MINIREVIEW
Parkinson’s disease:geneticversustoxin-induced rodent
models
Mu
¨
gen Terzioglu
1
and Dagmar Galter
2
1 Department of Laboratory Medicine, Karolinska Institutet, Stockholm, Sweden
2 Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
Introduction
Parkinson’s disease (PD) is a common neurodegenera-
tive disease with a complex etiology resulting from
genetic factors, environmental exposures, or a combi-
nation of both.
The clinical key symptoms are motor dysfunctions
such as bradykinesia, resting tremor and muscle
rigidity combined with postural instability, but many
patients also suffer from autonomic and cognitive dis-
turbances. Selective degeneration of dopamine neurons
in the substantia nigra (SN) causes the major PD
symptoms, but there is often widespread neurodegener-
ation and pathology in other regions of the brain,
including the proteinaceous inclusions called Lewy
bodies (LBs) and dystrophic neurites called Lewy
neurites. By the time clinical manifestations appear,
about 60–70% of the dopamine fibers in the caudate
Keywords
6-OHDA; conditional knockout mice;
DAT-cre; dopamine system; Engrailed;
intracellular aggregates; mitochondrial
dysfunction; MPTP; PARK genes;
progressive neurodegeneration; a-synuclein
Correspondence
D. Galter, Department of Neuroscience,
Karolinska Institutet, Retzius va
¨
g8,
171 77 Stockholm, Sweden
Fax: +46 8 32 37 42
Tel: +46 8 524 87018
E-mail: dagmar.galter@ki.se
(Received 23 October 2007, revised 17
December 2007, accepted 7 January 2008)
doi:10.1111/j.1742-4658.2008.06302.x
Parkinson’s disease (PD), a common progressive neurodegenerative disor-
der, is characterized by degeneration of dopamine neurons in the substantia
nigra and neuronal proteinaceous aggregates called Lewy bodies (LBs).
The etiology of PD is probably a combination of environmental and
genetic factors. Recent progress in molecular genetics has identified several
genes causing PD, including a-synuclein, leucine-rich repeat kinase 2
(LRRK2), Parkin, DJ-1 and PTEN-induced kinase 1 (PINK1), many of
them coding for proteins found in LBs and ⁄ or implicated in mitochondrial
function. However, the mechanism(s) leading to the development of the
disease have not been identified, despite intensive research. Animal models
help us to obtain insights into the mechanisms of several symptoms of PD,
allowing us to investigate new therapeutic strategies and, in addition, pro-
vide an indispensable tool for basic research. As PD does not arise sponta-
neously in animals, characteristic and specific functional changes have to
be induced by administration of toxins or by genetic manipulations. This
review will focus on the comparison of three types of rodent animal models
used to study different aspects of PD: (a) animal models using neurotoxins;
(b) genetically modified mouse models reproducing findings from PD link-
age studies or based on ablation of genes necessary for the development
and survival of dopamine neurons; and (c) tissue-specific knockouts in mice
targeting dopamine neurons. The advantages and disadvantages of these
models are discussed.
Abbreviations
6-OHDA, 6-hydroxydopamine; cre, cre-recombinase; DA, dopamine; DAT, dopamine transporter; En, Engrailed; IR, immunoreactive; LB,
Lewy body;
L-dopa, L-3,4-dihydroxyphenylalanine; LRRK2, leucine-rich repeat kinase 2; MAO-B, monoamine oxidase B; MPP
+
, 1-methyl-4-
phenyl-2,3-dihydropyridium ion; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; PD, Parkinson’s disease; PINK1, PTEN-induced kinase 1;
ROS, reactive oxygen species; SN, substantia nigra; TFAM, mitochondrial transcription factor A; TH, tyrosine hydroxylase; VMAT, vesicular
monoamine transporter; VTA, ventral tegmental area.
1384 FEBS Journal 275 (2008) 1384–1391 ª 2008 The Authors Journal compilation ª 2008 FEBS
putamen and at least 50% of the dopamine neurons in
the SN are already lost. Although slow in most cases,
progression of the disease is irreversible, and different
drug treatments ameliorate symptoms without arrest-
ing or slowing down the pace of neurodegeneration.
In order to understand the underlying mechanisms
and to develop new drugs or therapies for PD, it is
important to have available animal models that reca-
pitulate key symptoms and the slow progression of the
disease as accurately as possible. Because the disease is
not known in any animal species, except perhaps mild
parkinsonism in aged nonhuman primates in captivity,
different models have been developed in several species
together with specific behavior tests to assess motor
dysfunctions.
This review focuses on rodent animal models and
compares the most recently available tissue-specific
knockout mouse models with older genetic and toxin-
induced animal models (Fig. 1).
Toxin-induced animal models
Early animal models developed for PD research used
neurotoxins specific for the dopamine (DA) system
such as 6-hydroxydopamine (6-OHDA) and 1-methyl-
4-phenyl-1,2,3,6 tetrahydropyridine (MPTP). For a
recent review on classic toxin-induced animal models,
see also Schober [1].
