Is there a circadian rhythm of postural control and perception of the vertical?

Daytime activity is largely regulated by the day/night pattern. Various physiological and cognitive functions display a variation during the diurnal period, where individuals manage their balance, spatial orientation and consequently their perception of the vertical. However, findings concerning daytime changes of postural control quality remain contradictory, mainly due to methodogical considerations. The aim of our study is to evaluate the effect of time of day on postural control and perception of the vertical.

Fifteen male subjects underwent six test sessions over a 24-hour period. Each session involved a postural balance test (static/dynamic; eyes open/closed) and a subjective evaluation of sleepiness, fatigue and subjective visual vertical (SVV) (light stick tilted from 10 to 40°; eight trials). No time-of-day effect was observed on postural balance. However, perception of the vertical fluctuates during the day and is better at 10 a.m. than at 10 p.m. Despite the gradual perception of the vertical deterioration over the day, postural balance does not show any fluctuation. This postural balance consistency throughout the day may be the result of compensation mechanisms.     

Does the circadian system regulate lactation?

Environmental variables such as photoperiod, heat, stress, nutrition and other external factors have profound effects on quality and quantity of a dairy cow's milk. The way in which the environment interacts with genotype to impact milk production is unknown; however, evidence from our laboratory suggests that circadian clocks play a role. Daily and seasonal endocrine rhythms are coordinated in mammals by the master circadian clock in the hypothalamus. Peripheral clocks are distributed in every organ and coordinated by signals from the master clock. We and others have shown that there is a circadian clock in the mammary gland. Approximately 7% of the genes expressed during lactation had circadian patterns including core clock and metabolic genes. Amplitude changes occurred in the core mammary clock genes during the transition from pregnancy to lactation and were coordinated with changes in molecular clocks among multiple tissues. In vitro studies using a bovine mammary cell line showed that external stimulation synchronized mammary clocks, and expression of the core clock gene, BMAL1, was induced by lactogens. Female clock/clock mutant mice, which have disrupted circadian rhythms, have impaired mammary development and their offspring failed to thrive suggesting that the dam's milk production was not adequate enough to nourish their young. We envision that, in mammals, during the transition from pregnancy to lactation the master clock is modified by environmental and physiological cues that it receives, including photoperiod length. In turn, the master clock coordinates changes in endocrine milieu that signals peripheral tissues. In dairy cows, it is clear that changes in photoperiod during the dry period and/or during lactation influences milk production. We believe that the photoperiod effect on milk production is mediated, in part by the 'setting' of the master clock with light, which modifies peripheral circadian clocks including the mammary core clock and subsequently impacts milk yield and may impact milk composition.     

Does the circadian pacemaker act through cyclic AMP to drive the melatonin rhythm in chick pineal cells?

Cyclic AMP is a key regulator of melatonin production in the chick pineal gland. Agents that raise cyclic AMP levels (such as forskolin), or cyclic AMP analogues (such as 8-bromocyclic AMP), increase melatonin synthesis and release, whereas agents that lower cyclic AMP levels (including light) decrease melatonin synthesis and release. A circadian oscillator in these cells also raises and lowers melatonin output. We have been investigating the relationships between cyclic AMP and the circadian pacemaker in the regulation of melatonin production. In the chick pineal (unlike certain neuronal systems), the weight of the evidence indicates that cyclic AMP is not on an entrainment pathway to the circadian pacemaker. Instead, cyclic AMP appears to act downstream from the pacemaker. The pacemaker might itself act directly through cyclic AMP, regulating melatonin content by raising and lowering cyclic AMP levels. If this were the case, and if the effects of cyclic AMP levels on melatonin output are saturable (as they must be), then, in the face of such saturating levels of cyclic AMP, the pacemaker should no longer raise or lower melatonin output. To test this prediction, maximally effective concentrations of forskolin and 8-bromocyclic AMP were determined. Both agents markedly increased melatonin output. After 36 hr, cells were refractory to additional stimulation of melatonin output by addition of both agents together, or by higher concentrations of forskolin (although cyclic AMP levels could still be raised further). Nonetheless, the circadian pacemaker continued to raise and lower melatonin output: The rhythm persisted in the face of saturating levels of cyclic AMP. It is therefore suggested that the circadian pacemaker in chick pineal cells acts with, not through, cyclic AMP to regulate melatonin synthesis. Cyclic AMP and the pacemaker act synergistically to regulate serotonin N-acetyltransferase activity and the melatonin rhythm, with cyclic AMP mediating acute effects and amplitude regulation.     

