Phase relationship of the circadian rhythms of feed intake, caecal motility and production of soft and hard faeces in domestic rabbits

In rabbits kept under 12:12 h light conditions, caecal contractions were recorded by implanted strain gauges or induction coils. In animals fed ad libitum caecal contraction frequency varied cyclically in phase with the circadian rhythm of feed intake. Both had their minimum during the time of soft faeces production. Thus all 3 functions seem to depend on the same circadian clock. The close link between caecotrophy and caecal contractions can, however, be upset by either time-restricted feeding or by fasting.     

限制食粪对东方田鼠食物消化和体重生长的影响

食粪行为是植食性小型哺乳动物为满足其营养需求所采取的一种适应对策。实验室条件下,限制1月龄和12月龄东方田鼠摄食粪便,测定了限制食粪对食物消化率和体重生长的影响,旨在进一步揭示食粪行为在植食性小型哺乳动物的营养及消化对策中的作用。结果表明,限制食粪使1月龄和12月龄东方田鼠的干物质消化率分别下降27.64 %和7.89 %,粗蛋白消化率分别下降21.39 %和12.68 %;限制食粪可显著抑制东方田鼠的体重增长,且限制食粪对幼体体重的影响较成体明显。因此,研究结果充分验证了限制食粪可降低东方田鼠的食物消化率及抑制其体重生长的假设。     

Intensity but not the colour temperature of light acts as an entraining agent for the circadian system of the tropical mouse Mus booduga

Abstract

Daily variations in the colour temperature of the sun have been established as the Zeitgeber for arctic animals (Krüll, 1976, 1985). In the tropical regions too, there is a variation in the colour temperature from dawn to dusk. Experiments were performed to analyse whether cyclical 12 : 12h variations (Table 1) in the colour temperature assist the field mouse Mus booduga in programming the activity‐rest cycle or if the intensity of light plays a major role. Results suggest that the variations in the colour temperature used in the present experiment are not sufficient to entrain the system. Different colour temperatures given in light pulses did not evoke varying phase shifts indicating that the circadian system was not responding to the colour temperatures. The phase shifts tended to be of the same magnitude. It is speculated that it is the intensity of light that is more important for determining the day and night cycles of Mus booduga than the differences in colour temperature.     

Phase shifts of human circadian rhythms due to shifts of artificial Zeitgebers

In special isolation units, circadian rhythms of human subjects have been investigated under the influence of artificial 24-h Zeitgebers, with 6-h advance and 6-h delay shifts of the Zeitgeber simulating time zone shifts. In most cases, the biological rhythms follow the Zeitgeber shifts in the course of several days: in rare cases, advancing Zeitgeber shifts are followed by delaying shifts of the biological rhythms, either of all variables or, partitioning, of only some of the variables. The rhythm of activity is re-entrained after both Zeitgeber shifts within a few days, independent of the shift direction. The rhythm of rectal temperature needs more time for re-entrainment than the activity rhythm; the rate of re-entrainment is consistently higher after advance than after delay shifts ('direction asymmetry'). Mean value and amplitude of the rectal temperature rhythm are, for some days, reduced after the advance but not after the delay Zeitgeber shift; among the different subjects, the reduction in amplitude is significantly correlated with the direction asymmetry. The rhythm of psychomotor performance (computation speed) re-entrains in parallel to that of rectal temperature; i.e. the performance level is decreased after advance but not after delay shifts. The direction asymmetry in the re-entrainment rates seems to contradict findings in flight experiments where this rate is mostly higher after westward than after eastward flights. Careful considerations, however, show that differences in the re-entrainment behavior after real and simulated time zone shifts disappear when the experimental designs are approximated and when identical procedures of analyzing the data are applied. The results of the time shift experiments are, in all respects tested, in agreement with theoretical postulations; hence, they confirm once more properties of the circadian system deduced earlier. On the other hand, the results are of practical importance since they state significant correlations between the re-entrainment behavior and rhythm parameters measured before the Zeitgeber shifts; this behavior, therefore, can be predicted from data obtained already before the Zeitgeber has been changed in any way: The duration of re-entrainment is correlated with the amplitude, and the decrement in performance with the phase of the rectal temperature rhythm. These practical implications may also apply to shift work.     

