EMIM 2018 ControlCenter

Online Program Overview Session: PW-29

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Neuroimaging II | Disease Models

Session chair: Abraham Martin - San Sebastián, Spain; Markus Aswendt - Cologne, Germany
 
Shortcut: PW-29
Date: Friday, 23 March, 2018, 11:30 AM
Room: Banquet Hall | level -1
Session type: Poster Session

Abstract

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# 258

Chronic Neural Inflammatory Response in C57/Bl6 mice to High Dose Radiotherapy Monitored Using 18F-DPA-714 PET, 1H MRS and DW-MRI (#263)

D. Forster1, M. Kassiou2, K. Williams1

1 University Of Manchester, Division of Informatics, Imaging and Data Sciences, Manchester, United Kingdom
2 THE UNIVERSITY OF SYDNEY, School of Chemistry, Sydney, Australia

Introduction

In cancer of the brain, a consequence of radiotherapy is cognitive decline. Studies in rodents have associated inflammation and hypoxia with brain radiotherapy, which likely contribute to the pathogenesis of cognitive impairment1-3. There is a need to understand the biological processes underlying these effects. We require a robust preclinical model. In this study, the response in the brains of C57 mice given high dose radiotherapy was monitored over 6 months using [18F] DPA-714 PET, neurometabolic profile was monitored using 1H-MRS and changes at the cellular level using DW-MRI.

Methods

C57 mice were split into two groups, the first group received 20 Gy IR to the right hemisphere of the brain, the second group were untreated controls. 1 hour dynamic DPA-714 PET scans were performed on an Inveon PET/CT scanner (Siemens, Germany) along with DW-MRI scans on a 3T preclinical MRI scanner (MRS 3000 Series MRI System, MR Solutions, UK) once per month for 6 months, along with baseline scans prior to radiotherapy. 1H-MRS scans were performed at 7T at 5 and 6 months. PET data was analysed using Inveon Research Workplace and MRS data was analysed using jMRUI.

Results/Discussion

Higher overall DPA-714 uptake was observed during months 1, 2 and 4 post IR (fig.1). This was a global effect, with the increase seen throughout the brain, not just the irradiated hemisphere. There was very little difference observed in DPA-714 uptake between the irradiated and unirradiated hemisphere.

1H-MRS scans revealed fluctuations in glutamate/glutamine levels in the radiotherapy group which were not observed in the control group (fig.2)

DW-MRI data are still undergoing analysis and will be included in the presentation

The increase in DPA uptake in months 1-4 post IR is indicative of increase microglial numbers and thus a prolonged inflammatory response to radiotherapy. Glutamate/glutamine fluctuations observed in the RT group could be indicative of altered glutamatergic neurotransmission and excitotoxicity.

Conclusions

Our data show that cerebral biological changes as a result of cranial radiotherapy can be observed in vivo using both PET and MR techniques.

Next we will include DCE-MRI – perfusion/blood brain barrier integrity and PET (FAZA - Hypoxia) imaging markers as well as ex vivo tissue analysis for microglia/hypoxia/perfusion/systemic inflammation/proteomics and then aim to establish whether these measurements can be related to cognitive deficits following brain radiotherapy and whether we can ameliorate cognitive decline by pharmacological intervention.

References

1Moravan MJ et al. Cranial irradiation leads to acute and persistent neuroinflammation with delayed increases in T-cell infiltration and CD11c expression in C57BL/6 mouse brain. Radiat Res. 2011 176(4):459-73.

2 Lee et al Whole brain radiation-induced cognitive impairment: pathophysiological mechanisms and therapeutic targets. Biomol Ther (Seoul). 2012 20(4):357-70.

3 Greene-Schloesser et al. Molecular pathways: radiation-induced cognitive impairment. Clin Cancer Res. 2013 19(9):2294-300.

