Behavioral and Morphological Studies of Fetal Neural Transplants into SCN-Lesioned Rats

We have studied the effects of fetal neuronal grafts on the temporal pattern of drinking behavior of suprachiasmatic nuclei (SCN)-lesioned adult rats. Additionally, in an independent set of animals, the immunohistochemical staining for vasopressin, vasoactive intestinal polypeptide, and neuropeptide Y and the retinal connections to the hypothalamus were studied. The behavioral experiments indicate that anterior hypothalamic transplants induced reorganization of the temporal pattern of drinking behavior when placed in the third ventricle of adult hosts bearing complete SCN lesions, but not when placed in a cavity in the occipital cortex. Such rhythmicity persists only when the animals were recorded under constant darkness but not under constant light, indicating that the restored rhythmicity was generated endogenously but that the oscillator was extremely sensitive to light. Fetal occipital cortex induced reorganization of the temporal pattern of previously arrhythmic hosts, but it disappeared when the animals were recorded under constant light or constant darkness. It is clear that this rhythmicity was exogenous. In contrast to the cortical transplants, the hypothalamic transplants showed a morphological organization similar to that found in the normal hypothalamus regardless of their placement in the host brain. From these observations it is concluded that development of neocortex is more affected by environmental factors than that of the hypothalamus. Both hypothalamic and cortical transplants induced sprouting of retinal fibers into the anterior hypothalamus and the grafted tissue. It is possible that such fibers could be the neuroanatomical substrate by which rhythmicity is induced by cortical tissue.     

TIME-OF-DAY EFFECTS ON THE INTERNAL SIMULATION OF MOTOR ACTIONS: PSYCHOPHYSICAL EVIDENCE FROM POINTING MOVEMENTS WITH THE DOMINANT AND NON-DOMINANT ARM

It is well known that circadian rhythms modulate human physiology and behavior at various levels. However, chronobiological data concerning mental and sensorimotor states of motor actions are still lacking in the literature. In the present study, we examined the effects of time-of-day on two important aspects of the human motor behavior: prediction and laterality. Motor prediction was experimentally investigated by means of imagined movements and laterality by comparing the difference in temporal performance between right and left arm movements. Ten healthy participants had to actually perform or to imagine performing arm-pointing movements between two targets at different hours of the day (i.e., 08:00, 11:00, 14:00, 17:00, 20:00, and 23:00?h). Executed and imagined movements were accomplished with both the right and left arm. We found that both imagined and executed arm pointing movements significantly fluctuated through the day. Furthermore, the accuracy of motor prediction, investigated by the temporal discrepancy between executed and imagined movements, was significantly better in the afternoon (i.e., 14:00, 17:00, and 20:00?h) than morning (08:00 and 11:00?h) and evening (23:00?h). Our results also revealed that laterality was not stable throughout the day. Indeed, the smallest temporal differences between the two arms appeared at 08:00 and 23:00?h, whereas the largest ones occurred at the end of the morning (11:00?h). The daily variation of motor imagery may suggest that internal predictive models are flexible entities that are continuously updated throughout the day. Likewise, the variations in temporal performance between the right and the left arm during the day may indicate a relative independence of the two body sides in terms of circadian rhythms. In general, our findings suggest that cognitive (i.e., mental imagery) and motor (i.e., laterality) states of human behavior are modulated by circadian rhythms. (Author correspondence: charalambos.papaxanthis@u-bourgogne.fr)     