Ultradian rhythms and the nutritional importance of caecotrophy in captive Brandt’s voles (<Emphasis Type="Italic">Lasiopodomys brandtii</Emphasis>)

Ingestion of soft faeces derived from caecal contents, caecotrophy, in herbivorous small mammals is considered an adaptation to the metabolic disadvantage of small body size, especially when feeding on diets of low quality. We investigated daily activity patterns in captive Brandt’s voles (Lasiopodomys brandtii), including feeding, locomotion, caecotrophy, and defaecation, by continuous 24 h visual observation; and estimated the contribution of soft faeces ingestion (caecotrophy) to intake of protein and energy. Brandt’s voles ingested 68.8 ± 7.4 fecal pellets per day, averaging 17 ± 2% of total faeces produced. The amount of faeces ingested did not differ between female and male voles or between night and day time. All animals showed average 3 h ultradian cycles in behaviour during the course of the day and night. The contributions of caecotrophy to the dietary intake of crude protein and metabolizable energy were estimated respectively as 9 and 8% on a high-protein, easily digested commercial rabbit pellet diet. However, the importance of caecotrophy to the field voles is likely to be higher on a natural diet of lower nutrient density. The rhythm of caecotrophy in voles depended mainly on the rhythm of the colonic separation mechanism in the proximal colon and passage in the distal colon, and may be regulated by feeding and other activity rhythms. Ultradian rhythms in caecotrophy helped to minimise potential conflicts in utilizing the gut, especially in balancing the caecal fermentation and salvaging nutrients contained in caecal bacteria.     

Change in the plasmocytic reaction of immunized animals during the use of antibiotics]

The effect of tetracycline and tetraolean on the shifts in the plasma-cell elements was studied experimentally on male albino rats of Wister line and rabbits immunized with foreign erythrocytes and typhoid fever vaccine respectively. It was noted that prolonged use of the antibiotics for 10 to 12 days inhibited proliferation of the plasmic cells, the inhibitory effect of tetracycline being more pronounced. At the same time an inhibitory effect of the antibiotics on the antibody formation in the animals was found in the experiments.     

Re-entrainment of circadian rhythms after phase-shifts of the Zeitgeber.

To describe anabrupt shift of the Zeitgeber sufficiently, it is necessary to indicate whether the phase has been advanced or delayed, for how many hours it has been shifted, and what part of the Zeitgeber has been lengthened or shortened respectively. The entrained circadian system usually follows a shift of the Zeitgeber in the same direction and by an equal amount. However, there can be exceptions to both of these rules: a) an instantaneous 12-h shift of a (symmertric) Zeitgeber always represents a delya (= doubling of one-half of its period). In contrast to this, the gradual re-entrainment of the circadian system can be accompalished by either advances or by delays (Fig. 2), it can occur in both dirctions simultaneously by splitting the rhythmic variable (Fig. 1),or it can represent an apparent advance not distinghushable from a delay ( Fig. 6); b) after complietion of re-entraiment, the phase-angle difference psi between organism and Zeitgeber an differ systematically from the pre-shift psi-value...     

The colonic separation mechanism in the guinea-pig (Cavia porcellus) and the chinchilla (Chinchilla laniger)

In guinea-pig, the concentration of nitrogen and viable bacteria were nearly twice as high in the contents of the colonic furrow compared to the contents of the corresponding lumen. Labelled bacteria infused into the proximal colon of guinea-pigs were transported in the furrow into the caecum. Both species produced two types of pellets, one nitrogen-rich intended for caecotrophy, and one nitrogen-poor delivered as faecal pellets. The furrow is part of a separation mechanism in both species saving bacteria for the animals.     

Influence of gravitational overload and hypokinesia on the structure of the vascular bed of the stomach]

Under study were effects of gravitation stresses, total hypokinesia and their combinations on blood vessels of the stomach. The work was carried out in 130 rabbits, 16 of them being used to study the normal structure of the gastric vascular bed. The vascular bed was injected with the Gerota's mass followed by clearing, making histological preparations and roentgenography. The investigation has revealed both quantitative and qualitative changes in the structure of the gastric blood vessels. The maximum endurable stress of the ventro-dorsal direction causes morphological shifts less pronounced than stresses of longitudinal directions. With prolonged terms of hypokinesia (1-12 weeks) morphological changes became more pronounced in all the layers of the stomach. A combination of successive gravitation stresses and hypokinesia during 4-12 weeks aggravated morphological changes which occurred after exposure to isolated above factors. The animals subjected to maximum endurable stresses before and after 4-week hypokinesia developed vascular changes more typical for the effects of gravitation. The pretraining of animals did not give a pronounced positive effect on the changes of the angioarchitectonics of all the gastric layers after a repeated stress following 4-week hypokinesia.     

