Reorganization of receptive fields following hearing loss in inferior colliculus neurons.

We explored frequency and intensity encoding in the inferior colliculus (IC) of the C57 mouse model of sensorineural hearing loss. Consistent with plasticity reported in the IC of other models of hearing loss, frequency response areas (FRAs) in hearing-impaired (HI) mice were broader with fewer high-frequency units than normal-hearing (NH) mice. The broad FRAs recorded from HI mice had lower cutoffs on the low frequency edge of the FRA. Characteristic frequency (CF) and sharpness of tuning (Q10) calculated from the FRA were used to divide the sample into four categories: low-CF sharp-FRA, low-CF broad-FRA, high-CF sharp-FRA, and high-CF broad-FRA units. Rate-intensity functions (RIFs) for CF tones and noise were used to determine the minimum and maximum response counts as well as the sound pressure levels resulting in 10%, 50%, and 90% of the maximum spike count. Tone RIFs of broad FRA units were shifted to the right of tone RIFs of sharp FRA units in both NH and HI mouse IC, regardless of the unit CF. The main effects of hearing loss were seen in the noise RIFs. The low-CF broad-FRA units in HI mice had elevated responses to noise, and the high-CF sharp-FRA units in HI mice had lower maximum rates, as compared with the units recorded from NH mice. These results suggest that, as the IC responds to peripheral hearing loss with changes in the representation of frequency, an altered balance between inhibitory and excitatory inputs to the neurons recorded from the HI mice alters aspects of the units' intensity encoding. This altered balance likely occurs, at least in part, outside of the IC.

A computational sensorimotor model of bat echolocation.

A computational sensorimotor model of target capture behavior by the echolocating bat, Eptesicus fuscus, was developed to understand the detection, localization, tracking, and interception of insect prey in a biological sonar system. This model incorporated acoustics, target localization processes, flight aerodynamics, and target capture planning to produce model trajectories replicating those observed in behavioral insect capture trials. Estimates of target range were based on echo delay, azimuth on the relative intensity of the echo at the two ears, and elevation on the spectral pattern of the sonar return in a match/mismatch process. Flapping flight aerodynamics was used to produce realistic model trajectories. Localization in all three spatial dimensions proved necessary to control target tracking and interception for an adequate model of insect capture behavior by echolocating bats. Target capture using maneuvering flight was generally successful when the model's path was controlled by a planning process that made use of an anticipatory internal simulation, while simple homing was successful only for targets directly ahead of the model bat.

Polynitrogen chemistry. Synthesis, characterization, and crystal structure of surprisingly stable fluoroantimonate salts of N5+.

The new N5+ salt, N5+ SbF(6)(-), was prepared from N(2)F(+)SbF(6)(-) and HN(3) in anhydrous HF solution. The white solid is surprisingly stable, decomposing only at 70 degrees C, and is relatively insensitive to impact. Its vibrational spectrum exhibits all nine fundamentals with frequencies that are in excellent agreement with the theoretical calculations for a five-atomic V-shaped ion of C(2)(v)symmetry. The N5+ Sb(2)F(11)(-) salt was also prepared, and its crystal structure was determined. The geometry previously predicted for free gaseous N5+ from theoretical calculations was confirmed within experimental error. The Sb(2)F(11)(-) anions exhibit an unusual geometry with eclipsed SbF(4) groups due to interionic bridging with the N5+ cations. The N5+ cation is a powerful one-electron oxidizer. It readily oxidizes NO, NO(2), and Br(2) but fails to oxidize Cl(2), Xe, or O(2).

Status of methods for assessing bacterial cell surface charge properties based on zeta potential measurements.

Surface interfacial physiology is particularly important to unicellular organisms with regard to maintenance of optimal cell function. Bacterial cell surfaces possess net negative electrostatic charge by virtue of ionized phosphoryl and carboxylate substituents on outer cell envelope macromolecules which are exposed to the extracellular environment. The degree of peripheral electronegativity influences overall cell surface polarity and can be assessed on the basis of zeta potential which is most often determined by estimating the electrophoretic mobility of cells in an electric field. The purpose of this review is to provide bacteriologists with assistance as they seek to better understand available instrumentation and fundamental principles concerning the estimation of zeta potential as it relates to bacterial surface physiology.

Background noise differentially effects temporal coding by tonic units in the mouse inferior colliculus.

