Circadian Parameters Research Articles

Light cycle during post-embryonic development affects adult circadian parameters of the cricket ( Gryllus bimaculatus) optic lobe pacemaker

The circadian pacemaker of the cricket Gryllus bimaculatus, driving the locomotor rhythm, has been localized in the optic lobe. The motion of the optic lobe pacemaker could be monitored by recording the efferent neural activity of the optic lobe from the distal cut end of the optic stalk which is a long nerve trunk connecting the medulla and lobula. We compared the circadian rhythm of the optic lobe efferents among the different developmental groups of animals, which were reared under the 24 h light-dark cycle with either of the following three light-to-dark ratios, i.e. 16-8, 12–12 or 8–16 h. Although all animals showed the electrical activity peaking in the subjective night, effects of lengthening the dark phase from 8 to 16 h on the optic lobe pacemaker occurred in the following three ways. (1) The ratio of subjective night-to-day increased about 2 times, (2) the rising phase was lengthened by 3 h, and (3) the rhythm's phase to the light cycle advanced by about 4 h. Possible mechanisms and the adaptive significance of these pacemaker plasticity are discussed.

Circadian Rhythms of Body Temperature and Activation and The Well-Being of Older Women

The circadian parameters of body temperature and activation were studied in relationship to the well-being of 18 healthy women, aged 65-80 years. The women took oral temperature readings with an IVAC 2000 electronic thermometer and completed 1 of 12 alternate forms of the Activation-Deactivation Adjective Check List every 2 hours during waking hours for 7 consecutive days (2 subjects followed this procedure for 3 midweek days in 2 consecutive weeks). Approximately 2 hours before going to bed, all subjects completed the General Well-Being Questionnaire that was modified for this study to measure daily fluctuations in well-being. Hypotheses were examined using cosinor analysis and Pearson correlations. Temperature and activation were demonstrated to manifest circadian periodicities. There were no correlations between the parameters of these rhythms and the well-being of the subjects.

Melatonin and the circadian rhythms of feeding and perch-hopping in the European starling,Sturnus vulgaris

The role of melatonin plasma titers in the control of free-running circadian rhythms was investigated in European starlings,Sturnus vulgaris, held in continuous dim light. Simultaneous recordings of plasma melatonin, perch-hopping and feeding activity revealed synchronous circadian variations in all three functions with high melatonin titers during resting and low titers during activity periods. Implanting birds with melatonin silastic capsules resulted in a 100-fold increase in plasma concentrations and an abolition of the endogenous melatonin rhythm. Feeding rhythms persisted during this treatment, although the activity time (α) was lengthened and the circadian period (τ) shortened. Similar changes were found in perchhopping activity, but in some birds, this activity was more or less suppressed. These data demonstrate that although melatonin plasma titers freerun synchronously with other circadian parameters, fluctuations in peripheral melatonin are not essential for the expression of circadian activity.

Marked enhancement by clorgyline of nocturnal and daytime melatonin release in rhesus monkeys

The type A monoamine oxidase (MAO)-inhibiting antidepressant clorgyline (1 mg/kg/24 days) administered to rhesus monkeys increased night-time cerebrospinal fluid (CSF) melatonin concentrations 3-fold and day-time maltonin values 5-fold. Other circadian parameters of melatonin release, including the peak time and duration of nocturnal melatonin elevation measured during continuous CSF collection periods of 90 min duration over 24-h cycles, were unaffected by clorgyline. While pinealocytes are thought to contain only MAO-B, treatment with the selective MAO-B inhibitor deprenyl (2 mg/kg/24 days) did not alter day or night-time melatonin concentrations. These results are consistent with MAO-A and non-selective MAO inhibitors acting via blockade of degradation of the preferential substrates of MAO-A, serotonin and/or norepinephrine, in adrenergic neurons entering the pineal gland. Further study is needed to evaluate the relative contributions of an increased availability of the melatonin precursor, serotonin, or a sustained net increase in alpha 1-or beta adrenoceptor-mediated input on pinealocytes to these marked changes in melatonin production.

Caudal photoreceptors synchronize the circadian rhythms in crayfish—I. Synchronization of ERG and locomotor circadian rhythms

1. 1. Electroretinogram (ERG) and motor activity circadian rhythms in crayfish under constant environmental conditions were recorded. 2. 2. Changes on the circadian parameters induced by application of a single light stimulus of 2000 Ix and 10 min duration on either the eyestalk or the 6th abdominal ganglion were analyzed. 3. 3. The synchronization ability exerted by the caudal photoreceptors on the ERG and on motor circadian rhythms is discussed. 4. 4. In gangliectomized crayfish, there is a phase inversion in ERG circadian rhythm and an increment of the total amount of activity in motor circadian rhythm, but there is no evidence of synchronization when a single stimulus is applied on the place occupied by the removed 6th abdominal ganglion. 5. 5. It is proposed that extraocular photoreceptors can participate in the entrainment by light of the circadian rhythms of crayfish.

