Reconstruction of 1,000 projection neurons reveals new cell types and organization of long-range connectivity in the mouse brain

Abstract

Neuronal cell types are the nodes of neural circuits that determine the flow of information within the brain. Neuronal morphology, especially the shape of the axonal arbor, provides an essential descriptor of cell type and reveals how individual neurons route their output across the brain. Despite the importance of morphology, few projection neurons in the mouse brain have been reconstructed in their entirety. Here we present a robust and efficient platform for imaging and reconstructing complete neuronal morphologies, including axonal arbors that span substantial portions of the brain. We used this platform to reconstruct more than 1,000 projection neurons in the motor cortex, thalamus, subiculum, and hypothalamus. Together, the reconstructed neurons comprise more than 75 meters of axonal length and are available in a searchable online database. Axonal shapes revealed previously unknown subtypes of projection neurons and suggest organizational principles of long-range connectivity.

Differential Striatal Axonal Arborizations of the Intratelencephalic and Pyramidal-Tract Neurons: Analysis of the Data in the MouseLight Database

“…Counting the number of intra-striatal axonal end-points, we have shown that there exists a large variety in the number of end-points across neurons in both neuron types. This variety seems in line with the suggested heterogeneity and existence of sub-types within each of PT and IT populations (Economo et al, 2018;Winnubst et al, 2019). More specifically, we found that, among MOs IT neurons, layer 5 neurons have a larger number of ipsilateral end-points than layer 2/3 neurons, and also bilateral-Str-targeting layer 2/3 neurons have a larger number of ipsilateral endpoints than contra-Str-non-targeting layer 2/3 neurons.…”

“…The MouseLight project has now developed the MouseLight database (http://mlneuronbrowser.janelia.org/), which contains reconstructed morphology data of about 1000 neurons and is open to public Winnubst et al, 2019). The article introducing this database performed several analyses including those for IT and PT neurons, which revealed great diversity of IT neuronal projection patterns and also PT neuronal subtypes projecting to 4 distinct targets.…”

Sex and pubertal status influence dendritic spine density onto frontal corticostriatal projection neurons

“…GFP+ cSTR neurons localized to both more superficial and deep coordinates compared to Tdtomato+ CPn neurons, but these two populations significantly overlapped 300-550 µM from the midline ( Figure 2C), consistent with previous studies (Morishima and Kawaguchi, 2006;Anderson et al, 2010;Dembrow et al, 2010;Kiritani et al, 2012;Li et al, 2015). Finally, in a separate experiment, we co-injected PL and DMS and observed that a subset of neurons in contralateral PL were co-labeled ( Figure S1), consistent with data showing that single corticostriatal neurons project to both contralateral cortex and contralateral striatum (Winnubst et al, 2019).…”

“…While we focused on cSTR neurons, we and others have shown that cSTR neurons overlap with cortico-cortical ITtype projection neurons (Sohur et al, 2014;Winnubst et al, 2019), suggesting that our results may apply more broadly to IT-type neurons within mPFC or broader frontal cortices. On the other hand, even within mPFC significant heterogeneity has been reported among IT-type neurons (Morishima and Kawaguchi, 2006;Anastasiades et al, 2019).…”

Mapping Mesoscale Axonal Projections in the Mouse Brain Using A 3D Convolutional Network

“…Recent application of deep convolutional neural networks (DCNNs) and Markov random fields to biomedical imaging have made excellent progress at segmenting grayscale CT and MRI volumes for medical applications (Alegro et al, 2017;Dong et al, 2018;Frasconi et al, 2014;Mathew et al, 2015;Thierbach et al, 2018). Other fluorescent imaging strategies including light-sheet, fMOST, and serial two-photon tomography have been combined with software like TeraVR, Vaa3D, Ilastik, and NeuroGPS-Tree to trace or otherwise reconstruct individual neurons (Peng et al, 2010;Quan et al, 2016;Wang et al, 2019;Winnubst et al, 2019;Zhou et al, 2018).…”