Renal trace elements in barren-ground caribou subpopulations: Temporal trends and differing effects of sex, age and season

Caribou (Rangifer tarandus) are a culturally significant food resource for communities in northern Canada and Greenland. Many barren-ground caribou subpopulations are currently in decline, some dramatically; understanding the influence of stressors, such as toxic trace metals, is important. These contaminants enter Arctic terrestrial environments via atmospheric transport from industrialized areas and from local sources, accumulating there in the environment. Understanding how trace element concentrations interact and are influenced by caribou sex, age and season of collection is essential to evaluating trends in these elements over time and differences among subpopulations. We used path analysis to model the direct and indirect relationships between these variables in the Porcupine subpopulation and in barren-ground caribou from the Canadian Arctic and Greenland. Renal cadmium (Cd), copper (Cu) and mercury (Hg) varied significantly among subpopulations. Hg was positively correlated with Cd, Cu and selenium (Se) in female Porcupine caribou whereas Cd and Cu were negatively correlated in male Porcupine caribou. Age, season and sex influenced all three element concentrations and should be considered when comparing elements among caribou subpopulations or years. Renal Cd decreased slightly from the Canadian Western Arctic to Greenland and increased slightly over time, possibly reflecting patterns of atmospheric deposition. Renal Hg did not change significantly over time, and differences among subpopulations did not follow specific geographical patterns. Renal Cu declined over time, the changes being markedly different among subpopulations, sexes and seasons. This temporal decline is likely due to changes in diet, which could be driven by various environmental factors. Declining Cu concentrations in caribou is of concern as low levels could negatively affect reproductive success and therefore caribou at a population level. Continuing to monitor element concentrations in caribou is essential to better comprehend potential threats facing the species, and to promote food security in communities harvesting this important resource.

Safety and tolerability of exenatide once weekly in patients with type 2 diabetes: an integrated analysis of 4,328 patients

BACKGROUND

Exenatide once weekly (QW) is a glucagon-like peptide-1 receptor agonist (GLP-1RA) for the treatment of type 2 diabetes. Safety and tolerability are key considerations in treatment selection. This analysis examines the safety and tolerability profile of exenatide QW, other approved GLP-1RAs (exenatide twice daily and liraglutide once daily), and a pooled population of commonly used non-GLP-1RA treatments.

METHODS

Intent-to-treat populations from eight randomized Phase III trials with 24-week and 30-week comparator-controlled periods were analyzed. Data were pooled for exenatide QW, exenatide twice daily, and non-GLP-1RA comparator groups; comparisons between exenatide QW and liraglutide were analyzed separately to better match study groups. The incidence of treatment-emergent adverse events with 95% confidence intervals and exposure-adjusted incidence were calculated. Duration and recurrence were analyzed for gastrointestinal adverse events and adverse events of special interest.

RESULTS

Incidences of serious adverse events did not differ between treatments. Discontinuations due to adverse events occurred numerically less frequently with exenatide QW than with other GLP-1RAs but numerically more frequently than with non-GLP-1RA comparators. The most frequent adverse events in the GLP-1RA groups were gastrointestinal and generally mild, with decreasing incidence over time. Gastrointestinal adverse event incidences appeared lower with exenatide QW versus other GLP-1RAs and greater than with non-GLP-1RA comparators. Injection site-related adverse events seemed highest with exenatide QW, but generally did not lead to withdrawal and abated over time. Hypoglycemia was infrequent overall, but occurred numerically more frequently in the non-GLP-1RA comparator group and increased with concomitant sulfonylurea use. Pancreatitis, thyroid cancer, renal failure, and gallbladder disease were rarely reported.

CONCLUSION

The overall safety and tolerability profile of exenatide QW was similar to that of other GLP-1RAs, with improved gastrointestinal tolerability. The safety and tolerability profile of exenatide QW compared with non-GLP-1RA comparators was similar overall, with the exception of a lower incidence of hypoglycemia and anticipated differences in gastrointestinal and injection site-related adverse events.

