Heat Activation and Inactivation of Bacterial Spores: Is There an Overlap?

Heat activation at a sublethal temperature is widely applied to promote Bacillus species spore germination. This treatment also has the potential to be employed in food processing to eliminate undesired bacterial spores by enhancing their germination and then inactivating the less-heat-resistant germinated spores at a milder temperature. However, incorrect heat treatment could also generate heat damage in spores and lead to more heterogeneous spore germination. Here, the heat activation and heat damage profile of Bacillus subtilis spores was determined by testing spore germination and outgrowth at both population and single-spore levels. The heat treatments used were 40 to 80°C and for 0 to 300 min. The results were as follows. (i) Heat activation at 40 to 70°C promoted l-valine- and l-asparagine-glucose-fructose-potassium (AGFK)-induced germination in a time-dependent manner. (ii) The optimal heat activation temperatures for AGFK and l-valine germination via the GerB plus GerK or GerA germinant receptors were 65°C and 50 to 65°C, respectively. (iii) Heat inactivation of dormant spores appeared at 70°C, and the heat damage of molecules essential for germination and growth began at 70 and 65°C, respectively. (iv) Heat treatment at 75°C resulted in both activation of germination and damage to the germination apparatus, and 80°C treatment caused more pronounced heat damage. (v) For the spores that should withstand adverse environmental temperatures in nature, heat activation seemed functional for a subsequent optimal germination process, while heat damage affected both germination and outgrowth. IMPORTANCE Bacterial spores are thermal-stress-resistant structures that can thus survive food preservation strategies and revive through the process of spore germination. The more heat resistant spores are, the more heterogeneous their germination upon the addition of germinants. Upon germination, spores can cause food spoilage and food intoxication. Here, we provide new information on both heat activation and inactivation regimes and their effects on the (heterogeneity of) spore germination.

Estimating the mechanical cost of transport in human walking with a simple kinematic data-driven mechanical model.

This work utilizes a simplified, streamlined approach to study the mechanical cost of transport in human walking. Utilizing the kinematic motion data of the center of mass, velocities and accelerations are determined using kinematic analysis; the applied force is then obtained using inverse dynamics. We calculate the mechanical cost of transport per step from both synthetic and measured data, using a very simple mechanical model of walking. The approach studied can serve as an informative gait characteristic to monitor rehabilitation in human walking.

Altrenogest treatment associated with a farrowing induction protocol to avoid early parturition in sows.

This study investigated the effect of altrenogest treatment on the farrowing development of sows, and birth weight (BW) and piglet survival until the third day of life. Three control groups were used: (i) sows that farrowed spontaneously before 114 day of gestation (CONT <114); (ii) sows that spontaneously farrowed at ≥114 day of gestation (CONT ≥114); (iii) sows that farrowed at ≥114 day with cloprostenol treatment (CONTCLOPR). Other sows were treated with altrenogest (Regumate(®) ) for 3 days (days 111, 112 and 113 of gestation): one group gave birth spontaneously (ALT) and the other group received altrenogest until day 113 and cloprostenol on day 114 (ALTCLOPR). There were no differences (p > 0.05) in farrowing duration, BW, coefficient of variation (CV) of BW, stillborn piglets, mummified foetuses, percentage of light piglets and survival until Day 3 between sows with and without cloprostenol treatment, in both control (CONT ≥114 vs CONTCLOPR) and altrenogest-treated sows (ALT vs ALTCLOPR). Further comparisons were performed taking into account three groups: sows with early delivery (CONT <114 - farrowing before 114 days of gestation; n = 56), sows with longer gestation (CONT ≥114 - with and without cloprostenol treatment sows; n = 103) and ALT sows (with and without cloprostenol treatment; n = 105). Gestation length of CONT ≥114 and ALT sows was similar (p > 0.05), but higher than in CONT <114 sows. There were no differences (p > 0.05) between groups in farrowing duration, CV of BW, and percentages of stillborn piglets and mummified foetuses. Sows of CONT <114 group had a larger litter size and a lower BW than sows of the other two groups (p < 0.05). Sows of CONT <114 group had a higher percentage of lighter piglets and a lower piglet survival rate (p < 0.05) than ALT sows. In conclusion, altrenogest treatment proved to be an efficient method to avoid early parturition in 3-5 parity sows resulting in heavier piglets at birth.

