Turning the corner with the flash-lag illusion

Previous attempts to measure localization bias around a right-angle turn (L-trajectory) have found either no spatial bias off the trajectory (Whitney, Cavanagh, & Murakami, 2000) or a bias, in different experiments, both 'inside' and 'outside' the trajectory (Nieman, Sheth, & Shimojo, 2010). However, Eagleman and Sejnowski (2007) presented data showing that the perceived location of a brief feature on two moving stimuli could be predicted from the vector sum of their directions after the feature appeared. Such a vector sum with an L-trajectory could predict that the perceived position before the turn should be biased 'sideways' off the trajectory, in the direction of the final motion. With stimuli that particularly facilitated accurate vernier judgments, and measuring bias via the flash-lag illusion, this is indeed what we observed. Our data thus favour Eagleman and Sejnowski's (2007) supposition. Further, the bias occurred before the change in direction, rather than after it, supporting the contention that it is motion after a point being sampled that affects its perception (Bachmann et al., 2003; Eagleman & Sejnowski, 2007; Krekelberg & Lappe, 2000; Nieman, Sheth, & Shimojo, 2010).

Abstract 610: A Pepstatin-Sensitive Aspartyl Peptidase as an Early Urinary Marker of Renal Injury in the Diabetic Hypertensive mRen2.Lewis Female Rat

We previously reported that induction of diabetes in estrogen-depleted, hypertensive mRen2.Lewis (mRen2) female rats leads to significant albuminuria, proteinuria and tubulointerstial oxidative stress at 28 days. The current study assessed the time course for the development of proteinuria and peptidase activities in the urine of the diabetic hypertensive mRen2 to begin to establish potential biomarkers of renal injury in this model. Heterozygous mRen2 underwent ovariectomy and diabetes was induced by a single administration of streptozotocin (65 mg/kg; STZ) at 15 weeks of age. Urinary samples were taken prior to (day 0) and 5 and 28 days following STZ. Aspartyl peptidases were assayed with the quenched fluorescent substrate Mca-GWPILFFRLW(Dnp)R in the presence or absence of the inhibitor pepstatin. Enzyme activities were expressed as nmols Mca per 30 min per mg creatinine. Pepstatin-sensitive activity [IC50 ∼ 0.4 nM] was detectable in the pre-diabetic urines [26 ± 9; n=8]; however, the diabetic rats exhibited a significant increase in urinary activity at days 5 and 28 [184 ± 25 and 204 ± 53, respectively; p<0.05 vs. day 0]. In contrast, pepstatin-insensitive activity was markedly lower and decreased between days 0 and 5 [22 ± 2 vs. 12 ± 4; p<0.05], but was unchanged at day 28 [34 ± 12]. Proteinuria was similar at days 0 and day 5, but significantly increased by day 28. Aspartyl peptidases in the kidney and urine that are sensitive to pepstatin include cathepsins D and E, as well as the enzyme napsin. However, immunoblots of concentrated urine samples using selective cathepsin and napsin antibodies failed to match protein expression to the increased activities in the diabetic rats. Finally, we assessed peptidase activity in isolated cortical slices from diabetic mRen2 to determine the extent of enzyme release. Aspartyl peptidase activity was readily detectable in the perfusate of the isolated kidney [6 ± 0.3 pmols Mca per min release, n=3] and completely inhibited by pepstatin suggesting that the urinary activity is of renal origin. We conclude that a pepstatin-sensitive aspartyl peptidase, potentially distinct from cathepsin D/E and napsin may constitute an early marker of renal injury in the diabetic hypertensive mRen2 strain.

New twists for an old turning illusion

A Vernier-offset illusion induced by rotating lines, introduced by Matin et al (1976 Perception & psychophysics 20 138-142) was re-examined using onset, offset, and reverse trajectories inspired by flash-lag illusion research, with both Vernier and alignment-with-vertical judgments being recorded. The pattern of illusions found was generally in agreement with a differential latency of stimulus ends account described by those authors, although certain variants of modern spatial projection theories, and a differential latency of attribute account, could also accommodate much of the data.

Practical considerations for conducting ecotoxicity test methods with manufactured nanomaterials: what have we learnt so far?