Does FSH signaling have a gender?

FSH is the main endocrine control of mammalian reproduction. FSH triggers somatic cells of the gonads which support germ cells metabolically, i.e. Sertoli cells of the seminiferous tubules, and granulosa cells harboring the oocyte, within the ovarian follicle. FSH leads to similar biological responses in both cell types since it stimulates proliferation and differentiation, according to the developmental stage. However, FSH receptor knock-out female mice are infertile, unlike male mice. Hence, FSH is not equally important in both sexes. Nevertheless, does FSH induce distinct signalling mechanisms in its target cells ? Here, we compare the signalling mechanisms induced by FSH in ovarian and testicular physiology.     

Does zoo herpetology have a future?

Fifty-two North American zoo reptile and amphibian departments were surveyed to determine their contributions to recognized American Zoo and Aquarium Association (AZA)-sponsored programs and formalized research projects over the past 10 years. Surveys also requested information concerning the allocation of resources for conservation and research programs, staff educational background, and entry level salaries. Twenty-two institutions responded to the survey, collectively indicating a total of 164 technical papers, 16 field studies, and 101 non-technical articles completed between 1987 and 1997. Of the 164 technical papers published, 130 (79%) were contributed by three institutions. Of the 16 field studies, seven were outside the United States, whereas nine focused on native species and ecosystems. Six of the reported field studies involved only financial or logistical support. Of the 101 non-technical articles, 42 (42%) were contributed by a single institution. Twenty-one formalized in-house research projects were reported. However, only four appeared to have a clearly defined objective. Survey respondents also reported nine species of reptiles and one amphibian taxon are managed by Species Survival Plans (SSPs). There are currently 12 Taxon Advisory Group (TAG) coordinators, with four of the current coordinators having served on multiple TAG committees. There are 41 AZA-approved studbooks for reptiles and two for amphibians, with 29 having actually been published to date. The average starting salary reported in our survey for entry level keeper positions was $19,500 (range, $13,500–30,000). The average level of education reported was high school graduate. There was no correlation between productivity and higher wages, or level of education. Only one institution received funding specifically for research. We conclude that zoo herpetology departments are not realizing their potential for formalized research and conservation projects and propose recommendations for future involvement. Zoo Biol 17:453–462, 1998. © 1998 Wiley-Liss, Inc.     

Does morality have a biological basis? An empirical test of the factors governing moral sentiments relating to incest.

Kin-recognition systems have been hypothesized to exist in humans, and adaptively to regulate altruism and incest avoidance among close genetic kin. This latter function allows the architecture of the kin recognition system to be mapped by quantitatively matching individual variation in opposition to incest to individual variation in developmental parameters, such as family structure and co-residence patterns. Methodological difficulties that appear when subjects are asked to disclose incestuous inclinations can be circumvented by measuring their opposition to incest in third parties, i.e. morality. This method allows a direct test of Westermarck's original hypothesis that childhood co-residence with an opposite-sex individual predicts the strength of moral sentiments regarding third-party sibling incest. Results support Westermarck's hypothesis and the model of kin recognition that it implies. Co-residence duration objectively predicts genetic relatedness, making it a reliable cue to kinship. Co-residence duration predicts the strength of opposition to incest, even after controlling for relatedness and even when co-residing individuals are genetically unrelated. This undercuts kin-recognition models requiring matching to self (through, for example, major histocompatibility complex or phenotypic markers). Subjects' beliefs about relatedness had no effect after controlling for co-residence, indicating that systems regulating kin-relevant behaviours are non-conscious, and calibrated by co-residence, not belief.     

Does glucagon have a positive inotropic effect in the human heart?

Glucagon is considered to exert cardiostimulant effects, most notably the enhancement of heart rate and contractility, due to the stimulation of glucagon receptors associated with Gs protein stimulation which causes adenylyl cyclase activation and the consequent increase in 3′,5′-cyclic adenosine monophosphate production in the myocardium. These effects have been extensively demonstrated in experimental studies in different animal species. However, efforts to extrapolate the experimental data to patients with low cardiac output states, such as acute heart failure or cardiogenic shock, have been disappointing. The experimental and clinical data on the cardiac effects of glucagon are described here.     

