Non-invasive monitoring of cardiac contractility: Trans-radial electrical bioimpedance velocimetry (TREV)

We describe methods and software resources for a bioimpedance measurement technique, 'trans-radial electrical bioimpedance velocimetry' (TREV) that allows for the non-invasive monitoring of relative cardiac contractility and stroke volume. After reviewing the relationship between the measurement and cardiac contractility, we describe the general recording methodology, which requires impedance measurements of the forearm. We provide open-source Jupyter-based software (operable on most computers) for deriving cardiac contractility from the impedance measurements. The software includes tools for removing variance associated with heart rate and respiration. We demonstrate the ability of this bioimpedance measurement for tracking beat-to-beat changes of contractility in a maximal grip force production task. Critically, the results demonstrate both a reactive increase in contractility with force production, and suggest there is a learned increase in contractility prior to grip onset, consistent with anticipatory allostatic autonomic regulation mediated by sympathetic inotropy. The method and software should be of broad utility for investigations of event-related cardiac dynamics in psychophysical studies.

Eye movements disrupt EEG alpha-band coding of behaviorally relevant and irrelevant spatial locations held in working memory

Oscillations in the alpha frequency band (∼8-12 Hz) of the human electroencephalogram play an important role in supporting selective attention to visual items and maintaining their spatial locations in working memory (WM). Recent findings suggest that spatial information maintained in alpha is modulated by interruptions to continuous visual input, such that attention shifts, eye closure, and backward masking of the encoded item cause reconstructed representations of remembered locations to become degraded. Here, we investigated how another common visual disruption-eye movements-modulates reconstructions of behaviorally relevant and irrelevant item locations held in WM. Participants completed a delayed estimation task, where they encoded and recalled either the location or color of an object after a brief retention period. During retention, participants either fixated at the center or executed a sequence of eye movements. Electroencephalography (EEG) was recorded at the scalp and eye position was monitored with an eye tracker. Inverted encoding modeling (IEM) was applied to reconstruct location-selective responses across multiple frequency bands during encoding and retention. Location-selective responses were successfully reconstructed from alpha activity during retention where participants fixated at the center, but these reconstructions were disrupted during eye movements. Recall performance decreased during eye-movements conditions but remained largely intact, and further analyses revealed that under specific task conditions, it was possible to reconstruct retained location information from lower frequency bands (1-4 Hz) during eye movements. These results suggest that eye movements disrupt maintained spatial information in alpha in a manner consistent with other acute interruptions to continuous visual input, but this information may be represented in other frequency bands.NEW & NOTEWORTHY Neural oscillations in the alpha frequency band support selective attention to visual items and maintenance of their spatial locations in human working memory. Here, we investigate how eye movements disrupt representations of item locations held in working memory. Although it was not possible to recover item locations from alpha during eye movements, retained location information could be recovered from select lower frequency bands. This suggests that during eye movements, stored spatial information may be represented in other frequencies.

Habituation of the stress response multiplex to repeated cold pressor exposure

Humans show remarkable habituation to aversive events as reflected by changes of both subjective report and objective measures of stress. Although much experimental human research focuses on the effects of stress, relatively little is known about the cascade of physiological and neural responses that contribute to stress habituation. The cold pressor test (CPT) is a common method for inducing acute stress in human participants in the laboratory; however, there are gaps in our understanding of the global state changes resulting from this stress-induction technique and how these responses change over multiple exposures. Here, we measure the stress response to repeated CPT exposures using an extensive suite of physiologic measures and state-of-the-art analysis techniques. In two separate sessions on different days, participants underwent five 90 s CPT exposures of both feet and five warm water control exposures, while electrocardiography (ECG), impedance cardiography, continuous blood pressure, pupillometry, scalp electroencephalography (EEG), salivary cortisol and self-reported pain assessments were recorded. A diverse array of adaptive responses are reported that vary in their temporal dynamics within each exposure as well as habituation across repeated exposures. During cold-water exposure there was a cascade of changes across several cardiovascular measures (elevated heart rate (HR), cardiac output (CO) and Mean Arterial Pressure (MAP) and reduced left ventricular ejection time (LVET), stroke volume (SV) and high-frequency heart rate variability (HF)). Increased pupil dilation was observed, as was increased power in low-frequency bands (delta and theta) across frontal EEG electrode sites. Several cardiovascular measures also habituated over repeated cold-water exposures (HR, MAP, CO, SV, LVET) as did pupil dilation and alpha frequency activity across the scalp. Anticipation of cold water induced stress effects in the time-period immediately prior to exposure, indexed by increased pupil size and cortical disinhibition in the alpha and beta frequency bands across central scalp sites. These results provide comprehensive insight into the evolution of a diverse array of stress responses to an acute noxious stressor, and how these responses adaptively contribute to stress habituation.