24-hour profile of plasma norepinephrine in affective disorders.

The circadian rhythm of plasma norepinephrine (NE) was investigated in the depressed (major affective disorder, DSM III; n = 12), recovered (after 3 weeks of treatment using usual antidepressant drugs; n = 12) and normal (volunteers, age and sex matched; n = 10) states. Data analysis (based on the evaluation of circadian parameters, on the chronogram method and on the chronobiological analysis) revealed a clear NE circadian rhythm in normal subjects, a rhythm which was disturbed in depression, with amplitude reduction and abnormal phase position. These abnormalities tended to disappear during recovery since circadian parameters were similar to those of controls. These circadian abnormalities could be linked to the impairment of the peripheral and central catecholaminergic systems. They may also support the chronobiological hypothesis of affective disorders.

Effects of partial destruction of the suprachiasmatic nuclei on two circadian parameters: wheel-running activity and short-day induced testicular regression

Many circadian rhythms in mammals are regulated by the suprachiasmatic nuclei located in the anterior hypothalamus. The suprachiasmatic nuclei are a heterogeneous population of neurons loosely segregated into regions. In an effort to determine if a regional specificity of control of different circadian rhythms exists within the SCN, the effect of small electrolytic lesions of the suprachiasmatic nuclei was examined on two parameters which are known to depend on the circadian system for their normal expression: wheel-running activity and short-day induced testicular regression. While some SCN lesions altered both the circadian rhythm of locomotor activity and the normal temporal pattern of gonadal regression on short-days, other partial lesions of the suprachiasmatic nuclei were found to effect one parameter without effecting the other. Detailed histological analysis of the neural damage sustained by the suprachiasmatic nuclei did not indicate an obvious regional specificity of function within the nuclei. However, the results do suggest that functionally specific neural pathways emerging from the suprachiasmatic nuclei carry circadian information to independent neural circuits responsible for locomotor activity and neuroendocrine-gonadal function.

Circadian rhythms of plasma renin activity and aldosterone: changes related to age, sex, recumbency and sodium restriction. Chronobiologic specification for reference values.

Plasma renin activity (PRA) and aldosterone (PA) levels are characterized by a circadian rhythmicity (CR). The present study revealed that this rhythmicity is influenced by several factors including posture, sodium intake and age. Time-qualified PRA and PA reference intervals can reduce the incidence of false positives and false negatives in a diagnostic work-up. The circadian rhythmicity of PRA and PA have been quantified in relation to posture, sodium intake and age. The cosinor procedure has been applied to quantify the properties of the circadian rhythmicity under these conditions. Chronograms and circadian parameters can be used to optimize the use of PRA and PA measurements in clinical practice. The chronobiological specification of reference values for PRA and PA is of valuable importance since the assessment of PRA and PA circadian rhythmicity has a diagnostic interest for a certain type of clinical disorder. It should be noted that several studies have described circannual variations for renin and aldosterone. The next step in the optimation of laboratory time-qualified reference values is the assessment of changes induced by the deterministic factors on a circannual domain.

Toward a chronophysiology of circulating aldosterone

The physiology of aldosterone secretion has been prominently investigated by homeostatic studies on the levels of the steroid in plasma and/or urine. Aldosterone secretion is, however, arranged in a rhythmic fashion along the 24-hr cycle. The dynamics of aldosterone should thus be reanalyzed chronobiologically in order to gain further insight into the physiology of the hormone. Such a revisitation has been performed in the present study on four groups of clinically healthy volunteers categorized according to sex and age. Aldosterone has been assayed in the plasma of systemic venous blood six times a day (0600, 0800, 1200, 1800, 2000, 0000) in different conditions of physical activity and sodium intake. Time-qualified data have been analyzed by the single-cosinor method and then summarized by the population-mean cosinor procedure to quantify the circadian rhythms in their properties (mesor, amplitude, acrophase). Differences in rhythmometric parameters have been tested by a multivariate analysis for vectorial units. (Hotelling's T 2 test). Cosinor analysis indicates that the dynamics of circulating aldosterone substantially changes in relation to posture. The habit of having a routine of diurnal activity leads the circadian rhythm of aldosterone to delay its acrophase from morning to afternoon. The postural shift of acrophase is essentially accompanied by an elevation in the 24-hr mean level. The restriction of salt intake is associated with an increase in mesor; the temporal localization of the circadian crest shows, however, a very high stability. Sex is not characterized by significant differences in the 24-hr patterns of aldosterone in the sense that young males and females show substantially identical time-qualified curves and circadian parameters. Increasing age until the seventh decade in life is responsible for changes mainly in 24-hr mean levels with a slight modification in amplitude. Such a chronophysiology for circulating aldosterone related to the motor-rest schedule, sodium intake, sex, and age, is of interest not only to heuristic but also to practical approaches in clinical medicine.

