Seasonal changes in the circadian activity rhythm of light-dark (LD) and completely dark (DD) regimen in the mouse submandibular gland in the presence of light-dark (LD) and completely dark (DD) regimen

Influence of seasons on circadian activity changes and the influence of one and six weeks of DD upon these changes of acid phosphatase (AP) and beta-acetylglucosaminidase (AM) was studied in the submandibular gland of sexually mature male mice. Total enzyme activity was determined in tissue homogenates at four-hour intervals in March, June, October, and February under standard LD12/12 conditions and after one and six weeks of the DD regime. The rhythms were analysed according to cosinor method. Under constant lighting conditions the seasonal differences in the AM circadian activity rhythm were found. AP activity was considerably less influenced by seasonal changes. Both enzyme activity changes were independent of each other and each rhythm was differently influenced by DD. In the case of AM the most pronounced circadian activity changes had the highest amplitude and mesor occurred in summer. The strongest influence of DD upon this enzyme activity rhythm was observed in spring and summer especially after the first week, after six weeks the acrophase returned to the LD group value (spring). In autumn and winter the reaction to DD was different to that of summer and spring. For AP the circadian changes of activity were non-rhythmic in spring, whereas in all other seasons the acrophases occurred almost at the same time in the afternoon. In DD the activity rhythm significantly changed after six weeks. In all seasons, except spring the circadian rhythm of activity was not observed after six weeks of DD. An attempt was made to explain the observed results by the certain kind of genetic memory present in laboratory animals the neurohormonal system of which is influenced by seasonal changes.     

Circadian rhythm of acid phosphatase activity in rat liver microsomes and dependence of NADH 5 alpha-reductase on phosphatase activity

The specific activity of acid phosphatase in male and female rats follows a circadian rhythm. Preincubation of liver microsomes with testosterone led to an increase of phosphatase activity and a loss of circadian rhythm. NADH 5 alpha-reductase was inactivated by several animal and bacterial acid and alkaline phosphatases while the acid phosphatase from potatoes was ineffective. The extent of inhibition depends on the course of circadian rhythm of NADH 5 alpha-reductase activity. Preincubation of microsomes in the presence of testosterone inhibited the NADH 5 alpha-reduction of testosterone. No such inhibition was observed after preincubation of microsomes with progesterone.     

Circadian clock of Drosophila montana is adapted to high variation in summer day lengths and temperatures prevailing at high latitudes

Photoperiodic regulation of the circadian rhythms in insect locomotor activity has been studied in several species, but seasonal entrainment of these rhythms is still poorly understood. We have traced the entrainment of activity rhythm of northern Drosophila montana flies in a climate chamber mimicking the photoperiods and day and night temperatures that the flies encounter in northern Finland during the summer. The experiment was started by transferring freshly emerged females into the chamber in early and late summer conditions to obtain both non-diapausing and diapausing females for the studies. The locomotor activity of the females and daily changes in the expression levels of two core circadian clock genes, timeless and period, in their heads were measured at different times of summer. The study revealed several features in fly rhythmicity that are likely to help the flies to cope with high variation in the day length and temperature typical to northern summers. First, both the non-diapausing and the diapausing females showed evening activity, which decreased towards the short day length as observed in the autumn in nature. Second, timeless and period genes showed concordant daily oscillations and seasonal shifts in their expression level in both types of females. Contrary to Drosophila melanogaster, oscillation profiles of these genes were similar to each other in all conditions, including the extremely long days in early summer and the cool temperatures in late summer, and their peak expression levels were not locked to lights-off transition in any photoperiod. Third, the diapausing females were less active than the non-diapausing ones, in spite of their younger age. Overall, the study showed that D. montana clock functions well under long day conditions, and that both the photoperiod and the daily temperature cycles are important zeitgebers for seasonal changes in the circadian rhythm of this species.     

Seasonal effects of pinealectomy on the locomotor activity rhythm in the lizard Sceloporus torquatus

Adult lizards (Sceloporus torquatus) were used to test whether seasonal differences in the effects of pinealectomy upon the locomotor activity rhythm exist. Animals were field collected and exposed to artificial light - dark cycles and constant temperature in winter and summer. Free running circadian rhythms under constant temperature and dim red light were monitored using infrared light-crossings. The effects of pinealectomy were assessed by analysing the circadian parameters of free running period and activity - rest ratio in constant darkness or light - dark cycles. Results obtained indicate that pinealectomy changes the free running period of locomotor activity rhythm, irrespective of season, while seasonal differences in activity-rest ratio were detected. Our findings support the hypothesis that seasonal regulation of circadian rhythms in lizards is accomplished, in part, via the output of the pineal gland.     

