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IntroductionImmunocompromised patients are prone to reactivations of multiple latent DNA viruses. Viral load monitoring by single-target quantitative PCRs (qPCR) is the current cornerstone for virus quantification. In this study, a metagenomic next-generation sequencing (mNGS) approach was used for identification and load monitoring of transplantation-related DNA viruses.MethodsLongitudinal plasma samples from six patients that were qPCR-positive for cytomegalovirus (CMV), Epstein-Barr virus (EBV), BK polyoma virus (BKV, adenovirus (ADV), parvovirus B19 (B19V), and torque teno-virus (TTV) were sequenced using the quantitative metagenomic Galileo Viral Panel Solution (Arc Bio, LLC) reagents and bioinformatics pipeline combination. Qualitative and quantitative performance was analysed with focus on viral load ranges relevant for clinical decision-making.ResultsAll pathogens identified by qPCR were also identified by mNGS. In addition, BKV, CMV, and HHV6B were detected by mNGS which were not ordered initially but could be confirmed by qPCR. Viral loads determined by mNGS correlated with the qPCR results, with inter-method differences in viral load per virus ranging from 0.19 log10 IU/ml for EBV to 0.90 log10 copies/ml for ADV. TTV, analysed by mNGS in a semi-quantitative way, showed a mean difference of 3.0 log10 copies/ml. Trends over time in viral load determined by mNGS and qPCR were comparable, and clinical thresholds for initiation of treatment were equally indicated by mNGS.ConclusionThe Galileo Viral Panel for quantitative mNGS performed comparable to qPCR with regard to detection and viral load determination, within clinically relevant ranges of patient management algorithms.

At the time SARS-CoV-2 was identified as the cause of coronavirus disease 2019 (COVID-19) no in vitro diagnostic (IVD) tests were available since it was a new virus. Very shortly after the release of the genomic sequence of SARS-CoV-2, laboratory-developed tests (LDTs) were developed, made available and implemented in several laboratories in the Netherlands and globally. In this study, the performance of an E-gene Sarbeco specific real-time reverse-transcriptase PCR (RT-PCR) was verified on the open modus of the geneLEAD VIII sample-to-answer platform. The results obtained from 134 clinical samples, of which 63 had been tested positive, showed almost complete concordance compared to the same PCR on the routine diagnostic systems and that was validated according to the national reference standard. The only discordant sample tested positive using the routine diagnostic workflow with a cycle threshold (CT) value of 37.7, while the sample tested negative using the geneLEAD VIII workflow. In addition, good performance was achieved in analyzing a blinded SARS-CoV-2 external quality assurance (EQA) panel. Implementation of the geneLEAD VIII platform as routine diagnostic tool resulted in testing 871 clinical samples with 115 positive results. In conclusion, the geneLEAD VIII SARS-CoV-2 workflow presented in this study showed excellent diagnostic performance and with a rapid turnaround time of approximately two hours it proved a valuable option for STAT SARS-CoV-2 testing in the absence of (rapid, CE-IVD) point-of-care testing platforms.

Background: Diagnosis of congenital viral infection at birth is generally attempted by direct detection of the virus by PCR in various neonatal materials. How to reliably diagnose intrauterine infection with parvovirus B19 (B19 V) at birth is unknown.Objectives: To evaluate the performance of B19 V DNA detection in cord blood (CB) or neonatal dried blood spots (DBS) in diagnosing fetal infection. Study design: Two cohorts of children diagnosed prenatally with an intrauterine B19 V infection were included in this study. CB samples of intrauterine B19 V infections that were sent to a reference laboratory for congenital infections in Stuttgart, Germany in the period 1995-2014 were tested in triplicate for B19 V DNA by quantitative PCR. DBS from children with intrauterine B19 V infection that underwent IUT at the LUMC, Leiden, the Netherlands in the period 2009-2014 were tested for B19 V DNA by quantitative B19 V PCR in triplicate.Results: Fourteen of twenty (70 %) CB samples tested positive for B19 V DNA. The positivity rate was 40 % (4/10) in those with a prenatal diagnosis< 20 weeks gestation. When intrauterine B19 V infection was diagnosed thereafter, 100 % (10/10) samples were B19 V DNA positive. Of the thirteen available DBS, twelve (92 %) tested positive. Viral load in CB and DBS corresponded inversely with time from fetal diagnosis to birth.Conclusion: B19 V DNA can be detected in neonatal blood samples of children following intrauterine B19 V infection, although the possibility of false-negatives, even in severe infections, should be considered. B19 V viral load at birth correlates with timing of infection.

