Pharmacometabolomic Approach to Investigate the Response to Metformin in Patients with Type 2 Diabetes: A Cross-Sectional Study

Metformin constitutes the foundation therapy in type 2 diabetes (T2D). Despite its multiple beneficial effects and widespread use, there is considerable inter-individual variability in response to metformin. Our objective is to identify metabolic signatures associated with poor and good responses to metformin, which may improve our ability to predict outcomes for metformin treatment. In this cross-sectional study, clinical and metabolic data for 119 patients with type 2 diabetes taking metformin were collected from the Qatar Biobank. Patients were empirically dichotomized according to their HbA1C levels into good and poor responders. Differences in the level of metabolites between these two groups were compared using orthogonal partial least square discriminate analysis (OPLS-DA) and linear models. Good responders showed increased levels of sphingomyelins, acylcholines, and glutathione metabolites. On the other hand, poor responders showed increased levels of metabolites resulting from glucose metabolism and gut microbiota metabolites. The results of this study have the potential to increase our knowledge of patient response variability to metformin and carry significant implications for enabling personalized medicine.

Cell anatomy and network input explain differences within but not between leech touch cells at two different locations

Mechanosensory cells in the leech share several common features with mechanoreceptors in the human glabrous skin. Previous studies showed that the six T (touch) cells in each body segment of the leech are highly variable in their responses to somatic current injection and change their excitability over time. Here, we investigate three potential reasons for this variability in excitability by comparing the responses of T cells at two soma locations (T2 and T3): (1) Differential effects of time-dependent changes in excitability, (2) divergent synaptic input from the network, and (3) different anatomical structures. These hypotheses were explored with a combination of electrophysiological double recordings, 3D reconstruction of neurobiotin-filled cells, and compartmental model simulations. Current injection triggered significantly more spikes with shorter latency and larger amplitudes in cells at soma location T2 than at T3. During longer recordings, cells at both locations increased their excitability over time in the same way. T2 and T3 cells received the same amount of synaptic input from the unstimulated network, and the polysynaptic connections between both T cells were mutually symmetric. However, we found a striking anatomical difference: While in our data set all T2 cells innervated two roots connecting the ganglion with the skin, 50% of the T3 cells had only one root process. The sub-sample of T3 cells with one root process was significantly less excitable than the T3 cells with two root processes and the T2 cells. To test if the additional root process causes higher excitability, we simulated the responses of 3D reconstructed cells of both anatomies with detailed multi-compartment models. The anatomical subtypes do not differ in excitability when identical biophysical parameters and a homogeneous channel distribution are assumed. Hence, all three hypotheses may contribute to the highly variable T cell responses, but none of them is the only factor accounting for the observed systematic difference in excitability between cells at T2 vs. T3 soma location. Therefore, future patch clamp and modeling studies are needed to analyze how biophysical properties and spatial distribution of ion channels on the cell surface contribute to the variability and systematic differences of electrophysiological phenotypes.

Exposure-Response Analysis of the Sodium-Glucose Cotransporter-2 Inhibitors Dapagliflozin and Empagliflozin on Kidney Hemodynamics in Patients with Type 2 Diabetes

Sodium-glucose cotransporter-2 (SGLT2) inhibitors improve markers for renal and cardiovascular outcomes in patients with and without type 2 diabetes (T2D). To assess whether individual differences in plasma drug exposure can explain inter-individual response variation, we characterized the exposure-response relationship for two SGLT2 inhibitors on several clinical and kidney hemodynamic variables. Data were obtained from two studies, RED and RECOLAR, assessing the effects of once-daily 10 mg dapagliflozin or empagliflozin, respectively, on kidney hemodynamics in patients with T2D. Individual plasma exposure was estimated using non-compartmental analyses and exposure-response relationships were assessed using linear mixed-effects models. In 23 patients participating in RED, the dapagliflozin geometric mean apparent area under the concentration-time curve during one dosing interval at steady state (AUC_0-tau,ss) was 1153.1 µg/L*h (coefficient of variation (CV) 81.8%) and associated, per doubling, with decreases in body weight (0.29 kg, p < 0.001), systolic blood pressure (0.80 mmHg, p = 0.002), measured glomerular filtration rate (mGFR) (0.83 mL/min, p = 0.03), and filtration fraction (0.09%, p = 0.04). In 20 patients participating in RECOLOR, the empagliflozin geometric mean AUC_0-tau,ss was 2035.7 nmol/L*h (CV 48.4%) and associated, per doubling, with decreases in body weight (0.13 kg, p = 0.002), systolic blood pressure (0.65 mmHg, p = 0.045), and mGFR (0.78 mL/min, p = 0.002). To conclude, dapagliflozin and empagliflozin plasma exposure was highly variable between patients and associated with inter-individual variation in response variables.

