Elevated sleep need in a stress-resilient Drosophila species

Sleep is broadly conserved across the animal kingdom, but can vary widely between species. It is currently unclear which types of selective pressures and sleep regulatory mechanisms influence differences in sleep between species. The fruit fly Drosophila melanogaster has become a successful model system for examining sleep regulation and function, but little is known about the sleep patterns and need for sleep in many related fly species. Here, we find that Drosophila mojavensis, a fly species that has adapted to extreme desert environments, exhibits strong increases in sleep compared to D. melanogaster. Long-sleeping D. mojavensis show intact sleep homeostasis, indicating that these flies carry an elevated need for sleep. In addition, D. mojavensis exhibit altered abundance or distribution of several sleep/wake related neuromodulators and neuropeptides that are consistent with their reduced locomotor activity, and increased sleep. Finally, we find that in a nutrient-deprived environment, the sleep responses of individual D. mojavensis are correlated with their survival time. Our results demonstrate that D. mojavensis is a novel model for studying organisms with high sleep need, and for exploring sleep strategies that provide resilience in extreme environments.

Weekend Light Shifts Evoke Persistent Drosophila Circadian Neural Network Desynchrony

We developed a method for single-cell resolution longitudinal bioluminescence imaging of PERIOD (PER) protein and TIMELESS (TIM) oscillations in cultured male adult Drosophila brains that captures circadian circuit-wide cycling under simulated day/night cycles. Light input analysis confirms that CRYPTOCHROME (CRY) is the primary circadian photoreceptor and mediates clock disruption by constant light (LL), and that eye light input is redundant to CRY; 3-h light phase delays (Friday) followed by 3-h light phase advances (Monday morning) simulate the common practice of staying up later at night on weekends, sleeping in later on weekend days then returning to standard schedule Monday morning [weekend light shift (WLS)]. PER and TIM oscillations are highly synchronous across all major circadian neuronal subgroups in unshifted light schedules for 11 d. In contrast, WLS significantly dampens PER oscillator synchrony and rhythmicity in most circadian neurons during and after exposure. Lateral ventral neuron (LNv) oscillations are the first to desynchronize in WLS and the last to resynchronize in WLS. Surprisingly, the dorsal neuron group-3 (DN3s) increase their within-group synchrony in response to WLS. In vivo, WLS induces transient defects in sleep stability, learning, and memory that temporally coincide with circuit desynchrony. Our findings suggest that WLS schedules disrupt circuit-wide circadian neuronal oscillator synchrony for much of the week, thus leading to observed behavioral defects in sleep, learning, and memory.

Sexual functioning and high sensory processing sensitivity

Introduction

The concept of Sensory Processing Sensitivity (SPS) was initially introduced by Aron in 1997 and involves complex processing of sensorial information and internal and external sensory stimuli, that is represented as an individual innate difference, as a temperamental property that concerns not only this deep sensorial processing but also to sharper general responsiveness to the environment. Its association with sexual functioning is still to be deeply determined.

Objectives

Through this research we aim to evaluate the levels of High Sensory Processing Sensitivity (HSPS) and to what extent these are related to sexual functioning, in addition to assessing the mediating role of gender in this relationship.

Methods

A total of 1,054 subjects between the ages of 18 and 80 (M age = 29.4; SD age = 11.9) participated in this study. Participants completed a demographic questionnaire, the Portuguese version of The Highly Sensitive Person Scale, and the Portuguese version of the Massachusetts General Hospital – Sexual Functioning Scale. The recruitment of the sample was internet-based.

Results

showed that the Sensitivity Sensory Processing and Sexual Functioning variables are negatively correlated and that there are statistically significant differences in sexual functioning according to gender (t(df)=7.042; p=<.05), males scoring higher; and participants with lower levels of HSPS presented higher levels of sexual functioning (t(df)=3.599; p<.05). Finally, logistic regression showed that Gender is responsible for 6.2% of the total variance of sexual functioning.