Malaria Detection Accelerated: Combing a High-Throughput NanoZoomer Platform with a ParasiteMacro Algorithm.

Eradication of malaria, a mosquito-borne parasitic disease that hijacks human red blood cells, is a global priority. Microscopy remains the gold standard hallmark for diagnosis and estimation of parasitemia for malaria, to date. However, this approach is time-consuming and requires much expertise especially in malaria-endemic countries or in areas with low-density malaria infection. Thus, there is a need for accurate malaria diagnosis/parasitemia estimation with standardized, fast, and more reliable methods. To this end, we performed a proof-of-concept study using the automated imaging (NanoZoomer) platform to detect the malarial parasite in infected blood. The approach can be used as a steppingstone for malaria diagnosis and parasitemia estimation. Additionally, we created an algorithm (ParasiteMacro) compatible with free online imaging software (ImageJ) that can be used with low magnification objectives (e.g., 5×, 10×, and 20×) both in the NanoZoomer and routine microscope. The novel approach to estimate malarial parasitemia based on modern technologies compared to manual light microscopy demonstrated 100% sensitivity, 87% specificity, a 100% negative predictive value (NPV) and a 93% positive predictive value (PPV). The manual and automated malaria counts showed a good Pearson correlation for low- (R2 = 0.9377, r = 0.9683 and p < 0.0001) as well as high- parasitemia (R2 = 0.8170, r = 0.9044 and p < 0.0001) with low estimation errors. Our robust strategy that identifies and quantifies malaria can play a pivotal role in disease control strategies.

Organization and dynamics of the SpoVAEa protein and its surrounding inner membrane lipids, upon germination of Bacillus subtilis spores.

The SpoVA proteins make up a channel in the inner membrane (IM) of Bacillus subtilis spores. This channel responds to signals from activated germinant receptors (GRs), and allows release of Ca2+-DPA from the spore core during germination. In the current work, we studied the location and dynamics of SpoVAEa in dormant spores. Notably, the SpoVAEa-SGFP2 proteins were present in a single spot in spores, similar to the IM complex formed by all GRs termed the germinosome. However, while the GRs' spot remains in one location, the SpoVAEa-SGFP2 spot in the IM moved randomly with high frequency. It seems possible that this movement may be a means of communicating germination signals from the germinosome to the IM SpoVA channel, thus stimulating CaDPA release in germination. The dynamics of the SpoVAEa-SGFP2 and its surrounding IM region as stained by fluorescent dyes were also tracked during spore germination, as the dormant spore IM appeared to have an immobile germination related functional microdomain. This microdomain disappeared around the time of appearance of a germinated spore, and the loss of fluorescence of the IM with fluorescent dyes, as well as the appearance of peak SpoVAEa-SGFP2 fluorescent intensity occurred in parallel. These observed events were highly related to spores' rapid phase darkening, which is considered as due to rapid Ca2+DPA release. We also tested the response of SpoVAEa and the IM to thermal treatments at 40-80 °C. Heat treatment triggered an increase of green autofluorescence, which is speculated to be due to coat protein denaturation, and 80 °C treatments induce the appearance of phase-grey-like spores. These spores presumably have a similar intracellular physical state as the phase grey spores detected in the germination but lack the functional proteins for further germination events.

Guidelines for the diagnosis of antibody-mediated rejection in pancreas allografts-updated Banff grading schema.

