Ultradian rhythmicity (circa 90 min) in physiologic processes ‐ evidence for multioscillatory phenomena

Abstract

Data accumulated in recent years have shown the existence of multiple about 90 min ultradian rhythms in gastric motility, urine flow and osmolality and physiologic indices of arousal. While these data support Kleitman's hypothesis that the REM‐NONREM sleep cycles are only fragments of a 24‐h rhythm (Basic Rest‐Activity Cycle) which is manifested in wakefulness in recurrent fluctuations in arousal, it further indicates that both the sleep and the waking rhythms are part of a more complex multioscillatory system with a dominant periodicity centered at 90 min.     

Ultradian Rhythms in Albino Rats during the Light Phase

The aim of this work is to investigate the ultradian rhythms of the rest-activity cycle of albino rats during the light phase. Occurrence (time-of-day) of 11 behavioral items was registered in a portable computer (HP95-LX). Each animal was visually and continuously observed for a interval of 2 hr, 3 hr after lights-on. Spectral analysis showed rest-activity cycles with statistically significant periods of 1 hr and also in the range of 10 to 20 min. As these rats were synchronized by a light-dark cycle (LD 12:12, 350:1 lux), these results suggest that ultradian rhythms are components of the circadian rest-activity cycle. The ultradian temporal organization of rest and activity behavioral items obtained by visual inspection is similar to the cycle of REM-NREM sleep stages obtained by EEG and described earlier in albino rats.     

Ultradian Rhythms in Albino Rats during the Light Phase

The aim of this work is to investigate the ultradian rhythms of the rest-activity cycle of albino rats during the light phase. Occurrence (time-of-day) of 11 behavioral items was registered in a portable computer (HP95-LX). Each animal was visually and continuously observed for a interval of 2 hr, 3 hr after lights-on. Spectral analysis showed rest-activity cycles with statistically significant periods of 1 hr and also in the range of 10 to 20 min. As these rats were synchronized by a light-dark cycle (LD 12:12, 350:1 lux), these results suggest that ultradian rhythms are components of the circadian rest-activity cycle. The ultradian temporal organization of rest and activity behavioral items obtained by visual inspection is similar to the cycle of REM-NREM sleep stages obtained by EEG and described earlier in albino rats.     

Daily rhythms of glycogen synthetase and phosphorylase activities in rat liver: Influences of food and light

In rats fed during the night time (from 8 p.m. to 8 a.m.) the activities of liver glycogen synthetase $\text{I}$ and phosphorylase $\text{a}$ varied rhythmically during a 24 hour period. There was an inverse relationship between their levels; the level of synthetase $\text{I}$ rose to a maximum at around 6 a.m. and that of phosphorylase $\text{a}$ attained the peak value at around 6 p.m. Eye enucleation of rats did not affect significantly the daily rhythms of the enzymes. However, when food was offered only during the day time, the phases of both enzyme rhythms were shifted by about 12 hours. On starvation for 24 hours, the glycogen level was reduced almost to nil, but the daily rhythms of the enzymes were retained. It is thus very likely that the daily variations of the enzyme activities are not merely a passive effect of food intake, and that food can be a synchronizer or zeitgeber which sets up the characteristic rhythms of glycogen metabolism in the liver.     

Effects of suprachiasmatic nuclei lesions on circadian and ultradian rhythms in body temperature in ocular enucleated rats

Abstract

To test the hypothesis that an oscillator located outside the suprachiasmatic nuclei (SCN) controls the circadian rhythm of body temperature, we conducted a study with 14 blinded rats, 10 of which receiving a SCN lesion. Body temperature was automatically and continuously recorded for about one month by intraperitoneal radio transmitters. Food intake, drinking and locomotor activity were also recorded. Periodograms revealed that 3 rats with histologically verified total bilateral SCN lesions did not exhibit any circadian rhythmicity. The 7 other rats appeared to have partial lesions. They showed shortening of period and severe amplitude reduction in all functions. Thus, no support was found for the hypothesis of a separate circadian ‘temperature oscillator’ located outside the SCN. Nevertheless, after large partial lesions body temperature showed more persistency than some of the other behavioral rhythms.