Investigating Search Among Physical and Virtual Objects Under Different Lighting Conditions

By situating computer-generated content in the physical world, mobile augmented reality (AR) can support many tasks that involve effective search and inspection of physical environments. Currently, there is limited information regarding the viability of using AR in realistic wide-area outdoor environments and how AR experiences affect human behavior in these environments. Here, we conducted a wide-area outdoor AR user study ($n=48$) using a commercially available AR headset (Microsoft Hololens 2) to compare (1) user interactions with physical and virtual objects in the environment (2) the effects of different lighting conditions on user behavior and AR experience and (3) the impact of varying cognitive load on AR task performance. Participants engaged in a treasure hunt task where they searched for and classified virtual target items (green "gems") in an augmented outdoor courtyard scene populated with physical and virtual objects. Cognitive load was manipulated so that in half the search trials users were required to monitor an audio stream and respond to specific target sounds. Walking paths, head orientation and eye gaze information were measured, and users were queried about their memory of encountered objects and provided feedback on the experience. Key findings included (1) Participants self-reported significantly lower comfort in the ambient natural light condition, with virtual objects more visible and participants more likely to walk into physical objects at night; (2) recall for physical objects was worse than for virtual objects, (3) participants discovered more gems hidden behind virtual objects than physical objects, implying higher attention on virtual objects and (4) dual-tasking modified search behavior. These results suggest there are important technical, perceptual and cognitive factors that must be considered if the full potential of "anywhere and anytime mobile AR" is to be realized.

Effects of changes in end-tidal PO2 and PCO2 on neural responses during rest and sustained attention

Impairments of cognitive function during alterations in arterial blood gases (e.g., high-altitude hypoxia) may result from the disruption of neurovascular coupling; however, the link between changes in arterial blood gases, cognition, and cerebral blood flow (CBF) is poorly understood. To interrogate this link, we developed a multimodal empirical strategy capable of monitoring neural correlates of cognition and CBF simultaneously. Human participants performed a sustained attention task during hypoxia, hypercapnia, hypocapnia, and normoxia while electroencephalographic (EEG) activity and CBF (middle and posterior cerebral arteries; transcranial Doppler ultrasound) were simultaneously measured. The protocol alternated between rest and engaging in a visual target detection task that required participants to monitor a sequence of brief-duration colored circles and detect infrequent, longer duration circles (targets). The target detection task was overlaid on a large, circular checkerboard that provided robust visual stimulation. Spectral decomposition and event-related potential (ERP) analyses were applied to the EEG data to investigate spontaneous and task-specific fluctuations in neural activity. There were three main sets of findings: (1) spontaneous alpha oscillatory activity was modulated as a function of arterial CO2 (hypocapnia and hypercapnia), (2) task-related neurovascular coupling was disrupted by all arterial blood gas manipulations, and (3) changes in task-related alpha and theta band activity and attenuation of the P3 ERP component amplitude were observed during hypocapnia. Since alpha and theta are linked with suppression of visual processing and executive control and P3 amplitude with task difficulty, these data suggest that transient arterial blood gas changes can modulate multiple stages of cognitive information processing.

Alloimmunisation rate of patients on Daratumumab: A retrospective cohort study of patients in England

OBJECTIVE

Whilst small-scale studies on rates of alloimmunisation of patients on Daratumumab have been undertaken, no large-scale study has been performed to date on this cohort of patients.