Conclusions

When working with highly sensitive people mental health professionals should take into account problems related to their sexual functioning in clinical practice.

Circadian Regulation of Light-Evoked Attraction and Avoidance Behaviors in Daytime- versus Nighttime-Biting Mosquitoes

Mosquitoes pose widespread threats to humans and other animals as disease vectors [1]. Day- versus night-biting mosquitoes occupy distinct time-of-day niches [2, 3]. Here, we explore day- versus night-biting female and male mosquitoes' innate temporal attraction/avoidance behavioral responses to light and their regulation by circadian circuit and molecular mechanisms. Day-biting mosquitoes Aedes aegypti, particularly females, are attracted to light during the day regardless of spectra. In contrast, night-biting mosquitoes, Anopheles coluzzii, specifically avoid ultraviolet (UV) and blue light during the day. Behavioral attraction to/avoidance of light in both species change with time of day and show distinct sex and circadian neural circuit differences. Males of both diurnal and nocturnal mosquito species show reduced UV light avoidance in anticipation of evening onset relative to females. The circadian neural circuits of diurnal/day- and nocturnal/night-biting mosquitoes based on PERIOD (PER) and pigment-dispersing factor (PDF) expression show similar but distinct circuit organizations between species. The basis of diurnal versus nocturnal behaviors is driven by molecular clock timing, which cycles in anti-phase between day- versus night-biting mosquitoes. Observed differences at the neural circuit and protein levels provide insight into the fundamental basis underlying diurnality versus nocturnality. Molecular disruption of the circadian clock severely interferes with light-evoked attraction/avoidance behaviors in mosquitoes. In summary, attraction/avoidance behaviors show marked differences between day- versus night-biting mosquitoes, but both classes of mosquitoes are circadian and light regulated, which may be applied toward species-specific control of harmful mosquitoes.

miR-206 is required for changes in cell adhesion that drive muscle cell morphogenesis in Xenopus laevis

MicroRNAs (miRNAs) are highly conserved small non-coding RNA molecules that post-transcriptionally regulate gene expression in multicellular organisms. Within the set of muscle-specific miRNAs, miR-206 expression is largely restricted to skeletal muscle and is found exclusively within the bony fish lineage. Although many studies have implicated miR-206 in muscle maintenance and disease, its role in skeletal muscle development remains largely unknown. Here, we examine the role of miR-206 during Xenopus laevis somitogenesis. In Xenopus laevis, miR-206 expression coincides with the onset of somitogenesis. We show that both knockdown and over-expression of miR-206 result in abnormal somite formation affecting muscle cell rotation, attachment, and elongation. In particular, our data suggests that miR-206 regulates changes in cell adhesion that affect the ability of newly formed somites to adhere to the notochord as well as to the intersomitic boundaries. Additionally, we show that β-dystroglycan and F-actin expression levels are significantly reduced, suggesting that knockdown of miR-206 levels affects cellular mechanics necessary for cell shape changes and attachments that are required for proper muscle formation.

The Role of Sdf-1α signaling in Xenopus laevis somite morphogenesis

BACKGROUND

Stromal derived factor-1α (sdf-1α), a chemoattractant chemokine, plays a major role in tumor growth, angiogenesis, metastasis, and in embryogenesis. The sdf-1α signaling pathway has also been shown to be important for somite rotation in zebrafish (Hollway et al., 2007). Given the known similarities and differences between zebrafish and Xenopus laevis somitogenesis, we sought to determine whether the role of sdf-1α is conserved in Xenopus laevis.

RESULTS

Using a morpholino approach, we demonstrate that knockdown of sdf-1α or its receptor, cxcr4, leads to a significant disruption in somite rotation and myotome alignment. We further show that depletion of sdf-1α or cxcr4 leads to the near absence of β-dystroglycan and laminin expression at the intersomitic boundaries. Finally, knockdown of sdf-1α decreases the level of activated RhoA, a small GTPase known to regulate cell shape and movement.