Ultradian rhythms in temperature persisted after partial and total lesions. Other functions showed parallel ultradian rhythms. In intact rats the ultradian peaks were restricted predominantly to the subjective night. After total lesions these peaks became more or less homogeneously distributed in time but more heterogeneously after partial lesions. So the SCN plays a role in the temporal structure of ultradian rhythms but does not generate them. Non‐24‐hour actograms showed instabilities of period and phase of ultradian rhythms. Intact and lesioned rats were similar with respect to the mean (about 3.5 hrs) and standard deviation (about 1.5 hrs) of ultradian periods in temperature. These features indicate that a mechanism outside the SCN is underlying ultradian rhythmicity, capable of generating short‐term oscillations. Two approaches, homeostatic sleep‐wake relaxation oscillations and multiple circadian oscillators, are discussed.     

III. Possible mechanisms involved in the presynaptic cholinotoxicity due to ethylcholine aziridinium (AF64A) invivo

AF64A is a toxin which can diminish irreversibly cholinergic transmission $\text{in}$$\text{vivo}$ (1, 2). Disruption of neurotransmitter function $\text{in}$$\text{vivo}$ is specific to the cholinergic system when AF64A is administered in nanomolar quantities (3, 4). The mechanisms involved appear to be mediated presynaptically (2). The neurochemical and behavioral consequences of AF64A administration are reminiscent of similar measures in patients with Alzheimer's disease (5,6). Consequently, we have suggested tentatively that the AF64A treated animal may be explored as a potential animal model of this debilitating disease state (7). In this report we provide a brief overview of our recent findings using this compound $\text{in}$$\text{vivo}$, attempt to correlate these findings with those of others with similar aziridinium agents $\text{in}$$\text{vitro}$, and propose a possible mechanism of action of AF64A $\text{in}$$\text{vivo}$, based on recent observations made in our laboratories.     

Chronobiology in mammalian health

Circadian rhythms are daily cycles of physiology and behavior that are driven by an endogenous oscillator with a period of approximately one day. In mammals, the hypothalamic suprachiasmatic nuclei are our principal circadian oscillators which influences peripheral tissue clocks via endocrine, autonomic and behavioral cues, and other brain regions and most peripheral tissues contain circadian clocks as well. The circadian molecular machinery comprises a group of circadian genes, namely Clock, Bmal1, Per1, Per2, Per3, Cry1 and Cry2. These circadian genes drive endogenous oscillations which promote rhythmically expression of downstream genes and thereby physiological and behavioral processes. Disruptions in circadian homeostasis have pronounced impact on physiological functioning, overall health and disease susceptibility. This review introduces the general profile of circadian gene expression and tissue-specific circadian regulation, highlights the connection between the circadian rhythms and physiological processes, and discusses the role of circadian rhythms in human disease.     

Ultradian rhythm unmasked in the Pdf clock mutant of Drosophila

A diverse range of organisms shows physiological and behavioural rhythms with various periods. Extensive studies have been performed to elucidate the molecular mechanisms of circadian rhythms with an approximately 24 h period in both Drosophila and mammals, while less attention has been paid to ultradian rhythms with shorter periods. We used a video-tracking method to monitor the movement of single flies, and clear ultradian rhythms were detected in the locomotor behaviour of wild type and clock mutant flies kept under constant dark conditions. In particular, the Pigment-dispersing factor mutant (Pdf ⁰¹ ) demonstrated a precise and robust ultradian rhythmicity, which was not temperature compensated. Our results suggest that Drosophila has an endogenous ultradian oscillator that is masked by circadian rhythmic behaviours.     