The hydroxylated derivative of the neurotransmitter
DA was first used in sympathetic heart denervation,
and soon after in the central nervous system [2]. When
the drug is stereotactically injected into the striatum,
the median forebrain bundle or the SN, it induces fast
and irreversible DA depletion through reactive oxygen
species (ROS) formation and toxic quinines [3]. The
relative specific toxicity of 6-OHDA for catecholamine
neurons results from its uptake by DA and noradrena-
lin transporters. Most widely used is the unilateral
lesion of the DA system in rats, where a quantifiable
circling behavior is induced after injection of DA
receptor agonists or amphetamine. In addition, several
other behavioral assessments, such as fine motor skill
tasks and the cylinder test, have been developed to
measure striatal DA loss [4]. Furthermore, rodent ani-
mal models for dyskinesia are mostly based on unilat-
eral intracerebral injections of 6-OHDA followed by
chronic l-3,4-dihydroxyphenylalanine (l-dopa treat-
ment [5,6,6a].
In 1982, an analog of the narcotic drug meperidine
was accidentally discovered to be a potent dopamine
neurotoxin when young drug addicts developed irre-
versible and severe PD symptoms following self-admin-
istration of what they hoped to be synthetic heroin [7].
The highly lipophilic substance that they had synthe-
sized, MPTP, crosses the blood–brain barrier easily
after systemic administration and is converted into the
active toxic metabolite 1-methyl-4-phenyl-2,3-dihydro-
pyridium ion (MPP
+
) by the enzyme monoamine oxi-
dase B (MAO-B), located mainly in serotoninergic
neurons and astrocytes. The metabolite MPP
+
is selec-
tively taken up into dopamine neurons by the DA
transporter (DAT), and irreversibly inhibits complex I
ABC
Fig. 1. Schematic illustration of different rodentmodels of PD. (A) Toxin-induced models: the four different toxins penetrate dopamine neu-
rons either specifically via DAT (6-OHDA and MPP
+
) or through diffusion (rotenone and paraquat) and inhibit complex I of the mitochondrial
electron transfer chain (consisting of complex I to complex V), leading to mitochondrial intoxication with enhanced production of ROS and
reduced production of ATP. Although all toxins do not exclusively act on dopamine neurons, they induce PD symptoms and key pathology,
indicating an increased susceptibility of the DA system to mitochondrial dysfunction. (B) Genetic models: on the basis of the PD-linked
genes a-Synuclein, Parkin, Pink1, DJ-1 and LRRK2, several mouse models have been generated in which all cells of the organism are
affected where the genes are active. Protein aggregations, altered protein handling and mitochondrial deficits have been detected in these
mouse models, mainly in the DA system. (C) Dopamine neuron-specific knockout models: using DAT promoter driven cre expression, three
mice models with targeted deletion of floxed genes have been generated to date: deleting the GDNF receptor Ret, the RNA-cleaving
enzyme complex Dicer and TFAM from dopamine neurons.
M. Terzioglu and D. Galter Animal models of Parkinson’s disease
FEBS Journal 275 (2008) 1384–1391 ª 2008 The Authors Journal compilation ª 2008 FEBS 1385
of the mitochondrial respiratory chain. As the suscepti-
bility to MPTP depends on the MAO-B activity, dif-
ferent mouse strains react very differently to the toxin.
Rats are relatively resistant to MPTP, whereas humans
are in danger of intoxication at quite low doses. In
mice, systemic MPTP treatment induces bradykinesia,
rigidity and posture abnormalities combined with a
depletion of dopamine neurons [8]. Continuous MPTP
infusion by minipumps has been reported to induce
development of intracellular inclusion bodies [9],
although these inclusions are not similar to the LBs
typically found in human disease [10].
More recent toxin-induced animal models make use
of agents with a general toxicity: mitochondrial func-
tion inhibitors such as the herbicide paraquat and the
insecticide rotenone, or proteasomal inhibitors such as
epoxomicin.
Paraquat is structurally similar to MPTP, but has
no selectivity for DAT and does not accumulate in
dopamine neurons after systemic administration. Nev-
ertheless, it induces a specific, although modest, loss of
tyrosine hydroxylase (TH)-positive neurons of the SN
pars compacta [11,12]. Rotenone, produced in the
roots and stems of tropical plants, inhibits the transfer
of electrons from complex I to ubiquinone in the mito-
chondrial electron transfer chain. Rotenone interferes
with mitochondrial function at the same site as
MPP
+
, but is only mildly toxic for humans and highly
unstable, with a short half-life in the environment. In
rodents, particularly in rats, chronic infusion can
induce a slowly progressing neurodegeneration of
dopamine neurons associated with intracellular multi-
form a-synuclein immunoreactive (IR) aggregates,
occurrence of widespread oxidatively modified DJ-1,
and proteasomal impairment [13]. However, the rote-
none model has low reproducibility, and many animals
die from acute toxicity, unrelated to central nervous
system involvement.
