Dose-dependent striatal changes in dopaminergic terminals and alpha-synuclein reactivity in a porcine model of progressive Parkinson’s disease

Parkinson disease (PD) is a common neurodegenerative disorder, resulting from a progressive dopaminergic neuron loss in the substantia nigra (SN). Alpha-synuclein positive neuronal inclusion bodies and progressive loss of dopaminergic striatal terminals is also well described in PD. Attempts to discover effective compounds halting PD progression have so far failed in clinical trials, perhaps because current animal models do not imitate the neuropathological progression of PD well enough. We recently established a progressive large animal PD model in Göttingen minipigs based on chronic infusion of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and here present the neuropatholigical findings.Sixteen Göttingen minipigs were used in the study. Twelve were implanted subcutaneously with infusion pumps for continuous intramuscular chronic MPTP delivery for 11 weeks (4-18 mg MPTP/day, n=12) or acute MPTP intoxication for 11 days (24 mg MPTP/day, n=2) and 9 weeks of recovery. Four pigs served as normal controls. Animals were euthanized with intracardial pentobarbital injections, transcardially perfused with 5 L 4% paraformaldehyde and the brains removed. The striatae and brain stems including the SN were paraffin embedded and immunohistochemically stained for tyrosine hydroxylase (TH) and alpha-synuclein.Stereological examination of the SN showed progressive nigral neuron loss with increased MPTP dosages. Occasional neuronal staining confined to the cytoplasm and cell membrane was observed in the SN but no neuronal inclusions. In the striatum, alpha-synuclein positive staining occurred in the acutely intoxicated animals and increased in intensity with increasing doses of chronic MPTP infusion. The 12 and 18 mg animals showed swollen TH-positive terminals in the striatum with a reduction in the number of fibers and terminals in the 18 mg group. Some sense of direction of fibers was preserved in these groups, but this was completely lost in the 24 mg animals, which additionally presented with smaller, fewer terminals. In the locus coeruleus, the 18 mg animals showed decreased TH fiber staining and increased intensity in the neuronal staining.We conclude that chronic infusion of MPTP in this large animal PD model shows neuropathological changes resembling those seen in the clinical state of PD. Animals receiving 18 mg MPTP/day for 11 weeks thus showed a decrease in nigral TH-positive neuron number and striatal terminals, intense striatal alpha-synuclein staining and pathology in the locus coeruleus. Use of this model thus holds promise for future neuroprotective studies in PD.