Circadian and seasonal cortico-medullary variations in pinealocyte nuclear size. A comparative statistical analysis.

Circadian and seasonal variations were observed in the karyometric index of pinealocytes in the cortical and medullary regions of the distal pineal body. The study involved 70 Wistar rats over a 24-hour interval (0:6, 10:00, 14:00, 18:00, 22:00, 02:00, 06:00 h) during two natural photoluminous periods, i.e. late summer (Long photoperiod) and Winter (Short photoperiod). The results show a difference between the high and low points of both photoperiods. Cortico-medullary differences are found at different times of day during long photoperiod (0:6; 10:00; 14:00 and 18:00 h.) and short photoperiod (14:00; 22:00 and 02:00 h.). The variance analyses between nuclear volume and point-time and between nuclear volume, point-time and location are significative. A high correlation between circadian rhythms and volumetric variations in both layers and photoperiod are found. The results also show significant differences in cortico-medullary karyometric indices between both seasons as well as between the diurnal and nocturnal hours of both photoperiods. It is suggested that the pineal body of the rat is influenced by circadian and seasonal photoperiod and may have groups of cells with different functional characteristics, depending on their location within the gland.     

Asynchrony in the Diurnal Rhythms of Dopaminergic D2 Receptors in Different Brain Regions of the Rat

Diurnal variations of dopaminergic D₂ receptors have been described in the striatum of rats, while other dopaminergic regions remain unstudied. Diurnal variations of dopamine D₂ receptors in the striatum, frontal cortex, and amygdala of the rat, were characterized by the stereospecific binding of [³H]-spiperone. Clear rhythms were found in all these areas, but asynchronous to each other. Striatal receptors had diurnal variations with a single peak at 00:00 hours. Frontal cortex receptors showed two peaks at 00:00 and 12:00 hours. Amygdaline complex receptors had two peaks at 18:00 and 06:00 hours. Saturation binding curves and their Scatchard analysis indicated that the diurnal variations in [³H]-spiperone binding are related to changes in receptor density rather than its affinity. The diurnal variations asynchrony in [³H]-spiperone binding to dopaminergic D₂ receptors from different neural regions, suggest different regulation in each area. Other functional implications of these rhythms remains to be established.     

Asynchrony in the Diurnal Rhythms of Dopaminergic D2 Receptors in Different Brain Regions of the Rat

Diurnal variations of dopaminergic D₂ receptors have been described in the striatum of rats, while other dopaminergic regions remain unstudied. Diurnal variations of dopamine D₂ receptors in the striatum, frontal cortex, and amygdala of the rat, were characterized by the stereospecific binding of [³H]-spiperone. Clear rhythms were found in all these areas, but asynchronous to each other. Striatal receptors had diurnal variations with a single peak at 00:00 hours. Frontal cortex receptors showed two peaks at 00:00 and 12:00 hours. Amygdaline complex receptors had two peaks at 18:00 and 06:00 hours. Saturation binding curves and their Scatchard analysis indicated that the diurnal variations in [³H]-spiperone binding are related to changes in receptor density rather than its affinity. The diurnal variations asynchrony in [³H]-spiperone binding to dopaminergic D₂ receptors from different neural regions, suggest different regulation in each area. Other functional implications of these rhythms remains to be established.     

Day-night changes in plasma melatonin levels,synaptophysin expression and ultrastructural properties of pinealocytes in developing female sheep under natural long and short photoperiods

The aim of the present study was to analyze the 24-h rhythm in plasma melatonin concentration and the day-night differences in synaptophysin expresion and ultrastructural characteristics of the pinealocytes in developing female sheep. Ewes of three different ages were examined: infantile (1-6 months old), pubertal and early fertile age (9-24 months old) and adult (36-60 months old). Experiments were conducted under natural non-stimulatory (long) and stimulatory (short) photoperiods. The obtained results were similar for both analyzed photoperiods. Plasma melatonin concentration, measured in samples obtained every 4 h, showed a similar pattern in the three age groups, with peak values at 02:00 h and troughs at 14:00 h. Mean value of plasma melatonin levels in 9-24 month-old sheep was significantly greater than that in younger or older sheep. The weight of pineal glands obtained at night (02:00 h) was significantly higher than in daylight (14:00 h). Pubertal and early fertile sheep had the largest pineal glands. The pineal volume, and the total number of pinealocytes per gland of 9-24 months-old sheep differed significantly from that of younger or older sheep. The pineal volume, and the mean volume of pinealocytes was significantly greater in animals killed at night. Number of pinealocytes did not vary between animals killed during daylight or at night. The mean volumen of pinealocytes did not show statistical differences between the age groups. In quantitative ultrastructural analysis of pinealocyte cells, the relative volume of mitochondria, rough endoplasmic reticulum and Golgi complexes was significantly greater in 9-24 month-old sheep and in animals killed at night. The relative volume of lipid droplets was highest in older sheep. Collectively, the data support the existence of developmental changes in pinealocyte morphology and quantity, partially in coincidence with a higher melatonin secretion rate.     

