John M. Sullivan

The role of ambient light level in fatal crashes: inferences from daylight saving time transitions

The purpose of this study was to estimate the size of the influence of ambient light level on fatal pedestrian and vehicle crashes in three scenarios. The scenarios were: fatal pedestrian crashes at intersections, fatal pedestrian crashes on dark rural roads, and fatal single-vehicle run-off-road crashes on dark, curved roads. Each scenarios sensitivity to light level was evaluated by comparing the number of fatal crashes across changes to and from daylight saving time, within daily time periods in which an abrupt change in light level occurs relative to official clock time. The analyses included 11 years of fatal crashes in the United States, between 1987 and 1997. Scenarios involving pedestrians were most sensitive to light level, in some cases showing up to seven times more risk at night over daytime. In contrast, single-vehicle run-off-road crashes showed little difference between light and dark time periods, suggesting factors other than light level play the dominant role in these crashes. These results are discussed in the context of the possible safety improvements offered by new developments in adaptive vehicle headlighting.

Fractal analysis of a voltage-dependent potassium channel from cultured mouse hippocampal neurons.

The kinetics of ion channels have been widely modeled as a Markov process. In these models it is assumed that the channel protein has a small number of discrete conformational states and the kinetic rate constants connecting these states are constant. In the alternative fractal model the spontaneous fluctuations of the channel protein at many different time scales are represented by a kinetic rate constant k = At1-D, where A is the kinetic setpoint and D the fractal dimension. Single-channel currents were recorded at 146 mM external K+ from an inwardly rectifying, 120 pS, K+ selective, voltage-sensitive channel in cultured mouse hippocampal neurons. The kinetics of these channels were found to be statistically self-similar at different time scales as predicted by the fractal model. The fractal dimensions were approximately 2 for the closed times and approximately 1 for the open times and did not depend on voltage. For both the open and closed times the logarithm of the kinetic setpoint was found to be proportional to the applied voltage, which indicates that the gating of this channel involves the net inward movement of approximately one negative charge when this channel opens. Thus, the open and closed times and the voltage dependence of the gating of this channel are well described by the fractal model.

HIGH-BEAM HEADLAMP USAGE ON UNLIGHTED RURAL ROADWAYS

In a survey conducted over 34 years ago, researchers found that drivers in the United States underuse their high beams in circumstances in which their use is prudent and advisable. High-beam use was also found to be inversely related to traffic density. Since that time, changes in beam pattern design, dimming controls, and perhaps driver awareness of the hazards of limited visibility may have sufficiently altered the driver behaviour to warrant a follow-up investigation. A survey of high-beam headlamp use was conducted on three unlit local roadways in the Ann Arbor area. Observers judged whether vehicles that were clear of both oncoming and preceding traffic, had their high or low beams turned on. Illuminance measures at approximate beam pattern locations were also recorded to support beam judgments. In addition, traffic density was estimated over 15-min intervals so that the relationship between beam use and traffic density could be examined. The results suggest that the pattern of high-beam underuse is similar to that observed in the late 1960s.

Trends and characteristics of animal-vehicle collisions in the United States

INTRODUCTION Since 1990, fatal animal-vehicle collisions (AVCs) in the United States have more than doubled. This paper examines annual AVC trends in the United States over a 19-year period, seasonal and diurnal patterns of AVC risk, the geographic distribution of crash risk by state, and the association between posted speed limit and AVC crash risk in darkness. METHOD AVCs were compiled from the Fatality Analysis Reporting System (FARS) and the General Estimates System (GES) for the years 1990-2008 to examine annual crash trends for fatal and nonfatal crashes. Seasonal trends for fatal AVCs were examined with the aggregated FARS dataset; seasonal trends for fatal and nonfatal AVCs were also examined by aggregating four years of Michigan crash data. State-by-state distributions of fatal AVCs were also described with the aggregated FARS dataset. Finally, the relationship between posted speed limit and the odds that a fatal or nonfatal AVC occurred in darkness were examined with logistic regressions using the aggregated FARS and Michigan datasets. RESULTS Between 1990 and 2008, fatal AVCs increased by 104% and by 1.3 crashes per trillion vehicle miles travelled per year. Although not all AVCs involve deer, daily and seasonal AVC crash trends follow the general activity pattern of deer populations, consistent with prior reports. The odds that a fatal AVC occurred in darkness were also found to increase by 2.3% for each mile-per-hour increase in speed; a similar, albeit smaller, effect was also observed in the aggregated Michigan dataset, among nonfatal crashes. CONCLUSION AVCs represent a small but increasing share of crashes in the United States. Seasonal and daily variation in the pattern of AVCs seem to follow variation in deer exposure and ambient light level. Finally, the relative risk that a fatal and nonfatal AVC occurred in darkness is influenced by posted speed limit, suggesting that a drivers limited forward vision at night plays a role in AVCs, as it does in pedestrian collisions. IMPACT ON INDUSTRY The association between speed limit and crash risk in darkness suggests that AVC risk might be reduced with countermeasures that improve a drivers forward view of the road.

