Rhythmic cortisol secretion in the equine: Analysis and physiological mechanisms

Abstract

Four Thoroughbred mares (no. 1–4) were maintained under constant temperature (24°C) and controlled light (L/D:12/12 with lights on at 06.00 hr) conditions. They were fed and watered ad libitum with fresh feed and water given at 09.00 hr. After a 45‐day pre‐conditioning period, blood samples were obtained by veinipuncture at 4‐hr intervals for 14 days to determine circadian and day‐to‐day variation. The horses exhibited a circadian rhythm with maximum values attained at about 12.00 hr, however, there are periods of days in which no rhythm is distinguishable. Ultradian rhythms with mean periods of 105 to 128 and 24 to 31 min are superimposed upon the circadian rhythm. The individual rhythms are quite variable from horse to horse and within the same horse. During periods of decline in plasma cortisol with metabolic half‐lives of approximately 70 min, secretion of cortisol was very low or had ceased. During periods of increasing plasma concentration, secretion was occurring at a faster rate than degradation. Rapid decreases in plasma concentration (metabolic half‐life of approximately 30 min) was accompanied by a rise in specific activity indicating cortisol with a high specific activity was entering the plasma pool from other storage pools.     

Circadian rhythms in human erythrocytes in vitro not confirmed

Abstract

Human erythrocytes, white and resealed erythrocyte ghosts, and hemolysates were analysed for the occurrence of circadian and ultradian rhythms in vitro. Although the experimental conditions were extensively varied, we did not find any indication for the existence of rhythmicity. These results are at variance with the reports by others.     

Review of diel rhythmic activities in physiological functions of scorpions

In this study I review the subject of biological rhythms in scorpions. This will include only some of the diel rhythmic endogenous physiological functions and not the locomotory rhythmicity, which will be dealt separately. Most studies reported here were conducted on 13 scorpion species that were studied in 39 different studies. Most of these (66.7%) were studies on a single species (Heterometrus fulvipes). Being a scorpionid, it sits and waits near its burrow not being very active, especially the females. The fact that experimenting was carried out irrespective of species diversity, gender, ecological or physiological conditions, and was usually done on animals kept in captivity for some time before the experimenting had started, is a major drawback to this kind of study. Although the main conclusion appears to be that enzymes reached their peak activity at 20.00 h, there are some exceptions showing otherwise that need further study in order to explain them.     

Circadian and light-induced conductance changes in putative pacemaker cells of Bulla gouldiana

The ocular circadian rhythm of compound action potential frequency in Bulla gouldiana is driven by rhythmic changes in the membrane potential of putative circadian pacemaker cells. Changes in the membrane potential of these neurons is required for light-induced phase shifts of the rhythm. We have tested the proposition that these changes in membrane potential reflect underlying changes in ionic conductances. We have found that: 1. Membrane conductance in the dark is highest during the subjective night when the cells are hyperpolarized, decreases as the cells depolarize spontaneously near projected dawn and is lowest during the subjective day. The changes in membrane potential and conductance follow a similar time course. 2. Long pulses of light delivered to eyes during their subjective night produce a characteristic response: There is initially a large, phasic depolarization accompanied by a burst of CAPs; this is followed by a repolarizing phase during which CAP activity is reduced to zero; and finally a tonic depolarization develops that is accompanied by a resumption of CAP activity at a steady rate. 3. During the subjective night, the tonic depolarization is accompanied by a decrease in conductance compared to the previous dark value. However, light pulses of similar duration delivered to eyes during their subjective day causes tonic depolarizations and increased CAP activity, but no measurable change in conductance. 4. Membrane responses to light are sensitive to agents that reduce Ca2+ flux. Light pulses during the subjective night produce a phasic depolarization, but the repolarization phase is eliminated in low Ca2+/EGTA seawater and is reduced in 5 mM Ni2+.(ABSTRACT TRUNCATED AT 250 WORDS)     

Daily rhythms of locomotor activity and the influence of a light and dark cycle on gut microbiota species in tambaqui (Colossoma macropomum)

This study aimed to assess the daily rhythms of locomotor activity and to quantify bacteria populations in the tambaqui digestive tract during light and dark periods. Photoelectric cells and a recording computational system were used to quantify the locomotor activity, and the existing Gram-positive and Gram-negative bacteria populations were evaluating during the daytime and night-time periods. The results showed a typical pattern for nocturnal locomotor activity (91%), and lower percentages of Gram-positive 6?×?10³, 24% and Gram-negative cocci (approximately 38%) were observed during the same periods compared with the diurnal period (76 and 62%, respectively). Additionally, lower percentages of Gram-positive (42%) and Gram-negative (44%) Bacillus were observed during the same periods compared with the diurnal period (29?×?10⁶ CFU/g, 58% and 23?×?10⁶ CFU/g (56%), respectively). These data should be considered when animals are subjected to high stress loads for more appropriate management strategies and collaborating with future studies of what is the best schedule to vaccinate or provide probiotics to fish.     

