The effect of short and long duration exercise on serum erythropoietin concentrations

Summary The effects of short and long duration exercise on serum erythropoietin concentrations [EPO]_s were studied in seven male cross-country skiers of national team standard and eight male marathon runners, respectively. The short duration exercise was performed as 60 min of cycling at an intensity of 80%–95% of maximal heart rate. Arterial blood oxygen saturations monitored by pulse-oximetry remained unchanged throughout exercise. The partial pressure of O₂ at which haemoglobin was half-saturated with O₂ calculated from forearm venous blood gas tension and blood O₂ saturation, and the erythrocyte 2,3-diphosphoglycerate did not change significantly during the exercise. Blood lactate concentrations were increased at the end of exercise [from 1.3 (SEM 0.1) to 3.6 (SEM 0.3) mmol · 1^–1]. The [EPO]_s determined (by enzyme-linked immunosorbent assay) pre-exercise, 5 min, 6 h, 19 h, and 30 h after the exercise were unchanged [from 16.1 (SEM 2.6) to 19.1 (SEM 3.2), 17.9 (SEM 3.0), 17.0 (SEM 2.5), and 18.6 (SEM 2.9) U·l^–1, respectively]. The [EPO]_s were not correlated to the earlier parameters. The long duration exercise consisted of habitual training, a 3 week break from training followed by 2 and 4 weeks of re-training. The [EPO]_s, body fat (BF), and serum free-testosterone concentrations determined at the end of each period remained unchanged. The maximal oxygen uptakes were decreased after the break from training and increased during retraining (P=0.04). Body mass (m _b) increased after the break in training (P=0.02). The [EPO]_s were correlated to BF,r=0.42,P=0.02;m _b,r=0.45,P=0.01; and free-testosterone concentrations,r=0.44,P=0.01. Thus, short and long-duration exercise had no direct influence on [EPO]_s; but relationships among [EPO]_s, free-testosterone concentrations and body composition were noted.     

Neural analysis of temporally patterned sounds in the frog's thalamus: processing of pulse duration and pulse repetition rate

We conducted a single unit study of auditory neurons in the central thalamic nucleus of the northern leopard frog. These cells, unlike those of the posterior thalamic nucleus (J. Comp. Physiol., 150 (1983) 333-344), were broadly tuned and sensitive to one or more temporal features (pulse duration and repetition rate) of complex sound signals. When compared with previous studies, these results suggest that temporal and spectral information may be processed separately by distinct populations of neurons within the frog's thalamus.     

Neural processing of amplitude-modulated sounds

Amplitude modulation (AM) is a temporal feature of most natural acoustic signals. A long psychophysical tradition has shown that AM is important in a variety of perceptual tasks, over a range of time scales. Technical possibilities in stimulus synthesis have reinvigorated this field and brought the modulation dimension back into focus. We address the question whether specialized neural mechanisms exist to extract AM information, and thus whether consideration of the modulation domain is essential in understanding the neural architecture of the auditory system. The available evidence suggests that this is the case. Peripheral neural structures not only transmit envelope information in the form of neural activity synchronized to the modulation waveform but are often tuned so that they only respond over a limited range of modulation frequencies. Ascending the auditory neuraxis, AM tuning persists but increasingly takes the form of tuning in average firing rate, rather than synchronization, to modulation frequency. There is a decrease in the highest modulation frequencies that influence the neural response, either in average rate or synchronization, as one records at higher and higher levels along the neuraxis. In parallel, there is an increasing tolerance of modulation tuning for other stimulus parameters such as sound pressure level, modulation depth, and type of carrier. At several anatomical levels, consideration of modulation response properties assists the prediction of neural responses to complex natural stimuli. Finally, some evidence exists for a topographic ordering of neurons according to modulation tuning. The picture that emerges is that temporal modulations are a critical stimulus attribute that assists us in the detection, discrimination, identification, parsing, and localization of acoustic sources and that this wide-ranging role is reflected in dedicated physiological properties at different anatomical levels.     