Modulation of mammalian circadian rhythms by tumor necrosis factor-α

Systemic low doses of the endotoxin lipopolysaccharide (LPS, 100?µg/kg) administered during the early night induce phase-delays of locomotor activity rhythms in mice. Our aim was to evaluate the role of tumor necrosis factor (Tnf)-alpha and its receptor 1/p55 (Tnfr1) in the modulation of LPS-induced circadian effects on the suprachiasmatic nucleus (SCN). We observed that Tnfr1-defective mice (Tnfr1 KO), although exhibiting similar circadian behavior and light response to that of control mice, did not show LPS-induced phase-delays of locomotor activity rhythms, nor LPS-induced cFos and Per2 expression in the SCN and Per1 expression in the paraventricular hypothalamic nucleus (PVN) as compared to wild-type (WT) mice. We also analyzed Tnfr1 expression in the SCN of WT mice, peaking during the early night, when LPS has a circadian effect. Peripheral inoculation of LPS induced an increase in cytokine/chemokine levels (Tnf, Il-6 and Ccl2) in the SCN and in the PVN. In conclusion, in this study, we show that LPS-induced circadian responses are mediated by Tnf. Our results also suggest that this cytokine stimulates the SCN after LPS peripheral inoculation; and the time-related effect of LPS (i.e. phase shifts elicited only at early night) might depend on the increased levels of Tnfr1 expression. We also confirmed that LPS modulates clock gene expression in the SCN and PVN in WT but not in Tnfr1 KO mice.

Highlights: We demonstrate a fundamental role for Tnf and its receptor in circadian modulation by immune stimuli at the level of the SCN biological clock.     

The Daily Melatonin Pattern in Djungarian Hamsters Depends on the Circadian Phenotype

Djungarian hamsters (Phodopus sungorus) bred at the Institute of Halle reveal three different circadian phenotypes. The wild type (WT) shows normal locomotor activity patterns, whereas in hamsters of the DAO (delayed activity onset) type, the activity onset is continuously delayed. Since the activity offset in those hamsters remains coupled to “light-on,” the activity time becomes compressed. Hamsters of the AR (arrhythmic) type are episodically active throughout the 24?h. Previous studies showed that a disturbed interaction of the circadian system with the light-dark (LD) cycle contributes to the phenomenon observed in DAO hamsters. To gain better insight into the underlying mechanisms, the authors investigated the daily melatonin rhythm, as it is a reliable marker of the circadian clock. Hamsters were kept individually under standardized laboratory conditions (LD 14:10, T?=?22°C?±?2°C, food and water ad libitum). WT, DAO (with exactly 5?h delay of activity onset), and AR hamsters were used for pineal melatonin and urinary 6-sulfatoxymelatonin (aMT6s) measurement. Pineal melatonin content was determined at 3 time points: 4?h after “light-off” [D?+?4], 1?h before “light-on” [L???1], and 1?h after “light-on” [L?+?1]). The 24-h profile of melatonin secretion was investigated by transferring the animals to metabolic cages for 27?h to collect urine at 3-h intervals for aMT6s analysis. WT hamsters showed high pineal melatonin content during the dark time (D?+?4, L???1), which significantly decreased at the beginning of the light period (L?+?1). In contrast, DAO hamsters displayed low melatonin levels during the part of the dark period when animals were still resting (D?+?4). At the end of the dark period (L???1), melatonin content increased significantly and declined again when light was switched on (L?+?1). AR hamsters showed low melatonin levels, comparable to daytime values, at all 3 time points. The results were confirmed by aMT6s data. WT hamsters showed a marked circadian pattern of aMT6s excretion. The concentration started to increase 3?h after “light-off” and reached daytime values 5?h after “light-on.” In DAO hamsters, in contrast, aMT6s excretion started about 6?h later and reached significantly lower levels compared to WT hamsters. In AR animals, aMT6s excretion was low at all times. The results clearly indicate the rhythm of melatonin secretion in DAO hamsters is delayed in accord with their delayed activity onset, whereas AR hamsters display no melatonin rhythm at all. Since the regulatory pathways for the rhythms of locomotor activity and melatonin synthesis (which are downstream from the suprachiasmatic nucleus [SCN]) are different but obviously convey the same signal, we conclude that the origin of the phenomenon observed in DAO hamsters must be located upstream of the SCN, or in the SCN itself. (Author correspondence: weinert@zoologie.uni-halle.de)     

Circadian Rhythms in 6-Sulphatoxymelatonin and Nocturnal Sleep in Blind Children

This article describes the relationship between melatonin secretion and sleep quality and subjective complaints about sleep in totally blind children. Eleven boarding-school children (mean age 15.2 years) participated. The major urinary melatonin metabolite 6-sulphatoxymelatonin (aMT6s) was measured five times a day for 48 h. Sleep-wake cycles were recorded by continuous actigraphic recordings during the same time period. Results showed that delayed secretory peaks in aMT6s were significantly associated with disturbed nocturnal sleep and with complaints about morning fatigue.     

