MRI and PET in Mouse Models of Myocardial Infarction

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 ...

Unversity of Cambridge

University of Cambridge

Complexins (Cplxs) are small, soluble, regulatory proteins that bind reversibly to the SNARE complex and modulate synaptic vesicle release. Cplx1 knockout mice (Cplx1(-/-)) have the earliest known onset of ataxia seen in a mouse model, although hitherto no histopathology has been described in these mice. Nevertheless, the profound neurological phenotype displayed by Cplx1(-/-) mutants suggests that significant functional abnormalities must be present in these animals. In this study, MRI was used to automatically detect regions where structural differences were not obvious when using a traditional histological approach. Tensor-based morphometry of Cplx1(-/-) mouse brains showed selective volume loss from the thalamus and cerebellum. Stereological analysis of Cplx1(-/-) and Cplx1(+/+) mice brain slices confirmed the volume loss in the thalamus as well as loss in some lobules of the cerebellum. Finally, stereology was used to show that there was loss of cerebellar granule cells in Cplx1(-/-) mice when compared to Cplx1(+/+) animals. Our study is the first to describe pathological changes in Cplx1(-/-) mouse brain. We suggest that the ataxia in Cplx1(-/-) mice is likely to be due to pathological changes in both cerebellum and thalamus. Reduced levels of Cplx proteins have been reported in brains of patients with neurodegenerative diseases. Therefore, understanding the effects of Cplx depletion in brains from Cplx1(-/-) mice may also shed light on the mechanisms underlying pathophysiology in disorders in which loss of Cplx1 occurs.

Tensor-based morphometry and stereology reveal brain pathology in the complexin1 knockout mouse.

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.

Characterizing infarction and selective neuronal loss following temporary focal cerebral ischemia in the rat: a multi-modality imaging study.

To demonstrate and validate a late gadolinium enhancement (LGE) imaging protocol, optimized for tissue viability assessment in interventional mouse models of myocardial infarction.

A fast protocol for infarct quantification in mice.

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.

A comparison of four PET tracers for brain hypoxia mapping in a rodent model of stroke.

Magnetic resonance imaging (MRI) has proved to be an ideal modality for non-destructive and highly detailed assessment of structural morphology in biological tissues. Here we used MRI to make a dataset of ex vivo brains from two different rodent models of Huntington's disease (HD), the R6/2 line and the YAC 128 mouse. We are making the whole dataset (399 transgenic HD and wildtype (WT) brains, from mice aged 9-80 weeks) publicly available. These data will be useful, not only to investigators interested in the study of HD, but also to researchers of computational neuroanatomy who may not have access to such large datasets from mouse models. Here we demonstrate a number of uses of such data, for example to produce maps of grey and white matter and cortical thickness. As an example of how the library might provide insights in mouse models of HD, we calculated whole brain grey matter volumes across different age groups with different numbers of cytosine-adenine-guanine (CAG) repeats in a fragment of the gene responsible for HD in humans. (The R6/2 dataset was obtained from an allelic series of R6/2 mice carrying a range of CAG repeat lengths between 109 and 464.) This analysis revealed different trajectories for each fragment length. In particular there was a gradient of decreasing pathology with longer CAG repeat lengths, reflecting our previous findings with behavioural and histological studies. There will be no constraints placed on the use of the datasets included here. The original data will be easily and permanently accessible via the University of Cambridge data repository (http://www.dspace.cam.ac.uk/handle/1810/243361).

Huntington's disease mouse models online: high-resolution MRI images with stereotaxic templates for computational neuroanatomy.

We have previously shown that impulsivity in rats predicts the emergence of compulsive cocaine seeking and taking, and is coupled to decreased D2/3 receptor availability in the ventral striatum. As withdrawal from cocaine normalises high impulsivity in rats, we investigated, using positron emission tomography (PET), the effects of response-contingent cocaine administration on D2/3 receptor availability in the striatum. Rats were screened for impulsive behavior on the five-choice serial reaction time task. After a baseline PET scan with the D2/3 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 D2/3 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 D2/3 receptor availability in the left, but not right, ventral striatum. We further report that D2/3 receptor availability was inversely related to baseline D2/3 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 D2/3 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.

Baseline-dependent effects of cocaine pre-exposure on impulsivity and D2/3 receptor availability in the rat striatum: possible relevance to the attention-deficit hyperactivity syndrome.

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.

Translating positron emission tomography studies in animals to stimulant addiction: promises and pitfalls.

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.

Voxel-based morphometry with templates and validation in a mouse model of Huntington's disease.

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.

Stephen J. Sawiak

Wolfson Brain Imaging Centre,
Department of Clinical Neurosciences,
Wolfson Brain Imaging Centre, Department of Clinical Neurosciences

Unversity of Cambridge

MRI and PET in Mouse Models of Myocardial Infarction

Stephen J. Sawiak

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Wolfson Brain Imaging Centre,Department of Clinical Neurosciences,Wolfson Brain Imaging Centre, Department of Clinical Neurosciences

Unversity of Cambridge

MRI and PET in Mouse Models of Myocardial Infarction

Wolfson Brain Imaging Centre,
Department of Clinical Neurosciences,
Wolfson Brain Imaging Centre, Department of Clinical Neurosciences