Monoaminergic Metabolic Imaging Of Unilateral And

Monoaminergic-metabolic imaging of unilateral and bilateral 6-hydroxidopamine
rat models of Parkinson’s disease: a longitudinal in-vivo study
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
4Clínica Universidad de Navarra, Pamplona, Spain
2CIBERNED,
• 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).
Animals:
Scanner:
Fourty-four male
Sprague-Dawley rats
3Universidad Complutense, Madrid, Spain
Madrid, Spain
5Pontificia Universidad Católica de Chile, Santiago de Chile, Chile
11C-DTBZ
PET
18F-FDG
Basal
L
fmolinet@unav.es
Mild UL
R
L
Severe UL
R
L
Bilateral
R
L
Philips MOSAIC
Basal
R
L
• PET imaging with a monoaminergic radiotracer (11C-(+)-α-dihydrotetrabenazine; 11CDTBZ) 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 6OHDA 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.
7 weeks after MFB lesion
1 week
11C-DTBZ
Lesion
6-OHDA
Basal
Jlkjlkj
1 week
3 weeks
1 week
18F-FDG
18F-FDG
18F-FDG
18F-FDG
18F-FDG
11C-DTBZ
11C-DTBZ
11C-DTBZ
11C-DTBZ
Autorad
1st week 2nd week 3rd week
Apomorphine
test
6th week Sacrifice
Apomorphine-induced rotational behavior of the
animals was measured for 1 h (0.05 mg/kg, s.c.)
7 weeks after last injection
1 week
1 week
Place
Cannula
Infusion Remove
6-OHDA Cannula
7 doses
(1/day)
(after last
dose)
3 weeks
2 weeks
1 week
11C-DTBZ
11C-DTBZ
11C-DTBZ
1st week
3rd week
6th week Sacrifice
Longitudinal Asymmetry and Catalepsy tests
18F-FDG
R
• 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.
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)
Sham UL
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
PET
Severe UL
Sham BL
Lesioned BL
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 %#
Autoradiography
Hypometabolism
autoradiography:
R
•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
FINAL IMAGE
Mild UL
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:
Surgery
L
Histopathological Analysis
Limb use asymmetry test:
Bilateral lesion
2 weeks
R
• 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).
Catalepsy-grid test:
18F-FDG
Unilateral
Region of Interest (ROI) Analysis
Apomorphine test:
1 week
L: left
R: right
6-OHDA-induced lesion and PET studies:
Unilateral lesion
1 week
PET
18F-FDG
autoradiography
Hypermetabolism
L
R
L: left
R: right
Hypometabolism
L
R
L
R
L
p < 0.001 (unc.)
Statistical
(SPM)
Parametric
Mapping
• Metabolic
PET
study:
hypometabolism in ipsilateral caudateputamen, 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.
• 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.
Supported by CIBERNED, UTE-FIMA