Assessment of a single trial impact on the amplitude of the averaged event related potentials

Widely used in neuroscience the averaging of event related potentials is based on the assumption that small responses to the investigated events are present in every trial but can be hidden under the random noise. This situation often takes place, especially in experiments performed at hierarchically lower levels of sensory systems. However, in the studies of higher order complex neuronal networks evoked responses might appear only under particular conditions and be absent otherwise. We encountered this problem studying a propagation of interoceptive information to the cortical areas in the sleep-wake cycle. Cortical responses to various visceral events were present during some periods of sleep, then disappeared for a while and restored again after a period of absence. Further investigation of the viscero-cortical communication required a method that would allow labeling the trials contributing to the averaged event related responses-"efficient trials," and separating them from the trials without any response. Here we describe a heuristic approach to solving this problem in the context of viscero-cortical interactions occurring during sleep. However, we think that the proposed technique can be applicable to any situation where neuronal processing of the same events is expected to be variable due to internal or external factors modulating neuronal activity. The method was first implemented as a script for Spike 2 program version 6.16 (CED). However, at present a functionally equivalent version of this algorithm is also available as Matlab code at https://github.com/george-fedorov/erp-correlations.

Responsiveness to left-prefrontal tDCS varies according to arousal levels

Over the past two decades, the postulated modulatory effects of transcranial direct current stimulation (tDCS) on the human brain have been extensively investigated. However, recent concerns on reliability of tDCS effects have been raised, principally due to reduced replicability and to interindividual variability in response to tDCS. These inconsistencies are likely due to the interplay between the level of induced cortical excitability and unaccounted structural and state‐dependent functional factors. On these grounds, we aimed at verifying whether the behavioural effects induced by a common tDCS montage (F3‐rSOA) were influenced by the participants' arousal levels, as part of a broader mechanism of state‐dependency. Pupillary dynamics were recorded during an auditory oddball task while applying either a sham or real tDCS. The tDCS effects were evaluated as a function of subjective and physiological arousal predictors (STAI‐Y State scores and pre‐stimulus pupil size, respectively). We showed that prefrontal tDCS hindered task learning effects on response speed such that performance improvement occurred during sham, but not real stimulation. Moreover, both subjective and physiological arousal predictors significantly explained performance during real tDCS, with interaction effects showing performance improvement only with moderate arousal levels; likewise, pupil response was affected by real tDCS according to the ongoing levels of arousal, with reduced dilation during higher arousal trials. These findings highlight the potential role of arousal in shaping the neuromodulatory outcome, thus emphasizing a more careful interpretation of null or negative results while also encouraging more individually tailored tDCS applications based on arousal levels, especially in clinical populations.

Biological and methodological factors affecting V ̇ O 2 max response variability to endurance training and the influence of exercise intensity prescription

NEW FINDINGS

What is the topic of this review? Biological and methodological factors associated with the variable changes in cardiorespiratory fitness in response to endurance training. What advances does it highlight? Several biological and methodological factors exist that each contribute, to a given extent, to response variability. Notably, prescribing exercise intensity relative to physiological thresholds reportedly increases cardiorespiratory fitness response rates compared to when prescribed relative to maximum physiological values. As threshold-based approaches elicit more homogeneous acute physiological responses among individuals, when repeated over time, these uniform responses may manifest as more homogeneous chronic adaptations thereby reducing response variability.

ABSTRACT

Changes in cardiorespiratory fitness (CRF) in response to endurance training (ET) exhibit large variations, possibly due to a multitude of biological and methodological factors. It is acknowledged that ∼20% of individuals may not achieve meaningful increases in CRF in response to ET. Genetics, the most potent biological contributor, has been shown to explain ∼50% of response variability, whilst age, sex and baseline CRF appear to explain a smaller proportion. Methodological factors represent the characteristics of the ET itself, including the type, volume and intensity of exercise, as well as the method used to prescribe and control exercise intensity. Notably, methodological factors are modifiable and, upon manipulation, alter response rates to ET, eliciting increases in CRF regardless of an individual's biological predisposition. Particularly, prescribing exercise intensity relative to a physiological threshold (e.g., ventilatory threshold) is shown to increase CRF response rates compared to when intensity is anchored relative to a maximum physiological value (e.g., maximum heart rate). It is, however, uncertain whether the increased response rates are primarily attributable to reduced response variability, greater mean changes in CRF or both. Future research is warranted to elucidate whether more homogeneous chronic adaptations manifest over time among individuals, as a result of exposure to more homogeneous exercise stimuli elicited by threshold-based practices.

The effects of a group exercise and education programme on symptoms and physical fitness in patients with fibromyalgia: a prospective observational cohort study

PURPOSE

Given the limited attention on a combined exercise and education approach for those with chronic musculoskeletal pain disorder such as fibromyalgia, the purpose of this was to evaluate the efficacy of a combined exercise and education programme on symptoms and physical fitness in participants with fibromyalgia.

MATERIALS AND METHODS

Using a prospective observational cohort study, participants with fibromyalgia (n = 75) volunteered. The 6-minute-walk-test (6MWT) and revised-fibromyalgia-impact-questionnaire (FIQR) were used before, after (6 weeks) and 6-months post an exercise and education programme.

RESULTS

Forty-three participants (age = 49.7 ± 15.2 y) completed the 6-week programme, with improvements observed for the 6MWT (67 m, p < 0.001) and FIQR (11 AU, p < 0.001), though only two (6MWT) and five (FIQR) participants, respectively, achieved the minimal clinically important difference (MCID). Using 74% of the intial sample, a small-to-moderate improvement in scores were observed across the 6-month period for the 6MWT (37 m, p = 0.002) and FIQR (3 AU, p = 0.01), with only two participants achieving the MCID for the 6MWT.

