Monoaminergic PET imaging and histopathological correlation in unilateral and bilateral 6-hydroxydopamine lesioned rat models of Parkinson's disease: a longitudinal in-vivo study

Carbon-11 labeled dihydrotetrabenazine (11C-DTBZ) binds to the vesicular monoamine transporter 2 and has been used to assess nigro-striatal integrity in animal models and patients with Parkinson's disease. Here, we applied 11C-DTBZ positron emission tomography (PET) to obtain longitudinally in-vivo assessment of striatal dopaminergic loss in the classic unilateral and in a novel bilateral 6-hydroxydopamine (6-OHDA) lesion rat model. Forty-four Sprague–Dawley rats were divided into 3 sub-groups: 1. 6-OHDA-induced unilateral lesion in the medial forebrain bundle, 2. bilateral lesion by injection of 6-OHDA in the third ventricle, and 3. vehicle injection in either site. 11C-DTBZ PET studies were investigated in the same animals successively at baseline, 1, 3 and 6 weeks after lesion using an anatomically standardized volumes-of-interest approach. Additionally, 12 rats had PET and Magnetic Resonance Imaging to construct a new 11C-DTBZ PET template. Behavior was characterized by rotational, catalepsy and limb-use asymmetry tests and dopaminergic striatal denervation was validated post-mortem by immunostaining of the dopamine transporter (DAT). 11C-DTBZ PET showed a significant decrease of striatal binding (SB) values one week after the unilateral lesion. At this point, there was a 60% reduction in SB in the affected hemisphere compared with baseline values in 6-OHDA unilaterally lesioned animals. A 46% symmetric reduction over baseline SB values was found in bilaterally lesioned rats at the first week after lesion. SB values remained constant in unilaterally lesioned rats whereas animals with bilateral lesions showed a modest (22%) increase in binding values at the 3rd and 6th weeks post-lesion. The degree of striatal dopaminergic denervation was corroborated histologically by DAT immunostaining. Statistical analysis revealed a high correlation between 11C-DTBZ PET SB and striatal DAT immunostaining values (r = 0.95, p < 0.001). The data presented here indicate that 11C-DTBZ PET may be used to ascertain changes occurring in-vivo throughout the evolution of nigro-striatal dopaminergic neurodegeneration, mainly in the unilateral 6-OHDA lesion rat

Statistical parametric maps of (18)F-FDG PET and 3-D autoradiography in the rat brain: a cross-validation study

PURPOSE: Although specific positron emission tomography (PET) scanners have been developed for small animals, spatial resolution remains one of the most critical technical limitations, particularly in the evaluation of the rodent brain. The purpose of the present study was to examine the reliability of voxel-based statistical analysis (Statistical Parametric Mapping, SPM) applied to (18)F-fluorodeoxyglucose (FDG) PET images of the rat brain, acquired on a small animal PET not specifically designed for rodents. The gold standard for the validation of the PET results was the autoradiography of the same animals acquired under the same physiological conditions, reconstructed as a 3-D volume and analysed using SPM. METHODS: Eleven rats were studied under two different conditions: conscious or under inhalatory anaesthesia during (18)F-FDG uptake. All animals were studied in vivo under both conditions in a dedicated small animal Philips MOSAIC PET scanner and magnetic resonance images were obtained for subsequent spatial processing. Then, rats were randomly assigned to a conscious or anaesthetized group for postmortem autoradiography, and slices from each animal were aligned and stacked to create a 3-D autoradiographic volume. Finally, differences in (18)F-FDG uptake between conscious and anaesthetized states were assessed from PET and autoradiography data by SPM analysis and results were compared. RESULTS: SPM results of PET and 3-D autoradiography are in good agreement and led to the detection of consistent cortical differences between the conscious and anaesthetized groups, particularly in the bilateral somatosensory cortices. However, SPM analysis of 3-D autoradiography also highlighted differences in the thalamus that were not detected with PET. CONCLUSION: This study demonstrates that any difference detected with SPM analysis of MOSAIC PET images of rat brain is detected also by the gold standard autoradiographic technique, confirming that this methodology provides reliable results, although partial volume effects might make it difficult to detect slight differences in small regions

The progression of dopaminergic depletion in unilateral 6-OHDA-lesioned rats: PET imaging and histopathologic studies. | 8th FENS Forum of Neuroscience (14-18 July 2012. Barcelona, Spain)