The first Banff proposal for the diagnosis of pancreas rejection (Am J Transplant 2008; 8: 237) dealt primarily with the diagnosis of acute T-cell-mediated rejection (ACMR), while only tentatively addressing issues pertaining to antibody-mediated rejection (AMR). This document presents comprehensive guidelines for the diagnosis of AMR, first proposed at the 10th Banff Conference on Allograft Pathology and refined by a broad-based multidisciplinary panel. Pancreatic AMR is best identified by a combination of serological and immunohistopathological findings consisting of (i) identification of circulating donor-specific antibodies, and histopathological data including (ii) morphological evidence of microvascular tissue injury and (iii) C4d staining in interacinar capillaries. Acute AMR is diagnosed conclusively if these three elements are present, whereas a diagnosis of suspicious for AMR is rendered if only two elements are identified. The identification of only one diagnostic element is not sufficient for the diagnosis of AMR but should prompt heightened clinical vigilance. AMR and ACMR may coexist, and should be recognized and graded independently. This proposal is based on our current knowledge of the pathogenesis of pancreas rejection and currently available tools for diagnosis. A systematized clinicopathological approach to AMR is essential for the development and assessment of much needed therapeutic interventions.

Virulence characteristics and antimicrobial susceptibility of uropathogenic Escherichia coli strains.

Eight virulence factors associated with uropathogenic Escherichia coli (UPEC) were investigated in 204 clinical isolates of E. coli recovered from urine cultures at counts ≥10(5). The bacteria were classified into two groups according to the number of leukocytes in urine samples from which they were isolated: group I ≤8 leukocytes/hpf, 104 strains; group II >8 leukocytes/hpf, 100 strains. Two multiplex PCR systems were used to detect genes encoding adhesin P (pap), adhesin S (sfa), afimbrial adhesin I (afa), siderophore aerobactin (aer), alpha-hemolysin (hly), cytotoxic necrotizing factor type 1 (cnf1), and traT associated with serum resistance. The PAI marker for the virulence island identified in strains CFT072 and CVD432, a marker of enteroaggregative E. coli, was also investigated using PCR. The susceptibility profile of E. coli strains was determined by disk diffusion method. Ninety percent UPEC showed at least one of the virulence genes, the prevalence being traT (76%), aer (41%), PAI (32%), sfa (26%), pap (25%), cnf1 (18%), afa (6%), and hly (5%). There was no significant difference in the distribution of virulence genes between groups I and II. A significantly higher degree of virulence was detected in UPEC group II. The CVD432 gene was not detected in any of the UPECs. Fifty-nine percent of the strains were resistant to at least one of the antimicrobials that we tested; the most common being resistance to ampicillin (51%) and trimethoprim-sulfamethoxazole (44%).

Quantitative Insights Into ß-Lactamase Inhibitor's Contribution in the Treatment of Carbapenemase-Producing Organisms With ß-Lactams.

Objectives: Carbapenemase-producing organisms (CPOs) are associated with high mortality rates. The recent development of ß-lactamase inhibitors (BLIs) has made it possible to control CPO infections safely and effectively with ß-lactams (BLs). This study aims to explicate the quantitative relationship between BLI's ß-lactamase inhibition and CPO's BL susceptibility restoration, thereby providing the infectious disease society practical scientific grounds for regulating the use of BL/BLI in CPO infection treatment. Methods: A diverse collection of human CPO infection isolates was challenged by three structurally representative BLIs available in the clinic. The resultant ß-lactamase inhibition, BL susceptibility restoration, and their correlation were followed quantitatively for each isolate by coupling FIBA (fluorescence identification of ß-lactamase activity) and BL antibiotic susceptibility testing. Results: The ß-lactamase inhibition and BL susceptibility restoration are positively correlated among CPOs under the treatment of BLIs. Both of them are dependent on the target CPO's carbapenemase molecular identity. Of note, without sufficient ß-lactamase inhibition, CPO's BL susceptibility restoration is universally low across all tested carbapenemase molecular groups. However, a high degree of ß-lactamase inhibition would not necessarily lead to a substantial BL susceptibility restoration in CPO probably due to the existence of non-ß-lactamase BL resistance mechanisms. Conclusion: BL/BLI choice and dosing should be guided by quantitative tools that can evaluate the inhibition across the entire ß-lactamase background of the CPO upon the BLI administion. Furthermore, rapid molecular diagnostics for BL/BLI resistances, especially those sensitive to ß-lactamase independent BL resistance mechanisms, should be exploited to prevent ineffective BL/BLI treatment.