This review paper reports the consensus of a technical workshop hosted by the European network, NanoImpactNet (NIN). The workshop aimed to review the collective experience of working at the bench with manufactured nanomaterials (MNMs), and to recommend modifications to existing experimental methods and OECD protocols. Current procedures for cleaning glassware are appropriate for most MNMs, although interference with electrodes may occur. Maintaining exposure is more difficult with MNMs compared to conventional chemicals. A metal salt control is recommended for experiments with metallic MNMs that may release free metal ions. Dispersing agents should be avoided, but if they must be used, then natural or synthetic dispersing agents are possible, and dispersion controls essential. Time constraints and technology gaps indicate that full characterisation of test media during ecotoxicity tests is currently not practical. Details of electron microscopy, dark-field microscopy, a range of spectroscopic methods (EDX, XRD, XANES, EXAFS), light scattering techniques (DLS, SLS) and chromatography are discussed. The development of user-friendly software to predict particle behaviour in test media according to DLVO theory is in progress, and simple optical methods are available to estimate the settling behaviour of suspensions during experiments. However, for soil matrices such simple approaches may not be applicable. Alternatively, a Critical Body Residue approach may be taken in which body concentrations in organisms are related to effects, and toxicity thresholds derived. For microbial assays, the cell wall is a formidable barrier to MNMs and end points that rely on the test substance penetrating the cell may be insensitive. Instead assays based on the cell envelope should be developed for MNMs. In algal growth tests, the abiotic factors that promote particle aggregation in the media (e.g. ionic strength) are also important in providing nutrients, and manipulation of the media to control the dispersion may also inhibit growth. Controls to quantify shading effects, and precise details of lighting regimes, shaking or mixing should be reported in algal tests. Photosynthesis may be more sensitive than traditional growth end points for algae and plants. Tests with invertebrates should consider non-chemical toxicity from particle adherence to the organisms. The use of semi-static exposure methods with fish can reduce the logistical issues of waste water disposal and facilitate aspects of animal husbandry relevant to MMNs. There are concerns that the existing bioaccumulation tests are conceptually flawed for MNMs and that new test(s) are required. In vitro testing strategies, as exemplified by genotoxicity assays, can be modified for MNMs, but the risk of false negatives in some assays is highlighted. In conclusion, most protocols will require some modifications and recommendations are made to aid the researcher at the bench.

Neuronal nitric oxide synthase inhibition improves diastolic function and reduces oxidative stress in ovariectomized mRen2.Lewis rats

OBJECTIVE

The loss of estrogen in mRen2.Lewis rats leads to an exacerbation of diastolic dysfunction. Because specific neuronal nitric oxide synthase (nNOS) inhibition reverses renal damage in the same model, we assessed the effects of inhibiting neuronal nitric oxide on diastolic function, left ventricular remodeling, and the components of the cardiac nitric oxide system in ovariectomized (OVX) and sham-operated mRen2.Lewis rats treated with N5-(1-imino-3-butenyl)-L-ornithine (L-VNIO; 0.5 mg/kg per day for 28 d) or vehicle (saline).

METHODS

Female mRen2.Lewis rats underwent either bilateral oophorectomy (OVX; n = 15) or sham operation (or surgical procedure) (sham; n = 19) at 4 weeks of age. Beginning at 11 weeks of age, the rats were randomized to receive either L-VNIO or vehicle.

RESULTS

The surgical loss of ovarian hormones, particularly estrogen, led to exacerbated hypertension, impaired myocardial relaxation, diminished diastolic compliance, increased perivascular fibrosis, and increased relative wall thickness. The cardiac tetrahydrobiopterin-to-dihydrobiopterin levels were lower among OVX rats compared with sham-operated rats, and this altered cardiac biopterin profile was associated with enhanced myocardial superoxide production and decreased nitric oxide release. L-VNIO decreased myocardial reactive oxygen species production, increased nitrite concentrations, attenuated cardiac remodeling, and improved diastolic function.

CONCLUSIONS

Impaired relaxation, diastolic stiffness, and cardiac remodeling were found among OVX mRen2.Lewis rats. A possible mechanism for this unfavorable cardiac phenotype may have resulted from a deficiency in available tetrahydrobiopterin and subsequent increase in nNOS-derived superoxide and reduction in nitric oxide synthase metabolites within the heart. Selective nNOS inhibition with L-VNIO attenuated cardiac superoxide production and limited remodeling, leading to improved diastolic function in OVX mRen2.Lewis rats.