CONCLUSIONS

The results in this study indiciate small-to-moderate improvements in the 6MWT and FIQR after a combined exercise and education programme, with direct delivery being more effective.Implications for rehabilitationA six-week exercise and education programme elicited moderate, short-term (6 weeks) benefits on physical fitness and key symptoms in patients with fibromyalgia.On average, these benefits were sustained in the long-term (6 months) following the programme but were small-to-moderate and lower than the MCID.Regular follow-up may be required to improve adherence to the education and exercise programme and maintain or increase the observed improvements in 6MWT and FIQR.

Proteinuria and cholesterol reduction are independently associated with less renal function decline in statin-treated patients; a post hoc analysis of the PLANET trials

Background

Statins have shown multiple effects on different renal risk factors such as lowering of total cholesterol (TC) and lowering of urine protein:creatinine ratio (U_PCR). We assessed whether these effects of statins vary between individuals, the extent of discordance of treatment effects on both TC and U_PCR within an individual, and the association of responses in TC and U_PCR with estimated glomerular filtration rate (eGFR) decline.

Methods

The PLANET I and II (Renal effects of Rosuvastatin and Atorvastatin in Patients Who Have Progressive Renal Disease) trials examined effects of atorvastatin and rosuvastatin on proteinuria and renal function in patients with proteinuria. We post hoc analysed 471 therapy-adherent proteinuric patients from the two trials and assessed the individual variability in U_PCR and TC response from 0 to 14 weeks and whether these responses were predictive of eGFR decline during the subsequent 9 months of follow-up.

Results

U_PCR and TC response varied between individuals: mean U_PCR response was −1.3% (5th–95th percentile −59.9 to 141.8) and mean TC response was −93.9 mg/dL (−169.1 to −26.9). Out of 471 patients, 123 (26.1%) showed a response in U_PCR but not in TC, and 96 (20.4%) showed a response in TC but not in U_PCR. eGFR (mL/min/1.73 m²) did not decrease significantly from baseline in both U_PCR responders [0.4; 95% confidence interval (CI) −1.6 to 0.9; P = 0.54] and TC responders (0.3; 95% CI −1.8 to 1.1; P = 0.64), whereas U_PCR and TC non-responders showed a significant decline in eGFR from baseline (1.8; 95% CI 0.6–3.0; P = 0.004 and 1.7; 95% CI 0.5–2.9; P = 0.007, respectively). A lack of response in both parameters resulted in the fastest rate of eGFR decline (2.1; 95% CI 0.5–3.7; P = 0.01). These findings were not different for rosuvastatin or atorvastatin.

Conclusions

Statin-induced changes in cholesterol and proteinuria vary between individuals and do not run in parallel within an individual. The initial fall in cholesterol and proteinuria is independently associated with a reduction in eGFR decline. This highlights the importance of monitoring both cholesterol and proteinuria after initiating statin therapy.

DNA Methylation as a Biomarker of Treatment Response Variability in Serious Mental Illnesses: A Systematic Review Focused on Bipolar Disorder, Schizophrenia, and Major Depressive Disorder

So far, genetic studies of treatment response in schizophrenia, bipolar disorder, and major depression have returned results with limited clinical utility. A gene × environment interplay has been proposed as a factor influencing not only pathophysiology but also the treatment response. Therefore, epigenetics has emerged as a major field of research to study the treatment of these three disorders. Among the epigenetic marks that can modify gene expression, DNA methylation is the best studied. We performed a systematic search (PubMed) following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA guidelines for preclinical and clinical studies focused on genome-wide and gene-specific DNA methylation in the context of schizophrenia, bipolar disorders, and major depressive disorder. Out of the 112 studies initially identified, we selected 31 studies among them, with an emphasis on responses to the gold standard treatments in each disorder. Modulations of DNA methylation levels at specific CpG sites have been documented for all classes of treatments (antipsychotics, mood stabilizers, and antidepressants). The heterogeneity of the models and methodologies used complicate the interpretation of results. Although few studies in each disorder have assessed the potential of DNA methylation as biomarkers of treatment response, data support this hypothesis for antipsychotics, mood stabilizers and antidepressants.

Coupling of synaptic inputs to local cortical activity differs among neurons and adapts after stimulus onset

Cortical activity contributes significantly to the high variability of sensory responses of interconnected pyramidal neurons, which has crucial implications for sensory coding. Yet, largely because of technical limitations of in vivo intracellular recordings, the coupling of a pyramidal neuron's synaptic inputs to the local cortical activity has evaded full understanding. Here we obtained excitatory synaptic conductance ( g) measurements from putative pyramidal neurons and local field potential (LFP) recordings from adjacent cortical circuits during visual processing in the turtle whole brain ex vivo preparation. We found a range of g-LFP coupling across neurons. Importantly, for a given neuron, g-LFP coupling increased at stimulus onset and then relaxed toward intermediate values during continued visual stimulation. A model network with clustered connectivity and synaptic depression reproduced both the diversity and the dynamics of g-LFP coupling. In conclusion, these results establish a rich dependence of single-neuron responses on anatomical, synaptic, and emergent network properties. NEW & NOTEWORTHY Cortical neurons are strongly influenced by the networks in which they are embedded. To understand sensory processing, we must identify the nature of this influence and its underlying mechanisms. Here we investigate synaptic inputs to cortical neurons, and the nearby local field potential, during visual processing. We find a range of neuron-to-network coupling across cortical neurons. This coupling is dynamically modulated during visual processing via biophysical and emergent network properties.