CONCLUSION

Our results show that sdf-1α signaling regulates somite cell migration, rotation, and myotome alignment by directly or indirectly regulating dystroglycan expression and RhoA activation. These findings support the conservation of sdf-1α signaling in vertebrate somite morphogenesis; however, the precise mechanism by which this signaling pathway influences somite morphogenesis is different between the fish and the frog.

Pf1 filamentous bacteriophage: refinement of a molecular model by simulated annealing using 3.3 A resolution X-ray fibre diffraction data

The filamentous bacteriophage Pf1 is structurally similar to the well known Ff (fd, fl, M13) strains, but it gives much better X-ray diffraction patterns, enabling a more detailed analysis of the molecular structure. The 46-residue protein subunit can be closely approximated by a single gently curved stretch of alpha-helix. The axes of the subunits are at a small angle to the virion axis, and several thousand subunits form an overlapping inter-digitated helical array surrounding a DNA core. We have derived a detailed model of the virion based on X-ray data and stereochemical constraints. We have considered potential sources of error in the diffraction data, and used the improved data to study regions where the protein subunit of Pf1 may deviate from a continuous alpha-helix. We use simulated annealing to escape from local minima, and various kinds of electron-density maps to guide the model building. Refinement of the model shows that the first few residues at the N terminus are non-helical, and there is a slight discontinuity in the alpha-helix near the middle of the sequence. The model is consistent both with general structural principles derived from high-resolution analysis of other proteins, and with specific chemical and spectroscopic data about Pf1. We apply the same refinement techniques to an alternative model with a non-helical surface loop between residues 13 and 19. Comparative analysis of models with and without a loop shows that the loop model is not supported by 3.3 A resolution X-ray diffraction data.

Data collection at short wavelengths in protein crystallography

The development of high-intensity X-ray sources and the use of insertion devices will make it possible to collect data routinely from protein crystals at very short wavelengths (lambda </= 0.5 A). Possible benefits of using shorter wavelengths can be inferred from the improvement in the quality of the data when using a wavelength lambda approximately 0.9 A instead of one close to the Cu Kalpha emission edge. In addition to fewer absorption errors, two factors might contribute to this improvement. These are an increase in the lifetime of the protein crystal and a better signal-to-background ratio. In this paper we address the second of these. In order to compare the quality of the data and the relative background level in the diffraction patterns at different wavelengths two data sets have been collected at lambda = 0.92 and 0.55 A. The results obtained from data processing and careful measurement of the background in the raw images suggest that, in the absence of absorption errors and radiation damage, data collection at very short wavelengths does not provide higher quality data. There is no improvement in the signal-to-background ratio in the short-wavelength data.

Automation of the collection and processing of X-ray diffraction data -- a generic approach

With modern detectors and synchrotron sources, it is now routine to collect complete data sets in 10-30 min. To make the most efficient use of these resources, it is desirable to automate the collection and processing of the diffraction data, ideally to a level at which multiple data sets can be acquired without any intervention. A scheme is described to allow fully automated data collection and processing. The design is modular, so that it can easily be interfaced with different beamline-control programs and different data-processing programs. An expert system provides a communication path between the data-processing software and the beamline-control software and takes decisions about the data collection based on project information provided by the user and experimental data provided by the data-processing program.

X-ray diffraction from DNA fibres under tension

When DNA fibres are stretched during drying, the polymer undergoes a conformational transition. We present quantitative results from X-ray diffraction studies on such fibres held at various ambient relative humidities. These indicate that the molecules are arranged in arrays which are crystalline in projection down the fibre axis. The packing can be explained in terms of a hexagonal cell with a lattice parameter, a, of approximately 13 A which varies with humidity. The patterns contain meridional intensities at 1/3.4 A(-1) and 1/6.5 A(-1), a strong off-meridional intensity at Z=1/5.6 A(-1) and diffuse scatter at Z=1/28 A(-1).