The main challenge of immunosuppressive therapy after solid organ transplantation is to create a new immunological balance that prevents organ rejection and does not promote opportunistic infection. Torque teno virus (TTV), a ubiquitous and non-pathogenic single-stranded DNA virus, has been proposed as a marker of functional immunity in immunocompromised patients. Here we investigate whether TTV loads predict the risk of common viral infection and allograft rejection in kidney transplantation recipients. In a retrospective cohort of 389 kidney transplantation recipients, individual TTV loads in were measured by qPCR in consecutive plasma samples during one year follow-up. The endpoints were allograft rejection, BK polyomavirus (BKPyV) viremia and cytomegalovirus (CMV) viremia. Repeated TTV measurements and rejection and infection survival data were analysed in a joint model. During follow-up, TTV DNA detection in the transplant recipients increased from 85 to 100%. The median viral load increased to 107 genome copies/ml within three months after transplantation. Rejection, BKPyV viremia and CMV viremia occurred in 23%, 27% and 17% of the patients, respectively. With every 10-fold TTV load-increase, the risk of rejection decreased considerably (HR: 0.74, CI 95%: 0.71-0.76), while the risk of BKPyV and CMV viremia remained the same (HR: 1.03, CI 95%: 1.03-1.04 and HR: 1.01, CI 95%: 1.01-1.01). In conclusion, TTV load kinetics predict allograft rejection in kidney transplantation recipients, but not the BKPyV and CMV infection. The potential use of TTV load levels as a guide for optimal immunosuppressive drug dosage to prevent allograft rejection deserves further validation.

BACKGROUND Human polyomaviruses (HPyVs), like herpesviruses, cause persistent infection in a large part of the population. In immunocompromised and elderly patients, PyVs cause severe diseases such as nephropathy (BK polyomavirus [BKPyV]), progressive multifocal leukoencephalopathy (JC polyomavirus [JCPyV]), and skin cancer (Merkel cell polyomavirus [MCPyV]). Like cytomegalovirus, donor‐derived PyV can cause disease in kidney transplant recipients. Possibly blood components transmit PyVs as well. To study this possibility, as a first step we determined the presence of PyV DNA in Dutch blood donations. STUDY DESIGN AND METHODS Blood donor serum samples (n = 1016) were analyzed for the presence of DNA of 14 HPyVs using HPyV species‐specific quantitative polymerase chain reaction (PCR) procedures. PCR‐positive samples were subjected to confirmation by sequencing. Individual PCR findings were compared with the previously reported PyV serostatus. RESULTS MC polyomavirus DNA was detected in 39 donors (3.8%), JCPyV and TS polyomavirus (TSPyV) DNA in five donors (both 0.5%), and HPyV9 DNA in four donors (0.4%). BKPyV, WU polyomavirus (WUPyV), HPyV6, MW polyomavirus (MWPyV), and LI polyomavirus (LIPyV) DNA was detected in one or two donors. Amplicon sequencing confirmed the expected product for BKPyV, JCPyV, WUPyV, MCPyV, HPyV6, TSPyV, MWPyV, HPyV9, and LIPyV. For JCPyV a significant association was observed between detection of viral DNA and the level of specific IgG antibodies. CONCLUSION In 5.4% of Dutch blood donors PyV DNA was detected, including DNA from pathogenic PyVs such as JCPyV. As a next step, the infectivity of PyV in donor blood and transmission via blood components to immunocompromised recipients should be investigated.