Exploring a brightness-drag illusion

A sudden luminance increment on a moving stimulus was perceived significantly along the trajectory, in the direction of motion, from its displayed position. A nonlinear relationship with stimulus speed, for a Fröhlich-like illusion, but not for the luminance-increment illusion, challenges certain models of spatial mislocalisation and argues for different processes underlying the two illusions.

The Magnocellular visual pathway and the flash-lag illusion

Determining how the visual system locates moving stimuli continues to be an experimental and theoretical challenge. By making a moving visual stimulus equiluminant with its background, and immersing it in luminance noise, the spatial lead it normal enjoys over a flashed stimulus (the flash-lag illusion) was completely eliminated (the illusion was actually reversed for 6 out of 11 participants). As this manipulation is typically used to reduce Magnocellular (M) visual pathway processing, this is strong evidence that processing in this pathway advances the moving stimulus' perceived position. However, when the flashed stimulus was also made equiluminant in luminance noise, the illusion reappeared, indicating that M pathway processing contributed to its perception too. The presence of the illusion when both stimuli were equiluminant in luminance noise indicates that the illusion can be generated in the absence of M cell activation. To explicate the result with moving stimuli, we displayed two adjacent moving stimuli, one luminance-modulated, and the other equiluminant in noise. The latter was perceived to significantly lag the former (an 'M-P-Hess' illusion), and 39% of the difference in flash-lag illusions, with comparable moving stimulus contrasts, could be accounted for by this illusion.

Characterization of a Moraxella species that causes epistaxis in macaques

Bacteria of the genus Moraxella have been isolated from a variety of mammalian hosts. In a prior survey of bacteria that colonize the rhesus macaque nasopharynx, performed at the Tulane National Primate Research Center, organisms of the Moraxella genus were isolated from animals with epistaxis, or "bloody nose syndrome." They were biochemically identified as Moraxella catarrhalis, and cryopreserved. Another isolate was obtained from an epistatic cynomolgus macaque at the U.S. Army Medical Research Institute of Infectious Diseases. Based on differences in colony and cell morphologies between rhesus and human M. catarrhalis isolates, we hypothesized that the nonhuman primate Moraxella might instead be a different species. Despite morphological differences, the rhesus isolates, by several biochemical tests, were indistinguishable from M. catarrhalis. Analysis of the cynomolgus isolate by Vitek 2 Compact indicated that it belonged to a Moraxella group, but could not differentiate among species. However, sequencing of the 16S ribosomal RNA gene from four representative rhesus isolates and the cynomolgus isolate showed closest homology to Moraxella lincolnii, a human respiratory tract inhabitant, with 90.16% identity. To examine rhesus macaques as potential hosts for M. catarrhalis, eight animals were inoculated with human M. catarrhalis isolates. Only one of the animals was colonized and showed disease, whereas four of four macaques became epistatic after inoculation with the rhesus Moraxella isolate. The nasopharyngeal isolates in this study appear uniquely adapted to a macaque host and, though they share many of the phenotypic characteristics of M. catarrhalis, appear to form a genotypically distinct species.

Prenatal betamethasone exposure alters renal function in immature sheep: sex differences in effects

Synthetic glucocorticoids are commonly given to pregnant women when premature delivery threatens. Antenatal administration of clinically relevant doses of betamethasone to pregnant sheep causes sex-specific compromises of renal function and increases in blood pressure in adult offspring. However, it is unclear whether such effects are present in immature lambs. Therefore, the aims of the present study were to determine whether antenatal betamethasone at 80-81 days of gestation increases blood pressure and adversely impacts renal function in adolescent ewes and rams. Prenatal steroid exposure increased blood pressure significantly in the young male (84 +/- 2 vs. 74 +/- 3 mmHg) and female sheep (88 +/- 5 vs. 79 +/- 4), but it did not alter basal glomerular filtration rate, renal blood flow (RBF), or sodium excretion in either sex. However, antenatal betamethasone exposure blocked increases in RBF (P = 0.001), and enhanced excretion of an acute Na load (P < 0.05) in response to systemic infusions of angiotensin (ANG)-(1-7) at 10 pmol.kg(-1).min(-1) in males. In females, the natriuretic response to combined ANG-(1-7), and Na load was significantly altered by prenatal betamethasone exposure. These findings indicate that blood pressure is increased in immature animals in response to antenatal steroid exposure and that sex-specific effects on renal function also exist. These changes may reflect greater risk for further loss of renal function with age.