Eye movements during combined pursuit, optokinetic and vestibular stimulation in macaque monkey

During natural behaviour in a visual environment, smooth pursuit eye movements (SP) usually override the vestibular-ocular reflex (VOR) and the optokinetic reflex (OKR), which stem from head-in-space and scene-relative-to-eye motion, respectively. We investigated the interaction of SP, VOR, and OKR, which is not fully understood to date. Eye movements were recorded in two macaque monkeys while applying various combinations of smooth eye pursuit, vestibular and optokinetic stimuli (sinusoidal horizontal rotations of visual target, chair and optokinetic pattern, respectively, at 0.025, 0.05, 0.1, 0.2, 0.4, and 0.8 Hz, corresponding to peak stimulus velocities of 1.25-40 degrees/s for a standard stimulus of -/+8 degrees). Slow eye responses were analysed in terms of gain and phase. During SP at mid-frequencies, the eyes were almost perfectly on target (gain 0.98 at 0.1 Hz), independently of a concurrent vestibular or optokinetic stimulus. Pursuit gain at lower frequencies, although being almost ideal (0.98 at 0.025 Hz with pursuit-only stimulation), became modified by the optokinetic input (gain increase above unity when optokinetic stimulus had the same direction as target, decrease with opposite direction). At higher stimulus frequencies, pursuit gain decreased (down to 0.69 at 0.8 Hz), and the pursuit response became modified by vestibular input (gain increase during functionally synergistic combinations, decrease in antagonistic combinations).Thus, the pursuit system in monkey dominates during SP-OKR-VOR interaction, but it does so effectively only in the mid-frequency range. The results can be described in the form of a simple dynamic model in which it is assumed that the three systems interact by linear summation. In the model SP and OKR dominate VOR in the low- to mid-frequency/velocity range, because they represent closed loop systems with high internal gain values (>>1) at these frequencies/velocities, whereas the VOR represents an open loop system with about unity-gain (up to very high frequencies). SP dominance over OKR is obtained by allowing an 'attentional/volitional' mechanism to boost SP gain and a predictive mechanism to improve its dynamics.

Central venous catheter motion: a pitfall in catheter localization on pediatric chest radiography

OBJECTIVE

We evaluated central venous catheter motion causing misinterpretation of catheter tip location in pediatric patients and in an experimental model.

MATERIALS AND METHODS

After the recognition of clinically significant catheter motion in 12 randomly selected patients, we conducted a prospective 2-month study of chest radiographs in our pediatric care unit and neonatal emergency department. Serial radiographs were examined for change in catheter tip position ascribed to motion artifact. An in vitro model was developed to replicate clinical parameters. Experimentally, catheter movement and exposure time were analyzed and their impact on catheter localization was recorded.

RESULTS

In the 12 randomly selected patients, radiographic assessment of central venous catheter tip localization on sequential radiographs caused minor to major misinterpretation of the position of the catheter tip and even total nonvisualization of the catheter. Ten (3.5%) of 352 prospectively interpreted pediatric emergency department radiographs showed similar findings. Catheter motion that caused blurring was reproduced in vitro using radiographic parameters typically used in a clinical setting.

CONCLUSION

Catheter motion can cause problems in assessing catheter tip position on pediatric emergency department chest radiographs. We reproduced this phenomenon in an in vitro model. Catheter removal or change in position may be mimicked by this artifact, and patient management may be affected. In our study, catheter localization was affected by catheter motion and exposure time.

