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PubMedDate not supplied

NMDA receptor diversity in the cerebellum: identification of subunits contributing to functional receptors.

Recent studies of N-methyl-D-aspartate (NMDA) receptors have led to the suggestion that there are two distinct classes of native NMDA receptors, identifiable from their single-channel conductance properties. 'High-conductance' openings arise from NR2A- or NR2B-containing receptors, and 'low-conductance' openings arise from NR2C- or NR2D-containing receptors. In addition, the low-conductance channels show reduced sensitivity to block by Mg2+. The readily identified cell types and simple architecture of the cerebellum make it an ideal model system in which to determine the contribution of specific subunits to functional NMDA receptors. Furthermore, mRNA for all of these four NR2 subunits are represented in this brain region. We have examined NMDA channels in Purkinje cells, deep cerebellar nuclei (DCN) neurons and Golgi cells. First we find that NR2D-containing NMDA receptors give rise to low-conductance openings in cell-attached recordings from Purkinje cells. The characteristic conductance of these events cannot, therefore, be ascribed to patch excision. Second, patches from some DCN neurons exhibit mixed populations of high- and low-conductance openings. Third, Golgi cells also exhibit a mixed population of high- and low-conductance NMDA receptor openings. The features of these low-conductance openings are consistent with the presence of NR2D-containing NMDA receptors, as suggested by in situ hybridization data. On the other hand the existence of high-conductance channels, with properties typical of NR2B-containing receptors, was not expected. Our results provide new evidence about the subunit composition of NMDA receptors in identified cerebellar cells, and suggest that examination of single-channel properties is a potentially powerful approach for determining the possible subunit composition of native NMDA receptors.

Animals↗
PubMed2002

The effects of a confectionery snack on attention in young boys.

The relationship between consumption of a confectionery snack after an overnight fast and cognitive function was examined using a variety of cognitive tasks, including spatial memory, verbal memory, attention, visual perception and short-term memory, in a sample of 21 boys, ages 9-12 years. Performance on the vigilance attention task was significantly improved when the participants consumed a confectionery snack compared to consumption of a noncalorie snack. Participants had significantly higher hit rates and significantly lower miss rates after the confectionery snack. In addition, false alarm rates increased as a function of time for the placebo condition and decreased for the confectionery condition. Thus, the confectionery snack enhanced ability to stay on task for an extended period of time, enabling the children to more accurately identify target information, as well as correctly reject nontarget information. Analysis of the types of errors made also revealed that when the children were in the confectionery condition they were less likely to make more glaring errors. No significant differences were found in tests of digit span, verbal memory, spatial memory or visual perception.

Attention↗
PubMed2000

Does a front-end nonlinearity confound VEP acuity measures in human infants?

The visual evoked potential is commonly used to estimate visual acuity in infants. The stimulus used is temporally modulated in order to drive the cortical response. Here it is proposed that distortion products generated by a front-end nonlinearity may contaminate the acuity estimate. Specifically, the nonlinearity might convert temporal modulation of a high spatial frequency grating into apparent whole-field flicker. Thus, the VEP may reflect an artifactual response to a high spatial frequency that is not resolved at the cortical level. If this were the case, one could null or attenuate the flicker response by adding whole-field flicker to the grating stimulus. We looked for such nulling effects in 18 infants aged 6-17 weeks. No consistent evidence was found for the nulling effect, so it was concluded that infant VEP acuity estimates are not significantly contaminated by the hypothesized distortion product.

Evoked Potentials, Visual↗
PubMed1998

Optical, receptoral, and retinal constraints on foveal and peripheral vision in the human neonate.

We examined the properties of the foveal, parafoveal, and near peripheral cone lattice in human neonates. To estimate the ability of these lattices to transmit the information used in contrast sensitivity and visual acuity tasks, we constructed ideal-observer models with the optics and photoreceptors of the neonatal eye at retinal eccentricities of 0, 5, and 10 degrees. For ideal-observer models limited by photon noise, the eye's optics, and cone properties, contrast sensitivity was higher in the parafovea and near periphery than in the fovea. However, receptor pooling probably occurs in the neonate's parafovea and near periphery as it does in mature eyes. When we add a receptor-pooling stage to the models of the parafovea and near periphery, ideal acuity is similar in the fovea, parafovea, and near periphery. Comparisons of ideal and real sensitivity indicate that optical and receptoral immaturities impose a significant constraint on neonatal contrast sensitivity and acuity, but that immaturities in later processing stages must also limit visual performance.

Contrast Sensitivity↗
PubMed1999

Use of an early nonlinearity to measure optical and receptor resolution in the human infant.

We measured the resolution of the optics and receptoral processes in human infants. To do so, we recorded visual-evoked potentials (VEPs) to sampled sinewave gratings, stimuli that generate highly visible distortion products at a nonlinearity early in the retina. We varied the spatial frequency content of the stimulus to determine the frequencies that can be transmitted through the optics and receptors and thereby generate distortion products. Data were collected from adults and 2- to 7-month-old infants. The results indicated that the resolution of the infants' optical/receptoral processes was within a factor of two of adults' even at the earliest ages tested. These first stages of processing, therefore, do not explain infants' poor performance in many visual tasks, or restrict the types of visual stimuli affecting more central mechanisms that undergo experience-dependent development.