Fig.1 Graph showing [18F] DPA-714 uptake in brains of RT and Control mice
It can be seen that DPA uptake is increased in the brains of mice given RT compared with control at 1,2 and 4 months post-RT. A general trend towards increased DPA-714 uptake with age was also observed in control mice
Fig.2 Showing Glutamate and Glutamine levels 5 and 6 months post-RT compared with control animals
It can be seen from the data that gluatamte and glutamine levels remain stable over time in control mice, whereas there are large fluctuations in both in the RT mice over time.  
# 259

Stroke Volume and Behavioral Tests corroborate the analysis of multi-parametric MRI data with ADC as a strong predictor (#546)

K. J. Patzwaldt1, P. Katiyar1, Y. Wang2, X. Yang2, R. K. Lerch1, J. A. Disselhorst1, S. Poli2, S. Castaneda Vega1, 3, B. J. Pichler1

1 Eberhard Karls Univesity of Tuebingen, Preclinical Imaging and Radiopharmacy, Tuebingen, Baden-Württemberg, Germany
2 Eberhard Karls Univesity of Tuebingen, Hertie Institute for Clinical Brain Research, Tuebingen, Baden-Württemberg, Germany
3 Eberhard Karls Univesity of Tuebingen, Radiology and Clinical Molecular Imaging, Tuebingen, Baden-Württemberg, Germany

Introduction

Fifteen million people suffer from ischemic stroke (IS) each year. Half of the survivors sustain permanent physical damage. Magnetic resonance imaging (MRI) allows non-invasive evaluations of stroke volume (SV), edema and perfusion. However, SV is often overestimated in T2 weighted images (T2WI).  Behavioral tests (BT) further allow the evaluation of functional outcome. In this work, we aimed to accurately assess the SV and functional changes using a Gaussian mixture model (GMM), BTs and different MRI features: apparent diffusion coefficient (ADC) maps, perfusion weighted images (PWI) and T2WI.

Methods

IS was induced in male rats using the middle cerebral artery temporary occlusion stroke model. MRI measurements were made at multiple time points until 1 week post-stroke using ADC, PWI and T2WI. Different BTs were also performed for each time point: Sticky Label, Open Field and Beam Walk. Data for the BTs were evaluated using a neuroscore. ADC maps and PWI were calculated and co-registered to the T2WIs. The MRI data for 24 h time point were divided into training and test sets. A GMM was applied on the training set (n=12) to discriminate two different biological compartments, stroke labeled (SL) voxels and non-stroke (negative labeled) areas. The labels obtained from the training set were used to train a Random Forest Classifier (RFC) and applied on the test dataset (n=4).

Results/Discussion

Strong correlations were found between the SV and the BTs (Pearson=0.77), between the SV and the fraction of SL voxels from the GMM and RFC (Pearson=0.82), and between the fraction of SL voxels and the BTs (Pearson=0.84). The ADC values of the stroke hemisphere negatively correlated to the fraction of SL voxels (Pearson=-0.73), whereas no relationship was found between the contralateral ADC and the fraction of SLs (Pearson=0.20). The characterized stroke compartments in the training step had an average ADC value of [401.82 ± 64.11] x10-6 mm2/s and a perfusion of [38.0 ± 17.93] ml/100g/min. The test dataset showed an average ADC value of [369.32 ± 70.44] x10-6 mm2/s in the stroke cluster and a perfusion of [31.9 ± 15.16] ml/100g/min. The average ADC and perfusion value of both training and test sets corroborated well with values in literature validating our analysis. A spatial correspondence was found between the stroke areas identified by the algorithm and the corresponding histology.

Conclusions

The correlations between the BTs and the fraction of SL voxels identified using imaging show that a comprehensive analysis of multiparametric MRI data can be predictive of the functional outcome. Together with histological corroboration, this analysis provides a strong methodological tool for assessing infarction severity. Based on this framework, we aim to model the evolution of the stroke region over the remaining time points and their interactions with functional deficits. This will, in turn, allow an objective characterization and evaluation of treatment efficacy at different time points.

Keywords: Ischemic stroke, Behavioral tests, MRI, multi-parametric analysis
# 260

Magnetic Resonance Imaging of Choroid Plexus during neuroinflammation (#264)

V. Hubert1, J. - B. Langlois2, F. Chauveau3, A. Durand4, T. - H. Cho4, E. Canet-Soulas1, R. Bolbos2, M. Wiart1

1 CarMeN Laboratory - Cardio, Metabolism, Diabetes and Nutrition, INSERM U1060/Université Lyon1/INRA U 1397/INSA Lyon, Bron, France
2 CERMEP - Imagerie du Vivant, Bron, France
3 Lyon Neuroscience Research Center, CRNL-BIORAN/CNRS UMR5292/INSERM U1028/Université de Lyon/Lyon 1, Bron, France
4 CREATIS, CNRS UMR5220/INSERM U1044/INSA de Lyon, Villeurbanne, France

Introduction

Choroid Plexus (CP) are highly vascularized organs located in brain ventricles. They constitute an important gate for entry of immune cells during neuroinflammatory disorders. However, to date, information on immune cells trafficking across CP remains limited (1). Magnetic resonance imaging (MRI) coupled with the injection of ultrasmall superparamagnetic iron oxide particles (USPIO) is a non-invasive technique for tracking phagocytes in inflammatory diseases (2). The aim of our study was to evaluate the potential of USPIO-enhanced MRI to detect early inflammatory alterations in CP.