Background BK polyomavirus (BKPyV) persistently infects the urinary tract and causes viremia and nephropathy in kidney transplantation (KTx), recipients. In a previous study, we observed an increased incidence and load of BKPyV viremia in KTx patients coinfected with human polyomavirus 9 (HPyV9). Here we sought confirmation of this observation and explored whether novel HPyVs that have been detected in urine (HPyV9 and trichodysplasia spinulosa polyomavirus [TSPyV]) potentially aggravate BKPyV infection. Methods A well-characterized cohort of 209 KTx donor-recipient pairs was serologically and molecularly analyzed for HPyV9 and TSPyV coinfection. These data were correlated with the occurrence of BKPyV viremia and BKPyVAN in the recipients within a year after KTx. Results Seropositivity for HPyV9 (19%) and TSPyV (89%) was comparable between donors and recipients and did not correlate with BKPyV viremia and BKPyVAN that developed in 25% and 3% of the recipients, respectively. Two recipients developed TSPyV viremia and none HPyV9 viremia. Modification of the predictive effect of donor BKPyV seroreactivity on recipient BKPyV viremia by HPyV9 and TSPyV was not observed. Conclusions Our data provide no evidence for a promoting effect of HPyV9 and TSPyV on BKPyV infection and BKPyVAN in renal allograft patients. Therefore, we do not recommend including HPyV9 and TSPyV screening in KTx patients.

Background. Identification of specific HLA alleles and T-cell epitopes that influence the course of BK polyomavirus (BKPyV) infection after kidney transplantation (KTx), including development of BKPyV-associated nephropathy (BKPyVAN), can be useful for patient risk stratification and possibly vaccine development. Methods. In a retrospective cohort of 407 living kidney donor-recipient pairs, donor and recipient HLA class I and II status were correlated with the occurrence of recipient BKPyV viremia and BKPyVAN in the first year after KTx. Relevant HLA alleles were systematically analyzed for candidate peptide epitopes in silico. Results. Although none of the 78 HLA alleles analyzed increased the risk of BKPyV viremia and BKPyVAN, a considerable reduction of BKPyV viremia and BKPyVAN cases was observed in HLA-B51-positive KTx recipients. Multivariate analysis showed that HLA-B51 positivity, found in 36 (9%) recipients, reduced the risk of viremia approximately fivefold (hazard ratio, 0.18; 95% confidence interval, 0.04-0.73; P = 0.017). Four HLA-B51-restricted putative cytotoxic T lymphocyte epitopes were identified, including a previously described HLA-B super-motif-containing peptide (LPLMRKAYL), encoded by 2 relevant T-antigens (small T and large T) and previously shown to be highly immunogenic. Conclusions. In conclusion, HLA-B51-positive kidney transplant recipients were less susceptible to BKPyV infection, which might be explained by efficient presentation of a particular BKPyV-derived immunogenic peptide.

BackgroundBK polyomavirus (BKPyV)–associated nephropathy (BKPyVAN) is a major threat for kidney transplant recipients (KTRs). The role of specific BKPyV genotypes/serotypes in development of BKPyVAN is poorly understood. Pretransplantation serotyping of kidney donors and recipients and posttransplantation genotyping of viremic recipients, could reveal the clinical relevance of specific BKPyV variants.MethodsA retrospective cohort of 386 living kidney donor-recipient pairs was serotyped before transplantation against BKPyV genotype I–IV viral capsid protein 1 antigen, using a novel BKPyV serotyping assay. Replicating BKPyV isolates in viremic KTRs after transplantation were genotyped using real-time polymerase chain reaction and confirmed by means of sequencing. BKPyV serotype and genotype data were used to determine the source of infection and analyze the risk of viremia and BKPyVAN.ResultsDonor and recipient BKPyV genotype and serotype distribution was dominated by genotype I (>80%), especially Ib, over II, III and IV. Donor serotype was significantly correlated with the replicating genotype in viremic KTRs (P < .001). Individual donor and recipient serotype, serotype (mis)matching and the recipient replicating BKPyV genotype were not associated with development of viremia or BKPyVAN after transplantation.ConclusionsBKPyV donor and recipient serotyping and genotyping indicates the donor origin of replicating BKPyV in viremic KTRs but provides no evidence for BKPyV genotype–specific virulence.

