Diurnal and seasonal cortisol, testosterone, and DHEA rhythms in boys and girls during puberty

Diurnal and seasonal rhythms of cortisol, testosterone, and DHEA were examined, as little is known about the relationship between these rhythmicities and pubertal development. Salivary samples were obtained from 60 boys and 60 girls at approximately 07:45, 08:00, 08:30, 12:00, 16:50, and 21:00 h. The participants' ages ranged from 8-14 yrs, and each participant was tested three times at six-month intervals. The study was conducted at a General Clinical Research Center (GCRC) and at the homes of the participants. All hormones showed diurnal fluctuations. The acrophase (peak time) of cortisol occurred earlier than for testosterone or DHEA and showed a seasonal effect, with the acrophase occurring earlier in spring than in summer. The cortisol acrophase also occurred later in the day for boys than for girls during later puberty. Seasonal effects were found only for cortisol with higher concentrations in the spring and summer. Cortisol concentrations were relatively stable across pubertal maturation, but significantly lower concentrations were observed at pubertal stage 3 compared to the other stages. Morning cortisol levels were also higher in boys at pubertal stage 2. Testosterone concentrations were higher in boys at pubertal stages 3 and 4, and DHEA was lower at pubertal stage 1 than 3 and 4 for both boys and girls. For the total sample, there was a positive correlation between DHEA and testosterone during early puberty (stages 1-3) but not later puberty (stages 4-5). Awakening secretory activity correlated with daytime secretory activity for testosterone and DHEA, but not for cortisol. These data provide novel chronobiological information on cortisol, testosterone, and DHEA as it relates to sexual maturation and encourage further study on both normal and abnormal endocrine rhythms.     

Diurnal and Seasonal Cortisol,Testosterone, and DHEA Rhythms in Boys and Girls during Puberty

Diurnal and seasonal rhythms of cortisol, testosterone, and DHEA were examined, as little is known about the relationship between these rhythmicities and pubertal development. Salivary samples were obtained from 60 boys and 60 girls at approximately 07∶45, 08∶00, 08∶30, 12∶00, 16∶50, and 21∶00 h. The participants' ages ranged from 8–14 yrs, and each participant was tested three times at six‐month intervals. The study was conducted at a General Clinical Research Center (GCRC) and at the homes of the participants. All hormones showed diurnal fluctuations. The acrophase (peak time) of cortisol occurred earlier than for testosterone or DHEA and showed a seasonal effect, with the acrophase occurring earlier in spring than in summer. The cortisol acrophase also occurred later in the day for boys than for girls during later puberty. Seasonal effects were found only for cortisol with higher concentrations in the spring and summer. Cortisol concentrations were relatively stable across pubertal maturation, but significantly lower concentrations were observed at pubertal stage 3 compared to the other stages. Morning cortisol levels were also higher in boys at pubertal stage 2. Testosterone concentrations were higher in boys at pubertal stages 3 and 4, and DHEA was lower at pubertal stage 1 than 3 and 4 for both boys and girls. For the total sample, there was a positive correlation between DHEA and testosterone during early puberty (stages 1–3) but not later puberty (stages 4–5). Awakening secretory activity correlated with daytime secretory activity for testosterone and DHEA, but not for cortisol. These data provide novel chronobiological information on cortisol, testosterone, and DHEA as it relates to sexual maturation and encourage further study on both normal and abnormal endocrine rhythms.     

Circadian rhythms of basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), insulin-like growth factor binding protein-3 (IGFBP-3), cortisol, and melatonin in women with breast cancer