Differential processing of terminal tone parts within structured and non-structured tones

Recent studies utilizing the mismatch negativity (MMN) event-related potential (ERP) revealed that when a repetitive sequence of sinusoidal tones is presented, the occasional insertion of a short deviation into some of the tones leads to the elicitation of an MMN only if it occurs during the initial 300 ms, but not beyond. In contrast, deviations occurring in speech sounds elicit MMN even beyond 300 ms. We conducted two experiments to resolve this conflict. We hypothesised that an additional transient within an otherwise unstructured tone may overcome this limitation. First, we tested for MMN to a deviance at the terminal part of a 650 ms tone which did or did not contain a gap. Only when the tone included the gap, MMN was obtained. Second, we compared the gap condition with two noise conditions, in which the gap was replaced by modulated white noise. The noise conditions differed with respect to the saliency of the perceived interruption of the tone. In all three conditions, MMN was elicited. These results demonstrate that structuring a sinusoidal tone by a gap or a noise interval is sufficient to regain MMN. It is suggested that the introduction of an additional transient triggers a new integration window overcoming the temporal constraints of automatic tone representation. This resolves the seeming contradiction between MMN studies using tonal and speech sounds.     

Changes in ventilation at the start and end of moderate and heavy exercise of short and long duration

Summary These experiments examined the effect of exercise intensity and duration on the magnitude of the abrupt change in ventilation at the start ( ) and end ( ) of exercise. Five subjects performed constant load treadmill exercise at 50% and 80% of their maximum oxygen consumption ( ) for 6 and 10 min while inspiring atmospheric air. The subjects also completed additional exercise tests at 80% for 10 min while inspiring an oxygen-enriched gas mixture. During each exercise trial ventilation was measured breath-by-breath. The and were determined by using non-linear curve-fitting techniques. The results showed that was greater at the start of the 80-% exercise tests compared to the 50-% tests and that at each level of exercise was greater than . The results also demonstrated that was inversely related to the intensity and duration of exercise. Furthermore, the was not altered subsequent to the inspiration of oxygen-enriched air. These findings have led us to postulate that the stimulus responsible for is reduced during exercise and that the degree of reduction is related to the intensity and duration of exercise. In addition, it was concluded that these changes might occur independently of peripheral chemoreceptor activity.     

Defining short and long sleep duration for future paediatric research: A systematic literature review

Short and long sleep patterns in children have been associated with a range of poor health outcomes. However, there is no consensus regarding the definitions of these abnormal sleep parameters in childhood for use in paediatric research. Given that there is a clear lack of definitions for sleep duration throughout paediatric sleep literature, this review aimed to establish recommendations for standard cut‐offs of short and long sleep for children aged 1–16 years to enable homogeneity in future studies of paediatric sleep duration. Four databases were systematically searched to identify prospective studies that defined short or long sleep patterns in children. Included papers (38) were assessed for methodological quality, and their definitions were extracted to examine the current applied cut‐offs in the literature for short or long sleep duration. The definitions were analysed in a regression model to summarize applied cut‐offs from subjective data into cut‐offs for short and long sleep duration. These models were fitted to reference values of three commonly cited paediatric population studies to establish new definitions of sleep duration for future use in research. Across the age groups there was little consensus in applied cut‐offs for short and long sleep duration. This study found the best compromise for short sleep was defined as the 2.5th centile (hours = 0.25*age + 11) and long sleep as the 97.5th centile (hours = 0.017*age² ? 0.68*age + 16) of sleep duration in children. Recommendations for the hourly cut‐offs of short and long sleep duration based on these percentiles were described.     

Predictive value of immunologic and virologic markers after long or short duration of HIV-1 infection

Laboratory markers that predict HIV-1 disease progression include plasma viral burden, CD4+ T-cell count, and CD38 expression on CD8 T cells. To better understand whether the predictive value of these markers is dependent on how long an individual has been infected, we analyzed data from the Multicenter AIDS Cohort Study early (median = 2.8 years) and late (median = 8.7 years) in the course of infection. Overall, we found that HIV RNA and CD38 levels were similarly predictive of AIDS early on compared with a relatively weaker CD4 cell count signal. Later in the course of infection, CD38 level remained the strongest predictive marker and CD4 cell count registered a marked increase in prognostic power. Among untreated individuals, there was little difference in prognosis (median time to AIDS) associated with given marker values regardless of infection duration. The prognosis given a specific viral load level tended to deteriorate late in the course of infection among those undergoing treatment with monotherapy or combination therapy, however. These data provide a unique historical look at the predictive value and prognostic significance of HIV-1 disease markers at different stages of infection in a large cohort, with direct relevance to current patients who are untreated or for whom treatment is ineffective.     

