Ethanol pharmacokinetics in white women: nonlinear model fitting versus zero-order elimination analyses

BACKGROUND

Studies have shown repeatedly that ethanol pharmacokinetics are not linear, yet most researchers still determine ethanol elimination by linear, zero-order kinetics. The goals of the present work were to: (1) fit four nonlinear pharmacokinetic models to mean breath alcohol concentration (BrAC)-time data of 27 women and determine the best-fit model; (2) fit the determined best-fit model to individual BrAC data and estimate the pharmacokinetic parameters; and (3) compare the method of nonlinear model fitting with the classical zero-order elimination method and determine in which cases the classical approach is justified.

METHODS

Twenty-seven healthy white women ingested four drinks (total of 0.67 g x kg(-1)) of ethanol on two test days. Approximately 24 breath ethanol samples (for pharmacokinetic analyses) and one blood sample (for hormonal markers) were taken per day. Pharmacokinetic model evaluation was based on the coefficient of variation, the weighted residual sum of squares, and the sequence of the weighted residuals. Because hormonal changes across the menstrual cycle did not significantly influence ethanol pharmacokinetics, data from the two test days were pooled.

RESULTS

The best-fit model was a one-compartment open model with first-order absorption and sequential first-order elimination, followed by Michaelis-Menten elimination kinetics. Fitting this model to the individual BrAC data yielded mean ka = 0.062 hr(-1), Vd = 0.457 L x kg(-1), ke = 0.011 hr(-1), Vmax = 0.136 g x L(-1) x hr(-1), and Km = 0.096 g x L(-1). For the classical analyses, mean time to peak BrAC = 1.83 hr, disappearance rate = 0.179 g x L(-1) x hr(-1), and area under the blood ethanol-time curve (AUC) = 2.884 g x L(-1) x hr. Correlational analyses showed that more frequent drinkers eliminated ethanol significantly faster and reached significantly lower AUC than less frequent drinkers.

CONCLUSIONS

After multiple dose ingestion in white women, classical zero-order elimination analyses can be applied only to a limited portion of the descending BrAC-time curve. They seem justified and practical from 0.5 hr after peak BrAC until BrAC reaches 0.2 g x L(-1). To describe ethanol pharmacokinetics across the entire BrAC-time curve, however, sophisticated nonlinear model fitting is required.

Interferon coordinately inhibits the disruption of PML-positive ND10 and immediate-early gene expression by herpes simplex virus

Interferons (IFNs) are important components of the innate immune response, limiting herpes simplex virus (HSV) infection. In recombinant HSV-infected cells, IFN inhibited expression of beta-galactosidase from the immediate-early gene, ICP4, promoter. The extent of inhibition was dependent on IFN dose, IFN type, cell type, and multiplicity of infection (moi). IFN inhibited gene transcription, leading to a complete block in ICP4 promoter-driven gene expression in 90% of cells. The same IFN treatments resulted in an increase in the size and number of nuclear domain 10 (ND10) structures that stained positive by immunofluorescence for the promyelocytic leukemia (PML) protein. In cultures infected at low moi with a recombinant HSV producing ICP4 as a fusion protein with green fluorescence protein, the appearance of green fluorescence in the nucleus coincided with loss of PML-positive ND10 in the same nucleus, even in the rare ICP4-expressing IFN-treated cells. IFN-dependent inhibition was nearly complete when the immediate-early promoter was in the viral genome but was minimal when the promoter was stably integrated into the cellular genome. These data reveal that IFN can completely block viral gene expression in infected cells and that enhancement of the ND10 structure, which is the site of initiation of HSV replication, correlates with the block in viral gene expression.

Plant part substitution--a way to conserve endangered medicinal plants?