Does the anterior cruciate have a modeling threshold? A case for the affirmative

Growing evidence supports a 1972 proposal that dynamic tension strains of a ligament above a threshold range, but below its ultimate strength, would make its cells synthesize more collagen to thicken and strengthen it. If so, when that strengthening reduced later strains to the bottom of that threshold range this "diametric modeling" would stop. A) Such a mechanism must create a "strength-safety factor" that would minimize or prevent voluntary activities from rupturing healthy ligaments, so chiefly injuries would rupture them. B) Such a mechanism should also make the usual largest loads on a healthy anterior cruciate ligament (ACL) determine its strength, and would make smaller loads mixed with large ones have little effect on its strength. C) In principle, when an ACL's strains exceeded that threshold range, diametric modeling would turn on, strengthen it, and reduce subsequent strains from the same loads. When its strains remained smaller, this mechanically-controlled modeling would turn off. Normal ACLs do have a strength-safety factor so they could have a diametric modeling threshold too, as we now know bone does. In healthy young adult humans available evidence suggests that threshold's value could lie in the region of 23 Newtons/mmC of the ACL's cross section area. If similar relationships applied to fascia, tendons and other ligaments (I suggest they do), they would form fundamental biomechanical properties of collagenous tissue organs.     

Does Cryptosporidium parvum have a clonal population structure?

Cryptosporidiosis, the disease caused in humans by the opportunistic parasite Cryptosporidium parvum, is the result of zoonotic or anthroponotic transmission. Molecular characterization of different isolates from humans and other mammalian species has recently shown this species to be heterogeneous; this heterogeneity has been linked to the host of isolation, suggesting that the parasites causing zoonotic cryptosporidiosis and those propagated by anthroponotic transmission are genetically distinct. Here, Fatih Awad-El-Kariem provides an update on the taxonomic and epidemiological significance of these observations, and discusses evidence for and against the clonality hypothesis as a model to explain strain variation in this species.     

Does PTH have a direct effect on intestine?

Dogma for the past three decades has dictated that parathyroid hormone (PTH) has no direct effect on intestine with regard to calcium or phosphate absorption, but rather that PTH acts to promote the synthesis of a hormonally active form of vitamin D, namely 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. However, diverse laboratories have each provided some evidence to suggest PTH does indeed have a direct effect on intestine. We will briefly review the evidence for biological effects, biochemical effects, and the presence of intestinal receptors for PTH, and conclude with the implications for biomedical research.     

Does carnitine have a role in fat absorption?

The effect of D-carnitine and tetradecylglycidic acid (TDGA), an inhibitor of carnitine palmitoyltransferase, on intestinal absorption of palmitic acid was determined. The proximal intestinal segment was ligated in adult male rats and filled with 0.5 microCi of 14C-palmitic acid alone or with either D-carnitine or TDGA. Thirty minutes later the radioactivity was determined in the intestinal lumen, intestinal wall and plasma. The absorption of palmitic acid was decreased in the presence of D-carnitine (10 mg/ml) as evidenced by significantly lower levels of radioactivity in the gut wall and the plasma and by significantly greater residual radioactivity in the lumenal contents. L-carnitine had no effect on plasma radioactivity but if D- and L-carnitine were given together the effect of D-carnitine was still in evidence. TDGA also inhibited intestinal absorption of palmitic acid.     

‘Rigid’ internal timing in the circadian rhythm of flight activity in a tropical bat

Summary The timing of the emergence activity of a colony of the bat Taphozous melanopogon occupying a cave environment in Madurai (lat. 9°58 N, long. 78°10 E) and consisting of approximately 150–180 animals of both sexes was studies at 10-day intervals for one year. Even though the time of sunset during the eyar varied over a range of 41 min, the bats displayed an astonishingly rigid time of emergence that was restricted to a narrow gate of 16 min from 18:25 to 18:41 h. The timing of the termination of the activity was less precise in all seasons. Light/dark cycles are clearly the Zeitgeber. Even so, the bats began flying when it was very dark (0.1 lx) during shorter days, and they flew out as the sun was disappearing in the evening horizon (50 or more lx) during long days. Evidently there is no invariant, fixed lower threshold intensity that uniformly elicits the onset of activity throughout the year as reported earlier by other authors (Aschoff, 1969; Erkert, 1974). It is proposed that the bats undergo a systematic seasonal shift in the threshold sensitivity to light in response to the photic Zeitgeber of the environment. The result is a remarkable precision in terms of the hours of the civil/calendar day in the emergence of Taphozous melanopogon.     