BACKGROUND

Patients with multiple myeloma (MM) who are relapsed or refractory to standard treatment are treated with the anti-CD38 therapeutic monoclonal antibody, Daratumumab. Due to the complexity of pre-transfusion compatibility testing, many MM patients in England are referred to Red Cell Immunohaematology (RCI) laboratories for investigation and provision of Red Blood Cell (RBC) components.

METHODS

Over a 4-month period, patients due to commence, or currently on anti-CD38 therapy were identified and flagged on the RCI Laboratory Information Management System (LIMS). Data was identified and extracted for further analysis. Interrogation of data was performed independently by two subject matter experts, with discrepancies resolved through further enquiry.

RESULTS

Of 734 English MM patients, we report an alloimmunisation rate of 0.4% whilst on an anti-CD38 TMAb. This is in line with other smaller cohort studies.

CONCLUSION

Given the low rate of RBC alloimmunisation, consideration should be given to revising the pre-transfusion testing regimen in this cohort. This may improve testing costs, turn-around times and evidence-based patient care.

Tracking the Contents of Spatial Working Memory during an Acute Bout of Aerobic Exercise

Recent studies have reported enhanced visual responses during acute bouts of physical exercise, suggesting that sensory systems may become more sensitive during active exploration of the environment. This raises the possibility that exercise may also modulate brain activity associated with other cognitive functions, like visual working memory, that rely on patterns of activity that persist beyond the initial sensory evoked response. Here, we investigated whether the neural coding of an object location held in memory is modulated by an acute bout of aerobic exercise. Participants performed a spatial change detection task while seated on a stationary bike at rest and during low-intensity cycling (∼50 watts/50 RPM). Brain activity was measured with EEG. An inverted encoding modeling technique was employed to estimate location-selective channel response functions from topographical patterns of alpha-band (8-12 Hz) activity. There was strong evidence of robust spatially selective responses during stimulus presentation and retention periods both at rest and during exercise. During retention, the spatial selectivity of these responses decreased in the exercise condition relative to rest. A temporal generalization analysis indicated that models trained on one time period could be used to reconstruct the remembered locations at other time periods, however, generalization was degraded during exercise. Together, these results demonstrate that it is possible to reconstruct the contents of working memory at rest and during exercise, but that exercise can result in degraded responses, which contrasts with the enhancements observed in early sensory processing.

All Quantum Resources Provide an Advantage in Exclusion Tasks

A key ingredient in quantum resource theories is a notion of measure. Such as a measure should have a number of fundamental properties, and desirably also a clear operational meaning. Here we show that a natural measure known as the convex weight, which quantifies the resource cost of a quantum device, has all the desired properties. In particular, the convex weight of any quantum resource corresponds exactly to the relative advantage it offers in an exclusion (or antidistinguishability) task. After presenting the general result, we show how the construction works for state assemblages, sets of measurements, and sets of transformations. Moreover, in order to bound the convex weight analytically, we give a complete characterization of the convex components and corresponding weights of such devices.

Dual Process Coding of Recalled Locations in Human Oscillatory Brain Activity

A mental representation of the location of an object can be constructed using sensory information selected from the environment and information stored internally. Human electrophysiological evidence indicates that behaviorally relevant locations, regardless of the source of sensory information, are represented in alpha-band oscillations suggesting a shared process. Here, we present evidence from human subjects of either sex for two distinct alpha-band-based processes that separately support the representation of location, exploiting sensory evidence sampled either externally or internally.SIGNIFICANCE STATEMENT Our sensory environment and our internal trains of thought are coded in patterns of brain activity and are used to guide coherent behavior. Oscillations in the alpha-frequency band are a predominant feature of human brain activity. This oscillation plays a central role in both selective attention and working memory, suggesting that these important cognitive functions are mediated by a unitary mechanism. We show that the alpha oscillation reflects two distinct processes, one that is supported by continuous sampling of the external sensory environment, and one that is based on sampling from internal representations coded in visual short-term memory. This represents a significant change in our understanding of the nature of alpha oscillations and their relationship to attention and memory.