Multiple Periodicities in the Circadian System of Unicellular Algae

Abstract Three periodicities in the circadian range are observed when measuring circadian parameters of unicellular organisms in long running experiments (more than 15 days). This is demonstrated for different organisms (Chlamydomonas, Euglena, Chlorella) and different parameters (auto­ kinesis, extracellular pH, CO2- and O2-partial pressure). Having excluded analytical and experimental artefacts (i.e. filter leakage and subpopulation effects), the multiple periodicities have to be interpreted in a physiological model. The three periodicities always exhibit two common features: The locations of the side peaks are symmetrical to the middle peak and their energy contribution is always the same. We therefore favour the model of multiplicative coupling between the circadian oscillator and a low frequency oscillator modulating the amplitude of the circadian rhythm. Since the low frequency rhythm is not correlated to any exogenously running periodicity of the experimental surroundings, it is considered as generated by an endogenous oscillator. This shows the existence of different biological long time oscillators in one single cell and contradicts the so-called master-clock hypothesis stating that one cell has only one clock related oscillator.

Circadian rhythms and temporal structure of the susceptibility to tonic-clonic seizures in the mouse

A circadian paradigm of susceptibility to tonic-clonic convulsions was established for two strains of mice. This research dealt with rhythmometric methods for estimating the main circadian parameters characterizing the temporal structure of these behavioral phenomena. Such experiments provided a quantitative approach for studying some neurobiological mechanisms regulating the seizure susceptibility.

Inactive renin of human plasma is a circadian variable

The present work has been devoted to examine the existence of a circadian rhythmicity for the circulating inactive renin as compared to its enzymologically active form. Studies have been carried out in 10 normotensives and 11 essential hypertensives (II WHO) who gave systemic venous blood at 0600, 0800, 1200, 1800, 2000, and 0000 hr on a routine of diurnal activity (0700–2300 hr)-nocturnal rest (2300-0700 hr), and on a usual intake of sodium (120–140mEq/24 hr) and potassium (50–70mEq/24 hr). Time-qualified data of inactive renin (assayed as prorenin, the cryoactivable form), and active renin (assayed as plasma renin activity, PRA) were fitted by a 24-hr cosine function to impute the circadian characteristics of possible rhythms. The Hotelling T 2 test was used to discern statistically significant differences in vectorial units of circadian parameters. Results showed that prorenin fluctuates in the plasma according to a circadian rhythm in normotensives as well as hypertensives. Chronobiologically, prorenin cycle is characterized by circadian properties consistently similar to those of the PRA rhythm. Moreover, prorenin was seen to be rhythmometrically arranged in a circadian periodism even in patients with essential hypertension. No statistically significant contrast has been found between clinically healthy subjects and essential hypertensives with respect to the rhythms of prorenin and PRA. Results support the conclusions that: (1) inactive renin is a component (of the renin-angiotensin system) which can be included in the map of biorhythmic variables of human plasma; (2) the rhythms of inactive and active renins are closely correlated; (3) the rhythm of inactive renin is substantially normal in essential hypertensive patients showing a circadian cyclicity for the enzymologically active form of renin.

Effect of fasting and somatostatin administration on circadian rhythms of jejunal cell renewal and plasma gastrin level in rats.

An antitrophic effect of somatostatin on intestinal cell renewal could be expected as somatostatin inhibited the release of gastrin and growth hormone, both trophic hormones of the intestine. A chronopharmacological dependence, i.e. a change in the effects as a function of the schedule of injection, was suspected as jejunal cell renewal was characterized by a circadian rhythm of DNA synthesis and mitosis. This study was undertaken to control the inhibiting effect of somatostatin on jejunal cell renewal, to test the pharmacological dependence of the action of somatostatin and whether the antitrophic effect could be related with any change in gastrin secretion. The cell renewal observed by DNA labeling, the count of mitoses on jejunal autohistoradiographies and the plasma gastrin level, determined by radioimmunoassay, were documented in male Wistar rats fasted for 12 h, sacrificed every 4 h from 30 min to 24 ½ h after a single intraperitoneal injection of 40 μg/100 g of somatostatin (cyclic form; Serono). Somatostatin was injected either at 10.30 h near the minimum of DNA labeling and mitosis, or at 22.30 h near the peak of these variables. When injected in the morning, somatostatin decreased the mean number of labeled cells and mitotic figures and disturbed the rhythm. When injected in the evening, somatostatin suppressed the circadian variation of cell renewal without changing the mean level of the variables. Circadian parameters of the plasma gastrin level were modified by the fasting schedule, the mean level was lower and the acrophase was delayed when fasting began during the night but somatostatin administration did not change the gastrin level and its circadian variation. The inhibiting effect of somatostatin on cell renewal was characterized by a chronopharmacological dependence, and was not related to a decrease of the plasma level of gastrin.