Temporal Patterns of Reported Single-Vehicle Car and Truck Accidents in Texas, U.S.A. During 1980-1983

Reported single car and truck accidents due specifically to driver 'fatigue' for the 4-year span of 1980-1983 were analyzed for 24-hr, 7-d and 1-yr patterns. Three types of data were examined: (1) accidents in rural Texas, (2) accidents only in San Antonio, the fourth largest city in Texas and (3) accident ratio (number of accidents per time interval divided by traffic volume for the interval) in this city.

A statistically significant seasonal variation of relatively low amplitude with peaks in May and July was detected only for accidents in rural areas. High-amplitude periodicities of 7 d were evident in all the data sets, with a peak on the weekend. A very prominent 24-hr pattern was detected as well, with the acrophase determined by single cosinor around 0300. A slight secondary peak in accidents, around 1500, was evident in the data from the rural areas. This secondary peak represented a 12-hr rhythm in addition to the 24-hr. Overall, features of the temporal patterns in accidents over 24 hr and over the year in urban and rural areas differed only slightly. Accident ratios yielded results similar to accident frequencies. However, with regard to the rural data, the shape of the 24-hr temporal pattern varied with driver age; older drivers exhibited a flatter curve with a more pronounced afternoon rather than early morning (around 0300) peak.     

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.     

The statistical analysis of tidal rhythms: Tests of the relative effectiveness of five methods using model simulations and actual data

Endogenous rhythms in intertidal organisms are often very complex and imprecise. Thus, confusing results are sometimes obtained when applying various interpretive analytical techniques. In an attempt to resolve this problem, ten different models representing typical organismic tidal‐rhythm displays were created and examined with five different inferential statistical techniques. The exercise was designed to test the relative effectiveness of these techniques in detecting the presence of known cycles in the models, and estimating their period lengths. The same comparison was then repeated on sets of animal‐derived data.

All of the five methods had their merits, but, depending on the model being examined, the results from the various methods were not identical. Three of the techniques produce harmonics, making data that contain multiple periods especially difficult to decipher. Often both tidal and circadian periods are displayed by shore dwellers; all five methods were able to find these two periods. But when the difference in circa period length was close, only one technique (array analysis) could make a distinction. This technique was also the only one able to handle data in which the period was not constant. Interestingly, this simplest of methods is probably the best all‐round method of discovery. Many more subtle, but important, differences were also noted, and it is recommended that more than one method always be used to ensure accuracy.     

Effects of a chronic reduction of short-wavelength light input on melatonin and sleep patterns in humans: Evidence for adaptation

Light is an important environmental stimulus for the entrainment of the circadian clock and for increasing alertness. The intrinsically photosensitive ganglion cells in the retina play an important role in transferring this light information to the circadian system and they are elicited in particular by short-wavelength light. Exposure to short wavelengths is reduced, for instance, in elderly people due to yellowing of the ocular lenses. This reduction may be involved in the disrupted circadian rhythms observed in aged subjects. Here, we tested the effects of reduced blue light exposure in young healthy subjects (n?=?15) by using soft orange contact lenses (SOCL). We showed (as expected) that a reduction in the melatonin suppressing effect of light is observed when subjects wear the SOCL. However, after chronic exposure to reduced (short wavelength) light for two consecutive weeks we observed an increase in sensitivity of the melatonin suppression response. The response normalized as if it took place under a polychromatic light pulse. No differences were found in the dim light melatonin onset or in the amplitude of the melatonin rhythms after chronic reduced blue light exposure. The effects on sleep parameters were limited. Our results demonstrate that the non-visual light system of healthy young subjects is capable of adapting to changes in the spectral composition of environmental light exposure. The present results emphasize the importance of considering not only the short-term effects of changes in environmental light characteristics.     

