Comment on "Differential rescue of light- and food-entrainable circadian rhythms"

Fuller et al. (Reports, 23 May 2008, p. 1074) reported that the dorsomedial hypothalamus contains a Bmal1-based oscillator that can drive food-entrained circadian rhythms. We report that mice bearing a null mutation of Bmal1 exhibit normal food-anticipatory circadian rhythms. Lack of food anticipation in Bmal1-/- mice reported by Fuller et al. may reflect morbidity due to weight loss, thus raising questions about their conclusions.     

Estradiol shortens the period of hamster circadian rhythms

Continuous administration of estradiol benzoate by means of subcutaneously implanted capsules shortened the free-running circadian period of locomotor activity of blind hamsters (Mesocricetus auratus) that had had their ovaries removed. Estradiol also advanced the phase of the wheel running of sighted female hamsters without ovaries that were entrained to a photoperiod with 12 hours of light and 12 of darkness. These results, and findings from hamsters undergoing natural estrous cycles, indicate that endogenous estradiol is involved in the regulation of circadian periodicity.     

Entrainment of circadian rhythms by sound in Passer domesticus

The circadian locomotor rhythm of house sparrows was entrained by a sound stimulus. The birds were maintained at a constant temperature in, dim green light. The entraining agent was 4 (1/2) 12 hours of tape-recorded bird song ,played each day. Variations in the response to this stimulus have been correlated with individual variations in free-running period. This is the first clear demonstration that a biological clock can be influenced by sound stimuli.     

The opioid peptide dynorphin, circadian rhythms, and starvation

Dynorphin, an opioid peptide whose functions are unknown, is found in brain, pituitary, and peripheral organs. Specific radioimmunoassays were used to measure dynorphin in the hypothalamus and pituitary, during the day and at night, as a function of food and water deprivation. Immunoreactive dynorphin was increased in the hypothalamus and decreased in the pituitary at night. Water deprivation led to more than 50 percent reduction in daytime levels of pituitary dynorphin and concomitant increases in hypothalamic dynorphin.     

Searching for genes underlying behavior: lessons from circadian rhythms

The success of forward genetic (from phenotype to gene) approaches to uncover genes that drive the molecular mechanism of circadian clocks and control circadian behavior has been unprecedented. Links among genes, cells, neural circuits, and circadian behavior have been uncovered in the Drosophila and mammalian systems, demonstrating the feasibility of finding single genes that have major effects on behavior. Why was this approach so successful in the elucidation of circadian rhythms? This article explores the answers to this question and describes how the methods used successfully for identifying the molecular basis of circadian rhythms can be applied to other behaviors such as anxiety, addiction, and learning and memory.     

Human circadian rhythms in continuous darkness: entrainment by social cues

Three groups of two subjects each were kept in underground chambers, first for 4 days in an artificial light-dark cycle, and thereafter for 4 days in complete darkness. They lived on a rigorous time schedule. Physiological as well as psychological functions were measured at 3-hour intervals. There were no differences in the results between the two sections of the experiment. Social cues are sufficient to entrain human circadian rhythms, and absence of light has no immediate effect on the functions measured.     

Testosterone induces "splitting" of circadian locomotor activity rhythms in birds

Under the influence of testosterone, the free-running circadian rhythm of locomotor activity of the starling, Sturnus vulgaris, tends to "split" into two components which temporarily run with different circadian frequencies: "splitting" occurred in intact birds whose testes grew, and in castrated birds that were injected with testosterone. Since "splitting" most probably reflects the temporal separation of two (or two groups of) circadian oscillators, these results suggest that testosterone affects the mutual coupling of circadian oscillators controlling locomotor activity.     