This article puts investments in the perceptive of the investor: investments are no goal in itself, but serve a purpose. Using this perspective, it aims to present concrete recommendations to individual investors and investment advisers about which portfolios should be held by private persons and how to construct these portfolios. Starting from the theoretical foundations that are based on the ‘Hierarchy of Human Needs’ (as proposed by A.H. Maslow in 1943), this article suggests to segregate portfolios into multiple sub-portfolios that each cater for a specific need. This postulation is then integrated with other key observations into a comprehensive, positive and normative portfolio theory. The result is a complete framework for personal financial decision making that is natural and helpful for both advisers and investors, and it integrates financial investments in an optimization of overall well-being.

This paper aims to offer an alternative formulation of the Behavioural Portfolio Theory as formulated by Hersh Shefrin and Meir Statman (2000) via the Theory of Needs from Abraham Maslow (1943). This alternative formulation, called Maslowian Portfolio Theory (MaPT), yields the same results but adds some interesting insight and practical applications for the financial advisor. MaPT starts from the needs of the investor and therefore can have the ambition to be a predictive theory rather than a descriptive theory. This paper also tries to fit portfolio selection theories with the needs of the investor, and to give very applicable advice.

Adenovirus infections after allogeneic stem cell transplantation (SCT), particularly in children, may be severe and protracted. Up to 51 different serotypes of adenovirus are presently recognized but serotyping is usually limited to initial viral isolates.A systematic and sustained analysis of adenovirus serotypes in a cohort of adenovirus-infected pediatric SCT recipients, correlated to transplant-associated variables.Eighty-three consecutive pediatric SCT recipients were studied by culture of feces and adenoviruses isolated were serotyped by neutralization. Upon persistent viral excretion, serotyping was repeated for at least two isolates of any infectious episode, including initial and final isolates, and patients with single and multiple serotypes were compared. In a subset of cases, serotyping of fecal isolates was compared to genotypic analysis.In 33 patients, adenovirus was isolated at least once after SCT. Serotyping uncovered 49 different adenoviruses, including three isolates without an assigned serotype. In 16 patients, a single serotype was present for a sustained period, whereas 12 patients (36%) showed multiple serotypes. Comparison of these groups demonstrated more frequent non-malignant primary disease with multiple infections (p0.01), but otherwise no significant differences were observed, although single serotype infections had a lower survival rate. Remarkably, serotype 31 appeared initially in 7 out of 12 patients with multiple infections. Genotyping by sequencing confirmed neutralization assays at least at the species level in 14 of 18 isolates.In 36% of adenovirus infections after SCT more than one serotype could be detected by sequential analysis. Multiple serotypes occurred more often with non-malignant disorders. Adenovirus serotype 31 was often included. This finding is relevant for diagnostic purposes and immunotherapeutic interventions and provides insight into the pathogenesis of this problem.

Human adenoviruses (HAdV) are a frequent cause of potentially fatal infections in patients after allogeneic stem cell transplantation, especially in children. Monitoring of serum/plasma by real-time quantitative PCR is a sensitive tool for the recognition of patients at risk of a potentially fatal infection and for the evaluation of the efficacy of treatment. Data from a retrospective study and from a prospective study demonstrate that recovery of immunity after transplantation is essential for the elimination of HAdV infection. The feasibility of several approaches for the manipulation of immunity in the immunocompromised host to prevent a fatal course of the infection is discussed.

