Cindy Casteels

Automated quantitative gait analysis in animal models of movement disorders

BackgroundAccurate and reproducible behavioral tests in animal models are of major importance in the development and evaluation of new therapies for central nervous system disease. In this study we investigated for the first time gait parameters of rat models for Parkinsons disease (PD), Huntingtons disease (HD) and stroke using the Catwalk method, a novel automated gait analysis test. Static and dynamic gait parameters were measured in all animal models, and these data were compared to readouts of established behavioral tests, such as the cylinder test in the PD and stroke rats and the rotarod tests for the HD group.ResultsHemiparkinsonian rats were generated by unilateral injection of the neurotoxin 6-hydroxydopamine in the striatum or in the medial forebrain bundle. For Huntingtons disease, a transgenic rat model expressing a truncated huntingtin fragment with multiple CAG repeats was used. Thirdly, a stroke model was generated by a photothrombotic induced infarct in the right sensorimotor cortex. We found that multiple gait parameters were significantly altered in all three disease models compared to their respective controls. Behavioural deficits could be efficiently measured using the cylinder test in the PD and stroke animals, and in the case of the PD model, the deficits in gait essentially confirmed results obtained by the cylinder test. However, in the HD model and the stroke model the Catwalk analysis proved more sensitive than the rotarod test and also added new and more detailed information on specific gait parameters.ConclusionThe automated quantitative gait analysis test may be a useful tool to study both motor impairment and recovery associated with various neurological motor disorders.

Towards a neurocircuitry in anorexia nervosa: Evidence from functional neuroimaging studies

Functional neuroimaging is widely used to unravel changes in brain functioning in psychiatric disorders. In the current study, we review single-photon emission tomography (SPECT), positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies in anorexia nervosa (AN), a difficult-to-treat eating disorder with the highest mortality rate among psychiatric disorders. We discuss the role of the parietal cortex, anterior and subgenual cingulate cortex, frontal cortex and temporal lobe in light of the cardinal symptoms of AN. The insights of the current review may ultimately lead to the development of new treatments.

Gender-dependent increases with healthy aging of the human cerebral cannabinoid-type 1 receptor binding using [(18)F]MK-9470 PET.

The endocannabinoid system (ECS) is implicated as a regulator of homeostasis of several cerebral functions and is a novel target for drug treatment of neuropyschiatric disorders. So far, the cerebral cannabinoid-type 1 receptor (CB1R) has only been studied using in vitro, animal model, electrophysiological and post-mortem data. We have used positron emission tomography (PET) using a high-affinity, subtype-selective radioligand, [(18)F]MK-9470, to assess the in vivo cerebral CB1R distribution and its variation with healthy aging and gender. Fifty healthy volunteers (25 M/25 F, 18-69 years) underwent [(18)F]MK-9470 PET. Parametric [(18)F]MK-9470 binding maps were constructed, corrected for partial volume effects and analyzed using statistical parametric mapping in a combined categorical (gender) and covariate (age) design. We found that [(18)F]MK-9470 binding to CB1R increased with aging but only in women (p(FWE)<0.05, corrected for multiple comparisons); this was most pronounced in the basal ganglia, lateral temporal cortex and limbic system, especially in the hippocampus. Men showed higher [(18)F]MK-9470 binding then women (p<0.001, uncorrected), in clusters of the limbic system and cortico-striato-thalamic-cortical circuit. Region-dependent and gender-related upregulation of [(18)F]MK-9470 binding with aging is in line with ex vivo findings in rodent studies and may be associated with a changing homeostatic capacity or compensation mechanisms in the ECS that is modulated by sex hormones. In vivo PET of the CB1R will likely improve our understanding of the ECS in several neurological and psychiatric disorders.

Regional changes in type 1 cannabinoid receptor availability in Parkinson's disease in vivo

The type 1 cannabinoid receptor (CB1) is a crucial modulator of synaptic transmission in brain and has been proposed as a potential therapeutic target in Parkinsons disease (PD), especially for treatment of levodopa-induced dyskinesias (LID). Our aim was to measure CB1 levels in brains of PD patients in vivo and to investigate the relation between CB1 availability and LID. We studied 12 healthy controls and 29 PD patients (9 drug-naïve patients with early PD, 10 patients with advanced PD and LID, and 10 patients with advanced PD without LID). PD patients were examined using the Unified Parkinsons Disease Rating Scale (UPDRS) and the modified Abnormal Involuntary Movement Scale (mAIMS). All subjects underwent positron emission tomography (PET) with the CB1-selective radioligand [(18)F] MK-9470 and magnetic resonance imaging (MRI). PD patients showed an absolute decrease in CB1 availability in the substantia nigra. By contrast, CB1 availability was relatively increased in nigrostriatal, mesolimbic, and mesocortical dopaminergic projection areas. CB1 availability did not differ significantly between advanced PD patients with and without LID. Within the group of PD patients with LID, there was no significant correlation between CB1 availability and LID severity. These data demonstrate regional changes in CB1 availability in PD in vivo, but do not support a role for dysregulation of CB1 levels in the pathogenesis of LID.