Matching X-ray source, optics and detectors to protein crystallography requirements

A review of the requirements for collecting X-ray diffraction data from protein crystals is given, with an emphasis on the properties of the crystal and its diffraction pattern. The size, unit-cell dimensions and perfection of the crystals can all be related to the required size and divergence of the incident X-ray beam, together with the size and spatial resolution of the detector. The X-ray beam causes primary radiation damage, even in frozen crystals. If the incident beam is very intense, temperature rises and gradients could occur in the crystal. The extent to which these problems can be overcome is also discussed.

A description of imperfections in protein crystals

An analysis is given of the contribution of various crystal imperfections to the rocking widths of reflections and the divergence of the diffracted beams. The crystal imperfections are the angular spread of the mosaic blocks in the crystal, the size of the mosaic blocks and the variation in cell dimensions between blocks. The analysis has implications for improving crystal perfection, defining data-collection requirements and for data-processing procedures. Measurements on crystals of tetragonal lysozyme at room temperature and 100 K were made in order to illustrate how parameters describing the crystal imperfections can be obtained. At 100 K, the dominant imperfection appeared to be a variation in unit-cell dimensions in the crystal.

Source, optical and detector requirements for X-ray diffraction and scattering

The standard curves used to describe the properties of synchrotron radiation sources usually consist of a plot of the flux or brightness from the source as a function of wavelength. These curves are useful for the case where a high flux or brightness is required. Many experiments do not fall into this category. An alternative description of the source requirements is to provide the maximum flux into the phase space volume defined by the specimen. A diagrammatic way of illustrating how this can be achieved is derived. This illustrates how the source, optics and detectors can be matched to the requirements of a particular experiment. This approach is illustrated using, as examples, a beamline on the SRS and two beamlines planned for DIAMOND, the proposed new UK third-generation source.

Beamline 14: a new multipole wiggler beamline for protein crystallography on the SRS

A new multipole wiggler device has been designed for the 2.0 GeV Synchrotron Radiation Source at Daresbury Laboratory in the UK. The nine-pole 2.0 T device will provide radiation for two beamlines dedicated to protein crystallography, one of which will be of high intensity. This article provides details of the design of the two stations and outlines methods being developed to combine dealing with the high heat load from the radiation while allowing both stations to be built as close to the centre of the fan as possible.

[The electrophysiological bases of aberrant intraventricular conduction during atrial fibrillation]

Twenty-four hours electrocardiogram from 4 patients with chronic atrial fibrillation and intraventricular aberrant conduction were analyzed. Aim of the study was to evaluate the reliability of the Ashman's and Akthar's rules in electrocardiographic differential diagnosis between aberrancy and ectopy. We computed parameters related to 10 RR interval preceding the aberrant conduction (AB+ Group), normal complex QRS (AB-Group) and ectopic QRS (E Group): coupling interval (CI), preceding CI cycle (PCL1), preceding PCL1 cycle (PCL2), the difference between PCL1 an PCL2 (delta PCL1), the difference between CI an PCL1 (delta CI), the mean value (RR10) and the standard deviation (RR10SD) of the 10 QRS complexes preceding the end of the sequence. Specificity of Akthar's rule was 48.7% (range 45-50%), sensibility was 90.1% (range 75-100%). PCL2, delta PCL1 and RR10DS were significantly different between AB+ and AB- Group but not between AB+, AB- and E Group. In this work Akthar's rule showed a better reliability than Ashman's rule but specificity was low (probably related to concealed conduction in atrio-ventricular node). RR10DS, but not RR10, were significantly higher in AB+ Group than AB- Group suggesting that acceleration of the cycle length can provoke CVA by increasing the difference between the refractory period of His bundle branches. Aberrant ventricular conduction cannot be determined by a mathematical rule. In the differential diagnosis of wide QRS during atrial fibrillation only morphological analysis of QRS and the study of coupling interval and compensatory pause are helpful.