Diurnal gait fluctuations in single- and dual- task conditions

ABSTRACT

Gait is one of the most basic movements, and walking activity accomplished in dual task conditions realistically represents daily life mobility. Much is known about diurnal variations of gait components such as muscle power, postural control, and attention. However, paradoxically only little is known about gait itself. The aim of this study was to analyze whether gait parameters show time-of-day fluctuation in simple and dual task conditions. Sixteen young subjects performed sessions at five specific hours (06:00, 10:00, 14:00, 18:00 and 22:00 h), performing a single (walking or counting) and a dual (walking and counting) task. When performing gait in dual task conditions, an additional cognitive task had to be carried out. More precisely, the participants had to count backwards from a two-digit random number by increments of three while walking. Spatio-temporal gait parameters and counting performance data were recorded for analysis. Walking speed significantly decreased, while stride length variability increased when the task condition switched from single to dual. In the single-task condition, diurnal variations were observed in both walking speed and counting speed. Walking speed was higher in the afternoon and in the evening (14:00 and 22:00 h) and lower in the morning (10:00 h). Counting speed was maximum at 10:00 and 14:00 h and minimum at 18:00 h. Nevertheless, no significant diurnal fluctuation was substanytiated in the dual task condition. These results confirm the existing literature about changes in gait between single and dual task conditions. A diurnal pattern of single-task gait could also be highlighted. Moreover, this study suggests that diurnal variations faded in complex dual task gait, when the cognitive load nearly reached its maximum. These findings might be used to reduce the risk for falls, especially of the elderly.     

Diurnal and circadian variations in indole contents in the goose pineal gland

ABSTRACT

The diurnal and circadian profiles of pineal indoles, except melatonin, are poorly characterized in birds. Moreover, there are no data on the effect of sudden changes in the light–dark cycle on these profiles. Therefore, we investigated the diurnal (Experiment I) and circadian variation (Experiment II) of nine pineal indoles (tryptophan, 5-hydroxytryptophan, serotonin, N-acetylserotonin, melatonin, 5-hydroxyindole acetic acid, 5-methoxytryptophol, 5-methoxyindole acetic acid, 5-methoxytryptamine) in geese, as well as the changes in the profiles of these substances in geese subjected to a reversed light–dark cycle (Experiment III). For the first 12 weeks of life, all geese were kept under a diurnal cycle of 12 h of light and 12 h of darkness (12L:12D). In Experiment I (n = 48), they were kept under these conditions for another 14 days before being sacrificed at 2-h intervals for sampling of the pineal glands. In Experiment II, the geese (n = 48) were divided into three groups (12L:12D, 24L:0D, 0L:24D) for 10 days before sampling at 6-h intervals. In Experiment III, 24 geese were exposed to a reversed light–dark cycle before sampling at 14:00 and 02:00 on the first, second and third days after light–dark cycle reversal. To determine the content of the indoles in the goose pineals, HPLC with fluorescence detection was used. We found that, with the exception of tryptophan, all the investigated indoles showed statistically significant diurnal variation. When geese were kept in constant darkness, most of the indoles continued to show this variation, but when geese were kept in constant light, the indoles did not show significant variation. When the light–dark cycle was reversed (12L:12D to 12D:12L), the profiles of NAS, melatonin, 5-MTAM and 5-MTOL reflected the new cycle within 2 days. The content of serotonin in geese in 12L:12D was higher than that observed in other birds under these conditions, which suggests that this compound may play a special role in the pineal physiology of this species. In conclusion, our results show that the daily variations in the metabolism of melatonin-synthesis–related indoles in the goose pineal gland are generated endogenously and controlled by environmental light conditions, as in other birds. However, comparison of the results obtained with the goose to those obtained with other species (chicken, duck) unambiguously shows that the profiles of pineal indoles differ markedly between species, in both the quantitative proportions of the compounds and the characteristics of the diurnal changes. These findings provide strong arguments for the need for comparative studies.     