A further rodenttoxin-induced model has been
proposed that uses systemic administration of the
proteasomal inhibitor epoxomicin [14]. In this PD
model, rats reproduced most of the key features of PD
pathology, including reduced amounts of dopamine
fibers in the striatum, and degeneration of dopamine
neurons in the SN accompanied by inflammation and
intracellular aggregates with a-synuclein- and ubiqu-
itin-like immunoreactivity. However, in a further inde-
pendent study, systemic administration of epoxomicin
failed to be effective in rats or monkeys [15], although
intracerebral injection of epoxomicin and other prote-
asomal inhibitors blocked MPP
+
- or rotenone-induced
dopamine neuron death in rats and induced round
a-synuclein IR inclusions in dopamine neurons [16].
In summary, most toxins used in PD animal models
inhibit mitochondrial function and reveal a greater
susceptibility of dopamine neurons to mitochondrial
dysfunction and ROS production.
Genetically modified mouse models
Although the majority of PD cases are sporadic, sev-
eral mutations in genes causing familial forms of PD
have been recently discovered, and many susceptibility
genes have also been identified, leading to new
approaches to the study of mechanisms leading to dis-
ease. Many animal models are based on genetically
modified mice with null mutations, an extra gene copy,
or point mutations of genes located in different PARK
loci [17,18].
For the recessively inherited loss-of-function muta-
tions in Parkin, DJ-1 and PINK1, all of which cause
early-onset PD, genetic mouse models can easily be
made by null mutation of such genes (knockout mice).
For the dominantly inherited gain-of-function muta-
tions such as in a-Synuclein and leucine-rich repeat
kinase 2 (LRRK2), transgenic mouse models have been
created in which extra copies of the gene are intro-
duced into the mouse genome or delivered by lenti- or
adeno-associated virus. Several mouse strains have
been created for a-Synuclein, where either the human
wild-type gene is overexpressed under various heterolo-
gous promoters, to reproduce the gene duplication and
triplication detected in PD families, or the PD-causing
a-Synuclein mutations A30P or A53T are expressed in
transgenic mice [19]. High levels of mutated a-synuc-
lein expression under the mouse prion protein pro-
moter induced, for example, a progressive phenotype
with intraneuronal inclusions, degeneration and mito-
chondrial DNA damage in the neurons [20]. Although
no PD key symptoms were detected, this model is
valuable for understanding the relationship of a-synuc-
lein-positive protein depositions and neuronal damage.
Data from mouse models with mutant or wild-type
LRRK2 overexpression or null mutation have not yet
been published.
None of the geneticmodels based on PD-linked
genes recapitulate the key symptoms of the disease,
such as loss of dopamine neurons, but more subtle
effects on the DA system have been detected, such as a
small decrease in DAT binding and slightly reduced
DA levels in the striatum, abnormal response to DA
agonists, including apomorphine and amphetamine,
and motor disturbances, including decreased spontane-
ous activity together with protein-handling defects [17].
In several geneticmodels the MPTP-induced toxicity
for dopamine neurons has been analyzed and found to
Animal models of Parkinson’s disease M. Terzioglu and D. Galter
1386 FEBS Journal 275 (2008) 1384–1391 ª 2008 The Authors Journal compilation ª 2008 FEBS
be modified: a-Synuclein knockout mice were reported
to be less sensitive to MPTP, whereas a-Synuclein
transgenic mice and Dj-1 knockout mice were reported
to be more susceptible to the toxin [21]. Studies of the
effects of toxins in genetic PD models can provide
important clues, because the etiology and progression
of the disease can be due to a combination of genetic
factors and environmental exposures. Moreover, many
genes implicated in PD are directly or indirectly
involved in mitochondrial function: PINK1, DJ-1 and
possibly Parkin and LRRK2 are at least partly local-
ized to mitochondria; in a-Synuclein transgenic mice,
mitochondrial pathology has been detected; in mice
lacking the mitochondrial protease HtrA2 ⁄ Omi, motor
impairment due to striatal cell loss has been reported
[22], and in PolG, the mitochondrial DNA polymerase,
genetic variants associated with PD have been identi-
fied [23]. These genetic findings together strongly sug-
gest mitochondrial involvement in the etiology of PD.
Detection of genes that are critical for the develop-
ment and survival of dopamine neurons has led to
additional mouse models, such as the spontaneously
occurring Pitx3-aphakia mouse or the Engrailed (En)
double-knockout mouse model.
