The findings by Kirik et al. are a breakthrough because they provide a human-like model of Parkinson's disease and make the earlier findings in rats (Kirik et al., 2002; Lo Bianco et al., 2002; Klein et al., 2002) even more relevant for Parkinson's disease. The authors note the involvement of α-synuclein and oxidative stress. To pursue this, and probably in rats for feasibility, subjects will be monitored for markers of oxidative stress and mitochondrial function after α-synuclein gene transfer. Alternatively, diets either rich or deficient in antioxidants can be tested for their effects on the α-synuclein vector-induced disease.

View all comments by Ronald Klein

"A model, a model...my kingdom for a model!"

At last, a model that appears to recapitulate not only some of the motor features of Parkinson's disease, but also the pathology. Even as we have come to understand the importance of α-synuclein in the pathophysiology of PD and other Lewy body disorders, the field has been hampered by the paucity of animal models that recapitulate the major pathology, particularly in regard to the substantia nigra. Kirik and colleagues should be applauded for at last contributing a primate model that is likely to advance the field. In addition, this technology can potentially be applied to rodent models that will substantially shorten the study time to test hypotheses regarding oxidative stress, free radicals, and mitochondrial function and the development of Parkinson's disease.—James Galvin, Washington University School of Medicine, St. Louis, Missouri.

View all comments by James Galvin

I liked the article on unilateral α-synuclein expression in the marmoset monkey as a model of Parkinson’s. The biggest problem with the model is that it has minimal behavioral effects compared to the MPTP model. With MPTP injected unilaterally in the internal carotid artery, the opposite side of the body becomes strongly Parkinsonian with slow movements of the arm and leg on that side. When animals are given apomorphine or amphetamine, they circle intensely—after amphetamine, in a direction towards the side of the lesion, and with apomorphine, in a direction opposite to the side of the lesion. For therapeutic interventions such as neurotransplantation, a robust behavioral component is essential. It is likely that dopamine depletion on the lesioned side was not severe enough to see strongly lateralized behavioral effects. Dopamine concentrations in the striatum and substantia nigra are not reported, but cell loss was 30 to 60 percent. In rats, dopamine concentrations in striatum have to be reduced by 95 percent to see drug-induced circling.

The primary value of the marmoset...  Read more

I liked the article on unilateral α-synuclein expression in the marmoset monkey as a model of Parkinson’s. The biggest problem with the model is that it has minimal behavioral effects compared to the MPTP model. With MPTP injected unilaterally in the internal carotid artery, the opposite side of the body becomes strongly Parkinsonian with slow movements of the arm and leg on that side. When animals are given apomorphine or amphetamine, they circle intensely—after amphetamine, in a direction towards the side of the lesion, and with apomorphine, in a direction opposite to the side of the lesion. For therapeutic interventions such as neurotransplantation, a robust behavioral component is essential. It is likely that dopamine depletion on the lesioned side was not severe enough to see strongly lateralized behavioral effects. Dopamine concentrations in the striatum and substantia nigra are not reported, but cell loss was 30 to 60 percent. In rats, dopamine concentrations in striatum have to be reduced by 95 percent to see drug-induced circling.

The primary value of the marmoset model is histologic. It shows that overexpression of α-synuclein can cause protein deposits in primate dopamine neurons and subsequent death of cells. We have shown this result in tissue culture experiments with rat and human embryonic dopamine neurons (Zhou et al., 2000 and Zhou et al., 2002), and a similar result was published in rats in 2002. The monkey outcome published by Kirik, et al. is important because it shows that adult primate dopamine neurons can suffer the same fate in the intact animal.

View all comments by Curt Freed