Modelling cyclists' comfort zones from obstacle avoidance manoeuvres.

This paper introduces a framework for modelling the cyclist's comfort zone. Unlike the driver's comfort zone, little is known about the cyclist's. The framework draws on existing literature in cognitive science about driver behaviour to explain experimental results from cycling field trials, and the modelling of these results. We modelled braking and steering manoeuvres from field data of cyclists' obstacle avoidance within their comfort zone. Results show that when cyclists avoided obstacles by braking, they kept a constant deceleration; as speed increased, they started to brake earlier, farther from the obstacle, maintaining an almost constant time to collision. When cyclists avoided obstacles by steering, they maintained a constant distance from the object, independent of speed. Overall, the higher the speed, the more the steering manoeuvres were temporally delayed compared to braking manoeuvres. We discuss these results and other similarities between cyclist and driver behaviour during obstacle avoidance. Implications for the design of acceptable active safety and infrastructure design are also addressed.

Reducing de novo donor-specific antibody levels during acute rejection diminishes renal allograft loss.

The effect of de novo DSA detected at the time of acute cellular rejection (ACR) and the response of DSA levels to rejection therapy on renal allograft survival were analyzed. Kidney transplant patients with acute rejection underwent DSA testing at rejection diagnosis with DSA levels quantified using Luminex single-antigen beads. Fifty-two patients experienced acute rejection with 16 (31%) testing positive for de novo DSA. Median follow-up was 27.0 +/- 17.4 months postacute rejection. Univariate analysis of factors influencing allograft survival demonstrated significance for African American race, DGF, cytotoxic PRA >20% (current) and/or >50% (peak), de novo DSA, C4d and repeat transplantation. Multivariate analysis showed only de novo DSA (6.6-fold increased allograft loss risk, p = 0.017) to be significant. Four-year allograft survival was higher with ACR (without DSA) (100%) than mixed acute rejection (ACR with DSA/C4d) (65%) or antibody-mediated rejection (35%) (p < 0.001). Patients with >50% reduction in DSA within 14 days experienced higher allograft survival (p = 0.039). De novo DSAs detected at rejection are associated with reduced allograft survival, but prompt DSA reduction was associated with improved allograft survival. DSA should be considered a potential new end point for rejection therapy.

Proteasome inhibition reduces donor-specific antibody levels.

BACKGROUND: Current antibody-mediated rejection (AMR) therapies (intravenous immunoglobulin, apheresis, rituximab, polyclonal antibodies) do not target the primary antibody producing B cells, that is, the plasma cell. We report the preliminary results from the first clinical experience with plasma cell targeted therapy with bortezomib. Bortezomib is approved by the US Food and Drug Administration for the treatment of plasma cell tumors (multiple myeloma). METHODS: Kidney transplant patients with mixed acute cellular rejection (ACR) and AMR episodes (by Banff '97 criteria, update 2005) were treated with bortezomib (1.3 mg/m(2) per dose x 4) at standard labeled doses. Patients were monitored by serial donor specific anti-HLA antibody (DSA) determinations [Luminex/Labscreen beads] and quantified by conversion to fluorescence intensity to molecules of equivalent soluble fluorescence (MESF). RESULTS: Five patients were treated with bortezomib. Each patient also had coexisting ACR. In each case, bortezomib treatment led to prompt ACR and AMR rejection reversal. DSA levels decreased significantly in all patients (except 1 patient who had short follow-up). Observed toxicities from bortezomib included a transient grade III thrombocytopenia (1 patient) and mild-to-moderate nausea, vomiting, and/or diarrhea (3/5 patients). Opportunistic infections were not observed. CONCLUSIONS: Bortezomib therapy provides effective reduction in DSA levels with long-term suppression. These preliminary results indicate that proteasome inhibition provides an effective means for reducing HLA antibody levels in transplant recipients.

Banff schema for grading pancreas allograft rejection: working proposal by a multi-disciplinary international consensus panel.