Tests of an asymmetric monochromator to provide increased flux on a synchrotron radiation beamline

Asymmetric channel-cut monochromators have been tested at the SRS. Results from both focused and unfocused beamlines have shown a threefold improvement in flux when compared with the flux obtained from a symmetric cut Si(111) monochromator. Some problems with using such monochromators and possible modifications are described.

Matching electrostatic charge between DNA and coat protein in filamentous bacteriophage. Fibre diffraction of charge-deletion mutants

The virion of Ff (fd, f1, M13) filamentous bacteriophage consists of a long tube of coat protein subunits in a shingled, helical array, surrounding a genome of circular single-stranded DNA. Modified fd virions have been generated by a mutation (K48A) that removes one positive charge from each coat protein subunit in the C-terminal region of the polypeptide chain facing the DNA. The number of nucleotides in the mutant DNA is unchanged, but the K48A virions are 35% longer than wild-type. We have measured the X-ray diffraction attributable to single virions in hydrated gels of wild-type and K48A bacteriophages. Most of the diffraction pattern shows no significant difference between wild-type and K48A. Since the DNA is only about 12% by weight of the wild-type virion, the diffraction pattern is dominated by the protein contribution, and the absence of significant differences indicates that there are no significant changes in the symmetry or structure of the protein coat. But there is a change in the diffraction pattern in a region where the DNA and protein contributions are comparable. The diffraction pattern of the K48A mutant shows an increase in intensity of one of the weaker equatorial peaks, relative to wild-type, in a region where the protein contribution has negative sign but the DNA contribution has positive sign. This is consistent with a decrease in the ratio of DNA:protein per unit length of the K48A mutant. The results support the view that the protein forms a sheath lined with positive charges interacting electrostatically and non-specifically with a negatively charged DNA core of matching charge density. The lower positive charge density lining the capsid in the K48A mutant means that correspondingly fewer nucleotides can be packaged per coat protein subunit, which in turn requires an elongation of the DNA inside the virion. A longer virion is thus required to package the same amount of DNA. Within the error of measurement, the number of positive charges on the protein interacting with the DNA is the same in K48A as in the wild-type, despite the fact that the mutant is 35% longer than the wild-type.

Radiation damage in protein crystals at low temperature

This paper describes the study of the effects of radiation damage on the quality of data collected from a protein crystal at 100 K. It is shown that radiation damage causes measurable effects in the diffraction pattern. This implies that, even at liquid nitrogen temperatures, there is a limit to the size of a crystal from which a complete data set can be collected.

[Infectious endocarditis in dentistry practice: recent controversies and modes of the use of antibiotic prophylaxis]

A survey by questionnaire to assess the daily practice of the antibiotic prophylaxis of infective endocarditis by physicians attending post-graduate schools of the Institutes of Oral Surgery and Stomatology (Group A n = 83) and Cardiology (Group B n = 46) of the Second University of Naples has been conducted. They were asked about dental procedure and cardiopathies that require prophylaxis for infective endocarditis, the relationship between infective endocarditis and rheumatic disease and the provision of antibiotic. Extraction of tooth and dental and oral surgery have been reported as the most risky procedures. Moreover provision of antibiotic prophylaxis was suggested to patients not at risk (pacemaker or coronary artery bypass), and was not suggested in high risk conditions (mitral valve prolapse with regurgitation and hypertrophic cardiomyopathy). Most of the 50-60% practitioners usually start the prophylaxis 24-48 hours before the procedure and prolong it for 48-72 hours. These results underline the need for improvement of the knowledge for the antibiotic prophylaxis of infective endocarditis.