Background: Circadian rhythms in plasma concentrations of many hormones and cytokines determine their effects on target cells. Methods: Circadian variations were studied in cortisol, melatonin, cytokines (basic fibroblast growth factor [bFGF], EGF, insulin-like growth factor-1 [IGF-1]), and a cytokine receptor (insulin-like growth factor binding protein-3 [IGFBP-3]) in the plasma of 28 patients with metastatic breast cancer. All patients followed a diurnal activity pattern. Blood was drawn at 3h intervals during waking hours and once during the night, at 03:00. The plasma levels obtained by enzyme-linked immunoassay (ELISA) or radioimmunoassay (RIA) were evaluated by population mean cosinor (using local midnight as the phase reference and by one-way analysis of variance (ANOVA). Results: Cortisol and melatonin showed a high-amplitude circadian rhythm and a superimposed 12h frequency. bFGF showed a circadian rhythm with an acrophase around 13:00 with a peak-to-trough interval (double amplitude) of 18.2% and a superimposed 12h frequency. EGF showed a circadian rhythm with an acrophase around 14:20, a peak-to-trough interval of 25.8%, and a superimposed 12h frequency. IGF-1 showed a high value in the morning, which is statistically different t test) from the low value at 10:00, but a regular circadian or ultradian rhythm was not recognizable as a group phenomenon. IGFBP-3 showed a low-amplitude (peak-to-trough difference 8.4%) circadian rhythm with the acrophase around 11:00 and low values during the night. Conclusions: (1) Circadian periodicity is maintained in hospitalized patients with metastatic breast cancer. (2) Ultradian (12h) variations were superimposed on the circadian rhythms of the hormones and several of the cytokines measured. (3) Studies of hormones and cytokines in cancer patients have to take their biologic rhythms into consideration. (4) The circadian periodicity of tumor growth stimulating or restraining factors raises questions about circadian and/ or ultradian variations in the pathophysiology of breast cancer. (Chronobiology International, 18(4), 709-727)     

Aminoglutethimide effect on circadian rhythms in urinary variables in a patient with idiopathic hyperaldosteronism

Aminoglutethimide (AG: 750 mg/day) was administered to a patient with idiopathic hyperaldosteronism (IHA) and circadian rhythms in urinary excretion of sodium (UNaV), potassium (UKV), aldosterone (AER) and 17-OHCS were analyzed by the single cosinor method. Urine was collected every 4h for 24h on the day before and on the 1st, 3rd and 7th day of AG administration, and above variables in each sample were determined. Circadian rhythms of 14 patients with primary aldosteronism (PA) who served as controls were also analyzed. In the present case, circadian acrophases in UNaV and AER studied before AG administration occurred at 22(19) and 07(05), respectively. They were similar to those of preoperative PA-patients. Circadian acrophase in UNaV occurred earlier with AG administration and on the 7th day it was at 14(05), a value similar to that of postoperative PA-patients. Circadian mesor in AER decreased remarkably from 4.1 to 0.6 micrograms/4h with AG administration, as did circadian mesor in UKV, whereas circadian mesor and acrophase in 17-OHCS did not change. Thus, the circadian characteristics in urinary variables in the present IHA-case were pathophysiologically similar to those of PA.     

Aspartate modulates the circadian patterns of a few biochemical variables in Wistar rats

D-aspartate was used to demonstrate possible sources of excitatory input to the suprachiasmatic nucleus (SCN) in rats. Aspartate (50 mg/kg bodyweight) was orally administrated chronically for 60 days to Wistar rats and 24 h rhythmic patterns of glucose, cholesterol, total protein and aspartate transaminase (AST) were studied under light - dark (LD 12:12 h) cycle. Our results showed acrophase advances in glucose and delays in cholesterol and AST rhythms. Increased mesor and altered amplitude values were found in all rhythms; aspartate levels in the brain were found to be significantly increased in aspartate treated animals. We hypothesised that the altered biochemical rhythms in aspartate treated rats could be due to (1) modulation of neurotransmission in SCN, (2) behavioural rhythms and (3) feeding rhythms.     

Circadian rhythms of DNA content in brain and kidney: effects of environmental stimulation

