Connon I. Thomas (1), Melissa A. Ryan (3), Naomi Kamasawa (1), Benjamin Scholl (2)
bioRxiv. (14 July 2023). DOI: https://doi.org/10.1101/2023.07.14.549063

Abstract

Postsynaptic mitochondria are critical to the development, plasticity, and maintenance of synaptic inputs. However, their relationship to synaptic structure and functional activity is unknown. We examined a correlative dataset from ferret visual cortex with in vivo two-photon calcium imaging of dendritic spines during visual stimulation and electron microscopy (EM) reconstructions of spine ultrastructure, investigating mitochondrial abundance near functionally- and structurally-characterized spines. Surprisingly, we found no correlation to structural measures of synaptic strength. Instead, we found that mitochondria are positioned near spines with orientation preferences that are dissimilar to the somatic preference. Additionally, we found that mitochondria are positioned near groups of spines with heterogeneous orientation preferences. For a subset of spines with a mitochondrion in the head or neck, synapses were larger and exhibited greater selectivity to visual stimuli than those without a mitochondrion. Our data suggest mitochondria are not necessarily positioned to support the energy needs of strong spines, but rather support the structurally and functionally diverse inputs innervating the basal dendrites of cortical neurons

How Our Software Was Used

A small set of manual mitochondria segmentations were used to train a U-Net++ deep model for the segmentation of all mitochondria within target dendrites. Dendrite segmentations were then used as a mask to apply the trained mitochondria network. Mitochondria morphology was measured using tools within Dragonfly.

Author Affiliation

(1) Electron Microscopy Core Facility, Max Planck Florida Institute for Neuroscience, 1 Max Planck Way, Jupiter, FL 33458, USA
(2) Department of Neuroscience, Perelman School of Medicine at the University ofPennsylvania, 415 Curie Blvd, Philadelphia, PA, 19104, USA
(3) Department of Neuroscience, Baylor College of Medicine, Houston, TX, 77030, USA