Postnatal development of female sheep pineal gland under natural inhibitory photoperiods: an immunocytochemical and physiological (melatonin concentration) study

The purpose of this study was to determine structural and immunocytochemical changes taking place during the day and at night in developing sheep pineal gland under natural non-stimulatory photoperiods (summer solstice). Additionally, the diurnal cycle of plasma melatonin levels was charted and differences between diurnal and nocturnal pineal melatonin concentrations were analyzed. 36 ewes of three different ages were examined: infants (1-6 months old), pubertal and early fertile age (9-24 months old) and adults (36-60 months old). Plasma and pineal gland melatonin levels were higher in pubertal sheep than in infants or adults. Pubertal sheep pineal glands were also heavier, contained a larger number of pinealocytes and interstitial cells and displayed more evident innervation and vascularisation than infants or adults. There was no difference in the number of pinealocytes and interstitial cells between animals killed during daylight or at night. Gland weight, pinealocyte nuclear profile areas and plasma melatonin concentrations were all significantly higher at night than during the day.     

Two morphological types of pineal window in catfish in relation to photophase and scotophase activity: a morphological and experimental study

The pineal window is a transparent/translucent pineal covering on the dorsal surface of the cranium of certain fishes and is associated with light reactions of fish. In the present study, catfish species Clarias batrachus, Heteropneustes fossilis, Mystus vittatus, M. seenghala, and M. cavassius were examined for the type of pineal window present. Two morphologically different types of pineal window were found: an opaque-looking pineal window in C. batrachus and H. fossilis and a translucent type of pineal window in M. vittatus, M. seenghala, and M. cavassius. The distributional pattern of pigments in the melanophores at the pineal window were studied in terms of Melanophore Index (MI). In all of the species studied, a pineal foramen, a subepidermal lens-like tissue, and pineal end vesicle were present. Experiments were carried out on catfish having the opaque pineal window, as it is uncommon in catfish. Catfish with normal and shielded pineal window were exposed to conditions of artificial constant illumination (LL) and darkness (DD) to evaluate the effects of altered photoperiods on the state of pigmentation of melanophores at the pineal window. Recordings of diel activity patterns, which are light dependent in catfish, were carried out under both natural and artificial photoperiods in fish with a normal or shielded window in order to assess its functional nature. The existence of two morphologically and functionally different types of pineal window in a relatively closely related group of catfish has been demonstrated in this study. The nature of the opaque type of pineal window has been reconsidered based on new experimental evidence.     

Diurnal Variations of Striatal D2 Dopaminergic Receptors and its Relation with Haloperidol-induced Catalepsy

In spite of the clear evidences for the blockade of dopaminergic D2 receptors as the mechanism of action for haloperidol-induced catalepsy, the contribution of pharmacokinetic and pharmacodynamic aspects on the diurnal modulation of haloperidol-induced catalepsy is controversial. We studied the diurnal variations of striatal dopamine receptors and its relation with catalepsy diurnal variations. The [3 H]-spiperone binding to dopamine receptors had a clear rhythm with a peak at 00:00 to 03:00 h, and a trough at 12:00 to 18:00 h. Haloperidol-produced catalepsy measured with the four-cork test, also showed a clear rhythm, with a peak at 00:00 h and trough at 9:00 h. The dose-response curves at peak and trough of catalepsy had the same ED 50 (0.12 mg), with time-related changes in the maximal effect. Similar diurnal variations between catalepsy and dopamine receptor binding, indicate a relevant role of temporal pharmacodynamics of haloperidol on the modulation of its behavioral effects.     

