[Show abstract][Hide abstract] ABSTRACT: Schizophrenia is associated with upregulation of dopamine (DA) release in the caudate nucleus. The caudate has dense connections with the orbitofrontal cortex (OFC) via the frontostriatal loops, and both areas exhibit pathophysiological change in schizophrenia. Despite evidence that abnormalities in dopaminergic neurotransmission and prefrontal cortex function co-occur in schizophrenia, the influence of OFC DA on caudate DA and reinforcement processing is poorly understood. To test the hypothesis that OFC dopaminergic dysfunction disrupts caudate dopamine function, we selectively depleted dopamine from the OFC of marmoset monkeys and measured striatal extracellular dopamine levels (using microdialysis) and dopamine D2/D3 receptor binding (using positron emission tomography), while modeling reinforcement-related behavior in a discrimination learning paradigm. OFC dopamine depletion caused an increase in tonic dopamine levels in the caudate nucleus and a corresponding reduction in D2/D3 receptor binding. Computational modeling of behavior showed that the lesion increased response exploration, reducing the tendency to persist with a recently chosen response side. This effect is akin to increased response switching previously seen in schizophrenia and was correlated with striatal but not OFC D2/D3 receptor binding. These results demonstrate that OFC dopamine depletion is sufficient to induce striatal hyperdopaminergia and changes in reinforcement learning relevant to schizophrenia.
The Journal of neuroscience : the official journal of the Society for Neuroscience. 05/2014; 34(22):7663-76.
[Show abstract][Hide abstract] ABSTRACT: Insidious changes in behaviour herald the onset of progressive neurodegenerative disorders such as Huntington's disease (HD), sometimes years before overt symptoms are seen. Sleep and circadian disturbances are particularly disruptive symptoms in patients with neurological disorders, but they are difficult to measure in humans. Here we studied circadian behaviour in transgenic HD sheep expressing the full-length human huntingtin protein with an expanded CAG repeat mutation in the juvenile range. Young HD sheep with no other symptoms exhibited circadian behavioural abnormalities that worsened with age. The most obvious change was a disturbed evening behaviour reminiscent of 'sundowning' that is seen in some patients with dementia. There were no structural abnormalities seen with MRI, even in 5-year-old HD sheep. Interestingly, detection of the circadian abnormalities depended upon their social grouping. Abnormalities emerged in sheep kept in an 'HD-only' flock, whereas the behaviour of HD sheep kept mixed with normal sheep was relatively normal. Sleep-wake abnormalities in HD patients are also likely to be hidden, and may precede overt symptoms by many years. Sleep disruption has deleterious effects, even in normal people. The knock-on effects of sleep-wake disturbance may exacerbate, or even cause symptoms such as irritability and depression that are common in early stage HD patients. HD sheep will be useful models for probing the mechanisms underlying circadian behavioural disorder in HD.
Human Molecular Genetics 01/2014; · 7.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Increasingly, evidence from studies in both animal models and patients suggests that cardiovascular dysfunction is important in HD. Previous studies measuring function of the left ventricle (LV) in the R6/2 model have found a clear cardiac abnormality, albeit with preserved LV systolic function. It was hypothesized that an impairment of RV function might play a role in this condition via mechanisms of ventricular interdependence.
To investigate RV function in the R6/2 mouse model of Huntington's disease (HD).
Cardiac cine-magnetic resonance imaging (MRI) was used to determine functional parameters in R6/2 mice. In a first experiment, these parameters were derived longitudinally to determine deterioration of cardiac function with disease progression. A second experiment compared the response to a stress test (using dobutamine) of wildtype and early-symptomatic R6/2 mice.
There was progressive deterioration of RV systolic function with age in R6/2 mice. Furthermore, beta-adrenergic stimulation with dobutamine revealed RV dysfunction in R6/2 mice before any overt symptoms of the disease were apparent.
This work adds to accumulating evidence of cardiovascular dysfunction in R6/2 mice, describing for the first time the involvement of the right ventricle. Cardiovascular dysfunction should be considered, both when treatment strategies are being designed, and when searching for biomarkers for HD.