Relationship of Type 1 Cannabinoid Receptor Availability in the Human Brain to Novelty-Seeking Temperament

CONTEXT Brain neurochemistry can partially account for personality traits as a variance of normal human behavior, as has been demonstrated for monoamine neurotransmission. Positron emission tomography using fluorine 18-labeled MK-9470 now enables quantification of type 1 cannabinoid receptors (CB1R) in the brain. OBJECTIVE To investigate whether there is a relationship between human temperament traits and regional cerebral CB1R availability. DESIGN Forty-seven [(18)F]MK-9470 baseline scanning sessions were performed and correlated with the temperament dimensions and subdimensions of the 240-item Cloninger Temperament and Character Inventory. SETTING Academic brain imaging center. PARTICIPANTS Forty-seven nonsmoking, healthy volunteers (paid). Main Outcome Measure Voxel-based correlation of temperament variables of the inventory with regional CB1R availability. RESULTS Novelty seeking was inversely correlated with global CB1R availability (r = -0.33, P = .02), with the most significant correlation in the left amygdala (r = -0.41, P = .005). In particular, the subdimension extravagance showed a highly significant inverse correlation to global CB1R availability (r = -0.53, P <.001), most pronounced in the amygdala, anterior cingulate, parietal cortex, and precuneus. Also, disorderliness was inversely correlated with global CB1R availability (r = -0.31, P = .04). CONCLUSIONS Low baseline cerebral CB1R availability is related to a high novelty-seeking personality, in particular to extravagance, most pronounced in the amygdala. Further investigation of the functional role of the CB1R is warranted in pathological behavior known to be strongly related to novelty seeking, such as addiction and eating disorders.

Changes in Cerebral CB1 Receptor Availability after Acute and Chronic Alcohol Abuse and Monitored Abstinence

Involvement of the type 1 cannabinoid receptor (CB1R) in the effects of alcohol on the brain is supported by animal experiments, but how in vivo CB1R levels are altered in alcoholic patients is still unclear. To assess the short-time effects of a binge drinking episode on CB1R availability, 20 healthy social drinkers underwent [18F]MK-9470-positron emission tomography (PET) at baseline and after intravenous ethanol administration (ALC ACU). Moreover, 26 alcoholic patients underwent sequential CB1R PET after chronic heavy drinking (ALC CHR) and after 1 month of abstinence (ALC ABST). Seventeen healthy subjects served as controls. Compared with baseline, ALC ACU resulted in a global increase of CB1R availability (+15.8%). In contrast, a global decreased CB1R availability was found in ALC CHR patients (−16.1%) compared with controls, which remained unaltered after abstinence (−17.0%). Voxel-based analysis showed that ALC CHR patients had reduced CB1R availability, especially in the cerebellum and parieto-occipital cortex. After abstinence, reduced CB1R availability extended also to other areas such as the ventral striatum and mesotemporal lobe. In conclusion, whereas the acute alcohol effect is an increase in CB1R availability, chronic heavy drinking leads to reduced CB1R availability that is not reversible after 1 month of abstinence. Longer follow-up is required to differentiate whether this is a compensatory effect of repeated endocannabinoid overstimulation or an enduring trait-like feature. An enhanced CB1R signaling may offer a new therapeutic direction for treatment of the negative affective state produced by alcohol withdrawal and abstinence, which is critical for the maintenance of alcohol addiction.

Diffusion tensor imaging in a rat model of Parkinson's disease after lesioning of the nigrostriatal tract

Parkinsons disease (PD) is characterised by degeneration of the nigrostrial connection causing dramatic changes in the dopaminergic pathway underlying clinical pathology. Till now, no MRI tools were available to follow up any specific PD‐related neurodegeneration. However, recently, diffusion tensor imaging (DTI) has received considerable attention as a new and potential in vivo diagnostic tool for various neurodegenerative diseases. To assess this in PD, we performed DTI in the acute 6‐hydroxydopamine (6‐OHDA) rat model of PD to evaluate diffusion properties in the degenerating nigrostriatal pathway and its connecting structures. Injection of a neurotoxin in the striatum causes retrograde neurodegeneration of the nigrostriatal tract, and selective degeneration of nigral neurons. The advantage of this model is that the lesion size is well controllable by the injected dose of the toxin. The degree of functional impairment was evaluated in vivo using the amphetamine rotation test and µPET imaging of the dopamine transporter (DAT). Despite a nearly complete lesion of the nigrostriatal tract, DTI changes were limited to the ipsilateral substantia nigra (SN). In this study we demonstrate, using voxel‐based statistics (VBS), an increase in fractional anisotropy (FA), whereas all eigenvalues were significantly decreased. VBS enabled us to visualise neurodegeneration of a cluster of neurons but failed to detect degeneration of more diffuse microstructures such as the nigrostriatal fibres or the dopaminergic endings in the striatum. VBS without a priori information proved to be better than manual segmentation of brain structures as it does not suffer from volume averaging and is not susceptible to erroneous segmentations of brain regions that show very little contrast on MRI images such as SN. Copyright

