Does anyone know or could recommend papers which looked at how many presynaptic terminals are occupied by at least one mitochondrion? I'm also looking for papers which had a look at different brain areas and if possible not only cultured neurons, but in vivo data.
Many papers describe differences in synaptic vesicle release, synaptic strength, etc due to the presence or absence of mitochondria, but none states how big the fractions of occupied/ unoccupied synapses actually are.
Thanks in advance for sharing your knowledge with me!
In the vertebrate retina synapses and cell bodies are separated in distinct layers. Some them are avascular, among which the chicken retina. In this avascular retina, mitochondria are very few in Mueller cells they are just at the border between cell bodies of neurons and synapses (ganglion cell and innerplexiform lyers) and the others are present in the outer retina close to the inner receptor segments and pigment epithelium.bellow the pigment epithelium there are the vascular plexus. This does not suggest a close relationship between mitochondria and synaptic terminals but between mitochondria and oxigen consumption
I don't think there is a fixed #, as mitochondria get shuttled back- and forwards depending on needs. These needs could be ranging from growth to signaling. In general, highly active neurons (such as Motos), have higher mito densities in axons and neurites.
would be interesting to see timelaps in response to drugs, etc.
I don´t know, but in this paper they quantified mitochondrial biomass in neurons:
http://jcb.rupress.org/content/184/5/707.short
Thanks for your answers! Concerning Adrian: yes it's definitly not a fixed number and for sure activity dependend. But the fraction of mobile mitochondria is rather low (10-20%), compared to the stationary fraction (80-90%). So I thought that one could (at least roughly) calculate the % of occupied presynaptic terminals. In a paper from 1998 Shepherd and Harris stated that less than 50% of presynaptic terminals in the hippocampus have mitochondria...but thats the only number I could find so far.
Hi Jil
It's an interesting question - likely to be different depending on brain region and neuron/synapse subtype. Link to the paper below shows differences in mitochondria # between climbing fiber and parallel fiber synapses:
http://www.jneurosci.org/content/18/20/8300.long
Thanks Matthew! The paper confirmes Shepherd & Harris finding that less than 50% of presynapses contain mitochondria. Would be indeed really interesting to compare that with differen brain areas/ neuron types.
The answers are really helpful. What I want to know further is that; is the situation same in nocturnal mammals?
Although it does not directly answer this question, the following review may be helpful (if you have not already come across it):
Devine MJ & Kittler JT, 2018 (Mitochondria at the neuronal presynapse in health & disease).