Safety and tolerability of exenatide twice daily in patients with type 2 diabetes: integrated analysis of 5594 patients from 19 placebo-controlled and comparator-controlled clinical trials

BACKGROUND

Exenatide twice daily is a first-in-class glucagon-like peptide receptor agonist approved for the treatment of type 2 diabetes. The objective of this analysis was to evaluate the safety profile of exenatide twice daily and to compare its profile with that of a pooled comparator (placebo and insulin) in patients with type 2 diabetes.

METHODS

Data from 19 completed, randomized, controlled clinical trials of exenatide twice daily (5 μg and 10 μg) were pooled and analyzed; the pooled data included 5594 intent-to-treat patients who were followed for 12-52 weeks. Incidence rates, exposure-adjusted incidence rates, and 95% confidence intervals around risk differences between groups were calculated.

RESULTS

Baseline demographics and exposure time were comparable between groups (exenatide, N = 3261; pooled comparator, N = 2333; mean exposure time 166-171 days). Transient, mild- to-moderate nausea was the most frequent adverse event with exenatide (36.9% versus 8.3% in the pooled comparator). The incidence of hypoglycemia (minor or major) with concomitant sulfonylurea (exenatide 26.5%, pooled comparator 20.7%) was higher than that without sulfonylurea (exenatide 3.1%, pooled comparator 2.7%) in all groups. Serious adverse events, discontinuations due to serious adverse events, and deaths were reported with similar frequency in the exenatide and pooled comparator groups. Composite exposure-adjusted incidence rates were not statistically different between groups for pancreatitis, renal impairment, or major adverse cardiac events; there was a difference in incidence rates for benign thyroid neoplasm (0.3% versus 0%).

CONCLUSION

Overall, this analysis, representing over 1500 patient-years of exposure, demonstrated that exenatide twice daily was safe and generally well tolerated in patients with type 2 diabetes. The incidence of most adverse events, including serious adverse events, was similar in both exenatide-treated and comparator-treated patients. The most distinct differences between groups were in gastrointestinal-related adverse events, which is consistent with other therapies within the glucagon-like peptide class.

Increased variability and abnormalities in pancreatic enzyme concentrations in otherwise asymptomatic subjects with type 2 diabetes

BACKGROUND

Recent studies have demonstrated an increased incidence of pancreatitis in patients with type 2 diabetes compared with obese nondiabetic individuals. Serum lipase and pancreatic amylase concentrations are used in conjunction with clinical findings to diagnose pancreatitis.

METHODS

In two large clinical trials of overweight/obese nondiabetic and type 2 diabetic subjects, lipase and pancreatic amylase were measured at screening and 2-5 weeks later at baseline (prior to treatment with study medication).

RESULTS

Lipase and pancreatic amylase concentrations were above the upper limit of normal (ULN) in 13% and 6% of type 2 diabetic subjects, respectively, and were approximately three-fold (3 ×) higher than the proportion of nondiabetic subjects with levels above ULN. Elevations exceeding ULN were seen in many subjects asymptomatic for pancreatitis; however, elevations >2 × ULN and >3 × ULN were uncommon, and elevations >3 × ULN were often associated with a history of dyslipidemia, hyperlipidemia, and gastrointestinal disorders. Additionally, enzyme concentrations varied within this 2-5-week screening period, including shifts between elevated and normal levels.

CONCLUSION

Results from this post hoc analysis suggest that, although pancreatic enzymes can be a useful marker for pancreatitis within the proper clinical context, diagnosis of pancreatitis may be confounded in populations known to have asymptomatic elevations associated with disease, such as type 2 diabetes. Further effort is needed to clarify the etiology and epidemiology of pancreatic enzyme elevations in type 2 diabetes.