En1 and En2 homeobox transcription factors are
expressed as early as embryonic day 8, and they play a
role in the development of the midbrain and cerebel-
lum. Later in development they have additional func-
tions, such as being survival factors for mesencephalic
dopamine neurons, where the two genes can compen-
sate for each other. Heterozygous knockout mice of
En1 and homozygous knockout of En2 (En1
+ ⁄ )
; En2
KO) have adult onset of PD-like features [24]. During
the first 3 months after birth, the number of dopamine
neurons in the SN declined by about 70%, and DA
levels in the striatum were reduced by 40%, but the
degeneration abated at this level for the next
15 months. The mice slowly developed reduced loco-
motor activity and other motor deficits, but further
investigations are needed to clarify whether the altered
motor behavior is related to the loss of dopamine
neuron function or is caused by other cells deprived of
En, such as cerebellar neurons, a subset of interneu-
rons in the spinal cord or Bergman glia.
The aphakia mouse, a recessive phenotype that
occurred spontaneously, is characterized by small eyes
that lack a lens, caused by a deletion in the promoter
region of Pitx3. The gene expression of this homeobox
transcription factor is restricted to the developing eye
and to midbrain dopamine progenitor cells from
embryonic day 11 to adult life. Adult aphakia mice
develop SN-specific dopamine neuron loss combined
with a severe reduction of DA levels in the dorsolateral
striatum, whereas ventral tegmental area (VTA) dopa-
mine neurons are spared overall [25]. No intracellular
aggregations or LB-like inclusions have been detected.
The motor deficits include reduced rearing and sensori-
motor impairments, and repeated l-dopa treatment
induces dyskinesia in this genetic model [26].
Tissue-specific knockout mouse
models
Recently, a new type of rodent animal model for PD
has been established, using conditional knockout strat-
egies in order to disrupt the expression of genes of
interest in a region- or neuron-specific manner. For
this purpose, mice that express cre-recombinase (cre)
under the control of the DAT promoter are predomi-
nantly used to target postmitotic dopamine neurons in
the midbrain [27–30]. Other mouse strains targeting
wider populations of neurons are also available: cre
expression driven by the TH promoter targets all cate-
cholamine neurons in the central and peripheral ner-
vous system [31,32]; Mice in which cre expression is
driven by the En1 promoter [33] or by wingless-1 [34]
target the early stages of the developing DA system,
although these mice are less convenient as PD models
because neither transcription factor is exclusively
expressed by dopamine neurons of the midbrain.
To generate mice with specific deletion of a particu-
lar gene, one of these cre-expressing mouse strains is
bred with mice homozygous for a floxed gene; that is,
both chromosomal copies of the gene are flanked by
LoxP recombination sites.
Examples of floxed genes used in conditional mouse
models are: the mitochondrial transcription factor A
(TFAM) [35], the microRNA enzyme Dicer [36], and
the receptors for neurotrophic factors Ret [for glial-
cell-line derived neurotrophic factor (GDNF)] and
TrkB [for brain-derived neurotrophic factor (BDNF)]
[37]. Deletion of TFAM, Ret or Dicer in dopamine
neurons induces progressive motor dysfunctions such
as slowness and pauperism of movements and limited
rearing at different ages: at a few weeks for Dicer,at
several months for TFAM and at more than 1 year
for Ret conditional knockout mice. In MitoPark mice,
which have respiratory chain-deficient dopamine neu-
rons due to cell-specific ablation of TFAM, the motor
impairments are ameliorated by l-dopa administra-
tion, a common treatment for PD patients. Moreover,
MitoPark mice respond differently to the same dose
of l-dopa, depending on the progression of the symp-
toms, very similar to PD patients: in younger mice, as
in less severe PD patients, l-dopa treatment results in
a greater locomotor response than in older mice and
M. Terzioglu and D. Galter Animal models of Parkinson’s disease
FEBS Journal 275 (2008) 1384–1391 ª 2008 The Authors Journal compilation ª 2008 FEBS 1387
Table 1. Summary of advantages and disadvantages of selected rodentmodels of PD. Scoring of dopamine neuron: slight loss (< 30%);
loss (30–70%); massive loss (< 70%). The construct validity of a model refers to the degree to which the rodent model reproduces known
PD etiology (low = no findings in PD patients indicate a role in PD etiology for the toxin or genetic modification that the model is based on;
poor = some findings point to a role in PD etiology; good = findings in PD patients indicate a causative role for genetic modifications repro-
duced in the model). KO, knockout.