Coronin promotes the rapid assembly and cross-linking of actin filaments and may link the actin and microtubule cytoskeletons in yeast

Coronin is a highly conserved actin-associated protein that until now has had unknown biochemical activities. Using microtubule affinity chromatography, we coisolated actin and a homologue of coronin, Crn1p, from Saccharomyces cerevisiae cell extracts. Crn1p is an abundant component of the cortical actin cytoskeleton and binds to F-actin with high affinity (Kd 6 x 10(-9) M). Crn1p promotes the rapid barbed-end assembly of actin filaments and cross-links filaments into bundles and more complex networks, but does not stabilize them. Genetic analyses with a crn1Delta deletion mutation also are consistent with Crn1p regulating filament assembly rather than stability. Filament cross-linking depends on the coiled coil domain of Crn1p, suggesting a requirement for Crn1p dimerization. Assembly-promoting activity is independent of cross-linking and could be due to nucleation and/or accelerated polymerization. Crn1p also binds to microtubules in vitro, and microtubule binding is enhanced by the presence of actin filaments. Microtubule binding is mediated by a region of Crn1p that contains sequences (not found in other coronins) homologous to the microtubule binding region of MAP1B. These activities, considered with microtubule defects observed in crn1Delta cells and in cells overexpressing Crn1p, suggest that Crn1p may provide a functional link between the actin and microtubule cytoskeletons in yeast.

Saccharomyces cerevisiae Duo1p and Dam1p, novel proteins involved in mitotic spindle function

In this paper, we describe the identification and characterization of two novel and essential mitotic spindle proteins, Duo1p and Dam1p. Duo1p was isolated because its overexpression caused defects in mitosis and a mitotic arrest. Duo1p was localized by immunofluorescence, by immunoelectron microscopy, and by tagging with green fluorescent protein (GFP), to intranuclear spindle microtubules and spindle pole bodies. Temperature-sensitive duo1 mutants arrest with short spindles. This arrest is dependent on the mitotic checkpoint. Dam1p was identified by two-hybrid analysis as a protein that binds to Duo1p. By expressing a GFP-Dam1p fusion protein in yeast, Dam1p was also shown to be associated with intranuclear spindle microtubules and spindle pole bodies in vivo. As with Duo1p, overproduction of Dam1p caused mitotic defects. Biochemical experiments demonstrated that Dam1p binds directly to microtubules with micromolar affinity. We suggest that Dam1p might localize Duo1p to intranuclear microtubules and spindle pole bodies to provide a previously unrecognized function (or functions) required for mitosis.

Exploiting chemical libraries, structure, and genomics in the search for kinase inhibitors

Selective protein kinase inhibitors were developed on the basis of the unexpected binding mode of 2,6,9-trisubstituted purines to the adenosine triphosphate-binding site of the human cyclin-dependent kinase 2 (CDK2). By iterating chemical library synthesis and biological screening, potent inhibitors of the human CDK2-cyclin A kinase complex and of Saccharomyces cerevisiae Cdc28p were identified. The structural basis for the binding affinity and selectivity was determined by analysis of a three-dimensional crystal structure of a CDK2-inhibitor complex. The cellular effects of these compounds were characterized in mammalian cells and yeast. In the latter case the effects were characterized on a genome-wide scale by monitoring changes in messenger RNA levels in treated cells with high-density oligonucleotide probe arrays. Purine libraries could provide useful tools for analyzing a variety of signaling and regulatory pathways and may lead to the development of new therapeutics.

Extended excretion of rotavirus after severe diarrhoea in young children

BACKGROUND

Rotaviruses are the major cause of severe childhood diarrhoea. Knowledge of the natural history of infection, including duration of intestinal virus shedding, is important in the understanding of transmission, sources of infection, and immune responses.

METHODS

We carried out a study of rotavirus excretion in 37 children admitted to hospital with severe rotavirus diarrhoea. Sequential faecal specimens were collected from each child during 100 days of surveillance, and screened for rotavirus by EIA and by amplification of genome double-stranded RNA by reverse-transcription PCR. IgA coproantibody was estimated by EIA.

