Reliability of the serial reaction time task: If at first you don't succeed, try, try, try again

Procedural memory is involved in the acquisition and control of skills and habits that underlie rule and procedural learning, including the acquisition of grammar and phonology. The serial reaction time task (SRTT), commonly used to assess procedural learning, has been shown to have poor stability (test-retest reliability). We investigated factors that may affect the stability of the SRTT in adults. Experiment 1 examined whether the similarity of sequences learned in two sessions would impact stability: test-retest correlations were low regardless of sequence similarity (r < .31). Experiment 2 added a third session to examine whether individual differences in learning would stabilise with further training. There was a small (but nonsignificant) improvement in stability for later sessions (Sessions 1 and 2: r = .42; Sessions 2 and 3: r = .60). Stability of procedural learning on the SRTT remained suboptimal in all conditions, posing a serious obstacle to the use of this task as a sensitive predictor of individual differences and ultimately theoretical advance.

Limited Evidence of an Association Between Language, Literacy, and Procedural Learning in Typical and Atypical Development: A Meta-Analysis

The ability to extract patterns from sensory input across time and space is thought to underlie the development and acquisition of language and literacy skills, particularly the subdomains marked by the learning of probabilistic knowledge. Thus, impairments in procedural learning are hypothesized to underlie neurodevelopmental disorders, such as dyslexia and developmental language disorder. In the present meta-analysis, comprising 2396 participants from 39 independent studies, the continuous relationship between language, literacy, and procedural learning on the Serial Reaction Time task (SRTT) was assessed across children and adults with typical development (TD), dyslexia, and Developmental Language Disorder (DLD). Despite a significant, but very small, relationship between procedural learning and overall language and literacy measures, this pattern was not observed at the group-level when examining TD, dyslexic, and DLD groups separately. Based on the procedural/declarative model, a positive relationship was expected between procedural learning and language and literacy measures for the typically developing group; however, no such relationship was observed. This was also the case for the disordered groups (ps > .05). Also counter to expectations, the magnitude of the relationship between procedural learning and grammar and phonology did not differ between TD and DLD (ps > .05), nor between the TD and dyslexic group on reading, spelling, and phonology (ps > .05). While lending little support to the procedural/declarative model, we consider that these results may be the consequence of poor psychometric properties of the SRTT as a measure of procedural learning.

The reliability of the serial reaction time task: meta-analysis of test-retest correlations

The Serial Reaction Time task, one of the most widely used tasks to index procedural memory, has been increasingly employed in individual differences research examining the role of procedural memory in language and other cognitive abilities. Yet, despite consistently producing robust procedural learning effects at the group level (i.e. faster responses to sequenced/probable trials versus random/improbable trials), these effects have recently been found to have poor reliability. In this meta-analysis (N = 7), comprising 719 participants (M = 20.81, s.d. = 7.13), we confirm this 'reliability paradox'. The overall retest reliability of the robust procedural learning effect elicited by the SRTT was found to be well below acceptable psychometric standards (r < 0.40). However, split-half reliability within a session is better, with an overall estimate of 0.66. There were no significant effects of sampling (participants' age), methodology (e.g. number of trials, sequence type) and analytical decisions (whether all trials were included when computing the procedural learning scores; using different indexes of procedural learning). Thus, despite producing robust effects at the group-level, until we have a better understanding of the factors that improve the reliability of this task using the SRTT for individual differences research should be done with caution.

Stronger Associations Between Sleep and Mental Health in Adults with Autism: A UK Biobank Study

This study examined sleep and its cognitive and affective correlates in adults with and without autism spectrum disorder (ASD), utilizing UK Biobank data. There were no group differences in subjective sleep duration [n = 220 ASD; n = 2200 general population (GP)]. Accelerometer measures of sleep duration or nighttime activity did not differ by group, but sleep efficiency was marginally lower in ASD (n = 83 ASD; n = 824 GP). Sleep efficiency was associated with wellbeing and mental health, and pathways between accelerometer sleep measures and wellbeing and mental health were significantly stronger for adults with ASD (who also reported substantially poorer wellbeing and > 5 × likelihood of experiencing mental distress). These findings highlight the need to monitor sleep to maintain good mental health in adult ASD.

Do naps benefit novel word learning? Developmental differences and white matter correlates

Memory representations of newly learned words undergo changes during nocturnal sleep, as evidenced by improvements in explicit recall and lexical integration (i.e., after sleep, novel words compete with existing words during online word recognition). Some studies have revealed larger sleep-benefits in children relative to adults. However, whether daytime naps play a similar facilitatory role is unclear. We investigated the effect of a daytime nap (relative to wake) on explicit memory (recall/recognition) and lexical integration (lexical competition) of newly learned novel words in young adults and children aged 10-12 years, also exploring white matter correlates of the pre- and post-nap effects of word learning in the child group with diffusion weighted MRI. In both age groups, a nap maintained explicit memory of novel words and wake led to forgetting. However, there was an age group interaction when comparing change in recall over the nap: children showed a slight improvement whereas adults showed a slight decline. There was no evidence of lexical integration at any point. Although children spent proportionally more time in slow-wave sleep (SWS) than adults, neither SWS nor spindle parameters correlated with over-nap changes in word learning. For children, increased fractional anisotropy (FA) in the uncinate fasciculus and arcuate fasciculus were associated with the recognition of novel words immediately after learning, and FA in the right arcuate fasciculus was further associated with changes in recall of novel words over a nap, supporting the importance of these tracts in the word learning and consolidation process. These findings point to a protective role of naps in word learning (at least under the present conditions), and emphasize the need to better understand both the active and passive roles that sleep plays in supporting vocabulary consolidation over development.

Sleep health among people with severe mental ill health during the COVID-19 pandemic: Results from a linked UK population cohort study

Objectives

Sleep problems are a transdiagnostic feature of nearly all psychiatric conditions, and a strong risk factor for initial and recurrent episodes. However, people with severe mental ill health (SMI) are often excluded from general population surveys, and as such the extent and associates of poor sleep in this population are less well understood. This study explores sleep health in an SMI sample during the COVID-19 pandemic, using multiple regression to identify risk factors, including daily routine, wellbeing and demographics.

Methods

An existing cohort of people with an SMI diagnosis were sampled. Participants were invited to complete a self-report survey about their health and the impacts of COVID-19 and associated public health measures. Sleep duration, efficiency, and quality were measured using items from the Pittsburgh Sleep Quality Index (PSQI).

Results

Two hundred forty-nine adults (aged 21-84 years) completed the survey. Mean sleep duration and efficiency were similar to general population estimates, at 7 h 19 min and 78%, respectively. However, 43% reported "bad" sleep quality that was associated with being younger in age as well as disturbed routine and declined wellbeing. Indeed, 37% reported a disturbed routine during the pandemic.

Conclusions

High estimates of perceived poor sleep quality in the SMI population align with previous findings. Supporting people with SMI to maintain routine regularity may work to protect sleep quality and wellbeing. Future research should more closely examine sleep health in people with SMI, using accessible and scalable measures of objective and subjective sleep, examining longitudinal trends.