Temporary desynchronization among circadian rhythms with lateral fornix ablation

Lateral or medial fornix suction ablations were performed on adult male rats in order to selectively ablate or leave intact, respectively, fibers which terminate in the region of the suprachiasmatic nucleus and hypophysiotropic area of the hypothalamus. Plasma adrenal corticosteroid secretion, locomotor activity, body temperature, and food and water intake were recorded at 4 h intervals over a period of 48 h in individual animals 7-10 days postoperatively. Lateral fornix ablation specifically disrupted adrenal corticosteroid periodicity. A least-squares spectrum analysis of the data indicated that corticosteroid may be under ultradian control after this lesion. All animals, regardless of treatment, exhibited normal circadian locomotor activity patterns. Aberrations in feeding, drinking and body temperature rhythms were occasionally observed. This represents a temporary dissociation between the rhythmic expression of corticosteroid secretion and activity, temperature, feeding and drinking. The evidence presented lends support to the multi-oscillator theory of circadian organization, and suggests that the anteroventral subiculum, via the medial corticohypothalamic tract, is important in the regulation of some, but not all, circadian parameters. In addition to the observations on the rhythmicity of locomotor activity, the extent to which the animals are active is also significantly different between groups; ie., the hyperactivity of fornix-transected animals previously reported by others was found to be associated with lateral and not medial fornix ablation.

Distribution of REM Sleep in Entrained 24 Hour and Free-Running Sleep-Wake Cycles

One hundred thirty sleep episodes of 6 subjects, living on a natural 24 hr day, were compared with 116 sleep times of the same subjects living isolated from external time cues. The polygraphic sleep recordings were analyzed for the distribution of REM sleep under both conditions. Additionally, the relationship between body temperature and REM sleep was analyzed by comparing sleep episodes in which the temperature minimum occurred early in the sleep episode with those in which there was a late temperature minimum. The results show that there is more REM sleep in the beginning of sleep in sleep episodes of free-running rhythms as compared to sleep episodes of entrained 24 hr rhythms. This higher amount of REM sleep is due to a longer first REM episode and shorter first NREM episodes. The comparison of the sleep episodes that differ in the position of the temperature minimum shows similar differences, i.e., more REM sleep in the beginning of sleep episodes in which the temperature minimum occurs earlier as compared to episodes in which the temperature minimum occurs later. It was hypothesized that the amount of REM sleep depends on the phase relationship between sleep and the circadian temperature cycle. From this point of view, the difference in the distribution of REM sleep in the entrained 24 hr rhythm, on the one hand, and the free-running rhythm, on the other hand, can be explained by the different courses of body temperature during sleep. That only the first REM episode is influenced by circadian parameters may indicate an exceptional role for this REM episode in contrast to the following episodes.

Circadian activity rhythms of the pig-tailed macaque, Macaca nemestrina, under constant illumination.

Locomotor activity was recorded in singly caged pig-tailed macaques Macaca nemestrina in constant conditions with intensities of illumination varying between 0.003 lux and 100 lux. Each animal was kept in at least 5 different conditions for 2-3 weeks each. Three quantities of the circadian rhythm: the period, the duration of activity as opposed to rest, and the amount of activity per period, could be shown to be positively correlated with light intensity. As in 6 other diurnal primate species, these findings contradict the so-called circadian rule according to which opposite correlations should exist between the circadian parameters and light intensity in diurnal and in nocturnal species of animals.

Circadian rhythms of rat locomotor activity after lesions of the midbrain raphe nuclei

Electrolytic lesions that damaged the midbrain raphe nuclei of albino rats increased the proportion of daily wheel-running behavior that occurred during the light phase of a LD 12∶:12 illumination cycle. In constant dim illumination, rats with midbrain raphe lesions generated free-running circadian locomotor rhythms with periods comparable to those of control animals. This suggests that the serotonergic projection from the midbrain raphe nuclei to the suprachiasmatic nuclei (SCN) of the hypothalamus is not critical to the generation and/or integration of circadian periodicity. Because of the disruptive effects of the lesions on activity, including the loss of a well-defined phase reference point, it was not possible to exclude more subtle effects of the raphe system on various circadian parameters. Nevertheless, the data are consistent with the hypothesis that the SCN are part of an autonomous circadian oscillatory system that does not depend on afferent input from the raphe nuclei.