Male adult Wistar rats kept under natural lighting show circadian rhythms of DNA content and DNA synthesis in the cerebral cortex, cerebellum and kidney. In the cerebral cortex the acrophases of the 2 rhythms almost coincide during the dark period. On the other hand, in kidney, the acrophase of DNA synthesis is phase-advanced by about 14 h with respect to the acrophase of DNA content, which occurs in the dark span, as in the cerebral cortex. Comparable results were obtained in 5 week-old rats raised under artificial lighting conditions (LD 7:19) and exposed for a few days to sensory and social stimulation (an enriched sensory environment). At variance with the latter data, the circadian changes of DNA content and synthesis flattened out and were not statistically significant in the cerebral cortex of 5 week-old rats kept for a few days under conditions of sensory and social deprivation (an impoverished sensory environment). A similar effect occurred in kidney with regard to the rhythm of DNA content, while the circadian rhythm of DNA synthesis remained statistically significant but was phase-delayed by about 6h with respect to the corresponding rhythm occurring in the enriched environment. In sensory impoverished rats, MESOR values of kidney wet weight and DNA specific activity were significantly higher than in sensory enriched rats, while MESOR values of DNA content were significantly lower. The data demonstrate the striking dependence of the circadian variations of DNA content and synthesis on the nature of environmental stimulation.     

The effect of various photoperiods on daily oscillations of serum corticosterone and insulin in rats.

The effect of various photoperiods on circadian rhythms of chosen parameters was investigated in laboratory rats. SPF male Wistar rats were adapted for six weeks to artificial light-dark cycles (LD 8:16, 12:12, 16:8). The light was switched on at 07.00 h in all regimens. The rats were killed at 3-hour intervals within 24 h, the serum concentration of corticosterone, insulin, glucose, food and water intake was determined. The external and computative acrophases of corticosterone varied in every photoperiod being dependent on the duration of light, the mesor values decreased in LD 16:8 in comparison with other photoperiods. The external acrophase of insulin was located 4 h after light onset in LD 8:16 and 12:12, in LD 16:8 one hour before light onset. The mesor values were approximately equal in all photoperiods. The circadian rhythms of glucose were similar in all regimens. Circadian variation of food and water consumption culminated at the same time in all regimens, the amount of food consumed in light increased with the light duration. Various photoperiods remarkably influenced circadian oscillations of corticosterone and in part food and water intake which could be considered as photoperiodic traits.     

Daily rhythms of lipid metabolic gene expression in zebra fish liver: Response to light/dark and feeding cycles

Despite numerous studies about fish nutrition and lipid metabolism, very little is known about the daily rhythm expression of lipogenesis and lipolysis genes. This research aimed to investigate the existence of daily rhythm expressions of the genes involved in lipid metabolism and their synchronization to different light/dark (LD) and feeding cycles in zebra fish liver. For this purpose, three groups of zebra fish were submitted to a 12:12?h LD cycle. A single daily meal was provided to each group at various times: in the middle of the light phase (ML); in the middle of the dark phase (MD); at random times. After 20 days of acclimation to these experimental conditions, liver samples were collected every 4?h in one 24-h cycle. The results revealed that most genes displayed a significant daily rhythm with an acrophase of expression in the dark phase. The acrophase of lipolytic genes (lipoprotein lipase – lpl, peroxisome proliferator-activated receptor – pparα and hydroxyacil CoA dehydrogenase – hadh) was displayed between ZT 02:17?h and ZT 18:31?h. That of lipogenic genes (leptin-a – lepa, peroxisome proliferator-activated receptor – pparγ, liver X receptor – lxr, insulin-like growth factor – igf1, sterol regulatory element-binding protein – srebp and fatty acid synthase – fas) was displayed between ZT 15:25?h and 20:06?h (dark phase). Feeding time barely influenced daily expression rhythms, except for lxr in the MD group, whose acrophase shifted by about 14?h compared with the ML group (ZT 04:31?h versus ZT 18:29?h, respectively). These results evidence a strong synchronization to the LD cycle, but not to feeding time, and most genes showed a nocturnal acrophase. These findings highlight the importance of considering light and feeding time to optimize lipid metabolism and feeding protocols in fish farming.     

