Antiphase oscillation of the left and right suprachiasmatic nuclei

An unusual property of the circadian timekeeping systems of animals is rhythm "splitting," in which a single daily period of physical activity (usually measured as wheel running) dissociates into two stably coupled components about 12 hours apart; this behavior has been ascribed to a clock composed of two circadian oscillators cycling in antiphase. We analyzed gene expression in the hypothalamic circadian clock, the suprachiasmatic nucleus (SCN), of behaviorally "split" hamsters housed in constant light. The results show that the two oscillators underlying the split condition correspond to the left and right sides of the bilaterally paired SCN.     

Light pulses that shift rhythms induce gene expression in the suprachiasmatic nucleus

Lighting cycles synchronize (entrain) mammalian circadian rhythms by altering activity of cells in the suprachiasmatic nucleus (SCN) of the hypothalamus, a circadian pacemaker. Exposure of hamsters and rats to light pulses at those phases of the circadian rhythm during which light can shift the rhythm caused increased immunoreactivity for the product of the immediate-early gene c-fos in cells in the region of the SCN that receives retinal fibers. Light pulses also increased messenger RNA for the Fos protein and for the immediate-early protein NGFI-A in the rat SCN. Similar increases in mRNA for NGFI-A were seen in the SCN of hamsters. Thus cells in this portion of the SCN undergo alterations in gene expression in response to retinal illumination, but only at times in the circadian cycle when light is capable of influencing entrainment.     

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.     

A mutation of the circadian system in golden hamsters

A mutation has been found that dramatically shortens the period of the circadian locomotor rhythm of golden hamsters. The pattern of inheritance of this mutation suggests that it occurred at a single, autosomal locus (tau). Wild-type animals have rhythms with free-running periods averaging about 24 hours; animals heterozygous for the mutation have periods of about 22 hours, whereas homozygous animals have rhythms with periods close to 20 hours. Animals that carry the mutant alleles exhibit abnormal entrainment to 24-hour light:dark cycles or are unable to entrain.     

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.     

Persisting circadian rhythm of cell division in a photosynthetic mutant of Euglena

A persisting, free-running, circadian rhythm of cell division in a heterotrophically grown mutant of Euglena gracilis var. bacillaris having impaired photosynthesis is obtained upon placing a culture that has been previously synchronized by a 10,14 light-dark cycle into continuous darkness at 19 degrees C (but not at 25 degrees C). A similar persisting rhythm is initiated in exponentially increasing cultures (growing in darkness at 19 degrees C) by a single "switch-up" in irradiance to continuous bright illumination. The results implicate an endogenous biological clock which "gates" the specific event of cell division in the cell developmental cycle.     

Transplantation of the cockroach circadian pacemaker

Surgical removal of the optic lobes of the cockroach Leucophaea maderae followed by transplantation of the optic lobes from another individual led to a restoration of the circadian activity rhythm in 4 to 8 weeks. The free-running period of the restored rhythm was determined by the period of the donor rhythm before surgery. The results suggest that the transplanted optic lobe contains a circadian clock that regenerates those neural connections with the host brain that are necessary to drive the circadian rhythm of activity.     

Circadian clock in culture: N-acetyltransferase activity of chick pineal glands oscillates in vitro

N-Acetyltransferase activity was measured in organ-cultured chick pineal glands. A circadian rhythm of enzyme activity persisted in cultured glands for up to 4 days. The phase of the rhythm in vitro closely approximates its phase in vivo. These observations demonstrate that the pineal gland of chicks contains (or is) a self-sustained circadian oscillator.     

Resetting the sporulation rhythm in Pilobolus with short light flashes of high intensity

The "clock-controlled" endogenous sporulation rhythm in the fungusPilobolus sphaerosporus has been investigated as part of a comparative study aimed at elucidating characteristic common features of circadian ((1)) rhythms. Pilobolus was chosen for inclusion in this study because of its demonstrated rhythm and sensitivity to light, and because it is a relatively simple plant. It has been shown that a single, high-intensity, 1/2000 second light flash will completely reset (shift the phase of) a rhythm persisting in continuous dim red light at constant temperature, and that one or more transient cycles occur before the phase shift is complete. The significance of these results is discussed.     

Synthetic polypeptide antagonists of the hypothalamic luteinizing hormone releasing factor

Two analogs of the hypothalamic luteinizing hormone releasing factor modified at the histidine-2 position were tested for biological activity (secretion of luteinizing hormone) in cultures of dispersed rat anterior pituitary cells. The analog in which glycine was substituted for histidine at position 2, [Gly(2)]LRF, behaves as a partial agonist releasing less than 50 percent of the luteinizing hormone secreted at maximum concentrations of the releasing factor, while the analog in which histidine at position 2 is deleted has no significant agonist activity at any of the doses tested. When added to the cultured cells at molar ratios 10(3) to 10(4) times that of the luteinizing hormone releasing factor, both analogs decrease the amount of luteinizing hormone secreted in response to the releasing factor.     

Circadian oscillations in rodents: a systematic increase of their frequency with age

The circadian activity rhythms of golden hamsters and two species of deermouse, when released from a light-dark cycle of 12 hours light and 12 hours of darkness into constant darkness, had progressively shorter periods as the animals became older. A possible bearing of this fact on the aging process is briefly outlined.     