[Surgical treatment of incessant atrial tachycardia: description of a case]

A 50 year old woman with no evidence of structural heart disease was referred for ectopic incessant repetitive atrial tachycardia uncontrolled by medical therapy. Intracavitary and transesophageal simultaneous recordings revealed the earliest atrial electrical activity to be located in the left atrium. Intraoperative electrophysiologic mapping demonstrated that the site of earliest atrial activation was in a small diverticulum of the left atrial appendage. Excision of the appendage and isolation of left atrium was carried out with restoration of sinus rhythm. The patient was arrhythmia-free till 24 months later. Surgical treatment appears to be an effective therapeutic option for drug-resistant ectopic atrial tachycardia.

[Double ventricular response to a single atrial stimulation caused by simultaneous anterograde conduction through two atrioventricular nodal pathways]

In a patient with atrioventricular nodal reentrant tachycardia, during programmed stimulation, an atrial extrastimulus induced a double ventricular response due to a single atrial depolarization, with simultaneous and delayed anterograde conduction through fast and slow pathways, and induced the tachycardia. Pacing-induced type I block involving both pathways put these pathways out of phase, so that the distal conduction system and the ventricle responded to both the fast and slow pathways anterograde impulses.

Molecular models and structural comparisons of native and mutant class I filamentous bacteriophages Ff (fd, f1, M13), If1 and IKe

The filamentous bacteriophages are flexible rods about 1 to 2 microns long and 6 nm in diameter, with a helical shell of protein subunits surrounding a DNA core. The approximately 50-residue coat protein subunit is largely alpha-helix and the axis of the alpha-helix makes a small angle with the axis of the virion. The protein shell can be considered in three sections: the outer surface, occupied by the N-terminal region of the subunit, rich in acidic residues that interact with the surrounding solvent and give the virion a low isoelectric point; the interior of the shell, including a 19-residue stretch of apolar side-chains, where protein subunits interact mainly with each other; and the inner surface, occupied by the C-terminal region of the subunit, rich in basic residues that interact with the DNA core. The fact that virtually all protein side-chain interactions are between different subunits in the coat protein array, rather than within subunits, makes this a useful model system for studies of interactions between alpha-helix subunits in a macromolecular assembly. We describe molecular models of the class I filamentous bacteriophages. This class includes strains fd, f1, M13 (these 3 very similar strains are members of the Ff group), If1 and IKe. Our model of fd has been refined to fit quantitative X-ray fibre diffraction data to 30 A resolution in the meridional direction and 7 A resolution in the equatorial direction. A simulated 3.3 A resolution diffraction pattern from this model has the same general distribution of intensity as the experimental diffraction pattern. The observed diffraction data at 7 A resolution are fitted much better by the calculated diffraction pattern of our molecular model than by that of a model in which the alpha-helix subunit is represented by a rod of uniform density. The fact that our fd model explains the fd diffraction data is only part of our structure analysis. The atomic details of the model are supported by non-diffraction data, in part previously published and in part newly reported here. These data include information about permitted or forbidden side-chain replacements, about the effect of chemical modification, and about spectroscopic experiments.(ABSTRACT TRUNCATED AT 400 WORDS)

[Linking in a phase-3 branch block: the electrocardiographic manifestations]

Two cases of phase 3 intraventricular block and linking phenomenon of type 1 and type 2 (or bigeminal rhythm linking) are presented. In the first case, complexes that follow the extrasystolic blocked beat are wide, although they are associated with relative long R-R cycle:type 1 linking. In the second case, bundle branch block and normal conduction alternate in bigeminal extrasystolic beats:type 2 linking. The linking phenomenon is due to concealed retrograde penetration of the bundle branch that is blocked in anterograde direction. It delays the cycle and the refractory period of the bundle branch. Therefore, in type 1 linking, the subsequent stimulus, although occurring with a long R-R cycle, is again blocked in the same bundle branch. In type 2 linking, the R-R cycle and refractory period, occurring after bundle branch block, are shorted because comprised between retrograde activation by extrastimulus and anterograde activation by subsequent sinus stimulus. The subsequent ectopic impulse, although premature, is normally conducted.