Journal of Huntington's disease. 01/2014; 3(1):25-32.
[Show abstract][Hide abstract] ABSTRACT: Accurate kinetic modelling of in vivo physiological function using
positron emission tomography (PET) requires determination of the tracer
time-activity curve in plasma, known as the arterial input
function (AIF). The AIF is usually determined by invasive blood sampling
methods, which are prohibitive in murine studies due to low total blood
volumes. Extracting AIFs from PET images is also challenging due to
large partial volume effects (PVE). We hypothesise that in combined PET
with magnetic resonance imaging (PET/MR), a co-injected bolus of MR
contrast agent and PET ligand can be tracked using fast MR acquisitions.
This protocol would allow extraction of a MR AIF from MR contrast agent
concentration-time curves, at higher spatial and temporal
resolution than an image-derived PET AIF. A conversion factor could then
be applied to the MR AIF for use in PET kinetic analysis. This work has
compared AIFs obtained from sequential DSC-MRI and PET with separate
injections of gadolinium contrast agent and 18F-FDG
respectively to ascertain the technique‧s validity. An automated
voxel selection algorithm was employed to improve MR AIF
reproducibility. We found that MR and PET AIFs displayed similar
character in the first pass, confirmed by gamma variate fits
(p<0.02). MR AIFs displayed reduced PVE compared to PET AIFs,
indicating their potential use in PET/MR studies.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2014; · 1.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mitochondrial complex I, the primary entry point for electrons into the mitochondrial respiratory chain, is both critical for aerobic respiration and a major source of reactive oxygen species. In the heart, chronic dysfunction driving cardiomyopathy is frequently associated with decreased complex I activity, from both genetic and environmental causes. To examine the functional relationship between complex I disruption and cardiac dysfunction we used an established mouse model of mild and chronic complex I inhibition through heart-specific Ndufs4 gene ablation. Heart-specific Ndufs4-null mice had a decrease of ∼50% in complex I activity within the heart, and developed severe hypertrophic cardiomyopathy as assessed by magnetic resonance imaging. The decrease in complex I activity, and associated cardiac dysfunction, occurred absent an increase in mitochondrial hydrogen peroxide levels in vivo, accumulation of markers of oxidative damage, induction of apoptosis, or tissue fibrosis. Taken together, these results indicate that diminished complex I activity in the heart alone is sufficient to drive hypertrophic cardiomyopathy independently of alterations in levels of mitochondrial hydrogen peroxide or oxidative damage.
PLoS ONE 01/2014; 9(4):e94157. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Radial acquisitions can suffer from trajectory errors leading to reduced image quality. Here we present a new method of trajectory correction that uses all spokes of a radial acquisition and compare it to an existing method that uses a two-spoke pre-scan calibration. For both methods, estimates of the necessary shifts were made using magnitude or phase data and the performances were compared. The additional effect of B0 correction was considered in all cases. Mouse cardiac scans were used for the comparisons and we also compared the quality of navigator signals obtained from the radial data with each technique.
The proposed method gave improved image quality over the existing method, as assessed by visual inspection and quantitative evaluation of artifacts. The typical shading artifacts seen in radial scans were significantly reduced with both approaches, with phase-based corrections generally outperforming magnitude-based methods. B0 correction gave further improvements in each case. Furthermore, modulation of navigator signals due to the acquisition angle was significantly reduced with the new technique. We show that our proposed method works well to reduce artifacts seen in mouse cardiac imaging that can make faster imaging feasible.