Model PD symptoms PD pathology Advantages Disadvantages
6-OHDA Motor impairments
after bilateral lesion
Easily quantifiable
turning behavior
after unilateral
lesion
Reduced DA levels in the
striatum
Massive loss of
dopamine neurons
No intracellular
aggregates
Works in mice, rats, and
monkeys
Well characterized
Used in dyskinesia
models
Does not pass the
blood–brain- barrier
(needs intracerebral
injection, which
increases variability)
Fast, massive
neurodegeneration
Poor construct validity
MPTP Motor
impairments
Reduced DA levels in the
striatum
Massive loss of
dopamine neurons
With chronic administration,
formation of aggregates
with little LB resemblance
Lipophilic
Systemic administration
Works mainly in mice
Well characterized
Good construct validity
Highly toxic to humans
(dangerous to
administer)
Reduced reliability
Paraquat Motor
impairments
Reduced DA levels
in the striatum
Loss of dopamine
neurons in the SN
No aggregate formation
Systemic administration Toxic for the whole
organism
Not well characterized
Low construct validity
Rotenone Motor
impairments
Reduced DA levels in the
striatum
Massive loss of
dopamine neurons
No aggregate formation
Systemic administration
Works only in rats
Toxic for the
whole organism
Low construct validity
Dj-1 KO, Pink1 KO,
Parkin KO
Little motor
impairment
Only slight DA pathology Good construct validity Slight DA pathology
a-Synuclein wild-type
and A53T, A30P
overexpression
Little motor
impairment
Little DA pathology
Intracellular aggregates
with little LB
resemblance
Good construct validity Slight DA pathology
En1
+ ⁄ )
, En2 KO Some motor
impairment
Reduced DA levels in
the striatum
Massive loss of
dopamine neurons
only in the SN during
the first 3 months
No aggregate formation
Slow neurodegeneration Poor construct validity
Other cell groups
affected in the central
nervous system
No progression of
degeneration after
3 months
Pitx3-aphakia Motor
impairment
Reduced DA levels in
the striatum
Massive loss of
dopamine neurons
in the SN only
Slow neurodegeneration Poor construct validity
Other cell groups
affected in the central
nervous system
MitoPark (DAT-cre,
Tfam lox ⁄ lox)
Motor
impairment
Reduced DA levels
in the striatum
Massive loss of
dopamine neurons,
predominantly in the
SN
Intracellular aggregates
with little LB
resemblance
Adult onset of
symptoms
Slow symptom
development
Good construct validity
Complex breeding
scheme
Animal models of Parkinson’s disease M. Terzioglu and D. Galter
1388 FEBS Journal 275 (2008) 1384–1391 ª 2008 The Authors Journal compilation ª 2008 FEBS
PD patients with severe motor dysfunctions [35]. In
parallel with behavioral changes in all three models,
the degeneration of dopamine nerve terminals in the
striatum and a progressive loss of dopamine neurons
specifically in the SN pars compacta occur. In con-
trast, VTA neurons appear to be more resistant to
the ablation of TFAM and Ret, because the loss of
nerve terminals in the ventral striatum and cell loss in
VTA occur later and are less pronounced than in the
SN pars compacta, similar to the pathological devel-
opment in PD [35,37]. Ablation of Dicer induces a
similar degree of degeneration in dopamine neurons
of the SN pars compacta and the VTA [36]. The
dopamine cell loss results in reduced DA levels in the
corresponding parts of the nigrostriatal system in
middle-aged MitoPark mice together with a marked
increase of DA turnover, as is typically seen in PD
and animal models with DA deficiency [35]. In Ret-
deficient mice, dopamine cell and nerve terminal
losses are less than 40%, even in 24-month-old mice,
and DA levels in the striatum are unaltered. How-
ever, evoked DA release after electrical stimulation
reveals a significant drop in 1-year-old mice and a
further reduction in older mice, consistent with pre-
symptomatic development in PD patients. Dopamine
neuron-specific ablation of TrkB, in contrast, did not
affect the motor behavior and nor did it induce any
PD-like neuropathology [37].
MitoPark mice display an additional pathological
hallmark of PD: affected dopamine neurons contain
cytoplasmic proteinaceous aggregates. However, unlike
LBs, these intracellular inclusions lack a-synuclein
immunoreactivity and they can also form in MitoPark
mice with a null mutation for a-synuclein, which
develop a progressive PD-like phenotype similar to
that seen in MitoPark mice with functional a-synuclein
genes. All other conditional mouse models for PD
described so far lack cytoplasmic inclusion bodies.
Conclusions
Regardless of whether a PD model is based on toxins
or on genome modifications, no single rodent model for
PD created to date reproduces all key symptoms of the
disease: slowly progressing motor disturbances com-
bined with loss of striatal dopamine fibers, and dopami-
ne cell loss in the SN accompanied by LB pathology.
Although toxin-induced models, particularly those
using drugs with a high specificity for dopamine
neurons, induce many of the key features of PD, they
are of lesser value in studies addressing PD etiology,
because only a few PD cases are caused by intoxication
with poisons (see also summary in Table 1). On the
other hand, geneticmodels based on genomic modifica-
tions found in PD patients have good construct validity
but show only rudimentary PD pathology. Those trans-
genic mouse models for a-synuclein exhibiting a more
pronounced PD phenotype have often used heterolo-
gous promoters (PDGFb, Thy1) that induce nonphysi-
ological high expression levels in restricted areas of the
brain. Interestingly, in some studies, geneticmodels are
combined with PD-specific toxins to analyze the effect
of the genetic modification on toxin susceptibility.