Retrieval practice transfer effects for multielement event triplets

Retrieval practice (RP) leads to improved retention relative to re-exposure and is considered a robust phenomenon when the final test conditions are identical to RP conditions. However, the extent to which RP 'transfers' to related material is less clear. Here, we tested for RP transfer effects under conditions known to induce integration of associated material at encoding, which may make transfer more likely. Participants learned multielement triplets (locations, animals and objects) and one pairwise association from each triplet was tested through RP, re-exposed, or not re-exposed (control). Two days later participants completed a final test of all pairwise associations. We found no evidence for an RP effect compared to re-exposure, but both tested/re-exposed pairs were better remembered than the not re-exposed control condition. We also found that transfer occurred from both tested to untested and re-exposed to not re-exposed pairs. Our results highlight that RP and re-exposure can boost retention for directly tested/re-exposed event pairs and associated but untested/not re-exposed event pairs, suggesting re-exposure of integrated information can be of pedagogical value. The results also question the boundary conditions for an increase in retention for RP relative to re-exposure, highlighting the need for a better theoretical understanding of RP effects.

The role of prior lexical knowledge in children's and adults' incidental word learning from illustrated stories

Children and adults benefit from a new word's phonological neighbors during explicit vocabulary instruction, suggesting that related prior knowledge can support new learning. This study examined the influence of lexical neighborhood structure during incidental word learning-limiting opportunities for strategically engaging prior knowledge-and tested the hypothesis that prior knowledge would provide additional support during subsequent consolidation. Children aged 8-10 years (Experiment 1) and adults (Experiment 2) were presented with 15 pseudowords embedded in a spoken story with illustrations, and were then tested on their recognition and recall of the new word-forms immediately, the next day, and one week later. The pseudowords had either no, one, or many English phonological neighbors, varying the potential connections to existing knowledge. After encountering the pseudowords in this incidental training paradigm, neither children nor adults benefited from phonological neighbors in recall, and children were better at recognizing items without neighbors. The neighbor influence did not change with opportunities for consolidation in either experiment, nor did it relate to learners' existing vocabulary ability. Exploratory analyses revealed that children experienced bigger benefits from offline consolidation overall, with adults outperforming children only for many-neighbor items one week after exposure. We discuss how the neighbor benefit in word learning may be constrained by learning context, and how the enhanced benefits of offline consolidation in childhood extend to vocabulary learning in more naturalistic contexts. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Sleep-dependent consolidation in children with comprehension and vocabulary weaknesses: it'll be alright on the night?

BACKGROUND

Vocabulary is crucial for an array of life outcomes and is frequently impaired in developmental disorders. Notably, 'poor comprehenders' (children with reading comprehension deficits but intact word reading) often have vocabulary deficits, but underlying mechanisms remain unclear. Prior research suggests intact encoding but difficulties consolidating new word knowledge. We test the hypothesis that poor comprehenders' sleep-associated vocabulary consolidation is compromised by their impoverished lexical-semantic knowledge.

METHODS

Memory for new words was tracked across wake and sleep to assess encoding and consolidation in 8-to-12-year-old good and poor comprehenders. Each child participated in two sets of sessions, one beginning in the morning (AM-encoding) and the other in the evening (PM-encoding). In each case, they were taught 12 words and were trained on a spatial memory task. Memory was assessed immediately, 12- and 24-hr later via stem-completion, picture-naming, and definition tasks to probe different aspects of word knowledge. Long-term retention was assessed 1-2 months later.

RESULTS

Recall of word-forms improved over sleep and postsleep wake, as measured in both stem-completion and picture-naming tasks. Counter to hypotheses, deficits for poor comprehenders were not observed in consolidation but instead were seen across measures and throughout testing, suggesting a deficit from encoding. Variability in vocabulary knowledge across the whole sample predicted sleep-associated consolidation, but only when words were learned early in the day and not when sleep followed soon after learning.

CONCLUSIONS

Poor comprehenders showed weaker memory for new words than good comprehenders, but sleep-associated consolidation benefits were comparable between groups. Sleeping soon after learning had long-lasting benefits for memory and may be especially beneficial for children with weaker vocabulary. These results provide new insights into the breadth of poor comprehenders' vocabulary weaknesses, and ways in which learning might be better timed to remediate vocabulary difficulties.

Make or break it: boundary conditions for integrating multiple elements in episodic memory

Event memories are characterized by the holistic retrieval of their constituent elements. Studies show that memory for individual event elements (e.g. person, object and location) are statistically related to each other, and that the same associative memory structure can be formed by learning all pairwise associations across separated encoding contexts (person-object, person-location, object-location). Counter to previous studies that have shown no differences in holistic retrieval between simultaneously and separately encoded event elements, adults did not show evidence of holistic retrieval from separately encoded event elements when using a similar paradigm adapted for children (Experiment 1). We conducted a further five online experiments to explore the conditions under which holistic retrieval emerges following separated encoding of within-event associations, testing for influences of trial length (Experiment 2), the number of events learned (Experiment 3a) and stimulus presentation format (Experiments 3b, 4a, 4b). Presentation of written words was optimal for integrating elements across encoding trials, whereas the addition of spoken words disrupted integration across separately presented associations. The use of picture stimuli also produced effect sizes smaller than those of previously published research. We discuss the ways in which memory integration processes may be disrupted by these differences in presentation format. The findings have practical implications for the utility of this paradigm across research and learning contexts.

Atypicalities in sleep and semantic consolidation in autism

Sleep is known to support the neocortical consolidation of declarative memory, including the acquisition of new language. Autism spectrum disorder (ASD) is often characterized by both sleep and language learning difficulties, but few studies have explored a potential connection between the two. Here, 54 children with and without ASD (matched on age, nonverbal ability and vocabulary) were taught nine rare animal names (e.g., pipa). Memory was assessed via definitions, naming and speeded semantic decision tasks immediately after learning (pre‐sleep), the next day (post‐sleep, with a night of polysomnography between pre‐ and post‐sleep tests) and roughly 1 month later (follow‐up). Both groups showed comparable performance at pre‐test and similar levels of overnight change on all tasks; but at follow‐up children with ASD showed significantly greater forgetting of the unique features of the new animals (e.g., pipa is a flat frog). Children with ASD had significantly lower central non‐rapid eye movement (NREM) sigma power. Associations between spindle properties and overnight changes in speeded semantic decisions differed by group. For the TD group, spindle duration predicted overnight changes in responses to novel animals but not familiar animals, reinforcing a role for sleep in the stabilization of new semantic knowledge. For the ASD group, sigma power and spindle duration were associated with improvements in responses to novel and particularly familiar animals, perhaps reflecting more general sleep‐associated improvements in task performance. Plausibly, microstructural sleep atypicalities in children with ASD and differences in how information is prioritized for consolidation may lead to cumulative consolidation difficulties, compromising the quality of newly formed semantic representations in long‐term memory.