Activity rhythms of enzymes in human red blood cell suspensions

Abstract

We have established the presence of a rhythm in the activity of 4 enzymes in in‐vitro cell suspensions of human red blood cells. Glucose 6‐phosphate dehydrogenase and glutamate oxaloacetate transaminase demonstrated semicircadian patterns of activity, while acid phosphatese and acetylcholine esterase exhibited circadian activity rhythms. The ratios between the highest to lowest activities varied from 2:1 to 10:1 among the various enzymes. The affinity of glucose 6 phosphate dehydrogenase to its substrate and coenzyme remained constant throughout the cycle. No evidence was obtained for the presence of a soluble inhibitor at the lower levels of the activity. Sonication of hemolysates with low glucose 6 phosphate dehydrogense activity yielded additional activity comparable to that of the peak activity. Sonication of hemolysates from the time of the peak activity did not change the original activity. The observations point to a role of the cell membrane in the biological clock.     

Entrainment of Melatonin Rhythms in Rams By Symmetrical Light-Dark Cycles of Different Period Length

The objective of this study was to investigate the entrainment of melatonin rhythms in rams using symmetrical light-dark cycles of different period length. Five groups of six He de France rams were kept in 12L: 12D for 7 weeks and then (i) 12L: 12D, (ii) 11L: 11D, (iii) 10L: 10D, (iv) 13L: 13D and (v) 14L: 14D for a further 3 weeks. Environmental factors other than the light dark cycle were not controlled. The onset and offset of the plasma melatonin rhythm in DD after 3 weeks of the respective light treatments was assessed for 48 hr, immediately after transferring to DD. The duration of secretion in DD was positively related to the length of the previous dark phase. The phase of the melatonin rhythm with respect to the anticipated dark phase suggested entrainment with no change in phase-relationship to the zeitgeber by 12L: 12D and 13L : 13D. Entrainment with a phase-delay or a phase-advance was apparent after 11L: 11D and 14L: 14D, but the individual rhythms were not all synchronized with respect to each other after 10L: 10D. Activity recordings for 2-3-week periods during 12L: 12D, 10L: 10D and 14L: 14D all showed a major 24-hr component at all times, with activity during the light phase in 12L: 12D. It appears that melatonin may be readily desynchronized from overt activity-rest cycles in sheep. The upper and lower entrainment limits are probably greater than 28 hr and close to 20 hr cycles, respectively.     

Comparative studies of tidal rhythms. VI. Several clocks govern the activity of two species of fiddler crabs

The tide‐associated persistent activity rhythms of the ocypod crabs, Uca pugnax and U. pugilator were observed in constant conditions, some for as long as three months. In some animals the twice/day peaks of activity were found to scan the day at significantly different rates from one another. Individual peaks in some animals split into two fragments. And at times, one peak would fade and then return, or vanish completely. These examples of the independence between tide‐related activity peaks have become the basis for a hypothesis that each peak is controlled by its own clock(s). The basic period of these clocks is “circalunidian”, with periods varying up to about 4–8% on either side of 24.8 hours.     

Using Covariance to Unravel the Effects of Meteorological Factors and Daily and Seasonal Rhythms

Many factors contribute to the activity of animals in the wild. Whilst daily and seasonal rhythms are likely to be present, and to represent underlying biological functions, these will normally be modified by several factors in the environment. Important amongst these are light, temperature, humidity and whether or not it is raining. There is also the problem that the factors might interact, the effect of, say, time of day, being modified by the concomitant temperature. Separating out the effects of these different factors experimentally can be extremely arduous, if not impossible. An alternative approach is to treat the environmental factors as covariants, and then to separate out their effects from the biological ones by statistical means, using Analysis of Covariance, ANCOVA. The potential of this method is illustrated in the current report by a consideration of exits and entries of a colony of bees from their hive. Hourly measurements of this behaviour were taken during the daylight hours for three consecutive days in 11 consecutive months of the year. At the same time, ambient temperature, light intensity, humidity and whether or not it was raining were recorded. ANCOVA enabled the effects of temperature, humidity, light and rainfall upon the exits from the hive and entries back into it to be separated from the effects of time of day and time of the year. The analyses allowed those climatic variables, in addition to time-of-day and time-of-year effects, that influenced behaviour to be identified. Such climatic variables have not been previously isolated, and this might have lead to a misinterpretation of similar results in the past. Having separated out any effects of climatic variables (the covariates), the interaction between time of day and time of the year could then be investigated. Furthermore it has been possible to quantify the effects upon behaviour of each covariate. Rainfall was shown to decrease activity by more than 80%. For the other variables (temperature, humidity and light intensity), the statistical model allowed for the possibility that an increase in the variable initially produced a rise in activity but that this was followed, if the variable continued to rise, by a fall in activity. For light intensity, only a very modest increase in activity was found, and this continued throughout the range of intensities measured. However, for both temperature and humidity, the effects were more marked and showed 'turning points'. That is, activity increased as the ambient temperature rose until activity peaked at about 33-35°C; after which activity began to fall. Similarly, entries into the hive rose with increasing humidity up to a value of 48%, but fell thereafter. By contrast, exits from the hive increased with increasing humidity throughout the range measured. In the biological system tested, this form of analysis has produced valuable information about the way different factors influence activity in a field study. The results strongly suggest that the proposed methodology has a much wider and more general application. The way in which this type of analysis might be elaborated is discussed.     