The effect of strength training at the same time of the day on the diurnal fluctuations of muscular anaerobic performances

The aim of this study was to examine the effects of training at the same time of the day on the diurnal variations of anaerobic performances to provide some recommendations to adjust training hours with the time of the day of competitive events. Thirty participants underwent 8 weeks of lower-extremity progressive resistance training performed 3 times per week designed to promote muscular strength and power. These subjects were randomly assigned to a morning training group (MTG, 07:00-08:00 hours, n = 10), an evening training group (ETG, 17:00-18:00 hours, n = 10), and a control group (CG, completed all tests but did not train, n = 10). Performance in the squat jump, the countermovement jump, the Wingate and 1 repetition maximum (1RM) during leg extension, leg curl, and squat tests was recorded just before and 2 weeks after an 8-week course of regular training. For all the subjects, the morning and evening tests were scheduled at the same time of the day as for the morning and evening training sessions. Before training, the results indicated a significant increase in performance from morning to evening tests (ca. 2.84-17.55% for all tests) for all groups. After training, the diurnal variations in anaerobic performances were blunted in the MTG. In fact, there was no significant difference in muscular power or strength between morning and evening tests. However, these intradaily variations in anaerobic performances persisted in the ETG and CG. From a practical point of view, adaptation to strength training is greater at the time of the day at which training was scheduled than at other times.     

Diurnal Variations of Striatal D2 Dopaminergic Receptors and its Relation with Haloperidol-induced Catalepsy

In spite of the clear evidences for the blockade of dopaminergic D2 receptors as the mechanism of action for haloperidol-induced catalepsy, the contribution of pharmacokinetic and pharmacodynamic aspects on the diurnal modulation of haloperidol-induced catalepsy is controversial. We studied the diurnal variations of striatal dopamine receptors and its relation with catalepsy diurnal variations. The [ 3 H]-spiperone binding to dopamine receptors had a clear rhythm with a peak at 00:00 to 03:00 h, and a trough at 12:00 to 18:00 h. Haloperidol-produced catalepsy measured with the four-cork test, also showed a clear rhythm, with a peak at 00:00 h and trough at 9:00 h. The dose-response curves at peak and trough of catalepsy had the same ED 50 (0.12 mg), with time-related changes in the maximal effect. Similar diurnal variations between catalepsy and dopamine receptor binding, indicate a relevant role of temporal pharmacodynamics of haloperidol on the modulation of its behavioral effects.     

Diurnal Rhythm of the Muscular Performance of Elbow Flexors During Isometric Contractions

The influence of time of day on elbow flexion torque was studied. Thirteen physical education students, 7 males and 6 females, made maximal and submaximal isometric contractions at 90° of elbow flexors using a dynamometer. The torque developed was measured on each contraction. The myoelectric activity of the biceps muscle was also measured at the same time by surface electromyography (EMG) and quantified from the root mean square (RMS) activity. Torque and surface EMGs were measured at 6:00, 9:00, 12:00, 15:00, 18:00, 21:00, and 24:00 h over the same day. Oral temperature before each test session was measured on each occasion after a 30-min rest period. We observed a diurnal rhythm in elbow flexor torque with an acro-phase at 18:00 h and a bathyphase at 6:00 h, in phase with the diurnal rhythm in oral temperature. However, the diurnal rhythm of temperature did not appear to have any influence on the torque. Links between neuromuscular efficiency and RMS/torque ratio were evaluated by measuring muscle activity along with torque. We also assessed variations in the level of maximal activity of the muscle under maximal voluntary contraction. Neuromuscular efficiency fluctuated during the day, with maximal and minimal efficiency at 18:00 h and 9:00 h, respectively, whereas activation level was maximal at 18:00 h and minimal at 9:00 h. The diurnal rhythm of torque was accounted for by variations in both central nervous system command and the contractile state of the muscle.     