[Show abstract][Hide abstract] ABSTRACT: Cerebral atrophy is one of the most widely brain alterations associated to aging. A clear relationship has been established between age-associated cognitive impairments and cerebral atrophy. The mouse lemur (Microcebus murinus) is a small primate used as a model of age-related neurodegenerative processes. It is the first non-human primate in which cerebral atrophy has been correlated with cognitive deficits. Previous studies of cerebral atrophy in this model were based on time consuming manual delineation or measurement of selected brain regions from magnetic resonance images (MRI). These measures could not be used to analyse regions that cannot be easily outlined such as the nucleus basalis of Meynert or the subiculum. In humans, morphometric assessment of structural changes with age is generally performed with automated procedures such as voxel-based morphometry (VBM). The objective of our work was to perform user-independent assessment of age-related morphological changes in the whole brain of large mouse lemur populations thanks to VBM. The study was based on the SPMMouse toolbox of SPM 8 and involved thirty mouse lemurs aged from 1.9 to 11.3 years. The automatic method revealed for the first time atrophy in regions where manual delineation is prohibitive (nucleus basalis of Meynert, subiculum, prepiriform cortex, Brodmann areas 13-16, hypothalamus, putamen, thalamus, corpus callosum). Some of these regions are described as particularly sensitive to age-associated alterations in humans. The method revealed also age-associated atrophy in cortical regions (cingulate, occipital, parietal), nucleus septalis, and the caudate. Manual measures performed in some of these regions were in good agreement with results from automatic measures. The templates generated in this study as well as the toolbox for SPM8 can be downloaded. These tools will be valuable for future evaluation of various treatments that are tested to modulate cerebral aging in lemurs.
Frontiers in Aging Neuroscience 01/2014; 6:82. · 5.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Pathological forms of impulsivity are manifest in a number of psychiatric disorders listed in DSM-5, including attention-deficit/hyperactivity disorder and substance use disorder. However, the molecular and cellular substrates of impulsivity are poorly understood. Here, we investigated a specific form of motor impulsivity in rats, namely premature responding, on a five-choice serial reaction time task.
We used in vivo voxel-based magnetic resonance imaging and ex vivo Western blot analyses to investigate putative structural, neuronal, and glial protein markers in low-impulsive (LI) and high-impulsive rats. We also investigated whether messenger RNA interference targeting glutamate decarboxylase 65/67 (GAD65/67) gene expression in the nucleus accumbens core (NAcbC) is sufficient to increase impulsivity in LI rats.
We identified structural and molecular abnormalities in the NAcbC associated with motor impulsivity in rats. We report a reduction in gray matter density in the left NAcbC of high-impulsive rats, with corresponding reductions in this region of glutamate decarboxylase (GAD65/67) and markers of dendritic spines and microtubules. We further demonstrate that the experimental reduction of de novo of GAD65/67 expression bilaterally in the NAcbC is sufficient to increase impulsivity in LI rats.
These results reveal a novel mechanism of impulsivity in rats involving gamma aminobutyric acidergic and structural abnormalities in the NAcbC with potential relevance to the etiology and treatment of attention-deficit/hyperactivity disorder and related disorders.
[Show abstract][Hide abstract] ABSTRACT: Despite widespread application to human imaging, voxel-based morphometry (VBM), where images are compared following grey matter (GM) segmentation, is seldom used in mice. Here VBM is performed for the R6/2 model of Huntington's disease, a progressive neurological disorder. This article discusses issues in translating the methods to mice and shows that its statistical basis is sound in mice as it is in human studies. Whole brain images from live transgenic and control mice are segmented into GM maps after processing and compared to produce statistical parametric maps of likely differences. To assess whether false positives were likely to occur, a large cohort of ex vivo magnetic resonance brain images were sampled with permutation testing. Differences were seen particularly in the striatum and cortex, in line with studies performed ex vivo and as seen in human patients. In validation, the rate of false positives is as expected and these have no discernible distribution through the brain. The study shows that VBM successfully detects differences in the Huntington's disease mouse brain. The method is rapid compared to manual delineation and reliable. The templates created here for the mouse brain are freely released for other users in addition to an open-source software toolbox for performing mouse VBM.