Circadian Rhythm in Gamma Glutamyltranspeptidase and Leucine Aminopeptidase Urinary Activity in Rats

Urinary gamma glutamyltranspeptidase (GGT) and leucine aminopeptidase (LAP), renal tubular brush border enzymes, have been shown to be sensitive indicators of renal tubular functions. This study documents circadian rhythms in the urinary activity of GGT and LAP, statistically validated and quantified by the cosinor method, in 15 male Wistar rats standardized to a LD 12:12 illumination schedule (light from 0800 hr to 2000 hr) and fed ad libitum. The acrophase of the circadian rhythms in urinary GGT and LAP activity occurred at the end of the rest span of the animals: between 1730 and 1915 for GGT (depending on the mode of expression of the activity) and between 1700 and 1910 for LAP. Of striking resemblance in their timing, both these rhythms were also of large amplitude (about 50% of the mesor for urinary GGT activity and about 45% for LAP one). The circadian acrophases of urinary GGT and LAP activity led in timing the circadian rhythms in urine volume and creatinine excretion by about 13hr. Such findings consistent with the circadian variations found by other investigators in GGT in kidney homogenates or in LAP in human urine thus reflect a periodicity in renal tubular function. The reasons for these circadian variations, still unknown at this time, are discussed. The influence recently demonstrated of the hormonal context on protein and enzyme synthesis at the tubule, and its phase relations to urinary enzyme excretion emphasize how much the circadian rhythm in urinary GGT and LAP activity is well included in the murine time structure. Therefore it should be of interest to consider the circadian rhythm in urinary GGT and LAP release as a marker rhythm of predictive value as to the side effects of nephrotoxic drugs.     

Circadian Rhythm in Gamma Glutamyltranspeptidase and Leucine Aminopeptidase Urinary Activity in Rats

Urinary gamma glutamyltranspeptidase (GGT) and leucine aminopeptidase (LAP), renal tubular brush border enzymes, have been shown to be sensitive indicators of renal tubular functions. This study documents circadian rhythms in the urinary activity of GGT and LAP, statistically validated and quantified by the cosinor method, in 15 male Wistar rats standardized to a LD 12:12 illumination schedule (light from 0800 hr to 2000 hr) and fed ad libitum. The acrophase of the circadian rhythms in urinary GGT and LAP activity occurred at the end of the rest span of the animals: between 1730 and 1915 for GGT (depending on the mode of expression of the activity) and between 1700 and 1910 for LAP. Of striking resemblance in their timing, both these rhythms were also of large amplitude (about 50% of the mesor for urinary GGT activity and about 45% for LAP one). The circadian acrophases of urinary GGT and LAP activity led in timing the circadian rhythms in urine volume and creatinine excretion by about 13hr. Such findings consistent with the circadian variations found by other investigators in GGT in kidney homogenates or in LAP in human urine thus reflect a periodicity in renal tubular function. The reasons for these circadian variations, still unknown at this time, are discussed. The influence recently demonstrated of the hormonal context on protein and enzyme synthesis at the tubule, and its phase relations to urinary enzyme excretion emphasize how much the circadian rhythm in urinary GGT and LAP activity is well included in the murine time structure. Therefore it should be of interest to consider the circadian rhythm in urinary GGT and LAP release as a marker rhythm of predictive value as to the side effects of nephrotoxic drugs.     

Comparative Study of the Activity/Rest Rhythms in Young and Old Ringdove (Streptopelia Risoria): Correlation with Serum Levels of Melatonin and Serotonin

Aging is characterized by changes in the circadian rhythms of melatonin, serotonin, and sleep/wakefulness, alterations that affect sleep quality. The authors studied the circadian rhythms of serotonin and melatonin in young and old ringdoves (Streptopelia risoria) (2–3 and 10–12 yrs old, respectively), animals that are characterized by being monophasic and active by day, like humans. The aim was to correlate the indole rhythms with the animals' activity/rest periods. The animals were kept under a 12∶12 h light/dark cycle, fed ad libitum, and housed in separate cages equipped for activity recording. Activity pulses were recorded with one actometer per animal (two perpendicular infrared transmitters) and were logged every 15 min by a computer program (DAS 16) throughout the experiment. Melatonin was measured by radioimmunoassay and serotonin by ELISA at intervals of 3 h (from 09∶00 to 18∶00 h) and 1 h (from 21∶00 to 06∶00 h), respectively. The results showed a reduction in nocturnal vs. diurnal activity of 89% and 61% in the young and old animals, respectively, with 100% considered to be the diurnal activity of each group. The amplitude of a cosine function fit to the melatonin concentrations of the old animals was half that of the young birds. The acrophase and nadir were at 02∶00 and 14∶00 h in the young and 01∶00 and 13∶00 h in the old animals, respectively. The amplitude of the corresponding cosine function fit to the serotonin concentrations in the old birds was one‐third that of the young animals. The acrophase and nadir were at 15∶00 and 03∶00 h in the young and 16∶00 and 04∶00 h in the old animals, respectively. For both melatonin and serotonin, the concentrations in the young animals were significantly higher than in the old at most of the measurement times. There was a clear negative correlation between the circadian rhythms of activity and the serum melatonin levels in both young and old animals. The equivalent correlation for serotonin was positive, and stronger in the case of the young animals. The results suggest a possible relationship between the observed decline in the amplitude of the old animals' melatonin and serotonin rhythms and the lower percentage reduction in their nocturnal relative to diurnal activity pulses compared to the young animals. In conclusion, the circadian rhythms of melatonin and serotonin undergo alterations with age that could be involved in the changes in age‐associated sleep.     