In natural environments, temporally complex signals often occur in a background of noise. The neural mechanisms underlying the preservation of temporal sensitivity in background noise are poorly understood. In the present study, we examined the ability of inferior colliculus (IC) units with primary-like and sustained response patterns ('tonic units') to encode silent gaps in quiet and in background noise. Minimum gap thresholds (MGTs), the shortest silent gap in a noise burst evoking a neural response, were measured in quiet and background noise for 34 IC units. Units were classified as background noise resistant (BNR; MGT did not change in background noise) or background noise sensitive (BNS; MGTs became elevated in background noise). In quiet, the MGTs of BNR and BNS units were comparable and both types of units encoded the gap by a cessation of activity during the gap. The addition of background noise had little effect on the response rate of BNR units either during or after the gap stimulus. In contrast, for BNS units, background noise reduced the response rate during the gap stimulus while increasing the response rate after the gap stimulus. Background noise also altered the first spike latency of BNS units. For BNS units, the mean first spike latency was no longer inversely related to BF, but this relationship was maintained in BNR units. These results suggest that the response of BNS units to background noise obliterates their response to the gap stimulus.

Heteronuclear NMR studies of cobalt corrinoids. 20. 31P chemical shift anisotropy of aquacobalamin and its complex with a haptocorrin from chicken serum.

Static light scattering measurements have been used to determine the molecular mass (65.3 kDa) and second virial coefficient (3.66 x 10(-4) mol mL g-2) for the complex between chicken serum haptocorrin (HC) and aquacobalamin (H2OCbl). Dynamic light scattering measurements have also been used to determine the translational diffusion coefficient of the H2OCbl-HC complex as a function of concentration. From the diffusion coefficient at infinite dilution (4.71 x 10(-7) cm2 s-1), the hydrodynamic radius (45.5 A) and rotational correlation time (85.4 ns) have been calculated. Using the latter, and measured values of the 31P NMR linewidths of the H2OCbl-HC complex at several field strengths, a detailed analysis of the 31P nuclear relaxation is possible. The chemical shift anisotropy term from the transverse relaxation equation is determined to be 95.7 ppm, and the average phosphorus-proton internuclear distance is 2.05 A. For comparison to protein-free H2OCbl, the chemical shift anisotropy of the phosphorus atom was studied by solid state NMR spectroscopy and the 31P relaxation by solution T1 measurements. These studies give values of 110.3 ppm for the chemical shift anisotropy term and 2.45 A for the average phosphorus-proton internuclear distance. The results are consistent with a significant change in the conformation of the H2OCbl phosphodiester upon binding to haptocorrin which could be due to a shortening of the axial Co-N bond.

Auditory motion induces directionally dependent receptive field shifts in inferior colliculus neurons.

This research focused on the response of neurons in the inferior colliculus of the unanesthetized mustached bat, Pteronotus parnelli, to apparent auditory motion. We produced the apparent motion stimulus by broadcasting pure-tone bursts sequentially from an array of loudspeakers along horizontal, vertical, or oblique trajectories in the frontal hemifield. Motion direction had an effect on the response of 65% of the units sampled. In these cells, motion in opposite directions produced shifts in receptive field locations, differences in response magnitude, or a combination of the two effects. Receptive fields typically were shifted opposite the direction of motion (i.e., units showed a greater response to moving sounds entering the receptive field than exiting) and shifts were obtained to horizontal, vertical, and oblique motion orientations. Response latency also shifted as a function of motion direction, and stimulus locations eliciting greater spike counts also exhibited the shortest neural latency. Motion crossing the receptive field boundaries appeared to be both necessary and sufficient to produce receptive field shifts. Decreasing the silent interval between successive stimuli in the apparent motion sequence increased both the probability of obtaining a directional effect and the magnitude of receptive field shifts. We suggest that the observed directional effects might be explained by "spatial masking," where the response of auditory neurons after stimulation from particularly effective locations in space would be diminished. The shift in auditory receptive fields would be expected to shift the perceived location of a moving sound and may explain shifts in localization of moving sources observed in psychophysical studies. Shifts in perceived target location caused by auditory motion might be exploited by auditory predators such as Pteronotus in a predictive tracking strategy to capture moving insect prey.

Regenerable biosensor platform: a total internal reflection fluorescence cell with electrochemical control.