CARDIOVASCULAR RHYTHMS AND CARDIAC BAROREFLEX SENSITIVITY IN AT1A RECEPTOR GAIN-OF-FUNCTION MUTANT MICE

A mutant mouse expressing a gain-of-function of the AT_1A angiotensin II receptor was engineered to study the consequences of a constitutive activation of this receptor on blood pressure (BP). Cardiovascular rhythms and spontaneous cardiac baroreflex sensitivity (BRS) were evaluated using telemetric BP recordings of five transgenic (AT_1AMUT) and five wild (AT_1AWT) mice. The circadian rhythms were described with the Chronos-Fit program. The gain of the transfer function between systolic BP (SBP) and pulse intervals used to estimate the spontaneous BRS (ms/mmHg) was calculated in the low frequency (0.15–0.60?Hz) band. Transgenic AT_1AMUT exhibited higher BP and heart rate (HR) levels compared to controls (SBP AT_1AMUT 134.6?±?5.9?mmHg vs. AT_1AWT 110.5?±?5.9; p?<?0.05; HR AT_1AMUT 531.0?±?14.9 vs. AT_1AWT 454.8?±?5.4 beats/min; p?=?0.001). Spontaneous BRS was diminished in transgenic mice (AT_1AMUT 1.23?±?0.17?ms/mmHg vs. AT_1AWT 1.91?±?0.18?ms/mmHg; p?<?0.05). Motor activity did not differ between groups. These variables exhibited circadian changes, and the differences between the strains were maintained throughout the cycle. The highest values for BP, HR, and locomotor activity were observed at night. Spontaneous BRS varied in the opposite direction, with the lowest gain estimated when BP and HR were elevated (i.e., at night, when the animals were active). It is likely the BP elevation of the mutant mice results from the amplification of the effects of AngII at different sites. Future studies are necessary to explore whether AT_1A receptor activation at the central nervous system level effectively contributed to the observed differences. (Author correspondence: jean-luc.elghozi@nck.aphp.fr)     

Sources of Thought Two 19th-century Chronobiologists: Thomas Laycock and Edward Smith

This article describes the works of two 19th-century chronobiologists. Thomas Laycock (1812-1876), who held the Chair of Medicine in Edinburgh from 1855-1876, published a series of seven articles in Lancet, all dedicated to periodicities in “vital phenomena.” Laycock considered the understanding of periodicities essential for the advancement of the treatment of diseases. Edward Smith (1818-1874) was a pioneer in experimental chronobiology. In his 1861 book entitled: Health and disease as influenced by daily, seasonal and other cyclical changes in the human, Smith summarized a large number of experiments in which he investigated the occurrence of periodicities in pulse rate, urine flow, urea excretion, and respiration. From his experimental results and those of others, Smith drew practical conclusions regarding patients' care, the timing of drug administration, and the design of night work.     

The Tick-Tock of Language: Is Language Processing Sensitive to Circadian Rhythmicity and Elevated Sleep Pressure?