The two genetic PD models based on ablation of the
transcription factors En and Pitx3 display many of the
key features of PD. Their drawbacks are low construct
validity, because few studies point to an involvement
of DA system development in PD etiology, and the
fact that many different cell populations in the brain
are affected in En or Pitx3 knockout mice as well as
dopamine neurons, making it difficult to interpret the
findings.
Tissue-specific knockout models for PD based on
cre expression directed by the DAT promoter combine
the advantages of the earlier models: (a) only dopa-
mine neurons are targeted like in toxin models
with mainly DA-specific neurotoxicity (6-OHDA and
Table 1. (Continued).
Model PD symptoms PD pathology Advantages Disadvantages
DAT-cre,
Ret lox ⁄ lox
No motor
impairment
Slight loss of dopamine
neurons in the SN
Slow loss of TH-IR fibers
No reduction in DA levels
Reduced DA release
No aggregate formation
Very slow progression
(preclinical model)
Low construct validity
Complex breeding
scheme
DAT-cre,
Dicer lox ⁄ lox
Motor
impairment
Massive loss of TH-IR fibers
in the striatum
Massive loss of
dopamine neurons in
the SN and VTA
No aggregate formation
Possibility of studying
the role of
post-transcriptional
mechanisms in PD
Fast and early onset of
degeneration
Complex breeding
scheme
Low construct validity
M. Terzioglu and D. Galter Animal models of Parkinson’s disease
FEBS Journal 275 (2008) 1384–1391 ª 2008 The Authors Journal compilation ª 2008 FEBS 1389
MPTP); (b) high reliability, due to complete penetra-
tion and minimal variability; and (c) depending on the
floxed gene, the time course of the development of
neuropathology varies, but in all models there is slow
and progressive neurodegeneration, in contrast to the
acute and violent degeneration seen, for instance, in
the 6-OHDA model. Slow progressive dopamine neu-
ron degeneration has also been achieved through
chronic MPTP administration, albeit associated with
high morbidity due to drug toxicity. The construct
validity of the models also varies with the floxed gene.
To date, genetic studies have not indicated distur-
bances of neurotrophic factors or their receptors as
causes of PD, reducing the construct validity for the
DAT-Ret
lox ⁄ lox
model. Dopamine neuron-specific dele-
tion of Dicer induces decreased expression of the micr-
oRNA miR133b, which reproduces a deficiency found
in midbrain tissue from PD patients and gives this
model good construct validity. There are several indi-
cations that mitochondrial dysfunction plays a promi-
nent role in the etiology and progression of PD, both
from genetic studies (genetic variants of the mtDNA
polymerase PolG have been associated with PD, and
higher loads of mtDNA point mutations or deletions
have recently been found in dopamine neurons from
PD patients) and from toxin studies (dopamine neu-
rons are more susceptible than other neurons to mito-
chondrial toxins such as rotenone or paraquat than
other neurons), conferring good construct validity also
to the MitoPark model.
What are the disadvantages of the tissue-specific
knockout models? There are high costs of animal care,
because of the slow development of the phenotype
(for MitoPark mice, about 5 months, and for DAT-
Ret
lox ⁄ lox
mice, more than 12 months), and because of
complex breeding schemes (only 25% of the offspring
in a litter have the affected genotype).
In conclusion, several recently generated rodent
models of PD reproduce more accurately the time
course of key symptoms and neuropathology develop-
ment seen in patients and are expected to further our
understanding of PD etiologies and help in the devel-
opment of new therapeutic strategies. Nevertheless, is
it important to keep in mind that several other neuro-
nal systems are affected in PD, changes that are not
reproduced in these disease models.
Acknowledgements
This work was supported by The Swedish Research
Council, The Swedish Brain Foundation, Swedish
Brain Power, the Swedish Parkinson Foundation and
Karolinska Institutet Funds.
References
1 Schober A (2004) Classic toxin-induced animal models
of Parkinson’sdisease: 6-OHDA and MPTP. Cell
Tissue Res 318, 215–224.
2 Ungerstedt U (1968) 6-Hydroxy-dopamine induced
degeneration of central monoamine neurons. Eur J
Pharmacol 5, 107–110.
3 Bove J, Prou D, Perier C & Przedborski S (2005)
Toxin-induced models of Parkinson’s disease. NeuroRx
2, 484–494.
4 Emborg ME (2004) Evaluation of animal models of
Parkinson’s disease for neuroprotective strategies.
J Neurosci Methods 139, 121–143.
5 Cenci MA, Whishaw IQ & Schallert T (2002) Animal
models of neurological deficits: how relevant is the rat?
Nat Rev Neurosci 3, 574–579.
6 Lundblad M, Usiello A, Carta M, Hakansson K, Fi-
sone G & Cenci MA (2005) Pharmacological validation
of a mouse model of l-DOPA-induced dyskinesia. Exp
Neurol 194, 66–75.