A new biosensor platform that provides simultaneous fluorescence detection and electrochemical control of biospecific binding has been developed and investigated using antibody-antigen and streptavidin-biotin interactions. Specifically, biotin was covalently bound to a transparent indium-tin oxide (ITO) working electrode, which also served as an integral part of a total internal reflection fluorescence (TIRF) flow cell. TIRF was used to monitor biospecific interactions, while electrochemical polarization was employed to control interactions between biotin and streptavidin or between biotin and anti-biotin antibodies. Both streptavidin and polyclonal anti-biotin antibodies bound kinetically irreversibly to the biotinylated surface. In the absence of electrochemical control, the assay exhibited an extremely slow release of the bound analytes, causing poor regeneration ability of the biosensor surface. However, electrochemical polarization was found to stimulate dissociation of kinetically irreversibly bound biotin-streptavidin and antibody-antigen complexes. A "square wave" polarization function stimulated dissociation more effectively than a "saw tooth" function over the same voltage range. Application of the square wave polarization resulted in regeneration of an active biotinylated surface. Electrochemical polarization also modified affinity and kinetics of protein adsorption, which could likely be used to promote biospecific interactions and/or to suppress nonspecific adsorption.

Technology assessment in healthcare: a review and description of a "best practice" technology assessment process.

BACKGROUND: Technology assessment has become a rapidly growing component of the healthcare system. It has assumed a functional role in operational settings and is rapidly impacting decisions involving purchasing, coverage, and reimbursement. This review is intended to assist the healthcare decision maker in considering the application of technology assessment in healthcare, so as to maximize the efficiency of future purchasing decisions. METHODS: This "best practice" was synthesized after identifying key institutions performing technology assessment in healthcare and analyzing their working processes, including literature review, consensus panel discussions, and expert opinion. RESULTS: We describe this best practice on a reiterative loop that consists of five processes: awareness, strategic appropriateness, analysis versus need, acquisition and implementation, and reassessment. Typical barriers to adoption of technology assessment are also identified and discussed. CONCLUSIONS: This review suggests a common terminology for the core processes involved in technology assessment, thereby facilitating a more uniform understanding among the different components of the healthcare system (i.e., payer, provider, and society) while recognizing their different perspectives.

Effect of polymyxin B nonapeptide on daptomycin permeability and cell surface properties in Pseudomonas aeruginosa, Escherichia coli, and Pasteurella multocida.

The present study was carried out to determine if sensitization of Gram-negative bacteria to the polyanionic antibiotic daptomycin by cationic molecules can be explained on the basis of decreased cell surface charge in order to better understand intrinsic resistance. Turbidimetric assessments of batch cultural growth kinetics revealed the outer membrane permeabilizer polymyxin B nonapeptide sensitized Pseudomonas aeruginosa and Escherichia coli to the hydrophobic probe novobiocin, whereas little or no sensitization was observed for two surface hydrophobicity variants of Pasteurella multocida. Polymyxin B nonapeptide and daptomycin synergistically inhibited growth of P. aeruginosa only. A hydrocarbon adherence assay revealed permeabilizing concentrations of polymyxin B nonapeptide increased cell surface hydrophobicity of P. aeruginosa and the hydrophobic P. multocida variant, while E. coli and the hydrophilic P. multocida variant remained unaffected. Measurement of cellular electrophoretic mobility showed polymyxin B nonapeptide permeabilization of P. aeruginosa to daptomycin occurred concomitantly with a significant decrease in cell surface charge, while no such sensitization occurred in organisms which failed to undergo polymyxin B nonapeptide-induced surface charge decreases. These data suggest that sensitization of Gram-negative bacteria to polyanionic lipopeptides by growth in the presence of polycationic outer membrane permeabilizers such as polymyxin B nonapeptide is dependent on diminution of overall cell surface charge and polarity, thereby allowing outer cell envelope permeation.

Predicting protein crystallization from a dilute solution property.

A dilute solution parameter obtained from static light-scattering measurements is proposed as a predictor for protein crystallization experiments. The osmotic second virial coefficients, B(22), have been measured for a variety of proteins in solvents that are known to promote crystallization and the values for B(22) were found to lie within a fairly narrow range which we refer to as a crystallization slot. Solution conditions which were known not to favor crystallization of the proteins resulted in B(22) values well outside the crystallization slot.