Methods

At day 0 (D0), 30 adult male C57Bl6 mice received an intraperitoneal injection of either:

  • LPS at low dose (2.5 mg/kg, n=2)
  • LPS at moderate dose (5mg/kg, n=14)
  • LPS at high dose (10 mg/kg, n=1)
  • vehicle (PBS, n=13)

48h later (D2), all mice underwent a baseline MRI session on a 7T rodent scanner with T2 and T2*-weighted imaging. They were then intravenously injected with USPIOs (P904, 25nm diameter, Guerbet, France, n=24 or Ferumoxytol, 17 to 31 nm diameter, AMAG, USA, n=6) at 2 mmol Fe/kg. Mice were re-imaged 48h later (D4) with the same sequences. Mice were sacrificed at the end of the last imaging session by intracardiac perfusion and their brains were prepared either for ex vivo high resolution MRI, histological analysis or Inductively Coupled Plasma Mass Spectrometry (ICP-MS).

Results/Discussion

Post-USPIO MRI showed a distinct signal loss in CP off all LPS-treated mice, which increased with LPS dose. After intracardiac perfusion, hypointense signals inside CP were still detectable on ex vivo high resolution MRI. Prussian Blue staining showed an accumulation of USPIOs in the CP stroma in LPS-treated mice, but not in control mice. And finally, preliminary fluorescence analysis showed a colocalization between USPIOs and cells positives for CD11b myeloid marker. Further analyses are being performed to quantify the amount of iron in LPS-treated mouse brain versus control mouse brain, and to assess the potential internalization of USPIOs by CP phagocytes.

Taking together, our data suggest that choroid plexus involvement during neuroinflammation may be visualized in vivo with our approach of USPIO-enhanced MRI. Ex vivo analysis point that USPIOs have entered CP of neuroinflamed mouse brains, where they seem to colocalize with CP immune cells.

Conclusions

In vivo imaging of CP immune cells is promising for a better understanding of neuroinflammatory disorder physiopathology. However, their deep location makes their imaging really challenging.

Based on our extensive experience of USPIO, we thought to develop a new approach: USPIO-enhanced MRI for the in vivo imaging of CP immune cells. The results showed that our approach might be relevant for the longitudinal study of CP involvement during neuroinflammatory disorders.

References

1. Nayak D, Zinselmeyer BH, Corps KN, McGavern DB. In vivo dynamics of innate immune sentinels in the CNS. Intravital 2012;1(2):95-106.

2. Chauveau F, Cho TH, Berthezene Y, Nighoghossian N, Wiart M. Imaging inflammation in stroke using magnetic resonance imaging. International journal of clinical pharmacology and therapeutics 2011;48(11):718-728.

USPIOs are detectable inside Choroïd Plexus of LPS treated mice, in vivo and ex vivo
A and B, in vivo T2* weighted images ; C and D, ex vivo high resolution T2* weighted images ; E and F, Prussian Blue and Hematoxylin/Eosin (HE) staining for iron detection (in blue) on 12 µm brain slices. 
Keywords: Choroid Plexus, Neuroinflammation, Magnetic Resonance Imaging, USPIO, Cell tracking
# 261

The signature of the serotonin system in the chronic corticosterone depression model: a study with [18F]MPPF, [18F]altanserin and [11C]DASB. (#113)

G. Pauwelyn1, N. Van Laeken1, R. Dockx2, 3, J. Verhoeven1, B. Descamps4, K. Kersemans5, K. Peremans2, C. Baeken3, I. Goethals5, C. Vanhove4, F. De Vos1