Prevention of hemolytic transfusion reactions with intravenous immunoglobulin prophylaxis in U- patients with anti-U

BACKGROUND

The U- phenotype is extremely rare and is found predominantly in black African populations at a frequency of between 0.2 and 1.7%. In European populations, U- units are therefore rare, with limited availability in the United Kingdom. Anti-U is clinically significant and is known to cause hemolytic transfusion reactions (HTRs) and hemolytic disease of the fetus and newborn. It has been suggested that intravenous immunoglobulin (IVIG) may be considered as an option among supportive therapy for urgent transfusion when clinically significant antigen-matched units are not available. We report three cases with anti-U transfused with least-incompatible RBC units, their outcomes, and their clinical management.

STUDY DESIGN AND METHODS

Intravenous immunoglobulin was prescribed when least-incompatible units must be issued in patients with anti-U to ameliorate acute HTR and prevent the development of delayed HTR. We report the outcome of these cases.

RESULTS

Of the case reports described, one patient with weak anti-U developed a delayed HTR after transfusion with incompatible units due to an anamnestic response. Two additional patients are described, with the use of IVIG as a precautionary measure to prevent the development of HTRs when transfused with antigen-positive incompatible units. No acute HTRs or delayed HTRs were noted upon follow-up.

CONCLUSION

U- units are not always readily available and transfusion support requires close collaborative working among a multidisciplinary team. Transfusion with antigen-positive incompatible units with IVIG cover both ameliorates acute HTRs and prevents the development of delayed HTRs.

Bombay phenotype (Oh ) and high-titer anti-H in pregnancy: two case reports and a review of the literature

BACKGROUND

Antenatal cases of Bombay-phenotype (O_h ) individuals and hemolytic disease of the fetus and newborn (HDFN) are not well described in the literature. We present two case reports of high-titer anti-H in pregnant O_h individuals and their serologic investigation, clinical management, and subsequent outcomes. We describe current published cases detailing pregnancy in O_h individuals, to add to the evidence base for clinical decision making and management of pregnancy.

STUDY DESIGN AND METHODS

We describe two case reports of high-titer anti-H in pregnancy in O_h individuals. We summarize published cases to date, to inform clinical decision making and antenatal management in individuals with the Bombay phenotype.

RESULTS

Of the case reports described, neither were affected by HDFN due to anti-H. Antibody titers were high in both cases (immunoglobulin G titer scores, 512 and 4000, respectively) and would be expected to cause some degree of HDFN, a surprising finding. Regular mean cerebral artery Doppler ultrasound was normal. Patient blood management (PBM) techniques ensured that the patient's hemoglobin (Hb) levels were monitored and maintained. Transfusion intervention was not required, with minimal blood loss recorded at birth in both cases.

CONCLUSION

High-titer anti-H in O_h pregnancies may, in rare cases, cause HDFN, but evidence suggests that this may not be the case in all pregnancies. We recommend a multidisciplinary approach, with prompt referral to a fetomaternal medicine unit, combined with PBM strategies, and a planned delivery with the provision of rare-phenotype units (if available and if indicated) on standby.

Acute Exercise Modulates Feature-selective Responses in Human Cortex

An organism's current behavioral state influences ongoing brain activity. Nonhuman mammalian and invertebrate brains exhibit large increases in the gain of feature-selective neural responses in sensory cortex during locomotion, suggesting that the visual system becomes more sensitive when actively exploring the environment. This raises the possibility that human vision is also more sensitive during active movement. To investigate this possibility, we used an inverted encoding model technique to estimate feature-selective neural response profiles from EEG data acquired from participants performing an orientation discrimination task. Participants (n = 18) fixated at the center of a flickering (15 Hz) circular grating presented at one of nine different orientations and monitored for a brief shift in orientation that occurred on every trial. Participants completed the task while seated on a stationary exercise bike at rest and during low- and high-intensity cycling. We found evidence for inverted-U effects; such that the peak of the reconstructed feature-selective tuning profiles was highest during low-intensity exercise compared with those estimated during rest and high-intensity exercise. When modeled, these effects were driven by changes in the gain of the tuning curve and in the profile bandwidth during low-intensity exercise relative to rest. Thus, despite profound differences in visual pathways across species, these data show that sensitivity in human visual cortex is also enhanced during locomotive behavior. Our results reveal the nature of exercise-induced gain on feature-selective coding in human sensory cortex and provide valuable evidence linking the neural mechanisms of behavior state across species.