FINDINGS

Duration of rotavirus excretion ranged from 4 to 57 days after onset of diarrhoea. Excretion ceased within 10 days in 16 (43%) children, and within 20 days in 26 (70%) children. Extended excretion was detected for 25-57 days in the remaining 11 (30%) children owing mainly to continued excretion of the primary infecting strain. Extended excretion was significantly associated with antirotavirus IgA coproantibody boosts during 100 days of surveillance (p=0.001, log-rank test), and with recurrence of mild diarrhoea symptoms during convalescence (p=0.006, Fisher's exact test).

INTERPRETATION

Severe rotavirus disease in young children may be followed by extended excretion of rotavirus. The risk of transmission to others may be greater than previously believed. Extended excretion could also explain some cases of the postgastroenteritis syndrome.

Rotavirus vaccines

Encouraging results have been reported from several large trials of tetravalent rhesus rotavirus vaccine, with efficacy of 70-80% against severe disease. A recent Venezuelan study showed similar results to trials in USA and Europe. The vaccine may soon be licensed in USA. It provides the exciting prospect of a strategy to prevent one of the world's major child killers. Other candidate vaccines are under development including human-bovine reassortants, neonatal strains, non-replicating rotaviruses, vector vaccines and other genetically engineered products. Second and third generation rotavirus vaccines are on the horizon. The need for a rotavirus vaccine is well accepted by paediatricians, but public health authorities need to be lobbied. Other issues which need to be addressed include relative importance of non-group A rotaviruses, possible administration with OPV, the influence of breast feeding, and most importantly, cost. It is essential that rotavirus vaccine is somehow made available to all of the world's children, not just those in developed countries.

Volitional control of anticipatory ocular smooth pursuit after viewing, but not pursuing, a moving target: evidence for a re-afferent velocity store

Although human subjects cannot normally initiate smooth eye movements in the absence of a moving target, previous experiments have established that such movements can be evoked if the subject is required to pursue a regularly repeated, transient target motion stimulus. We sought to determine whether active pursuit was necessary to evoke such an anticipatory response or whether it could be induced after merely viewing the target motion. Subjects were presented with a succession of ramp target motion stimuli of identical velocity and alternating direction in the horizontal axis. In initial experiments, the target was exposed for only 120 ms as it passed through centre, with a constant interval between presentations. Ramp velocity was varied from +/- 9 to 45 degrees/s in one set of trials; the interval between ramp presentations was varied from 640 to 1920 ms in another. Subjects were instructed either to pursue the moving target from the first presentation or to hold fixation on another, stationary target during the first one, two or three presentations of the moving display. Without fixation, the first smooth movement was initiated with a mean latency of 95 ms after target onset, but with repeated presentations anticipatory smooth movements started to build up before target onset. In contrast, when the subjects fixated the stationary target for three presentations of the moving target, the first movement they made was already anticipatory and had a peak velocity that was significantly greater than that of the first response without prior fixation. The conditions of experiment 1 were repeated in experiment 3 with a longer duration of target exposure (480 ms), to allow higher eye velocities to build up. Again, after three prior fixations, the anticipatory velocity measured at 100 ms after target onset (when visual feedback would be expected to start) was not significantly different to that evoked after the subjects had made three active pursuit responses to the same target motion, reaching a mean of 20 degrees/s for a 50 degrees/s target movement. In a further experiment, we determined whether subjects could use stored information from prior active pursuit to generate anticipatory pursuit in darkness if there was a high expectancy that the target would reappear with identical velocity. Subjects made one predictive response immediately after target disappearance, but very little response thereafter until the time at which they expected the target to reappear, when they were again able to re-vitalize the anticipatory response before target appearance. The findings of these experiments provide evidence that information related to target velocity can be stored and used to generate future anticipatory responses even in the absence of eye movement. This suggests that information for storage is probably derived from a common pre-motor drive signal that is inhibited during fixation, rather than an efference copy of eye movement itself. Furthermore, a high level of expectancy of target appearance can facilitate the release of this stored information in darkness.