Melatonin and biological rhythms

Circadian and seasonal rhythms are a fundamental feature of all living organisms. The functional mechanism involved is built around internal biological clock(s) and the hormone melatonin (Mel) is one of its critical components. Although numerous other sources have been identified (retina, harderian gland, gut), in vertebrates Mel is primarily produced by the pineal gland during the dark period of the light-dark cycle. This rhythmic Mel is generated directly by circadian clock(s). The Mel rhythm is thus an important efferent hormonal signal from the clock. The periodic secretion of Mel might thus be used as a circadian mediator of a system that can 'read' the message.The duration of the nocturnal Mel production is directly proportional to the length of the dark period. It is through these changes in duration that the brain integrates the photoperiodic information. In essence, the Mel rhythm appears to be an endocrine code of the environmental light-dark cycle conveying photic information that is used by organisms for both circadian and seasonal temporal organization. The major question arising from this effect of Mel concerns it precise mechanism of action. From the data reported in the present minireview, it appears that the photoneuroendocrine mechanism is not fundamentally different in vertebrates at least as far as the role of Mel is concerned.     

Comparative study on the activity, pH optimum and thermal stability of some glycosidases and acid phosphatase from pig and mule leukocytes.

1. alpha-D-mannosidase, beta-D-galactosidase, alpha-L-fucosidase, beta-N-acetylgalactosaminidase, alpha-D-glucosidase and acid phosphatase activities were studied in circulating blood leukocytes from Sus scropha var. domestica L. (pig) and Equus asinus x caballus (mule) by spectrophotometric procedures using p-nitrophenyl derivatives as substrates and three different buffer solutions. 2. The highest specific activity corresponds to acid phosphatase. The specific activities of the glycosidases, all relatively close together in all cases, were low in comparison with that of phosphatase. 3. Generally, each of the above-mentioned enzymes shows one common peak for the pH optimum between 3.5 and 6.0, except alpha-D-glucosidase, which shows two peaks. 4. The pH optima values are generally similar in three buffer solutions employed. 5. Specific activities of the studied enzymes show a parallelism in leukocytes from both pig and mule. Also, this parallelism is observed in their pH optima values. 6. Thermal stability of alpha-D-mannosidase is high whereas that of acid phosphatase is low, in both materials. For other enzymes, differences in the thermal stability was observed according to their source.     

Circadian rhythms in digestive enzymes in the small intestine of rats. I. Patterns of the rhythms in various regions of the small intestine.

The activities of the digestive enzymes, maltase [EC 3.2.1.20], sucrase [EC 3.2.1.26], trehalase [EC 3.2.1.28], Leucine aminopeptidase [EC 3.4.11.1], and alkaline phosphatase [EC 3.1.3.1] were measured in various regions of the small intestine of rats. The activities of all these enzymes were much higher in the jejunum than in the ileum, and in the distal regions of the ileum no sucrase, trehalase or alkaline phosphatase activity was detected. In the jejunum, the activities of all the enzymes tested exhibited clear circadian variations with the highest activity at 0000-0400 h and the lowest at 1200 h when the rats were fed ad libitum. In the ileum, maltase and sucrase also exhibited circadian variations, but the amplitude of the rhythm was smaller than that in the jejenum. Trehalase and alkaline phosphatase did not show any circadian variation in the ileum. Leucine aminopeptidase showed a circadian variation in the ileum with the same amplitude as in the jejunum. The phase of the circadian variations shifted about half a day when the rats were fed in the daytime, but the amplitude of the rhythm did not change.     

Short-term and circadian rhythms in the behaviour of the vole,Microtus agrestis (L.)

