The avian chB6 (Bu-1) alloantigen can mediate rapid cell death

The control of cell death is critical in the immune system. T and B lymphocytes must be censored during their development to remove nonfunctional or self-reactive lymphocytes. However, the molecules controlling cell deletion during lymphopoiesis have not been defined. B cells removed from the avian bursa of Fabricius rapidly undergo cell death in culture. We screened bursal B cells with a panel of Abs and lectins to identify molecules affecting their viability. Abs to the chB6 alloantigen caused a rapid loss of cell viability as measured by staining with propidium iodide. ChB6 Abs also cause adhesion between B cells. Transfection of cDNA encoding chB6 reconstituted the allele-specific cell death and adhesion effects in avian cell lines. These effects can be separated by binding cells onto Ab-coated plastic dishes. In these experiments, cells were killed in the absence of cell:cell contact. The ability of chB6 cross-linking to evoke cell aggregation and cell death is also observed when chB6 is expressed in growth factor-dependent mammalian cells. In these cells growth factor can almost completely prevent cell death but not cell aggregation. This suggests that known cell survival stimuli can suppress the cell death brought about by chB6 cross-linking. These results show that chB6 may have an important role in controlling cell survival and/or adhesion during avian B cell development.     

Effects of synaptic vesicles on actin polymerization

We have analyzed the effects of synaptic vesicles on actin polymerization by using a time-resolved spectrofluorometric assay. We have found that synaptic vesicles have complex effects on the kinetics of actin polymerization, which vary depending on whether the synaptic vesicle-specific phosphoprotein synapsin I is absent or present on their membrane. Synapsin I bound either to synaptic vesicles or to pure phospholipid vesicles exhibits phosphorylation-dependent actin-nucleating activity. Synaptic vesicles depleted of endogenous synapsin I decrease the rate and the final extent of actin polymerization, an effect which is not observed with pure phospholipid vesicles. Thus, the state of association of synapsin I with synaptic vesicles, which is modulated by its state of phosphorylation, may affect actin assembly and the physico-chemical characteristics of the synaptic vesicle microenvironment.     

A randomized, double-blind, placebo controlled comparison of droperidol, ondansetron, and metoclopramide for the prevention of vomiting following outpatient strabismus surgery in children

STUDY OBJECTIVE: To compare the efficacy of ondansetron, droperidol, or metoclopramide with placebo in preventing postoperative vomiting following strabismus surgery. STUDY DESIGN: Randomized, double-blind, placebo-controlled clinical trial. SETTING: University outpatient surgery center. PATIENTS: 160 ASA physical status I and II children ages 1 to 12 years who were scheduled for strabismus surgery. INTERVENTIONS: Administration of either ondansetron 100 mcg/kg, metoclopramide 250 mcg/kg, droperidol 75 mcg/kg, or placebo intravenously after induction of anesthesia. MEASUREMENTS AND MAIN RESULTS: Both ondansetron and droperidol were superior to metoclopramide and placebo in preventing predischarge vomiting, with incidences of 5%, 5%, 32%, and 25%, respectively. However, there was no difference in the incidence of postdischarge vomiting among the groups (ondansetron 25%, droperidol 25%, metoclopramide 20%, and placebo 25%). CONCLUSIONS: While both ondansetron and droperidol are more effective than metoclopramide when compared with placebo in decreasing the incidence of predischarge vomiting, none of these drugs was more effective than placebo in decreasing the incidence of postdischarge vomiting. Recovery from anesthesia was not significantly different among the groups as assessed by time to awakening, initial Steward score, and time to discharge.     