1 Ghent University, Laboratory of Radiopharmacy, Gent, Belgium
2 Ghent University, Faculty of Veterinary Medicine, Gent, Belgium
3 Ghent University, Department of Psychiatry and Medical Psychology, Gent, Belgium
4 Ghent University, Institute Biomedical Technology – Medisip – Infinity, Gent, Belgium
5 Ghent University hospital, Department of Radiology and Nuclear Medicine, Gent, Belgium

Introduction

Abnormalities in the serotonin system have been proposed to underlie in the pathophysiology of major depressive disorder (MDD). An interesting avenue is to explore the role of a dysregulated hypothalamic-pituitary-adrenal (HPA) axis, observed in patients suffering from MDD, in the disturbed serotonergic neurotransmission. The present study aimed to further explore this hypothesis, using the corticosterone (CORT) rodent depression model combined with PET imaging. To our knowledge, this is the first preclinical study using PET to evaluate the effects of chronic CORT on the serotonin system. 

 

Methods

The CORT depression model was induced by means of three weeks of chronic CORT administration (40 mg/kg, s.c.) to male Long-Evans rats. Next to examining the CORT-induced effects on the behavioral level, the total body weight, the plasma corticosterone levels, and non-invasive imaging was done using three highly selective PET-radiotracers. These included [18F]MPPF, [18F]altanserin and [11C]DASB, which allowed the visualization of the serotonin 5-HT1A receptor, the 5-HT2A receptor, and the serotonin transporter, respectively.

Results/Discussion

The chronic CORT administration resulted in significantly lowered body weight, significantly elevated plasma corticosterone levels, and induced depression-like behavior. Compared to the control group, induction of the CORT depression model resulted in significantly decreased BPND of [18F]MPPF on the 5HT1A receptors in the medial prefrontal cortex and anterior cingulate cortex (ACC). At the 5-HT2A receptor level, the [18F]altanserin BPND was significantly increased in all cortical regions except for the ACC. No significant differences in regional BPND of [11C]DASB were detected. Overall, our findings at the 5HT1A and 5-HT2A receptor level are in line with previous ex vivo studies in rats [1,2]. Furthermore, a diminished density of the 5-HT1A receptors and an elevated 5HT2A receptors has also been repeatedly observed in patients suffering from MDD [3,4].

Conclusions

The present study emphasizes the potential role of a dysregulated HPA-axis in the disturbed serotonergic neurotransmission at the 5HT1A and 5HT2A receptor level, seen in patient with MDD. Furthermore, these results indicate the relevance and reliability of the corticosterone depression model in the investigation of the mode of action for current and novel antidepressant therapies on the serotonin 5-HT1A and 5-HT2A receptors in the brain.

References

[1] Savitz J, Lucki I, Drevets WC. Progress in Neurobiology 5-HT 1A receptor function in major depressive disorder 2009;88:17–31. doi:10.1016/j.pneurobio.2009.01.009.

[2] Fernandes C, McKittrick CR, File SE, McEwen BS. Decreased 5-HT(1A) and increased 5-HT(2A) receptor binding after chronic corticosterone associated with a behavioural indication of depression but not anxiety. Psychoneuroendocrinology 1997;22:477–91. doi:10.1016/S0306-4530(97)00052-8.

[3] Wang L, Zhou C, Zhu D, Wang X, Fang L, Zhong J, et al. Serotonin-1A receptor alterations in depression: a meta-analysis of molecular imaging studies. BMC Psychiatry 2016;16:319. doi:10.1186/s12888-016-1025-0.

[4] Savitz JB, Drevets WC. Neuroreceptor imaging in depression. Neurobiol Dis 2013;52:49–65. doi:10.1016/j.nbd.2012.06.001

 

[18F]MPPF

Effect of the CORT and control protocol on the regional [18F]MPPF BPND values. Compared to the control group, induction of the CORT model resulted in significantly reduced (* = p < 0.05) BPND values in the ACC and the MPFC. ACC=anterior cingulate cortex; Am=amygdala; Hip=hippocampus; and MPFC=medial prefrontal cortex.