Accurate diagnosis and grading of rejection and other pathological processes are of paramount importance to guide therapeutic interventions in patients with pancreas allograft dysfunction. A multi-disciplinary panel of pathologists, surgeons and nephrologists was convened for the purpose of developing a consensus document delineating the histopathological features for diagnosis and grading of rejection in pancreas transplant biopsies. Based on the available published data and the collective experience, criteria for the diagnosis of acute cell-mediated allograft rejection (ACMR) were established. Three severity grades (I/mild, II/moderate and III/severe) were defined based on lesions known to be more or less responsive to treatment and associated with better- or worse-graft outcomes, respectively. The features of chronic rejection/graft sclerosis were reassessed, and three histological stages were established. Tentative criteria for the diagnosis of antibody-mediated rejection were also characterized, in anticipation of future studies that ought to provide more information on this process. Criteria for needle core biopsy adequacy and guidelines for pathology reporting were also defined. The availability of a simple, reproducible, clinically relevant and internationally accepted schema for grading rejection should improve the level of diagnostic accuracy and facilitate communication between all parties involved in the care of pancreas transplant recipients.

Ovulation and fertility responses for sows receiving once daily boar exposure after weaning and OvuGel® followed by a single fixed time post cervical artificial insemination.

Boar exposure is used to stimulate follicle development and estrus in sows after weaning and also to improve semen uptake and sperm transport with insemination. However, the need and value of boar exposure is uncertain when ovulation induction is used. These studies were designed to determine the effect of daily boar exposure after weaning when used with ovulation induction and fixed time post-cervical artificial insemination (PCAI). In experiment 1, sows were weaned into stalls and assigned to receive 3 min of daily fenceline boar exposure (BE, n = 7) or no boar exposure (NBE, n = 8). All sows received OvuGel at 96 h after weaning and BE or NBE 30 min prior to a single PCAI 24 h after OvuGel. Ovaries were assessed daily for follicle size from weaning until ovulation. Cervical contractions were measured 30 min following BE or NBE and before PCAI, while uterine contractions were measured for 1 h following PCAI. In experiment 2, weaned sows (n = 244) were assigned by parity to receive once daily BE for 1.5 min each day or NBE. OvuGel, PCAI and ultrasound methods were performed similarly as in experiment 1. Results from experiment 1 indicated BE did not significantly influence follicle size or measures of fertility. However, BE did increase the frequency of cervical contractions (P < 0.05), but with no effect on the uterus. Results from experiment 2 indicated BE had no effect on catheter passage for PCAI but did increase the proportion of sows ovulating within 48 h after OvuGel (77.7 vs 67.5%, P = 0.05), and tended (P = 0.10) to increase the proportion of sows inseminated 24 h before ovulation (70.3 vs. 61.0%). However, BE had no effect on adjusted farrowing rate (84.4 vs. 77.4%) or total pigs born (13.2 vs. 12.5) for BE and NBE, respectively. There were treatment and parity interactions for follicle size at time of OvuGel and at time of PCAI (P < 0.05) with BE minimizing parity effects on follicle size. Parity effects were also evident on farrowing rate and litter size when inseminations occurred >24 h from ovulation but not when inseminations occurred ≤24 h before ovulation. The results indicate that boar exposure for only minutes each day after weaning had beneficial effects for improving follicle development, ovulation induction, and AI timing, most notably in parity 1 sows, but had no beneficial or detrimental effects on the ability to perform PCAI.

A1 and A2 adenosine receptors in rabbit cortical collecting tubule cells. Modulation of hormone-stimulated cAMP.