Parkinson´s disease(PD) is characterize by a progressive death of dopaminergic neurons in the substantia nigra causing a dopamine depletion in the striatum, which is associated with metabolic compensatory changes. The rat with 6-hydroxydopamine (6-OHDA)-induced lesion in one hemisphere has been widely used as a model of PD. However, the series of pathophysiological and compensatory mechanisms associated with the lesion are not well understood. We performed a neuroimaging study aiming to define the functional changes associated with dopamine striatal depletion. Sprague-Dawley rats were unilaterally lesion using 4µg/4µl and 8µg/4µl of 6-OHDA by intracraneal injection in the median forebrain bundle. PET imaging was performed using a monoaminergic (11C-Dihydrotetrabenazine; 11C-DTBZ) and a metabolic (18F-fluorodeoxyglucose; 18F-FDG) radiotracer and conducted 1 day and 1, 2 , 3 and 6 weeks after the lesion in each animal. Analysis based on regions of interest was done for 11C-DTBZ PET (striatum) and SPM8 analysis for 18F-FDG studies (whole brain). Brains were obtained at the end of the imaging studies and immunostained to reveal optical density measurements of dopamine transporter (DAT) and vesicular monoamine transporter (VMAT2) in the striatum. The 6-OHDA lesion was not associated with a progressive dopaminergic striatal depletion, since DTBZ PET values obtained in the first and sixth weeks were similar (low dose: 65%; high dose: 82%). Pre-synaptic dopamine markers correlated with the striatal binding of 11C-DTBZ. These results suggest that dopamine depletion occurred within the firsts days after the neurotoxin administration. However, dynamic metabolic patterns were evident in both groups of animals. Remarkably, the analysis revealed the 8µg/4µl dose caused a hypometabolism in the somatosensory cortex ipsilateral to lesion (after 2 weeks) and a hypermetabolism in contralateral regions (mainly enthorhinal cortex) related to motor control during evolution. These findings show that this model could provide useful in vivo information about compensatory mechanisms

Construction of different radionuclide templates of rat brains and their use on a new statistic parametric mapping analysis protocol for PET studies. | International WorkshopCNA´10: Bio-medical applications of Micro-PET (20-21 September 2010. Sevilla, Spain)

This work shows the development of protocols to create new 18F‐FDG and 11C‐DTBZ (dyhidrotetrabenazine, a VMAT2 transporter ligand) templates of rat brain for spatial normalisation and definition of standardised areas in images used for setting up SPM analysis of PET data

Monoaminergic and metabolic Positron Emission Tomography of unilateral and bilateral 6-OHDA rat models of Parkinson's disease: a longitudinal in-vivo study. | 15º Congreso Nacional de la Sociedad Española de NeuroCiencia (25-27 de Septiembre de 2013. Oviedo, Spain)

Parkinson´s disease (PD) is characterized by nigro-striatal loss and dopaminergic striatal depletion. The aim of this work is to characterize in-vivo a time-course pattern of functional changes associated with dopaminergic striatal reduction in rat models of PD using Positron Emission Tomography (PET). Forty-four male Sprague-Dawley rats (300-350gr) were used. PET imaging with monoaminergic (11C-(+)-α-dihydrotetrabenazine; 11C-DTBZ) and metabolic (18F-fluorodeoxyglucose; 18F-FDG) radiotracers were performed in a longitudinal study during 6 weeks of the following groups: a) unilaterally lesioned rats by injection of 4µg/4µl (low dose) and 8µg/4µl (high dose) of 6-hydroxydopamine (6-OHDA) in the left median forebrain bundle; and b) bilateral lesion model, in rats receiving intraventricular injection of 100µg/4µl/day of 6-OHDA during 7 days. At the 8th week, the glucose metabolism was also evaluated ex vivo by 18F-FDG autoradiography. Bilaterally lesioned animals were not assessed with metabolic analyses. 11C-DTBZ PET images showed a significant decrease of Striatal Binding (SB) values one week after the lesion (35% SB in the low and 20% SB in the high dose group of unilateral model, and 50% SB in the bilateral model). In the 6th week, no significant differences in these values were found in the unilaterally lesion rats, whereas animals with bilateral lesion showed a higher binding value (65% SB). Remarkably, the metabolic PET study in the unilateral model revealed hypometabolism in ipsilateral somatosensory cortex and hypermetabolism in contralateral entorhinal cortex since the 2nd week onwards. Additionally, the autoradiography analysis showed hypometabolism in bilateral somatosensory cortex and ipsilateral caudate-putamen, motor cortex and thalamus, and also hypermetabolism in the contralateral entorhinal cortex. 11C-DTBZ PET is a sensitive method to ascertain dopaminergic depletion in both the bilateral and, unilateral 6-OHDA rat models. 18F-FDG studies showed a dynamic metabolic pattern that can provide useful in vivo information to monitor brain changes