Lag Schedules and Functional Communication Training: Persistence of Mands and Relapse of Problem Behavior

We evaluated the effects of lag schedules of reinforcement and functional communication training (FCT) on mand variability and problem behavior in two children with autism spectrum disorder. Specifically, we implemented FCT with increasing lag schedules and compared its effects on problem behavior with baseline conditions. The results showed that both participants exhibited low rates of problem behavior during treatment relative to baseline during and following schedule thinning (up to a Lag 5 schedule arrangement). Variable and total mands remained high during schedule thinning. With one participant, variable manding persisted when the value of the lag schedule was reduced to zero. The current results are discussed in terms of implications for training multiple mand topographies during FCT for the potential prevention and/or mitigation of clinical relapse during challenges to treatment.

Anodal tDCS Enhances Verbal Episodic Memory in Initially Low Performers

The left dorsolateral prefrontal cortex (DLPFC) is involved in encoding and retrieval of episodic memories, and thus, is frequently targeted in non-invasive brain stimulation paradigms, aiming for its functional modulation. Anodal transcranial direct current stimulation (tDCS), that boosts neuronal excitability in stimulated cortical areas, has been found to increase cognitive skills differentially, depending on the initial performance. We hypothesize that the benefit of tDCS on verbal episodic memory can be extrapolated from the participants’ baseline performance. In the present randomized, double-blind, parallel group study, healthy young adults (n = 43) received either real anodal or sham tDCS over their left DLPFC during the encoding phase of a verbal episodic memory task. Forty words were presented visually thrice with immediate vocal retrieval after each block and an additional delayed recall. We conducted a moderation analysis to test the modulating effect of initial episodic memory retrieval, adjusted for primacy and recency effects, on delayed recall under real or sham stimulation. Despite the absence of a significantly beneficial tDCS effect at the group level, we found that the number of remembered midlist words in the first retrieval significantly moderated the stimulation effect in such a way that initially low performers experienced the highest gain from real stimulation. These results suggest that anodal tDCS to the left DLPFC improves memory functions only so far. While only marginal stimulation-induced gains occur in cognitively unimpaired populations, greater stimulation benefits might be expected in individuals with clinically relevant deficiencies in the verbal episodic memory domain.

Greater response variability in adolescents is associated with increased white matter development

Adolescence is a period of learning, exploration, and continuous adaptation to fluctuating environments. Response variability during adolescence is an important, understudied, and developmentally appropriate behavior. The purpose of this study was to identify the association between performance on a dynamic risky decision making task and white matter microstructure in a sample of 48 adolescents (14–16 years). Individuals with the greatest response variability on the task obtained the widest range of experience with potential outcomes to risky choice. When compared with their more behaviorally consistent peers, adolescents with greater response variability rated real-world examples of risk taking behaviors as less risky via self-report. Tract-Based Spatial Statistics (TBSS) were used to examine fractional anisotropy (FA) and mean diffusivity (MD). Greater FA in long-range, late-maturing tracts was associated with higher response variability. Greater FA and lower MD were associated with lower riskiness ratings of real-world risky behaviors. Results suggest that response variability and lower perceived risk attitudes of real-world risk are supported by neural maturation in adolescents.

The albuminuria-lowering response to dapagliflozin is variable and reproducible among individual patients

AIMS

Albuminuria reduction is essential for renal and cardiovascular protection. We characterized the efficacy of dapagliflozin, a sodium-glucose co-transporter 2 inhibitor, on albuminuria. Secondly, we assessed whether the albuminuria-lowering effect varies among patients, and whether this variability in response is reproducible.

MATERIAL AND METHODS

A double-blind, randomized, placebo controlled crossover trial was conducted. Patients with type 2 diabetes and albumin:creatinine ratio > 100 mg/g on a stable dose of an angiotensin-converting enzyme inhibitor (ACEi) or angiotensin receptor blocker (ARB) were enrolled. Patients were assigned to 6-week treatment periods with dapagliflozin 10 mg/d or placebo in random order, separated by 6-weeks wash-out periods. After the 2 treatment periods, half of the patients were re-exposed for 6 weeks to dapagliflozin 10 mg/d. Primary outcome was change in 24-hour urinary albumin excretion rate (24 h UAE). To assess reproducibility in individual albuminuria response, responses from the first and second exposure to dapagliflozin were correlated.

RESULTS

A total of 33 patients (age, 61 years; female gender, 24.2%; median 24 h UAE, 470 mg/24 h) completed the study. Dapagliflozin, as compared to placebo, reduced 24 h UAE by 36.2% (95% CI, 22.9-47.2; P  < .001). Systolic blood pressure fell by 5.2 mm Hg (95% CI, 0.5-10.0) and eGFR by 5.3 (95% CI, 2.7-8.0). All effects were reversible directly after treatment discontinuation. In a subgroup of 15 patients who were exposed twice to dapagliflozin, 24 h UAE responses showed a large variation among individuals: first exposure (range, -76% to +52%) and second exposure (-90% to +95%) and first and second individual response were significantly correlated (r = 0.69 [95% CI, 0.27-0.89]; P  < .004).