HEK293S cells have functional retinoid processing machinery.

Rhodopsin activation is measured by the early receptor current (ERC), a conformation-associated charge motion, in human embryonic kidney cells (HEK293S) expressing opsins. After rhodopsin bleaching in cells loaded with 11-cis-retinal, ERC signals recover in minutes and recurrently over a period of hours by simple dark adaptation, with no added chromophore. The purpose of this study is to investigate the source of ERC signal recovery in these cells. Giant HEK293S cells expressing normal wild-type (WT)-human rod opsin (HEK293S) were regenerated by solubilized 11-cis-retinal, all-trans-retinal, or Vitamin A in darkness. ERCs were elicited by flash photolysis and measured by whole-cell recording. Visible flashes initially elicit bimodal (R1, R2) ERC signals in WT-HEK293S cells loaded with 11-cis-retinal for 40 min or overnight. In contrast, cells regenerated for 40 min with all-trans-retinal or Vitamin A had negative ERCs (R1-like) or none at all. After these were placed in the dark overnight, ERCs with outward R2 signals were recorded the following day. This indicates conversion of loaded Vitamin A or all-trans-retinal into cis-retinaldehyde that regenerated ground-state pigment. 4-butylaniline, an inhibitor of the mammalian retinoid cycle, reversibly suppressed recovery of the outward R2 component from Vitamin A and 11-cis-retinal–loaded cells. These physiological findings are evidence for the presence of intrinsic retinoid processing machinery in WT-HEK293S cells similar to what occurs in the mammalian eye.

Time-Resolved Rhodopsin Activation Currents in a Unicellular Expression System

The early receptor current (ERC) is the charge redistribution occurring in plasma membrane rhodopsin during light activation of photoreceptors. Both the molecular mechanism of the ERC and its relationship to rhodopsin conformational activation are unknown. To investigate whether the ERC could be a time-resolved assay of rhodopsin structure-function relationships, the distinct sensitivity of modern electrophysiological tools was employed to test for flash-activated ERC signals in cells stably expressing normal human rod opsin after regeneration with 11-cis-retinal. ERCs are similar in waveform and kinetics to those found in photoreceptors. The action spectrum of the major R(2) charge motion is consistent with a rhodopsin photopigment. The R(1) phase is not kinetically resolvable and the R(2) phase, which overlaps metarhodopsin-II formation, has a rapid risetime and complex multiexponential decay. These experiments demonstrate, for the first time, kinetically resolved electrical state transitions during activation of expressed visual pigment in a unicellular environment (single or fused giant cells) containing only 6 x 10(6)-8 x 10(7) molecules of rhodopsin. This method improves measurement sensitivity 7 to 8 orders of magnitude compared to other time-resolved techniques applied to rhodopsin to study the role particular amino acids play in conformational activation and the forces that govern those transitions.

WARNING RELIABILITY AND DRIVER PERFORMANCE IN NATURALISTIC DRIVING

Objective: This study examines how naturalistic driving performance is influenced by the perceived reliability of an in-vehicle warning system using a unique measure of perceived reliability. Background: Prior studies of warning reliability conducted in simulator and test-track experiments demonstrate that the objective reliability of a warning can influence a drivers responsiveness to that warning. Methods: Driver responses to lateral drift warnings (LDWs) were examined to determine if the latency to initiate a corrective steering response was related to the subjective reliability of prior system performance. An operational definition of subjective reliability was developed based on measures of the proportion of LDWs responded to by a steering correction in the preceding 24-hr period — the day proportion. Age, gender, weather condition, light level, road class, weekday status, and day proportion were used to model correction latency in a linear model. Results: A main effect of day proportion was found, suggesting that reaction time to respond decreases by about 375 ms as the day proportion increases from 0 to 1. Conclusion: The study illustrates a method of quantifying subjective reliability and performance using naturalistic data. The results suggest that latency to make a steering correction is inversely related to the perceived reliability of the warning system in the 24 hr preceding the warning. Application: The results have direct application to the method of assessing the efficacy of in-vehicle collision warning systems, suggesting that use of a perceived reliability measure may better predict a drivers disposition to respond to a warning.

Differences in geometry of pedestrian crashes in daylight and darkness.