Effect of photoperiod on pineal gland volume and pinealocyte size in the Chinese hamster, Cricetulus griseus

Male adult (200-day-old) Chinese hamsters (Cricetulus griseus) raised from weaning under either LD 16:8 or LD 8:16 were used. The pineal gland of the Chinese hamster consists of superficial (major) and deep (minor) components and a continuous, or interrupted, narrow parenchymal stalk interposed between them. The volume of the superficial pineal including the parenchymal stalk is greater under LD 16:8 than under LD 8:16. Under both photoperiods, pinealocytes in the superficial pineal have larger nuclei and more abundant cytoplasm than those in the deep pineal. Nuclei in the superficial pineal appear pale and usually have irregular profiles, whereas those in the deep pineal appear dark and have round profiles. In the superficial pineal, pinealocyte nuclei are larger, paler, and more irregular; and, in addition, nuclear density is lower under LD 16:8 than under LD 8:16. Similar, but less prominent, photoperiod-induced changes occur in the volume of the deep pineal, the size of pinealocytes, and pinealocyte nuclear morphology in the deep pineal. The results indicate that the development and differentiation of pinealocytes in both pineal portions may be advanced under long photoperiods and delayed under short photoperiods, although pinealocytes in the deep pineal may remain not fully differentiated even in adults. Since testicular weights and body weights are similar under both photoperiods, the photoperiod may exert marked influences on the development of the pineal gland without affecting reproductive activity and growth rates of animals.     

Diurnal and day-to-day variations in isometric and isokinetic strength

ABSTRACT

Time-of-day effects in strength performance have been extensively investigated due to their relevance in competitive sports. However, most studies use large measurement intervals making it difficult to monitor potential performance changes throughout the day. Furthermore, previous studies have exclusively focused on how the time of day affects strength on a group level and ignored the individual differences in the times of peak performance. Therefore, the main purpose of this study was to investigate the diurnal and day-to-day variations in isometric and isokinetic leg, arm and trunk strength over six different times of the day. Following a familiarization test, 19 trained males (age: 24.1 ± 2.5 years) performed isometric and isokinetic strength assessments at six different times of the day (7:00, 10:00, 13:00, 16:00, 19:00, and 21:00) with an isokinetic dynamometer. An eighth test session was performed at the same time of the day as the seventh test session to investigate the day-to-day variations and the difference between diurnal and day-to-day variations were compared. All tests were separated by at least 48 h. The start time for the first session was randomized. The mean maximum isometric leg strength was 5.85 ± 0.80 N.kg^?1 and 4.99 ± 0.78 N.kg^?1at the peak and at the nadir of the day, respectively. The mean difference (95% CI) was 0.86 ± 0.47 N.kg^?1 (0.62; 1.10) for the diurnal variation and 0.30 ± 0.42 N.kg^?1 (0.09; 0.52) for the day-to-day variation. The mean maximum isometric arm strength was 1.68 ± 0.33 N.kg^?1 at the peak and 1.46 ± 0.19 N.kg^?1 at the nadir of the day, respectively. The mean difference (95% CI) was 0.21 ± 0.16 N.kg^?1 (0.14; 0.29) for the diurnal variation and 0.06 ± 0.05 N.kg^?1 (0.03; 0.08) for the day-to-day variation. The linear mixed-effects model showed little evidence for differences in isometric leg strength between the different times of the day (all p-values >0.983). The present study demonstrated that diurnal variations in leg and arm strength are nearly three times higher than the day-to-day variations, but there was only little evidence for a time-of-day effect on a group level. The diurnal variations observed herein without time-of-day effects are suggestive that individuals achieve their peak performance at different times of the day. Therefore, performance tests should be carried out at the same time of the day to ensure comparability. Furthermore, depending on the difference between the time of competition and the time of peak performance, as well as the individual magnitude in diurnal variation, some athletes can have a clear disadvantage.Abbreviation: 95% CI, 95% confidence interval; SD, standard deviation; ICC, intraclass correlation coefficient.     

Sex differences in secretion pattern of neonatal rat Harderian gland under various environmental lighting conditions

1. Secretion pattern of Harderian gland of neonatal rats maintained under (a) diurnal lighting conditions; (b) continuous light or (c) continuous darkness was studied at light microscopy level. 2. All animals were placed in especially designed cages at 13:00 hr on day 1 and studied on day 7 at 13:00 and 23:00 hr, respectively. 3. Acini with intraluminal secretion were counted in glands from each animal and the results were separately grouped for male and female animals. 4. A diurnal rhythm in secretion pattern of rat Harderian gland in neonatal period was demonstrated. 5. A statistically significant difference was observed in the gland secretion pattern between males and females at both, 13:00 and 23:00 hr when the animals were kept under diurnal lighting conditions. 6. Under continuous light or continuous darkness, the diurnal rhythm in secretion pattern was lost and no significant differences were seen when data from males were compared to those from female neonates. 7. Results are discussed in terms of the possible function of Harderian gland as element of an extraretinal photoreceptor system involved in the regulation of pineal function in neonatal rats.     