Biological and psychological rhythms: An integrative approach to rhythm disturbances in autistic disorder

Biological rhythms are crucial phenomena that are perfect examples of the adaptation of organisms to their environment. A considerable amount of work has described different types of biological rhythms (from circadian to ultradian), individual differences in their patterns and the complexity of their regulation. In particular, the regulation and maturation of the sleep–wake cycle have been thoroughly studied. Its desynchronization, both endogenous and exogenous, is now well understood, as are its consequences for cognitive impairments and health problems. From a completely different perspective, psychoanalysts have shown a growing interest in the rhythms of psychic life. This interest extends beyond the original focus of psychoanalysis on dreams and the sleep–wake cycle, incorporating central theoretical and practical psychoanalytic issues related to the core functioning of the psychic life: the rhythmic structures of drive dynamics, intersubjective developmental processes and psychic containment functions. Psychopathological and biological approaches to the study of infantile autism reveal the importance of specific biological and psychological rhythmic disturbances in this disorder. Considering data and hypotheses from both perspectives, this paper proposes an integrative approach to the study of these rhythmic disturbances and offers an etiopathogenic hypothesis based on this integrative approach.     

Time-related predator/prey interactions between birds and fish in a northern Swedish river

Summary Seasonal and diel activity patterns of mergansers, gulls, and terns along a river in northern Sweden were documented, as were those of their fish prey. The seasonal and diel activity patterns of goosandersMergus merganser and gulls (Larus canus, L. argentatus, andL. fuscus) were closely related to that of the river lampreyLampetra fluviatilis. During the peak spawning of the river lamprey, birds showed a nocturnal peak in fishing activity. During the summer solstice, birds were active for 24 h. The activity patterns of red-breasted merganserMergus serrator, ternsSterna spp., and three-spined sticklebacksGasterosteus aculeatus were also similar. Activity pattern of the prey apparently influenced breeding time, diel activity and foraging area of the twoMergus species. Social relations between gulls probably corrdinated their peak in fishing, which coincided with the time lampreys were most efficiently exploited.     

Interaction of endogenous and exogenous factors controlling locomotor activity rhythms in Carcinus exposed to tidal salinity cycles

The shore crab Carcinus maenas (L.) reported hitherto not to express endogenous circatidal rhythmicity in winter, is shown not to lose the ability to express such rhythmicity. Crabs maintained in constant reduced salinity in winter exhibit circatidal and circadian rhythms similar to the normal endogenous rhythms of summer caught crabs.In sinusoidal changes of salinity of tidal periodicity, reductions of salinity and increases to ambient sea water induced increased locomotor activity. The former were purely exogenous responses but the latter were also observed to entrain the underlying endogenously controlled circatidal pattern of behaviour.The occurrence of separate exogenous and endogenous responses to different phases of imposed salinity cycles has implications when seeking to understand rhythmic locomotor activity of crabs on the shore and in the search for components of the underlying physiological clock mechanism.     