Creation of ultra-rare restriction sites in intact eucaryotic chromosomes mediated by bacterial methylases: an approach to sequencing and analyzing tumor and normal genomes.

The limited restriction of eucaryotic chromosomes would facilitate our understanding of the aberrant genomes of genetic diseases and cancer. We have described methods for methylating eucaryotic chromosomes embedded in agarose plugs. We now describe how Cla I methylase can be utilized in a methylation-dependent restriction cleavage with Dpn I to restrict eucaryotic genomes into a limited number of fragments. We have restricted the genomes of Saccharomyces cerevisiae at four sites and cleaved the three chromosomes of Schizosaccharomyces pombe into eleven fragments. Unlike the recently published methodologies using DNA sequences inserted into procaryotic and eucaryotic genomes, the methodologies described here use unaltered eucaryotic genomes for highly limited restriction. This methodology has applications in speeding, simplifying, and reducing the cost of sequencing the human genome.

Methylation of intact chromosomes by bacterial methylases in agarose plugs suitable for pulsed-field electrophoresis. Methylation of intact chromosomes in agarose by methylases.

Conditions were determined for the methylation of intact yeast chromosomes by EcoRI, HhaI, and MspI bacterial methylases using an endonuclease protection assay while the chromosomes were embedded in agarose plugs suitable for transverse-field electrophoresis. Parameters were also established for the methylation of human chromosomes by EcoRI methylase. Methylation of embedded chromosomes by EcoRI methylase required prewashes with EDTA. EcoRI, HhaI, and MspI methylases showed optimal activity when nonacetylated bovine serum albumin, high levels of S-adenosylmethionine, and high levels of methylase were used. The use of bacterial methylases for methylation of embedded chromosomes will allow investigators to normalize variations in cellular DNA methylation prior to restriction and create new and rare endonuclease recognition sites which will facilitate the detection of chromosomal alterations and deletions.

Acute myocardial infarction associated with single vessel coronary artery disease: an analysis of clinical outcome and the prognostic importance of vessel patency and residual ischemic myocardium.

The long-term outcome and the significance of residual ischemic myocardium, as assessed by predischarge exercise thallium scintigraphy and vessel patency, were studied in 97 patients with single vessel coronary artery disease by angiography 12 +/- 4 days after uncomplicated myocardial infarction. During a mean follow-up period of 39 +/- 17 months, no patients died, 6 (6%) had a recurrent nonfatal infarction and 25 (26%) experienced rapidly progressive angina requiring hospitalization. Although neither exercise-induced angina nor ST segment depression was predictive of a recurrent cardiac event, the mean number of infarct zone scan segments showing thallium redistribution (1.0 +/- 1.0 versus 0.5 +/- 0.8, p = 0.01) and the percent of patients with infarct zone redistribution (61 versus 39%, p = 0.05) were greater in those patients who experienced a late ischemic event. Kaplan-Meier analysis demonstrated a lower event-free survival rate in patients with redistribution (n = 45) than in those without redistribution (n = 52) (p = 0.019). Although no patient received immediate thrombolytic therapy, the infarct-related vessel was angiographically patent in 40 patients (41%). Vessel patency did not influence event-free survival, although a patent vessel, as compared with an occluded vessel, was associated with a greater prevalence of non-Q wave infarction (58 versus 21%, p less than 0.001), fewer persistent infarct zone thallium defects (1.2 +/- 1.1 versus 2.0 +/- 1.2, p = 0.001), more reversible infarct zone thallium defects (1.0 +/- 1.0 versus 0.5 +/- 0.9, p = 0.02) and a trend toward a higher left ventricular ejection fraction (53 +/- 10% versus 49 +/- 12%, p = 0.07). In summary, uncomplicated myocardial infarction in patients with single vessel coronary artery disease is associated with a very low incidence of subsequent death and reinfarction. The presence of infarct zone thallium redistribution, compared with its absence, is predictive of a higher cardiac event rate. These data should be considered when recommending prophylactic percutaneous transluminal angioplasty after uncomplicated myocardial infarction in asymptomatic patients with single vessel coronary disease. On the basis of these results, future randomized trials designed to evaluate the therapeutic efficacy of revascularization in asymptomatic postinfarction patients with single vessel disease should limit enrollment to those patients with residual ischemia located within the infarct zone.