Trends in Breast MRI Use Among Women with BRCA Mutations: A National Claims Analysis 2006–2016

Women with BRCA mutations are recommended to receive breast MRI as an adjunct to annual mammography for breast cancer screening however adoption of these guidelines is unclear. We estimated breast MRI use from 2006–2016 among insured US women to understand use over time. Methods: Using medical care claims, we conducted a cohort study of breast MRI use in commercially-insured women aged 20–64 years continuously enrolled for ≥1 year in a large national insurer between 2006–2016. Women were identified as BCRA mutation carriers without a personal history of breast cancer using ICD9/10 diagnosis codes. We used CPT codes to identify breast MRIs and developed claims-based algorithms to categorized MRI indication as: screening, diagnostic or other. We calculated annual age-specific and age-adjusted rates of use overall and by indication among BCRA mutation carrier women. We used autoregressive time series models to estimate the yearly trend. Results: We identified 12,457 women with BRCA mutations during the study period. Breast MRI use overall among BRCA+ women aged 20–64 was 47/1000 women in 2006 and increased on average by 11 MRIs per year to a rate of 174/1000 in 2016 (P &lt; 0.001). Across this time period, use for screening accounted for over 80% of breast MRIs and rates mirrored the overall trend with a 4.8-fold increase from 31/1000 in 2006 to 146/1000 women by 2016. Over the same time period, use of breast MRI for diagnostic workup or other indications remained stable. Use of screening breast MRI was highest among older women aged 50–64 compared with women &lt;40 and 40–49 years (in 2016, 189, 95, and 177/1000, respectively) Discussion: Breast MRI screening increased dramatically over the past decade in women with BRCA mutations concordant with clinical guidelines. Additional research is needed to understand use of breast imaging relative to health outcomes for this high-risk population.

Offline consolidation supersedes prior knowledge benefits in children's (but not adults') word learning

Prior linguistic knowledge is proposed to support the acquisition and consolidation of new words. Adults typically have larger vocabularies to support word learning than children, but the developing brain shows enhanced neural processes that are associated with offline memory consolidation. This study investigated contributions of prior knowledge to initial word acquisition and consolidation at different points in development, by teaching children and adults novel words (e.g., ballow) that varied in the number of English word-form "neighbours" (e.g., wallow, bellow). Memory for the novel word-forms was tested immediately after training, the next day and 1 week later, to assess the time-course of prior knowledge contributions. Children aged 7-9 years (Experiments 1, 3) and adults (Experiment 2) recalled words with neighbours better than words without neighbours when tested immediately after training. However, a period of offline consolidation improved overall recall and reduced the influence of word-form neighbours on longer term memory. These offline consolidation benefits were larger in children than adults, supporting theories that children have a greater propensity for consolidating phonologically distinctive language information. Local knowledge of just a single word-form neighbour was enough to enhance learning, and this led to the individual differences in word recall that were related to adults' global vocabulary ability. The results support the proposal that the relative contributions of different learning mechanisms change across the lifespan, and highlight the importance of testing theoretical models of word learning in the context of development.

Preoperative breast MRI and mortality in older women with breast cancer

PURPOSE

The survival benefit from detecting additional breast cancers by preoperative magnetic resonance imaging (MRI) continues to be controversial.

METHODS

We followed a cohort of 4454 women diagnosed with non-metastatic breast cancer (stage I-III) from 2/2005-6/2010 in five registries of the breast cancer surveillance consortium (BCSC). BCSC clinical and registry data were linked to Medicare claims and enrollment data. We estimated the cumulative probability of breast cancer-specific and all-cause mortality. We tested the association of preoperative MRI with all-cause mortality using a Cox proportional hazards model.

RESULTS

917 (20.6%) women underwent preoperative MRI. No significant difference in the cumulative probability of breast cancer-specific mortality was found. We observed no significant difference in the hazard of all-cause mortality during the follow-up period after adjusting for sociodemographic and clinical factors among women with MRI (HR 0.90; 95% CI 0.72-1.12) compared to those without MRI.

CONCLUSION

Our findings of no breast cancer-specific or all-cause mortality benefit supplement prior results that indicate a lack of improvement in surgical outcomes associated with use of preoperative MRI. In combination with other reports, the results of this analysis highlight the importance of exploring the benefit of preoperative MRI in patient-reported outcomes such as women's decision quality and confidence levels with decisions involving treatment choices.

Breast Density and Risk of Invasive Breast Cancer among Older Women Undergoing Mammography: The Breast Cancer Surveillance Consortium Cohort Study

This study examined whether breast density is associated with risk of breast cancer in women age ≥65 years undergoing screening mammography in community practice. Methods: We used prospective cohort data between 1996 and 2012 from the Breast Cancer Surveillance Consortium (BCSC). We calculated separate cumulative incidence models for breast cancer incidence according to Breast Imaging Reporting and Data System (BI-RADS) breast density for women ages 65–74 and ages ≥75. Multivariable Cox proportional hazards regression models were fitted to determine the risk of invasive breast cancer adjusted for BCSC registry, race/ethnicity, BMI, hormone therapy use and benign breast disease. Results: Among the 403,268 women included in the study, approximately 40% were ages ≥75. The annual incidence rate of invasive breast cancer increased with increasing breast density among women ages 65–74 [BI- RADS fatty breasts: 2.2% (95% CI, 2.1%–2.4%) vs. heterogeneously or extremely dense breasts: 4.7% (95% CI, 4.6%–4.9%)] and women ages 75+ [BI-RADS fatty breasts: 2.3% (95% CI, 2.1%–2.5%) vs. heterogeneously or extremely dense: 4.3% (95% CI, 4.1%–4.5%)]. Women with BI-RADS fatty breasts had a decreased risk of breast cancer among women ages 65–74 [HR: 0.66 (95% CI: 0.58%–0.78%) and women ages ≥75 [HR: 0.73 (95% CI: 0.62%–0.87%). Women with BI-RADS heterogeneously or extremely dense breasts were found to have increased risk of breast cancer among women ages 65–74 [HR: 1.39 (95% CI: 1.28%–1.51%)] and women ages ≥75 [HR: 1.23 (95% CI: 1.10%–1.37%)]. Conclusions: Older women with higher BI-RADS density had a significantly increased risk of breast cancer. These findings add further evidence that breast density continues to be associated with an increased risk of breast cancer, even among women age ≥75 years.

