Mitochondria in hippocampal presynaptic and postsynaptic compartments differ in size as well as intensity

Abstract

Experimental observations have hinted that, in different compartments of a neuron, mitochondria can be different in their structure, behavior and activity. However, mi-tochondria have never been systematically compared at the subcellular level in neu-rons. Using electron microscopy, we analyzed several thousands of mitochondria in the synapses of rat hippocampal neurons in vitro and in vivo. We focused on examining the intensity and size of mitochondria as these structural features have been correlated to the activity of mitochondria. We compared mitochondria in the presynaptic compartment to those in the postsynaptic compartment. We found that, at least in the synapses of hippocampal neurons, presynaptic mitochondria are smaller in diameter and overall higher in intensity (darker) than postsynaptic mitochondria. Our finding highlights the need for developing technologies that would measure the activity of individual mito-chondria at single-mitochondria resolution in real time.