Chytrid infections exhibit historical spread and contemporary seasonality in a declining stream-breeding frog.

Species with extensive geographical ranges pose special challenges to assessing drivers of wildlife disease, necessitating collaborative and large-scale analyses. The imperilled foothill yellow-legged frog (Rana boylii) inhabits a wide geographical range and variable conditions in rivers of California and Oregon (USA), and is considered threatened by the pathogen Batrachochytrium dendrobatidis (Bd). To assess drivers of Bd infections over time and space, we compiled over 2000 datapoints from R. boylii museum specimens (collected 1897-2005) and field samples (2005-2021) spanning 9° of latitude. We observed a south-to-north spread of Bd detections beginning in the 1940s and increase in prevalence from the 1940s to 1970s, coinciding with extirpation from southern latitudes. We detected eight high-prevalence geographical clusters through time that span the species' geographical range. Field-sampled male R. boylii exhibited the highest prevalence, and juveniles sampled in autumn exhibited the highest loads. Bd infection risk was highest in lower elevation rain-dominated watersheds, and with cool temperatures and low stream-flow conditions at the end of the dry season. Through a holistic assessment of relationships between infection risk, geographical context and time, we identify the locations and time periods where Bd mitigation and monitoring will be critical for conservation of this imperilled species.

Understanding pharmaceutical exposure and the potential for effects in marine biota: A survey of bonefish (Albula vulpes) across the Caribbean Basin.

Most research on pharmaceutical presence in the environment to date has focused on smaller scale assessments of freshwater and riverine systems, relying mainly on assays of water samples, while studies in marine ecosystems and of exposed biota are sparse. This study investigated the pharmaceutical burden in bonefish (Albula vulpes), an important recreational and artisanal fishery, to quantify pharmaceutical exposure throughout the Caribbean Basin. We sampled 74 bonefish from five regions, and analyzed them for 102 pharmaceuticals. We assessed the influence of sampling region on the number of pharmaceuticals, pharmaceutical assemblage, and risk of pharmacological effects. To evaluate the risk of pharmacological effects at the scale of the individual, we proposed a metric based on the human therapeutic plasma concentration (HTPC), comparing measured concentrations to a threshold of 1/3 the HTPC for each pharmaceutical. Every bonefish had at least one pharmaceutical, with an average of 4.9 and a maximum of 16 pharmaceuticals in one individual. At least one pharmaceutical was detected in exceedance of the 1/3 HTPC threshold in 39% of bonefish, with an average of 0.6 and a maximum of 11 pharmaceuticals exceeding in a Key West individual. The number of pharmaceuticals (49 detected in total) differed across regions, but the risk of pharmacological effects did not (23 pharmaceuticals exceeded the 1/3 HTPC threshold). The most common pharmaceuticals were venlafaxine (43 bonefish), atenolol (36), naloxone (27), codeine (27), and trimethoprim (24). Findings suggest that pharmaceutical detections and concentration may be independent, emphasizing the need to monitor risk to biota regardless of exposure diversity, and to focus on risk quantified at the individual level. This study supports the widespread presence of pharmaceuticals in marine systems and shows the utility of applying the HTPC to assess the potential for pharmacological effects, and thus quantify impact of exposure at large spatial scales.

Measuring executive function in sheep (Ovis aries) using visual stimuli in a semi-automated operant system.

BACKGROUND: Cognitive impairment is a distinguishing feature of many neurodegenerative diseases. The intra-dimensional (ID) extra-dimensional (ED) attentional set shift task is part of a clinical battery of tests used to evaluate executive function in Huntington's and Alzheimer's disease patients. The IDED task, however, has not translated well to pre-clinical rodent models of neurological disease. NEW METHOD: The ability to perform executive tasks coupled with a long lifespan makes sheep (Ovis aries) an ideal species for modelling cognitive decline in progressive neurodegenerative conditions. We describe the methodology for testing the performance of sheep in the IDED task using a semi-automated system in which visual stimuli are presented as coloured letters on computer screens. RESULTS: During each stage of IDED testing, all sheep (n = 12) learned successfully to discriminate between different colours and letters. Sheep were quick to learn the rules of acquisition at each stage. They required significantly more trials to reach criterion (p < 0.05) and made more errors (p < 0.05) following stimulus reversal, with the exception of the ED shift (p > 0.05). COMPARISON WITH EXISTING METHOD(S): Previous research shows that sheep can perform IDED set shifting in a walk-through maze using solid objects with two changeable dimensions (colour and shape) as the stimuli. Presenting the stimuli on computer screens provides better validity, greater task flexibility and higher throughput than the walk-through maze. CONCLUSION: All sheep completed each stage of the task, with a range of abilities expected in an outbred population. The IDED task described is ideally suited as a quantifiable and clinically translatable measure of executive function in sheep.