Resynchronization of the Circadian Corticosterone Rhythm After a Light/Dark Shift in Juvenile and Adult Mice

Most of the extensive literature concerning the resynchronization of circadian rhythms after a Zeitgeber shift is devoted to the dependence of resynchronization on the mode of the shift and the strength of the Zeitgeber, as well as on the circadian function investigated. Ontogenetic influences have rarely been investigated. Therefore, we studied the resynchronization of several circadian rhythms in juvenile and adult female laboratory mice. We present here the results concerning the corticosterone rhythm. The daily rhythms were determined as transverse profiles (2-h intervals) before as well as 3, 7, and 14 days after an 8-h phase delay of the light/dark cycle produced by a single prolongation of dark time. The corticosterone concentration in serum was determined radioimmunologically. In the control animals the daily patterns were bimodal, with main maxima at the end of the light time and secondary ones just after lights on. Ontogenetic differences were small. In adult mice the amplitude was slightly increased due to an increase in the maximum values, and the time of highest hormone concentrations was slightly phase advanced. In juvenile mice, a distinct daily pattern with a phase position in relation to the light/dark cycle corresponding to that of control animals was present on the 3rd day after the Zeitgeber shift. The daily mean as well as the minimum and maximum values increased initially and reached the values of control animals during the second week. In adult animals, a pronounced daily rhythm with the normal phase position was present only at the 7th postshift day. The amplitude, daily mean, and maximum values were decreased, and the minimum values were increased. The initial values were not reached even after 2 weeks. The results show that resynchronization was faster in juvenile mice compared with adult mice. As a possible cause for the observed age-related differences, a not yet stabilized phase-coupling between various circadian rhythms is supposed.     

Resynchronization of the Circadian Corticosterone Rhythm After a Light/Dark Shift in Juvenile and Adult Mice

Most of the extensive literature concerning the resynchronization of circadian rhythms after a Zeitgeber shift is devoted to the dependence of resynchronization on the mode of the shift and the strength of the Zeitgeber, as well as on the circadian function investigated. Ontogenetic influences have rarely been investigated. Therefore, we studied the resynchronization of several circadian rhythms in juvenile and adult female laboratory mice. We present here the results concerning the corticosterone rhythm. The daily rhythms were determined as transverse profiles (2-h intervals) before as well as 3, 7, and 14 days after an 8-h phase delay of the light/dark cycle produced by a single prolongation of dark time. The corticosterone concentration in serum was determined radioimmunologically. In the control animals the daily patterns were bimodal, with main maxima at the end of the light time and secondary ones just after lights on. Ontogenetic differences were small. In adult mice the amplitude was slightly increased due to an increase in the maximum values, and the time of highest hormone concentrations was slightly phase advanced. In juvenile mice, a distinct daily pattern with a phase position in relation to the light/dark cycle corresponding to that of control animals was present on the 3rd day after the Zeitgeber shift. The daily mean as well as the minimum and maximum values increased initially and reached the values of control animals during the second week. In adult animals, a pronounced daily rhythm with the normal phase position was present only at the 7th postshift day. The amplitude, daily mean, and maximum values were decreased, and the minimum values were increased. The initial values were not reached even after 2 weeks. The results show that resynchronization was faster in juvenile mice compared with adult mice. As a possible cause for the observed age-related differences, a not yet stabilized phase-coupling between various circadian rhythms is supposed.     

Effect of Behavioural Feedback on Circadian Clocks of the Nocturnal Field Mouse Mus booduga