Three types of IS-A statement in diagnostic classifications: three types of knowledge needed for development and maintenance

Update mechanisms for diagnostic classifications should capture changes in medical knowledge but also allow for comparability across versions. This paper provides a basis for such a mechanism by describing types of IS-A statement and types of knowledge used in the construction of diagnostic classifications. Three types of IS-A statement are used: 'A is by definition a B', 'A is probably a B' and 'A is in theory necessarily a B'. Each relates to a different type of knowledge: knowledge of linguistic conventions, of probabilities, and of empirical theories and their status, respectively. Consequently, the development and maintenance of diagnostic classifications requires a collaboration of medical terminologists and medical scientists. The role of the latter is especially important during updating. Updating is necessitated by changing probabilities and by the introduction or changing status of empirical theories. The linguistic notion of hyponymy oversimplifies the issue.     

Behavioural responses of Mallorcan midwife toad tadpoles to natural and unnatural snake predators

Calibration of phototherapy equipment can prove to be difficult. One problem is that the self-shielding produced by a patient reduces the irradiance relative to that determined when the cabinet is empty. A model has been developed to determine the factor to apply to the irradiance measured with the cabinet empty to give the irradiance with the patient present, i.e. the self-shielding correction factor. The model assumes that the cabinet consists of a number of discrete infinite line sources backed by perfect mirrors. The patient is treated as a barrier that prevents some of these sources being seen by the detector in the mirror it faces. The model was tested using a Waldmann 8001 K unit and three UV meters for UVA and UVB sources. The measurements suggested some modifications to the model--for UVA multiple reflections were important and for UVB the reflectors were only 30% efficient. The correction factors obtained were 0.87 for UVA and 0.96 for UVB.     

The UL8 subunit of the herpes simplex virus type-1 DNA helicase-primase optimizes utilization of DNA templates covered by the homologous single-strand DNA-binding protein ICP8

The herpes simplex virus type-1 DNA helicase-primase is a heterotrimer encoded by the UL5, UL8, and UL52 genes. The core enzyme, specified by the UL5 and UL52 genes, retains DNA helicase, DNA-dependent nucleoside triphosphatase, and primase activities. The UL8 subunit has previously been implicated in increasing primer stability and in stimulating primer synthesis by the core enzyme. To further characterize the function of the UL8 subunit, we have examined its effect on the activities of the UL5/52 core enzyme using DNA templates covered by the herpes simplex virus type-1 single-strand DNA-binding protein ICP8. We found that while ICP8 stimulated the DNA helicase activity of the UL5/52 proteins up to 3-fold, maximum stimulation by ICP8 required the presence of UL8 protein. Moreover, UL8 protein was required to reverse the inhibitory effect of ICP8 on the DNA-dependent ATPase and primase activities of the UL5/52 proteins. These observations were specific for ICP8 since the heterologous Escherichia coli single-strand DNA-binding protein could not substitute for ICP8. These data suggest that UL8 protein mediates an interaction between the UL5/52 core enzyme and ICP8 that optimizes the utilization of ICP8-covered DNA templates during DNA replication.     

Fixation conditions, the foveola and saccadic latency

Saccades are often elicited in the laboratory by the abrupt step-displacement of a single lit point which is initially the foveolar fixation point and then the eccentric refixation target. This was our Control condition. Four experiments modified the fixation arrangements to examine the effect of altered foveolar stimulation on saccadic latency and accuracy to targets within the central +/- 6 deg of the visual field. (1) No foveolar fixation point: The subject fixated the empty space midway between a pair of fixation guides, which later collapsed into a single refixation target. Latencies for small saccades were similar to the Control values. (2) No foveolar fixation point and no real refixation target: A pair of fixation guides underwent a yoked displacement, and it was easy to fixate and track the invisible midpoint. The smallest saccades were hypermetric, and the typical pattern of latency variation with retinal eccentricity was exaggerated in scale. (3) Spatial effects of a persistent non-target: The precise position of a non-target was important, latency increases being in the ipsilateral hemifield when the non-target was intrafoveolar and unilateral, bilateral when intrafoveolar and on the midline, and local when the non-target was extrafoveolar. (4) Temporal effects of a foveolar fixation point: Blanking an otherwise persistent fixation point for as little as 1 msec at the time of target presentation reduced the expected latency increase. We conclude that the position and timing of foveolar illumination can be critical for saccades of all sizes.