A method of continuous recording of the blood flow in the brain in experiments of short and long duration

Summary A change in the intensity of the direct electric current passing through the needle-formed thermo-resistance (connected into the bridge circuit forming the input to the amplifier) raises the temperature of the thermistor to 1°C over that of the inflowing blood. This makes it possible to register the blood flow at various areas of the brain.Presented by Academician K. M. Bykov     

Differential changes in long-interval intracortical inhibition and silent period duration during fatiguing hand exercise

During fatiguing exercise corticomotor excitability increases as force declines, which may serve to increase motor output to the exercising muscle, but paradoxically at the same time there is an increase in silent period (SP) duration which is thought to represent a build-up of intracortical inhibition. Paired-pulse TMS at long interstimulus intervals can also be used to derive an index of long-interval cortical inhibition (LICI), however this has not yet been investigated in fatigue. Our aim was to measure LICI during and after a fatiguing exercise and determine if the changes in the index of LICI parallel the changes in SP duration. To do this, we used single and paired-pulse TMS to measure motor evoked potential (MEP) amplitude, LICI and SP duration during, and for 10 min after, a 10-min intermittent maximal fatiguing exercise of the index finger, designed to fatigue the first dorsal interosseous (FDI) muscle (force after 10-min of exercise 64 ± 7% of baseline, P < 0.05). Single-pulse MEP amplitude and SP duration were increased during fatiguing exercise (minute 10; 179 ± 24% and 128 ± 9% of baseline, respectively, P < 0.05), in contrast the measure of LICI was reduced compared to baseline (minute 10; 0.45 ± 0.17 vs. baseline; 0.70 ± 0.10, P < 0.05). These results suggest that SP duration and LICI may reflect processes occurring in different neuronal populations. The increased SP duration may correspond to processes of central fatigue in centres ‘upstream’ of primary motor cortex (M1), whereas the decrease in LICI, together with increased MEP amplitude, are consistent with an increase in M1 output during fatigue that may serve to compensate for reduced central drive.     

Correlates of long sleep duration

STUDY OBJECTIVE: Sleeping more than 7 to 8 hours per day has been consistently associated with increased mortality. Whether this association is causal and what pathways explain this association are unknown. We sought to identify factors that could potentially explain the association between long sleep and mortality. DESIGN: Cross-sectional epidemiologic survey. PARTICIPANTS: Middle-aged women (n = 60,028) participating in the Nurses Health Study II who reported a habitual sleep duration of 7 hours or more. RESULTS: Multiple sclerosis (odds ratio [OR] = 3.7, 95% confidence interval [3.0-4.5]), antidepressant use (OR = 3.1, [2.9-3.3]), benzodiazepine use (OR = 3.0 [2.6-3.3]), and systemic lupus erythematosus (OR = 2.9, [2.3-3.6]) were the factors most strongly associated with prolonged sleep. Combining these data with prevalence information and a range of plausible associations with mortality, the confounding rate ratio was estimated. This parameter is the ratio of the unadjusted long sleep-mortality rate ratio to the rate ratio adjusted for the factor and measures the extent that the factor can alter the long sleep-mortality association, either through confounding or as a causal intermediate. Based on this parameter, psychiatric and socioeconomic factors have the greatest potential to influence the long sleep-mortality relationship. Assuming each factor doubles mortality risk, the confounding rate ratios for depression, antidepressant use, and unemployment were 1.10, 1.18, and 1.12. Lesser influential factors were benzodiazepine use, poverty, low societal status, sedentary lifestyle, and obesity. CONCLUSION: Depression and low socioeconomic status are strong candidates for producing the statistical association between long sleep and mortality, either as confounders or as causal intermediates. Future causal research on the effects of long sleep should include a detailed assessment of psychiatric disease and socioeconomic status.     