Magnetic Resonance Imaging 07/2013; · 2.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Addiction is a chronically relapsing brain disorder that insidiously affects the motivational and cognitive control systems of susceptible individuals. Clinical research over the last two decades has profited from the technique of positron emission tomography (PET), a non-invasive imaging technique that allows the longitudinal assessment of addiction-relevant biomarkers in current and former drug users. The vast majority of this research has unsurprisingly focused on the brain dopamine (DA) systems given their pivotal role in primary drug reinforcement and the rich abundance of dopaminergic PET tracers. However, the provocative failure of dopaminergic medications in addiction has fuelled the search for alternative treatments. This article considers current controversies in this field as well as prospects for elucidating neurotransmitter mechanisms in addiction beyond DA.
Current opinion in neurobiology 05/2013; · 7.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have previously shown that impulsivity in rats predicts the emergence of compulsive cocaine seeking and taking, and is coupled to decreased D(2/3) receptor availability in the ventral striatum. Since withdrawal from cocaine normalises high impulsivity in rats, we investigated, using positron emission tomography (PET), the effects of response-contingent cocaine administration on D(2/3) receptor availability in the striatum. Rats were screened for impulsive behavior on the 5-choice serial reaction time task. After a baseline PET scan with the D(2/3) ligand [(18)F]fallypride, rats were trained to self-administer cocaine for 15 days under a long-access schedule. As a follow up, rats were assessed for impulsivity and underwent a second [(18)F]fallypride PET scan. At baseline, we found that D(2/3) receptor availability was significantly lower in the left, but not right, ventral striatum of high-impulsive rats compared with low-impulsive rats. While the number of self-administered cocaine infusions was not different between the two impulsivity groups, impulsivity selectively decreased in high-impulsive rats withdrawn from cocaine. This effect was accompanied by a significant increase in D(2/3) receptor availability in the left, but not right, ventral striatum. We further report that D(2/3) receptor availability was inversely related to baseline D(2/3) receptor availability in the ventral striatum of high-impulsive rats, as well as to the left and right dorsal striatum of both low-impulsive and high-impulsive rats. These findings indicate that the reduction in impulsivity in high-impulsive rats by prior cocaine exposure may be mediated by a selective correction of deficient D(2/3) receptor availability in the ventral striatum. A similar baseline-dependent mechanism may account for the therapeutic effects of stimulant drugs in clinical disorders such as ADHD.Neuropsychopharmacology accepted article preview online, 11 February 2013; doi:10.1038/npp.2013.44.
Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology 02/2013; · 8.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Chronic heart failure, as a result of acute myocardial infarction, is a leading cause of death worldwide. Combining diagnostic imaging modalities may aid the direct assessment of experimental treatments targeting heart failure in vivo. Here we present preliminary data using the Cambridge combined PET/MRI imaging system in a mouse model of acute myocardial infarction. The split-magnet design can deliver uncompromised MRI and PET performance, for better assessment of disease and treatment in a preclinical environment.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 02/2013; 702:47–49. · 1.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Simultaneous PET–MR acquisition provides the high temporal and spatial resolution of MRI with the specificity of PET. In PET, accurate modelling of physiological function in vivo requires the time-activity curve of tracer in blood plasma, known as the arterial input function (AIF). As the gold standard method of blood sampling is inherently prohibitive in the small animal case, here we discuss how we prepare to rapidly sample MRI signals from gadolinium-doped tracer to obtain the tracer input functions from a simultaneous PET-MR measurement. ΔR2⁎ measurements taken from EPI images were used to obtain first pass bolus AIFs in the rat brain from DSC-MRI datasets of 5 rats. AIFs obtained using our automatic algorithm were found to be consistent between animals and compared well with manual methods without need for a priori voxel selection. A variable flip angle FLASH sequence used for T1 mapping was successfully tested in a phantom study, providing accurate measurements of Gd concentration.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 02/2013; 702:126–128. · 1.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: INTRODUCTION: Severe brain hypoxia in the territory of the occluded artery is a key feature of ischemic stroke. This region can be imaged using positron emission tomography (PET) and the standard hypoxia radiotracer (18)F-fluoromisonidazole ((18)F-FMISO). However, the utility of (18)F-FMISO is limited by its slow accumulation in the lesion. Therefore, this study investigated three hypoxia-sensitive radiotracers, namely the nitroimidazole (18)F-fluoroazomycin arabinoside ((18)F-FAZA) and two (64)Cu bis(thiosemicarbazone) complexes ((64)Cu-ATSM and (64)Cu-ATSE), expected to have improved pharmacokinetic profiles relative to (18)F-FMISO, in a rodent model of ischemic stroke. METHODS: In anaesthetised Wistar rats, the distal middle cerebral artery was permanently occluded by electrocoagulation, the radiotracers administered intravenously and animals PET scanned for up to 3hours, followed by T2-weighted magnetic resonance imaging to map the infarct. RESULTS: As expected, late and prominent (18)F-FMISO retention was observed despite lower tracer delivery into the affected region. Time-activity curves revealed that both (64)Cu-ATSM and (64)Cu-ATSE showed rapid entry and efflux from the brain, but did not show significant accumulation in the lesion. (18)F-FAZA showed limited brain penetration, and accumulation in the lesion was inconsistent, low and as slow as (18)F-FMISO. CONCLUSIONS: This study suggests further development of these radiotracers as hypoxia markers for ischemic stroke may not be warranted.