6a Santini E, Valjent E & Fisone G (2008) Parkinson’s dis-
ease: Levodopa-induced dyskinesia and signal transduc-
tion. FEBS J doi:10.1111/j.1742-4658.2008.06296
7 Langston JW, Ballard P, Tetrud JW & Irwin I (1983)
Chronic Parkinsonism in humans due to a product of
meperidine-analog synthesis. Science 219, 979–980.
8 Sedelis M, Hofele K, Auburger GW, Morgan S, Huston
JP & Schwarting RK (2000) MPTP susceptibility in the
mouse: behavioral, neurochemical, and histological
analysis of gender and strain differences. Behav Genet
30, 171–182.
9 Fornai F, Schluter OM, Lenzi P, Gesi M, Ruffoli R,
Ferrucci M, Lazzeri G, Busceti CL, Pontarelli F, Batta-
glia G et al. (2005) Parkinson-like syndrome induced by
continuous MPTP infusion: convergent roles of the
ubiquitin–proteasome system and alpha-synuclein. Proc
Natl Acad Sci USA 102, 3413–3418.
10 Maries E, Dass B, Collier TJ, Kordower JH & Steece-
Collier K (2003) The role of alpha-synuclein in Parkin-
son’s disease: insights from animal models. Nat Rev
Neurosci 4, 727–738.
11 McCormack AL, Thiruchelvam M, Manning-Bog AB,
Thiffault C, Langston JW, Cory-Slechta DA & Di
Monte DA (2002) Environmental risk factors and
Parkinson’s disease: selective degeneration of nigral
dopaminergic neurons caused by the herbicide para-
quat. Neurobiol Dis 10, 119–127.
12 Ossowska K, Smialowska M, Kuter K, Wieronska J,
Zieba B, Wardas J, Nowak P, Dabrowska J, Bortel A,
Biedka I et al. (2006) Degeneration of dopaminergic
mesocortical neurons and activation of compensatory
processes induced by a long-term paraquat administra-
tion in rats: implications for Parkinson’s disease.
Neuroscience 141, 2155–2165.
Animal models of Parkinson’s disease M. Terzioglu and D. Galter
1390 FEBS Journal 275 (2008) 1384–1391 ª 2008 The Authors Journal compilation ª 2008 FEBS
13 Betarbet R, Canet-Aviles RM, Sherer TB, Mastroberar-
dino PG, McLendon C, Kim JH, Lund S, Na HM,
Taylor G, Bence NF et al. (2006) Intersecting pathways
to neurodegeneration in Parkinson’sdisease: effects of
the pesticide rotenone on DJ-1, alpha-synuclein, and the
ubiquitin–proteasome system. Neurobiol Dis 22, 404–420.
14 McNaught KS, Perl DP, Brownell AL & Olanow CW
(2004) Systemic exposure to proteasome inhibitors
causes a progressive model of Parkinson’s disease. Ann
Neurol 56, 149–162.
15 Kordower JH, Kanaan NM, Chu Y, Suresh BR, Stan-
sell J III, Terpstra BT, Sortwell CE, Steece-Collier K &
Collier TJ (2006) Failure of proteasome inhibitor
administration to provide a model of Parkinson’s dis-
ease in rats and monkeys. Ann Neurol 60, 264–268.
16 Sawada H, Kohno R, Kihara T, Izumi Y, Sakka N, Ibi
M, Nakanishi M, Nakamizo T, Yamakawa K, Shibasa-
ki H et al. (2004) Proteasome mediates dopaminergic
neuronal degeneration, and its inhibition causes alpha-
synuclein inclusions. J Biol Chem 279, 10710–10719.
17 Fleming SM, Fernagut PO & Chesselet MF (2005)
Genetic mouse models of parkinsonism: strengths and
limitations. NeuroRx 2, 495–503.
18 Melrose HL, Lincoln SJ, Tyndall GM & Farrer MJ
(2006) Parkinson’sdisease: a rethink of rodent models.
Exp Brain Res 173, 196–204.
19 Richfield EK, Thiruchelvam MJ, Cory-Slechta DA,
Wuertzer C, Gainetdinov RR, Caron MG, Di Monte
DA & Federoff HJ (2002) Behavioral and neurochemi-
cal effects of wild-type and mutated human alpha-syn-
uclein in transgenic mice. Exp Neurol 175, 35–48.
20 Martin LJ, Pan Y, Price AC, Sterling W, Copeland
NG, Jenkins NA, Price DL & Lee MK (2006) Parkin-
son’s disease alpha-synuclein transgenic mice develop
neuronal mitochondrial degeneration and cell death.
J Neurosci 26, 41–50.
21 Bohlen und HO (2005) Modeling neurodegenerative dis-
eases in vivo review. Neurodegener Dis 2, 313–320.