CONCLUSION

Dapagliflozin significantly reduces albuminuria when given as adjunct to ACEi or ARB. The albuminuria response to dapagliflozin markedly varies among patients. This variation is not a random phenomenon, but is reproducible upon re-exposure. These data support personalized therapy approaches to optimize diabetic kidney disease.

An analysis of procedures that affect response variability

Response variability is sensitive to antecedent and consequent manipulations. Researchers have investigated inducement, direct production through reinforcement, and stimulus control of response variability. Recently, researchers have shown that lag reinforcement schedules reliably increase variability but may also produce higher-order stereotypy. There has been limited investigation of appropriate variability levels and alternation between repetition and variation. In a three-part study, we evaluated levels of variability across a group of children, the effects of various procedures on producing response variability and novelty, and the use of schedule-correlated stimuli for producing rapid alternation between repetition and variation. In Study 1, there was a nearly bimodal distribution of children emitting either low or high variability. In Study 2, for most children, fixed lag 4 and variable lag 4 schedules produced the highest levels of variability and novelty. In Study 3, responding was brought under control of schedule-correlated stimuli, allowing for rapid alternation between repetition and variation.

Bidirectional variability in motor cortex excitability modulation following 1 mA transcranial direct current stimulation in healthy participants

Due to the high interindividual response variability following transcranial direct current stimulation (tDCS), it is apparent that further research of the long‐lasting effects of the stimulation technique is required. We aimed to investigate interindividual variability following anodal tDCS and cathodal tDCS in a large‐scale prospective cross‐over study. Motor cortex physiology measurements were obtained using transcranial magnetic stimulation (TMS) in 59 healthy participants comparing motor‐evoked potential (MEP) magnitudes following two tDCS paradigms: 1 mA anodal tDCS for 13 min and 1 mA cathodal tDCS for 9 min. Analysis compared MEP changes over time for both polarities. Additionally, we applied hierarchical cluster analysis to assess the dynamics of poststimulation changes. Overall, anodal tDCS resulted in a significant increase in corticospinal excitability lasting for 40 min poststimulation, whereas cathodal tDCS did not alter corticospinal excitability. Cluster analysis revealed for cathodal tDCS both a cluster showing significant stable MEP reduction and a second cluster displaying MEP increase over time. Two diametrical clusters were also found for anodal tDCS. Regardless of polarity, individuals with MEP increase following stimulation showed steeper cortical recruitment curves compared to the clusters with decreased MEP magnitudes. The observed findings confirm a bidirectional modulation of corticospinal excitability following 1 mA tDCS in separate subgroups and the relationship to cortical recruitment.

Can Neuromodulation also Enhance Social Inequality? Some Possible Indirect Interventions of the State

There is evidence that noninvasive brain stimulation (NIBS), and especially transcranial direct current stimulation (tDCS), can improve some cognitive functions, at least temporarily. However, as the improvement only applies to some “lucky” people, it may raise ethical, social and legal issues related to fairness in selective contexts (exams, competitions, job interviews). In this regard, an important element tends to be overlooked: the variability in individual response to tDCS in particular. If intensive study or practice and massive doses of chemical enhancers can have slightly different effects over different people, tDCS can sometimes be completely ineffective. The variability in individual response, if tDCS were widely used, could add to the already present natural inequalities between people, or even create new ones, leaving some in a disadvantaged condition. The discussion of the various ethical, social and legal consequences of different individual responses to tDCS might also address a potential indirect intervention by the State. In fact, if NIBS were to be widespread in competitive contexts, those who do not benefit from tDCS would be disadvantaged compared to those able to enhance their skills thanks to neuromodulation technologies. The most disadvantaged people for their lower response to tDCS could then acquire the right to receive and use free and safe cognitive enhancing drugs or other forms of bettering cognitive skills and functions, so as to reduce the gap between them and those who respond well to tDCS, in the light of the principle of equal opportunity.

Renal endothelial function is associated with the anti-proteinuric effect of ACE inhibition in 5/6 nephrectomized rats

In healthy rats, the physiological variation of baseline endothelial function of intrarenal arteries correlates with the severity of renal damage in response to a subsequent specific renal injury. However, whether such a variation in endothelial function may also condition or predict the variable response to angiotensin-converting enzyme-inhibiting treatment in these individuals has not been addressed before. To study this, 5/6 nephrectomy was performed to induce renal injury and chronic kidney disease in a group of healthy Wistar rats. At the time of nephrectomy, interlobar arteries were obtained from the extirpated right kidney and studied in vitro for endothelium-dependent relaxation to acetylcholine. Six weeks thereafter, treatment with lisinopril was started (n = 11) and continued for 9 wk. Proteinuria (metabolic cages) and systolic blood pressure (SBP; tail cuff) were evaluated weekly, and these were analyzed in relation to renal endothelial function at baseline. 5/6 Nephrectomy induced an increase in SBP and progressive proteinuria. Treatment with lisinopril reduced SBP and slowed proteinuria, albeit to a variable degree among individuals. The acetylcholine-induced renal artery dilation at baseline negatively correlated with lisinopril-induced reduction of proteinuria (r(2) = 0.648, P = 0.003) and with the decrease in SBP (r(2) = 0.592, P = 0.006). Our data suggest that angiotensin-converting enzyme-inhibitor attenuates the progression of renal damage the most in those individuals with decreased basal renal endothelial-mediated vasodilation.