Current topics in red cell biology: report on the Red Cell Special Interest Group meeting held at NHS Blood and Transplant Bristol on 30 October 2015

The Red Cell Special Interest Group (SIG) meeting, hosted by the British Blood Transfusion Society, provides an annual forum for the presentation of UK- and European-based red cell research. The 2015 meeting was held on Friday 30 October at the National Health Service Blood & Transplant (NHSBT) facility in Filton, Bristol and provided an exciting and varied programme on the themes of erythropoiesis, malaria biology and pathophysiology and red cells properties in stress and disease. Ten speakers presented on these topics over the course of one day. The meeting was well attended by over 90 delegates. Posters were presented during the lunch break, and abstracts from the posters are published at the end of this issue.

Multiple stages of information processing are modulated during acute bouts of exercise

Acute bouts of aerobic physical exercise can modulate subsequent cognitive task performance and oscillatory brain activity measured with electroencephalography (EEG). Here, we investigated the sequencing of these modulations of perceptual and cognitive processes using scalp recorded EEG acquired during exercise. Twelve participants viewed pseudo-random sequences of frequent non-target stimuli (cars), infrequent distractors (obliquely oriented faces) and infrequent targets that required a simple detection response (obliquely oriented faces, where the angle was different than the infrequent distractors). The sequences were presented while seated on a stationary bike under three conditions during which scalp recorded EEG was also acquired: rest, low-intensity exercise, and high-intensity exercise. Behavioral target detection was faster during high-intensity exercise compared to both rest and low-intensity exercise. An event-related potential (ERP) analysis of the EEG data revealed that the mean amplitude of the visual P1 component evoked by frequent non-targets measured at parietal-occipital electrodes was larger during low-intensity exercise compared to rest. The P1 component evoked by infrequent targets also peaked earlier during low-intensity exercise compared to rest and high-intensity exercise. The P3a ERP component evoked by infrequent distractors measured at parietal electrodes peaked significantly earlier during both low- and high-intensity exercise when compared to rest. The modulation of the visual P1 and the later P3a components is consistent with the conclusion that exercise modulates multiple stages of neural information processing, ranging from early stage sensory processing (P1) to post-perceptual target categorization (P3a).

Acute exercise and aerobic fitness influence selective attention during visual search

Successful goal directed behavior relies on a human attention system that is flexible and able to adapt to different conditions of physiological stress. However, the effects of physical activity on multiple aspects of selective attention and whether these effects are mediated by aerobic capacity, remains unclear. The aim of the present study was to investigate the effects of a prolonged bout of physical activity on visual search performance and perceptual distraction. Two groups of participants completed a hybrid visual search flanker/response competition task in an initial baseline session and then at 17-min intervals over a 2 h 16 min test period. Participants assigned to the exercise group engaged in steady-state aerobic exercise between completing blocks of the visual task, whereas participants assigned to the control group rested in between blocks. The key result was a correlation between individual differences in aerobic capacity and visual search performance, such that those individuals that were more fit performed the search task more quickly. Critically, this relationship only emerged in the exercise group after the physical activity had begun. The relationship was not present in either group at baseline and never emerged in the control group during the test period, suggesting that under these task demands, aerobic capacity may be an important determinant of visual search performance under physical stress. The results enhance current understanding about the relationship between exercise and cognition, and also inform current models of selective attention.

Recombinant blood group proteins facilitate the detection of alloantibodies to high-prevalence antigens and reveal underlying antibodies: results of an international study

BACKGROUND

Alloantibodies to high-prevalence red blood cell (RBC) antigens are not easily identified by routine serologic techniques. This multicenter study was conducted to test the effectiveness of recombinant blood group proteins (rBGPs) at regional and international RBC reference laboratories.