Adenosine analogs were used to investigate the cellular mechanisms by which adenosine may alter renal tubular function. Cultured rabbit cortical collecting tubule (RCCT) cells, isolated by immunodissection, were treated with 5'-N-ethylcarboxamideadenosine (NECA), N6-cyclohexyladenosine (CHA), and R-N6-phenylisopropyladenosine (PIA). All three analogs produced both dose-dependent inhibition and stimulation of RCCT cell cyclic AMP (cAMP) production. Stimulation of cAMP accumulation occurred at analog concentrations of 0.1 microM to 100 microM with the rank order of potency NECA greater than PIA greater than CHA. Inhibition occurred at concentrations of 1 nM to 1 microM with the rank order of potency CHA greater than PIA greater than NECA. These effects on cAMP production were inhibited by 1,3-diethyl-8-phenylxanthine and isobutylmethylxanthine. CHA (50 nM) blunted AVP- and isoproterenol-stimulated cAMP accumulation. This modulation of hormone-induced cAMP production was abolished by pretreatment of RCCT cells with pertussis toxin. Prostaglandin E2 production was unaffected by 0.1 mM CHA. These findings indicate the presence of both inhibitory (A1) and stimulatory (A2) receptors for adenosine in RCCT cells. Moreover, occupancy of the A1 receptor causes inhibition of both basal and hormone-stimulated cAMP formation through an action on the inhibitory guanine nucleotide-binding regulatory component, Ni, of the adenylate cyclase system.

Molecular epidemiology of SPM-1-producing Pseudomonas aeruginosa by rep-PCR in hospitals in Parana, Brazil.

BACKGROUND: Infections caused by multidrug resistant microorganisms are a global health problem, and Pseudomonas aeruginosa is an important nosocomial pathogen, easily disseminated in the hospital environment. The aim of this study was to determine SPM-1 in P. aeruginosa strains in 30 Brazilian hospitals and the genetic similarity of isolates. METHODS: We analyzed 161 isolates of carbapenem-resistant P. aeruginosa. Imipenem/EDTA and imipenem strip were used for phenotypic detection of MBL production; and real-time polymerase chain reaction (PCR) for genetic detection. Genetic similarity was determined by rep-PCR. RESULTS: We obtained 136/161 (84.5%) isolates with positive phenotypic result for metallo-ß-lactamase (MBL) and the blaSPM-1 gene was identified in 41 isolates. There was a predominant profile (>95% of genetic similarity) in 92.7% of isolates. This predominant profile was widely disseminated in Paraná state. CONCLUSION: SPM-1 is the main MBL identified in carbapenem-resistant P. aeruginosa in Southern Brazil. The genetic similarity among some isolates suggests a clonal expansion.

Speed choice and mental workload of elderly cyclists on e-bikes in simple and complex traffic situations: a field experiment.

To study the speed choice and mental workload of elderly cyclists on electrical assisted bicycles (e-bikes) in simple and complex traffic situations compared to these on conventional bicycles, a field experiment was conducted using two instrumented bicycles. These bicycles were identical except for the electric pedal support system. Two groups were compared: elderly cyclists (65 years of age and older) and a reference group of cyclists in middle adulthood (between 30 and 45 years of age). Participants rode a fixed route with a length of approximately 3.5 km on both bicycles in counterbalanced order. The route consisted of secluded bicycle paths and roads in a residential area where cyclist have to share the road with motorized traffic. The straight sections on secluded bicycle paths were classified as simple traffic situations and the intersections in the residential area where participants had to turn left, as complex traffic situations. Speed and mental workload were measured. For the assessment of mental workload the peripheral detection task (PDT) was applied. In simple traffic situations the elderly cyclists rode an average 3.6 km/h faster on the e-bike than on the conventional bicycle. However, in complex traffic situations they rode an average only 1.7 km/h faster on the e-bike than on the conventional bicycle. Except for the fact that the cyclists in middle adulthood rode an average approximately 2.6 km/h faster on both bicycle types and in both traffic conditions, their speed patterns were very similar. The speed of the elderly cyclists on an e-bike was approximately the speed of the cyclists in middle adulthood on a conventional bicycle. For the elderly cyclist and the cyclists in middle adulthood, mental workload did not differ between bicycle type. For both groups, the mental workload was higher in complex traffic situations than in simple traffic situations. Mental workload of the elderly cyclists was somewhat higher than the mental workload of the cyclists in middle adulthood. The relatively high speed of the elderly cyclists on e-bikes in complex traffic situations and their relatively high mental workload in these situations may increase the accident risk of elderly cyclist when they ride on an e-bike.

Adenosine receptors and signaling in the kidney.