Nuclear Medicine and Biology 01/2013; · 2.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Heart failure originating from myocardial infarction (MI) is a leading
cause of death worldwide. Mouse models of ischaemia and reperfusion
injury (I/R) are used to study the effects of novel treatment strategies
targeting MI, however staging disease and treatment efficacy is a
challenge. Damage and recovery can be assessed on the cellular, tissue
or whole-organ scale but these are rarely measured in concert. Here, for
the first time, we present data showing measures of injury in infarcted
mice using complementary techniques for multi-modal characterisation of
the heart. We use in vivo magnetic resonance imaging (MRI) to assess
heart function with cine-MRI, hindered perfusion with late gadolinium
enhancement imaging and muscular function with displacement encoded with
stimulated echoes (DENSE) MRI. These measures are followed by positron
emission tomography (PET) with 18-F-fluorodeoxyglucose to assess
cellular metabolism. We demonstrate a protocol combining each of these
measures for the same animal in the same imaging session and compare how
the different markers can be used to quantify cardiac recovery on
different scales following injury.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2013; · 1.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Myocardial infarction is one of the leading causes of death in the Western world. The similarity of the mouse heart to the human heart has made it an ideal model for testing novel therapeutic strategies. In vivo magnetic resonance imaging (MRI) gives excellent views of the heart noninvasively with clear anatomical detail, which can be used for accurate functional assessment. Contrast agents can provide basic measures of tissue viability but these are nonspecific. Positron emission tomography (PET) is a complementary technique that is highly specific for molecular imaging, but lacks the anatomical detail of MRI. Used together, these techniques offer a sensitive, specific and quantitative tool for the assessment of the heart in disease and recovery following treatment. In this paper we explain how these methods are carried out in mouse models of acute myocardial infarction. The procedures described here were designed for the assessment of putative protective drug treatments. We used MRI to measure systolic function and infarct size with late gadolinium enhancement, and PET with fluorodeoxyglucose (FDG) to assess metabolic function in the infarcted region. The paper focuses on practical aspects such as slice planning, accurate gating, drug delivery, segmentation of images, and multimodal coregistration. The methods presented here achieve good repeatability and accuracy maintaining a high throughput.
[Show abstract][Hide abstract] ABSTRACT: Stimulation of the nitric oxide (NO) - soluble guanylate (sGC) - protein kinase G (PKG) pathway confers protection against acute ischaemia/reperfusion injury, but more chronic effects in reducing post-myocardial infarction (MI) heart failure are less defined. The aim of this study was to not only determine whether the sGC stimulator riociguat reduces infarct size but also whether it protects against the development of post-MI heart failure.