Summary The activity behaviour of the vole, Microtus agrestis, has been recorded in order to investigate the relationship between short-term rhythm and circadian rhythm. A simple device was developed, allowing separate monitoring of the time spent in or outside the nest, wheel-running, eating and drinking. Under natural light conditions during summer, a distinct differentiation between a short term rhythm of eating and drinking during the day-time and a circadian rhythm of wheel-running during the night was observed. The short-term rhythm depends closely on metabolic demands (hunger, thirst, excretion). Control of these demands by an endogenous oscillation could not be substantiated. The circadian rhythm of wheel-running activity is, however, controlled by an endogenous oscillation, synchronized by light conditions. It is subjected to seasonal variations. a) The threshold of light intensity below which wheel-running occurs is lowest during summer (<0.5 lx) and is higher during spring and autum (> 5 lx). b) Wheel-running is controlled by a circadian oscillation during summer only whereas it is an integrated part of the short-term rhythm during spring and autumn (experiments during the winter have not yet been performed). Experiments gave evidence that the properties of the cage can deeply influence the amount and pattern of wheel-running activity. It is concluded that wheel-running reflects a certain level of excitation, which may be caused by different behavioural intentions. The seasonal changes of the control of wheel-running activity are discussed with respect to this assumption. The relevancy of locomotor activity patterns as usually recorded in the laboratory to reveal the physiological and ecological significance of endogenously controlled behavioural patterns is discussed.Supported by the Deutsche Forschungsgemeinschaft     

Turkey retina and pineal gland differentially respond to constant environment

Dynamics of rhythmic oscillations in the activity of arylalkylamine N-acetyltransferase (AA-NAT, the penultimate and key regulatory enzyme in melatonin biosynthesis) were examined in the retina and pineal gland of turkeys maintained for 7 days in the environment without daily light-dark (LD) changes, namely constant darkness (DD) or continuous light (LL). The two tissues differentially responded to constant environment. In the retina, a circadian AA-NAT activity rhythm disappeared after 5 days of DD, while in the pineal gland it persisted for the whole experiment. No circadian rhythm was observed in the retinas of turkeys exposed to LL, although rhythmic oscillations in both AA-NAT and melatonin content were found in the pineal glands. Both tissues required one or two cycles of the re-installed LD for the full recovery of the high-amplitude AA-NAT rhythm suppressed under constant conditions. It is suggested that the retina of turkey is less able to maintain rhythmicity in constant environment and is more sensitive to changes in the environmental lighting conditions than the pineal gland. Our results indicate that, in contrast to mammals, pineal glands of light-exposed galliformes maintain the limited capacity to rhythmically produce melatonin.     

Influence of the seasons on the circadian rhythm of blood glucose and tissue glycogen in male Wistar rats

Adult, ad libitum fed male Wistar rats were adapted for three weeks to standard laboratory conditions and a 12:12 h light:dark regimen (7 a.m. to 7 p.m., 7 p.m. to 7 a.m.). In January, in April, in July and in October they were decapitated at 3-hour intervals and the glucose level was determined in their blood and the glycogen concentration in their liver, skeletal muscle, heart and white and brown adipose tissue. The influence of the seasons on circadian variation of the given parameters was not the same in all the tissues. Circadian variation of the liver and heart glycogen concentration was the least affected. The liver glycogen curves attained the maximum at the beginning of the light part of the day in all the seasons except the autumn; the rhythm was present everywhere. The rhythm was not demonstrated in the heart in the winter only and except for the summer the curves attained the maximum at the end of the dark part of the day. Pronounced seasonal changes were observed in the blood glucose and skeletal muscle glycogen concentration, whose curves reached the maximum in various parts of the day and where the rhythm was absent in the autumn - and in the case of skeletal muscle in the summer as well. The glycogen concentration in the two adipose tissues displayed the greatest seasonal changes. The shape of the circadian oscillation curves and their maxima in the various seasons were very different, with absence of the rhythm in the autumn. Determination of the influence of the photoperiodic reactions and of changes in hormones and the key enzymes regulating the main metabolic routes might help to explain the basis of circaannual variations in the metabolism of the laboratory rat.     