The master circadian pacemaker emits signals that trigger organ-specific oscillators and, therefore, constitutes a basic biological process that enables organisms to anticipate daily environmental changes by adjusting behavior, physiology, and gene regulation. Although circadian rhythms are well characterized on a physiological level, little is known about circadian modulations of higher cognitive functions. Thus, we investigated circadian repercussions on language performance at the level of minimal syntactic processing by means of German noun phrases in ten young healthy men under the unmasking conditions of a 40 h constant-routine protocol. Language performance for both congruent and incongruent noun phrases displayed a clear diurnal rhythm with a peak performance decrement during the biological night. The nadirs, however, differed such that worst syntactic processing of incongruent noun phrases occurred 3 h earlier (07:00 h) than that of congruent noun phrases (10:00 h). Our results indicate that language performance displays an internally generated circadian rhythmicity with optimal time for parsing language between 3 to 6 h after the habitual wake time, which usually corresponds to 10:00–13:00 h. These results may have important ramifications for establishing optimal times for shiftwork changes or testing linguistically impaired people.     

Circadian Rhythms in Human Body Composition

The study investigates how the human body composition (BC) changes as a function of the day-night cycle. The BC was investigated using bioelec-trical impedance analysis (BIA) of 10 clinically healthy subjects (CHS), mon-itored in supine position (readings at 2-h intervals), avoiding mealtimes, di-etary abuses, and bladder and intestinal retention. Time series data were analyzed for their temporal characteristics and circadian rhythm (CR). Ail the variables of BC (lean body mass, fat body mass, body cell mass, total body water, intracellular and extracellular body water, sodium and potassium exchangeable pool) showed a within-day variability with nighttime crests. Such an oscillatory synchronism corroborates the hypothesis that the rest time plays a fundamental role, via its anabolic effects, in conferring the noc-turnal phase to the CR of the human BC.     

Temporal Morphology and Cap Formation in Acetabularia-Ii. Effects of Morphactin and Auxin

Afin d'apporter des arguments supplémentaires à?hypothese selon laquelle les rhythms circadiens sont impliqués dans la morphogénèse, des expériences ont été réalisées de manière a mettre en évidence la relation éventuelle de dépendance entre le moment (dans le cycle de 24 heures) où commence le traitement et ? effet (1) de la morphactine, un inhibiteur compétitif de ?'auxine et (2) de ? auxine (IAA).

Les résultats ont montré que (1) ? effet inhibiteur de la morphactine varie considérablement selon le moment auquel le traitement a commencé, plusieurs semaines avant ? expression morphogénétique; (2) le maximum d'inhibition change avec le stade de développement et le degré d'inhibition diminue avec le temps; (3) ?'IAA accélerè la formation du chapeau lorsque le traitement a commencé pendant la phase de croissance rapide des algues; ? effet depend du moment (du cycle de 24 heures) auquel il a commencé son effet diminue au cours du temps; (4) lorsque le traitement a commencé avec des algues plus petites que les precédéntes, il exerce un effet transitoirement inhibiteur qui dépend du moment du cycle de 24 heures auquel il a commence; (5) les fragments anucléés aussi répondent différentiellement à un traitement à ? IAA commencé a différents moments du cycle de 24 heures; ? effet est plus net quand des mRNA ont été accumulés; (6) ? effet de ? IAA n'est pas cumulé a celui d'une perturbation du cycle L-D; celui de la morphactine n'est pas modifyé ou est légérement amélioré par une perturbation du cycle L-D.

Mots clefs–Acetabularia, rhymes circadiens, morphogénèse, auxine, morphactine.

In order to support the hypothesis that circadian rhythms are implicated in cap formation, experiments were undertaken on the possible time-dependency of the effects of (a) a competitive inhibitor of auxins, morphactin and (b) of auxin (IAA). It was found that: (i) the inhibitory effect of morphactin varies dramatically with the time at which the several weeks' treatment was first begun; (ii) the maximum inhibition varies with development and decreases with time; (iii) IAA accelerates cap formation when the algae are submitted to IAA during the exponential growth phase; the effect is time dependent and decreases with time; (iv) IAA first applied on smaller algae has a transient inhibitory effect which is time dependent; (v) anucleate fragments also respond differentially to an IAA treatment begun at several times in the 24-hr cycle, most clearly when newly formed mRNA have been accumulated and (vi) the effect of iAA is not cumulative with that of a LD shift; that of morphactin is not, or only slightly, improved by a LD shift.