The hydrologic structure of Taal Volcano has favored development of an extensive hydrothermal system whose prominent feature is the acidic Main Crater Lake (pH 3500 mg/kg) and low SO4/Cl ratios (

The possible use of ammonium-ferrichexacyano-ferrate (AFCF) as a countermeasure for soil-plant transfer of radiocaesium is evaluated. On a sandy agricultural soil, AFCF application rates of 10 and 100 g AFCF m−2 reduced radiocaesium transfer to ryegrass by a factor of 25 and 225, respectively, without affecting plant growth. Even additions of only 1 g AFCF m−2 resulted in a 4-fold reduction of the radiocaesium transfer factor. Additions of less than 0.1 g AFCF m−2 were not effective in reducing radiocaesium transfer to rye grass. Reductions in transfer with AFCF addition can be estimated and have been quantified using an appropriate regression equation.

Despite extensive analysis of the BRCA1 and BRCA2 genes, germline mutations are detected in

The type of soil and humus has to be considered as primordial for the evaluation of the Cs availability and for its transfer dynamics. Previous studies on the radiocesium distribution through a forest soil profile indicate that the intermediate layer, OAh (organic and mineral particles intimately mixed) accumulates Cs in a more efficient way than the deeper mineral layer. Our study on the physico-chemical parameters influencing Cs retention shows however, that humic compounds do not particularly influence the Cs retention. On the contrary, the K interaction with mineral particles induces a clear increase in the Cs fixation. This observation suggests that K inducing collapse is responsible for a higher Cs retention. In the OAh layer, an original collapsed state of the mica structure would benefit the Cs fixation.

This paper summarizes the data obtained during a period of 3 years in 'in situ' (distribution of the Chernobyl radiocesium fallout in a Belgian Ardenne spruce stand) and in controlled conditions (spruces growing in contaminated lysimeters and in nutrient media). Experiments in controlled conditions show that deposited radiocesium (thermogenetated aerosols) is washed out very quickly; the short ecological half-lives are confirmed by the post-Chernobyl observations in the NPP contaminated zone. Moreover, field observations reveal that spruce contamination levels remain more or less stable, with seasonal variations (translocation of cesium-137 during the spring and storage in the wood trunk and in the old needles during the winter). Studies conducted on throughfall water pointed out a high seasonally significant correlation between K and cesium-137. Studies of the cycles of stable K and Cs in needles and throughfall water sampled monthly for a year, confirm that radiocesium movements in trees are closely related to the potassium cycle and to the tree physiological status. Five years after the accident, forests seem to be at a steady state without any significant decontamination, throughfall losses being compensated by root absorption. On the other hand, field experiments conducted on spruce litter show that in Belgium, litter decomposition is a very slow process: K and Cs losses are quite negligible after 400 days. These results emphasize the radiological role of the litter. The relative distribution of deposited radioactivity in the different compartments of the forest ecosystem is given, the soil compartment being the main reservoir of radioactivity (particularly the upper Of and OAh organic soil horizons). Soil-tree transfer factors obtained in lysimeters contaminated by cesium-137 (calculated on the soil solution basis) range from 4 to 40 depending on the soil solution concentration of the different soil layers exploited by the root system. Cesium exchangeable fractions (CaCl2 and NH4Ac) represent up to 15% of the total soil activity. In our spruce forest soils (brown acid), a geochemical barrier is present (OAh horizon) where radiocesium presents a quite complete fixation.

The organic and mineral horizons of a forest brown acid soil sampled in Belgium (Haute Ardenne, Vielsalm) were artificially contamined with a solution of (CsCl)-Cs-137. If the sequential extractions (CaCl2, NH4Ac, CuCl2 and HNO3, 1N) realised on a pure mineral substrate remove 40% of the total Cs-137 content, the same reagents can only remove 8% of total caesium when they react with the organic substrate (Of + OAh). Other controlled experiments with the different layers of the soil profile show, on the other hand, that if a pool of Cs-137 is available for exchange in the Of and B horizons (31 and 18%, respectively, of total caesium for NH4Ac), the quantities of exchangeable Cs-137 (CaCl2 and NH4Ac) and the present one in soil solution of the transition OAh and Ah horizons are near zero (0.1 and 2.7% of total caesium for NH4Ac, respectively). This result seems to contradict the available quantities of potassium cation. This suggests, firstly, that the organic matter, or more probably organomineral complexes, interact strongly on the behaviour of Cs-137 in the profile hemiorganic layers and, secondly, that the Cs-137 has a special behaviour of its own.

