1. Neuroscience
Download icon

A genuine layer 4 in motor cortex with prototypical synaptic circuit connectivity

  1. Naoki Yamawaki
  2. Katharine Borges
  3. Benjamin A Suter
  4. Kenneth D Harris
  5. Gordon M G Shepherd  Is a corresponding author
  1. Northwestern University, United States
  2. University College London, United Kingdom
Research Article
  • Cited 61
  • Views 4,873
  • Annotations
Cite this article as: eLife 2014;3:e05422 doi: 10.7554/eLife.05422

Abstract

Motor cortex (M1) is classically considered an agranular area, lacking a distinct layer 4 (L4). Here, we tested the idea that M1, despite lacking a cytoarchitecturally visible L4, nevertheless possesses its equivalent in the form of excitatory neurons with input-output circuits like those of L4 neurons in sensory areas. Consistent with this idea, we found that neurons located in a thin laminar zone at the L3/5A border in the forelimb area of mouse M1 have multiple L4-like synaptic connections: excitatory input from thalamus, largely unidirectional excitatory outputs to L2/3 pyramidal neurons, and relatively weak long-range corticocortical inputs and outputs. M1-L4 neurons were electrophysiologically diverse but morphologically uniform, with pyramidal-type dendritic arbors and locally ramifying axons including branches extending into L2/3. Our findings therefore identify pyramidal neurons in M1 with the expected prototypical circuit properties of excitatory L4 neurons, and question the traditional assumption that motor cortex lacks this layer.

Article and author information

Author details

  1. Naoki Yamawaki

    Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, United States
    Competing interests
    The authors declare that no competing interests exist.
  2. Katharine Borges

    Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, United States
    Competing interests
    The authors declare that no competing interests exist.
  3. Benjamin A Suter

    Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, United States
    Competing interests
    The authors declare that no competing interests exist.
  4. Kenneth D Harris

    Institute of Neurology, Department of Neuroscience, Physiology, and Pharmacology, University College London, London, United Kingdom
    Competing interests
    The authors declare that no competing interests exist.
  5. Gordon M G Shepherd

    Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, United States
    For correspondence
    g-shepherd@northwestern.edu
    Competing interests
    The authors declare that no competing interests exist.

Ethics

Animal experimentation: This study was performed in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. All of the animals were handled according to approved institutional animal care and use committee (IACUC) protocols (1248, 1331, 3310) of Northwestern University.

Reviewing Editor

  1. Sacha B Nelson, Brandeis University, United States

Publication history

  1. Received: October 31, 2014
  2. Accepted: December 18, 2014
  3. Accepted Manuscript published: December 19, 2014 (version 1)
  4. Version of Record published: January 14, 2015 (version 2)

Copyright

© 2014, Yamawaki et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

Metrics

  • 4,873
    Page views
  • 745
    Downloads
  • 61
    Citations

Article citation count generated by polling the highest count across the following sources: Scopus, Crossref, PubMed Central.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Download citations (links to download the citations from this article in formats compatible with various reference manager tools)

Open citations (links to open the citations from this article in various online reference manager services)

Further reading

    1. Neuroscience
    2. Structural Biology and Molecular Biophysics
    Johannes Elferich et al.
    Research Article Updated

    Mechanosensory transduction (MT), the conversion of mechanical stimuli into electrical signals, underpins hearing and balance and is carried out within hair cells in the inner ear. Hair cells harbor actin-filled stereocilia, arranged in rows of descending heights, where the tips of stereocilia are connected to their taller neighbors by a filament composed of protocadherin 15 (PCDH15) and cadherin 23 (CDH23), deemed the ‘tip link.’ Tension exerted on the tip link opens an ion channel at the tip of the shorter stereocilia, thus converting mechanical force into an electrical signal. While biochemical and structural studies have provided insights into the molecular composition and structure of isolated portions of the tip link, the architecture, location, and conformational states of intact tip links, on stereocilia, remains unknown. Here, we report in situ cryo-electron microscopy imaging of the tip link in mouse stereocilia. We observe individual PCDH15 molecules at the tip and shaft of stereocilia and determine their stoichiometry, conformational heterogeneity, and their complexes with other filamentous proteins, perhaps including CDH23. The PCDH15 complexes occur in clusters, frequently with more than one copy of PCDH15 at the tip of stereocilia, suggesting that tip links might consist of more than one copy of PCDH15 complexes and, by extension, might include multiple MT complexes.

    1. Neuroscience
    Thomas Akam et al.
    Research Article

    Laboratory behavioural tasks are an essential research tool. As questions asked of behaviour and brain activity become more sophisticated, the ability to specify and run richly structured tasks becomes more important. An increasing focus on reproducibility also necessitates accurate communication of task logic to other researchers. To these ends, we developed pyControl, a system of open-source hardware and software for controlling behavioural experiments comprising a simple yet flexible Python-based syntax for specifying tasks as extended state machines, hardware modules for building behavioural setups, and a graphical user interface designed for efficiently running high-throughput experiments on many setups in parallel, all with extensive online documentation. These tools make it quicker, easier, and cheaper to implement rich behavioural tasks at scale. As important, pyControl facilitates communication and reproducibility of behavioural experiments through a highly readable task definition syntax and self-documenting features. Here, we outline the system’s design and rationale, present validation experiments characterising system performance, and demonstrate example applications in freely moving and head-fixed mouse behaviour.