Cumulative Incidence of Non-breast Cancer Mortality and Breast Cancer Risk by Comorbidity and Age among Older Women Undergoing Screening Mammography: The Medicare-linked Breast Cancer Surveillance Consortium Cohort Study

Due to an increasing comorbidity burden with aging, the margin of benefit from screening mammography in women ages ≥65 is highly variable. This study examined 10-year cumulative risk of non-breast cancer mortality and breast cancer by comorbidity and age in a screening population. Methods: We used prospective cohort data from the Breast Cancer Surveillance Consortium (BCSC), which included 198,362 women ages ≥65 years who have undergone at least one screening mammogram. We calculated cumulative incidence of non-breast cancer mortality and risk of breast cancer 10 years following the screening mammogram for women ages 65–74, 75–84 and ≥85 years stratified by the Charlson Comorbidity Index (CCI scores 0, 1 and ≥2). Results: During a median follow-up time of 8.1 years (interquartile range, 4.6 to 10 years), 34,768 died from non-breast cancer causes and 6,327 women were diagnosed with invasive breast cancer of whom 359 died from breast cancer and 942 from non-breast cancer causes. The 10-year cumulative risk of invasive breast cancer following a screening mammogram did not significantly decrease with elevating CCI score and age for women ages 65–74 [CCI 0 = 4.0% (95% CI, 3.9%–4.1%) vs. CCI ≥2 = 3.8% (95% CI, 3.3%–4.3%)], ages 75–84 [CCI 0 = 3.7% (95% CI, 3.5%–3.9%) vs. CCI ≥ 2 = 3.4% (95% CI, 2.8%–4.0%)], and ages ≥85 [CCI 0 = 2.7%, (95% CI, 2.3%–3.2%) vs. CCI ≥ 2 = 2.5% (95% CI, 1.4%–3.6%)]. Cumulative risk of non-breast cancer mortality significantly increased with increasing CCI and age for women ages 65–74 [CCI 0 = 11% (95% CI, 10%–11%] vs. CCI ≥ 2 = 45% (95% CI, [43%–46%)], ages 75–84 [CCI 0 = 29% (95% CI, 29%–30%) vs. CCI ≥2 = 62% (95% CI, 60%–63%)], and ages ≥85 [CCI 0 = 59%, (95% CI, 57%–60%) vs. CCI ≥2 = 84% (95% CI, 81%–86%)]. Conclusion: Risk of non-breast cancer mortality was high and significantly increased with rising comorbidity burden and age whereas breast cancer risk was low and non-significantly decreased with both. These results suggest that women with a CCI score of ≥2 or ages ≥75 years may experience minimal benefit from continuing routine screening mammography. Future research is needed to delineate the specific benefits and harms of screening mammography in subsets of older women defined by age and comorbidity burden.

Consolidation of vocabulary is associated with sleep in typically developing children, but not in children with dyslexia

Sleep is known to play an active role in consolidating new vocabulary in adults; however, the mechanisms by which sleep promotes vocabulary consolidation in childhood are less well understood. Furthermore, there has been no investigation into whether previously reported differences in sleep architecture might account for variability in vocabulary consolidation in children with dyslexia. Twenty-three children with dyslexia and 29 age-matched typically developing peers were exposed to 16 novel spoken words. Typically developing children showed overnight improvements in novel word recall; the size of the improvement correlated positively with slow wave activity, similar to previous findings with adults. Children with dyslexia showed poorer recall of the novel words overall, but nevertheless showed overnight improvements similar to age-matched peers. However, comparisons with younger children matched on initial levels of novel word recall pointed to reduced consolidation in dyslexics after 1 week. Crucially, there were no significant correlations between overnight consolidation and sleep parameters in the dyslexic group. This suggests a reduced role of sleep in vocabulary consolidation in dyslexia, possibly as a consequence of lower levels of learning prior to sleep, and highlights how models of sleep-associated memory consolidation can be usefully informed by data from typical and atypical development.

Consolidating new words from repetitive versus multiple stories: Prior knowledge matters

Prior knowledge is proposed to support the consolidation of newly acquired material. The current study examined whether children with superior vocabulary knowledge show enhanced overnight consolidation, particularly when new words are encountered in varying stories. Children aged 10 and 11 years (N = 42) were exposed to two sets of eight spoken novel words (e.g., "crocodol"), with one set embedded in the same story presented twice and the other presented in two different stories. Children with superior vocabulary knowledge showed larger overnight gains in explicit phonological and semantic knowledge when novel words had been encountered in multiple stories. However, when novel words had been encountered in repetitive stories, existing knowledge exerted no influence on the consolidation of explicit phonological knowledge and had a negative impact on the consolidation of semantic knowledge. One full day (24 h) after story exposure, only very weak evidence of lexical integration (i.e., slower animacy decisions toward the basewords [e.g., "crocodile"] than toward the control words) was observed for novel words learned via repetitive (but not multiple) stories. These data suggest that although the consolidation of explicit new word knowledge learned through multiple contexts is supported by prior knowledge, lexical integration might benefit more from repetition.

The effect of coloured overlays and lenses on reading: a systematic review of the literature

PURPOSE

There are many anecdotal claims and research reports that coloured lenses and overlays improve reading performance. Here we present the results of a systematic review of this literature and examine the quality of the evidence.

METHODS

We systematically reviewed the literature concerning the effect of coloured lenses or overlays on reading performance by searching the PsychInfo, Medline and Embase databases. This revealed 51 published items (containing 54 data sets). Given that different systems are in use for issuing coloured overlays or lenses, we reviewed the evidence under four separate system headings (Intuitive, Irlen, Harris/Chromagen and Other), classifying each published item using the Cochrane Risk of Bias tool.

RESULTS

Although the different colour systems have been subjected to different amounts of scientific scrutiny, the results do not differ according to the system type, or whether the sample under investigation was classified as having visual stress (or a similarly defined condition), reading difficulty, or both. The majority of studies are subject to 'high' or 'uncertain' risk of bias in one or more key aspects of study design or outcome, with studies at lower risk from bias providing less support for the benefit of coloured lenses/overlays on reading ability. While many studies report improvements with coloured lenses, the effect size is generally small and/or similar to the improvement found with a placebo condition. We discuss the strengths and shortcomings of the published literature and, whilst acknowledging the difficulties associated with conducting trials of this type, offer some suggestions about how future trials might be conducted.

CONCLUSIONS

Consistent with previous reviews and advice from several professional bodies, we conclude that the use of coloured lenses or overlays to ameliorate reading difficulties cannot be endorsed and that any benefits reported by individuals in clinical settings are likely to be the result of placebo, practice or Hawthorne effects.

Eye-tracking the time-course of novel word learning and lexical competition in adults and children

Lexical competition is a hallmark of proficient, automatic word recognition. Previous research suggests that there is a delay before a new spoken word becomes engaged in this process, with sleep playing an important role. However, data from one method - the visual world paradigm - consistently show competition without a delay. We trained 42 adults and 40 children (aged 7-8) on novel word-object pairings, and employed this paradigm to measure the time-course of lexical competition. Fixations to novel objects upon hearing existing words (e.g., looks to the novel object biscal upon hearing "click on the biscuit") were compared to fixations on untrained objects. Novel word-object pairings learned immediately before testing and those learned the previous day exhibited significant competition effects, with stronger competition for the previous day pairings for children but not adults. Crucially, this competition effect was significantly smaller for novel than existing competitors (e.g., looks to candy upon hearing "click on the candle"), suggesting that novel items may not compete for recognition like fully-fledged lexical items, even after 24h. Explicit memory (cued recall) was superior for words learned the day before testing, particularly for children; this effect (but not the lexical competition effects) correlated with sleep-spindle density. Together, the results suggest that different aspects of new word learning follow different time courses: visual world competition effects can emerge swiftly, but are qualitatively different from those observed with established words, and are less reliant upon sleep. Furthermore, the findings fit with the view that word learning earlier in development is boosted by sleep to a greater degree.