Rhythms in human bone marrow and blood cells

In 24h studies of bone marrow (BM), circadian stage-dependent variations were demonstrated in the proliferative activity of BM cells from subsets of 35 healthy diurnally active men. On an average, the percentage of total BM cells in deoxyribonucleic acid (DNA) synthesis phase was 188% greater at midday than at midnight (circadian rhythm: p = 0.018; acrophase or peak time of 13: 16h). Patients with malignant disease (n = 15) and a normal cortisol circadian rhythm showed higher fractions of BM cells in S-phase at midday. Colony-forming units--granulocyte/macrophage (CFU-GM), an indicator of myeloid progenitor cells, showed the same circadian variation as DNA S-phase (average range of change or ROC = 136%; circadian rhythm: p < 0.001; acrophase of 12:09h). Deoxyribonucleic acid S-phase and CFU-GM in BM both showed a circannual rhythm (p = 0.015 and 0.008) with an identical acrophase of August 12. The daily peak in BM glutathione content, a tripeptide involved in cellular defense against cytotoxic damage, preceded BM proliferative peaks by 4-5 h (ROC = 31-90%; circadian rhythm: p = 0.05; acrophase of 08:30h). Myeloid (ROC = 57%; circadian rhythm: p = 0.056; acrophase at 08:40h) and erythroid (ROC = 26%; circadian rhythm: p = 0.01; acrophase of 13:01h) precursor cells were positively correlated (r = 0.41; p < 0.001), indicating a circadian temporal relationship and equal influence on S-phase of total BM cells. Yield of positive selected CD34+ progenitor stem cells also showed significant circadian variation (ROC = 595%; circadian rhythm: p = 0.02; acrophase of 12:40h). Thus, the temporal synchrony in cell cycling renders BM cells more sensitive at specific times to hematopoietic growth factors and cell cycle-specific cytotoxic drugs. Moreover, proper timing of BM harvesting may improve progenitor cell yield. When using marker rhythms in the blood to allow for individualized timing of BM procedures, the times of low values in white blood corpuscles, neutrophils, and lymphocytes and high values in cortisol were predictive of the times of highest BM erythroid, myeloid, and total S-phase numbers occurring in the following 12 h.     

Development of diurnal rhythm in some metabolic parameters in foals

1. The development of diurnal rhythm activity of FDPA, AspAT and A1AT and in levels of cortisol, T3 and T4 was observed in the blood serum of six foals. 2. The studies began when a foal was 7 days old and were repeated every month until foals reached 1 year of age. Blood samples were taken every 4 hr for one day each month. 3. As a control group four barren mares were used, kept and examined in the same conditions. 4. In mature mares, diurnal rhythms in activity of A1AT (acrophase at 2200 hr), AspAt (2400 hr) and cortisol (0630 hr) but in T3 only in summer months (acrophase at 0100 hr) were observed. 5. During the first 6 months of foal life, significantly higher mean levels of FDPA, A1AT, T3 and T4 than in control mares were found. 6. The cortisol level in foals was half as much as that of mature mares throughout the year. 7. In foals the diurnal rhythm in A1AT activity occurred in the 5th month and in AspAt--in the 12th month (acrophase at 2400 hr), but in cortisol levels it was developed already in the second month of foal life (acrophase at 0830 hr).     