Background Norovirus, Rotavirus group A, Astrovirus, Sapovirus and Adenovirus serotypes 40 and 41, are common causes of gastroenteritis. Conventional diagnosis of these causative agents is based on antigen detection and electron microscopy. Objective To improve the diagnostic possibilities for viral gastroenteritis, two internally controlled multiplex real-time PCRs have been developed. Study design Individual real-time PCRs were developed and optimized for the specific detection of Norovirus genogroup I, Norovirus genogroup II, Rotavirus group A, Astrovirus, Adenovirus group F and Sapovirus. Subsequently, the PCRs were combined to two multiplex PCR reactions. The multiplex assays were clinically evaluated using 239 fecal samples submitted to our laboratory over a 1-year period for the routine detection of Rotavirus and/or Adenovirus antigens using the Vikia® Rota/Adeno test (bioMerieux, Boxtel, The Netherlands). Results In general, the multiplex real-time PCR assays showed comparable sensitivity and specificity to the individual assays. A retrospective clinical evaluation showed increased pathogen detection in samples from 14% using conventional methods to 45% using PCR. Subsequently, the assay was implemented as a routine diagnostic tool. From September 2007 up to December 2009, 486 positive results were obtained in 1570 samples (31%) analyzed. Norovirus genogroup II was found the most frequently (61.1%), followed by Adenovirus (9.9%), Rotavirus (9.3%), Astrovirus (6.0%), Norovirus genogroup I (3.3%) and Sapovirus (0.4%). Conclusions Two internally controlled multiplex real-time PCR assays for the simultaneous detection of Astrovirus, Adenovirus group F, Rotavirus, Norovirus genogroups I and II and Sapovirus have shown significant improvement in the diagnosis of viral gastroenteritis.

Adenoviruses have been recognized as important pathogens in immunocompromised hosts. Particularly in pediatric allogeneic stem cell transplant recipients, the morbidity of the patients and mortality in those patients with disseminated infections have been found to increase over the last few years. Severe infections are predominantly but not exclusively caused by subgroup C adenoviruses. A multiplex real-time PCR assay using molecular beacons as probes was developed to enable monitoring of adenovirus DNA in those patients with simultaneous identification of subgroups. An internal control was coamplified in the multiplex PCR to check for the DNA isolation procedure as well as the presence of inhibitors in the clinical samples. The assay has been applied retrospectively in patient groups with different clinical outcomes of infection. In fatal cases, significantly higher adenovirus loads developed, exceeding even 10 11 copies/ml of serum or plasma. Patients with viral loads over 10 6 copies/ml appear to have an increased risk for fatal complications. This quantitative real-time PCR assay has been prospectively used clinically since 2002 to study the course of adenovirus infection. In addition, the assay provides objective start and end points of therapeutic interventions, including the clinically important evaluation of antiviral drugs.

Successful preemptive cytomegalovirus (CMV) therapy in transplant patients depends on the availability of sensitive, specific, and timely diagnostic tests for CMV infections. The pp65 antigenemia assay has been used for this purpose with considerable success. Quantification of CMV DNA is currently regarded to be an alternative diagnostic approach. The precise relationship between these two methods has still to be defined, but is essential to compare diagnostic results. This study compared the results of both assays with a large series of transplant recipients in different categories. An internally controlled quantitative real-time CMV DNA PCR was used to test 409 plasma samples from solid organ transplant (SOT) and stem cell transplant (SCT) patients. Levels of CMV DNA in plasma correlated well with classified outcomes of the pp65 antigenemia test. Despite this correlation, the quantitative CMV PCR values in a class of antigen test results were within a wide range, and the definition of an optimal cutoff value for initiating treatment required further analysis by a receiver-operating characteristic curve analysis. This is essential for reactivating infections in particular. For the SCT patients the optimal cutoff value of CMV DNA load defining relevant viral reactivation (in this assay, 10,000 copies/ml) was slightly higher than that for the SOT patients (6,300 copies/ml). Based on a comparison with the established pp65 antigenemia assay, quantification of CMV DNA in plasma appeared to be capable of guiding the clinical management of transplant recipients. This approach may have important advantages, which include a superior reproducibility and sensitivity, allowing the inclusion of kinetic criteria in clinical guidelines.