The effect of 'novel running wheels' on circadian clocks of the nocturnal field mouse Mus booduga was investigated during free-running and entrained conditions. In order to find out whether daily access to novel running wheels can entrain the locomotor activity rhythms experimental animals (n = 6) were provided with 'novel running wheels' at a fixed time of the day. The control animals (n = 5) were handled similar to the experimental animals but were not given access to novel running wheels. The results show that daily access to novel running wheels entrained the free-running locomotor activity rhythm of these mice. The post-entrainment free-running period (τ) of the experimental animals was significantly shorter than the pre-entrainment τ, whereas the pre- and post-treatment τ of the control animals did not differ significantly. In separate set of experiments, the effect of access to novel running wheels on the rate of re-entrainment was studied after a 6 h phase advance/delay in 24 h (12:12 h) light/dark (LD) cycles. Experimental animals were given access to novel running wheels for 3-h, 1 h after the 'lights-off' only on the first day of the 'new LD cycles'. Experimental animals took fewer cycles to re-entrain to 6-h phase advanced LD cycles compared to the control animals. After a phase delay in the LD cycles by 6h, the experimental animals took more number of cycles to re-entrain compared to the control animals. These results thus suggest that access to novel running wheel can act as a Zeitgeber for the circadian clocks of the nocturnal mouse M. booduga, and can also modify the rates of re-entrainment to phase shifted LD cycles, in a time-dependent manner.     

Phase delay of the natural photoperiod alters reproductive timing in the marsupial Antechinus stuartii

The dasyurid marsupial Antechinus stuartii (20–40 g) has a brief, highly synchronized mating period in spring followed by complete male mortality. Analysis of breeding times in nature suggests that the rate of change of photoperiod is the main Zeitgeber for reproductive timing in this species. To test this hypothesis the natural photoperiod was phase delayed by two months, one experiment beginning in late summer, and the other in the autumn, before the spring breeding period.
The reproductive cycle of males and females exposed to the delay in summer was synchronously delayed by two months, coincident with the exact duration of the delay. Animals exposed to the two month phase delay in autumn also exhibited a delay in reproductive timing, but it was less synchronized than either the control or the other experimental group. Reproduction in control animals exposed to natural photoperiod was synchronous with that of a wild population monitored simultaneously. It is therefore likely that the rate of change of photoperiod is the dominant Zeitgeber for the reproductive cycle in this species.     

Asymmetric re‐entrainment and phase response of the circadian activity rhythm of a nocturnal marsupial (Petaurus breviceps: Phalangeridae)

Abstract

Sugar Gliders (Petaurus breviceps) re‐entrain faster after 8‐h delay shifts of an LD 12:12 and an LD 8:16 (31–56:0.3 lux each) than after 8‐h advance shifts of these Zeitgeber cycles. In order to test whether this asymmetric re‐entrainment behavior is related to, or even caused by the phase response characteristics of the circadian system, the phase response of the activity rhythm to short and long light pulses was studied. Short light pulses (15 min of 31–56 lux against a background intensity of 0.3 lux) caused only relatively small delay shifts when applied around the onset, and more pronounced advance shifts when given at the end of the activity time (α). Onset and end of activity shifted by different amounts. Long light pulses produced by 8‐h advances and delays of one single lighttime of an LD 12:12 elicited pronounced phase delays when applied at the beginning of the activity time, but only minor phase advances when given at the posterior part of α. These results indicate that in Petaurus breviceps the phase response characteristics to long light pulses exerting parametric effects of light are responsible for the pronounced asymmetry effect in re‐entrainment. Differing phase responses of onset and end of activity point to a two‐oscillator structure of the circadian pacemaker system in this marsupial.     

Influence of food intake on the 24-hr variations of plasma iron concentration in the rabbit

Circadian variations in plasma iron levels were first reported in humans in 1937. Influences of the sleeping pattern and of plasma cortisol and adrenaline levels on these variations as well as the reproducibility of the phenomenon itself are discussed controversially in the literature. The influence of food intake, however, was not considered in most of the studies and is therefore subject of this investigation. Circadian plasma iron and plasma transferrin variations were determined in rabbits and compared under free access to food and under starvation (caecotrophy was not prevented). Population-mean-cosinor analysis of circadian plasma iron concentrations showed similar variations in the fed and starved condition (mesor: 116.6 micrograms/dl vs 118.1 micrograms/dl, acrophase 0752 hr vs 0728) except for a significant increase of the circadian amplitude under free access to food (30.9 micrograms/dl vs 22.3 micrograms/dl, P less than 0.05). There was no variation in plasma transferrin, which shows that 24 hr variations in plasma iron are not caused by modulation of plasma transferrin. These findings demonstrate a circadian rhythm for plasma iron, the amplitude of which is increased by food intake.     