Fifty glorious years

Since the second world war, dentistry has undergone momentous changes, not only in clinical and mechanical developments but also in changes in people's perceptions of what care their dentist can offer them. Dental graduates today will be surprised at the great difference between their own education and that of their 1946 counterparts. This is one dentist's record of the last 50 years in dentistry and how certain advancements have affected his working life.

Skin prick testing in general practice: a pilot study

Allergy skin prick testing is regarded as a routine diagnostic procedure in hospital settings, but its role in general practice is not yet defined. Our aim was to explore the ways in which skin prick testing might facilitate the work of general practice nurses engaged in asthma patient care. A structured questionnaire was completed by 18 practice nurses before and again after administering allergy skin tests to four common aeroallergens (dust mite, grass pollen, cat and dog danders) to 319 consecutive attenders with known or suspected asthma. Nurses' decisions about whether or not to give allergen avoidance advice were reversed after skin testing in 63 (22%) cases for dust mite, 67 (23%) cases for grass pollen, 38 (13%) cases for cat fur and 49 (17%) cases for dog hair. Had allergen avoidance interventions been targeted only at patients with both a positive skin test and a positive clinical history, the number of planned interventions would have declined from 305 before skin testing to 142 after. The findings suggest that allergy skin prick testing was feasible and acceptable in general practice, and that one role may be to reduce the number of allergen avoidance interventions offered to patients unlikely to benefit.

Reduced penetrance of the Huntington's disease mutation

Controversy persists concerning the significance of Huntington disease (HD) alleles in the 36-39 repeat range. Although some clinically affected persons have been documented with repeats in this range, elderly unaffected individuals have also been reported. We examined 10 paternal transmissions of HD alleles of 37-39 repeats in collateral branches of families with de novo HD. All 10 descendants, including many who are elderly, are without symptoms of HD. Forty percent of the transmissions were unstable, although none varied by more than one repeat. The observation that individuals with alleles of 37-39 repeats may survive unaffected beyond common life expectancy supports the presence of reduced penetrance for HD among some persons with repeat sizes which overlap the clinical range. Non-penetrance may be increased in the collateral branches of de novo mutation families when compared to penetrance estimates from patient series. There was no CAA-->CAG mutation for the penultimate glutamine in either a de novo expanded 42 repeat allele or the corresponding non-penetrant 38 repeat allele in a family with fresh mutation to HD.

Direct analysis and identification of proteins in mixtures by LC/MS/MS and database searching at the low-femtomole level

A method to directly identify proteins contained in mixtures by microcolumn reversed-phase liquid chromatography electrospray ionization tandem mass spectrometry (LC/MS/MS) is studied. In this method, the mixture of proteins is digested with a proteolytic enzyme to produce a large collection of peptides. The complex peptide mixture is then separated on-line with a tandem mass spectrometer, acquiring large numbers of tandem mass spectra. The tandem mass spectra are then used to search a protein database to identify the proteins present. Results from standard protein mixtures show that proteins present in simple mixtures can be readily identified with a 30-fold difference in molar quantity, that the identifications are reproducible, and that proteins within the mixture can be identified at low femtomole levels. Based on these studies, methodology has been developed for direct LC/MS/MS analysis of proteins enriched by immunoaffinity precipitation, specific interaction with a protein-protein fusion product, and specific interaction with a macromolecular complex. The approach described in this article provides a rapid method for the direct identification of proteins in mixtures.

DNA double-strand-break sensitivity, DNA replication, and cell cycle arrest phenotypes of Ku-deficient Saccharomyces cerevisiae

In mammalian cells, the Ku heterodimer is involved in DNA double-strand-break recognition and repair. We have established in yeast a connection between Ku activity and DNA double-strand-break damage repair, and a connection between Ku activity and commitment to DNA replication. We generated double-stranded DNA breaks in yeast cells in vivo by expressing a restriction endonuclease and have shown that yeast mutants lacking Ku p70 activity died while isogenic wild-type cells did not. Moreover, we have discovered that DNA damage occurs spontaneously during normal yeast mitotic growth, and that Ku functions in repair of this damage. We also observed that mitotically growing Ku p70 mutants have an anomalously high DNA content, suggesting a role for Ku in regulation of DNA synthesis. Finally, we present evidence that Ku p70 function is conserved between yeast, Drosophila, and humans.