Human growth hormone release: relation to slow-wave sleep and sleep-walking cycles

Release of human growth hormone during sleep is significantly related to slow, synchronized stages of sleep and therefore would seem to be controlled by related neural mechanisms. When sleep-waking cycles are reversed by 12 hours, the release of growth hormone with sleep is reversed; thus release does not follow an inherent circadian rhythm independent of sleep.     

不同投喂频率下黄颡鱼幼鱼的摄食节律研究

对黄颡鱼幼鱼在日过量投喂8次和投喂1次条件下的摄食节律进行了研究。日过量投喂8次时黄颡鱼幼鱼表现出明显的摄食节律,摄食率高峰值出现在晚上20:00,低峰值出现在上午8:00。夜间时段摄食率显著高于白天时段摄食率,不同时间段的摄食率差异极显著。日不同时间段过量投喂1次时,高峰值出现在晚上23:00,低峰值出现在上午11:00,但8个时间段的摄食率差异不显著。投喂8次组的日摄食率远高于1次组。结果表明黄颡鱼幼鱼为夜行性摄食,但投喂频率、投喂量等因素直接影响其摄食节律。     

Luteinizing hormone-releasing activity in hypophysial stalk blood and elevation by dopamine

Pituitary halves incubated in pituitary stalk plasma release more luteinizing hormone than their opposite halves incubated in plasma from peripheral blood. Glands incubated in stalk plasma from dopamine-treated rats release more luteinizing hormone than glands incubated in stalk plasma from untreated controls. Luteinizing hormone-releasing activity in stalk plasma may be due to the luteinizing hormone-releasing factor, and the secretion of luteinizing hormone-releasing factor may be controlled by a dopaminergic mechanism.     

高血压脑患者出血手术治疗后心率近日节律的变化

目的研究高血压脑出血手术治疗后心率近日节律的变化特征。方法对100例高血压基底节区脑出血患者进行开颅血肿清除术。术后连续9d监测心率,每小时记录1次。分别用单一和平均群体余弦法进行心率的近日节律分析。结果手术后第1～7天心率的近日节律消失(P>0.05),第8天恢复出现近日节律。结论高血压脑出血手术治疗对心率近日节律的影响严重。脑部手术后近日节律的恢复可能和术后脑水肿的发生、发展有密切的关系。     

Circadian changes in enzyme concentration account for rhythm of enzyme activity in gonyaulax

A circadian rhythm in the activity of luciferase is partly responsible for rhythmic bioluminescence in the dinoflagellate alga Gonyaulax polyedra. The cyclic activity of this enzyme can be attributed to a corresponding rhythm in the concentration of immunologically reactive luciferase protein. Hence protein turnover (synthesis or degradation or both) is used by the endogenous clock to control the daily rhythm of bioluminescence.     

Suppression of ovulation in the rat by an orally active antagonist of luteinizing hormone-releasing hormone

A synthetic antagonist of luteinizing hormone-releasing hormone blocked ovulation in rats in a dose-dependent manner when given by gavage on the afternoon of proestrus. Ovulation was delayed for at least 1 day in all animals given 2 milligrams of antogonist and in some of the animals treated with 1 or 0.5 milligram. Oral administration of 2 milligrams also blocked the preovulatory surge of luteinizing hormone. This demonstration that antagonists of luteinizing hormone-releasing hormone can have oral antiovulatory activity clearly enhances their therapeutic potential.     

Circadian activity rhythm of the deer mouse, Peromyscus: effect of deuterium oxide

Chemical modification of a vertebrate activity rhythm, the circadian (approximately 24-hour) rhythm of Peromyscus leucopus noveboracensis, has been demonstrated. Activity in a running wheel was used to measure the rhythms of mice kept individually in conditions of continuous darkness. Deuterium oxide was presented in the drinking water. The length of the periods of rhythm increased directly and linearly with the increase in concentration of deuterium oxide. There is no threshold for this effect, and the maximum concentration of deuterium oxide (30 percent) that was presented resulted in a 6 percent lengthening of the period of circadian rhythm. The mice reverted to rhythms similar in period length to control values after deuterium oxide was withdrawn from their drinking water.     

Ornithine decarboxylase stimulation in rat ovary by luteinizing hormone

In normal albino rats with a 4-day estrous cycle, the activity of ovarian ornithine decarboxylase undergoes a transitory rise on the evening of proestrus and only at that time. The response could be elicited by the administration of either luteinizing hormone or human chorionic gonadotrophin. When antiserum to luteinizing hormone was injected at 2 p.m. on the day of proestrus, the induction of ornithine decarboxylase was blocked, an indication that the enzyme is under luteinizing hormone control. The strategic positioning of the induction of ornithine decarboxylase between the normal release of luteinizing hormone and ovulation impties that putrescine is associated with the ovulatory process, and opens a new avenue of research on the control of ovulation.     

Indole metabolism in the pineal gland: a circadian rhythm in N-acetyltransferase

The activity of N-acetyltransferase in the rat pineal gland is more than 15 times higher at night than during the day. This circadian rhythm persists in complete darkness, or in blinded animals, and is suppressed in constant lighting. The N-acetyltransferase rhythm is 180 degrees out of phase with the serotonin rhythm and is similar to the norepinephrine and melatonin rhythms. Experiments in vitro indicate that norepinephrine, not serotonin, regulates the activity of N-acetyl-transferase through a highly specific receptor.