热应激诱导大鼠小肠昼夜节律基因差异表达的研究

采用石蜡切片H.E染色观察热应激大鼠小肠形态学变化,利用Realtime-PCR技术对小肠中昼夜节律相关基因的表达进行研究。结果:大鼠小肠上皮出现严重损伤,肠黏膜绒毛顶端上皮细胞脱落,固有层裸露;热应激导致Per2和DBP基因瞬时表达极大升高,节律性受到严重影响,Bmal1基因瞬时表达差异不明显,其mRNA表达量峰值后移。     

Multiple circadian oscillators regulate the timing of behavioral and endocrine rhythms in female golden hamsters

A single daily "surge" in pituitary luteinizing hormone release was observed in ovariectomized-estrogen-treated hamsters expressing an intact circadian rhythm of locomotor activity. In contrast, two luteinizing hormone surges occurred within a single 24-hour period in hamsters whose activity rhythm had dissociated or "split" into two distinct components. These observations indicate that both behavioral and endocrine circadian rhythms are regulated by the same multioscillator system, which seems to be composed of at least two distinct circadian oscillators.     

Two c-type cytochromes from light- and dark-grown Euglena

A pigment-protein complex can be extracted, in aqueous 2-percent digitonin, from Euglena grown in the light. When further fractionated by acetone and ammonium sulfate this flagellate yields a c-type cytochrome. By similar extraction of dark-grown, nonphotosynthetic Euglena, another c-type cytochrome can be isolated. The cytochrome from the light-grown Euglena- is like that of cytochrome c isolated from a photosynthetic bacterium. The cytochrome from the dark-grown Euglena is like cytochrome f found in the chloroplasts of higher plants.     

Geological rhythms and cometary impacts

Time-series analysis reveals two dominant, stable long-term periodicities approximately equal to 33 +/- 3 and 260 +/- 25 million years in the known series of geological and biological upheavals during the Phanerozoic Eon. Because the cycles of these episodes agree in period and phase with the cycles of impact cratering on Earth, these results suggest that periodic comet impacts strongly influence global tectonism and biological evolution. These two periodicities could arise from interactions of the solar system with interstellar clouds as the solar system moves cyclically through the Galaxy.     

Stromatoporoid growth rhythms and rates

Stromatoporoids are major contributors to framework construction in Paleozoic reefs. The Devonian species Parallellostroma densilaminata (Fagerstrom), P. winchelli (Galloway and Ehlers), and Stictostroma sp. form large rhythmically structured colonies that competitively overgrow corals. Their competitive interactions and important role as reef builders place considerable value on growth rate information. Identification of common growth periods in these interacting species provides a methodfor quantifying vertical and lateral stromatoporoid growth and a means for identifying an annual periodicity of calcification.     

Phagocytosis of light- and dark-adapted rod outer segments by cultured pigment epithelium

Pigment epithelial cells in culture retain their ability to phagocytize rod outer segments. These cells phagocytize rod outer segments isolated from light-adapted rats, or from dark-adapted rats killed after the time at which the lights would normally be turned on. However, they phagocytize for fewer rod outer segments prepared in the dark from the retinas of rats killed before the onset of the normal light cycle. Phagocytosis of dark rod outer segments is variable, but that of light outer segments is reproducible. It is postulated that the effect of light is to synchronize the chemical events that occur at the surface of the rods to prepare them for phagocytosis. These processes also occur in the dark, but more slowly and irregularly than in the light.     

Activity rhythms and adiurnal light-dark control

The running-wheel activity pattern of mature male rats was successfully synchronized to light-dark cycles as long as 48 hours and as short as 16 hours. Even after 6 months' exposure to "days" longer than the normal 24 hours, the animals returned promptly to circadian rhythmicity when placed under freerunning conditions of continuous dark. That such rhythms also reappeared when the light condition of the 36-hour cycle was reduced from 660 to 33 lumens per square meter suggests that brightness may be the critical factor in the unexpectedly broad range of entrainment demonstrated.     

Regulation of circadian rhythmicity

Daily rhythms in many behavioral, physiological, and biochemical functions are generated by endogenous oscillators that function as internal 24-hour clocks. Under natural conditions, these oscillators are synchronized to the daily environmental cycle of light and darkness. Recent advances in locating circadian pacemakers in the brain and in establishing model systems promise to shed light on the cellular and biochemical mechanisms involved in the generation and regulation of circadian rhythms.