The suitability of cataract patients for day surgery

Day-case surgery is increasingly possible for patients requiring cataract surgery. Current criteria may exclude many patients who would be suitable for day-case admission. Most patients indicated a preference for in-patient care, but this may be a reflection of their actual experience. Patient education and information is vital.

Dosage suppressors of a benomyl-dependent tubulin mutant: evidence for a link between microtubule stability and cellular metabolism

To identify factors important for the regulation of microtubule stability in yeast, dosage suppressors of the hyperstable microtubule phenotype of the budding yeast tub2-150 beta-tubulin mutation were isolated. Of the two suppressors reported here, one (JSN2) encodes a tRNAVal, and the other (JSN3) is an antimorphic allele of the methionine biosynthesis transcription factor Met4p. Furthermore, growth of tub2-150 mutants and suppression of tub2-150 mutants by JSN3 are sensitive to levels of methionine in the growth medium. We explore several possible explanations for these findings, including the potential involvement of the general amino acid control and the involvement of Cbflp, a component of yeast kinetochores that is also necessary for Met4p-mediated transcription.

A comparison of predictive and nonpredictive ocular pursuit under active and passive stimulation conditions in humans

A technique has been developed for the comparison of predictive and nonpredictive ocular pursuit in human subjects, with the objective of estimating the contribution made by predictive processes to the normal pursuit response. Subjects were presented with a target moving at constant velocity in the horizontal plane and instructed to actively pursue the target or to passively stare at it. In the predictive mode (PRD), a step-ramp stimulus with velocity ranging from 12.5 to 50 degrees/s was presented at regular intervals of 1.728 s, in alternating directions, with target exposure durations (PD) that varied from 80 to 640 ms. In the interval between presentations, subjects were in complete darkness. In the nonpredictive mode (RND), similar step-ramp stimuli were presented but with randomized direction and timing of target exposure. In the nonpredictive mode, during both active and passive stimulation, the smooth component of eye velocity was initiated after a mean delay of 125 ms. In the predictive mode, eye velocity started to build up well before target onset, even during passive stimulation. It was found that the time of initiation of this anticipatory response was closely associated with the time at which the target would have changed direction even though the target could not be seen at this time. Eye velocity measured 100 ms after target onset was negligible in the nonpredictive mode, whereas in the predictive mode, it progressively increased with target velocity, reaching a maximum of 18 degrees/s when target velocity was 50 degrees/s and PD was greater than 240 ms. Examination of the difference in the eye velocity trajectories for the predictive and nonpredictive modes indicated that the greatest contribution of prediction occurred approximately 150 ms after target onset and its effects were evident in the predictive response for at least 300 ms. This effect was reflected in the reaction time between target onset and the occurrence of peak eye velocity. In the nonpredictive mode, this progressively increased from 250 ms to 400 ms as PD increased from 80 to 640 ms, whereas in the predictive mode peak velocity occurred an average of 50 ms earlier for all values of PD. The results demonstrate the significant contribution that predictive processes make to normal ocular pursuit behavior and the importance of timing control in this process. They also indicate that this process is not dependent on volitional control, but can be seen as an automatized response during passive stimulation.