Visual tracking of moving targets requires the combination of smooth pursuit eye movements with catch-up saccades. In primates, catch-up saccades usually take place only during pursuit initiation because pursuit gain is close to unity. This contrasts with the lower and more variable gain of smooth pursuit in cats, where smooth eye movements are intermingled with catch-up saccades during steady-state pursuit. In this paper, we studied in detail the role of retinal slip in the prediction of target motion during smooth and saccadic pursuit in the cat. We found that the typical pattern of pursuit in the cat was a combination of smooth eye movements with saccades. During smooth pursuit initiation, there was a correlation between peak eye acceleration and target velocity. During pursuit maintenance, eye velocity oscillated at approximately 3 Hz around a steady-state value. The average gain of smooth pursuit was approximately 0.5. Trained cats were able to continue pursuing in the absence of a visible target, suggesting a role of the prediction of future target motion in this species. The analysis of catch-up saccades showed that the smooth-pursuit motor command is added to the saccadic command during catch-up saccades and that both position error and retinal slip are taken into account in their programming. The influence of retinal slip on catch-up saccades showed that prediction about future target motion is used in the programming of catch-up saccades. Altogether, these results suggest that pursuit systems in primates and cats are qualitatively similar, with a lower average gain in the cat and that prediction affects both saccades and smooth eye movements during pursuit.

Vasomotion has been studied on segments of rat mesenteric and femoral arteries perfused in vitro. We have investigated 1) the effect of perfusion flow on the characteristics of vasomotion and 2) the nature and patterns of vasomotion. We have found that perfusion flow is not a control parameter that contributes to the genesis of vasomotion but that it affects, in most cases only slightly, the frequency and amplitude of vasomotion. We have found evidence that vasomotion is low-dimensional chaotic. The correlation dimension ranged between 2 and 4, and the average Lyapunov’s coefficient was ∼0.1. A great variety of vasomotion patterns was observed with features that are typical of nonlinear deterministic systems: regular and irregular vasomotion, quasiperiodicity, period doubling and higher-order periods, intermittency, mixed modes, and bursting activity. Vasomotion patterns appeared occasionally to be highly sensitive to perturbations in perfusion flow, which also supported the existence of nonlinear dynamics. Finally, entrainment (phase locking) was observed when arteries were perfused with oscillatory flow with frequency in the neighborhood of the frequency of vasomotion.

Arteries often exhibit spontaneous rhythmic activity, which is manifested by low-frequency oscillations in vessel caliber, a phenomenon termed vasomotion. Vasomotion is predominant in microcirculation [1–3], but it has recently been shown to exist in large muscular arteries [4–6]. In small arteries and arterioles, vasomotion influences perfusion [7], enhances filtration through the wall and lymphatic drainage [8] and may represent some form of homeostasis. In large arteries, the physiological significance of vasomotion remains obscure, although it has been demonstrated that vasomotion considerably affects the elastic properties of conduit vessels, and vasomotion in the coronary arteries has been suggested to be an initiating factor of coronary spasm [6, 9]. The mechanisms contributing to vasomotion are yet to be defined. Vasomotion has been closely linked to the myogenic mechanism [10–12]. A number of studies claim that vasomotion results from instabilities in the system that controls intracellular calcium [13–15]. Mechanical factors, such as wall stress and intimal shear, appear to modulate vasomotion [3, 16, 17] but it has been suggested that these mechanical factors are not control variables of the system that generates vasomotion [18]. The plurality of experimental patterns observed, sensitivity to initial conditions and nonlinear (fractal) analysis of vasomotion signals has suggested that vasomotion is a chaotic process [13]. The objectives of the present study are: 1 To examine the influence of mechanical forces due to pressure (wall stress) and flow (intimal shear) on the characteristics of spontaneous vasomotion. To determine whether mechanical stimuli are control variables of the system that generates vasomotion. 2 To assess the nature of vasomotion. To examine its patterns and determine whether low-dimensional deterministic chaos is involved.

