Abstract
The secondary motor cortex (MOs) plays crucial roles in cognitive and executive processes and has reciprocal connections with numerous cortices in rodents. However, descriptions of the neuronal morphologies and projection patterns of the MOs at the level of a single neuron are lacking, severely hindering the comprehensive understanding of the wiring diagram of the MOs. Herein, we used a Cre-dependent adeno-associated virus (AAV) to fluorescently label ~80 pyramidal neurons nearby or in the MOs and acquired an uninterrupted whole-brain 3D dataset at a voxel resolution of 0.2 × 0.2 × 1 μm with a whole-brain fluorescence imaging system (fMOST). Based on our 3D dataset, we reconstructed the complete morphologies of 36 individual intratelencephalic (IT) neurons nearby or in the MOs and analyzed the projection patterns and projection strengths of these neurons at a single-neuron level based on several parameters, including the projection areas, the total number of branches, the fiber length, and the total number of terminal tips. We obtained a neuron with an axonal length of 318.43 mm, which is by far the longest reported axonal length. Our results show that all individual neurons in the MOs, regardless of whether they are located in layer 2/3 or layer 5, display diverse projection patterns and projection strengths, implying that these neurons might be involved in different brain circuits at different intensities. The results lay a solid foundation for exploring the relationship between neuronal morphologies and behavioral functions of the MOs at the level of a single neuron.
Highlights
The secondary motor cortex (MOs) is located in the anterior lateral area of the brain cortex in rodents
We coadministered a cocktail of two associated virus (AAV) genomes encoding the Cre recombinase and a fluorescent protein whose expression depends on Cre recombinase expression to label neurons in the MOs
We processed the dataset into 100-μm coronal sections and manually cropped the coronal images around the MOs based on the propidium iodide (PI)-stained cytoarchitectonic information (Hezel et al, 2012) and Allen Reference Atlas to obtain a normative anatomy of region position for labeled neurons (Figure 1C)
Summary
The secondary motor cortex (MOs) is located in the anterior lateral area of the brain cortex in rodents. Recent studies have provided evidence for potential roles of the MOs in cognitive and executive processes, such as decision making, Brain-Wide Single IT Neuron Reconstruction goal-directed actions, skill learning, and spatial memory (Sul et al, 2010, 2011; Gremel and Costa, 2013; Cao et al, 2015; Siniscalchi et al, 2016; Yamawaki et al, 2016). Using genetic and anatomical manipulations, many researchers have revealed direct pathways from the MOs to the striatum, which integrates inputs from multiple regions to direct motor control (Wall et al, 2013; Rothwell et al, 2015; Hintiryan et al, 2016; Melzer et al, 2017). Usually only one direct pathway from the MOs to its connected regions has been described in each of these studies, resulting in a lack of knowledge of the overall projections of the MOs and severely hindering the comprehensive understanding of how the MOs is wired to process information at a global scale
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