Does the parallel evolution pattern between the replication-segregation proteins and HU have a biological significance?

The bacterial chromosome is a highly compacted nucleoproteic structure. Its apparent disordered morphology is difficult to conciliate with newly discovered mechanisms governing the propagation of genetic information between mother and daughter cells. Recent experiments in bacterial genetics, biochemistry and cytology from a number of laboratories are beginning to unravel how at each cell division, DNA replication and segregation proteins interact spatially with specific DNA motifs to orchestrate replication and movement of replication forks and chromosomes. We propose here a method to confirm and perhaps extend these experiments by in silico protein sequence comparisons and phylogeny. This analysis showed a parallel evolution between the histone-like protein HU and key protein factors involved in DNA replication and chromosome segregation.     

Athletes’ rest-activity circadian rhythm differs in accordance with the sport discipline

The correct expression of circadian rhythmicity is crucial for the body homeostasis. The rest-activity circadian rhythms (RARs) are involved in the control of the sleep-wake cycle and altered RARs could lead to a compromised health status. Many studies focused on examining sleep behavior and circadian rhythms in physically active subjects or athletes but, unexpectedly, no data on RARs are available. Therefore, we studied the existence of the RAR in athletes and the possible difference in RAR’s characteristics among sport disciplines. The study had a prospective observational design and RARs were recorded for five consecutive training days through actigraphy (Actiwatch 2 actigraph; Philips Respironics, OR, USA) in 43 athletes (mean age: 25.6 ± 3.2 years). Athletes competed in three different disciplines and had different training schedules and competition levels: professional triathletes (N = 10; 6 females and 4 males) had 2 morning (08:30–12:00) and 1 afternoon (15:00–17:00) training sessions, professional volleyball players (N = 19; 12 females and 7 males) used to train once in the morning (09:00–11:30) and once in the afternoon (15:00–18:00), and non-professional soccer players (N = 14; all males) trained always late in the evening (20:30–22:30). To determine the existence of RARs, the activity counts (A.C.) data were analyzed using the single and the population mean cosinor method; a one-way analysis of variance (ANOVA) followed by the Tukey–Kramer post-hoc test was used for the comparison of RAR characteristics among soccer, volleyball and triathlon athletes. Partial eta squared (?_p²) was used to determine the magnitude of the effect for significant outcomes (α = 0.05) in ANOVA. The presence of a significant RAR both for each of the 43 athletes (p < 0.001) and for the three categories of athletes (p < 0.001) was observed. RARs differed among sport disciplines: the Midline Estimating Statistic of Rhythm (MESOR) was significantly higher in triathletes (mean: 347 A.C. with 95% Confidence Interval [CI]: 314–379) compared to both volleyball (mean: 188 A.C. with 95% CI: 173–203; p < 0.001) and soccer players (mean: 289 A.C. with 95% CI: 267–312; p < 0.01) with ?_p² = 0.72. Amplitude (A) values showed the same significant trend of MESOR data (ANOVA: p < 0.001; ?_p² = 0.65) while the acrophase (Φ) occurred at 18:28 for soccer players, significantly later than triathlon (15:20 h; p < 0.001) and volleyball players (16:24 h; p < 0.001) (ANOVA: p < 0.001; ?p2 = 0.84). The higher training duration and intensity reached by triathlon athletes in the morning sessions caused a phase advance of their RAR’s acrophase Φ and higher MESOR and A amplitude compared to volleyball players and triathletes. Therefore, different sport disciplines require different training schedules, training loads and intensities that translate into different RARs. Strength coaches and medical staff of professional teams should strongly consider actigraphy as a practical and powerful tool to monitor RARs, sleep behavior, and the activity levels of their athletes; highlighting potential circadian disruptions through actigraphy could be helpful to prevent musculoskeletal injuries.