Here we investigated the stability and transport of axonal mitochondria using live-cell
imaging of cultured mouse hippocampal neurons. We first characterised the long-term stability of stationary find more mitochondria. At a given moment, about 10% of the mitochondria were in a state of transport and the remaining 90% were stationary. Among these stationary mitochondria, 40% of them remained in the same position over several days. The rest of the mitochondria transited to mobile state stochastically and this process could be detected and quantitatively analysed by time-lapse imaging with intervals of 30 min. The stability of axonal mitochondria increased from 2 to 3 weeks in culture, was decreased by tetrodotoxin treatment, and was higher near synapses. Stationary mitochondria should be generated by pause of moving mitochondria and subsequent stabilisation. Therefore, we next analysed pause events of moving mitochondria by repetitive imaging at 0.3 Hz. We found that the probability of transient pause increased with selleck screening library field stimulation, decreased with tetrodotoxin treatment, and was higher near synapses. Finally, by combining parameters obtained from time-lapse imaging with different time scales, we could
estimate transition rates between different mitochondrial states. The analyses suggested specific developmental regulation in the probability of paused mitochondria to transit into stationary state. These findings indicate that multiple mitochondrial behaviors, especially those regulated by neuronal activity and synapse location, determine their distribution in the axon. The elaborate structure of the neuron requires a regulatory mechanism to allocate a sufficient
number of organelles to its subcellular compartments, such as the soma, neurites and synapses. Proper distribution of the mitochondria is critical for multiple neuronal functions including energy production, calcium homeostasis, apoptosis, synaptic transmission and plasticity (Chang & Reynolds, 2006; MacAskill & Kittler, 2010). Impaired mitochondrial distribution PtdIns(3,4)P2 has been linked to neurodegenerative disorders (Chen & Chan, 2009). Recent studies have identified a number of signaling pathways and key molecules that regulate mitochondrial trafficking and retention in the axon (Goldstein et al., 2008; Sheng & Cai, 2012). However, the underlying mechanism for maintaining proper axonal mitochondrial distribution is largely unknown. Mitochondrial distribution is thought to be correlated with a spatial pattern of metabolic demands. Axonal mitochondria are enriched at presynaptic sites, nodes of Ranvier and the axon initial segments (Hollenbeck & Saxton, 2005). The recycling of synaptic vesicles (SVs) requires energy derived from ATP hydrolysis (Harris et al., 2012) and mitochondria near the presynaptic sites are thought to help this process (Kang et al., 2008; Ma et al., 2009).