Population growth, urbanization and the unrestricted collection of medicinal plants from the wild is resulting in an over-exploitation of natural resources in southern Africa. Therefore, the management of traditional medicinal plant resources has become a matter of urgency. In southern Africa the most frequently used medicinal plants are slow-growing forest trees, bulbous and tuberous plants, with bark and underground parts being the parts mainly utilized. A strategy which would satisfy the requirements of sustainable harvesting, yet simultaneously provide for primary health care needs, would be the substitution of bark or underground parts with leaves of the same plant. This paper outlines the concept of plant substitution, using preliminary results of our recent investigations into four of the most important and most threatened South African medicinal plants - Eucomis autumnalis (bulb), Siphonochilus aethiopicus (rhizome), Ocotea bullata (bark), and Warburgia salutaris (bark) - as a demonstration of the kind of research necessary. Extracts of various plant parts were compared chemically using TLC-analysis, and pharmacologically in terms of antibacterial activity and cyclooxygenase-1 inhibition in vitro. The importance of the concept of plant part substitution as a strategy for the conservation of medicinal plants in southern Africa is discussed in terms of the results obtained.

Supraspinal fatigue during intermittent maximal voluntary contractions of the human elbow flexors

Responses to transcranial magnetic stimulation in human subjects (n = 9) were studied during series of intermittent isometric maximal voluntary contractions (MVCs) of the elbow. Stimuli were given during MVCs in four fatigue protocols with different duty cycles. As maximal voluntary torque fell during each protocol, the torque increment evoked by cortical stimulation increased from approximately 1.5 to 7% of ongoing torque. Thus "supraspinal" fatigue developed in each protocol. The motor evoked potential (MEP) and silent period in the elbow flexor muscles also changed. The silent period lengthened by 20-75 ms (lowest to highest duty cycle protocol) and recovered significantly with a 5-s rest. The MEP increased in area by >50% in all protocols and recovered significantly with 10 s, but not 5 s, of rest. These changes are similar to those during sustained MVC. The central fatigue demonstrated by the torque increments evoked by the stimuli did not parallel the changes in the electromyogram responses. This suggests that part of the fatigue developed during intermittent exercise is "upstream" of the motor cortex.

Ischaemia after exercise does not reduce responses of human motoneurones to cortical or corticospinal tract stimulation

Motor unit firing rates and voluntary activation of muscle decline during sustained isometric contractions. After exercise, the responses to motor cortical and corticospinal stimulation are reduced. These changes may reflect motoneuronal inhibition mediated by group III and IV muscle afferents. To determine whether the post-contraction depression of the responses to corticospinal or motor cortical stimulation could be maintained by continued firing of ischaemically sensitive group III and IV muscle afferents, we examined responses in muscles that were held ischaemic after exercise. Following a sustained maximal voluntary contraction (MVC) of the elbow flexors lasting 2 min, the response to stimulation of the corticospinal tract was reduced but the usual recovery (over approximately 2 min) was not delayed when the muscles were maintained ischaemic for 2 min after the contraction. Following a sustained MVC, the time course of the reduction in the response to motor cortical stimulation (a gradual decrease over approximately 2 min, maintained for > 10 min) was also not altered if the muscle was held ischaemic. Mean arterial blood pressure rose to 155 +/- 12 mmHg during the 2 min MVC, declined to 125 +/- 9 mmHg immediately after it, but remained at this level without returning to pre-exercise levels (102 +/- 10 mmHg) until circulation to the arm was restored. This confirms that the sustained MVC activated a reflex dependent on group III and IV muscle afferents. This study shows that ischaemically sensitive group III and IV muscle afferents do not mediate depression of responses to motor cortical or corticospinal stimulation after fatiguing exercise. It also suggests that firing of such afferents does not directly inhibit motoneurones or motor cortical output cells.

Relationship of CogScreen-AE to flight simulator performance and pilot age

OBJECTIVES

We report on the relationship between CogScreen-Aeromedical Edition (AE) factor scores and flight simulator performance in aircraft pilots aged 50-69.

METHODS

Some 100 licensed, civilian aviators (average age 58+/-5.3 yr) performed aviation tasks in a Frasca model 141 flight simulator and the CogScreen-AE battery. The aviation performance indices were: a) staying on course; b) dialing in communication frequencies; c) avoiding conflicting traffic; d) monitoring cockpit instruments; e) executing the approach; and f) a summary score, which was the mean of these scores. The CogScreen predictors were based on a factor structure reported by Kay (11), which comprised 28 CogScreen scores. Through principal components analysis of Kay's nine factors, we reduced the number of predictors to five composite CogScreen scores: Speed/Working Memory (WM), Visual Associative Memory, Motor Coordination, Tracking, and Attribute Identification.