[18F]altanserin
Effect of the CORT and control protocol on the regional [18F]altanserin BPND values. Compared to the control group, induction of the CORT model resulted in significantly increased  (* = p < 0.05) BPND values in the EC, IC, MC, MPFC and OC. ACC=anterior cingulate cortex; Am=amygdala; EC=entorhinal cortex; IC=insular cortex; MC=motor cortex; MPFC=medial prefrontal cortex; OC=orbitofrontal cortex.
Keywords: [18F] MPPF, [18F]Altanserin, [11C]DASB, Corticosterone, Depression, HPA-axis
# 262

Structural remodeling in a rat model of brain stem ischemia revealed by diffusion tensor imaging (#90)

L. Wachsmuth1, J. Minnerup2, J. - K. Strecker2, K. Diederich2, C. Faber1

1 University of Muenster, Clinical Radiology, Muenster, Germany
2 University of Muenster, Neurology, Muenster, Germany

Introduction

In a considerable number of human stroke patients ischemic lesions occur in the brain stem. However, animal models of brain stem stroke are rare compared to models of cortical stroke. Mechanisms of degeneration and recovery cannot be simply inferred from studying hemispheric cortical lesions, because different brain areas exhibit varying potential for neurogenesis, and plasticity may differ in phylogenetically distinct regions. Here we used diffusion tensor imaging as a noninvasive means to assess structural connectivity in a rat model of brain stem ischemia.

Methods

Focal brain stem ischemia was induced by photothrombosis with Rose Bengal in 8 rats. Pre, 2, 4, and 8 weeks after surgery, MRI was performed at 9.4T (Bruker Biospec). We obtained T2w RARE anatomical and diffusion tensor data with EPI-DTI. Probability maps based on seed regions in left and right thalamus were computed with DTI&Fiber Tools (University Hospital Freiburg). The probability of connectivity between seed regions was calculated by pixelwise multiplication of both maps1. Resulting maps were overlaid with FA maps. ROI analysis was used to count the number of pixels (above the threshold of 0.75) comprising the connected area ipsi- and contralateral. Neurological deficits were assessed by behavioral testing (beam balance, Rotarod, foot print) and scoring over the course of the study.

Results/Discussion

At two weeks after surgery T2w anatomical images revealed ischemic brain stem lesions as hyperintense areas in 6 of 8 rats (figure 1A). At 8 weeks after surgery only small hyperintense areas remained in 4 of 6 ischemic rats (figure 1A, insert). Neurological functions improved over time, as shown by behavioral testing. Probability maps of connectivity between seed regions in left and right thalamus revealed a central area with high probability values (>0.75) aligned with the medial longitudinal fissure between right and left brain at Bregma -2 mm (Figure 1B, yellow arrows). At baseline, this area was symmetrically located across the midline. 8 weeks after surgery a higher number of connected pixels was found contralateral (Figure 1C, 2). The higher number of connected pixels on the contralesional site at the level of thalamus agrees with the occurrence of midline crossing fibers in this area, identified by anterograde cell tracing in an additional animal cohort of this study.

Conclusions

Probabilistic fiber tracking provides information about structural connectivity, and is sensitive enough to resolve structural remodeling remote from the lesion. The congruent results from fiber tracking, histological fiber tracing, and behavioral testing may indicate neuronal remodeling by axonal sprouting and add evidence for a potential compensatory mechanism for the observed partial recovery after brain stem stroke.

References

Kreher BW, Schnell S, Mader I, Il’yasov KA, Hennig J, Kiselev VG, Saur D, Connecting and merging fibers: Pathway extraction by combining Probability maps, Neuroimage 2008; 43(1):81-89).

Figure 1

A T2w anatomical image at 2 weeks after surgery shows a hyperintense ischemic lesion in the brain stem. At 8 weeks after surgery (insert) hyperintensities were less apparent. Probability maps at B baseline and C 8 weeks after surgery overlaid on respective FA maps. At 8 weeks after surgery the area with a high level of connectivity (yellow arrows) was bigger contralateral to the lesion site.

Figure 2

Quantitative analysis of the number of voxels per hemisphere (threshold >0.75) visited by both probability maps, as indicated in figure 1B, C. Mean values and SD are given. Data were tested for normal distribution and compared with a paired t-test.

