24-hr Rhythm Research Articles

The effects of conditioned behaviour and environmental factors on plasma corticosteroid levels in pigs

Young pigs have been subjected to various conditioning procedures or environmental factors and the changes in plasma corticosteroid levels measured. Pigs in an escape avoidance situation soon learned to avoid most of the shocks. It was possible to demonstrate conditioned suppression of food reinforced operant behaviour. However, neither the escape avoidance conditioning nor the conditioned suppression technique resulted in large increases in plasma corticosteroids compared with those elicited by administration of ACTH. Exposure of pigs to cold, or chasing them, resulted in larger increases of plasma corticosteroids than the conditioning procedures. A marked 24 hr rhythm in plasma corticosteroid levels was demonstrated.

Twenty-four hour pattern of luteinizing hormone secretion in normal men with sleep stage recording.

ABSTRACT Plasma luteinizing hormone (LH) was measured by radioimmunoassay at 20-min intervals around the clock for 24 hr in 5 normal adult men. During the nocturnal S-hr sleep period, polygraphic monitoring of sleep stages was carried out. All 5 subjects showed episodic secretion of LH characterized by rapid rises and the declining slopes approximated the half-life of LH. Calculation of LH “half-life” from the declining phase of the LH secretory episodes gave variable estimates within subjects and between subjects (65–114 min). The longer T1/2 estimates calculated by this method, contrasted with previous studies where LH half-life was determined directly by the measurement of LH disappearance, is probably the result of small amounts of LH being secreted during the declining phase of the LH secretory episode. This study failed to show a 24-hr LH rhythm or relationship of LH secretory activity to the sleep-wake cycle. The marked temporal variability of the LH system throughout the 24-hr period clearly demon...

Synthesis of cardiac glycogen in relation to its 24-hr rhythm in rats.

Synthesis of cardiac glycogen in relation to its 24-hr rhythm in rats.

Postnatal development of a norepinephrine response to light in the rat pineal and salivary glands

Under the control of environmental lighting, the pineal and salivary glands of the rat showed a 24-hr rhythm in norepinephrine content. In animals maintained in diurnal lighting, the norepinephrine content of both tissues was highest at the end of a dark period and lowest at the end of a light period. When animals were placed in constant darkness, the norepinephrine levels remained high, whereas in constant light, they remained low. At birth, the norepinephrine content of the salivary and pineal glands was low, but adult levels were attained between 6 and 10 days of age. At 6 days, no norepinephrine response to light was evident in either the pineal or salivary glands. Between the eighth and tenth days, constant light levels became significantly lower than constant dark levels in both tissues, demonstrating the development of a response to light. The 24-hr rhythm took 10 days to develop in animals kept in diurnal light. The present experiments indicated that visual control of these sympathetic neurons was functional by the tenth day of life in the rat. In the newborn rat, control of the salivary gland norepinephrine response to light could be mediated by extraretinal photoreceptors, but in the adult animal, the eye was essential.

Adrenocortical function in pregnant rats: Handling and the 24-hour rhythm

The temporal course of the adrenocortical response to handling was determined on Day 16 of pregnancy in previously handled and non-handled rats. Fifteen days of prior handling did not influence the plasma corticosterone response to handling stimulation measured at either the peak or the trough in the 24-hr adrenocortical rhythm. Corticosterone levels in animals sampled at the peak of the 24-hr adrenocortical rhythm were elevated 60 min after handling stimulation which was found to be a function of elevated resting corticosterone levels. In a second experiment the 24-hr adrenocortical rhythm in pregnant animals was characterized by peak values which occurred approximately two hr before darkness but, unlike nonpregnant animals, these peak values were sustained throughout most of the dark period.

Daily variation of body temperature, liver catalase activity, and plasma iron concentration in normal and tumor-bearing rats.