A sequence learning impairment in dyslexia? It depends on the task

Language acquisition is argued to be dependent upon an individuals' sensitivity to serial-order regularities in the environment (sequential learning), and impairments in reading and spelling in dyslexia have recently been attributed to a deficit in sequential learning. The present study examined the learning and consolidation of sequential knowledge in 30 adults with dyslexia and 29 typical adults matched on age and nonverbal ability using two tasks previously reported to be sensitive to a sequence learning deficit. Both groups showed evidence of sequential learning and consolidation on a serial response time (SRT) task (i.e., faster and more accurate responses to sequenced spatial locations than randomly ordered spatial locations during training that persisted one week later). Whilst typical adults showed evidence of sequential learning on a Hebb repetition task (i.e., more accurate serial recall of repetitive sequences of nonwords versus randomly ordered sequences), adults with dyslexia showed initial advantages for repetitive versus randomly ordered sequences in the first half of training trials, but this effect disappeared in the second half of trials. This Hebb repetition effect was positively correlated with spelling in the dyslexic group; however, there was no correlation between sequential learning on the two tasks, placing doubt over whether sequential learning in different modalities represents a single capacity. These data suggest that sequential learning difficulties in adults with dyslexia are not ubiquitous, and when present may be a consequence of task demands rather than sequence learning per se.

Abstract P4-01-15: Impact of Preoperative MRI on the Surgical Treatment of Breast Cancer: A SEER-Medicare Analysis

Background: Preoperative magnetic resonance imaging (MRI) use has increased for women with invasive breast cancer and ductal carcinoma in situ (DCIS). Prior studies have disputed whether preoperative MRI is associated with increased rates of mastectomy. We evaluated the rates of mastectomy versus breast conserving surgery (BCS) and their association with preoperative MRI in older women.

Methods: We identified women in SEER-Medicare 66 years or older diagnosed with DCIS or invasive breast cancer between 2002 and 2007 treated within 6 months of diagnosis with mastectomy or breast conserving surgery (BCS) with or without radiotherapy (RT). Preoperative MRI was defined as MRI occurring before a woman's first surgery after her initial diagnosis. We looked for surgical treatment (BCS or mastectomy) and radiotherapy, age at diagnosis, year of diagnosis and cancer type, overall and separately by receipt of MRI. We examined the association of surgical treatment with MRI using multivariable logistic regression adjusting for age at diagnosis, year of diagnosis, cancer type and radiotherapy.

Results: Among the 70,758 women identified, 5,126 (7.2%) had a preoperative MRI. The overall use of MRI increased from 1.2% in 2002 to 18.0% in 2007 (p &lt; 0.0001). Women with MRI were more likely to undergo mastectomy than those without MRI (331 per 1000 vs. 314 per 1000; respectively, p &lt; 0.0001) and more likely to undergo BCS RT (432 per 1000 vs. 354 per 1000; respectively, p &lt; 0.0001).

Conclusion: The use of preoperative MRI has increased in recent years and is significantly associated with increased rates of BCS RT and mastectomy. Limitations of this study include that it is an observational analysis and that selection bias may exist for MRI and aggressive treatment that is not related to what is observed on MRI. Further studies are needed to understand how patient characteristics and information obtained from MRI influence treatment choices.

Accessing and selecting word meaning in autism spectrum disorder

BACKGROUND

Comprehension difficulties are commonly reported in autism spectrum disorder (ASD) but the causes of these difficulties are poorly understood. This study investigates how children with ASD access and select meanings of ambiguous words to test four hypotheses regarding the nature of their comprehension difficulties: semantic deficit, weak central coherence, reduced top-down control and inhibition deficit.

METHODS

The cross-modal semantic priming paradigm was used. Children heard homonym primes in isolation or as final words in sentences biased towards the subordinate meaning and then named picture targets depicting dominant or subordinate associates of homonyms.

RESULTS

When homonyms were presented in isolation, children with ASD and controls showed priming for dominant and subordinate pictures at 250ms ISI. At 1,000ms ISI, the controls showed dominant (but not subordinate) priming whilst the ASD group did not show any priming. When homonyms were presented in subordinate sentence contexts, both groups only showed priming for context-appropriate (subordinate) meanings at 250ms ISI, suggesting that context has an early influence on meaning selection. At 1,000ms ISI the controls showed context-appropriate (but not inappropriate) priming whereas the ASD group showed both appropriate and inappropriate priming.

CONCLUSIONS

Children with ASD showed intact access to semantic information early in the time course of processing; however, they showed impairments in the selection of semantic representations later in processing. These findings suggest that a difficulty with initiating top-down strategies to modulate online semantic processing may compromise language comprehension in ASD. Implications for intervention are discussed.

The N400 effect in children: relationships with comprehension, vocabulary and decoding

Using event-related potentials (ERPs), we investigated the N400 (an ERP component that occurs in response to meaningful stimuli) in children aged 8-10 years old and examined relationships between the N400 and individual differences in listening comprehension, word recognition and non-word decoding. Moreover, we tested the claim that the N400 effect provides a valuable indicator of behavioural vocabulary knowledge. Eighteen children were presented with picture-word pairs that were either 'congruent' (the picture depicted the spoken word) or 'incongruent' (they were unrelated). Three peaks were observed in the ERP waveform triggered to the onset of the picture-word stimuli: an N100 in fronto-central channels, an N200 in central-parietal channels and an N400 in frontal, central and parietal channels. In contrast to the N100 peak, the N200 and N400 peaks were sensitive to semantic incongruency with greater peak amplitudes for incongruent than congruent conditions. The incongruency effects for each peak correlated positively with listening comprehension but when the peak amplitudes were averaged across congruent/incongruent conditions they correlated positively with non-word decoding. These findings provide neurophysiological support for the position that sensitivity to semantic context (reflected in the N400 effect) is crucial for comprehension whereas phonological decoding skill relates to more general processing differences reflected in the ERP waveform. There were no correlations between ERP and behavioural measures of expressive or receptive vocabulary knowledge for the same items, suggesting that the N400 effect may not be a reliable estimate of vocabulary knowledge in children aged 8-10 years.

Adrenal lipid profiles of chemically sympathectomized normoxic and hypoxic neonatal rats

Neonatal hypoxia is a common condition that elicits a coordinated endocrine response. In the neonatal rat, hypoxia induces an ACTH-independent increase in corticosterone which can be partially blocked by chemical sympathectomy. The present study sought to characterize the effects of sympathectomy on the adrenal lipid profile, since previous work suggested that augmented plasma corticosterone during hypoxia may be due to changes in adrenal lipid metabolism. Newborn rats were exposed to normoxia or hypoxia from birth to seven days of age, and guanethidine was used to produce the sympathectomy. Plasma epinephrine and norepinephrine were not significantly affected by hypoxia, while guanethidine decreased plasma norepinephrine in normoxic and hypoxic pups. Hypoxia alone increased the concentration of cholesterol esters in the adrenal gland; this increase was due to increases in cholesterol ester-associated oleic (18:1n9), docosahexaenoic (22:6n3), arachidonic (20:4n6), and adrenic (22:4n6) acids. Hypoxia also increased diglyceride-associated adrenic acid. Guanethidine treatment attenuated the hypoxia-induced increase in cholesterol ester-bound arachidonic and adrenic acids. Guanethidine also decreased saturated fatty acid concentrations and increased n3 fatty acid-enriched triglycerides. The results support the idea that the ACTH-independent corticosterone response to hypoxia in the neonatal rat is mediated by specific, sympathetically driven alterations in the adrenal lipid profile.