软质与硬质地表对树木花粉日飘散变化的影响

以油松(Pinus tabulaeformis)、白玉兰(Magnolia denudata)、白皮松(Pinus bungeana)、臭椿(Ailanthus altissima)为被试树种,对比研究了春季静风晴朗天气中软质与硬质两种地表条件下不同树种在距树10m高度1.5m处花粉浓度的日变化特征。研究结果表明:(1)4个树种在相同地表环境的花粉浓度日变化趋势基本一致,但同一树种花粉浓度的日变化特征在软、硬两种地表条件下的差异明显。软质地面一天内空气中花粉浓度最大值出现14:00时前后,04:00时花粉浓度最低,这与全天内空气温度的变化正好一致,而与空气相对湿度的变化恰好相反。硬质地表近地空间空气中的花粉浓度则呈现"双峰型"日变化特征,两次峰值分别出现在14:00时和20:00时,硬质地面花粉浓度20:00时晚高峰的出现时间与硬质地面温度日峰值一致。(2)分析硬质地表20:00时花粉浓度高峰出现的原因可能与硬质地面的散热特性有关,硬质地面夜间释放积蓄热量的过程会在一定程度上增强近地面空气的对流运动,并辅助空气中的花粉粒子不断飘散,形成花粉浓度晚高峰。(3)相对于软质地面来讲,硬质地表对空气中花粉飘散的影响作用持续时间更长,这也在一定程度上延长了致敏花粉的危害时间,加剧了致敏花粉的污染程度。研究还进一步在花粉致敏树种栽植、地表覆盖方式等方面进行了讨论;同时建议花粉症患者根据花粉污染发生规律合理规避花粉浓度聚集高峰期出行,从而有效缓解致敏花粉对易感人群的健康威胁。     

A single nocturnal exposure to 2-7 millitesla static magnetic fields does not inhibit the excretion of 6-sulfatoxymelatonin in healthy young men

The present study sought to evaluate possible acute effects on 6-sulfatoxymelatonin (aMT6s) excretion, a surrogate for melatonin levels in blood, in volunteers exposed to static magnetic fields with flux densities representative for workers in light metal reduction plants and operators of medical MRI in hospitals. Eleven healthy male volunteers (23-43 years) participated. Urine samples were collected for two consecutive 24 h periods from 22:00 hours day 1 (exposure day) through day 2 (day after exposure) and then for 24 h from 07:00 hours on day 7 (control day). On the day of exposure the subjects slept in the MRI room from 22:00 hours until 07:00 hours next morning, thus receiving a 9 h exposure to the magnetic field (2-7 mT). On the day after exposure and on the control day, they slept at home and otherwise performed their ordinary daily activities. Total daily urine production was collected in four parts: 22:00-07:00 hours, 07:00-11:00 hours, 11:00-18:00 hours, 18:00-22:00 hours, and the volume for each interval was measured and recorded. Samples were transferred to coded bottles and frozen for later RIA analysis of aMT6s. Pairs of values of mean hourly aMT6s excretion, both diurnal and for the four daily intervals, were compared using two-sided Wilcoxon signed ranks test. The day of exposure and the day after exposure were not significantly different from the control day, either for the total diurnal secretion or the interval data. In summary, the study shows no association between a single nocturnal exposure to a static magnetic field of strength 2-7 mT and excretion of aMT6s in urine.     

Diurnal variation in temperature, mental and physical performance, and tasks specifically related to football (soccer)