Homozygous cell typing for the rabbit RLA-D antigens in animals from commercial breeders

We have previously reported that several of theRLA haplotypes of our rabbits have anRLA-D allele in common, i. e., they fail to cross stimulate in the MLC test. To investigate the possibility that these haplotypes originated in unrelated animals, a panel of homozygous rabbits was selected to partially characterize noninbred rabbits from five commercial sources for their alleles at theRLA-D locus. In the 47 rabbits tested, 4 homozygous animals and 12 heterozygous animals were detected with the four alleles chosen for typing. At least two independent pairs of rabbits shared identicalRLA-D genotypes. Our results indicate that theRLA-D locus is not extremely polymorphic and that rabbits cannot be assumed to be completely mismatched for theRLA complex simply because they are from different breeds or from independent suppliers.     

Light control of the circadian activity rhythm in mouse‐eared bats (Myotis myotis Borkh. 1797)

Abstract

The aim of this study was to analyse the effect of light respectively illumination cycles on the activity rhythm of the insectivorous bat Myotis myotis (M.m.). A new electronic registration system devised for this purpose can be applied almost universally in recording the activity of terrestrial animals.

M.m. is a strictly dark‐active species with a bimodal activity pattern of bigeminus character. Under constant conditions, M.m. reveals a free running circadian activity rhythm. Its period length varies between 22.6 and 27.8 h and is positively correlated with the intensity of illumination. The range of entrainment of the circadian activity rhythm of M.m. is unusually wide. Accordingly, M.m. resynchronizes very quickly after phase shifts of the Zeitgeber LD. Activity maxima in the range of 10^‐4 lx occur in LD 12:12 with constant illumination in L and varied illumination in D as well as in LL with varying intensity.

It is to be discussed whether the wide variability of different parameters in the circadian system of M.m. compared with those of other Chiroptera can be interpreted as an adaptation to ecological factors.     

Ambient temperature cycles entrain the free-running circadian rhythms of the stripe-faced dunnart,Sminthopsis macroura

Summary We examined the effect of cycles of 12 h warm (35 ± 2 °C) and 12 h (21 ± 2 °C) ambient temperature (Ta) upon the circadian activity rhythms of stripe-faced dunnarts, Sminthopsis macroura, free-running in conditions of constant dark (DD) or constant light (LL). It was hypothesized that dunnarts would entrain to the temperature cycles (TaHLs) or show perturbations of period, and that LL would act synergistically with the TaHLs in these effects. Under DD, 2 of 6 animals showed clear entrainment to the TaHLs. Other animals exhibited changes of period () and heavy negative masking of activity during the warm fraction of the TaHLs. Under LL, 3 of 12 animals entrained to the TaHLs. It was concluded that Ta is a significant though weak Zeitgeber for S. macroura compared to light. It is possible that TaHLs entrain homeotherm activity rhythms by altering the rhythm of body temperature, which is usually tightly coupled to activity.Abbreviations TaHL a cycle of Higher and Lower ambient temperature - TaC Constant Ta - Tb body temperature     

草食性小型哺乳动物的食粪行为

食粪行为广泛存在于草食性中小型哺乳动物中,是特指动物取食由盲肠内容物所形成的粪便的行为。这些动物具有特殊的结肠分离机制,能够产生两种不同的粪便。食粪行为延长了食物在消化道中的平均滞留时间;提高了对高纤维食物的消化率;弥补了食物中氨基酸和维生素的缺乏,满足了动物对这些营养物质的需求;是动物消化过程中的一个特殊组成部分。食粪行为的节律性是动物对取食和食粪的风险权衡的结果。食粪行为的发展是与动物草食性的特点紧密相关的,是动物对身体较小、食物质量低和天敌威胁等不利因素适应的结果。本对这些方面的研究进展进行了综述。     

Influence of sympathetic withdrawal on early postinfarction arrhythmias

In this work we studied the incidence and characteristics of early postinfarction arrhythmias in rabbits with sympathetic denervation. The electrical and haemodynamic changes were analyzed. Three groups of animals submitted to coronary occlusion were studied. A control group of normal animals (I), another group of animals injected with practolol prior to occlusion (5 mg/kg i.v.) (II) and a third group of animals in which stellate ganglia were surgically excised prior to occlusion (III). In the control group incidence of early postinfarction arrhythmias was 60% (12 of 20) while in Groups II and III incidence was only 25% (3 of 12 rabbits). The influence of excision or pharmacological blockade of sympathetic system and their role in the genesis of the early arrhythmias is discussed.