Proton conduction through full-length gp91phox requires histidine 115

The NADPH oxidase of neutrophils is a transmembrane electron transfer complex, containing a flavin adenine dinucleotide and two hemes, all of which are suggested to be contained within gp91 (phox), one of four subunits of the enzyme. The transfer of electrons through the NADPH oxidase is associated with an efflux of protons. gp91 (phox) has previously been demonstrated to function as the proton conduction pathway. The mutation of histidines 111, 115, and 119 to leucines and of histidine 115 to leucine within the N-terminal 230-amino-acid fragment of gp91 (phox) has previously been demonstrated to result in the loss of proton conduction through this N-terminal fragment. In this paper we have investigated the role of these histidines in proton conduction by the full-length gp91 (phox). Stable CHO cell lines were established which expressed full-length gp91 (phox) in which histidines 111, 115, and 119 had been mutated to leucines (CHO91H111/115/119) and in which histidine 115 had been mutated to leucine (CHO91H115L). The expression of gp91 (phox) and its cellular localisation in these cell lines were comparable between wild-type and the mutant gp91 (phox). The mutation of histidines 111, 115, and 119 to leucines or just histidine 115 to leucine resulted in an almost total loss of both the arachidonate-activated influx and efflux of protons, in comparison with that observed for wild-type gp91 (phox). Therefore, histidine 115 is required for proton conduction by both full-length gp91 (phox) and the N-terminal 230-amino-acid fragment of gp91 (phox). Histidine 115 has recently been proposed to act as a coordinating ligand for the outer heme iron of the NADPH oxidase. On the basis of observations for cytochrome c oxidase, we propose a model for this dual role of histidine 115.

New technology for improved vaccine safety and efficacy

Nearly all of the 2000 vaccines presently licensed by the US Department of Agriculture for veterinary use in the United States are conventional vaccines containing either killed or modified live whole bacteria or viruses. Recent advances in molecular biology, immunology, microbiology, and genetics and in understanding microbial pathogenesis have led to the development of a wide variety of new approaches for developing safer and more effective vaccines. This article briefly describes these new technologies and their potential advantages and disadvantages as compared with conventional killed and modified live vaccines.

Activation of NADPH oxidase-related proton and electron currents in human eosinophils by arachidonic acid

1. Effects of arachidonic acid (AA) on proton and electron currents in human eosinophils were studied using the permeabilized-patch voltage-clamp technique, using an applied NH4+ gradient to control pH(i). 2. Superoxide anion (O2-) release was assessed by cytochrome c reduction in human eosinophils. Significant O2- release was stimulated by 5-10 microM AA. 3. AA activated diphenylene iodinium (DPI)-inhibitable inward current reflecting electron efflux through NADPH oxidase. These electron currents (I(e)) were elicited in human eosinophils at AA concentrations (3-10 microM) similar to those that induced O2- release. 4. The voltage-gated proton conductance (g(H)) in eosinophils stimulated with AA was profoundly enhanced: H+ current amplitude (I(H)) increased 4.6 times, activation was 4 times faster, and the H+ conductance-voltage (g(H)-V) relationship was shifted to substantially more negative voltages. The electrophysiological effects of AA resembled those reported for PMA, except that AA did not consistently slow tau(tail) (deactivation of H+ currents). 5. The stimulation of both proton and electron currents by AA was reversible upon washout. Repeated exposure elicited repeated responses. The activation of H+ currents by AA was dissociable from its activation of NADPH oxidase; H+ currents were enhanced at low concentrations of AA that did not elicit detectable I(e) or when NADPH oxidase was inhibited by DPI. 6. Most of the effects of AA on H+ currents qualitatively resemble those reported in whole-cell studies, reflecting a more direct action than PMA. The results are compatible with AA being an immediate activator of both NADPH oxidase and proton channels in human eosinophils.

Inhibition of the neutrophil NADPH oxidase and associated H+ channel by diethyl pyrocarbonate (DEPC), a histidine-modifying agent: evidence for at least two target sites

Diethyl pyrocarbonate (DEPC), a histidine-modifying reagent, has been utilized to demonstrate the importance of histidine residues in the functioning of proteins. In previous studies of the NADPH oxidase, histidine residues have been determined to be important in the ability of gp91(phox) to function as an H(+) pathway and in the binding of haem and FAD. We have investigated the ability of DEPC to inhibit H(+) flux and superoxide generation by human neutrophils. Proton flux through the NADPH oxidase-associated H(+) channel was inhibited by DEPC only if applied simultaneously with an activator of the channel. This suggested that the site modified by DEPC is not accessible in the closed channel. Superoxide generation by the NADPH oxidase was also inhibited by DEPC when applied after or simultaneously with the activator. Translocation of the NADPH oxidase cytosolic components, p67(phox) and p47(phox), to the membrane was unaffected by DEPC. In a cell-free system, DEPC-treated membranes failed to support superoxide generation or the reduction of Iodonitrotetrazolium Violet and showed a loss of the characteristic cytochrome b(558) spectrum. Superoxide generation by DEPC-treated cytosol was inhibited slightly. Therefore it can be concluded that there are two sites within the NADPH oxidase that interact with DEPC, one in the H(+) pathway, only accessible in the activated oxidase, and a second accessible prior to activation of the NADPH oxidase. The latter non-proton pathway DEPC site is located within the membrane components of the NADPH oxidase and is associated with the binding of haem in the enzyme complex.

Identifying and characterizing one-time and never users of mammography screening services among medicare eligible women

BACKGROUND

Despite eligibility for a screening mammogram once every 2 years from 1991 to 1997, only a small percentage of Medicare women utilized this benefit. We examined mammography use among 388,707 North Carolina Medicare women from 1994 to 1997 to identify characteristics of one-time and never users of mammography.

METHODS

Data were obtained from North Carolina Medicare mammography claims and enrollment files from 1994 to 1997. Women ages 65+ as of 01/01/1994, continuously enrolled in Medicare from 1994 to 1997, and alive as of 12/31/1997 were included in the sample (n = 388,707). Mammogram use was categorized as never, once, or at least twice during 1994/1995 and 1996/1997. Women with at least one mammography claim during 1994/1995 and at least one mammography claim during 1996/1997 were called repeat users, women with one mammography claim during the 4 years were labeled one-time users, and women with zero mammography claims during the 4 years were termed never users. Multivariate logistic regression analyses were conducted to determine associations between characteristics and mammography frequency.

RESULTS

Biennial mammography claims data rates were 35.3% in 1994/1995 and 41.8% in 1996/1997. Compared with all other users, one-time users (n = 108,899) were more likely to be ages 65-74 (vs 75-84 and 85+), live in an urban versus rural county, and be eligible for Medicare only versus Medicare and Medicaid. Never users (n = 184,545) were more likely to be ages 85+, be non-Caucasian, live in a rural county, and be eligible for both Medicare and Medicaid versus Medicare.

