A Quantitative Study on the Distribution of Mitochondria in the Neuropil of the Juvenile Rat Somatosensory Cortex

Abstract

Mitochondria play a key role in energy production and calcium buffering, among many other functions. They provide most of the energy required by neurons, and they are transported along axons and dendrites to the regions of higher energy demands. We have used focused ion beam milling and scanning electron microscopy (FIB/SEM) to obtain stacks of serial sections from the somatosensory cortex of the juvenile rat. We have estimated the volume fraction occupied by mitochondria and their distribution between dendritic, axonal, and nonsynaptic processes. The volume fraction of mitochondria increased from layer I (4.59%) to reach its maximum in layer IV (7.74%) and decreased to its minimum in layer VI (4.03%). On average, 44% of mitochondrial volume was located in dendrites, 15% in axons and 41% in nonsynaptic elements. Given that dendrites, axons, and nonsynaptic elements occupied 38%, 23%, and 39% of the neuropil, respectively, it can be concluded that dendrites are proportionally richer in mitochondria with respect to axons, supporting the notion that most energy consumption takes place at the postsynaptic side. We also found a positive correlation between the volume fraction of mitochondria located in neuronal processes and the density of synapses.

Area-Specific Synapse Structure in Branched Posterior Nucleus Axons Reveals a New Level of Complexity in Thalamocortical Networks

“…6aЈ,bЈ), the large majority (70%) of postsynaptic spines in MC-L4/3 displayed this structural sub-element responsible for spine motility but also stabilization of the presynaptic and postsynaptic apposition zone during synaptic transmission. Mitochondria were found inside 2 of the 68 spines postsynaptic to S1-L1 Po boutons, despite the exceedingly rare occurrence of spine mitochondria in rodent somatosensory cortex (Santuy et al, 2018).…”

Lipopolysaccharide induces human olfactory ensheathing glial apoptosis by promoting mitochondrial dysfunction and activating the JNK-Bnip3-Bax pathway

“…Cellular viability and function are highly regulated by mitochondria, that act in response to stress stimuli, including oxidative stress, the inflammation response, and ischemia in the nervous system (Santuy et al 2018;Tao-Cheng 2018). There are three general mechanisms by which mitochondria affect cell viability and death: (i) ATP depletion , (ii) mediation of cellular oxidative stress (Zhou et al 2018e), and (iii) release of proapoptotic factors that initiate caspase-dependent (Zhou et al 2018d) and/or caspase-independent death pathways (Zhu et al 2018b).…”

Area-specific synapse structure in branched axons reveals a subcellular level of complexity in thalamocortical networks

“…4a’-4b’), while the large majority (70%) of postsynaptic spines in MC-L4/3 displayed this structural subelement responsible for spine motility but also stabilization of the pre-and postsynaptic apposition zone during synaptic transmission. Mitochondria were found inside 2 of the 68 dendritic spines postsynaptic to S1-L1 Po boutons, despite the exceedingly rare occurrence of spine mitochondria in rodent somatosensory cortex 30 .…”