Morphological and biochemical changes of pituitary gonadotropes in male golden hamsters submitted to short and long photoperiods

Golden hamsters are seasonal breeders, and a pattern of regression-recrudescence in their hypothalamic-pituitary axis is observed when adult animals are exposed to less than 12.5 h daylight for a prolonged period of time. The purpose of the present work was to investigate the possible morphological and biochemical changes of gonadotrope cell population in male golden hamsters submitted to both short (SP) and long photoperiods (LP). Thus, adult male golden hamsters were exposed to SP (6 h light, 18 h darkness) for 8, 16, 22 and 28 weeks or maintained under LP (14 h light, 10 h darkness). Pituitaries were processed using both light and electron microscopy, and serum levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were assessed by heterologous radioimmunoassay. Volume density [VD = Sigma cell area/reference area (RA)] and cell density (CD = number of cells/RA) of gonadotropes were measured with an image analysis system (Imaging Technology, Software Optimas 5.2). When analyzing the gonadotrope population from animals submitted either to SP or LP, no significant differences were found. At the ultrastructural level, we found a decrease (p < 0.05) in the exocytotic profiles and the individual mean area of secretory granules of both gonadotropes in hamsters maintained under SP for 16 and 22 weeks. Exposure to short days resulted in a decline in serum levels showing a nadir after 16 weeks (p < 0.05). Gonadotropin levels of the hamsters under prolonged exposure to short cycles spontaneously returned to normal values after 22 weeks. In summary, we found a decrease in the ultrastructural and biochemical parameters suggesting an altered release of FSH and LH in male golden hamsters submitted to SP, with a spontaneous recrudescence phase appearing at the end of the study.     

Predicting the duration of ocular pursuit in humans

This study examines the effects of expectation on the timing of ocular pursuit termination. Human subjects pursued repeated, constant velocity (15 or 30°/s) target motion stimuli (ramps), moving left or right. Ramps were of constant duration (RD=240, 480, 720 or 960 ms), resulting in anticipatory slowing of eye velocity prior to ramp termination and target extinction. At unexpected intervals RD was increased or decreased, but velocity remained constant. When RD increased eye velocity continued to decline, even though the target remained visible and continued to move. It took ~180 ms before eye velocity started to recover towards the steady state velocity level for the continued target motion. When RD decreased, eye velocity continued as if for a longer ramp duration, again taking ~180 ms before eye velocity started to decrease. These results suggest that timing of the response to the expected ramp duration had been pre-programmed on the basis of prior experience of ramp duration. Moreover, adjustments to timing occurred rapidly, within the second presentation of the new RD. Responses were compared to control conditions with randomised ramp duration. Eye velocity declined later in the controls for RD720 ms, as expected, but exhibited similar decline in predictable and randomised conditions for RD=960 ms. Further controls established that eye velocity could only be reliably maintained until the end of the ramp when the target was expected to continue in motion after the end of the ramp. The results suggest that estimates of stimulus duration are made continuously in all conditions, based on expectancy of target termination.     

The isocapnic buffering phase and mechanical efficiency: relationship to cycle time trial performance of short and long duration.

The purpose of this study was to determine the relationship between the isocapnic buffer (beta(isocapnic)) and hypocapnic hyperventilation (HHV) phases as well as performance in a short (20-min) and long (90-min) time trial (TT) in trained athletes. In addition, gross (GE, %) and delta (deltaE, %) efficiency were calculated and the relationship between these variables and the average power output (W) in each TT was determined. Thirteen male endurance athletes (Mean +/- SD age 31 +/- 6 yrs; body mass 75.6 +/- 6.3 kg; height 185 +/- 6 cm) completed a continuous incremental test to exhaustion for determination of the beta(isocapnic) and HHV phases. A second submaximal test was used to determine GE and deltaE. The average power output (W) was measured in a 20-min and 90-min cycling TT. The beta(isocapnic) phase (W) was significantly correlated to the average power output (W) in the 20-min TT (r = 0.58; p < 0.05), but not in the 90-min TT (r = 0.28). The HHV phase (W) was not significantly correlated to the average power output in the 20-min or 90-min TT. No significant correlation was found for GE or for deltaE and performance in the TT. The data from this study shows that beta(isocapnic) together with HHV is not likely to be a useful indicator of cycle TT performance of 20- to 90-min duration. Furthermore, GE and deltaE determined from a submaximal incremental stepwise test are not related to cycling TT performance of different duration.     