Football (soccer) training and matches are scheduled at different times throughout the day. Association football involves a variety of fitness components as well as psychomotor and game-related cognitive skills. The purpose of the present research, consisting of two separate studies, was to determine whether game-related skills varied with time of day in phase with global markers of both performance and the body clock. In the first study, eight diurnally active male association football players (19.1+/-1.9 yrs of age; mean+/-SD) with 10.8+/-2.1 yrs playing experience participated. Measurements were made on different days at 08:00, 12:00, 16:00, and 20:00 h in a counterbalanced manner. Time-of-day changes in intra-aural temperature (used as a marker of the body clock), grip strength, reaction times, flexibility (markers of aspects of performance), juggling and dribbling tasks, and wall-volley test (football-specific skills) were compared. Significant (repeated measures analysis of variance, ANOVA) diurnal variations were found for body temperature (p<0.0005), choice reaction time (p<0.05), self-rated alertness (p<0.0005), fatigue (p<0.05), forward (sit-and-reach) flexibility (p<0.02), and right-hand grip strength (p<0.02), but not left-hand grip strength (p=0.40) nor whole-body (stand-and-reach) flexibility (p=0.07). Alertness was highest and fatigue lowest at 20:00 h. Football-specific skills of juggling performance showed significant diurnal variation (p<0.05, peak at 16:00 h), whereas performance on the wall-volley test tended to peak at 20:00 h and dribbling showed no time-of-day effect (p=0.55). In a second study, eight diurnally active subjects (23.0+/-0.7 yrs of age) completed five test sessions, at the same times as in the first study but with a second session at 08:00 h. Test-re-test comparisons at 08:00 h for all components indicated good reliability. Intra-aural temperature showed a significant time-of-day effect (p<0.001) with mean temperature at 16:00 h (36.4 degrees C) higher than at 08:00 h (35.4 degrees C). There was no significant effect of chronotype on the temperature acrophase (peak time) (p>0.05). Diurnal variation was found for performance tests, including sit-and-reach flexibility (p<0.01) and spinal hyper-extension (p<0.05). Peaks occurred between 16:00 and 20:00 h and the daytime changes paralleled the temperature rhythm. Diurnal variation was also found for football-specific tests, including dribbling time (p<0.001, peak at 20:00 h) and chip test performance (p<0.01), being more accurate at 16:00 h (mean error=0.75 m) than at 08:00 h (mean error=1.01 m). Results indicate football players perform at an optimum between 16:00 and 20:00 h when not only football-specific skills but also measures of physical performance are at their peak. Body temperature peaked at a similar time, but positive mood states seemed to peak slightly earlier. While causal links cannot be established in these experiments, the results indicate that the diurnal variation of some aspects of football performance is affected by factor(s) other than body temperature alone.     

Circadian Changes in Anxiolysis-Related Behavior of Syrian Hamsters. Correlation with Hypothalamic GABA Release

The diurnal variations in anxiolysis and exploratory behavior were examined in a plus-maze paradigm in Syrian hamsters exposed to 14 h light: 10 h dark photoperiods or to constant darkness for 3 days. The percent of time spent in open arms and the percent of entries to open arms (both indexes of anxiety-related behavior) as well as the number of crosses to both arms (an index of locomotor behavior) showed significant daily variations under the two lighting conditions, maxima being found at night (2400-0400 h). Flumazenil (5 mg/kg) injected at the middle of the light (at 1600 h) or dark period (at 0400 h) decreased by 39-54 % anxiolysis-related behavior without affecting locomotor activity significantly. 3 H-?-aminobutyric acid (GABA) release from preoptic-medial basal hypothalamic explants obtained from hamsters exposed to 14 h light: 10 h dark photoperiods attained maximal values at 2400-0400 h. The results further supported the existence of circadian changes in anxiolysis-related behavior in Syrian hamsters that correlated with an increased hypothalamic GABA release.     

The effects of sleep deprivation and time of day on cognitive performance

The extent to which the diurnal fluctuations of different cognitive processes could be affected by sleep loss may be explored to predict performance decrements observed in the real world. Twenty healthy male subjects voluntarily took part in 8 test sessions at 06:00, 10:00, 14:00, and 18:00 h, following either a night with or without sleep in random order. Measurements included oral temperature, simple reaction time, sign cancelation, Go/NoGo, and the Purdue pegboard test. The results indicate that simple reaction time and motor coordination had morning–afternoon variations closely following the rhythms of temperature and vigilance. Inhibitory attention (Go/NoGo) presented no morning–afternoon variations. Sleep deprivation may affect the profiles of cognitive performance depending on the processes solicited. Sustained and inhibitory attention are particularly affected in the morning (after 24 and 28 waking hours), while a complex task (visuo-motor coordination) would be affected after 32 waking hours only.