Keywords: rat, stroke, brainstem ischemia, probabilistic mapping, DTI-MRI
# 263

Does a Multi-Nutrient Diet have Similar Benificial Effects on Stroke in Female Mice as it has in Male Mice? (#480)

M. Wiesmann1, B. Zinnhardt2, N. M. Timmer1, D. Reinhardt2, S. Eligehausen2, L. Wachsmuth3, S. Hermann2, P. J. Dederen1, M. Hellwich1, A. Königs1, H. Ben Jeddi1, M. T. Kuhlmann2, A. Heerschap4, A. H. Jacobs2, 5, A. J. Kiliaan1

1 Department of Anatomy, Radboud University Medical Center, Centre for Medical Neuroscience, Donders Institute for Brain, Cognition & Behaviour, Preclinical Imaging Centre PRIME, Nijmegen, Netherlands
2 European Institute for Molecular Imaging (EIMI), Westfälische Wilhelms University Münster, Münster, Germany
3 Department of Clinical Radiology of the University Hospital, Westfälische Wilhelms University Münster, Münster, Germany
4 Department of Radiology & Nuclear Medicine, Radboud university medical center, Nijmegen, Netherlands
5 Department of Geriatrics, Johanniter Hospital, Evangelische Kliniken, Bonn, Germany

Introduction

Occlusion of the middle cerebral artery (MCAo) is among the most common causes of ischemic stroke in humans. Cerebral ischemia leads to brain lesions existing of an irreversibly injured core and an ischemic boundary zone, the penumbra, containing damaged but potentially salvageable tissue. Stroke can affect females very differently from males, and therefore preclinical research on underlying mechanisms and the effects of interventions should not be restricted to male subjects, and treatment strategies for stroke should be tailored to benefit both sexes.

Methods

Using a transient occlusion (30 min) of the middle cerebral artery (tMCAo) intraluminal filament mouse model we investigated the neurorestorative efficacy of a dietary approach (Fortasyn) comprising docosahexaenoic acid, eicosapentaenoic acid, uridine, choline, phospholipids, folic acid, vitamins B12, B6, C, and E, and selenium as therapeutic approach to counteract neuroinflammation and impairments of cerebral connectivity, cerebral blood flow (CBF), and motor function. Following tMCAo, female and male adult C57BL/6j mice were either maintained on Control diet or switched to the Fortasyn diet.

Results/Discussion

At several time points after tMCAo, behavioral tests, and MRI and PET scanning were conducted to identify the impact of the multicomponent diet on the elicited neuroinflammation, loss of cerebral connectivity, and the resulting impairment of motor function after experimental stroke. In this international multi-center preclinical study male mice on the multicomponent diet showed decreased neuroinflammation, improved functional and structural connectivity, beneficial effect on CBF, and also improved motor function after tMCAo (Figure 1a). We found that the multinutrient intervention had diverse effects on the stroke-induced impairments in females. Similar to previous observations in male stroke mice, brain integrity, sensorimotor integration and neurogenesis benefitted from Fortasyn, but impairments in activity and motor skills were not improved in female stroke mice (Figure 1b).

Conclusions

Our present data show that this specific dietary intervention may have beneficial effects on structural and functional recovery and therefore therapeutic potential after ischemic stroke in both male and female subjects. In this presentation an overview on the differences and similarities of the dietary effects will be given.

Graphical abstract summarizing the effect of a multicomponent diet after experimental stroke.
(A) The multi-component diet enhanced CBF, structural and functional connectivity, and decreased neuroinflammation concomitant with an improved motor function in male adult C57BL/6j mice after tMCAo. (B) In addition, brain integrity, sensorimotor integration, and neurogenesis benefitted from Fortasyn, while impairments in activity and motor skills were not improved in female stroke mice.
Keywords: Cerebral Ischemia, Neuroinflammation, Cerebral Connectivity, Cerebral Blood Flow, MRI, PET
# 264

Mapping alteration of dopaminergic neurons in a rat model of Parkinson Disease through the comparison of the presynaptic PET tracers [18F]-LBT999 and 6-[18F]fluoro-L-m-tyrosine (#63)

P. Roost1, 2, M. Gaudin1, 2, M. Guillermier1, 2, F. Gubellini1, 2, N. Cresto1, 2, L. Eymin1, 2, C. Josephine1, 2, M. - C. Gaillard1, 2, A. Bemelmans1, 2, Y. Bramoullé1, 2, E. Brouillet1, 2, P. Hantraye1, 2, N. van Camp1, 2

1 Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA), Département des Recherches Fondamentales (DRF), Institut de Biologie François Jacob, MIRCen, Fontenay-aux-Roses, France
2 Centre National de la Recherche Scientifique (CNRS), Université Paris-Sud, UMR 9199, Neurodegenerative Diseases Laboratory, Fontenay-aux-Roses, France

Introduction

The pathological features of Parkinson’s Disease (PD) are driven by the loss of the dopaminergic projection neurons in the substantia nigra (SN) resulting in a dopamine (DA) deficiency in the striatum [1]. We developed a pathologically relevant rodent PD model; overexpressing the mutant (A53T) human alpha-synuclein protein in the SN [2]. Our aims are triple: 1- map neuronal loss and DA deficiency over time using two different presynaptic PET tracers, 2- evaluate the sensitivity of each radioligand, and 3- correlate individual PET data to behaviour and histological results.