Diurnal rhythms in psychological reward functioning in healthy young men: ‘Wanting’, liking,and learning

A range of evidence suggests that human reward functioning is partly driven by the endogenous circadian system, generating 24-hour rhythms in behavioural measures of reward activation. Reward functioning is multifaceted but literature to date is largely limited to measures of self-reported positive mood states. The aim of this study was to advance the field by testing for hypothesised diurnal variation in previously unexplored components of psychological reward: ‘wanting’, liking, and learning using subjective and behavioural measures. Risky decision making (automatic Balloon Analogue Risk Task), affective responsivity to positive images (International Affective Pictures System), uncued self-reported discrete emotions, and learning-contingent reward (Iowa Gambling Task) were measured at 10.00 hours, 14.00 hours, and 19.00 hours in a counterbalanced repeated measures design with 50 healthy male participants (aged 18–30). As hypothesised, risky decision making (unconscious ‘wanting’) and ratings of arousal towards positive images (conscious wanting) exhibited a diurnal waveform with indices highest at 14.00 hours. No diurnal rhythm was observed for liking (pleasure ratings to positive images, discrete uncued positive emotions) or in a learning-contingent reward task. Findings reaffirm that diurnal variation in human reward functioning is most pronounced in the motivational ‘wanting’ components of reward.     

Avian circannual clocks: adaptive significance and possible involvement of energy turnover in their proximate control

Endogenous circannual clocks are found in many long-lived organisms, but are best studied in mammal and bird species. Circannual clocks are synchronized with the environment by changes in photoperiod, light intensity and possibly temperature and seasonal rainfall patterns. Annual timing mechanisms are presumed to have important ultimate functions in seasonally regulating reproduction, moult, hibernation, migration, body weight and fat deposition/stores. Birds that live in habitats where environmental cues such as photoperiod are poor predictors of seasons (e.g. equatorial residents, migrants to equatorial/tropical latitudes) rely more on their endogenous clocks than birds living in environments that show a tight correlation between photoperiod and seasonal events. Such population-specific/interspecific variation in reliance on endogenous clocks may indicate that annual timing mechanisms are adaptive. However, despite the apparent adaptive importance of circannual clocks, (i) what specific adaptive value they have in the wild and (ii) how they function are still largely untested. Whereas circadian clocks are hypothesized to be generated by molecular feedback loops, it has been suggested that circannual clocks are either based upon (i) a de-multiplication ('counting') of circadian days, (ii) a sequence of interdependent physiological states, or (iii) one or more endogenous oscillators, similar to circadian rhythms. We tested the de-multiplication of days (i) versus endogenous regulation hypotheses (ii) and (iii) in captive male and female house sparrows (Passer domesticus). We assessed the period of reproductive (testicular and follicular) cycles in four groups of birds kept either under photoperiods of LD 12L:12D (period length: 24h), 13.5L:13.5D (27 h), 10.5L:10.5D (23 h) or 12D:8L:3D:1L (24-h skeleton photoperiod), respectively, for 15 months. Contrary to predictions from the de-multiplication hypothesis, individuals experiencing 27-h days did not differ (i.e. did not have longer) annual reproductive rhythms than individuals from the 21- or 24-h day groups. However, in line with predictions from endogenous regulation, birds in the skeleton group had significantly longer circannual period lengths than all other groups. Birds exposed to skeleton photoperiods experienced fewer light hours per year than all other groups (3285 versus 4380) and had a lower daily energy expenditure, as tested during one point of the annual cycle using respirometry. Although our results are tantalizing, they are still preliminary as birds were only studied over a period of 15 months. Nevertheless, the present data fail to support a 'counting of circadian days' and instead support hypotheses proposing whole-organism processes as the mechanistic basis for circannual rhythms. We propose a novel energy turnover hypothesis which predicts a dependence of the speed of the circannual clock on the overall energy expenditure of an organism.     

Circadian rhythms and feeding time in fishes

Synopsis Although several studies have described effects of meal frequency and timing of meals on growth performance and body composition of different species of fishes, the mechanisms by which such variables influence the energy partitioning processes is not known. They may interact with the natural feeding rhythm of the fish, or with various behavioural and physiological parameters that exhibit circadian-like patterns; however, in most cases, the endogenous character of such rhythms is not clear. The time of feeding, perse, can act as a Zeitgeber and override the effect of the light/dark alternation. Fish that are fed always at the same time of day show typical pre-feeding activity. Blood levels of some nutrients and hormones also show peaks or troughs at the time of feeding, but whether these are pre-feeding or post-prandial events is not clear. These results from fish are compared with similar studies with mammals. The existence and location of an endogenous multi-oscillator system is also discussed.