STUDY DESIGN AND METHODS

Single or mixed soluble rBGPs (Lu, Yt, Kn, JMH, Sc, Rg, Ch, Do, and Cr) were assessed for their ability to inhibit the reactivity of antibodies to specific antigens. Initially, the effect of rBGPs was validated by testing panels of well-characterized patient serum samples containing antibodies to high-prevalence antigens in the hemagglutination inhibition assay. Subsequently, the rBGPs were prospectively used for routine antibody identification and the results were compared to those obtained with RBC-based diagnostics.

RESULTS

Panels of predefined antibodies to high-prevalence antigens were completely and specifically neutralized by the corresponding rBGP specificities. For prospective identification, antibodies to high-prevalence antigens (n = 62) were specifically inhibited by the corresponding rBGP specificities except for some Complement Receptor 1-related antibodies, which may be directed to epitopes not expressed on the truncated recombinant Kn. In 14 cases, additional clinically relevant alloantibodies were identified. In cross-matching, the rBGPs were successfully used to inhibit the reactivity of clinically irrelevant antibodies to high-prevalence antigens to determine compatibility between donor and recipient.

CONCLUSION

rBGPs enable the identification of antibodies to high-prevalence antigens without the need for rare RBC reagents, which are often unavailable. Underlying antibodies can be reliably detected and cross-matching results validated, resulting in a more efficient blood supply for immunized patients.

The distribution of and relationship between autistic traits and social anxiety in a UK student population

Traits associated with autism and social anxiety were assessed in a UK student population (n = 1325) using the Autism-spectrum Quotient and the Liebowitz Social Anxiety Scale. Clinically relevant levels of autistic traits were observed in 3.3% of the cohort; 10.1% of the cohort reported clinically relevant levels of social anxiety; 1.8% of the cohort met clinically relevant cut-offs for both conditions. There was a significant positive correlation between scores on the two scales (r = .51); students with high levels of autistic traits were more likely to report increased social anxiety than those with average or low levels of autistic traits. Level of social anxiety was best predicted by autistic traits associated with social skill, attention switching and communication, accounting for 33% of the variance in social anxiety scores. Social skill was a better predictor of social anxiety in males than females; attention switching ability was a better predictor of social anxiety in females than males. Students with high levels of autistic traits displayed heightened anxiety to situations and activities necessary for the successful completion of their degree. Implications for student well-being and attainment are discussed.

Experience with a third generation recombinant factor VIII concentrate (Advate) for immune tolerance induction in patients with haemophilia A

The development of an inhibitor represents one of the most challenging complications in patients with haemophilia A. Optimal management is immune tolerance induction (ITI), typically through the administration of high doses of factor VIII (FVIII) concentrate. Among 12 patients who underwent ITI using Advate, a third-generation recombinant FVIII product that is free of animal and human protein additives, tolerance was achieved in nine (75%), including seven of 10 patients (70%) with high-titre inhibitors. ITI is ongoing in two patients and not yet successful; immune tolerance failed in the third patient. The median time to success was 4.0 months for group as a whole and for patients with high-titre inhibitors. Treatment was well tolerated, and no adverse events were observed. Advate was found to be equivalent to other FVIII products with regard to both ITI success rates and the incidence of adverse effects when used in these immune tolerance regimens.

McLeod Syndrome: life-long neuropsychiatric disorder due to a novel mutation of the XK gene

A 50-year-old man presented with worsening, virtually lifelong, chorea and progressive behavioural disturbance, involving disinhibition and hoarding, over 10 years. Clinical assessment revealed chorea, dysarthria, areflexia, an inappropriately jovial, impulsive manner and neuropsychological evidence of frontosubcortical dysfunction. Investigation results included an elevated creatine kinase, caudate atrophy and hypoperfusion, acanthocytes in the peripheral blood and the McLeod phenotype. DNA studies demonstrated a single-base deletion at position 172 in exon 1 of the XK gene, giving rise to a premature stop codon at position 129 in exon 2.