Exenatide once weekly treatment maintained improvements in glycemic control and weight loss over 2 years

BACKGROUND

The once-weekly (QW) formulation of the glucagon-like peptide-1 receptor agonist exenatide has been demonstrated to improve A1C, fasting plasma glucose (FPG), body weight, serum lipid profiles, and blood pressure in patients with type 2 diabetes through 52 weeks of treatment. In this report, we describe the 2-year results of the open-label, open-ended extension to the DURATION-1 trial of exenatide QW for type 2 diabetes.

METHODS

A 2-stage protocol was used: patients received either exenatide QW (2 mg) or exenatide twice daily for 30 weeks (5 μg for the first 4 weeks and 10 μg thereafter), followed by 1.5 years of treatment with exenatide QW (2 mg), for a total of 2 years (104 weeks) of exenatide treatment. Of the 295 (intent-to-treat [ITT]) patients who entered the trial, 73% (n = 216) completed 2 years of treatment (completer population). Baseline characteristics (mean ± SE) for these patients were: A1C, 8.2 ± 0.1%; FPG, 168.4 ± 43.0 mg/dL; body weight, 101.1 ± 18.7 kg; and diabetes duration, 7 ± 5 years.

RESULTS

In the completer population, significant improvements (LS mean ± SE [95% CI]) were maintained after 2 years of treatment in A1C (-1.71 ± 0.08% [-1.86 to -1.55%]), FPG (-40.1 ± 2.9 mg/dL [-45.7 to -34.5 mg/dL]), and body weight (-2.61 ± 0.52 kg [-3.64 to -1.58 kg]) compared with baseline. The percentages of patients who achieved an A1C of <7.0% and ≤6.5% at 2 years were 60% and 39%, respectively. A significant reduction in systolic blood pressure (SBP; -3.0 ± 1.0 mmHg [-4.9 to -1.1 mmHg]) was maintained through 2 years of treatment. Serum lipid profiles were also significantly improved, including triglycerides (geometric LS mean change from baseline, -15 ± 2.7% [-21% to -10%]), total cholesterol (-8.6 ± 2.8 mg/dL [-14.0 to -3.1 mg/dL]), and low-density lipoproteins (-4.5 ± 2.2 mg/dL [-8.9 to -0.01 mg/dL]). Changes in A1C, body weight, FPG, SBP, and lipids in the ITT population were similar to those seen in the completer population. Nausea (predominantly mild in intensity) was the most common adverse event, although the frequency and intensity of nausea decreased over time. No severe hypoglycemia was observed.

CONCLUSIONS

Exenatide QW was well tolerated during the 2-year treatment period. This study demonstrated sustained glucose control and weight loss throughout 2 years of treatment with exenatide QW.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00308139.

Is there a brainstem substrate for action selection?

The search for the neural substrate of vertebrate action selection has focused on structures in the forebrain and midbrain, and particularly on the group of sub-cortical nuclei known as the basal ganglia. Yet, the behavioural repertoire of decerebrate and neonatal animals suggests the existence of a relatively self-contained neural substrate for action selection in the brainstem. We propose that the medial reticular formation (mRF) is the substrate's main component and review evidence showing that the mRF's inputs, outputs and intrinsic organization are consistent with the requirements of an action-selection system. The internal architecture of the mRF is composed of interconnected neuron clusters. We present an anatomical model which suggests that the mRF's intrinsic circuitry constitutes a small-world network and extend this result to show that it may have evolved to reduce axonal wiring. Potential configurations of action representation within the internal circuitry of the mRF are then assessed by computational modelling. We present new results demonstrating that each cluster's output is most likely to represent activation of a component action; thus, coactivation of a set of these clusters would lead to the coordinated behavioural response observed in the animal. Finally, we consider the potential integration of the basal ganglia and mRF substrates for selection and suggest that they may collectively form a layered/hierarchical control system.