The use of a discrimination-training procedure to teach mand variability to children with autism

We investigated the effects of a script-fading and discrimination-training procedure on mand variability in preschoolers with autism. Participants were taught to vary their vocal mands in the presence of written scripts, a green placemat, and a lag schedule of reinforcement. They were also taught to engage in repetitive mands in the presence of the same written scripts and a red placemat. When the scripts were removed, all 3 participants continued to engage in varied manding in the presence of the green placemat and lag schedule, and they continued to engage in repetitive manding in the presence of the red placemat. When the lag schedule was also removed, 2 of the 3 participants continued to engage in varied responding in the presence of the green placemat and repetitive responding in the presence of the red placemat. Finally, all 3 participants demonstrated generalization and maintenance of mand variability during snack sessions with their peers.

Inter- and intra-subject variability of motor cortex plasticity following continuous theta-burst stimulation

BACKGROUND

The potential of non-invasive brain stimulation (NIBS) for studying, and inducing, functionally relevant neuroplasticity is dependent on protocols that can induce lasting, robust and reliable effects. A current limiting factor is the large inter- and intra-subject variability in NIBS-induced neuroplastic responses. There has been some study of inter-subject response variability and factors that contribute to it; however, intra-subject response variability has, so far, received little investigation.

OBJECTIVES

By testing participants on multiple occasions we aimed to (1) compare inter- and intra-subject variability of neuroplastic responses induced by continuous theta-burst stimulation (cTBS); (2) determine whether the transcranial magnetic stimulation (TMS) intensity used to measure cTBS-induced neuroplastic responses contributes to response variability; (3) determine whether assessment of factors known to influence response variability can be used to explain some of the variability in cTBS-induced neuroplastic responses across experimental sessions.

METHODS

In three separate experimental sessions, motor-evoked potential (MEP) input-output (IO) curves were obtained before and after cTBS, and questionnaire-based assessments of physical activity and perceived stress were obtained.

RESULTS

cTBS-induced MEP suppression was greatest at the upper end of the IO curve (150-180% resting motor threshold; RMT) and most consistent across subjects and across experimental sessions when assessed with a TMS intensity of 150% RMT. The magnitude of cTBS-induced MEP suppression evoked at 150% RMT correlated with self-reported perceived stress, but not with self-reported physical activity.

CONCLUSIONS

The most reliable TMS intensity to probe cTBS-induced long-term depression (LTD)-like neuroplastic responses is 150% RMT. This is unlikely to simply be a ceiling effect and, we suggest, may be due to changes in the descending volley evoked at higher stimulus intensities. The perceived stress scale appears to be sufficiently sensitive to measure the influence of subject stress on LTD-like neuroplastic responses.

Slow dynamics in features of synchronized neural network responses

In this report trial-to-trial variations in the synchronized responses of neural networks are explored over time scales of minutes, in ex-vivo large scale cortical networks. We show that sub-second measures of the individual synchronous response, namely-its latency and decay duration, are related to minutes-scale network response dynamics. Network responsiveness is reflected as residency in, or shifting amongst, areas of the latency-decay plane. The different sensitivities of latency and decay durations to synaptic blockers imply that these two measures reflect aspects of inhibitory and excitatory activities. Taken together, the data suggest that trial-to-trial variations in the synchronized responses of neural networks might be related to effective excitation-inhibition ratio being a dynamic variable over time scales of minutes.

Heterogeneity of physical function responses to exercise training in older adults

OBJECTIVES

To describe the interindividual variability in physical function responses to supervised resistance and aerobic exercise training interventions in older adults.

DESIGN

Data analysis of two randomized, controlled exercise trials.

SETTING

Community-based research centers.

PARTICIPANTS

Overweight and obese (body mass index (BMI)≥27.0 kg/m2) sedentary men and women aged 65 to 79 (N=95).

INTERVENTION

Five months of 4 d/wk of aerobic training (AT, n=40) or 3 d/wk of resistance training (RT, n=55).

MEASUREMENTS

Physical function assessments: global measure of lower extremity function (Short Physical Performance Battery (SPPB)), 400-m walk, peak aerobic capacity (VO2 peak), and knee extensor strength.

RESULTS

On average, both exercise interventions significantly improved physical function. For AT, there was a 7.9% increase in VO2 peak; individual absolute increases varied from 0.4 to 4.3 mL/kg per minute, and four participants (13%) showed no change or a decrease in VO2 peak. For RT, knee extensor strength improved an average of 8.1%; individual increases varied from 1.2 to 63.7 Nm, and 16 participants (30%) showed no change or a decrease in strength. Usual gait speed, 400-m walk time, chair rise time, and SPPB improved for the majority of AT participants and usual gait speed, chair rise time, and SPPB improved for the majority of RT participants, but there was wide variation in the magnitude of improvement. Only change in 400-m walk time with RT was related to exercise adherence (correlation coefficient=-0.31, P=.004).

CONCLUSION

Despite sufficient levels of adherence to both exercise interventions, some participants did not improve function, and the magnitude of improvement varied widely. Additional research is needed to identify factors that optimize responsiveness to exercise to maximize its functional benefits in older adults.

The persistence of cognitive deficits in remitted and unremitted ADHD: a case for the state-independence of response inhibition

BACKGROUND

Response inhibition, working memory, and response variability are possible endophenotypes of ADHD based on their association with the disorder and evidence of heritability. One of the critical although rarely studied criteria for a valid endophenotype is that it persists despite waxing and waning of the overt manifestations of the disorder, a criterion known as state-independence. This study examined whether these aspects of cognition exhibit state-independence in ADHD.