INTRODUCTION Previous studies have shown that increased risk in darkness is particularly great for pedestrian crashes, suggesting that attempts to improve headlighting should focus on factors that likely influence those crashes. The current analysis was designed to provide information about how details of pedestrian crashes may differ between daylight and darkness. METHOD All pedestrian crashes that occurred in daylight or dark conditions in Michigan during 2004 were analyzed in terms of the variables included in the State of Michigan crash database. Additional analysis of the narratives and diagrams in police accident reports was performed for a subset of 400 of those crashes-200 sampled from daylight and 200 sampled from darkness. RESULTS Several differences were found that appear to be related to the characteristic asymmetry of low-beam headlamps, which (in the United States) distributes more light on the passengers side than the drivers side of the vehicle. These results provide preliminary quantification of the how the photometric differences between the right and left sides of typical headlamps may affect pedestrian crash risk. IMPACT ON INDUSTRY The results suggest that efforts to provide supplemental forward vehicle lighting in turns may have safety benefits for pedestrians.

Development of Lead Hammerhead Ribozyme Candidates against Human Rod Opsin mRNA for Retinal Degeneration Therapy

To identify lead candidate allele-independent hammerhead ribozymes (hhRz) for the treatment of autosomal dominant mutations in the human rod opsin (RHO) gene, we tested a series of hhRzs for potential to significantly knockdown human RHO gene expression in a human cell expression system. Multiple computational criteria were used to select target mRNA regions likely to be single stranded and accessible to hhRz annealing and cleavage. Target regions are tested for accessibility in a human cell culture expression system where the hhRz RNA and target mRNA and protein are coexpressed. The hhRz RNA is embedded in an adenoviral VAI RNA chimeric RNA of established structure and properties which are critical to the experimental paradigm. The chimeric hhRz-VAI RNA is abundantly transcribed so that the hhRzs are expected to be in great excess over substrate mRNA. HhRz-VAI traffics predominantly to the cytoplasm to colocalize with the RHO mRNA target. Colocalization is essential for second-order annealing reactions. The VAI chimera protects the hhRz RNA from degradation and provides for a long half-life. With cell lines chosen for high transfection efficiency and a molar excess of hhRz plasmid over target plasmid, the conditions of this experimental paradigm are specifically designed to evaluate for regions of accessibility of the target mRNA in cellulo. Western analysis was used to measure the impact of hhRz expression on RHO protein expression. Three lead candidate hhRz designs were identified that significantly knockdown target protein expression relative to control (p<0.05). Successful lead candidates (hhRz CUC [see in text downward arrow] 266, hhRz CUC [see in text downward arrow] 1411, hhRz AUA [see in text downward arrow] 1414) targeted regions of human RHO mRNA that were predicted to be accessible by a bioinformatics approach, whereas regions predicted to be inaccessible supported no knockdown. The maximum opsin protein level knockdown is approximately 30% over a 48h paradigm of testing. These results validate a rigorous computational bioinformatics approach to detect accessible regions of target mRNAs in cellulo. The opsin knockdown effect could prove to be clinically significant when integrated over longer periods in photoreceptors. Further optimization and animal testing are the next step in this stratified RNA drug discovery program. A recently developed novel and efficient screening assay based upon expression of a dicistronic mRNA (RHO-IRES-SEAP) containing both RHO and reporter (SEAP) cDNAs was used to compare the hhRz 266 lead candidate to another agent (Rz525/hhRz485) already known to partially rescue retinal degeneration in a rodent model. Lead hhRz 266 CUC [see in text downward arrow] proved more efficacious than Rz525/hhRz485 which infers viability for rescue of retinal degeneration in appropriate preclinical models of disease.

Low-cost monochromatic microsecond flash microbeam apparatus for single-cell photolysis of rhodopsin or other photolabile pigments

Delivery of intense, brief flashes of monochromatic light are required in single-cell physiological experiments to photolyze cellular chromophores or pigments. In the xenon flash instrument constructed, flashes are collimated, made monochromatic with selectable bandpass filters and imaged into a small-core fiber. The flash is transmitted over meters to the epiflourescent port of a microscope where additional optics again collimate the beam. The objective lens of the microscope functions to condense flash energy into a microbeam in the specimen (field) plane and to image the cell under parafocal conditions. Spot diameters are 228 and 166 μm (full width half maximum) for 40× and 60× objectives. Flash intensities can be measured with this instrument during experiments using the microscope phase/differential interference contrast condenser to couple the microbeam to a calibrated photodiode. Flash intensities between 108 and 109 photons/μm2 were achieved across the near-ultraviolet/visible spectrum. Flash dura...