22 Martins LM, Morrison A, Klupsch K, Fedele V,
Moisoi N, Teismann P, Abuin A, Grau E, Geppert M,
Livi GP et al. (2004) Neuroprotective role of the
Reaper-related serine protease HtrA2 ⁄ Omi revealed by
targeted deletion in mice. Mol Cell Biol 24, 9848–9862.
23 Biskup S & Moore DJ (2006) Detrimental deletions:
mitochondria, aging and Parkinson’s disease. Bioessays
28, 963–967.
24 Sgado P, Alberi L, Gherbassi D, Galasso SL, Ramakers
GM, Alavian KN, Smidt MP, Dyck RH & Simon HH
(2006) Slow progressive degeneration of nigral dopami-
nergic neurons in postnatal Engrailed mutant mice.
Proc Natl Acad Sci USA 103, 15242–15247.
25 Nunes I, Tovmasian LT, Silva RM, Burke RE & Goff
SP (2003) Pitx3 is required for development of substan-
tia nigra dopaminergic neurons. Proc Natl Acad Sci
USA 100, 4245–4250.
26 Ding Y, Restrepo J, Won L, Hwang DY, Kim KS &
Kang UJ (2007) Chronic 3,4-dihydroxyphenylalanine
treatment induces dyskinesia in aphakia mice, a novel
genetic model of Parkinson’s disease. Neurobiol Dis 27,
11–23.
27 Zhuang X, Masson J, Gingrich JA, Rayport S & Hen
R (2005) Targeted gene expression in dopamine and
serotonin neurons of the mouse brain. J Neurosci
Methods 143, 27–32.
28 Backman CM, Malik N, Zhang Y, Shan L, Grinberg
A, Hoffer BJ, Westphal H & Tomac AC (2006) Charac-
terization of a mouse strain expressing Cre recombinase
from the 3¢ untranslated region of the dopamine trans-
porter locus.
Genesis 44, 383–390.
29 Turiault M, Parnaudeau S, Milet A, Parlato R, Rouzeau
JD, Lazar M & Tronche F (2007) Analysis of dopamine
transporter gene expression pattern – generation of
DAT-iCre transgenic mice. FEBS J 274, 3568–3577.
30 Ekstrand MI, Falkenberg M, Rantanen A, Park CB,
Gaspari M, Hultenby K, Rustin P, Gustafsson CM &
Larsson NG (2004) Mitochondrial transcription fac-
tor A regulates mtDNA copy number in mammals.
Hum Mol Genet 13, 935–944.
31 Lindeberg J, Usoskin D, Bengtsson H, Gustafsson A,
Kylberg A, Soderstrom S & Ebendal T (2004) Trans-
genic expression of Cre recombinase from the tyrosine
hydroxylase locus. Genesis 40, 67–73.
32 Gelman DM, Noain D, Avale ME, Otero V, Low MJ
& Rubinstein M (2003) Transgenic mice engineered to
target Cre ⁄ loxP-mediated DNA recombination into
catecholaminergic neurons. Genesis 36, 196–202.
33 Borgkvist A, Puelles E, Carta M, Acampora D, Ang
SL, Wurst W, Goiny M, Fisone G, Simeone A & Usi-
ello A (2006) Altered dopaminergic innervation and
amphetamine response in adult Otx2 conditional
mutant mice. Mol Cell Neurosci 31, 293–302.
34 Baquet ZC, Bickford PC & Jones KR (2005) Brain-
derived neurotrophic factor is required for the establish-
ment of the proper number of dopaminergic neurons in
the substantia nigra pars compacta. J Neurosci 25,
6251–6259.
35 Ekstrand MI, Terzioglu M, Galter D, Zhu S, Hofstetter
C, Lindqvist E, Thams S, Bergstrand A, Hansson FS,
Trifunovic A et al. (2007) Progressive parkinsonism in
mice with respiratory-chain-deficient dopamine neurons.
Proc Natl Acad Sci USA 104, 1325–1330.
36 Kim J, Inoue K, Ishii J, Vanti WB, Voronov SV, Mur-
chison E, Hannon G & Abeliovich A (2007) A Micro-
RNA feedback circuit in midbrain dopamine neurons.
Science 317, 1220–1224.
37 Kramer ER, Aron L, Ramakers GM, Seitz S, Zhuang
X, Beyer K, Smidt MP & Klein R (2007) Absence of
Ret signaling in mice causes progressive and late
degeneration of the nigrostriatal system. PLoS Biol 5,
e39, doi:10.1371/journal.pbio.0050039.
M. Terzioglu and D. Galter Animal models of Parkinson’s disease
FEBS Journal 275 (2008) 1384–1391 ª 2008 The Authors Journal compilation ª 2008 FEBS 1391
. MINIREVIEW
Parkinson’s disease: genetic versus toxin-induced rodent
models
Mu
¨
gen Terzioglu
1
and Dagmar Galter
2
1. tissue-specific
knockout mouse models with older genetic and toxin-
induced animal models (Fig. 1).
Toxin-induced animal models
Early animal models developed for