rat models of parkinson’s disease: a longitudinal in-vivo...
TRANSCRIPT
Monoaminergic-metabolic imaging of unilateral and bilateral 6-hydroxidopamine
rat models of Parkinson’s disease: a longitudinal in-vivo study
Supported by CIBERNED, UTE-FIMA
F. Molinet-Dronda1,2, B. Gago1,2, A. Quiroga-Varela1,2, M. Delgado3, M. Collantes1, E. Prieto4, E. Iglesias1,2, C. Juri4,5, I. Peñuelas1,4, J. A. Obeso1,2,4 1Center for Applied Medical Research, Pamplona,Spain 2CIBERNED, Madrid, Spain 3Universidad Complutense, Madrid, Spain
4Clínica Universidad de Navarra, Pamplona, Spain 5Pontificia Universidad Católica de Chile, Santiago de Chile, Chile
Animals:
Fourty-four male
Sprague-Dawley rats
Scanner:
Philips MOSAIC
6-OHDA-induced lesion and PET studies:
• PET imaging with a monoaminergic radiotracer (11C-(+)-α-dihydrotetrabenazine; 11C-
DTBZ) was performed for a longitudinal study during 6 weeks in the following groups:
a) unilaterally lesioned rats by injection of 4µg/4µl (mild lesion) or 8µg/4µl (severe
lesion) of 6-OHDA in the left median forebrain bundle (unilateral model, UL)
b) bilaterally lesioned rats receiving a intraventricular injection of 100µg/4µl/day of 6-
OHDA during 7 days (bilateral model, BL)
• PET imaging with a metabolic radiotracer (18F-fluorodeoxyglucose; 18F-FDG) was also
performed for a longitudinal study during 6 weeks, but only in the unilateral model.
18F-FDG autoradiography:
•At 7th week, the glucose metabolism was also evaluated ex-vivo in rats of the
unilateral model by 18F-FDG autoradiography of brain sections.
•The process of the autoradiographic images was the following:
Representative 3D image of 18F-FDG autoradiography
FINAL IMAGE
Jlkjlkj
1 week
Lesion
6-OHDA
18F-FDG
11C-DTBZ
Basal
1 week
18F-FDG
11C-DTBZ
1st week
1 week
18F-FDG
11C-DTBZ
2nd week
1 week
18F-FDG
11C-DTBZ
3rd week
3 weeks
18F-FDG
11C-DTBZ
6th week
1 week
7 weeks after MFB lesion
Unilateral lesion
18F-FDG
Autorad
Sacrifice
Apomorphine
test
Infusion
6-OHDA
7 doses
(1/day)
Surgery
Place
Cannula
2 weeks
Remove
Cannula
(after last
dose)
1 week 1 week 2 weeks 3 weeks 1 week
7 weeks after last injection
Bilateral lesion
11C-DTBZ
1st week
11C-DTBZ
3rd week
11C-DTBZ
6th week
Sacrifice
Longitudinal Asymmetry and Catalepsy tests
Sham UL Mild UL Severe UL Sham BL Lesioned BL
18F-FDG PET
Basal Unilateral
11C-DTBZ PET
Basal Severe UL Bilateral Mild UL
R L R L R L R L R L R L
L: left
R: right
Region of Interest (ROI) Analysis • 11C-DTBZ PET images showed a significant decrease of
Striatal Binding (SB) values one week after the lesion (39%
SB and 22% SB in mild and severe unilateral lesion groups
respectively, and ~53% SB in both hemispheres in the
bilateral model). Significant differences between
unilaterally mild and severe lesion groups were also shown.
• At the 6th week, no significant differences were found
between unilaterally mild and severe lesioned rats (mild,
34% SB; severe, 20% SB) whereas animals with bilateral
lesion showed a higher binding value (~68% SB).
Histopathological Analysis • Optical density values showed that mild and severe
lesions induced a significant and similar DAT
immunoreactivity reduction in the left striatum.
• In the BL model, not differences were found between
both sides of the striatum.
• 11C-DTBZ PET is a sensitive method to ascertain dopaminergic depletion in both bilateral and unilateral 6-OHDA-lesioned rat models.
• PET images of 11C-DTBZ show that the 6-OHDA lesion is not associated with a progressive dopaminergic striatal depletion, suggesting that
it occurs within the firsts days after the neurotoxin administration.
• Dynamic metabolic pattern shown with 18F-FDG is evident in the unilateral model.
• Accordingly, these 18F-FDG PET studies of 6-OHDA–lesioned rat models could provide useful in-vivo information to monitor brain changes
for a better knowledge about basal ganglia compensatory mechanisms.
• Parkinson´s disease (PD) is a neurodegenerative disorder characterized by progressive death of dopaminergic neurons in the substantia
nigra causing dopamine depletion in the striatum, which is associated with metabolic compensatory changes.
• The rat with a 6-hydroxydopamine (6-OHDA)-induced lesion in one hemisphere has been widely used as a model of PD. However, the
pathophysiological and compensatory mechanisms associated with the lesion are not well understood.
• Several attempts have been done to develop a bilateral animal model that could better resemble PD features such as the
degeneration in both hemispheres or a progressive dopaminergic depletion.
• The aim of this neuroimaging study is to characterize and define in-vivo a time-course pattern of functional changes associated with
dopaminergic striatal reduction in unilateral and bilateral 6-OHDA rat models of PD using Positron Emission Tomography (PET).
Statistical Parametric Mapping
(SPM) • Metabolic PET study:
hypometabolism in ipsilateral caudate-
putamen, somatosensory, motor and
insular cortex, and hypermetabolism in
contralateral entorhinal cortex since
the 2nd week onwards.
• Autoradiography analysis showed
an hypometabolism in bilateral
somatosensory cortex and ipsilateral
caudate-putamen, motor cortex and
thalamus, and also hypermetabolism
in the contralateral entorhinal cortex.
PET Autoradiography
Sham UL Mild UL Severe UL Sham BL Lesion BL
Left 95.3 ± 16.4 % 28.7 ± 20.9 %# 19.8 ± 6.5 %# 100 ± 34.9 % 72.2 ± 15.3 %#
Right 100 ± 13.3 % 100 ± 12.7 % 100 ± 12.2 % 100 ± 30.6 % 67.5 ± 15.4 %#
Apomorphine test: Apomorphine-induced rotational behavior of the
animals was measured for 1 h (0.05 mg/kg, s.c.)
Catalepsy-grid test: Rats were gently placed on a wire grid at 45º above
the surface and the intensity of the cataleptic state
was assessed by the duration of immobile episode
during one minute (0: 0 to 14 sec; 1: 15 to 29 sec; 2:
30 to 59 sec; 3: ≥60 sec)
Limb use asymmetry test: Animals were placed in a transparent cylinder for 5
min to quantify the independent use of the right or
left forelimbs for contacting the wall
Immunohistochemistry: Dopamine transporter (DAT) immunolabeling was estimated in coronal striatal sections (40 µm-thick) using a specific primary antibody (Santa Cruz
Biotechnology) and ImageJ software (NIH), with the
optical density of the caudate-putamen region
measured
Hypometabolism
L R
Hypermetabolism
L R
Hypometabolism
L R L R
p < 0.001 (unc.)
L: left
R: right