METHODS

One hundred and seventy-nine children diagnosed with ADHD in a rigorous baseline assessment were contacted for follow-up assessment in adolescence. Of this sample, 130 (73%) were reascertained. At follow-up, children previously diagnosed with ADHD were identified as remittent (n = 24), persistent (n = 64), or in partial remission (n = 42) based on symptoms and impairment of the disorder. Response inhibition, working memory, and response variability were assessed both in childhood (baseline) and adolescence (follow-up) and were compared with age-matched controls (40 children and 28 adolescents) seen at either time point.

RESULTS

Relative to controls, ADHD children showed baseline deficits in response inhibition, working memory, and response variability. Only the group difference in response inhibition remained significant in adolescence. In general, cognitive performance among ADHD participants improved with age and did so regardless of changes in ADHD symptoms and impairment. Within the ADHD group, however, cognitive performance in childhood and in adolescence did not differ amongst those with persistent, remittent, and partially remittent forms of the disorder.

CONCLUSIONS

Results demonstrate that response inhibition not only distinguishes ADHD children from their unaffected peers but is also state-independent, such that deficits remain present irrespective of changes in the disease phenotype. In other words, inhibitory deficits measured in childhood persist into adolescence even when the ADHD phenotype remits. These findings provide further evidence that the ability to stop prepotent actions is an endophenotype of ADHD.

Reaction time variability in ADHD: a review

For the past decade, intra-individual variability in reaction times on computerized tasks has become a central focus of cognitive research on Attention-Deficit/Hyperactivity Disorder (ADHD). Numerous studies document increased reaction time variability among children and adults with ADHD, relative to typically developing controls. However, direct comparisons with other disorders with heightened reaction time variability are virtually nonexistent, despite their potential to inform our understanding of the phenomenon. A growing literature examines the sensitivity of reaction time variability to theoretically and clinically relevant manipulations. There is strong evidence that stimulus treatment reduces reaction time variability during a range of cognitive tasks, but the literature is mixed regarding the impact of motivational incentives and variation in stimulus event rate. Most studies of reaction time variability implicitly assume that heightened reaction time variability reflects occasional lapses in attention, and the dominant neurophysiological interpretation suggests this variability is linked to intrusions of task-negative brain network activity during task performance. Work examining the behavioral and neurophysiological correlates of reaction time variability provides some support for these hypotheses, but considerably more work is needed in this area. Finally, because conclusions from each of domains reviewed are limited by the wide range of measures used to measure reaction time variability, this review highlights the need for increased attention to the cognitive and motivational context in which variability is assessed and recommends that future work always supplement macro-level variability indices with metrics that isolate particular components of reaction time variability.

Increased variability in tacting under a lag 3 schedule of reinforcement

Research has shown that variability may be an operant dimension of behavior. One method of reinforcing response variability is to use a lag schedule of reinforcement (Page & Neuringer, 1985). Several studies have shown that a Lag 1 schedule is effective in increasing variable responding with human participants (e.g., Esch, Esch, & Love, 2009; Lee, McComas, & Jawor, 2002). In these arrangements, however, the return to baseline responding during reversal phases suggests that the resulting behavior change may not be maintained following intervention. The purpose of the present study was to investigate the effects of a Lag 3 schedule on increasing and maintaining variability of tacts in 2 children diagnosed with developmental disabilities. Results demonstrated increased variability in tacting for both participants and maintenance in variable responding after a 3-week follow-up.

Increasing response diversity in children with autism

Repetitive and invariant behavior is a diagnostic feature of autism. We implemented a lag reinforcement schedule to increase response diversity for 6 participants with autism aged 6 to 10 years, 4 of whom also received prompting plus additional training. These procedures appeared to increase the variety of building-block structures, demonstrating that an intervention that includes differential reinforcement can increase response diversity for children with an autism spectrum disorder.

Beyond Genetics-Stratified and Personalised Medicines Using Multiple Parameters

Prescribers have been practicing stratified medicine for many years. Patient characteristics, usually non-genetic, including age, comorbidities and concomitant medications are taken into account when deciding which drug to prescribe. In addition, the majority of drugs require dose adjustments across patient subgroups, usually determined by non-genetic differences between the subgroups. Whilst pharmacogenetics hold promise for enhancing treatment stratification and even treatment individualisation, non-genetic factors will continue to be very important. Both non-genetic and genetic factors must be considered to improve understanding and quantification of the variability in treatment outcomes and to guide stratification and targeting of patient subgroups to the right drug and also to the right range of doses within that subgroup. Development of stratified medicines must consider non-genetic as well as genetic factors and, where appropriate, include stratification through optimising the dose for each patient or subgroup as well as by choosing the drug most likely to deliver efficacy to that patient or group.

