Presynaptic boutons that contain mitochondria are more stable

Abstract

10Addition and removal of presynaptic terminals reconfigures neuronal circuits of the 11 mammalian neocortex, but little is known about how this presynaptic structural plasticity is 12 controlled. Since mitochondria can regulate presynaptic function, we investigated whether the 13 Figure 1 -Tracking bouton plasticity and mitochondrial positioning in axons of motor cortex 1 neurons. (A) AAV expressing cytosolic EGFP and a mitochondrial targeting sequence (MTS) 2 conjugated to TagRFP was injected in to M1/M2 and a glass cranial window was implanted over 3 S1. (B) A series of coronal brain slices showing viral injection site across the M1/M2 border (inset, 4 top) and the axonal projection site at S1 under the cranial window (inset, bottom). Only the 5 ipsilateral half of brain sections are shown. Pr = parietal cortex, D = dorsal, L = lateral, A = anterior. 6 (C) Cropped 2P images from in vivo imaging show axons with high EPB (EPB-rich) or TB (TB-rich) 7 densities. (D) (top) Imaging timeline for tracking bouton structural plasticity (loss and gain). Viral 8 injection and cranial window implantation were performed 24 days prior to initial 2P imaging. 9 Arrowheads indicate imaging timepoints. (bottom) Structure and mitochondrial localisation in a 10 single cropped axon over 35 days imaged using in vivo 2P microscopy. Some boutons are labelled 11 with arrowheads to show examples of stable (yellow), lost (red) or gained (green) boutons. (E) 12Gaussian mixture modelling (GMM) was used to determine two potential populations (EPB-rich 13and TB-rich) that result in the observed sample distribution of EPB and TB densities for each 14 axonal segment (mean across time). Axons that had posterior probabilities below 70% were not 15 assigned to a group (circled; see Methods). Contour lines indicate the slope of the GMM 16 distribution. 17 18 A substantial projection from the motor cortex is made up of long-range axons that ramify in 19

Presynaptic Boutons That Contain Mitochondria Are More Stable

“…We thank Lilly UK for the gift of the AAV used in this study. This manuscript has been released as a preprint in BioRxiv (Lees et al, 2019).…”

Computation of the mitochondrial age distribution along the axon length

“…Some recent research (Smit-Rigter et al 2016; Lees et al 2020) suggest that in vivo mitochondria may stay in the stationary state for longer periods of time than in vitro . The model parameters can be adjusted to characterize transitions between anterograde, retrograde, and stationary states.…”

Ultrastructure of giant thalamic terminals in the auditory cortex

“…High mitochondrial proportions also facilitate synaptic transmission through rapid vesicle turnover including their mobilization from reserve pools upon repetitive/intense stimulation (Vos, Lauwers, & Verstreken, ) and through effective buffering and sequestering of calcium (Billups & Forsythe, ; Devine & Kittler, ). High mitochondrial proportions were present in MGm boutons of all sizes indicating that even smaller boutons may have a higher impact on postsynapses and are more stable (Lees, Johnson, & Ashby, ) than other cortical boutons of comparable size. Other studies have shown that layer IV thalamocortical boutons are also relatively rich in mitochondria (mitochondrial fraction: 0.21; Kharazia & Weinberg, ) and were, in contrast to layer II boutons, considered as “drivers” (Viaene, Petrof, & Sherman, ).…”