The long and the short of tails

Amniote tails display a wide variety of features for adaptation to diverse environments. Each feature originates from its own distinct developmental processes, and these processes in turn attest to an organism's evolutionary history. In this perspective, we discuss the ontogeny of tails from embryonic to adult stages, amniote tail regeneration, the mechanisms underlying tail length and neural systems, and the benefits of studying tails across vertebrates, in mammals, birds, and non-avian reptiles.     

Differential representation of speech sounds in the human cerebral hemispheres

Various methods in auditory neuroscience have been used to gain knowledge about the structure and function of the human auditory cortical system. Regardless of method, hemispheric differences are evident in the normal processing of speech sounds. This review article, augmented by the authors' own work, provides evidence that asymmetries exist in both cortical and subcortical structures of the human auditory system. Asymmetries are affected by stimulus type, for example, hemispheric activation patterns have been shown to change from right to left cortex as stimuli change from speech to nonspeech. In addition, the presence of noise has differential effects on the contribution of the two hemispheres. Modifications of typical asymmetric cortical patterns occur when pathology is present, as in hearing loss or tinnitus. We show that in response to speech sounds, individuals with unilateral hearing loss lose the normal asymmetric pattern due to both a decrease in contralateral hemispheric activity and an increase in the ipsilateral hemisphere. These studies demonstrate the utility of modern neuroimaging techniques in functional investigations of the human auditory system. Neuroimaging techniques may provide additional insight as to how the cortical auditory pathways change with experience, including sound deprivation (e.g., hearing loss) and sound experience (e.g., training). Such investigations may explain why some populations appear to be more vulnerable to changes in hemispheric symmetry such as children with learning problems and the elderly.     

Meta-analysis of short sleep duration and obesity in children and adults

BACKGROUND: Recent epidemiological studies suggest that short sleep duration may be associated with the development of obesity from childhood to adulthood. OBJECTIVES: To assess whether the evidence supports the presence of a relationship between short sleep duration and obesity at different ages, and to obtain an estimate of the risk. METHODS: We performed a systematic search of publications using MEDLINE (1996-2007 wk 40), EMBASE (from 1988), AMED (from 1985), CINHAL (from 1982) and PsycINFO (from 1985) and manual searches without language restrictions. When necessary, authors were contacted. Criteria for inclusion were: report of duration of sleep as exposure, BMI as continuous outcome and prevalence of obesity as categorical outcome, number of participants, age, and gender. Results were pooled using a random effect model. Sensitivity analysis was performed, heterogeneity and publication bias were also checked. Results are expressed as pooled odds ratios (OR [95% confidence intervals, CIs]) and as pooled regression coefficients (beta; 95% CIs). RESULTS: Of 696 studies identified, 45 met the inclusion criteria (19 in children and 26 in adults) and 30 (12 and 18, respectively) were pooled in the meta-analysis for a total of 36 population samples. They included 634,511 participants (30,002 children and 604,509 adults) from around the world. Age ranged from 2 to 102 years and included boys, girls, men and women. In children the pooled OR for short duration of sleep and obesity was 1.89 (1.46 to 2.43; P < 0.0001). In adults the pooled OR was 1.55 (1.43 to 1.68; P < 0.0001). There was no evidence of publication bias. In adults, the pooled beta for short sleep duration was -0.35 (-0.57 to -0.12) unit change in BMI per hour of sleep change. CONCLUSIONS: Cross-sectional studies from around the world show a consistent increased risk of obesity amongst short sleepers in children and adults. Causal inference is difficult due to lack of control for important confounders and inconsistent evidence of temporal sequence in prospective studies.     

Temporal grouping affects the automatic processing of deviant sounds

The present study investigates the influence of auditory temporal grouping on automatic sound processing. We compared the mismatch negativity (MMN) event-related potential elicited by successive deviant tones in a condition in which sounds were organized in tone pairs with respective MMN obtained in a non-paired sequence. When successive deviants belonged to different tone pairs the second deviant elicited a higher MMN amplitude than the corresponding deviant in the non-paired condition. Moreover, this temporal grouping had immediate effects on the extraction of rules as revealed by the finding that first and single deviants at the second position of a tone pair elicited larger MMNs than corresponding deviants in the non-paired condition or first and single deviants at the first position of a tone pair. Results demonstrate that auditory objects generated by temporal proximity are treated as relatively encapsulated units and that automatic deviance-detection may rely on multiple hierarchically organized representations of sound sequences.