Purification and characterization of phospholamban from canine cardiac sarcoplasmic reticulum.

Phospholamban, the putative protein regulator of the Ca2+ pump of cardiac sarcoplasmic reticulum, was purified to apparent homogeneity from canine cardiac sarcoplasmic reticulum vesicles by selective extraction with sodium cholate, followed by adsorption to calcium oxalate, solubilization in Zwittergent 3-14, and specific elution from p-hydroxymercuribenzoate-agarose. Phospholamban, isolated in the dephosphorylated state, was purified 80-fold in 15% yield (approximately 2 mg of phospholamban/g of sarcoplasmic reticulum protein). Nondissociated phospholamban exhibited an apparent Mr = 25,000 in sodium dodecyl sulfate-polyacrylamide gels. Partially dissociated phospholamban, induced by boiling in sodium dodecyl sulfate, exhibited five distinct mobility forms in sodium dodecyl sulfate-polyacrylamide gels, of apparent molecular weights between 5,000-6,000 and 25,000. Phospholamban was phosphorylated to a level of 190 nmol of Pi/mg of protein by cAMP-dependent protein kinase, consistent by minimum stoichiometry with a subunit molecular weight of approximately 5,000. Phospholamban prepared by the present method was different in several respects from the proteins that have been isolated in other laboratories. Pure phospholamban was cysteine rich, containing 6 residues/100 amino acid residues. Dephosphorylated phospholamban was strongly basic with a pI = 10; phosphorylation decreased the pI to approximately 6.7. Pure phospholamban (and phospholamban present in sarcoplasmic reticulum vesicles) was not readily extracted into acidified chloroform/methanol, suggesting that the protein does not behave as an acidic proteolipid. The purified protein was highly antigenic. Phospholamban was localized by immunochemical methods to cardiac membranes enriched in sarcoplasmic reticulum, but was absent from sarcoplasmic reticulum membranes prepared from fast skeletal muscle. The method described for isolation of cardiac phospholamban is highly reproducible and relatively simple, and should be useful for further detailed studies designed to probe the molecular structure of the protein.

Revision operations after primary gastric surgery.

A single surgeon working in a district general hospital gives his experience over 31 years of 179 reoperations after a primary gastric operation has failed to relieve symptoms of duodenal ulcer.

Potential identification of chemical carcinogens in a viral transformation system.

Chemical carcinogens from several diverse chemical classes i.e.; aromatic amines, polycyclic hydrocarbons, nitrosamines, hormonal derivatives, metals and direct alkylating agents cause a 6.2-60.5-fold increase in the frequency of murine sarcoma virus (MSV)-induced transformation in a normal rat kidney (NRK) cell system. Exogenous metabolic activation with a rat liver S-9 homogenate is required for expression of this activity by procarcinogens. Non-carcinogenic analogs of these compounds fail to cause significant increases in the transformation frequency either with or without prior metabolic activation. Iododeoxyuridine, a mutagen also does not cause enhancement of transformation. This system may serve as the basis for a rapid and quantifiable means of identifying chemical carcinogens while introducing a new model for the understanding of the interactions between oncornaviruses and chemical carcinogens.

Radical versus modified radical mastectomy for breast cancer.

A prospective randomised trial (534 patients, 1969-75) was designed to determine whether radical mastectomy conferred advantages over modified radical mastectomy for breast cancer in terms of total survival, local recurrence, distant metastasis, and disease-free interval. The results showed no significant difference in outcome as regards these variables between the two treatments.

Porcine superoxide dismutase. Isolation and characterization of a relatively basic cuprozinc enzyme.

A cuprozinc superoxide dismutase has been isolated from pig liver. The enzyme is similar to previously described cuprozinc superoxide dismutases in that it is a dimer of about 32 000 molecular weight consisting of approximately two equally sized subunits, and 2 atoms of copper and two atoms of zinc per molecule. It differs, however, from previously described cuprozinc superoxide dismutases because of its higher isoelectric point; pI 6.8 vs 4.9 for bovine enzyme. The diffusion coefficient for the porcine enzyme was determined to be 7.53 x 10(-7) cm2 s-1, while the equivalent spherical hydrodynamic radius was computed as 28.5 A. The enzyme was observed to undergo self-association with time. Sulfhydryl interaction is postulated to be involved.