Interseasonal variation in the circadian rhythms of locomotor activity and temperature selection in sleepy lizards, <Emphasis Type="Italic">Tiliqua rugosa</Emphasis>

Few studies in non-mammalian vertebrates have examined how various effectors of the circadian system interact. To determine if the daily locomotor and behavioural thermoregulatory rhythms of Tiliqua rugosa are both controlled by the circadian system in different seasons, lizards were tested in laboratory thermal gradients in four seasons and in constant darkness. Circadian rhythmicity for both rhythms was present in each season, being most pronounced in spring and summer and least evident in autumn. Most lizards displayed a unimodal locomotor activity pattern across all seasons. However, some individuals presented a bimodal locomotor activity pattern in spring and summer. Seasonal variations in the phase relationships of both rhythms to the light:dark (LD) cycle were demonstrated. No seasonal differences in the free-running period lengths of either rhythm were detected, raising the possibility that a single circadian pacemaker drives both rhythms in this species. Our present results demonstrate that both rhythms are similarly controlled by the circadian system in each season. Although seasonal variations in the thermal preferences of reptiles both in the field and laboratory have previously been well documented, this study is the first to demonstrate circadian rhythms of temperature selection in a reptile species in each season.     

Activity of acid and alkali phosphatase in guinea pigs exposed to the static magnetic fields

The influence of static homogeneous magnetic field on alkali and acid phosphatase in guinea pigs (regarding the twenty four hours rhythm) was studied. The increase of acid phosphatase activity was determined by the time of exposure to magnetic field. No changes in alkali phosphatase activity were observed.     

Changes in the activity of some lysosomal enzymes and in the fine structure of submandibular gland due to experimental diabetes

The aim of this study was to establish and quantify changes in the activities of the some lysosomal enzymes and to determine the type of changes in the ultrastructure of the submandibular gland in rabbits caused during progression of diabetes. The experiment was conducted on 89 New Zealand rabbit males. Diabetes was induced by the intravenous administration of 10% alloxan solution at a dose of 10-mg/kg-body weight. On the seventh day after alloxan administration, the level of glucose in blood was determined. Rabbits were divided into five groups: intact (n=18), 21-day diabetes (n=18), 42-day diabetes (n=17), 90-day diabetes (n=19) and 180-day diabetes (n=17). From killed animals in each group, the submandibular glands were removed and fixed or stored. Enzyme activities were assayed by spectrophotometric methods using substrates (Sigma) which release 4-methyloumbeliferol when they react with the proteases. Fixation procedure was done according to standard methods. Semi-thin and ultra-thin specimens were prepared by use of clearly visible after 42 days of diabetes. Mitochondria were damaged, accumulation of large amounts of lipids in the intracellular spaces was observed. After 90 days the presence of vacuoli and swollen lysosomes were observed, some cells also contained myelin figures. After 180 days the greatest changes were observed in the blood vessels, which had thickened walls and were often occluded. We concluded that the total activity of acid phosphatase and beta-N-acetyl-glucosaminidase in the submandibular gland was correlated with the level of glucose but there was no correlation between total beta-galactosidase activity and the serum concentration level of glucose has been detected during course of diabetes. The activities of the free fractions of acid phosphatase, beta-galactosidase and beta-N-acetyl-glucosaminidase in the submandibular gland were higher than the bound fractions in all groups of rabbits. The changes in the ultrastructure of the submandibular gland were correlated with changes in serum glucose level and with lysosomal enzymes activities during progression of experimental diabetes in rabbits.     

Influence of dietary intake and physical activity on annual rhythm of human blood cholesterol concentrations

Seasonal variation in the plasma total cholesterol (TC) and high-density lipoprotein cholesterol (HDL-C) have been repeatedly reported, with contradictory results regarding the pattern of seasonal variation of these parameters. Furthermore, it is still not well established whether the variation is due to changes in the nutrition or changes in physical activity depending on the season. The aim of this study was therefore to determine plasma TC and HDL-C in different groups of healthy participants: 19 vegetarians with a constant diet independent of the season, 14 athletes with almost constant physical activity over the year, and 114 controls in the age groups 20-26 years (mean age 24 + 1.5 years) and 40-48 years (mean age 44.3 + 2.1 years). Over 2 years, blood samples were collected every 2-3 months and were analyzed for plasma TC and HDL-C. At all visits, body mass index (BMI) and waist-to-hip ratio (WHR) were calculated, and nutrition and physical activity profiles were obtained. The seasonal model was calculated using object-oriented software for the analysis of longitudinal data in S (OSWALD); multiple regression analysis was used to determine the influence of age, gender, diet, and physical activity on seasonal changes of the lipid parameters. In all groups, we found an annual rhythm of the plasma TC and HDL-C concentrations, which can be mathematically described by a sine curve with a maximum in winter and a minimum in summer. This rhythm was independent of the age, gender, BMI, diet, or physical activity. The observed seasonal differences between the maximum and the minimum were about 5%-10% for TC and about 5%-8% for HDL-C concentration. These differences were greater than the determined circadian (TC 3.5%, HDL-C 4%) and day-to-day changes for TC and HDL-C (coefficient of variation <5% for both). In conclusion, annual rhythm of TC and HDL-C is not primarily induced by seasonal differences in dietary intake or physical activity. Therefore, the annual rhythm in cholesterol levels is most likely determined by endogenous factors or factors directly related to seasonal changes in the environment.     

