Spontaneous Partial Recovery of Striatal Dopaminergic Uptake Despite Nigral Cell Loss in Asymptomatic MPTP-Lesioned Minipigs

Abstract

\n The gold standard animal model of Parkinson’s disease is the non-human primate rendered parkinsonian with the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxin. Low availability, ethical issues, and primate-specific biohazards make alternative large animal models necessary. Here, we investigate the temporal evolution of presynaptic dopaminergic function after MPTP in another large animal model, the Göttingen minipig. We subcutaneously injected seven sedated minipigs with 1–2 mg/kg of MPTP, and two minipigs with saline, three times a week over 4 weeks. We monitored behavioral deficits using a validated motor scale and a Gait4Dog® walking mat. Minipig brains were imaged with (+)-⍺-[11C]-dihydrotetrabenazine ([11C]-DTBZ) and [18F]-fluorodopa ([18F]-FDOPA) PET at baseline and 1, 3, 9 and 12 months after the final MPTP injection. Immunohistochemical tyrosine hydroxylase (TH) staining was used to assay nigral TH\u2009+\u2009area loss post-mortem. The minipigs showed only mild bradykinesia and impaired coordination at early timepoints after MPTP. PET revealed decreases of striatal [11C]-DTBZ and [18F]-FDOPA uptake post-MPTP with a partial spontaneous recovery of [18F]-FDOPA after 9 months. Postmortem histological analysis showed a loss of 71% TH-immunopositive area in the substantia nigra. When testing the efficacy of putative neuroprotective agents, partial spontaneous recovery of dopamine terminal function must be taken into account in the MPTP minipig model of parkinsonism.