Methods

A total of twelve rats were unilaterally injected in the SN with a viral vector (AAV2/6) overexpressing mutated (A53T) human alpha-synuclein, and were studied either at 6 weeks post-injection (6wpi, n=7, 543±36g) or 12wpi (n=4, 573±40g). PET imaging was performed using a ligand substrate for AADC, 6-[18F]fluoro-L-m-tyrosine (“FMT”, 60min acquisition, 31.3-60.8MBq; pre-treatment by IP injection of 10mg/kg benserazide 30’ before imaging [3]), and a ligand for DA transporter (DAT), [18F]-LBT999 [4](“LBT", 90min acquisition, 40.3-63.0MBq). For behaviour, rats were subjected for 5 minutes to the cylinder test, in which contralateral and ipsilateral paw use was compared. After the in vivo studies rats were sacrificed for histological studies using tyrosine hydroxylase immunohistochemistry.

Results/Discussion

From LBT and FMT PET scans, quantitative uptake images (BPnd and Ki) were calculated using Logan and Patlak graphical methods with the cerebellum as a reference. Unilateral AAV injections allowed the contralateral striatum to serve as internal control. Injection of benserazide was not effective in 36% of the animals, in which Ki could not reasonably be estimated. Additionally, Ki images showed more non-specific binding than BPnd images. At 12wpi we observed a decreased BPnd in the ipsilateral striatum, and similarly for the Ki of the quantifiable scans. These results are in concordance with the behavioural observations, showing roughly only 30% use of the contralateral forepaw. Absolute correlative analysis and histological comparisons are still ongoing. At 6wpi we did not observe any asymmetry with FMT, however preliminary LBT data suggest an asymmetric uptake in some animals. Absolute quantification is still ongoing; these results will be correlated with behaviour and histology data.

Conclusions

We created an AAV rat model of PD that shows progressive DA deficiency and neuronal loss detectable by FMT and LBT PET imaging. Preliminary data suggest that the DAT tracer is more sensitive to detect a mild PD phenotype as compared to the AADC tracer. This phenomenon has previously been described, and is possibly due to a combination of reduced nerve terminal DAT binding sites and downregulation of DAT in surviving neurons, in an attempt to increase DA availability [5]. Further analysis of PET data will allow correlating PET data to behavioural and histological measurements.

References

1.            Dauer, W. and S. Przedborski, Parkinson's disease: mechanisms and models. Neuron, 2003. 39(6): p. 889-909.

2.            Cresto, N., ; Gaillard M.C.; Joséphine, C.; Aurégan, G.; Guillermier, M.; Bernier, S.; Jan, C.; Petit, F. Gipchtein, P.; Joliot, A.; Hantraye, P.; Cambon, K.; Bemelmans, A.; Brouillet, E., THE LRRK2 G2019S MUTATION BUT NOT ITS DEAD KINASE FORM INCREASES THE NEUROTOXICITY OF MUTANT A53T A-SYNUCLEIN. Neurodegener Dis 2017;17(suppl 1):8-590 – Page 448, 2017.

3.            Becker, G., et al., Comparative assessment of 6-[18 F]fluoro-L-m-tyrosine and 6-[18 F]fluoro-L-dopa to evaluate dopaminergic presynaptic integrity in a Parkinson's disease rat model. J Neurochem, 2017.

4.            Serriere, S., et al., In vivo PET quantification of the dopamine transporter in rat brain with [(1)(8)F]LBT-999. Nucl Med Biol, 2014. 41(1): p. 106-13.

5.            Arena, J.E. and A.J. Stoessl, Optimizing diagnosis in Parkinson's disease: Radionuclide imaging. Parkinsonism Relat Disord, 2016. 22 Suppl 1: p. S47-51.