RESULTS

Speed/WM scores had the highest correlation with the flight summary score, Spearman r(rho) = 0.57. A stepwise-forward multiple regression analysis indicated that four CogScreen variables could explain 45% of the variance in flight summary scores. Significant predictors, in order of entry, were: Speed/WM, Visual Associative Memory, Motor Coordination, and Tracking (p<0.05). Pilot age was found to significantly improve prediction beyond that which could be predicted by the four cognitive variables. In addition, there was some evidence for specific ability relationships between certain flight component scores and CogScreen scores, such as approach performance and tracking errors.

CONCLUSIONS

These data support the validity of CogScreen-AE as a cognitive battery that taps skills relevant to piloting.

Transcranial magnetic stimulation (TMS) in controlled treatment studies: are some "sham" forms active?

BACKGROUND

Carefully designed controlled studies are essential in further evaluating the therapeutic efficacy of transcranial magnetic stimulation (TMS) in psychiatric disorders. A major methodological concern is the design of the "sham" control for TMS. An ideal sham would produce negligible cortical stimulation in conjunction with a scalp sensation akin to real treatment. Strategies employed so far include alterations in the position of the stimulating coil, but there has been little systematic study of their validity. In this study, we investigated the effects of different coil positions on cortical activation and scalp sensation.

METHODS

In nine normal subjects, single TMS pulses were administered at a range of intensities with a "figure eight" coil held in various positions over the left primary motor cortex. Responses were measured as motor-evoked potentials in the right first dorsal interosseus muscle. Scalp sensation to TMS with the coil in various positions over the prefrontal area was also assessed.

RESULTS

None of the coil positions studied met the criteria for an ideal sham. Arrangements associated with a higher likelihood of scalp sensation were also more likely to stimulate the cortex.

CONCLUSIONS

The choice of a sham for TMS involves a trade-off between effective blinding and truly inactive "stimulation." Further research is needed to develop the best sham condition for a range of applications.

How can we learn about developmental processes from cross-sectional studies, or can we?

OBJECTIVE

Cross-sectional studies are often used in psychiatric research as a basis of longitudinal inferences about developmental or disease processes. While the limitations of such usage are often acknowledged, these are often understated. The authors describe how such inferences are often, and sometimes seriously, misleading.

METHOD

Why and how these inferences mislead are here demonstrated on an intuitive level, by using simulated data inspired by real problems in psychiatric research.

RESULTS

Four factors with major roles in the relationship between cross-sectional studies and longitudinal inferences are selection of time scale, type of developmental process studied, reliability of measurement, and clarity of terminology. The authors suggest how to recognize inferential errors when they occur, describe how to protect against such errors in future research, and delineate the circumstances in which only longitudinal studies can answer crucial questions.

CONCLUSIONS

The simple conclusion is that one must always use the results of cross-sectional studies to draw inferences about longitudinal processes with trepidation.

Impaired response of human motoneurones to corticospinal stimulation after voluntary exercise

1. Activation of descending corticospinal tracts with transmastoid electrical stimuli has been used to assess changes in the behaviour of motoneurones after voluntary contractions. Stimuli were delivered before and after maximal voluntary isometric contractions (MVCs) of the elbow flexor muscles. 2. Following a sustained MVC of the elbow flexors lasting 5-120 s there was an immediate reduction of the response to transmastoid stimulation to about half of the control value. The response recovered to control levels after about 2 min. This was evident even when the size of the responses was adjusted to accommodate changes in the maximal muscle action potential (assessed with supramaximal stimuli at the brachial plexus). 3. To determine whether the post-contraction depression required activity in descending motor paths, motoneurones were activated by supramaximal tetanic stimulation of the musculocutaneous nerve for 10 s. This did not depress the response to transmastoid stimulation. 4. Following a sustained MVC of 120 s duration, the response to transcranial magnetic stimulation of the motor cortex gradually declined to a minimal level by about 2 min and remained depressed for more than 10 min. 5. Additional studies were performed to check that the activation of descending tracts by transmastoid stimulation was likely to involve excitation of direct corticospinal paths. When magnetic cortical stimuli and transmastoid stimuli were timed appropriately, the response to magnetic cortical stimulation could be largely occluded. 6. This study describes a novel depression of effectiveness of corticospinal actions on human motoneurones. This depression may involve the corticomotoneuronal synapse.