[Slow and fast AV nodal pathways in tachycardia complicating Wolff-Parkinson-White syndrome: report of a case]

Electrophysiologic studies in a patient with intermittent ventricular pre-excitation revealed several types of paroxysmal narrow-QRS tachycardia (PSVT). One type of PSVT was characterized by normal retrograde atrial sequences with P waves occurring simultaneously with QRS. This type of PSVT reflected AV nodal reentry with anterograde slow pathway and retrograde fast pathway conduction. A second PSVT reflected alternation of anterograde fast and slow AV nodal pathway conduction and retrograde anomalous pathway conduction. A third PSVT reflected anterograde slow AV nodal pathway and retrograde anomalous pathway conduction. Moreover, discontinuous AV nodal conduction curves (A1A2/H1H2), characteristic of dual AV nodal pathway conduction, were obtained with programmed atrial extra stimulation. These observations suggest that dual AV nodal pathway conduction can coexist with abnormal bypass tract and can be the cause of PSVT in patients with Wolff-Parkinson-White syndrome.

[Electric alternans of QRS: its electrophysiologic significance in narrow QRS supraventricular paroxysmal tachycardia]

The results of 22 patient's transesophageal electrophysiologic studies were analyzed to value the meaning of QRS alternans during narrow QRS tachycardia. Standard ECG showed ventricular pre-excitation in eight patients. QRS alternans were in six of them: heart rate was included between 230 and 374 m/sec (301.8 +/- 42 m/sec); in the remaining 16 patients, heart rate was included between 240 and 450 m/sec (350.0 +/- 42 m/sec). Our findings suggest that QRS alternans is related to the rate of tachycardia rather than to the presence of an accessory pathway.

[Phase 3 and phase 4 bundle of branch block]

Intermittent left bundle branch blocks are present in the ECGs of 1 patient with mitral valve disease. By occurring either after short or long cycles they represent respectively phase 3 and phase 4 blocks. Such mechanisms emphasize the relationship between automatism and conduction. The occurrence of block and of normal conduction during cycles of the same length, its correlation with the conduction of the previous cycle, demonstrate the presence of a functional linking between successive impulses. This linking may occur every time a potential or active macroreentry circuit exist. In our case the circuit is formed by the 2 bundle branches which join distally in the ventricular septum.

[Ergometric test in the diagnostic and prognostic evaluation of arrhythmia]

One thousand three hundred patient's stress tests were analyzed to value arrhythmia outline and its relationship with anamnesis and clinical data. The patients were divided into two groups: group A, with no arrhythmias at rest, and group B with arrhythmias at rest. All classic nosographic arrhythmias were considered. In some teenager patients with arrhythmias at rest and no organic cardiopathy, anomalies disappeared during stress, showing the benignity of the phenomenon. Supraventricular stress induced arrhythmias has 1.2% of incidence in normal subjects, but 81% in heart disease patients. Supraventricular tachycardia was induced in 6 patients. Ventricular stress induced arrhythmias are found in 4.9%. Two cases of sudden death occurred in our groups.

[Permanent atrial standstill and atrial disease]

A case of permanent atrial standstill suspected upon electrocardiogram is reported, and confirmed by electrophysiological investigation. The originality of this case resides in the fact that the atrial standstill marks the developmental outcome of a bradycardia-tachycardia syndrome. This developmental sequence is the subject on discussion. It is concluded that a combination of auricular muscle lesion and sinus node tissue remains the most plausible anatomical and pathophysiological substratum of the bradycardia-tachycardia syndrome which developed into atrial standstill.

[EGG and arrhythmia in subjects with implanted dual-chamber VDD and DDD pacemakers]

The ECGs of four patients with implanted dual chamber VDD and DDD PMKs are shown to demonstrate the difficulty of their interpretation and show some arrhythmias related to dual chamber pacing. In the first patient the DDD PMK caused a high ventricular frequency synchronizing on the atrial fibrillation "f" waves which occurred suddenly some time after PMK implantation; this problem was solved by programming the PMK in VVI. The second and third case, with implanted DDD and VDD PMK respectively, exemplify atrial sensing dysfunction due to atrial catheter displacement. In the fourth patient, with implanted VDD PMK, VDD stimulation periods and VVI ones alternated due to non-adjusted programming. Therefore, the paper re-emphasizes the need for accurate and periodic controls of patients with implanted PMK to correct dysfunction or undesirable patterns of stimulation.

