Six methods for measuring the period of circadian rhythms (tau) have been compared using real and artificial data. The modified periodogram technique estimates tau by fitting a data-specific form estimate to time series data with a period that minimizes the variance of data around the form estimate. The onset periodogram converts raw data to new values that reflect rapid increases of data magnitude, then fits a form estimate to these new values. Iterative cosinor determines the period of the single cosine curve that best describes the data. The iterative harmonic derives a form estimate, consisting of a cosine function plus a series of true harmonics, which most closely describes the data. Other methods measure the slope of the line fitting each day's acrophase (regressive cosinor) or subjectively selected phase markers (eyefitting).Our analyses indicate that the estimated value of tau can vary depending on the method used. Periodogram and iterative harmonic methods provided the most consistently satisfactory estimates of tau from all sets of data examined. Eyefitting and onset periodogram methods accurately estimated tau from artificial data based on hamster activity rhythms, but were less useful for estimating temperature tau. The eyefitting procedure was less replicable than the automated methods for estimating tau. The choice of analysis method ultimately depends upon the character of the data to be analyzed and the nature of the hypotheses to be tested.
Urinary cross-linking amino acids (pyridinoline and deoxypyridinoline) are used as biochemical markers of bone resorption. Therefore, the study of their diurnal behavior might provide information on whether circadian variability could be observed in bone remodelling. We showed a significant circadian rhythm of both urinary pyridinoline and deoxypyridinoline in healthy premenopausal females with higher concentrations at 05.35 and 0457, respectively. The reported observations suggest an increased rate of bone resorption during the night in subjects living on a usual day-night schedule. Moreover, these findings focus the attention on the importance of the sampling time for the comparison of data from different studies and from patients with different pathological conditions.
48 right-handed subjects performed verbal and spatial hemifield tachistoscopic tasks, half of them in spring and the other half in autumn. Significant differences were detected showing increased right visual field (left hemisphere) advantage in spring and increased left visual field (right hemisphere) advantage in autumn. Results may help to explain the reported seasonal propensity towards elevated mood in spring and towards depressed mood in autumn as related to the relative role of both hemispheres.
The effects of intravitreal injections of indoleamines or their inhibitors on the quail ERG were investigated. The ratio of b- to a-wave in amplitudes showed daily fluctuations in the control eyes. Repeated injections of para-chlorophenylalanine (PCPA), an indoleamines synthesis inhibitor, reduced the ratio to the nocturnal levels. And the level was restored by serotonin injection during the daytime but not during the night. Melatonin application into the diurnal eye slightly but significantly reduced the ratio. Furthermore, 5,7-dihydroxytryptamine (5,7DHT) which destroyed the indoleamine-accumulating amacrine cells had a similar effect. These results suggest that the activity of the retinal indoleamines serotonin and melatonin may be involved in circadian changes of the quail ERG.
Women with and without seasonal affective disorder (SAD) were studied on two winter days separated by a week of light treatment (LT) at 2500 lux either in the morning (0800-1000h; 8 patients and 4 controls) or afternoon (1600-1800 h; 5 patients and 3 controls), and on a summer day (7 patients of the morning subgroup and 7 controls). Blood samples were drawn at 4-h intervals beginning at 0800 h until either 0000 h (7 controls and 6 patients) or until 0400 h of the next day (7 patients of the morning group). Serum samples were assayed for cortisol (COR), prolactin (PRL), thyrotropin (TSH), triiodothyronine (T3), thyroxine (T4) and thyroxine-binding globulin (TBG).The circadian patterns of three hormones - TSH, COR and PRL - were normal and similar in all groups, and did not alter either by LT or change in season. After LT diurnal mean of TSH levels increased significantly in patients and non significantly in controls. In controls other hormones levels either increased significantly (T3) or showed the tendency towards increase (COR, PRL, T4), while in patients T3, T4 and TBG levels either decreased or remain lower than in controls. Therefore, following LT the levels of thyroid hormones in patients became significantly lower than in controls. No significant seasonal variations in diurnal means of the hormones were found either in patients or in controls. A thyroid malfunction seems to be a trait marker of winter SAD. We also suggest that circadian phase alteration is not of main importance in SAD pathogenesis and effect of LT.
Chloroplast GAPDH (NADP+-glyceraldehyde-3-phosphate dehydrogenase) (EC 1.2.1.13) is one of the photosynthetic enzymes which make up the set of reactions responsible for carbon fixation in plants. We here report that fully expanded green corn leaves showed diurnal variations in GAPDH mRNA level as well as enzyme activity in response to light:dark cycles. In continuous bright light the mRNA, but not the enzyme activity rhythm persisted. This is the first time a circadian rhythm in GAPDH mRNA level is reported; the existence of light-driven rhythms in higher plants is thus further established.
In the plasmodial stage the slime mold Physarum polycephalum exhibits oscillatory phenomena. The ectoplasm contracts regularly, resulting in oscillatory (shuttle) streaming of the endoplasm. This periodic phenomenon represents a biological clock that is not well understood. We have studied quantitatively the stability of the rhythmic contractions in Physarum over long intervals of time using an electrical method that permits in situ measurements of the undisturbed plasmodium. The measured resistance curves were analyzed with fast Fourier transform, and the power spectra revealed one fundamental frequency with several higher harmonics. The period determined from the fundamental frequency (typically 1.8 minutes) was quite stable over 40 hours at defined temperature, humidity and growth conditions, but deviations by a factor of 2 occurred on shorter time scales. The period of the different Physarum specimens varied from 1 to 6 minutes at room temperature.
Cytological studies of the pineal and the testes in free-living roseringed parakeets (Psittacula krameri) show that the activities of both organs undergo definite annual changes. The features of hyperactivity of pinealocytes were noted during the months of April through September, after which a gradual loss of the signs of cellular activity occurred till March, when the pineal appeared to be highly regressed, followed by an abrupt change in the opposite direction in April to repeat the cycle. On the other hand, studies of the testes indicated that the species attains maximum testicular maturation during March, after which sudden regression occurs and the testes remain in the quiescent state till September when recovery of spermatogenesis takes place and steady growth and development towards the annual peak follow. A significant negative correlation was found between the seasonal values for nuclear diameter of the pinealocytes and each of the studied parameters of testes. Among the considered climatological variables, the duration of light or photoperiod length appeared to be positively correlated with the karyometric values of pinealocytes during each annual cycle.
The daily activity cycles of three species of sunfishes (Lepomis macrochirus, L. cyanellum, L. gibbosus) were compared by measuring hourly activity under a 12:12 light/dark cycle with half-hour dawn and dusk periods. Two different feeding times were also tested. Time-series analyses showed a strong 24 hour component in the activity cycles of all three species, although an analysis of ARIMA models indicated that green sunfish activity was less predictable from hour to hour than was that of the other two species. The distribution of activity over the light/dark cycle was similar for pumpkin-seed and green sunfish, both species exhibiting generally diurnal activity cycles with a tendency toward crepuscular peaks. Overall activity was higher for bluegill sunfish than for green or pumpkin-seed sunfish, and bluegills exhibited a higher level of activity during the dark portion of the cycle than did the other two species.