The brainstem reticular formation is a small-world, not scale-free, network

Recently, it has been demonstrated that several complex systems may have simple graph-theoretic characterizations as so-called 'small-world' and 'scale-free' networks. These networks have also been applied to the gross neural connectivity between primate cortical areas and the nervous system of Caenorhabditis elegans. Here, we extend this work to a specific neural circuit of the vertebrate brain--the medial reticular formation (RF) of the brainstem--and, in doing so, we have made three key contributions. First, this work constitutes the first model (and quantitative review) of this important brain structure for over three decades. Second, we have developed the first graph-theoretic analysis of vertebrate brain connectivity at the neural network level. Third, we propose simple metrics to quantitatively assess the extent to which the networks studied are small-world or scale-free. We conclude that the medial RF is configured to create small-world (implying coherent rapid-processing capabilities), but not scale-free, type networks under assumptions which are amenable to quantitative measurement.

A computational model of action selection in the basal ganglia. I. A new functional anatomy

We present a biologically plausible model of processing intrinsic to the basal ganglia based on the computational premise that action selection is a primary role of these central brain structures. By encoding the propensity for selecting a given action in a scalar value (the salience), it is shown that action selection may be recast in terms of signal selection. The generic properties of signal selection are defined and neural networks for this type of computation examined. A comparison between these networks and basal ganglia anatomy leads to a novel functional decomposition of the basal ganglia architecture into 'selection' and 'control' pathways. The former pathway performs the selection per se via a feedforward off-centre on-surround network. The control pathway regulates the action of the selection pathway to ensure its effective operation, and synergistically complements its dopaminergic modulation. The model contrasts with the prevailing functional segregation of basal ganglia into 'direct' and 'indirect' pathways.

A computational model of action selection in the basal ganglia. II. Analysis and simulation of behaviour

In a companion paper a new functional architecture was proposed for the basal ganglia based on the premise that these brain structures play a central role in behavioural action selection. The current paper quantitatively describes the properties of the model using analysis and simulation. The decomposition of the basal ganglia into selection and control pathways is supported in several ways. First, several elegant features are exposed--capacity scaling, enhanced selectivity and synergistic dopamine modulation--which might be expected to exist in a well designed action selection mechanism. The discovery of these features also lends support to the computational premise of selection that underpins our model. Second, good matches between model globus pallidus external segment output and globus pallidus internal segment and substantia nigra reticulata area output, and neurophysiological data, have been found which are indicative of common architectural features in the model and biological basal ganglia. Third, the behaviour of the model as a signal selection mechanism has parallels with some kinds of action selection observed in animals under various levels of dopaminergic modulation.

The basal ganglia: a vertebrate solution to the selection problem?

A selection problem arises whenever two or more competing systems seek simultaneous access to a restricted resource. Consideration of several selection architectures suggests there are significant advantages for systems which incorporate a central switching mechanism. We propose that the vertebrate basal ganglia have evolved as a centralized selection device, specialized to resolve conflicts over access to limited motor and cognitive resources. Analysis of basal ganglia functional architecture and its position within a wider anatomical framework suggests it can satisfy many of the requirements expected of an efficient selection mechanism.

Is the short-latency dopamine response too short to signal reward error?

Unexpected stimuli that are behaviourally significant have the capacity to elicit a short-latency, short-duration burst of firing in mesencephalic dopaminergic neurones. An influential interpretation of the experimental data that characterize this response proposes that dopaminergic neurones have a crucial role in reinforcement learning because they signal error in the prediction of future reward. In this article we propose a different functional role for this 'short-latency dopamine response' in the mechanisms that underlie associative learning. We suggest that the initial burst of dopaminergic-neurone firing could represent an essential component in the process of switching attentional and behavioural selections to unexpected, behaviourally important stimuli. This switching response could be a crucial prerequisite for associative learning and might be part of a general short-latency response that is mediated by catecholamines and prepares the organism for an appropriate reaction to biologically significant events. Any act which in a given situation produces satisfaction becomes associated with that situation so that when the situation recurs the act is more likely than before to recur also. E.L. Thorndike (1911) 1.