X-ray diffraction evidence for the existence of 102.0- and 230.0-nm transverse periodicities in striated muscle

Synchrotron radiation techniques have enabled us to record meridional x-ray diffraction patterns from frog sartorius muscle at resolutions ranging from approximately 2,800 to 38 nm (i.e., overlapping with the optical microscope and the region normally accessible with low angle diffraction cameras). These diffraction patterns represent the transform of the low resolution structure of muscle projected on the sarcomere axis and sampled by its repeat. Altering the sarcomere length results in the sampling of different parts of this transform, which induces changes in the positions and the integrated intensities of the diffraction maxima. This effect has been used to determine the transform of the mass projection on the muscle axis in a quasicontinuous fashion. The results reveal the existence of maxima arising from long-range periodicities in the structure. Determination of the zeroes in the transforms has been used to obtain phase information from which electron density maps have been calculated. The x-ray diffraction diagrams and the resulting electron density maps show the existence of a series of mass bands, disposed transversely to the sarcomere axis and distributed at regular intervals. A set of these transverse structures is associated with thin filaments, and their 102.0-nm repeat suggests a close structural relationship with their known molecular components. A second set, spaced by approximately 230.0 nm, is also present; from diffraction theory one has to conclude that this repeat simultaneously exists in thick and thin filament regions.

The information available from anomalous scattering on fibres at different wavelengths

The contribution of a particular atom in a molecule to the total X-ray scattering can be altered by varying the wavelength in the region of the absorption edge of the atom. It is shown that only the changes in the real part of the anomalous scattering of the atom provide significant changes in a pattern from a fibre containing molecules with helical symmetry. Changes due to the imaginary component are small and Friedel differences cannot be observed, owing to the fibre disorder. The information which can be obtained is equivalent to that given by a truly isomorphous heavy-atom derivative. For the general case this is not sufficient to provide unambiguous phase information. If a twofold axis is present at right angles to the fibre axis then the amplitudes are real and the phase problem can, in favourable cases, be solved.

The solution conformations of the subclasses of human IgG deduced from sedimentation and small angle X-ray scattering studies

The solution conformations of human immunoglobulin G subclass molecules have been investigated by sedimentation and small-angle X-ray scattering techniques. Both methods qualitatively indicate IgG3 to be an extended molecule relative to IgG1. Sedimentation data have been collected for a number of paraproteins of all four subclasses and the hinge-deleted IgG1Dob protein. The known crystal structure of Dob allows the use of this protein as a basis for the proposal of models of the average conformations of IgG subclasses which are consistent with experimental s(0)20,w values. IgG1 is suggested to have a hinge length of 0-15 A and non-coplanar Fab arms; IgG2 to be effectively hingeless with folded-back Fab arms; IgG3 to have an extended hinge of the order of 100 A and IgG4 to be effectively hingeless and T-shaped. The possible correlation of these conformations with subclass function is discussed.

The organisation of collagen fibrils in the human corneal stroma: a synchrotron X-ray diffraction study

The low angle equatorial diffraction pattern from the human corneal stroma shows that the collagen fibrils have two preferred orientations: inferior-superior and medial-lateral. We have not observed this effect in any other animal species. This arrangement, which was found to be more pronounced in the posterior than in the anterior stroma, was maintained until the last 1 to 2 millimetres before the limbus at which point uniaxial orientation was observed along the circumference. Our interpretation of this result is that most collagen fibrils wrap around the circumference of the cornea and relatively few continue radially into the limbus where uniformity of collagen fibril diameters is lost.