Phomalairdenone: a new host-selective phytotoxin from a virulent type of the blackleg fungus Phoma lingam

The chemical structure and bioactivity of phomalairdenone (7), a new sesquiterpenic host-selective phytotoxin produced by an unusual virulent type isolate of the blackleg fungus [Phoma lingam, perfect stage Leptosphaeria maculans (Desm.) Ces. et de Not.] are reported.

Assessing depressive symptoms in multiple sclerosis: is it necessary to omit items from the original Beck Depression Inventory?

Overlap between depression scale item content and medical symptoms may exaggerate depression estimates for patients with multiple sclerosis (MS). We reconsider Mohr and co-workers' (1997) recommendation to omit Beck Depression Inventory (BDI) items assessing work ability (item 15), fatigue (17), and health concerns (20) for MS patients. Subjects were medical patients with either MS (n = 105) or a medical disorder for which the BDI is empirically supported [diabetes mellitus (DM), n = 71; chronic pain (CP), n = 80], psychiatric patients with depressive disorder (MDD; n = 37), and healthy controls (HC; n = 80). Relative scores for the eight "somatic" BDI items were analyzed by multivariate analysis of variance with demographic variables and BDI total as covariates. The only significant difference was MS > HC (item 15). On raw scores, MS patients exceeded HCs on items 15 and 21 (sexual disinterest), but this was attributable to the low HC item endorsement. There were no other differences on somatic items or item-total correlations. Scale consistency was good across groups, regardless of item omission. Somatic items were unassociated with major MS parameters. We thus encourage continued application of the full BDI for assessing depressive symptoms in patients with MS.

Altered responses of human elbow flexors to peripheral-nerve and cortical stimulation during a sustained maximal voluntary contraction

The short-latency electromyographic response evoked by transcranial magnetic stimulation (MEP) increases in size during fatigue, but the mechanisms are unclear. Because large changes occur in the muscle action potential, we tested whether changes in the response to stimulation of the peripheral motor nerve could fully account for the increase in the MEP. Subjects (n=8) performed sustained maximal voluntary contractions (MVCs) of the right elbow flexors for 2 min. During the contraction, the MEP and the response to supramaximal stimulation of motor-nerve fibres in the brachial plexus were alternately recorded. During the contraction, responses to motor-nerve stimulation increased in area by 87+/-35% (mean+/-SD) in the biceps brachii and 74+/-30% in the brachioradialis, but the area of the MEPs increased by 153+/-86% and 175+/-122%, respectively. Thus, the increase in the MEP was greater than the increase in the peripheral M-wave. The onset latency of the MEP in the biceps brachii increased by 0.7+/-0.6 ms (range: -0.2 to 1.9 ms) during the sustained contraction. A smaller increase occurred in response to peripheral nerve stimulation (0.3+/-0.3 ms; from -0.3 to 0.9 ms). In the contralateral elbow flexors, neither responses to transcranial magnetic stimulation nor responses to motor-nerve stimulation changed in size or latency. During the sustained contraction, the short silent period after stimulation of the peripheral nerve (48+/-5 ms in biceps brachii and 48+/-4 ms in brachioradialis) increased in duration by about 12 ms (to 61+/-12 ms and 60+/-9 ms, respectively), whereas the silent period following transcranial magnetic stimulation increased from 238+/-39 ms in biceps brachii and 243+/-34 ms in brachioradialis to 325+/-41 ms and 343+/-42 ms, respectively. During a sustained MVC, while the motor responses to peripheral and to cortical stimulation grow concurrently, growth of the MEP cannot be entirely accounted for by changes in the muscle action potential. Hence, some of the increase in MEP size during fatigue must reflect changes in the central nervous system. Increased latency of the MEPs and lengthening of the peripherally evoked silent period are consistent with decreased excitability of the alpha motoneurone pool. Thus, an increased response from the motor cortex to the magnetic stimulus remains a likely contributor to the increase in the size of the MEP in fatigue.