Examining predictors of reaction times in children with ADHD and normal controls

A microanalysis of task events in a common go/no-go task was completed to examine how task events impact individual reaction times. Predictors of long reaction times were analyzed to better understand increased intra-individual variability (IIV) among children with ADHD compared with normal controls. Sixty-five children with ADHD and 65 normal controls matched on gender, ethnicity, and age completed a go/no-go task. Children across both groups were slower before and after omission errors than all other trials. They were also slower on the trial before successfully inhibiting their response to no-go trials. Children with ADHD exhibited a pronounced slowing on trials prior to omission errors and trials prior to successful inhibitions compared with the normal control group. Pre-error slowing in children with ADHD may represent the beginning stages of attentional disengagement that subsequently results in the absence of responding (i.e., errors of omission or successful inhibition). While these event-related increases in reaction time explain some of the increased IIV observed in children with ADHD, the removal of these trials did not remove the pronounced between-group differences in IIV, suggesting that additional unmeasured processes are contributing to IIV in children with ADHD.

Operational correlates of prostanoid TP receptor expression in human non-pregnant myometrium are unaffected by excision site or menstrual cycle status of the donor

1. Cumulative concentration-effect curves for the selective prostanoid TP receptor agonist, U46619, were constructed in strips of human non-pregnant myometrium grouped according to tissue excision site (top, lateral wall, lower uterine segment, sub-serosal or sub-endometrial), tissue orientation (strips cut either parallel or perpendicular to the serosa) and donor menstrual status (proliferative or secretory phase). 2. U46619 was excitatory in all tissues. There was no significant difference in either pEC50 or maximum response between groups (P<0.05). The range of pEC50 values was 6.8+/-0.1 (lateral wall, proliferative phase, n=5) to 7.1+/-0.3 (lateral wall, secretory phase, n=5). The range of maximum response values was 0.9+/-0.8 N cm-2 (lateral wall, proliferative phase, n=5) to 3.1+/-1.0 N cm-2 (lateral wall, secretory phase, n=5). 3. Saturation binding analyses were conducted using the radiolabelled TP receptor agonist, [125I]-BOP. Binding parameters were estimated for membranes prepared from human non-pregnant myometrium excised from the lateral wall and grouped according to donor menstrual status. 4. There were no significant differences in the mean pKd and [R]tot values for [125I]-BOP binding between the two groups (proliferative phase: pKd=8.3+/-0.3, [R]tot=412+/-319 fmol mg protein-1, n=5; secretory phase: pKd=8.5+/-0.4, [R]tot=369+/-192 fmol mg protein-1, n=6; P<0.05). 5. These data indicate that U46619-mediated responses in human non-pregnant myometrium are not influenced by tissue excision site, tissue orientation or donor menstrual status and that [125I]-BOP binding is not influenced by donor menstrual status. This suggests that the TP receptor population is homogeneous throughout the human non-pregnant myometrium, and not subject to hormonal regulation.

The variable discharge of cortical neurons: implications for connectivity, computation, and information coding

Cortical neurons exhibit tremendous variability in the number and temporal distribution of spikes in their discharge patterns. Furthermore, this variability appears to be conserved over large regions of the cerebral cortex, suggesting that it is neither reduced nor expanded from stage to stage within a processing pathway. To investigate the principles underlying such statistical homogeneity, we have analyzed a model of synaptic integration incorporating a highly simplified integrate and fire mechanism with decay. We analyzed a "high-input regime" in which neurons receive hundreds of excitatory synaptic inputs during each interspike interval. To produce a graded response in this regime, the neuron must balance excitation with inhibition. We find that a simple integrate and fire mechanism with balanced excitation and inhibition produces a highly variable interspike interval, consistent with experimental data. Detailed information about the temporal pattern of synaptic inputs cannot be recovered from the pattern of output spikes, and we infer that cortical neurons are unlikely to transmit information in the temporal pattern of spike discharge. Rather, we suggest that quantities are represented as rate codes in ensembles of 50-100 neurons. These column-like ensembles tolerate large fractions of common synaptic input and yet covary only weakly in their spike discharge. We find that an ensemble of 100 neurons provides a reliable estimate of rate in just one interspike interval (10-50 msec). Finally, we derived an expression for the variance of the neural spike count that leads to a stable propagation of signal and noise in networks of neurons-that is, conditions that do not impose an accumulation or diminution of noise. The solution implies that single neurons perform simple algebra resembling averaging, and that more sophisticated computations arise by virtue of the anatomical convergence of novel combinations of inputs to the cortical column from external sources.

Response variability of neurons in primary visual cortex (V1) of alert monkeys

Response variability of neurons limits the reliability and resolution of sensory systems. It is generally thought that response variability in the visual system increases at cortical levels, but the causes of the variability have not been identified. We have measured the response variability of neurons in primary visual cortex (V1) of alert monkeys. We recorded from 80 single cells distributed over all V1 layers and from 8 parvocellular cells of the lateral geniculate nucleus. All cells were stimulated with a bar of near-optimal orientation, color, and dimensions while continuously monitoring the eye movements of fixation. To minimize the effects of eye movements, responses that occurred while the eye was relatively steady were selected for analysis. The impulses elicited by each stimulus presentation were counted, and the variance and coefficient of variation were computed. Both measures of response variability were much lower than reported previously for V1 cells of both alert and anesthetized monkeys. Our data show that fixational eye movements cause a large component of response variance in alert monkeys. Moreover, the reliability of V1 neurons is not obviously degraded compared with lateral geniculate nucleus cells. The high reliability of neurons in alert monkeys is consistent with expectations from conventional biophysical models, and it suggests that activity in a modest number of neurons may suffice to form a perceptual decision.