Mice were subjected to 30 min ischaemia via ligation of the left main coronary artery to induce MI and either placebo or riociguat (1.2 µmol/l) were given as a bolus 5 min before and 5 min after onset of reperfusion. After 24 hours, both, late gadolinium-enhanced magnetic resonance imaging (LGE-MRI) and (18)F-FDG-positron emission tomography (PET) were performed to determine infarct size. In the riociguat-treated mice, the resulting infarct size was smaller (8.5±2.5% of total LV mass vs. 21.8%±1.7%. in controls, p = 0.005) and LV systolic function analysed by MRI was better preserved (60.1%±3.4% of preischaemic vs. 44.2%±3.1% in controls, p = 0.005). After 28 days, LV systolic function by echocardiography treated group was still better preserved (63.5%±3.2% vs. 48.2%±2.2% in control, p = 0.004).
Taken together, mice treated acutely at the onset of reperfusion with the sGC stimulator riociguat have smaller infarct size and better long-term preservation of LV systolic function. These findings suggest that sGC stimulation during reperfusion therapy may be a powerful therapeutic treatment strategy for preventing post-MI heart failure.
PLoS ONE 01/2013; 8(12):e83910. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND AND PURPOSE: Current models dictate that, depending on occurrence of early reperfusion, the ischemic penumbra either undergoes or escapes infarction (i.e., "pan-necrosis"). However, tissue outcome following temporary middle-cerebral artery occlusion (tMCAo) in rodents can also include selective neuronal loss (SNL), which even if subtle may impede functional recovery. In order to explore the pathophysiology of ischemic stroke, determine potential therapeutic targets and monitor effects of therapy, in vivo imaging surrogates of these varied histopathological outcomes applicable in the clinical setting would be useful. Although hyperintense signal on T(2)-weighted MRI in the chronic post-stroke stage is considered a reliable surrogate of tissue infarction, SNL is not associated with T(2)W abnormal signal. In the clinical setting, the neuron-specific PET ligand (11)C-flumazenil (FMZ) has been used to identify both pan-necrosis and peri-infarct SNL, but this inference has not been histopathological confirmed so far. Here we investigated the late tissue sequelae of tMCAo in the rodent using in vivo T(2)W MRI and FMZ-PET against post mortem immunohistochemistry as gold standard. METHODS: Adult spontaneously hypertensive rats (SHRs) underwent 45min distal-clip middle-cerebral artery occlusion and, 28days later, FMZ-PET and T(2)W-MRI, immediately followed by immunohistochemistry for neuronal loss (NeuN), activated microglia and astrocytosis. Based on standard histopathological definitions, ischemic lesions were classified into pan-necrosis, partial infarction or SNL. NeuN changes and FMZ binding across the whole hemisphere were quantified in the same set of 44 regions-of-interest according to previously validated protocols; linear regressions between these two measures were carried out both within and across subjects. RESULTS: Both cortical pan-necrosis/partial infarction and SNL were present in all rats except one, where SNL was isolated and extensive. Infarction/partial infarction, but not SNL, was associated with T(2)W hyperintense signals and cortical atrophy. In contrast, FMZ binding was decreased in all types of lesions including SNL, in proportion with NeuN staining intensity both within (p<0.05 to <0.001) and across (p<0.001) subjects, including the subject that showed pure SNL (p=0.01). CONCLUSION: This novel study revealed three main facts: i) long-term histopathological cortical changes following 45min tMCAo in SHRs included all three of SNL, partial infarction and frank infarction; ii) T2W MRI showed conspicuous high signal lesions for complete or partial infarction, but no changes for SNL; and iii) FMZ-PET was sensitive to all three types of tMCAo-induced histopathological changes, including isolated SNL, suggesting it is a valid surrogate for the histological sequelae of focal cerebral ischemia. In addition, the finding of almost universal completed cortical infarction at 28days differed from our previous findings at 14-day survival using exactly the same experimental protocol and rat strain, where SNL was the almost exclusive outcome, suggesting a phenomenon of delayed cortical infarct maturation whereby the extensive neuronal loss present at two weeks matures into infarction at four. Prospective studies are needed to investigate this intriguing observation.
Neurobiology of Disease 11/2012; · 5.62 Impact Factor