Relationship of age and simulated flight performance

OBJECTIVE

To determine the relationship between age and aviator performance on a flight simulator.

DESIGN

A cross-sectional observational study.

PARTICIPANTS

The sample consisted of 100 aviators aged 50 to 69 (mean = 58).

MAIN OUTCOME MEASURES

Pilots were tested on a Frasca 141 flight simulator (Urbana, IL), linked to a UNIX-based IRIS 4D computer (Silicon Graphics, Mountain View, CA), which both generated graphics of the environment in which the pilots flew and collected data concerning the aircraft's flight conditions.

RESULTS

We found that increased age was significantly associated with decreased aviator performance on a flight simulator.

CONCLUSIONS

Although there was a significant relationship between increased age and decreased aviator performance, age explained 22% or less of the variance of performance on different flight tasks; hence, other factors are also important in explaining the performance of older pilots.

Probabilistic sensitivity analysis incorporating the bootstrap: an example comparing treatments for the eradication of Helicobacter pylori

Decision-analytic models are frequently used to evaluate the relative costs and benefits of alternative therapeutic strategies for health care. Various types of sensitivity analysis are used to evaluate the uncertainty inherent in the models. Although probabilistic sensitivity analysis is more difficult theoretically and computationally, the results can be much more powerful and useful than deterministic sensitivity analysis. The authors show how a Monte Carlo simulation can be implemented using standard software to perform a probabilistic sensitivity analysis incorporating the bootstrap. The method is applied to a decision-analytic model evaluating the cost-effectiveness of Helicobacter pylori eradication. The necessary steps are straightforward and are described in detail. The use of the bootstrap avoids certain difficulties encountered with theoretical distributions. The probabilistic sensitivity analysis provided insights into the decision-analytic model beyond the traditional base-case and deterministic sensitivity analyses and should become the standard method for assessing sensitivity.

Effects of galvanic vestibular stimulation during human walking

1. To identify vestibular influences on human walking, galvanic vestibular stimulation was applied to normal adult subjects as they walked to a previously seen target. A transmastoidal step stimulus commenced as subjects started walking. With the eyes shut, the galvanic stimulus caused large turns towards the side with the anodal current. 2. Ability to perceive the trajectory of gait without visual cues was measured by guiding blindfolded subjects from one arbitrary point to another, either walking or seated in a wheelchair. On reaching a destination position and removing the blindfold, subjects pointed to indicate the starting position. Subjects made considerable errors in estimating the trajectory, but were equally accurate whether in the wheelchair or walking. 3. To determine the effects of vestibular stimulation on the perception of trajectory, the galvanic stimulus was applied to blindfolded subjects as they were guided from one point to another in the wheelchair. The vestibular stimulus produced an illusory shift in the trajectory travelled. This shift was towards the side with the cathode, i.e. in the opposite direction to the turn produced by the stimulus during walking. 4. We conclude that galvanic vestibular stimulation during walking causes subjects to turn from their planned trajectory. In part, this altered course may compensate for an altered perception of trajectory produced by the stimulus. However, altered perception of the vertical or the base of support, or direct vestibulo-fugal influences on the leg muscles could contribute to the changes in gait.

Synergistic anti-varicella-zoster virus activity of interferon-alpha 2a and acyclovir in corneal cells

Human corneal stromal (HCS) cells in cultures established from donor corneas can serve as host cells for replication of varicella-zoster virus (VZV). Comparative infectious centers assays suggest that HCS cells are more restrictive hosts than MRC-5 cells, a line of human embryonic lung fibroblasts, commonly used for VZV isolation. VZV propagated in MRC-5 cells was infectious for both MRC-5 and HCS cells, but titers in HCS were one fifth of those in MRC-5 cells. Inhibition of VZV replication in HCS cells by acyclovir (ACV), recombinant human interferon-alpha 2a (IFN-alpha 2a), or the combination of these two antivirals was detected by both an infectious centers-plaque-reduction assay and an ELISA method using monoclonal anti-VZV antibody. In the infectious centers-plaque-reduction assay combinations of ACV with IFN-alpha 2a showed synergistic anti-VZV activity. VZV protein synthesis, as detected by the ELISA, was a less sensitive measure of the antiviral effects producing an ED50 value of 50 microM for ACV, five to ten times the ED50 determined in the plaque reduction assay. In the ELISA, high titers of IFN-alpha 2a (2000 IU/ml) decreased virus antigen expression only slightly, while combinations of ACV and IFN-alpha 2a were synergistic in their detected anti-VZV activity. These data document the replication of VZV in HCS cells and demonstrate that VZV is sensitive to the synergistic antiviral action of combinations of IFN-alpha 2a and ACV.