[Depressive states and chronic asthenic syndromes in general practice]

It has been shown in Great Britain that general practitioners fail to recognize as many as 50% of the cases of depressive illness that present to them. The diagnosis is missed particularly when it is the physical type of symptom, such as asthenia, that is prominent. The Royal College of Psychiatrists, in association with the Royal College of General Practitioners, has launched the "Defeat Depression" campaign which includes amongst its aims the intention to provide up-to-date educational materials to family doctors on the recognition and treatment of depression. We have held two consensus meetings jointly with psychiatrists and primary care physicians and the results have been published in the British Medical Journal (2). One of our key recommendations is that, when medication is used to treat depressive illness in general practice, the antidepressants should be continued for six months after full remission has taken place. At present patients in general practice take their drugs for a total of three or four weeks. One of the reasons for patients abandoning their medication prematurely has been revealed by surveys that we have carried out on the general public. The lay person has little confidence in the efficacy of antidepressants and, perhaps more importantly, believes that they are addictive. It is therefore no surprise, then, that patients are keen to stop their antidepressants before they become dependent on them.(ABSTRACT TRUNCATED AT 250 WORDS)

The lymphoblast beta-adrenergic receptor in bipolar depressed patients: effect of chronic incubation with lithium chloride

We have recently reported a study of beta-adrenergic receptor binding characteristics in lymphoblast cell lines derived from patients with bipolar disorder (BD) and healthy, matched control subjects. In the present study we have investigated the effects of incubating cells from the same subjects with lithium chloride (1 mM) for 7 days prior to assay. There was no difference in beta-adrenergic receptor number between control and BD cell lines and incubation with lithium had no effect on receptor number in either group. Exposure of the cells to isoprenaline (1 nM) for 24 h immediately prior to assay caused significantly less down-regulation in BD cells (15 +/- 5%) than control cells (39 +/- 4%), as described previously. Incubation with lithium significantly increased the down-regulation response to isoprenaline in BD cells (39 +/- 6%) but not in control cells (30 +/- 7%). After lithium, the agonist-induced decrease in beta-AR number in BD cells was no longer significantly different from that in control cells. We conclude that lithium selectively enhanced the agonist down-regulation of beta-adrenergic receptors in cells derived from patients with bipolar disorder. The functional significance of this result and the potential biochemical mechanisms responsible for this effect are discussed.

Lack of efficacy of fluoxetine in recurrent brief depression and suicidal attempts

Recurrent brief depression (RBD) fulfills DSM-III-R symptom criteria for major depression but the episodes are of shorter duration than the 2 weeks required by DSM-III-R. The clinical importance of the disorder has been observed in prophylactic studies of suicidal behavior. The possibility that antidepressants with selective action on the reuptake of serotonin might be effective in preventing recurrences of brief depression has been investigated. Fluoxetine in a dose of 120 mg a week, administered biweekly, had no effect on the recurrence rate, which was maintained at approximately the same rate on fluoxetine (1 every 18.7 days) as with placebo (1 every 17.6 days). In a group of patients with two or more prior episodes of suicidal behavior, there were 18 attempted suicides in the 54 patients treated with fluoxetine and the same number in the 53 patients treated with placebo. Fluoxetine neither raised nor lowered the suicide attempt rate as compared with placebo, providing no evidence to support the drug's role in either suicide provocation or prevention. Since fluoxetine is clearly effective with recurrent major depression, it would appear that recurrent brief depression has a different pharmacology.

