To be or not to be pink(1): contradictory findings in an animal model for Parkinson’s disease

The PTEN-induced putative kinase 1 knockout rat (Pink1) is marketed as an established model for Parkinson's disease, characterized by development of motor deficits and progressive degeneration of half the dopaminergic neurons in the substantia nigra by 8 months of age. In this study, we address our concerns about the reproducibility of the Pink1 rat model. We evaluated behavioural function, number of substantia nigra dopaminergic neurons and extracellular striatal dopamine concentrations by microdialysis. Strikingly, we and others failed to observe any loss of dopaminergic neurons in 8-month-old male Pink1 rats. To understand this variability, we compared key experimental parameters from the different studies and provide explanations for contradictory findings. Although Pink1 rats developed behavioural deficits, these could not be attributed to nigrostriatal degeneration as there was no loss of dopaminergic neurons in the substantia nigra and no changes in neurotransmitter levels in the striatum. To maximize the benefit of Parkinson's disease research and limit the unnecessary use of laboratory animals, it is essential that the research community is aware of the limits of this animal model. Additional research is needed to identify reasons for inconsistency between Pink1 rat colonies and why degeneration in the substantia nigra is not consistent.