Acknowledgement

This project has been funded by the European Union Horizon 2020 Programme (H2020-MSCA-ITN-2015) under the Marie Skłodowska-Curie Innovative Training Network and Grant Agreement No. 676408.

Representative quantitative PET images at 12wpi

PET imaging was performed at 12 week post unilateral injection in the SN with AAV2/6 overexpressing mutated (A53T) human alpha-synuclein. Images show decreased AADC uptake (Ki) and DAT binding (BPnd) in the ipsilateral striatum. The DAT ligand seems to be more sensitive to dopaminergic alterations.

Keywords: PET, Parkinson, Rodent, DAT, AADC, Dopamine
# 265

Evaluation of Gd-retention in the brain of a BCCAo rat model after repeated doses of Gadodiamide MRI Contrast Agent (#131)

F. Arena1, 2, P. Bardini1, 2, G. M. Marini1, 2, E. Gianolio1, F. La Cava1, 2, S. Aime1

1 University of Torino, Department of Molecular Biotechnology and Health Sciences, Torino, Italy
2 Center of Preclinical Imaging-Bioindustry Park, Department of Molecular Biotechnology and Health Sciences, Colleretto Giacosa (TO), Italy

Introduction

In recent years, several imaging studies in humans and animal models confirmed that repeated administration of linear Gd-based CAs could determine the formation of Gd deposition in specific brain structures (1-4). Even if no neurotoxic effect of Gd insoluble deposits has been evidenced on the healthy brain tissue (5), it seems interesting to investigate if alterations of the blood-brain barrier (BBB) can facilitate the accumulation of Gd. Here we report an investigation on the amount of retained Gd in a Bilateral Common Carotid Artery occlusion (BCCA0) rat model administered with Gadodiamide.

Methods

A total dose of 13.2 mmol/Kg of Gadodiamide was injected in BCCAo injured rats and compared to that of Sham ones. An additional control group treated with saline was included. Before Gadodiamide administration, as well as, after the 9th, 15th and 21st injection, a brain MRI was obtained using a T1-weighted MSME sequence on a clinical 3T scanner. The ratios of signal intensities in Dentate Nucleus and Hippocampus to Reference (DN/REF and Hf/REF) were determined. Evaluation of R1 signal in DN and Hf were also performed. Total Gd concentration in cortex, sub-cortical brain and cerebellum was measured with ICP-MS and the BBB regional permeability Ktrans value in DN and Hf of injured rats was calculated with DCE-MRI.

Results/Discussion

A significantly increased signal intensity ratio of DN/REF (Fig.1) and Hf/REF was observed after 21 injections of Gadodiamide in BCCAo compromised rats compared to that of Sham ones. The DN and Hf R1 value were significantly higher for the BCCAo group as compared with those of Sham group and saline. The Gd concentration in the BCCAo rats was significantly higher in the cerebellum (0.98 ± 0.17 mg/g) and in the subcortical (0.49 ± 0.09 mg/g) compared with the cerebellum (0.80 ± 0.11 mg/g) and the subcortical (0.37 ± 0.12 mg/g) of Sham rats. The Ktrans calculated in the DN and Hf area after the injury in the BCCAo rats was significantly higher compared to that calculated at the beginning of experiment, while no significant difference was observed in the Ktrans values at the end of experiment.

Conclusions

Higher signal intensity and Gd concentration was observed in DN and Hf of animals subjected to BCCAo injury can be associated with an increase in BBB permeability due to the applied vascular dementia animal model.

References

  1. McDonald RJ, et al. (2015) Radiology 275(3):772-782.
  2. Errante Y, et al. (2014) Invest Radiol 49(10):685-690.
  3. Kanda T, et al. (2014) Radiology 270(3):834-841.
  4. Quattrocchi CC, et al. (2015) Investigative Radiology 50(7):470-472.
  5. Smith AP, et al. (2017) Radiology 282(3):743-751.

 

Figure 1
(A) Representative T1w MRI scan of DN in the cerebellum before (left column), after 9 (middle column) and 21 injections (right column) in BCCAo and Sham rats treated with Gadodiamide and saline. Increased signal intensities of the DN are indicated by white arrows. (B) Percent change of DN/REF compared with baseline after 21 injections of Gadodiamide.
Keywords: Magnetic Resonance Imaging, Gadolinium deposition, Dentate Nucleus, Gadodiamide, Hippocampus, Bilateral common carotid artery occlusion