Monoaminergic PET imaging and histopathological correlation in unilateral and bilateral 6-hydroxydopamine lesioned rat models of Parkinson's disease: a longitudinal in-vivo study

Carbon-11 labeled dihydrotetrabenazine (11C-DTBZ) binds to the vesicular monoamine transporter 2 and has been used to assess nigro-striatal integrity in animal models and patients with Parkinson's disease. Here, we applied 11C-DTBZ positron emission tomography (PET) to obtain longitudinally in-vivo assessment of striatal dopaminergic loss in the classic unilateral and in a novel bilateral 6-hydroxydopamine (6-OHDA) lesion rat model. Forty-four Sprague–Dawley rats were divided into 3 sub-groups: 1. 6-OHDA-induced unilateral lesion in the medial forebrain bundle, 2. bilateral lesion by injection of 6-OHDA in the third ventricle, and 3. vehicle injection in either site. 11C-DTBZ PET studies were investigated in the same animals successively at baseline, 1, 3 and 6 weeks after lesion using an anatomically standardized volumes-of-interest approach. Additionally, 12 rats had PET and Magnetic Resonance Imaging to construct a new 11C-DTBZ PET template. Behavior was characterized by rotational, catalepsy and limb-use asymmetry tests and dopaminergic striatal denervation was validated post-mortem by immunostaining of the dopamine transporter (DAT). 11C-DTBZ PET showed a significant decrease of striatal binding (SB) values one week after the unilateral lesion. At this point, there was a 60% reduction in SB in the affected hemisphere compared with baseline values in 6-OHDA unilaterally lesioned animals. A 46% symmetric reduction over baseline SB values was found in bilaterally lesioned rats at the first week after lesion. SB values remained constant in unilaterally lesioned rats whereas animals with bilateral lesions showed a modest (22%) increase in binding values at the 3rd and 6th weeks post-lesion. The degree of striatal dopaminergic denervation was corroborated histologically by DAT immunostaining. Statistical analysis revealed a high correlation between 11C-DTBZ PET SB and striatal DAT immunostaining values (r = 0.95, p < 0.001). The data presented here indicate that 11C-DTBZ PET may be used to ascertain changes occurring in-vivo throughout the evolution of nigro-striatal dopaminergic neurodegeneration, mainly in the unilateral 6-OHDA lesion rat

Cerebral metabolic pattern associated with progressive parkinsonism in non-human primates reveals early cortical hypometabolism.

Dopaminergic denervation in patients with Parkinson's disease is associated with changes in brain metabolism. Cerebral in-vivo mapping of glucose metabolism has been studied in severe stable parkinsonian monkeys, but data on brain metabolic changes in early stages of dopaminergic depletion of this model is lacking. Here, we report cerebral metabolic changes associated with progressive nigrostriatal lesion in the pre-symptomatic and symptomatic stages of the progressive 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkey model of Parkinson's Disease. Monkeys (Macaca fascicularis) received MPTP injections biweekly to induce progressive grades of dopamine depletion. Monkeys were sorted according to motor scale assessments in control, asymptomatic, recovered, mild, and severe parkinsonian groups. Dopaminergic depletion in the striatum and cerebral metabolic patterns across groups were studied in vivo by positron emission tomography (PET) using monoaminergic ([11C]-dihydrotetrabenazine; 11C-DTBZ) and metabolic (2-[18F]-fluoro-2-deoxy-d-glucose; 18F-FDG) radiotracers. 11C-DTBZ-PET analysis showed progressive decrease of binding potential values in the striatum of monkeys throughout MPTP administration and the development of parkinsonian signs. 18F-FDG analysis in asymptomatic and recovered animals showed significant hypometabolism in temporal and parietal areas of the cerebral cortex in association with moderate dopaminergic nigrostriatal depletion. Cortical hypometabolism extended to involve a larger area in mild parkinsonian monkeys, which also exhibited hypermetabolism in the globus pallidum pars interna and cerebellum. In severe parkinsonian monkeys, cortical hypometabolism extended further to lateral-frontal cortices and hypermetabolism also ensued in the thalamus and cerebellum. Unbiased histological quantification of neurons in Brodmann's area 7 in the parietal cortex did not reveal neuron loss in parkinsonian monkeys versus controls. Early dopaminergic nigrostriatal depletion is associated with cortical, mainly temporo-parietal hypometabolism unrelated to neuron loss. These findings, together with recent evidence from Parkinson's Disease patients, suggest that early cortical hypometabolism may be associated and driven by subcortical changes that need to be evaluated appropriately. Altogether, these findings could be relevant when potential disease modifying therapies become available