Adult↗
PubMed2002

Monitoring of particulate matter outdoors.

Recent studies of the size and composition of atmospheric particulate matter (PM) have demonstrated the usefulness of separating atmospheric PM into its fine and coarse components. The need to measure the mass and composition of fine and coarse PM separately has been emphasized by research in exposure, epidemiology, and toxicology of atmospheric PM. This paper provides a background on the size distribution and properties of PM relevant to the differences between fine and coarse particles. Various decisions that must be made when deciding how to separate, collect, and measure PM are discussed. Techniques for monitoring fine and coarse particles, including the US Federal Reference Method for PM2.5 and several techniques for PM10-2.5, are presented. Problems encountered in collecting semivolatile PM and in weighing atmospheric PM collected on a filter are described. Continuous monitoring methods for PM mass and for PM components (carbon, nitrate, and sulfate) are described and brief descriptions are given of analytical techniques for the chemical characterization of collected PM. This information should be especially useful for environmental workers familiar with monitoring methods for total suspended particles or PM10 but who will need to measure PM2, and PM10-2.5 in the future.

Air Pollutants↗
PubMed2000

Assays for transglutaminases in cell death.

Several in vivo and in vitro experimental model systems demonstrate a direct relationship between the expression and activity of tissue transglutaminase [tTG; also called transglutaminase type 2 (TGase 2)] and programmed cell death or apoptosis. This is based on mRNA and protein studies, sense and antisense transfection, identification of N epsilon-(gamma-glutamyl)-lysine cross-links in extracted apoptotic bodies, and in blue mouse experiments. In the epidermis, apoptosis occurs under particular conditions in the proliferative basal layer with the involvement of the tTG enzyme. However, in epidermal keratinocytes other TGases (TGase 1, TGase 3, and perhaps TGase X) are normally activated in a terminal differentiation program, called cornification, that leads to cell death. These cells perform their functions after death, providing an elastic physical and permeability barrier to the skin. In fact, TGase 1 mutations cause the skin disease lamellar ichthyosis. Because all TGases share strong similarities in structure and function, being involved in mechanisms of cell death, this chapter describes the current assays for TGases at the mRNA, protein, and enzymatic levels. We also describe procedures to produce, purify, and characterize recombinant TGases, to identify mutation in disease, to isolate cross-linked bodies, and to analyze the N epsilon-(gamma-glutamyl)-lysine isopeptide cross-links. Finally, we discuss general rules for the interpretation and comparison of these events in cell death.

Amino Acid Sequence↗
PubMed1990

Immunoassay of peanut allergens in food-processing materials and finished foods.

To quantitate trace amounts of peanut allergens in food-processing materials and finished foods, we established a solid-phase radioimmunoassay inhibition using pooled sera from five peanut-sensitive subjects and a roasted peanut-meal extract covalently linked to polyacrylamide beads. Test samples were extracted, dialyzed, lyophilized, and reconstituted at 10 to 225 mg of dry weight per milliliter concentrations. The peanut-allergen content of test samples was expressed relative to a reference extract of roasted peanut meal that was assigned an arbitrary potency of 100,000 U/ml. In confectionery products spiked with varying quantities of peanut (0.7% to 0.0175%), the recovery of peanut allergen ranged from 31% to 94%. The sensitivity of the assay was 2.5 U/mg of dry weight from these samples (0.00875% peanut). Peanut allergens were undetectable in virgin vegetable oil used to roast peanuts, but 600 to 7600 U/mg of dry weight were present in oil after varying periods of use. The allergen content of used oil was reduced to 8 U/mg of dry weight by filtration and steam cleaning. The availability of such assays provides a means of monitoring finished food products for potential allergens. This monitoring in turn will provide the means to correlate symptoms experienced by sensitive patients with the exact quantity of allergen ingested. At the present time, there is little information on the quantities of ingested peanut allergen that pose risks to peanut-sensitive subjects.

Allergens↗
PubMed2002

Time-dependent properties of human root dentin.

OBJECTIVES: The aim of this study was to investigate the creep, stress relaxation and strain rate behavior of human root dentin under compressive loading. METHODS: Cylindrical root dentin samples of 3.5mm outer diameter, 1.5mm internal canal diameter and 6-10mm long were prepared from freshly extracted teeth. The samples were tested in a closed-loop servohydraulic testing machine at constant load or displacement, and varied strain rate. In vivo strain rates were estimated using strain gauges bonded to human teeth. RESULTS: A family of creep curves, determined at different loads within dentin's elastic region, was found to be consistent with a material having linear viscoelastic behavior. A positive correlation (r(2)=0.79, P<0.001) was found between creep rate and stress. Young's modulus (E) was found to be a function of the strain rate with rates of loading in the range 10-500,000Ns(-1). Loading at constant displacement showed stress to be a decreasing function of time (i.e. stress relaxation). SIGNIFICANCE: Dentin showed linear-viscoelastic behavior under various conditions of compressive loading. Time dependent properties of dentin should be taken into account in restorative dentistry.

Algorithms↗