In vivo quantification of glial activation in minipigs overexpressing human α-synuclein.

Parkinson's disease is characterized by a progressive loss of substantia nigra (SN) dopaminergic neurons and the formation of Lewy bodies containing accumulated alpha-synuclein (α-syn). The pathology of Parkinson's disease is associated with neuroinflammatory microglial activation, which may contribute to the ongoing neurodegeneration. This study investigates the in vivo microglial and dopaminergic response to overexpression of α-syn. We used positron emission tomography (PET) and the 18 kDa translocator protein radioligand, [11 C](R)PK11195, to image brain microglial activation and (+)-α-[11 C]dihydrotetrabenazine ([11 C]DTBZ), to measure vesicular monoamine transporter 2 (VMAT2) availability in Göttingen minipigs following injection with recombinant adeno-associated virus (rAAV) vectors expressing either mutant A53T α-syn or green fluorescent protein (GFP) into the SN (4 rAAV-α-syn, 4 rAAV-GFP, 5 non-injected control minipigs). We performed motor symptom assessment and immunohistochemical examination of tyrosine hydroxylase (TH) and transgene expression. Expression of GFP and α-syn was observed at the SN injection site and in the striatum. We observed no motor symptoms or changes in striatal [11 C]DTBZ binding potential in vivo or striatal or SN TH staining in vitro between the groups. The mean [11 C](R)PK11195 total volume of distribution was significantly higher in the basal ganglia and cortical areas of the α-syn group than the control animals. We conclude that mutant α-syn expression in the SN resulted in microglial activation in multiple sub- and cortical regions, while it did not affect TH stains or VMAT2 availability. Our data suggest that microglial activation constitutes an early response to accumulation of α-syn in the absence of dopamine neuron degeneration.

α2-adrenoceptor binding in Flinders-sensitive line compared with Flinders-resistant line and Sprague-Dawley rats.

OBJECTIVES: Disturbances in the noradrenergic system, including alterations in the densities of α2-adrenoceptors, are posited to be involved in the pathophysiology of depression. In this study, we investigate the binding of α2-adrenoceptors in regions relevant to depression in an animal model of depression. METHODS: Using in vitro autoradiography techniques and the selective α2-ligand, [3H]RX 821002, we investigated the density of α2-adrenoceptors in female Flinders-sensitive line (FSL) rats, a validated model of depression, and in two traditional control groups - female Flinders-resistant line (FRL) and Sprague-Dawley (SD) rats. RESULTS: The α2-adrenoceptor density was increased in most regions of the FSL rat brain when compared with SD rats (10% across regions). Moreover, the α2-adrenoceptor density was further increased in the FRL rats compared with both FSL (10% across regions) and SD rats (24% across regions). CONCLUSIONS: The increase in α2-adrenoceptor binding in cortical regions in the FSL strain compared with the SD control strain is in accord with α2-adrenoceptor post-mortem binding data in suicide victims with untreated major depression. However, the differences in binding observed in the two control groups were unexpected and suggest the need for further studies in a larger cohort of animals of both sexes.

Selecting the Best Animal Model of Parkinson's Disease for Your Research Purpose: Insight from in vivo PET Imaging Studies.

Parkinson's disease (PD) is a debilitating neurodegenerative multisystem disorder leading to motor and non-motor symptoms in millions of individuals. Despite intense research, there is still no cure, and early disease biomarkers are lacking. Animal models of PD have been inspired by basic elements of its pathogenesis, such as dopamine dysfunction, alpha-synuclein accumulation, neuroinflammation and disruption of protein degradation, and these have been crucial for a deeper understanding of the mechanisms of pathology, the identification of biomarkers, and evaluation of novel therapies. Imaging biomarkers are non-invasive tools to assess disease progression and response to therapies; their discovery and validation have been an active field of translational research. Here, we highlight different considerations of animal models of PD that can be applied to future research, in terms of their suitability to answer different research questions. We provide the reader with important considerations of the best choice of model to use based on the disease features of each model, including issues related to different species. In addition, positron emission tomography studies conducted in PD animal models in the last 5 years are presented. With a variety of different species, interventions and genetic information, the choice of the most appropriate model to answer research questions can be daunting, especially since no single model recapitulates all aspects of this complex disorder. Appropriate animal models in conjunction with in vivo molecular imaging tools, if selected properly, can be a powerful combination for the assessment of novel therapies and developing tools for early diagnosis.

The application of iPSCs in Parkinson's disease.

The discovery and application of induced pluripotent stem cells (iPSCs) provide a novel treatment modality for diseases, which remain incurable. Particularly, in the treatment of neurodegenerative diseases such as Parkinson's disease (PD), iPSC­technology holds an interesting prospect for replacement therapy. Currently, the prognostic improvement of PD is limited and relies on symptomatic treatment. However, the symptomatic dopamine­replacement therapies lose their long­duration responses, and novel regenerative treatment modalities are needed. Animal models have provided valuable information and identified pathogenic mechanisms underlying PD but the lack of models that recapitulate the complex pathophysiology of the disease postpones further development of novel therapeutics. This review summarizes the possible uses of iPSCs in PD and discusses the future investigations needed for iPSCs as a possible treatment of PD patients.

Preclinical PET Studies of [11C]UCB-J Binding in Minipig Brain.

PURPOSE: Loss of neuronal synapse function is associated with a number of brain disorders. The [11C]UCB-J positron emission tomography (PET) tracer allows for in vivo examination of synaptic density, as it binds to synaptic vesicle glycoprotein 2A (SV2A) expressed in presynaptic terminals. Here, we characterise [11C]UCB-J imaging in Göttingen minipigs. PROCEDURES: Using PET imaging, we examined tracer specificity and compared kinetic models. We explored the use of a standard blood curve and centrum semiovale white matter as a reference region. We compared in vivo [11C]UCB-J PET imaging to in vitro autoradiography, Western blotting and real-time quantitative polymerase chain reaction. RESULTS: The uptake kinetics of [11C]UCB-J could be described using a 1-tissue compartment model and blocking of SV2A availability with levetiracetam showed dose-dependent specific binding. Population-based blood curves resulted in reliable [11C]UCB-J binding estimates, while it was not possible to use centrum semiovale white matter as a non-specific reference region. Brain [11C]UCB-J PET signals correlated well with [3H]UCB-J autoradiography and SV2A protein levels. CONCLUSIONS: [11C]UCB-J PET is a valid in vivo marker of synaptic density in the minipig brain, with binding values close to those reported for humans. Minipig models of disease could be valuable for investigating the efficacy of putative neuroprotective agents for preserving synaptic function in future non-invasive, longitudinal studies.