SummaryA comparison was made between the daily variations observed in body temperature, liver catalase activity, and plasma iron concentration in normal and tumor-bearing rats. All three of these measurements were found to have a 24-hr rhythm in normal Holtzman and Fischer rats. With rats bearing either the Walker 256 carcinoma or a 20-methylcholanthrene-induced tumor, these daily cyclic rhythms were altered. It is suggested that care must be exercised in choosing the time of day to compare normal and tumor-bearing animals.

Rhythmicity in the maternal behaviour of Rattus norvegicus

Using a dual-chambered maternity cage the time that a lactating rat spent with its litter was recorded continuously from birth of the litter until weaning. Under a 12-hr light-dark regimen there was a precise 24-hr rhythm in maternal behaviour; the greatest amount of time with the litter occurring during the middle of the light period and the least amount of time occurring during the period of darkness. The cycle was independent of litter size and the absolute magnitude of the time spent with the litter which decreased over the 21-day observation period. Animals rearing litters under an LD:6 schedule also showed a 24-hr maternal behaviour rhythm. Animals maintained under an LD:12 schedule but transferred to continuous light when pregnant and animals maintained for two generations under constant light showed a free-running maternal behaviour rhythm with a period of approximately 24 hr.

Continuous recording of maternal behaviour in Rattus norvegicus

Summary It was assumed that the time a lactating rat spends with its litter can be taken as a reflection of maternal behaviour. This was measured continuously in a dual-chambered apparatus which permitted the female to be with or away from its litter for any amount of time at any time of the day. It was found that the total time and the duration of each period that the mother spends with its litter shows an orderly decrease over the 21 days post-partum. Further analyses of these data indicated that there is a 24-hr rhythm in maternal behaviour. The rhythm appears to be inversely related to and may be a direct reflection of the rat's characteristic 24-hr activity cycle. A comparison of the time spent with the litter with data obtained from a modified version of Seitz's maternal-behaviour scale yielded similar changes over time for those tests of the scale which did not involve any disruption of the ongoing behaviour of the mother or litter. Otherwise, there was no consistent relationship between these two measures or within the scale itself. Administration of the maternal-behaviour scale to females rearing litters in a single cage indicated that the above findings could be attributed to the use of the dual-chambered apparatus. These data further suggested that some aspects of the maternal-behaviour scale may be artifacts of the conditions of housing or method of administration, and may reflect emotional reactivity rather than maternal behaviour, per se. The continuous recording of maternal behaviour was also found to differentiate between females rearing large and small litters. The time spent with the litter over the 21-day post-partum period decreased more rapidly in females rearing litters of twelve than in females rearing litters of four animals. The data are interpreted as support for the assumption that the time that a lactating rat spends with its litter can be taken as a reflection of maternal behaviour. The main advantages of this procedure are that it provides a continuous recording that is not subject to sampling error or experimenter bias, and it takes advantage of the ongoing mother-litter interactions which are initiated by the animals themselves rather than forced by the proximity of a single cage or by the intervention of an experimenter.

Hormonal factors altering rhythmicity of tyrosine-alpha-ketoglutarate transaminase in rat liver.

The activity of a hepatic enzyme, tyrosine transaminase (TT), was shown to vary with a 24-hr rhythm controlled by at least 3 endocrine glands. This enzyme, known to be induced by glucocorticoids or by long-term thyroxine treatment, was measured in male rats at 2- or 4-hr intervals with a 12-hr day-night lighting. A base line enzyme activity of 3.32–4.20 ×lO3 U/mg protein was seen in the intact animals between 0800 and 1600. Activity then rose rapidly to reach a single sharp peak at 2200 hr that was 4–5 times greater than base line. Alterations in this pattern were noted following adrenalectomy, thyroidectomy, or hypophysectomy. In the adrenalectomized animals the rise at 1600 and peak at 2200 hr seen in the intact animal were absent, but enzyme activity at 2400 and 0400 hr was unchanged from normal. Following thyroidectomy enzyme activity rose at 1600 hr, reaching a peak at 2200 that was significantly higher than in the intact animal (p<.01). Activity then fell at 2400 to concentrations not significantly ...