Color vision and neuroretinal function in diabetes.

PURPOSE: We investigate how type 2 diabetes (T2DM) and diabetic retinopathy (DR) affect color vision (CV) and mfERG implicit time (IT), whether CV and IT are correlated, and whether CV and IT abnormality classifications agree. METHODS: Adams desaturated D-15 color test, mfERG, and fundus photographs were examined in 37 controls, 22 T2DM patients without DR (NoRet group), and 25 T2DM patients with DR (Ret group). Color confusion score (CCS) was calculated. ITs were averaged within the central 7 hexagons (central IT; ≤4.5°) and outside this area (peripheral IT; ≥4.5°). DR was within (DRIN) or outside (DROUT) of the central 7 hexagons. Group differences, percentages of abnormalities, correlations, and agreement were determined. RESULTS: CCS was greater in the NoRet (P = 0.002) and Ret (P < 0.0001) groups than in control group. CCS was abnormal in 3, 41, and 48 % of eyes in the control, NoRet, and Ret groups, respectively. Ret group CV abnormalities were more frequent in DRIN than in DROUT subgroups (71 vs. 18 %, respectively; P < 0.0001). CCS and IT were correlated only in the Ret group, in both retinal zones (P ≤ 0.028). Only in the Ret group did CCS and peripheral IT abnormality classifications agree (72 %; P < 0.05). CONCLUSION: CV is affected in patients with T2DM, even without DR. Central DR increases the likelihood of a CV deficit compared with non-central DR. mfERG IT averaged across central or peripheral retinal locations is less frequently abnormal than CV in the absence of DR, and these two measures are correlated only when DR is present.

Design of a light stimulator for fetal and neonatal magnetoencephalography.

The design, safety analysis and performance of a fetal visual stimulation system suitable for fetal and neonatal magnetoencephalography studies are presented. The issue of fetal, neonatal and maternal safety is considered and the maximum permissible exposure is computed for the maternal skin and the adult eye. The risk for neonatal eye exposure is examined. It is demonstrated that the fetus, neonate and mother are not at risk.

Towards optimal filtering of "standard" multifocal electroretinogram (mfERG) recordings: findings in normal and diabetic subjects.

AIMS: To study the effects of two commonly used pre-amplifier filtering bandwidths on normal multifocal electroretinogram (mfERG) responses and their comparative abilities to detect retinal disease. METHODS: 103 standard mfERGs were recorded simultaneously in two channels with different pre-amplifier settings (10-100 Hz and 10-300 Hz) from one eye of each of 20 normal subjects, 17 diabetics with non-proliferative diabetic retinopathy (NPDR), and 12 diabetics without retinopathy. Signal to noise ratios (SNR) of the normal subjects' first order mfERGs were compared between channels. All subjects' amplitudes and implicit times were derived using a "template stretching" method. For comparison, implicit time was also measured using a "template sliding" method. mfERG amplitudes and implicit times were compared between the channels and among subject groups. RESULTS: Normal mean amplitudes and implicit times were similar for the two channels. However, normal 10-100 Hz recordings had significantly higher SNR and lower intersubject variability than 10-300 Hz recordings. In NPDR, the 10-100 Hz channel identified significantly more implicit time and amplitude abnormalities. In the diabetics without retinopathy, 10-100 Hz filtering identified significantly more implicit time abnormalities than 10-300 Hz filtering. For both filter settings, diabetic implicit times were more often abnormal than amplitudes. The 10-100 Hz channel was superior for both implicit time measurements. CONCLUSION: Standard mfERGs recorded from normal eyes and filtered 10-100 Hz contain less noise, higher SNR, and less intersubject variability than those filtered at 10-300 Hz. This underlies the finding that the 10-100 Hz filter setting identifies more retinal dysfunction than the 10-300 Hz setting.

The fast oscillation of the electrooculogram reveals sensitivity of the human outer retina/retinal pigment epithelium to glucose level.

The effect of acute blood glucose elevations on human outer retinal function was examined. Electrooculograms were recorded as the background light cycled on/off with a 2-min period, eliciting rapid changes in the corneo-retinal standing potential known as the fast-oscillation of the electrooculogram. Recordings were made while subjects fasted and after they consumed 100 g of D-glucose. In all subjects, blood glucose levels strongly affected fast oscillation amplitude, which reflects photoreceptor-driven changes in RPE cell chloride concentration. The sensitivity of RPE metabolism to glucose fluctuations may relate to changes in the blood-retinal barrier that are known to occur in diabetes (e.g. macular edema).

Multifocal electroretinogram delays reveal local retinal dysfunction in early diabetic retinopathy.