Effects of Simulated Hypo‐ and Hyper‐Reproductive Conditions on the Characteristics of Circadian Rhythm in Hypothalamic Concentration of Serotonin and Dopamine and in Plasma Levels of Thyroxine,Triiodothyronine, and Testosterone in Japanese Quail,Coturnix coturnix japonica

In this study, hypo‐ and hyper‐reproductive conditions, as measured by concentrations of plasma testosterone in male Japanese quail held on long days LD 16:8, were experimentally simulated with injections of 5‐hydroxytryptophan (5‐HTP) and L‐dihydroxyphenylalanine, (L‐DOPA) with 8 h and 12 h phase angle differences between them in intact and melatonin‐treated birds. The effects of these treatments were assessed on the characteristics of the circadian rhythm in the hypothalamic concentration of serotonin (5‐HT), dopamine (DA), and plasma levels of thyroxine (T₄), triiodothyronine (T₃), and testosterone (T). These rhythms were also studied in sham‐operated (SO), pinealectomized (Px), vehicle‐ (Veh), and melatonin (Mel)‐treated birds. On the basis of the circadian mesors of the testosterone rhythms, three distinct categories could be identified: category A (i.e., normal breeding concentrations of plasma testosterone), which includes control, sham‐operated, and vehicle‐treated groups; category A⁺ (i.e., concentrations of plasma testosterone higher than that found in normal breeding quail), which includes 12 h, 12 h+vehicle‐treated, and Px quails; and category A^? (concentrations of plasma testosterone lower than that found in normal breeding quail), which includes 8 h, melatonin‐, and 12 h+melatonin‐treated groups. It is evident that in normal and hypergonadal conditions (i.e., birds belonging to categories A and A⁺) the circadian rhythm in hypothalamic serotonin maintained a positive phase angle of about 16 h. In contrast, birds of category A^? (i.e., in a hypogonadal condition) exhibited a negative phase angle of about 2 h. The present results clearly suggest that the internal phase relationship between the circadian rhythms in hypothalamic serotonin and dopamine might play a crucial role in strategizing and conferring a particular reproductive status to the birds. The role of circadian mechanisms involving circulating thyroid hormones in conferring reproductive status is completely ruled out, as no definite internal phase angle between these two hormonal rhythms was witnessed vis‐à‐vis different treatment groups. The testosterone peaks always occurred at the same time irrespective of breeding status of the bird, but with significant variation in its amplitude (high in hypergonadal and low in hypogonadal condition). It is suggested that administration of 5‐HTP and L‐DOPA at specific time interval and variation in pineal functions that modulate reproductive responses also alter the circadian pattern (acrophase and amplitude) of hypothalamic serotonin and dopamine, maintaining a specific phase relation between these cycles and breeding status. These findings strengthen our previous reports that a specific circadian phase relation of serotonergic and dopaminergic oscillations regulates reproduction. The present study strongly supports interdependence and specific relation of the two systems (gonadal activity and circadian pattern/phase relation of neural oscillation) in both natural and experimentally simulated conditions.     

Circadian rhythms of glucose, triiodothyronine and insulin in relation to composition of diet and meal-timing in rats

A possible role of nutrition as a synchronizer has been recently emphasized, particularly the effect of controlled diet composition of circadian variations of many functions of the organism. The aim of the study was to determine whether diet composition (low or high fat diet) could be a synchronizer of circadian rhythms of glucose, insulin and triiodothyronine. The effect of diet composition on diurnal changes in glucose tolerance was also tested. After 24 h starvation period the biochemical parameters in the serum were measured every 4 hours i.e. 600, 1000, 1400, 1800, 2200, 200. Glucose tolerance was tested between 500-700, 1100-1300, 1700-1900 and 2300-100. The circadian variations of glucose and insulin levels were observed in animals fed both diets. An increase of glucose level was noted during reduced activity of the animals and the acrophase was recorded at 1659 h (low fat diet) and 1514 h (high fat diet). The acrophase of insulin level was observed at 526 h (low fat diet) and 352 hrs (high fat diet) in the period of activity of the animals. Circadian changes of triiodothyronine level were noted in animals fed the low fat diet only, the acrophase appeared at 1447. Simultaneously, no variations occurred in animals fed the high fat diet. A consequence of the high fat diet was also a disappearance of diurnal variations in glucose tolerance test at 60, 90 and 120 min.     