‘Emotionality’ and adrenal cortical function: Effects of strain, tests, and the 24-hour corticosterone rhythm

Summary Open-field testing of rats and mice did not yield significant behaviour-steroid correlations in experiment 1. In experiment 2 albino and hooded rats maintained under a 12 hr light-dark regimen were observed in a reaction-to-handling situation and an open-field at the peaks and troughs in the previously determined 24 hr rhythm in adrenal cortical activity. Strain differences were observed in the reaction-to-handling test and to a lesser extent in the open-field, and were independent of the time of testing. Hooded animals had heavier adrenal glands than albinos, but neither adrenal weight nor plasma and adrenal corticosterone values were related to emotionality. The plasma corticosterone response to behavioural testing varied as a function of the test and the time at which it occurred.

Circadian Rhythm of Metabolic Rate in Pocket Mice

Perognathus longimembris, under a variety of conditions, demonstrated essentially a 24-hr rhythm in oxygen consumption. The amplitude, correlation with light cycle, and duration of periods of high and low metabolism varied. In September, mice provided with food and held at 22–24° C had a rhythm closely synchronized with a 12-hr light cycle (high in dark); mice were hypometabolic 12.5% of the days. In May, mice were more often out of synchrony and were hypometabolic 32.5% of the days. Without food at 22° C, mice became torpid every day; the first period of torpor began in the dark, and the rhythm of oxygen consumption was thereafter reversed. At 10° C without food, mice failed to arouse to a normal metabolic rate every day; sometimes they were deeply hypometabolic for 48–56 hr. A circadian rhythm of reduced amplitude continued, however, and arousals to normal rate occurred approximately on multiples of 24 hr. Arousals continued to occur in mice without food at 10° C despite exposure to or state of animals under the following conditions: constant darkness with or without sound, air with 4.5% CO2, obesity, 9 months' prior conditioning to 10° C, 1,400 R acute whole-body gamma radiation. Mice acclimatized to 10° C had the shortest periods of normal metabolism and obese mice the longest. In P. longimembris (mean wt 10.7 g), P. inornatus (14.6 g) and P. formosus (20.5 g) at 10° C without food, frequency and extent of hypometabolism varied inversely with body weight.

The 24-hr rhythm of emergence of Ephestia kühniella Zell. from the pupa

The endogenous 24-hr emergence rhythm of the moth Ephestia kühniella Zell. was unaffected by a daily variation of atmospheric pressure or humidity. Decrease in temperature from 30° to 25°C initiated a new rhythm of emergence; the opposite change did not affect the existing emergence rhythm. A change from light to darkness stimulated emergence; a change from darkness to light retarded it. A single decrease of temperature or change of light intensity initiated a new rhythm of emergence. A 16-hr periodicity of emergence was initiated by a corresponding periodicity of temperature but the rhythm reverted to a 24-hr periodicity immediately the temperature variations ceased. No 24-hr rhythm of oxygen consumption by the pupa in uniform conditions could be detected. The time between peak periods of emergence appeared to increase when pupae were kept in constant conditions in a gas mixture containing 7 per cent oxygen. The endogenous emergence rhythm was displaced by about 12 hr after pupae had been kept at 0·5°C for 12 hr.

Studies in diurnal rhythms—VIII. The endogenous chronometer in Gryllus campestris L. (Orthoptera: Gryllidae)

The field cricket, G. campestris, is normally active during the daytime. The 24-hr rhythm of activity and rest persists in constant darkness, its phase being temperature-independent. The internal “clock” system of the insect can be reset by brief exposure to light, or by return to higher temperatures after a period at 5°C. It can be reset by light even when locomotory activity has been suppressed by drought. The suggestion is made that this may be achieved by the synchronization of a number of internal “clocks” whose phase duration is innate.