Circadian changes of D-alanine and related compounds in rats and the effect of restricted feeding on their amounts

The circadian changes of D-alanine (D-Ala), an intrinsic D-amino acid found in mammals, were investigated in rats with diurnal and nocturnal habits, and the profiles were compared to those of L-Ala, other D-amino acids and several hormones. Determination of D-Ala in the rat plasma, pancreas and anterior pituitary gland was carried out using a sensitive and selective two-dimensional HPLC system combining a micro-ODS column and an enantioselective column after fluorescence derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F). The amount of D-Ala was high during the sleeping period and low during the active period in rats with both diurnal and nocturnal habits, indicating for the first time that the D-Ala is closely related to the activity rhythm of animals. In contrast, L-Ala and other D-amino acids did not show any clear circadian changes. The circadian change of D-Ala inversely correlated with that of the plasma insulin level in rats with both diurnal and nocturnal habits. Considered together with our previous findings that D-Ala is localized in the insulin secreting beta-cells in the rat pancreas, it is strongly suggested that D-Ala has some functional relationships to insulin in mammals.     

Avian Melatonin Synthesis: Photic and Circadian Regulation of Serotonin N-Acetyltransferase mRNA in the Chicken Pineal Gland and Retina

Abstract: The circadian rhythms in melatonin production in the chicken pineal gland and retina reflect changes in the activity of serotonin N -acetyltransferase (arylalkylamine N -acetyltransferase; AA-NAT; EC 2.3.1.87). Here we determined that the chicken AA-NAT mRNA is detectable in follicular pineal cells and retinal photoreceptors and that it exhibits a circadian rhythm, with peak levels at night. AA-NAT mRNA was not detected in other tissues. The AA-NAT mRNA rhythm in the pineal gland and retina persists in constant darkness (DD) and constant lighting (LL). The amplitude of the pineal mRNA rhythm is not decreased in LL. Light appears to influence the phase of the clock driving the rhythm in pineal AA-NAT mRNA in two ways: The peak is delayed by ∼6 h in LL, and it is advanced by >4 h by a 6-h light pulse late in subjective night in DD. Nocturnal AA-NAT mRNA levels do not change during a 20-min exposure to light, whereas this treatment dramatically decreases AA-NAT activity. These observations suggest that the rhythmic changes in chicken pineal AA-NAT activity reflect, at least in part, clock-generated changes in mRNA levels. In contrast, changes in mRNA content are not involved in the rapid light-induced decrease in AA-NAT activity.     

The circadian system of ruin lizards: a seasonally changing neuroendocrine loop?

Previous studies have shown that the amplitude of daily melatonin production in cultured ruin lizard pineal organs explanted in the summer is significantly higher than that from organs explanted in the winter. To test whether seasonal photoperiodic changes are decoded autonomously by the pineal gland, pineals explanted in summer were cultured in vitro and exposed to changes between winter and summer photoperiods. The changes in photoperiod duration did not affect the daily profiles of in vitro melatonin production. The discrepancy between the present in vitro results and those from lizards exposed to winter or summer photoperiods before pineal explantation supports the view that circadian information entering the pineal gland via its innervation is involved in determining seasonal changes of melatonin production in ruin lizards. We further examined whether a central component of the circadian system of ruin lizards, specifically the retinae of the lateral eyes, expresses similar seasonal changes in function as does the pineal gland. We did not find any difference between summer and autumn-winter in the effectiveness of either bilateral retinalectomy or optic nerve lesion-at the level of the optic chiasm-in altering circadian locomotor behavior in constant conditions. Both surgical procedures mostly induced a shortening of the free-running period of the locomotor rhythm of similar magnitude in all seasons. Thus, the retinae do not appear to participate in the seasonal reorganization of the circadian system in ruin lizards.