PURPOSE: To identify local retinal abnormalities in diabetic patients with and without retinopathy, by using the multifocal electroretinogram (M-ERG). METHODS: Electroretinograms were recorded at 103 discrete retinal locations in each eye of eight persons with nonproliferative diabetic retinopathy (NPDR) and eight diabetic persons without retinopathy, using VERIS (EDI, San Mateo, CA). The amplitude and implicit time of each local (first-order) retinal response were derived and compared with normal values obtained from 16 age-matched, nondiabetic subjects. Maps of local response amplitude and implicit time were compared with fundus photographs taken at the time of testing. RESULTS: In eyes with NPDR, the implicit times of responses from retinal sites manifesting clinical pathologic fundus lesions (e.g., microaneurysms and focal edema), were markedly delayed (e.g., up to 7 msec from normal). Responses from adjacent retinal sites that were more normal in clinical appearance were also delayed, but to a lesser extent (e.g., 2-5 msec). Smaller, yet significant local response delays were also found in eyes without retinopathy. By contrast, local response amplitudes bore no consistent relationship to fundus abnormalities in eyes with retinopathy, and amplitudes were typically normal in eyes without retinopathy. CONCLUSIONS: The M-ERG reveals local retinal dysfunction in diabetic eyes even before retinopathy. The magnitude of delay of local ERG implicit time reflects the degree of local clinical abnormality in eyes with retinopathy. Local response delays found in some eyes without retinopathy suggest that the M-ERG detects subclinical local retinal dysfunction in diabetes. Analysis of M-ERG implicit time, independent of amplitude, improves the sensitivity of detection of local retinal dysfunction in diabetes.

Positive selection as a developmental progression initiated by alpha beta TCR signals that fix TCR specificity prior to lineage commitment.

During positive selection, immature thymocytes commit to either the CD4+ or CD8+ T cell lineage ("commitment") and convert from short-lived thymocytes into long-lived T cells ("rescue"). By formal precursor-progeny analysis, we now identify what is likely to be the initial positive selection step signaled by alpha beta TCR, which we have termed "induction". During induction, RAG mRNA expression is downregulated, but lineage commitment does not occur. Rather, lineage commitment (which depends upon the MHC class specificity of the alpha beta TCR) only occurs after downregulation of RAG expression and the consequent fixation of alpha beta TCR specificity. We propose that positive selection can be viewed as a sequence of increasingly selective developmental steps (induction-->commitment-->rescue) that are signaled by alpha beta TCR engagements of intrathymic ligands.

Flow cytometric analysis of lymphocyte subsets in migraine patients during and outside of an acute headache attack.

We have conducted flow cytometric studies of two subsets of lymphocyte markers in groups of migraineurs during (n = 12; group B) and outside (n = 10; group C) of a migraine without aura attack (total n = 22; group A), including a group of patients tested in both of these phases (n = 5; group D), and compared these results with those obtained from a population of age-comparable, sex- and race-matched healthy volunteers (n = 12; group E). Comparison of the first set of lymphocytes (CD3+CD16 + 56+, CD3-CD16 + 56+, CD3-CD19+, CD3+CD19+, and CD3+HLA - DR+) between the patients in group A and the controls (group E) showed differences, reflecting greater group A percentages of CD3+CD16 + CD56+ and CD3-CD19+ lymphocytes. Furthermore, these differences reached statistical significance only for the CD3+CD16 + CD56+ lymphocytes, and then solely for the patients in group C (Scheffe's test, p < 0.05). Paired analysis of the above lymphocyte markers for subjects in group D failed to show significant differences between patients when they were having and not having a migraine attack, raising the possibility that results from a larger study could show meaningful increases in percentages of CD3+CD16 + CD56+ lymphocytes as one of the immune parameters useful for differentiating migraineurs from controls. Comparison of a second set of lymphocyte markers (CD19+CD5+, CD20+CD72-, CD20-CD72+, CD20+CD72+) among either the different groups of patients or between the patients and controls failed, however, to show statistically significant differences, emphasizing the apparent specificity of the findings described above for CD3+CD16 + CD56+ lymphocytes. Our results, albeit of a preliminary nature, suggest the occurrence of significant, differential changes in lymphocyte subset immunophenotyping between groups of pain-free migraineurs and patients during an acute migraine episode or controls. Corroboration of these findings may prove useful in clinical laboratory practice to identify changes in immunological parameters specifically associated with migraineurs, and help towards a better understanding of the etiology and pathophysiology of this condition.

Optical and structural development of the crystalline lens in childhood.