Ultradian, circahoral and circadian structures in endothermic vertebrates and humans

1. For more than 30 years many studies have been carried out concerning rhythms with periods approaching 24 hr (circadian rhythms). 2. The latter have been demonstrated as resulting from environmental 24 hr synchronizers (zeitgebers), but they usually persist in the absence of a 24 hr synchronization, which proves their endogenous nature. 3. Biological rhythms with periods less than 20 hr (ultradian rhythms) and particularly those approaching 1 hr (circahoral rhythms) have been determined: for motility, rest-activity, sleep phases, endocrine secretions and other physiological functions. 4. These ultradian and circahoral rhythms have been found in rodents, birds, monkeys and humans. 5. Existing at all stages of ontogeny, they have been proved to be endogenous and species and strain specific. 6. As these ultradian rhythms can be influenced by environmental factors and sometimes by circadian rhythms they are not truly periodic, so therefore cannot be computed by the usual processes of mathematical time analysis.     

Characterization and Modeling of Intermittent Locomotor Dynamics in Clock Gene-Deficient Mice

The scale-invariant and intermittent dynamics of animal behavior are attracting scientific interest. Recent findings concerning the statistical laws of behavioral organization shared between healthy humans and wild-type mice (WT) and their alterations in human depression patients and circadian clock gene (Period 2; Per2) mutant mice indicate that clock genes play functional roles in intermittent, ultradian locomotor dynamics. They also claim the clinical and biological importance of the laws as objective biobehavioral measures or endophenotypes for psychiatric disorders. In this study, to elucidate the roles of breakdown of the broader circadian regulatory circuit in intermittent behavioral dynamics, we studied the statistical properties and rhythmicity of locomotor activity in Per2 mutants and mice deficient in other clock genes (Bmal1, Clock). We performed wavelet analysis to examine circadian and ultradian rhythms and estimated the cumulative distributions of resting period durations during which locomotor activity levels are continuously lower than a predefined threshold value. The wavelet analysis revealed significant amplification of ultradian rhythms in the BMAL1-deficient mice, and instability in the Per2 mutants. The resting period distributions followed a power-law form in all mice. While the distributions for the BMAL1-deficient and Clock mutant mice were almost identical to those for the WT mice, with no significant differences in their parameter (power-law scaling exponent), only the Per2 mutant mice showed consistently and significantly lower values of the scaling exponent, indicating the increased intermittency in ultradian locomotor dynamics. Furthermore, based on a stochastic priority queuing model, we explained the power-law nature of resting period distributions, as well as its alterations shared with human depressive patients and Per2 mutant mice. Our findings lead to the development of a novel mathematical model for abnormal behaviors in psychiatric disorders.     

Neurobiology of tetrahydro-beta-carbolines

Tetrahydro-β-carbolines (THβC's) are tricyclic compounds structurally related to the indoleamines. Recent studies have reported the $\text{in}$$\text{vitro}$ and $\text{in}$$\text{vivo}$ formation of these compounds in brain and other tissues. This information and other data indicating that THβC's interact relatively specifically with various aspects of the serotonergic neurotransmitter system has suggested that THβC's may serve as endogenous neuromodulators of neurotransmitters. Evidence for the formation of these compounds as well as their neurochemical, neuroendocrinological, and behavioral effects is described in this review.     

Association of nucleosidediphosphate kinase with microtubules.

A nucleosidediphosphate kinase activity (EC 2.7.4.6) which phosphorylates GDP to GTP is present in bovine brain microtubule protein prepared by cycles of assembly-disassembly. This activity persists through 5 cycles of assembly-disassembly and sediments with microtubules in sucrose density gradients, but is not associated with the tubulin dimer. It is proposed that the kinase is an integral part of the microtubule and is therefore a microtubule associated protein (MAP). Several isozymes of nucleosidediphosphate kinase exist in our preparations with a pI 7.6 form predominant. It may be speculated that this enzyme affects tubulin assembly $\text{in vivo}$ by modulating the $\text{GTP}\text{GDP}$ ratio in the microtubule environment.     

