 575-583.

Refinetti, R. (1999). Relationship between the daily rhythms of locomotor activity and body temperature in eight mammalian species. American Journal of Physiology 277: R1493-R1500.

Refinetti, R. (1998). Influence of early environment on the circadian period of the tau-mutant hamster. Behavior Genetics 28: 153-158.

Refinetti, R. and Menaker, M. (1997). Is energy expenditure in the hamster primarily under homeostatic or circadian control? Journal of Physiology 501: 449-453.

Refinetti, R. (1997). Phase relationship of the body temperature and locomotor activity rhythms in free-running and entrained rats. Biological Rhythm Research 28 (Suppl.): 19-24.

Shoemaker, J. A. and Refinetti, R. (1996). Day-night difference in the preferred ambient temperature of human subjects. Physiology and Behavior 59: 1001-1003.

Osborne, A. R. and Refinetti, R. (1995). Effects of hypothalamic lesions on the body temperature rhythm of the golden hamster. NeuroReport 6: 2187-2192.

Refinetti, R. and Menaker, M. (1993). Independence of heart rate and circadian period in the golden hamster. American Journal of Physiology 264: R235-R238.

1. Adaptation of organisms to the thermal environment may be accomplished in two basic ways: by increased tolerance to temperature variations or by active regulation of body temperature. Most organisms do not regulate body temperature (or regulate it in a limited fashion) but are very well adapted to the thermal environment.

2. Thermal physiologists refer to organisms whose temperature varies with that of the environment as poikilothermic organisms; conversely, they refer to organisms whose temperature is regulated at a relatively constant level despite variations in ambient temperature as homeothermic organisms.

3. The distinction between poikilothermy and homeothermy is too broad for most uses. A finer distinction must be made to account for thermoregulatory differences limited to autonomic processes. Organisms that can generate enough heat endogenously to warm up their bodies above ambient temperature without resorting to behavior are called endothermic organisms; conversely, organisms that require external sources to warm up their bodies above ambient temperature are called ectothermic organisms. Mammals and birds are generally endothermic, whereas all other life forms on Earth are ectothermic. There are several exceptions, however.

4. Both endotherms and ectotherms have a vast repertoire of autonomic and behavioral responses that can be used in the control of body temperature. These responses may be employed on three basic time scales: as short-term responses, as seasonal acclimatization, or as part of the evolutionary process.

5. Short-term regulation of body core temperature in vertebrates relies strongly on a region of the brain comprised of the preoptic area and anterior hypothalamus (POAH).

The process of regulation of body temperature has been of great interest to Dr. Refinetti since his early days as an undergraduate student. The lab investigates behavioral and autonomic temperature regulation in animals and the psychophysics of thermal sensation in humans. The following are some of our research articles on thermal physiology:

Refinetti, R. and Kenagy, G. J. (2018). Circadian rhythms of body temperature and locomotor activity in the antelope ground squirrel, Ammospermophilus leucurus. Journal of Thermal Biology 72: 67-72.

Al-Haidary, A. A., Abdoun, K. A., Samara, E. M., Okab, A. B., Sani, M., and Refinetti, R. (2016). Daily rhythms of physiological processes in the dromedary camel under natural and laboratory conditions. Research in Veterinary Science 107: 273-277.

Piccione, G., Gianesella, M., Morgante, M., and Refinetti, R. (2013). Daily rhythmicity of core and surface temperatures of sheep kept under thermoneutrality or in the cold. Research in Veterinary Science 95: 261-265

Piccione, G., Giudice, E., Fazio, F., and Refinetti, R. (2011). Association between obesity and reduced body temperature in dogs. International Journal of Obesity 35: 1011-1018.

Kart Gür, M., Refinetti, R., and Gür, H. (2009). Daily rhythmicity and hibernation in the Anatolian ground squirrel under natural and laboratory conditions. Journal of Comparative Physiology B 179: 155-164.

Refinetti, R. and Piccione, G. (2005). Intra- and inter-individual variability in the circadian rhythm of body temperature of rats, squirrels, dogs, and horses. Journal of Thermal Biology 30: 139-146.

Piccione, G., Caola, G., and Refinetti, R. (2003). Daily and estrous rhythmicity of body temperature in domestic cattle. BMC Physiology 3: 7.

Refinetti, R. (2003). Metabolic heat production, heat loss, and the circadian rhythm of body temperature in the rat. Experimental Physiology 88: 423-429.

Piccione, G., Caola, G., and Refinetti, R. (2002). Effect of shearing on the core body temperature of three breeds of Mediterranean sheep. Small Ruminant Research 46: 211-215.

