Characterising a new sheep model of Parkinson's disease using unilateral
intracerebral injection of 6-hydroxydopamine into the substantia nigra
Abstract
New therapeutic agents developed for treating neurological disorders are
often tested successfully on rodents, and yet 80–90% of these prove
ineffective when transitioning to clinical application. Testing in an
appropriate large-animal model should improve translational success and
is frequently expected by regulatory bodies. In this project, we aimed
to establish a novel sheep model of Parkinson’s disease as a
large-brained experimental model for translational research. Our
objective was to create a sheep model of Parkinson’s disease by
unilaterally infusing the neurotoxin 6-hydroxydopamine into the
substantia nigra pars compacta. This approach, previously used to induce
parkinsonism in rat and non-human primate models, causes dopaminergic
imbalance and induces rotational behaviour in quadrupeds challenged with
dopaminergic receptor agonists. In the present sheep study, the mixed
dopamine receptor agonist apomorphine, 0.25 mg/kg, and dopamine D2
agonist ropinirole, 0.16 mg/kg, were used to induce rotational behaviour
and confirm dopamine depletion. Behavioural signs were then measured and
characterised in the field using automated movement tracking with
simultaneous video recordings. Post-mortem, the extent of the
6-hydroxydopamine lesions were evaluated through tyrosine hydroxylase
immunohistochemistry and quantifying levels of catecholamines (dopamine,
3,4-dihydroxyphenylacetic acid, and homovanilic acid) quantified using
high-performance liquid chromatography. Our new sheep model of
Parkinson’s disease using 6-hydroxydopamine is safe and offers a number
of regulatory, ethical, and financial advantages over non-human primate
1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine models. It provides a
platform to evaluate novel anti-parkinsonian agents and medical devices
with the promise of greater success for translation into clinical
application than has been achieved using small animal models.