The activity of vertical burst neurons (BNs) was recorded in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF-BNs) and in the interstitial nucleus of Cajal (NIC-BNs) in head-restrained cats while performing saccades or smooth pursuit. BNs emitted a high-frequency burst of action potentials before and during vertical saccades. On average, these bursts led saccade onset by 14 +/- 4 ms (mean +/- SD, n = 23), and this value was in the range of latencies ( approximately 5-15 ms) of medium-lead burst neurons (MLBNs). All NIC-BNs (n = 15) had a downward preferred direction, whereas riMLF-BNs showed either a downward (n = 3) or an upward (n = 5) preferred direction. We found significant correlations between saccade and burst parameters in all BNs: vertical amplitude was correlated with the number of spikes, maximum vertical velocity with maximum of the spike density, and saccade duration with burst duration. A correlation was also found between instantaneous vertical velocity and neuronal activity during saccades. During fixation, all riMLF-BNs and approximately 50% of NIC-BNs (7/15) were silent. Among NIC-BNs active during fixation (8/15), only two cells had an activity correlated with the eye position in the orbit. During smooth pursuit, most riMLF-BNs were silent (7/8), but all NIC-BNs showed an activity that was significantly correlated with the eye velocity. This activity was unaltered during temporary disappearance of the visual target, demonstrating that it was not visual in origin. For a given neuron, its ON-direction during smooth pursuit and saccades remained identical. The activity of NIC-BNs during both saccades and smooth pursuit can be described by a nonlinear exponential function using the velocity of the eye as independent variable. We suggest that riMLF-BNs, which were not active during smooth pursuit, are vertical MLBNs responsible for the generation of vertical saccades. Because NIC-BNs discharged during both saccades and pursuit, they cannot be regarded as MLBNs as usually defined. NIC-BNs could, however, be the site of convergence of both the saccadic and smooth pursuit signals at the premotoneuronal level. Alternatively, NIC-BNs could participate in the integration of eye velocity to eye position signals and represent input neurons to a common integrator.

We have shown that the patterns of vasomotion induced by histamine in isolated rabbit ear resistance arteries can be described in terms of iterative circle maps that model the dynamics of coupled nonlinear oscillators. Cyclopiazonic acid (CPA), an inhibitor of the sarcoplasmic reticulum Ca2+-adenosinetriphosphatase pump, consistently transformed chaotic behavior into characteristic periodic oscillations known as mixed-mode responses, which consist of mixtures of large- and small-amplitude excursions and represent frequency-locked states. Quasiperiodicity, which reflects the interaction of oscillators with incommensurate frequencies, was also observed, although in a smaller number of experiments. The patterns of mixed-mode complexes found at different CPA concentrations allowed the derivation of firing numbers, i.e., number of large oscillations/sum of number of small and large oscillations, and the sequences in which they emerged conformed to Farey arithmetic. Two-dimensional return maps derived by Poincaré section of phase space representations of the dynamics were used to compute the mean number of rotations per iteration on the circle, i.e., the winding number. Plots of winding number against firing number revealed a devil’s staircase-type structure. Experiments with verapamil, a voltage-operated L-type Ca2+-channel antagonist, confirmed that influx of extracellular Ca2+was essential to sustain chaos, quasiperiodicity, and mixed-mode responses. Nonlinear coupling between cytosolic and membrane events in rabbit ear arteries thus results in a self-organized dynamics that collapses to that predicted by the theory of simple circle maps.

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