CONCLUSIONS

These results demonstrate different demographic characteristics for one-time and never mammography users. This approach of using multiple years of claims data to segment the targeted population provides the opportunity to tailor interventions to subgroups.

NADPH oxidase subunit gp91phox: a proton pathway

The generation of superoxide by the NADPH oxidase is an electrogenic process resulting in a rapid depolarisation of the membrane potential of the cell. The efflux of H+ ions through an arachidonate-activatable, Zn(2+)-inhibitable H+ pathway accompanies the efflux of electrons and provides the necessary charge compensation. Inhibition of H+ flux leads to inhibition of superoxide generation. The protein gp91phox, a transmembrane component of the NADPH oxidase, was demonstrated to be capable of acting as the NADPH oxidase-associated H+ channel in a stable CHO cell line, CHO91. The N-terminal 230 amino acids contain all that is required for the protein to form an H+ channel and specifically histidine 115 is important to the ability of gp91phox to conduct H+ ions. The recording of outward currents from CHO91 cells, in the whole-cell configuration, demonstrated that gp91phox is also capable of functioning as a voltage-gated H+ conductance pathway. The similarity in properties between voltage-elicited outward currents, from both wild type and the mutations, and the arachidonate-activated H+ flux strongly suggests that these H+ pathways are one in the same. Among the recently identified homologues of gp91phox only NOH-1S has so far been demonstrated to also act as an H+ conductance pathway.

Surface electrode somatosensory-evoked potentials in spinal surgery: implications for indications and practice

STUDY DESIGN

A retrospective study of 442 major spinal operations with spinal cord monitoring performed in a University Hospital between 1982 and 1992 was performed.

OBJECTIVES

To assess the reliability of the authors' method for monitoring by somatosensory-evoked potential recording, to determine criteria for intraoperative corrective action, and to redefine the need for the wake-up test.

SUMMARY OF BACKGROUND DATA

The routine use of somatosensory-evoked potential monitoring in spinal surgery remains controversial. In Nottingham, the authors have used a method of recording from either scalp or high cervical electrodes.

METHODS

The recordings and outcomes of all monitored spinal operations between the years 1982 and 1992 were reviewed.

RESULTS

In 442 procedures, 23 technical failures (no reliable monitoring) occurred. Most technical failures were in patients with severe preoperative neurology, identifiable by somatosensory-evoked potential recording before operation. In the remaining 419 procedures, a significant intraoperative change in response occurred in 70 procedures (16.7%). Using the definitions of the American EEG Society, the authors identified 10 true-positives and 60 false-positives. There were no false-negatives. A wake-up test was performed if an amplitude drop greater than 50% from baseline value persisted after attempts to correct any possible identifiable intraoperative cause. This occurred in only 21 patients (5%). In the true-positive group, somatosensory-evoked potential recordings remained persistently abnormal despite an apparently normal subsequent wake-up test. The sensitivity of the method according to current definitions was 100% and the specificity 85.33%.

CONCLUSIONS

Modified guidelines are needed for routine intraoperative use of somatosensory-evoked potential monitoring in spinal surgery. Such guidelines should avoid the term "false-positive" as currently defined and concentrate on the causative analysis of abnormal responses that warn of critical spinal cord dysfunction before that becomes irreversible and allow for appropriate action. Information from this monitoring method alerted the surgeon to the possible need for corrective action in an additional 9.78% of the reported patients, who traditionally would have been regarded as false-positives. A wake-up test still is indicated in patients with persistent suppression of their somatosensory-evoked potential despite correction of any identifiable cause and in cases of technical failure. The current method proved flexible, versatile, and reliable for future use.

Considerations on photochemical genotoxicity: report of the International Workshop on Genotoxicity Test Procedures Working Group

Recent toxicological observations have caused concern regarding the need to test, for example, pharmaceuticals and cosmetic products for photochemical genotoxicity. The objective of this report is to give assistance on how to adapt existing test methods to investigate the potential of light-absorbing compounds to induce genotoxic effects on photoactivation. In general, the Organization for Economic Co-Operation & Economic Development (OECD) draft guideline on in vitro phototoxicity testing served as a basis for consideration. Concomitant exposure of the cells to the test compound and solar simulated light was considered appropriate as the initial, basic test condition. Optimization of the exposure scheme, e.g., a change of the irradiation spectrum, might be indicated depending on the initial test results. Selection of test compound concentrations should be based on results obtained with the dark version of the respective test system but might have to be modified if phototoxic effects are observed. Selection of the irradiation dose has to be performed individually for each test system based on dose-effect studies. The irradiation should induce per se a small, reproducible toxic or genotoxic effect. The report includes a specification of necessary controls, discusses factors that might have an impact on the irradiation characteristics, and gives a rationale for the omission of an external metabolic activation system. It also addresses the question that physicochemical and pharmacokinetic properties might trigger the need to test a chemical for photochemical genotoxicity. Relevant experimental observations are presented to back up the recommendations. The working group did not reach a consensus as to whether a single, adequately perfomed in vitro test for clastogenicity would be sufficient to exclude a photogenotoxic liability or whether a test battery including a gene mutation assay would be needed for product safety testing regarding photochemical genotoxicity.

Evidence that the product of the human X-linked CGD gene, gp91-phox, is a voltage-gated H(+) pathway

Expression of gp91-phox in Chinese hamster ovary (CHO91) cells is correlated with the presence of a voltage-gated H(+) conductance. As one component of NADPH oxidase in neutrophils, gp91-phox is responsible for catalyzing the production of superoxide (O(2).(2)). Suspensions of CHO91 cells exhibit arachidonate-activatable H(+) fluxes (Henderson, L.M., G. Banting, and J.B. Chappell. 1995. J. Biol. Chem. 270:5909-5916) and we now characterize the electrical properties of the pathway. Voltage-gated currents were recorded from CHO91 cells using the whole-cell configuration of the patch-clamp technique under conditions designed to exclude a contribution from ions other than H(+). As in other voltage-gated proton currents (Byerly, L., R. Meech, and W. Moody. 1984. J. Physiol. 351:199-216; DeCoursey, T.E., and V.V. Cherny. 1993. Biophys. J. 65:1590-1598), a lowered external pH (pH(o)) shifted activation to more positive voltages and caused the tail current reversal potential to shift in the manner predicted by the Nernst equation. The outward currents were also reversibly inhibited by 200 microM zinc. Voltage-gated currents were not present immediately upon perforating the cell membrane, but showed a progressive increase over the first 10-20 min of the recording period. This time course was consistent with a gradual shift in activation to more negative potentials as the pipette solution, pH 6.5, equilibrated with the cell contents (reported by Lucifer yellow included in the patch pipette). Use of the pH-sensitive dye 2'7' bis-(2-carboxyethyl)-5(and 6) carboxyfluorescein (BCECF) suggested that the final intracellular pH (pH(i)) was approximately 6.9, as though pH(i) was largely determined by endogenous cellular regulation. Arachidonate (20 microM) increased the amplitude of the currents by shifting activation to more negative voltages and by increasing the maximally available conductance. Changes in external Cl(-) concentration had no effect on either the time scale or the appearance of the currents. Examination of whole cell currents from cells expressing mutated versions of gp91-phox suggest that: (a) voltage as well as arachidonate sensitivity was retained by cells with only the NH(2)-terminal 230 amino acids, (b) histidine residues at positions 111, 115, and 119 on a putative membrane-spanning helical region of the protein contribute to H(+) permeation, (c) histidine residues at positions 111 and 119 may contribute to voltage gating, (d) the histidine residue at position 115 is functionally important for H(+) selectivity. Mechanisms of H(+) permeation through gp91-phox include the possible protonation/deprotonation of His-115 as it is exposed alternatively to the interior and exterior faces of the cell membrane (see Starace, D.M., E. Stefani, and F. Bezanilla. 1997. Neuron. 19:1319-1327) and the transfer of protons across an "H-X-X-X-H-X-X-X-H" motif lining a conducting pore.