PURPOSE: To document the development of key optical and structural parameters of the crystalline lens throughout childhood and examine possible mechanisms by which lens power remains coordinated with the growth of the eye to maintain emmetropia. METHODS: Using cycloplegic autorefraction, video-based phakometry, and ultrasonography, the authors measured refractive error and crystalline lens parameters in 994 children in the first through eighth grades, who participated in the Orinda Longitudinal Study of Myopia, between one and five times from 1989 through 1993. Polynomial growth curves were fit to the data by maximum likelihood estimation. The average annual rates of change in each parameter from each subject's longitudinal data were also estimated. RESULTS: The lens radii of curvature flattened throughout childhood, yet decreases in lens equivalent power stopped after 10 years of age. This indicates that the refractive index of the lens increased during later childhood. Lens thinning in early childhood also ceased after 10 years of age. The spherical volume of the lens showed no appreciable net increase, but the axial length of the eye continued to grow throughout childhood. The prevalence of myopia in our data increased sharply at age 10 years, reaching 21.3% by the age of 14 years. CONCLUSIONS: Concurrent thinning and flattening of the crystalline lens imply that the lens is mechanically stretched by the equatorial growth of the eye during childhood. Changes in the patterns of lens development near the age of 10 years, concurrent with the onset of myopia, suggest that forces arise which interfere with equatorial growth. Such forces might diminish the decreases in lens power and amplify axial elongation to promote myopia.

Temporal response characteristics of the spatiochromatic visual evoked potential: nonlinearities and departures from psychophysics.

Although the visual evoked potential (VEP) for isoluminant stimuli has been characterized in terms of spatiochromatic parameters, temporal tuning along various chromatic directions has received less systematic attention. Additionally, there has been little categorical comparison of psychophysical appearance with VEP responses obtained for temporal variation of these patterns. At appropriate contrasts the VEP's for color axes (LM, S) show a robust and contrast-sensitive temporal tuning peak at 4 Hz. Contrast response functions at 4 Hz for the LM color axis are markedly nonmonotonic. However, there is a clear monotonicity with contrast for VEP latencies along these color axes. The anomalous behavior does not appear to be due to interactions between chromatic signals, to luminance artifact, or to rod intrusion. These anomalies in the temporal characteristics of the chromatic VEP may reflect interactions between chromatic responses and inherent cortical responsivity not linked to psychophysical behavior.

Acute effects of blood glucose on chromatic visually evoked potentials in persons with diabetes and in normal persons.

PURPOSE: To determine whether specific chromatic pathways are selectively affected by short-term variations in blood glucose levels in observers with and without diabetes. METHODS: Ten subjects with diabetes, all with type 1 diabetes and no retinopathy, and eight age-similar normal subjects were tested. Cortical visually evoked potentials (VEPs) in response to stimuli designed to selectively activate the short-wavelength-sensitive (S) or long- and middle-wavelength-sensitive (LM) chromatic (isoluminant) pathways or the achromatic pathway were recorded over a period of several hours. Capillary blood glucose also was measured repeatedly over the same period. The relation between VEP latency and blood glucose was determined. RESULTS: The S-pathway VEP latency was correlated significantly with blood glucose in a slight majority (6/10) of persons with diabetes; S-pathway latency was longer at higher blood glucose levels. This association between S-pathway latency and blood glucose was not dependent on the pattern of blood glucose variation over time (i.e., significant correlations between blood glucose and latency were observed in persons for whom blood glucose increased, decreased, or rose and then fell over time). No dependence on blood glucose was observed for LM- or achromatic-pathway VEP latency in subjects with diabetes. CONCLUSIONS: Acute variations in blood glucose of subjects with diabetes over hours selectively affect the function of the short-wavelength-sensitive chromatic pathway. The findings are discussed within the context of known mechanisms by which elevated glucose affects cellular metabolism with a time course consistent with the transient nature of the effect observed.

Optimum parameters for short-wavelength automated perimetry.

PURPOSE: To determine the optimum parameters for short-wavelength automated perimetry (SWAP) and to recommend these for standardization of the procedure. METHODS: We used a variety of stimulus and background configurations to determine the optimum background spectral distribution and luminance, and the optimum target spectral distribution, maximum luminance, and duration. We measured threshold versus intensity curves to determine which combination provided (a) the greatest isolation of the short-wavelength sensitive mechanisms and (b) the largest dynamic range for perimetry. We also evaluated the effect of lens absorption and cataract on these two factors. RESULTS: A broad-band yellow background at 100 candela/m2 with a narrow-band 440-nm (27-nm half-bandwidth), 1.8 degrees diameter (Goldmann size V) stimulus presented for 200 ms was optimum at all retinal eccentricities. Specific recommendations for how to modify existing perimeters are given. CONCLUSION: Agreement regarding the optimum parameters for SWAP should lead to standardization of the test that will facilitate comparison of results from different centers. Normative data can be collected at several sites and incorporated into statistical analysis packages currently available with various perimeters. This will greatly improve the clinical utility of this test.