Non-invasive imaging of neuropathology in a rat model of α-synuclein overexpression

Parkinsons disease is a neurodegenerative disorder affecting the dopaminergic neurons in the substantia nigra. Aggregation of alpha-synuclein appears to play a central role in the pathogenesis. Novel animal models for neurodegeneration have been generated by lentiviral vector-mediated locoregional overexpression of disease-associated genes in the adult brain. We have used lentiviral vectors to overexpress a clinical mutant of alpha-synuclein, A30P, in the rat substantia nigra. This overexpression induced time-dependent cytoplasmic and neuritic accumulation of alpha-synuclein and neurodegeneration. A subgroup of the rats developed asymmetric rotational behavior after administration of amphetamine. In addition, these animals displayed reduced dopamine transporter binding visualized by 123I-FP-CIT microSPECT imaging. The behavioral and microSPECT data were validated by histological analysis. There was a strong correlation between the reduction of dopaminergic neurons in the substantia nigra and the reduction of dopamine transporter binding in the striatum. MicroSPECT imaging enables non-invasive imaging of the neurodegeneration allowing longitudinal follow-up in this new animal model for Parkinsons disease and the evaluation of neuroprotective drugs.

Longitudinal follow-up and characterization of a robust rat model for Parkinson's disease based on overexpression of alpha-synuclein with adeno-associated viral vectors

Testing of new therapeutic strategies for Parkinsons disease (PD) is currently hampered by the lack of relevant and reproducible animal models. Here, we developed a robust rat model for PD by injection of adeno-associated viral vectors (rAAV2/7) encoding α-synuclein into the substantia nigra, resulting in reproducible nigrostriatal pathology and behavioral deficits in a 4-week time period. Progressive dopaminergic dysfunction was corroborated by histopathologic and biochemical analysis, motor behavior testing and in vivo microdialysis. L-DOPA treatment was found to reverse the behavioral phenotype. Non-invasive positron emission tomography imaging and magnetic resonance spectroscopy allowed longitudinal monitoring of neurodegeneration. In addition, insoluble α-synuclein aggregates were formed in this model. This α-synuclein rat model shows improved face and predictive validity, and therefore offers the possibility to reliably test novel therapeutics. Furthermore, it will be of great value for further research into the molecular pathogenesis of PD and the importance of α-synuclein aggregation in the disease process.

In vivo type 1 cannabinoid receptor mapping in the 6-hydroxydopamine lesion rat model of Parkinson's disease

Type 1 cannabinoid (CB1) receptors are expressed in high concentrations in the central nervous system, including the basal ganglia, and could have direct or indirect effects on motor behavior through modulation of dopaminergic, glutamatergic and GABA-ergic neurotransmission. Using the CB1 receptor radioligand [(18)F]MK-9470 and small-animal PET, we investigated for the first time in vivo cerebral changes in [(18)F]MK-9470 binding in the 6-hydroxydopamine (6-OHDA) rat model of Parkinsons disease (PD), parallel to dopamine transporter (DAT) imaging, tyrosine hydroxylase (TH) staining, and behavioral measurements. In the 6-OHDA model, relative [(18)F]MK-9470 PET binding decreased in the contralateral cerebellum (-9%, p<0.0004) and caudate-putamen bilaterally (ipsilateral -8%, contralateral -7%; p=0.001 and p<0.0003, respectively). The number of TH(+) neurons in the substantia nigra was inversely correlated to CB1 receptor binding in the ipsilateral cerebellum (p=1.10(-6)). The behavioral outcome was positively related to regional CB1 receptor binding in the contralateral somatosensory cortex (p=4.10(-6)). In vivo [(18)F]MK-9470 PET imaging points to changes in endocannabinoid transmission, specifically for CB1 receptors in the 6-OHDA model of PD, with mainly involvement of the caudate-putamen, but also distant regions of the motor circuitry, including the cerebellum and somatosensory cortex.