Role of histidines identified by mutagenesis in the NADPH oxidase-associated H+ channel

The efflux of protons through a H+ channel acts as the charge compensation pathway for the electrogenic generation of superoxide (O-2) by human neutrophil NADPH oxidase. It has previously been shown that the N-terminal 230 amino acids of the product of the X-linked chronic granulomatous gene gp91(phox) contain all that is required for it to function as the arachidonate-activable, NADPH oxidase-associated H+ channel (Henderson, L. M., Thomas, S., Banting, G., and Chappell, J. B. (1997) Biochem. J. 325, 701-705). To identify functionally important amino acids, Chinese hamster ovary (CHO) cell lines were constructed that expressed point mutations in the N terminus of gp91(phox). No H+ flux was observed in CHO cell lines expressing the N-terminal gp91(phox) mutants H111L, H115L, and H119L, or H115L, or H115K. Partial retention of H+ channel function was, however, observed in the H115D CHO cell line. The addition of arachidonic acid to R91E,R92E CHO cells elicited a full H+ channel response. The buffering capacity and response of 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein to H+ were the same in all cell lines. Therefore, it can be concluded that His-115 is important to the ability of gp91(phox) to function as the NADPH oxidase-associated H+ channel and that the mechanism of H+ conduction involves protonation and deprotonation of an amino acid with an appropriate pK value.

Proton and chloride currents in Chinese hamster ovary cells

Proton and anion conductances were studied in Chinese hamster ovary (CHO) cells using tight-seal whole-cell recording. The pipette solution contained tetramethylammonium, TMA+, methanesulfonate, MeSO3-, highly buffered to pH 5.5. An outwardly rectifying anion conductance was observed in nearly all cells, with a relative permeability of MeSO3- < or = 0.5 that of Cl-. The anion conductance was small immediately after establishing whole-cell configuration, increased rapidly to a maximum at approximately 5 min, and then decreased more slowly to a small value over tens of minutes. A small voltage-activated H+ selective conductance was observed in most cells. H+ currents were studied after the Cl- conductance has subsided. The average H+ current at +40 mV at pHo 7.0 was 1.6 pA/pF. This H+ conductance was activated by membrane depolarization and enhanced at high pHo, and exhibited activation and deactivation kinetics comparable with H+ currents in other mammalian cells.

Aneuploidy: a report of an ECETOC task force

Aneuploidy plays a significant role in adverse human health conditions including birth defects, pregnancy wastage and cancer. Although there is clear evidence of chemically induced aneuploidy in experimental systems, to date there are insufficient data to determine with certainty if chemically induced aneuploidy contributes to human disease. However, since there is no reason to assume that chemically induced aneuploidy will not occur in human beings, it is prudent to address the aneugenic potential of chemicals in the safety assessment process. A wide range of methods has been described for the detection of chemically induced aneuploidy including subcellular systems, tests with fungi, plants and Drosophila as well as in vitro mammalian systems and in vivo mammalian somatic and germ cell assays. However, none of these methods is sufficiently validated or widely used in routine screening. Underlying the efforts to develop aneuploidy-specific assays is the presumption that current genetic toxicology tests do not detected chemicals that have aneuploidy-inducing potential. To address this, we have critically evaluated data from standard genetic toxicology assays for 16 known or suspected aneugens. The conclusions from the review are listed below. 1. At present there are only nine chemicals that can be classified as definitive aneugens, as determined by positive results in in vivo rodent assays. 2. As expected, the majority of definitive and suspected aneugens are negative in the bacterial mutation assay. 3. The majority of definitive aneugens evaluated induce polyploidy in vitro. With few exception, they also induced structural chromosome aberrations in vitro. 4. All of the definitive aneugens that have been sufficiently tested induce micronuclei in rodent bone marrow cells in vivo. A number of these chemicals also induced structural chromosome aberrations in vivo. 5. There is no evidence for a unique germ cell aneugen, that is a chemical that induces aneuploidy in germ cells and not in somatic cells. Furthermore, an analysis of several databases indicates the proportion of chemicals which induce polyploidy and not chromosome aberrations in vitro is low. Based on these conclusions, the following recommendations are made: for screening purposes, a standard genotoxicity test battery (including an in vitro cytogenetic assay with an assessment of polyploidy and clastogenicity at the same harvest time) should be performed; in the absence of polyploidy induction in vitro no further evaluation of aneuploidy-inducing potential is needed; if polyploidy is observed, in vitro follow-up testing to investigate further the aneuploidy-inducing potential should be conducted; such follow-up testing will generally start with the conduct of a standard in vivo somatic cell micronucleus assay; if the in vivo somatic cell micronucleus assay is negative, with adequate evidence of exposure of the bone marrow to the test compound, no further testing of aneuploidy-inducing potential is needed; if the in vivo somatic cell micronucleus assay is positive, further information on mechanisms of micronucleus induction can be obtained by using kinetochore/centromeric staining in vitro and/or in vivo; an assessment of potential germ cell aneuploidy activity may then be considered; aneuploidy induction which does not involve the direct interaction of a chemical or its metabolite(s) with DNA is expected to have a threshold. This must be considered in the risk assessment of such chemicals; this is not addressed by current risk assessment guidelines.

The arachidonate-activatable, NADPH oxidase-associated H+ channel is contained within the multi-membrane-spanning N-terminal region of gp91-phox

The generation of superoxide by the NADPH oxidase of neutrophils is accompanied by the efflux of H+ ions through a H+ channel. gp91-phox, a protein component of the oxidase, has been shown previously to function as a H+ channel [Henderson, Banting and Chappell (1995) J. Biol. Chem. 270, 5909-5916]. We have constructed a CHO cell line (CHO-N) that expresses an N-terminal fragment of gp91-phox containing the predicted multiple transmembrane domains of the protein. These cells exhibit H+ fluxes in response to an imposed proton motive force and in the presence of arachidonate (to open the channel). The H+ fluxes were indistinguishable from those observed in cells expressing full-length gp91-phox. Therefore the N-terminal 230 amino acids of gp91-phox contain all that is required to function as the NADPH oxidase-associated H+ channel.