Alterations of Dopaminergic Synapse and Mitochondrial Structure by Parkinson’s Disease Toxins

Immunostaining with anti-tyrosine hydroxylase (TH) revealed that a small subset (~2.5%) of primary neurons (from rat embryonic E13-14 midbrains) is dopaminergic (DA). In this study, we tested whether DA neurons in culture are selectively degenerated by well-known PD toxins such as rotenone (5-100nM) and MPP+ (10μM). Both toxins significantly decreased the number of DA neurons and neurite length after 24-hour incubation. Interestingly, our results showed that mitochondria in DA neurites were also degenerated by these toxins. Since mitochondria play a critical role in proper synapse signaling and PD is directly linked to mitochondria dysfunction, we wanted to study altered properties of DA synaptic mitochondria in the early stage of PD. With triple staining of antiTH, a fixable synaptic marker FM1-43fx and a mitochondrial dye MitoTracker Orange (MTO), we identified DA synaptic mitochondria. Our data demonstrated that DA synaptic mitochondria are degenerated by MPP+ and rotenone, and that this effect likely occurs prior to the degeneration of DA cell bodies. Therefore, our cellular PD model can be used to study presymptomatic alterations underlying development of PD pathology. Our study will help to understand mechanisms underlying selective loss of DA neurons, which is possibly due to the degeneration of DA synaptic mitochondria.