Chronobiologia最新文献

136 infants died of sudden infant death syndrome (SIDS) and 140 infants died suddenly and unexpectedly from life-threatening conditions (LTC) from 1983 to 1989 in Leningrad entered the study. 24-hour distribution of death cases was evaluated in both studied groups. The increased incidence of SIDS was revealed from 04(00) to 06(00). There was not significant difference between circadian variation of SIDS and that of death from LTC. The early morning seems to be the time when the risk factors that lead to sudden death are likely to be prominent.

One of us introduces a chronobiology course to students at the University of Milan, Italy, with a succinct statement that may well serve to summarize the foregoing 24 points. Its few lines distill the preceding details and formulate the raison d'être of Chronobiology: Chronobiology is: not only a science in its own right; not only a methodology; not only a new kind of statistical analysis; not just an aspect of biology, but a new way of invariably approaching any problem in biology, notably medicine.

Christoph Wilhelm Hufeland (1762-1836) was one of the eminent physicians at the time of Goethe. When only 21 years old, he followed his father as a medical practitioner in Weimar. In 1793 he became Professor of Medicine at the University of Jena, from where he moved, in 1801, to Berlin as the physician in ordinary to king Friedrich Wilhelm III, council of state, and Professor at the leading hospital, the Charité. Hufeland pioneered in what today would be called public hygiene. Many of his lectures and publications were addressed to the educated laymen. In his most read book, the 'Makrobiotik', he emphasizes the importance of the 24-h periodicity as a basic unit of biological chronometry. In view of this, Hufeland has become a kind of 'patron saint' to modern chronobiologists.

The concept of sensation measurement with the entailing subjective scales is explained. It is shown that linearity between, e.g. sensation halving values and standard values implies that subjective sensation (output) grows as a power function of the physical measure of the stimulus (input). This outcome can be used in the scaling of subjective duration, based on reproduction experiments, i.e., experiments in which the participants are required to reproduce given time intervals, e.g., indicated by noise. It will be shown that what is reproduction for the participant is halving for the experimenter, making it possible to determine the parameters of the power function. The model is confirmed experimentally for humans and rats, the rats having a lower exponent than adults. In a recent experiment it was shown that the reproduced durations differ between female and male observers as well as for different sound intensities. These differences could be attributed to differences in parameter values. An interesting observation is that almost all power functions exhibit a discontinuity, possibly indicating a switch between different neural loops as the durations become longer.

In this review article an insight has been made into the strong possibility of the role of vasopressin (VP) in the control of circadian rhythms which has emerged from the results of the recent experiments in this field. A role for VP, which is identified in the suprachiasmatic nuclei (SCN) of mammals, as a neurotransmitter/neuromodulator in the central nervous system has been postulated for some time now. The presence of certain abnormalities in the circadian rhythms in VP deficient Brattleboro rats has suggested that this neuropeptide is a likely candidate in controlling circadian rhythms. The coexistence of VP and corticotropin releasing factor (CRF), their interrelation with reference to their role in the hypothalamus-pituitary-adrenocortical glucocorticoid axis not only in states of stress but also in day-to-day life has also been discussed. The possible role of dynorphin, which is co-synthesized with VP in the hypothalamic neurons, and other opioids in the control of circadian rhythms has been highlighted. The pineal, SCN relation in the process of development of circadian rhythms has also been reviewed briefly.

As an integrative discipline in physiology and medical research, chronobiology renders possible the discovery of new regulation processes regarding the central mechanisms of epilepsy. In this context, the temporal fluctuations of seizure susceptibility rhythmometrically detected tend to demonstrate 1. that tonic-clonic events are circadian stage-dependent processes whose temporal characteristics (i.e. MESOR, amplitude, acrophase) and clinical parameters (e.g. neurological components, severity of motor discharges) are predictable on the basis of mathematical models, and 2. that the generalized epileptic onsets may respond to telencephalic integrations modulated by centrencephalic circadian processes of vigilance. Considering the data model assumed for our rhythmometric analyses, the circadian psychophysiological patterns of epilepsy also express dynamic biologic systems which reveal some intermodulating endogenous processes between vigilance and seizure susceptibility. The new chronophysiology investigations considered at a rhythmometric level of resolution suggest several heuristic perspectives regarding 1. the central pathophysiology of epilepsy and 2. the behavioral classification of convulsive events. Such circadian studies also show that chronobiology raises some working hypotheses in psychophysiology and permits the development of new theoretical concepts in the field of neurological science.

To determine whether consecutive parturitions within individual rats are likely to occur around the same time of the 24h day, female rats mated prior to ovulation and maintained on a LD 12:12 photoperiod, were observed over either two or three parturitions. A subgroup of females was placed on constant light during the second gestation in order to determine the role of photoperiod in the temporal synchronization of consecutive births. The major findings were 1. individual females tended to give birth around the same time of the day on consecutive births so long as the photoperiod remained constant; 2. the small percentage of births occurring during darkness, the less-prevalent time of the photoperiod for birthing, were anomalous births for individual females; and 3. litter weight was a significant factor in predicting time of birth for females, but this effect interacted with photoperiod. These data elucidate the importance of knowing previous birth time, litter weight, and photoperiod on predicting the time of parturition in the rat.

Few works already carried out have examined the relative role of genetic and external factors on the determination of the rhythmicity of the human sleep/wake cycle. In order to make a preliminary approach in this field, we investigated the diversity of patterns of allocation of sleep periods among 29 families living at the Combu Island, a socioculturally very homogeneous human group of the Brazilian Amazon. The individuals were interviewed through a questionnaire designed by Horne and Ostberg (1976), with the language of the questions adjusted to the way-of-life of the riverine people. A large predominance of the morning type was observed (95.35%), what constitutes a strong deviation in relation to other populations studied, suggesting the occurrence of a masking effect. The individual scores presented a positive correlation with the age (r = 0.31; p less than 0.01), and a significant intersexual difference was also verified (t = 3.08; p less than 0.01). This intersex difference is explained, in part, by analyzing the socioeconomic patterns of the community. The offspring/parent regression of the individual scores indicated a low dependency between genitors and their direct descendents (p greater than 0.7), and the estimative of heritability obtained (0.14) is artificial, since the offspring/mother and offspring/midparent regression coefficients were negative. Statistically non-significant coefficients of correlation and/or regression showed a highly randomic populational distribution of scores for the Horne-Ostberg's test. Such findings suggest that the intensity of the masking over the sleep/wake cycle varies among human populations, and that the individual tendency towards morningness/eveningness is strongly related to sociocultural factors.

In this paper a remarkable statistical link between sunspot cycles and prevalence of hip fractures in the elderly is shown. Hip fractures in old people are due to: 1. increased bone fragility for metabolic bone disease; 2. increased propension to fall. Though it is obvious that a correlation does not imply any causal relationship, reasonable conjectures can be allowed. The hypothesis of an 11-year cyclic variation of ultraviolet radiation as a cause of hip fractures is untenable; one may better assume that solar flares can negatively influence the nervous postural regulation leading to a greater propensity to accidental falls.