Extended length heterobifunctional coupling agents for protein conjugations

A series of extended length heterobifunctional coupling agents is described. The successive aminocaproic acid homologation of succinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate, a known 9-atom long maleimide active ester linker, yielded 16-, 23-, and 30-atom long maleimide active ester homologues. The performance study of these coupling agents in automated microparticle enzyme immunoassays showed that, in the alpha fetoprotein assay, in which the linkers were employed in the construction of the alkaline phosphatase-antibody conjugates, the signal increased 64% when the length of the linker was incremented from 9 atoms to 23 atoms and 82% for the 30-atom long linker as compared with the 9-atom homologue. Similar improvements were observed in the performance of carbohydrate antigen, marker of ovarian cancer (CA-125), immunoassay where the linkers were used for conjugation of the capture antibody anti-CA-125 to the microparticle. Thus, a 300% signal improvement resulted when a 30-atom linker was used instead of the 9-atom homologue. The observed differences in the performance of the conjugates are interpreted as resulting from improved antibody binding and lowering of the steric hindrance of the complementarity-determined region of the antibody when longer coupling agents were used.

Using the confluence model of sexual aggression to predict men's conflict with women: a 10-year follow-up study

We tested a model describing the characteristics of sexually aggressive men that may also be useful for understanding the causes of other antisocial acts against women. This model hypothesizes that sexual aggressors can be identified by two sets of characteristics, labeled hostile masculinity and impersonal sex. To test this model, we followed up a sample of men 10 years after first studying them when they were young adults. We sought to predict which men would be in distressed relationships with women, be aggressive sexually, be nonsexually aggressive, or some combination of these. These behaviors were measured not only by questioning the men themselves but also by questioning many of the men's female partners. Some couples' videotaped conversations were also analyzed. The data supported the ability of the model to predict behavior 10 years later. We also developed the model further and identified the common and unique characteristics contributing to sexual aggression as compared with the other conflictual behaviors studied. The data supported the usefulness of hierarchical modeling incorporating both general factors that contribute to various interpersonal conflicts as well as specific factors uniquely pertaining to dominance of women.

Microtubule stability in budding yeast: characterization and dosage suppression of a benomyl-dependent tubulin mutant

To better understand the dynamic regulation of microtubule structures in yeast, we studied a conditional-lethal beta-tubulin mutation tub2-150. This mutation is unique among the hundreds of tubulin mutations isolated in Saccharomyces cerevisiae in that it appears to cause an increase in the stability of microtubules. We report here that this allele is a mutation of threonine 238 to alanine, and that tub2-150 prevents the spindle from elongating during anaphase, suggesting a nuclear microtubule defect. To identify regulators of microtubule stability and/or anaphase, yeast genes were selected that, when overexpressed, could suppress the tub2-150 temperature-sensitive phenotype. One of these genes, JSN1, encodes a protein of 125 kDa that has limited similarity to a number of proteins of unknown function. Overexpression of the JSN1 gene in a TUB2 strain causes that strain to become more sensitive to benomyl, a microtubule-destabilizing drug. Of a representative group of microtubule mutants, only one other mutation, tub2-404, could be suppressed by JSN1 overexpression, showing that JSN1 is an allele-specific suppressor. As tub2-404 mutants are also defective for spindle elongation, this provides additional support for a role for JSN1 during anaphase.

Using the confluence model of sexual aggression to predict men's conflict with women: a 10-year follow-up study

We tested a model describing the characteristics of sexually aggressive men that may also be useful for understanding the causes of other antisocial acts against women. This model hypothesizes that sexual aggressors can be identified by two sets of characteristics, labeled hostile masculinity and impersonal sex. To test this model, we followed up a sample of men 10 years after first studying them when they were young adults. We sought to predict which men would be in distressed relationships with women, be aggressive sexually, be nonsexually aggressive, or some combination of these. These behaviors were measured not only by questioning the men themselves but also by questioning many of the men's female partners. Some couples' videotaped conversations were also analyzed. The data supported the ability of the model to predict behavior 10 years later. We also developed the model further and identified the common and unique characteristics contributing to sexual aggression as compared with the other conflictual behaviors studied. The data supported the usefulness of hierarchical modeling incorporating both general factors that contribute to various interpersonal conflicts as well as specific factors uniquely pertaining to dominance of women.