Effect of ascorbic acid on neurochemical, behavioral, and physiological systems mediated by catecholamines

Ascorbic acid, at concentrations below that normally present in the brain, inhibited the dopamine-sensitive adenylate cyclase $\text{in}$$\text{vitro}$. Ascorbate had no effect on the norepinephrine-sensitive adenylate cyclase. To study the $\text{in}$$\text{vivo}$ effect of ascorbic acid on central dopaminergic systems, mice (C57 B1/6J) were injected with pharmacological doses (2 g/kg) of ascorbate, which produced a significant elevation in brain ascorbate concentration. Injecting the mice with ascorbate (2 g/kg) blocked the amphetamine-induced (15 mg/kg) increase in stereotype behavior which has been reported to be mediated by dopaminergic neural systems. Ascorbate had no effect on the amphetamine-induced locomotor activity thought to be mediated by norepinephrine systems. Ascorbate (1 g/kg) attenuated apmorphine-induced hypothermia in this same strain of mice. This demonstrates the specific neurochemical, physiological, and behavioral alterations in dopaminergic systems produced by ascorbic acid and suggests possible therapeutic uses for ascorbate in conditions involving functional dopamine excess.     

Ultradian rhythms in renal excretion in dogs

Urine flow, urinary osmolality, concentrations of sodium and potassium were measured every 10 min for 24 hours in 6 female dogs, whose sleep-wake stages were monitored electrographically. Experiments were conducted under hydration and progressive dehydration conditions. Visual examination and spectral analysis revealed significant diurnal ultradian rhythms of about 200 min/cycle in urine flow, which were out of phase with similar rhythms in osmolality in different hydratory conditions. Diurnal rhythms with similar characteristics were found in urinary potassium only in the hydration condition. Sodium excretions did not show consistent rhythmic patterns. No consistent rhythms were found in nocturnal urine parameters in different hydratory conditions. The variations in renal activities were related to the dogs' diurnal ultradian sleep-wake cycle, urine volume increased and osmolality decreased during diurnal waking episodes, and conversely volume decreased and osmolality increased during the diurnal sleep episodes.     

Cytochrome P450cam catalyzed epoxidation of dehydrocamphor

In addition to the normal 5-$\text{exo}$-hydroxylation of camphor, bacterial cytochrome P450 is shown to carry out the facile epoxidation of dehydrocamphor to give $\text{exo}$-5,6-epoxycamphor. A detailed kinetic study of the reaction demonstrates that epoxidation and hydroxylation reactions occur with nearly identical rates both in the reconstituted system containing flavoprotein dehydrogenase, iron-sulfur protein, and NADH as well as in the single turnover reaction beginning with ferrous, oxygenated cytochrome P450. Dehydrocamphor is not a suicide substrate for the enzyme since competent enzyme remains after several thousand reaction cycles per P450 molecule.     

Mitnahme,frequenzdemultiplikation und maskierung der Laufaktivität von Carabus-Arten (Coleoptera) durch Lichtzyklen

Undulatory light cycles synchronize the endogenous periodicity of activity without masking the activity simultaneously. The primary range of entrainment ranges from 17 to 36 hr. This remarkable width indicates that the self-sustained circadian oscillation of Carabus tends to a relaxation type. The phase angle differences measured at both the borders of the range of entrainment differ by 180°. In the case of resonance (τ ～ T) the phase angle difference is rearly zero. Short rectangular light-dark cycles ($\text{1}\text{1}\text{–}\text{6}\text{6}\text{hr}$) frequently mask the activity. Simultaneously they entrain the endogenous rhythm by frequency reduction. Masking by short light-dark cycles was constant in some individuals, but between individuals variable ‘phase angle differences’ were observed.     