Refinetti, R. (1999). Amplitude of the daily rhythm of body temperature in eleven mammalian species. Journal of Thermal Biology 24: 477-481.

Refinetti, R. (1998). Homeostatic and circadian control of body temperature in the fat-tailed gerbil. Comparative Biochemistry and Physiology 119A: 295-300.

Refinetti, R. and Susalka, S. J. (1997). Circadian rhythm of temperature selection in a nocturnal lizard. Physiology and Behavior 62: 331-336.

Refinetti, R. (1996). Comparison of the body temperature rhythms of diurnal and nocturnal rodents. Journal of Experimental Zoology 275: 67-70.

Refinetti, R. (1995). Body temperature and behavior of golden hamsters (Mesocricetus auratus) and ground squirrels (Spermophilus tridecemlineatus) in a thermal gradient. Journal of Comparative Physiology A 177: 701-705.

Refinetti, R. (1995). Effects of suprachiasmatic lesions on temperature regulation in the golden hamster. Brain Research Bulletin 36: 81-84.

Refinetti, R. and Menaker, M. (1992). Body temperature rhythm of the tree shrew, Tupaia belangeri. Journal of Experimental Zoology 263: 453-457.

Refinetti, R. (1990). Is there modal opponency in the thermal senses? Journal of Thermal Biology 15: 255-258.

Refinetti, R. and Carlisle, H. J. (1989). Thermoregulation during pentobarbital and ke- tamine anesthesia in rats. Journal de Physiologie 83: 300-303.

Refinetti, R. and Carlisle, H. J. (1987). A reevaluation of the role of the lateral hypothalamus in behavioral temperature regulation. Physiology and Behavior 40: 189-192.

Refinetti, R. (1984). Behavioral temperature regulation in the pill bug, Armadillidium vulgare (Isopoda). Crustaceana 47: 29-43.

1. Data analysis involves both graphical and numerical procedures. In circadian physiology, the goal of data analysis is to characterize one or more of the six parameters of circadian rhythmicity: mean level, amplitude, phase, period, wave form, and robustness.

2. Calculation of the mean level and amplitude of a rhythm can be based directly on the raw data or on a cosine curve fitted to the data. Phase can be determined by inspection of actograms, computation of the peak of the smoothed rhythm, or identification of the acrophase of the fitted cosine curve.

3. The period of a rhythm is most commonly determined by various methods of inspection of actograms, by Fourier analysis, by the Enright (chi square) periodogram, or by the Lomb-Scargle periodogram. There is no standard procedure to quantify the wave form of circadian rhythms. Robustness, which is an index of the degree of stationarity of the rhythm, may be estimated by periodogram analysis of filtered data sets.

4. Tests of statistical significance are essential for the distinction between real rhythms and random oscillations. Generally, one can be more confident about the results of the tests if one has a long time series covering several cycles of the rhythm, but significance tests can be conducted on "educed" rhythms as well.

For computer programs for the analysis of biological rhythms, visit the Software section of this web site.

Methods for data collection, data analysis, and computer simulation are continuously being developed and tested in the lab. The following are some of our publications on data analysis procedures:

Refinetti, R., Cornélissen, G., and Halberg, F. (2007). Procedures for numerical analysis of circadian rhythms. Biological Rhythm Research 38: 275-325.

Refinetti, R. (2004). Non-stationary time series and the robustness of circadian rhythms. Journal of Theoretical Biology 227: 571-581.

Refinetti, R. (1996). Demonstrating the consequences of violations of assumptions in analysis of variance. Teaching of Psychology 23: 51-54.

Refinetti, R. (1993). Comparison of six methods for the determination of the period of circadian rhythms. Physiology and Behavior 54: 869-875.

Refinetti, R. (1992). Analysis of the circadian rhythm of body temperature. Behavior Research Methods, Instruments, and Computers 24: 28-36.

Refinetti, R. (1991). Use of chi square periodogram in the analysis of estrous rhythmicity. International Journal of Biomedical Computing 27: 125-132.

Refinetti, R. (1991). An extremely simple procedure for the analysis of circadian and estrous periodicity. Physiology and Behavior 50: 655-659.

Refinetti, R. (1989). Computation of effective body mass for metabolic studies of lean and obese rats. Metabolism 38: 763-766. (Erratum in Metabolism 39: 215)

Refinetti, R. and Carlisle, H. J. (1987). A computational formula for heat influx in animal experiments. Journal of Thermal Biology 12: 263-266.