Effects of menstrual cycle and female sex steroids on ethanol pharmacokinetics

This study investigated the influence of menstrual cycle and female sex steroid levels on ethanol pharmacokinetics. In a within-subjects design, 24 female volunteers each consumed 0.67 g x kg(-1) ethanol during the menstrual and luteal phases of their menstrual cycle. On each test day, we collected blood samples before ethanol administration to determine estradiol (E2) and progesterone (P) levels and to confirm ovulation. We took 20 or more postdrink breath ethanol concentration readings and examined pharmacokinetic differences between the two phases, using classical pharmacokinetic measures, as well as Michaelis-Menten measures. Despite highly significant differences in measured E2 as well as P levels on the 2 test days, and despite excluding subjects with anovulatory cycles from the analysis, there were no significant differences between menstrual and luteal phases for any of the pharmacokinetic variables. We found no correlation between E2 or P levels and any of the pharmacokinetic measures. In summary, we found no evidence that the tested menstrual cycle phases or varying E2 and progesterone levels significantly influence ethanol pharmacokinetics. Because previous studies about the topic have used few subjects and revealed controversial results, we consider our negative findings based on 24 subjects meaningful.

Gender differences in moderate drinking effects

Women appear to become more impaired than men after drinking equivalent amounts of alcohol, achieving higher blood alcohol concentrations even when doses are adjusted for body weight. This finding may be attributable in part to gender differences in total body water content. Men and women appear to eliminate approximately the same total amount of alcohol per unit body weight per hour. However, women seem to eliminate significantly more alcohol per unit of lean body mass per hour than men. Some studies report that women are more susceptible than men to alcohol-related impairment of cognitive performance, especially in tasks involving delayed memory or divided attention functions. Psychomotor performance impairment, however, does not appear to be affected by gender. This article provides an overview of alcohol metabolism (pharmacokinetics) and reviews recent studies on gender differences in alcohol absorption, distribution, elimination, and impairment. Speculation that gender differences in alcohol pharmacokinetics or alcohol-induced performance impairment may be caused by the menstrual cycle and variations in female sex hormones are discussed. It is concluded that the menstrual cycle is unlikely to influence alcohol pharmacokinetics.

Reduced excitability of the cortico-spinal system during the warning period of a reaction time task

Seven subjects made a wrist flexion movement as rapidly as possible in response to a cutaneous shock on the opposite hand. In some trials, an auditory warning signal was given 0.5 s beforehand. In random trials, transcranial magnetic stimulation (TMS) was used to elicit EMG responses (MEPs) in forearm flexor and extensor muscles 0-500 ms before the cutaneous shock. H-reflexes were elicited in flexor muscles at the same intervals. The warning stimulus reduced reaction time from about 400 ms to 200 ms. MEPs in the flexor muscles were significantly suppressed from 125 ms after the warning stimulus until the time of the cutaneous shock whilst MEPs in the extensors, and H-reflexes in the flexor were either unaffected, or reduced by a smaller amount at a later time. Responses in relaxed contralateral muscles were unchanged. If the task was changed to a choice reaction, in which the imperative stimulus (but not the warning signal) indicated whether to flex or extend the wrist, then there was no change in the MEPs or H-reflex in the warning period. A similar effect was seen if the duration of the warning period was extended from 0.5 to 2 s in a simple reaction (flexion) task. We conclude that increased excitability of the corticospinal output is not required to speed up reaction times. The time taken to discharge cortical output elements is relatively unimportant compared with the time needed to process the sensory input and link it to the motor output.