Comparative study of the activity/rest rhythms in young and old ringdove (Streptopelia risoria): correlation with serum levels of melatonin and serotonin

Aging is characterized by changes in the circadian rhythms of melatonin, serotonin, and sleep/wakefulness, alterations that affect sleep quality. The authors studied the circadian rhythms of serotonin and melatonin in young and old ringdoves (Streptopelia risoria) (2-3 and 10-12 yrs old, respectively), animals that are characterized by being monophasic and active by day, like humans. The aim was to correlate the indole rhythms with the animals' activity/rest periods. The animals were kept under a 12:12 h light/dark cycle, fed ad libitum, and housed in separate cages equipped for activity recording. Activity pulses were recorded with one actometer per animal (two perpendicular infrared transmitters) and were logged every 15 min by a computer program (DAS 16) throughout the experiment. Melatonin was measured by radioimmunoassay and serotonin by ELISA at intervals of 3 h (from 09:00 to 18:00 h) and 1 h (from 21:00 to 06:00 h), respectively. The results showed a reduction in nocturnal vs. diurnal activity of 89% and 61% in the young and old animals, respectively, with 100% considered to be the diurnal activity of each group. The amplitude of a cosine function fit to the melatonin concentrations of the old animals was half that of the young birds. The acrophase and nadir were at 02:00 and 14:00 h in the young and 01:00 and 13:00 h in the old animals, respectively. The amplitude of the corresponding cosine function fit to the serotonin concentrations in the old birds was one-third that of the young animals. The acrophase and nadir were at 15:00 and 03:00 h in the young and 16:00 and 04:00 h in the old animals, respectively. For both melatonin and serotonin, the concentrations in the young animals were significantly higher than in the old at most of the measurement times. There was a clear negative correlation between the circadian rhythms of activity and the serum melatonin levels in both young and old animals. The equivalent correlation for serotonin was positive, and stronger in the case of the young animals. The results suggest a possible relationship between the observed decline in the amplitude of the old animals' melatonin and serotonin rhythms and the lower percentage reduction in their nocturnal relative to diurnal activity pulses compared to the young animals. In conclusion, the circadian rhythms of melatonin and serotonin undergo alterations with age that could be involved in the changes in age-associated sleep.     

RETINAL CIRCADIAN RHYTHMS IN HUMANS *

Circadian rhythms in the retina may reflect intrinsic rhythms in the eye. Previous reports on circadian variability in electrophysiological human retinal measures have been scanty, and the results have been somewhat inconsistent. We studied the circadian variation of the electrooculography (EOG), electroretinography (ERG), and visual threshold (VTH) in subjects undergoing a 36h testing period. We used an ultrashort sleep-wake cycle to balance effects of sleep and light-dark across circadian cycles. Twelve healthy volunteers (10 males, 2 females; mean age 26.3 years, standard deviation [SD] 8.0 years, range 19-40 years) participated in the study. The retinal functions and oral temperature were measured every 90 min. The EOG was measured in the light, whereas the ERG and the VTH were measured in the dark. Sleep was inferred from activity detected by an Actillume monitor. The EOG peak-to-peak responses followed a circadian rhythm, with the peak occurring late in the morning (acrophase 12:22). The ERG b-wave implicit time peaked in the early morning (acrophase 06:46). No statistically significant circadian rhythms could be demonstrated in the ERG a-wave implicit time or peak-to-peak amplitude. The VTH rhythm peaked in the early morning (acrophases 07:59 for blue and 07:32 for red stimuli). All retinal rhythms showed less-consistent acrophases than the temperature and sleep rhythms. This study demonstrated several different circadian rhythms in retinal electrophysiological and psychophysical measures of healthy subjects. As the retinal rhythms had much poorer signal-to-noise ratios than the temperature rhythm, these measures cannot be recommended as circadian markers. (Chronobiology International, 18(6), 957-971, 2001)     