Antenatal risk factors for childhood diabetes mellitus; a case-control study of medical record data in Yorkshire, UK

Environmental risk factors for childhood insulin-dependent diabetes mellitus (IDDM) have been investigated using data abstracted from the obstetric records of mothers participating in a population-based case-control study of children (0-15 years) diagnosed with IDDM during 1993-1994. A univariate analysis of 196 age and sex matched sets (129 triplets, 67 pairs) gave significantly raised odds ratios (OR) for mothers over 35 years (OR 2.13, 95%CI 1.04-4.36) and the following exposures in pregnancy: amniocentesis (3.85, 1.34-11.04), oedema, proteinuria and/or hypertensive disorders (1.62, 1.03-2.54), excessive weight gain (7.12, 1.50-33.79) and complications in labour (1.49, 1.00-2.21). The risk previously associated with caesarean deliveries was confirmed and the trend of increasing risk with age was significant. Adjusting separately for mothers with IDDM (4 cases, 0 control subjects), parity and small for gestational age failed to have any influence on the pregnancy risk factors or caesarean delivery. Case mothers undergoing amniocentesis were significantly younger compared to their control counterparts (p = 0.02) and the majority were given the test to determine fetal maturity, late in pregnancy, rather than to identify chromosomal abnormalities. Oedema, proteinuria and/or hypertension conferred an increased risk throughout pregnancy, particularly in the first two trimesters. No specific pattern of risk was present for any age group. Multivariate modelling of the significant OR, using conditional logistic regression, retained excessive weight gain as significant. The overall results present a risk profile of older mothers whose babies may be exposed to adverse intrauterine conditions and delivery by caesarean section.

A biologically plausible model of early visual motion processing. II: psychophysical application

We test the model of early visual processing introduced in the companion paper by simulating a range of psychophysical phenomena. We present new data concerning our ability to discriminate the speed of drifting gratings when spatiotemporally apertured in a variety of ways. We shall investigate the role played by the aperture in modifying the grating's behaviour from its idealisation as a pure Fourier component and show that this is not negligible. Other phenomena which we simulate and explain relate to the way perceived velocity is influenced by contrast and spatial frequency. Many of our explanations are couched in terms of the relative number of cells occurring within each locale of the Fourier domain. This use of the cell density map is a unifying concept and avoids the necessity for a range of separate mechanisms. We argue that a neurophysiologically detailed model is necessary in order to explain psychophysical data (Weber fractions) which vary over less than an order of magnitude, and small deviations from veridical encoding of velocity.

A biologically plausible model of early visual motion processing. I: theory and implementation

A model of local image encoding is described which explicitly incorporates quantitative data about the number density, bandwidth and receptive field organisation of neurons involved in motion detection. The model solves the problem of extracting local velocity on the basis of inputs tuned to spatiotemporal frequency and sensitive to contrast. The spatiotemporally tuned, opponent motion filters are followed by a compressive non-linearity and comprise a first stage. The inter-stage signals are interpreted as those from single neurons and the second stage is modelled as a neural-network layer. The second stage uses semilinear units and models the effect of lateral, on-centre off-surround, intra-layer connections. Characterisation of the first stage leads to a clarification of the concept of the psychophysical 'channel' and its relation to physiological data. The quantitative parametrisation of the model allows the simulation of several psychophysical phenomena which are reported in a companion paper.

Rotation and radical motion thresholds support a two-stage model of differential-motion analysis

Lower motion thresholds for rotational and radial flow have been measured for stimuli consisting of four closely packed circular apertures, each containing patches of drifting grating or plaid. Detection and direction thresholds were measured for gratings and plaids as a function of the relative orientation of the pattern components. There was a similarity between both types of threshold, supporting the existence of specialised rotation and radial-flow detectors. Further, thresholds increased with the relative component orientation for both gratings and plaids. This suggests that component information from a first stage, tuned spatiotemporally and to orientation, is being used directly to compute the optic flow in a two-stage process. A model based on this architecture is described by means of simple template receptive-field arrays with separable temporal and spatial tuning at the first stage.