Plasma progesterone concentration in Bos taurus and Bos indicus heifers

Progesterone concentrations were determined by radioimmunoassay in the plasma of heifers of German Brown Swiss, Holstein-Friesian and White Fulani cattle during two consecutive estrous cycles in the dry and wet seasons in a tropical climate. Seasonal differences in the levels were not significant but peak levels were significantly higher in the $\text{Bos}$$\text{taurus}$ than in the $\text{Bos}$$\text{indicus}$ heifers. The low levels at estrus and the gradual rise five days after estrus were similar among the heifers. The levels on the 1st and 2nd days preceding estrus were significantly higher in the $\text{Bos}$$\text{taurus}$ than in the $\text{Bos}$$\text{indicus}$ heifers, and suggest a possible tendency for the former to be more susceptible to infertility arising from high progesterone levels 1 and 2 days preceding estrus and insemination. The genital tract and ovaries at the mature luteal phase were generally smaller in the $\text{Bos}$$\text{indicus}$ than in the $\text{Bos}$$\text{taurus}$ heifers.     

Circadian control of singing in crickets: Two different pacemakers for early-evening and before-dawn activity

(1) Under LD 12:12 and constant temperature, calling song patterns of the Australian Field Cricket Teleogryllus commodus were frequently divided into two more or less distinct activity components. The first began 1–3 h before the $\text{L}\text{D}\text{-transition}$ and ended with the sudden lights-off, whereas the second was restricted mainly to the second half of the night. In subsequent continuous light (LL) the circadian activity pattern was usually a unimodal band. Its onset slope was always a continuation of the first onsets in the preceding LD-cycle. In those cases where shortly after the $\text{LD}\text{LL}$ transition the rhythm split into two components, both corresponded to those in LD. (2) In “atypical” LD-aatterns only the second component appeared during the late night. In such cases, the onset slope of the subsequent free-running rhythm did not start at the preceding LD-entrained onsets, but was advanced by several hours. (3) In free-running rhythms the mean value of the onset slopes ($\text{τ}{}_{\mathrm{o}}\text{= 25.1 ± 0.07}\text{h}$) did not differ significantly from that of the end slopes ($\text{τ}{}_{\mathrm{e}}\text{= 25.0 ± 0.07}\text{h}$). However, in individual activity patterns, simultaneous differences in onset and end slopes of up to 0.7 h were found. τ_o- and τ_e-values recorded directly after the $\text{LD}\text{LL}\text{-transition}$ did not correlate with the preceding phase angle difference between the entrained activity and the zeitgeber. (4) Under constant conditions after-effects such as spontaneous period changes and phase shifts in the slopes of activity onset and/or end occurred mainly between five and 20 days after the $\text{LD}\text{LL}\text{-transition}$. (5) Period changes and phase delays in the onset and end slopes were also found when crickets were exposed to low temperature pulses (2 ± 2°C, 2h duration). Following the cold treatment both period changes and phase shifts in the onset slope frequently differed from those in the end slope. (6) The results are consistent with a concept of two activity components controlled by weakly coupled circadian pacemakers. This is clearly evident in split rhythms but is also true for unimodal patterns. Normally the two components partly overlap and their existence is concealed in the undivided activity band. They are only revealed in unimodal patterns if individual oscillatory properties such as different period lengths or phase shifts appear in the onset or the end slope.     

Photosynthetic control and photophosphorylation in photosystem II of isolated spinach chloroplasts

Two cycles of photosynthetic control have been observed in isolated spinach chloroplasts in the presence of lipophilic class III electron acceptors, which may accept electrons at PS II. $\text{ADP}\text{O}$ ratios of 0.8 to 0.9 were recorded;rates of oxygen evolution were stimulated by phosphorylating reagents and uncouplers. Addition of the plastoquinone antagonist DBMIB decreased photosynthetic control, oxygen evolution and photophosphorylation. We believe that there is a coupling site associated with PSII which can be rate limiting. Comparison of the $\text{P}\text{2e}$ ratios observed with class I and class III electron acceptors leads us to propose that more than 0.6 and possibly approaching one molecule of ATP can be formed for every pair of electrons transported from water to PSII acceptors.