Development and relationships of locomotor, feeding, and oxygen consumption rhythms in house crickets

ABSTRACT. Locomotor, feeding, drinking, and oxygen consumption rhythms in adult virgin Acheta domesticus L. all appear to peak in the first half of the scotophase, be entrained cophasically by a LD 14:10 h cycle, have a lights-off Zeitgeber and persist in LL with a π c. 25 h for the locomotor rhythm and c. 23 h for the oxygen consumption rhythm. There is no evidence of these rhythms in last instar larvae. The onset of the locomotor rhythm requires 3 days at 30°C but 5–7 days at 25–28°C after the final ecdysis in virgins, indicating a temperature related development of the locomotor rhythm. Oxygen consumption rhythms are lacking in 2-day-old virgins but present in 8-day-old virgins. Feeding rhythms can be recorded in virgins as young as 2 days (before locomotor rhythm developed). Both oxygen consumption and locomotor rhythms persist during starvation. The results suggest that a central brain oscillator drives both feeding and locomotor rhythms independently, but that the oxygen consumption rhythm is derived from the metabolic demands associated with the other rhythms.     

Geographical and species variation in circadian rhythm parameters in nemobiine crickets

Abstract. . Locomotor activity rhythms were studied in eight species of nemobiine crickets with different habitat preferences. They showed similar patterns with a major peak of activity around dusk and a minor one around dawn. These patterns did not change within the natural range of daylengm (12–16 h). The acrophase time of the rhythm varied between -3.2 and +3.5 h as measured from dusk, and the free-running period (T) varied between 22.8 and 24.5 h. In the Dianemobius fascipes species complex these circadian parameters varied among nine local strains (8^oS to 43^oN) but did not show any latitudinal trend. In a temperate strain of this species complex (Dianemobius nigrofasciatus from Teshikaga, 43^oN), two lines which differed from each other in mean T by 1.4h were selected, and a high heritability of T, 0.78 + 0.20 (mean±SE) was obtained. On the other hand, in a subtropical strain (Dianemobius fascipes from Ishigaki Island, 24^oN), low heritabilities, 0.35 ± 0.15 for acrophase and 0.17 ± 0.21 for T, were obtained from the full-sib correlations. The variation in i seemed to be random and not related to fitness.     

RETINAL CIRCADIAN RHYTHMS IN HUMANS*

Circadian rhythms in the retina may reflect intrinsic rhythms in the eye. Previous reports on circadian variability in electrophysiological human retinal measures have been scanty, and the results have been somewhat inconsistent. We studied the circadian variation of the electrooculography (EOG), electroretinography (ERG), and visual threshold (VTH) in subjects undergoing a 36h testing period. We used an ultrashort sleep-wake cycle to balance effects of sleep and light-dark across circadian cycles. Twelve healthy volunteers (10 males, 2 females; mean age 26.3 years, standard deviation [SD] 8.0 years, range 19–40 years) participated in the study. The retinal functions and oral temperature were measured every 90 min. The EOG was measured in the light, whereas the ERG and the VTH were measured in the dark. Sleep was inferred from activity detected by an Actillume monitor. The EOG peak-to-peak responses followed a circadian rhythm, with the peak occurring late in the morning (acrophase 12:22). The ERG b-wave implicit time peaked in the early morning (acrophase 06:46). No statistically significant circadian rhythms could be demonstrated in the ERG a-wave implicit time or peak-to-peak amplitude. The VTH rhythm peaked in the early morning (acrophases 07:59 for blue and 07:32 for red stimuli). All retinal rhythms showed less-consistent acrophases than the temperature and sleep rhythms. This study demonstrated several different circadian rhythms in retinal electrophysiological and psychophysical measures of healthy subjects. As the retinal rhythms had much poorer signal-to-noise ratios than the temperature rhythm, these measures cannot be recommended as circadian markers. (Chronobiology International, 18(6), 957–971, 2001)