Mitochondria and release at hippocampal synapses

Abstract

Mitochondria are present in some, but not all presynaptic terminals in the hippocampus. Mitochondria are capable of sequestering and storing large amounts of calcium, but it is unclear whether they influence release probability at these synapses. Using FM dye imaging techniques and confocal microscopy, we have examined the relationship between mitochondrial presence/absence and presynaptic vesicle release from rat hippocampal neurones in primary dissociated culture at room temperature. Following staining with the mitochondrial dye mitotracker green, we were able to resolve putative individual mitochondria associated with neuronal processes. The majority of mitochondria were positionally stable, although some exhibited periods of rapid motility (up to 0.4 microm/s) interspersed with periods of immobility. Co-staining with mitotracker green and the synaptic vesicle dye FM 4-64 indicated that 180 of 506 (36%) synapses were devoid of mitochondria. A comparison of vesicular release in response to stimulation at 1 Hz and at 10 Hz revealed no differences in release properties between synapses with and without mitochondria.

Glycolytic Enzymes Localize to Synapses under Energy Stress to Support Synaptic Function

“…How are changing energy demands at presynaptic sites dynamically met? Mitochondrial localization is an important mechanism for meeting local energy demands at the synapse, yet many presynaptic terminals, while rich in ATP, lack mitochondria (Chavan et al, 2015; Waters and Smith, 2003; Xu-Friedman et al, 2001). The capacity of the glycolytic machinery to produce ATP molecules at a faster rate than oxidative phosphorylation, and to dynamically assemble into metabolic compartments based on energy needs, might fill demands for changing levels of energy consumption at intensely active synapses, at synapses that lack mitochondria, or at synapses in which mitochondria has been damaged.…”

Synaptic Vesicle Exocytosis in Hippocampal Synaptosomes Correlates Directly with Total Mitochondrial Volume

“…Mitochondria constitute part of the presynaptic structure, yet not all synapses have mitochondria (Shepherd and Harris, 1998; Waters and Smith, 2003). It is quite possible that those mitochondria-free presynaptic terminals are inactive or temporarily without mitochondria, since mitochondria are known to relocate into and out of the synapse depending on its activity (Hollenbeck, 1996; Rintoul et al, 2003; Kang JS et al, 2008).…”

“…It is quite possible that those mitochondria-free presynaptic terminals are inactive or temporarily without mitochondria, since mitochondria are known to relocate into and out of the synapse depending on its activity (Hollenbeck, 1996; Rintoul et al, 2003; Kang JS et al, 2008). Experiments in cultured hippocampal neurons have shown that presynaptic terminals without mitochondria can be readily stained and distained with synaptic FM dyes for a prolonged time (Waters and Smith, 2003). This suggests that mitochondria-free terminals are likely capable of synaptic release.…”

The Role of Mitochondrially Derived ATP in Synaptic Vesicle Recycling

“…Importantly, we identified mitochondria by their co-expression of mito-mTagBFP, and all mito-mTagBFP-positive structures tested (30 out of 30) were immunopositive for the mitochondrial marker Tom20. This approach ensured that we considered only mitochondria within transfected neurons, which was essential for definitively determining that mitochondria were present within a given axon (43). To prevent false-negatives (i.e.…”