It is now generally accepted that adenosine is capable of regulating a wide range of physiological functions. Nowhere is the diversity of this action better illustrated than in the kidney. When adenosine binds to plasma membrane receptors on a variety of cell types in the kidney, it stimulates functional responses that span the entire spectrum of renal physiology, including alterations in hemodynamics, hormone and neurotransmitter release, and tubular reabsorption. These responses to adenosine appear to represent a means by which the organ and its constituent cell types can regulate their metabolic demand such that it is maintained at an appropriate level for the prevailing metabolic supply. Extracellular adenosine, produced from the hydrolysis of adenosine 5'-monophosphate and stimulated by increased substrate availability and enzyme induction, acts on at least two types of cell surface receptors to stimulate or inhibit the production of cyclic adenosine-3',5'-monophosphate and also acts in some renal cells to stimulate the production of inositol phosphates and elevation of cytosolic calcium concentration. To understand when and why this complicated system becomes activated, how it interacts with other known extracellular effector systems, and ultimately how to manipulate the system to therapeutic advantage by selective agonists or antagonists, requires a detailed knowledge of renal adenosine receptors and their signaling mechanisms. The following discussion attempts to highlight our knowledge in this area, to present a modified hypothesis for adenosine as a feedback regulator of renal function, and to identify some important questions regarding the specific cellular mechanisms of adenosine in renal cell types.

Reading with a macular scotoma. I. Retinal location of scotoma and fixation area.

To investigate how patients with macular scotomas use residual functional retinal areas to inspect visual detail, a scanning laser ophthalmoscope (SLO) was used to map the retinal locations of scotomas and areas used to fixate. Three patients with dense macular scotomas of at least 20 months duration and with no explicit low vision training were tested. SLO stimuli were produced by computer modulation of the scanned laser beam, and could be placed on known retinal loci by direct observation of the retina on a television monitor. Videotaped SLO images were analyzed to produce retinal maps that are corrected for shifts of stimulus position due to fixational eye movement, thus showing the true retinal locations of scotomas and fixation loci. Major findings were as follows: 1) each patient used a single, idiosyncratic retinal area, immediately adjacent to the scotoma to fixate, and did not attempt to use the nonfunctional foveola, 2) fixation stability with the eccentric fixation locus was as good as, or better than, that of ocularly normal subjects trying to fixate at comparable eccentricities, 3) fixation stability was not systematically related to clinical visual acuity, and 4) there is good agreement as to the shape and overall size of SLO and standard clinical tangent screen scotoma maps for these three patients.

Tubuloglomerular feedback: new concepts and developments.

Luminal [NaCl] at the macula densa (MD) has two established effects: regulation of glomerular arteriolar resistance through tubuloglomerular feedback (TGF) and control of renin secretion. TGF acts as a minute-to-minute stabilizer of distal salt delivery, thereby minimizing the impact of random perturbations in filtration and absorption forces on NaCl excretion. During long-lasting perturbations of MD [NaCl], control of renin secretion becomes the dominant function of the MD. The potentially maladaptive effect of TGF under chronic conditions is prevented by TGF adaptations permitting adjustments in glomerular filtration rate to occur. TGF adaptation is mechanistically coupled to the endpoint targeted by chronic deviations in MD [NaCl], the rate of local and systemic angiotensin II generation. Studies of TGF in transgenic mice are expected to provide further insights into the mechanisms mediating between luminal [NaCl] and afferent arterioles. TGF responses are virtually abolished in mice in which either the AT1A gene or the angiotensin converting enzyme gene is rendered nonfunctional by homologous recombination. In contrast, TGF responses are unaltered in nitric oxide synthase I knockout mice. Thus, an intact renin-angiotensin system appears to be critical for the TGF signaling pathway.

The critical role of relative luminance relations in White's effect and grating induction.

It has been proposed that both White's effect and the grating induction effect are examples of brightness induction phenomena modeled in terms of local spatial filters. We have shown that for these illusions to occur it is necessary that the luminance of the gray target elements falls between that of the inducing stripes of the square-wave pattern. This critical role of luminance relationships is not predicted by existing models of these illusions.