A novel bioassay for the determination of neutralizing antibodies to IFN-beta1b

We have adapted the new MxA gene-induction bioassay to measure neutralizing antibodies to interferon-beta1b (IFN-beta1b, the active ingredient in Betaseron) in sera from patients treated with Betaseron. This antibody assay has been validated to quantify neutralizing titers of 1:20 and above, with a precision of +/- 0.20 in log10. We have used this MxA gene-induction antibody assay to reinvestigate serum samples from multiple sclerosis (MS) patients treated with Betaseron. The titers measured were closely comparable to those obtained in antiviral assays. Data obtained by both methods show that neutralizing antibodies may appear and subsequently disappear over time in the sera of some patients treated with Betaseron. Sera from some patients contain binding antibodies to IFN-beta1b. It was shown that binding antibody titers do not correlate quantitatively or qualitatively with neutralizing antibody titers, and indeed, a number of patients develop high levels of binding antibodies but never form measurable levels of neutralizing antibodies.

Movement detection at the human big toe

1. To be detected, movements of the interphalangeal joint of the big toe must be greater than at other joints. This poor acuity may arise because the anatomy of the foot and ankle results in poor coupling between the toe and the muscles that operate it. To vary this coupling, the effect of ankle position on proprioceptive acuity at the toe was measured. 2. We measured proprioceptive acuity at the toe with the ankle in different positions and found that ankle plantarflexion did improve acuity. This implies that, with the ankle at mid-range or dorsiflexed, toe movement is inadequately transferred to muscle fascicles. 3. To determine actual changes in fascicle length of the toe extensor, movements of extensor hallucis longus near the toe and at the muscle-tendon junction were measured during surgical exposure in one subject. Ankle position greatly affected movement transfer from toe to muscle-tendon junction: no tendon movement was transferred with the ankle dorsiflexed, but all movement was transferred with the ankle plantarflexed. 4. When the relationship between joint rotation and muscle fascicle length measured in vivo was used to express the smallest detectable movements of the toe as proportional changes in muscle fascicle length, these detectable changes were similar to those at all other limb joints. This suggests that change in muscle fascicle length is of major interest to the nervous system.

Influence of nicotine on simulator flight performance in non-smokers

In a placebo-controlled study, we investigated the influence of nicotine on late-day aviation performance in 15 non-smoking subjects. In a within-subjects design, subjects were tested on 2 days, each lasting 8 h and consisting of three 75-min simulator flights (late-afternoon practice, evening test, night test). Prior to each test, subjects received either nicotine polacrilex 2 mg or placebo gum. As expected, overall performance was significantly better after nicotine, compared to placebo (P < 0.01). Post-hoc analysis of individual flight tasks showed that nicotine improved scores on approach to landing, a task which appears to require sustained attention. We conclude that nicotine may improve late-day flight performance in non-smoking aviators.

The stages of Alzheimer's disease: a reappraisal

'Stages', as used in clinical practice and research, are defined, their value described, and criteria are proposed for their evaluation. The specific interest is in staging Alzheimer's disease (AD). Two staging systems, one based on the Global Deterioration Scale (GDS) and one based on the Mini-Mental State Exam (MMSE), are compared in terms of these criteria, as an illustration of the process involved. We propose that there is not one unique staging system, that different staging criteria might be appropriate to different research or clinical needs, depending on which part of the temporal course of the disease is of primary interest, and on whether the focus is on cognitive, functional, neurological, behavioral, economic, or other issues. GDS staging seems a better choice for the later stages of AD when the focus is on functional change. MMSE staging seems a better choice for tracking the earlier stages of AD when the focus is on cognitive change.

Everyday problem solving among individuals with Alzheimer's disease

Loss of functioning on complex tasks of daily living is an early indicator of dementia. The performance of 65 older adults with mild to moderate levels of Alzheimer's disease was examined on the Everyday Problems Test for the Cognitively Challenged Elderly (EPCCE), self-report inventories of functional performance, and a broad battery of clinical and neuropsychological measures. The EPCCE was designed to assess older adults on a set of complex tasks of daily living that involved not only global cognitive processes, but also higher-order executive functions. Participants solved an average of 45% of EPCCE tasks with significant differences in scores by disease severity. Performance was significantly related to global cognitive functioning and disease severity, and in particular to executive functions. Significant additional variance was accounted for by these executive functions beyond the variance accounted for by global cognitive measures.