Refined atomic model of wheat serine carboxypeptidase II at 2.2-A resolution

The crystal structure of the homodimeric serine carboxypeptidase II from wheat (CPDW-II, M(r) 120K) has been determined and fully refined at 2.2-A resolution to a standard crystallographic R factor of 16.9% using synchrotron data collected at the Brookhaven National Laboratory. The model has an rms deviation from ideal bond lengths of 0.018 A and from bond angles of 2.8 degrees. The model supports the general conclusions of an earlier study at 3.5-A resolution and will form the basis for investigation into substrate binding and mechanistic studies. The enzyme has an alpha + beta fold, consisting of a central 11-stranded beta-sheet with a total of 15 helices on either side. The enzyme, like other serine proteinases, contains a "catalytic triad" Ser146-His397-Asp338 and a presumed "oxyanion hole" consisting of the backbone amides of Tyr147 and Gly53. The carboxylate of Asp338 and imidazole of His397 are not coplanar in contrast to the other serine proteinases. A comparison of the active site features of the three families of serine proteinases suggests that the "catalytic triad" should actually be regarded as two diads, a His-Asp diad and a His-Ser diad, and that the relative orientation of one diad with respect to the other is not particularly important. Four active site residues (52, 53, 65, and 146) have unfavorable backbone conformations but have well-defined electron density, suggesting that there is some strain in the active site region. The binding of the free amino acid arginine has been analyzed by difference Fourier methods, locating the binding site for the C-terminal carboxylate of the leaving group. The carboxylate makes hydrogen bonds to Glu145, Asn51, and the amide of Gly52. The carboxylate of Glu145 also makes a hydrogen bond with that of Glu65, suggesting that one or both may be protonated. Thus, the loss of peptidase activity at pH > 7 may in part be due to deprotonation of Glu145. The active site does not reveal exposed peptide amides and carbonyl oxygen atoms that could interact with substrate in an extended beta-sheet fashion. The fold of the polypeptide backbone is completely different than that of trypsin or subtilisin, suggesting that this is a third example of convergent molecular evolution to a common enzymatic activity. Furthermore, it is suggested that the active site sequence motif "G-X-S-X-G/A", often considered the hallmark of serine peptidase or esterase activity, is fortuitous and not the result of divergent evolution.(ABSTRACT TRUNCATED AT 400 WORDS)

Recent advances in antidepressant drugs

Tricyclic antidepressants (TCAs) are notorious for a number of disadvantages, but particularly for an array of side-effects that leads to poor compliance, and also for a dangerous toxicity in overdose. Lofepramine is a new tricyclic that seems safer. Selective serotonin reuptake inhibitors (SSRIs) are more limited in their actions. Side-effects include nausea and insomnia, but on the whole the side-effect profile is an improvement on the TCAs. A miscellaneous group of novel antidepressants includes mianserin and trazodone (which both produce drowsiness) and viloxazine (which causes nausea). The reversible inhibitors of monoamine oxidase A (RIMAs) are a group of drugs that, by producing inhibition selectively of monoamine oxidase A (MOA-A), still allow metabolism of tyramine by MAO-B. Moclobemide is a RIMA that has proved itself to be very effective in severe depressive illness. It is remarkably safe and has an exceptionally low incidence of side-effects. It may be expected to be associated with a high acceptability in depressed patients.

Pharmacotherapy in the prevention of suicidal behavior

Prevention or reduction of suicide remains a serious challenge for the medical community. Psychotherapeutic and psychosocial interventions have not been shown to reduce the incidence of suicide attempts and analytic psychotherapy has been shown to increase suicidal behavior. The efficacy of pharmacotherapy in reducing suicide attempts in patients with a history of repeated suicidal behavior has been shown with low doses of the neuroleptic agent flupenthixol compared with placebo. Supporting findings have been reported with trifluoperazine. There is evidence to suggest that some antidepressants may not be neutral in their effect on suicidal behavior. Maprotiline, for example, was associated with an increase in suicide attempts compared with placebo in a large long-term treatment study despite its significant efficacy in preventing relapse of depression. Differential lethality indices taken from large community studies support the notion that noradrenergic drugs such as maprotiline, desipramine, and nortriptyline are associated with a higher than expected incidence of death from overdose, and the suicide-provoking potential may relate to some noradrenergic property. The studies of serotonergic antidepressants do not suggest that they are suicide-provoking agents; rather they appear to be neutral or protective. Prospective prophylactic studies are needed to test the ability of potential treatments for the reduction of suicidal behavior.