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J Physiol. 2016 Apr 1;594(7):1891-910. doi: 10.1113/JP271891. Epub 2016 Mar 11.

Primary visual cortex shows laminar-specific and balanced circuit organization of excitatory and inhibitory synaptic connectivity.

Xu X1,2, Olivas ND1,3, Ikrar T1, Peng T4,5, Holmes TC6, Nie Q2,4,5, Shi Y1.

Author information

1
Department of Anatomy and Neurobiology, School of Medicine.
2
Department of Biomedical Engineering.
3
Present address: Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA.
4
Department of Mathematics.
5
Center for Complex Biological Systems.
6
Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, CA, USA.

Abstract

KEY POINTS:

Using functional mapping assays, we conducted a quantitative assessment of both excitatory and inhibitory synaptic laminar connections to excitatory neurons in layers 2/3-6 of the mouse visual cortex (V1). Laminar-specific synaptic wiring diagrams of excitatory neurons were constructed on the basis of circuit mapping. The present study reveals that that excitatory and inhibitory synaptic connectivity is spatially balanced across excitatory neuronal networks in V1.

ABSTRACT:

In the mammalian neocortex, excitatory neurons provide excitation in both columnar and laminar dimensions, which is modulated further by inhibitory neurons. However, our understanding of intracortical excitatory and inhibitory synaptic inputs in relation to principal excitatory neurons remains incomplete, and it is unclear how local excitatory and inhibitory synaptic connections to excitatory neurons are spatially organized on a layer-by-layer basis. In the present study, we combined whole cell recordings with laser scanning photostimulation via glutamate uncaging to map excitatory and inhibitory synaptic inputs to single excitatory neurons throughout cortical layers 2/3-6 in the mouse primary visual cortex (V1). We find that synaptic input sources of excitatory neurons span the radial columns of laminar microcircuits, and excitatory neurons in different V1 laminae exhibit distinct patterns of layer-specific organization of excitatory inputs. Remarkably, the spatial extent of inhibitory inputs of excitatory neurons for a given layer closely mirrors that of their excitatory input sources, indicating that excitatory and inhibitory synaptic connectivity is spatially balanced across excitatory neuronal networks. Strong interlaminar inhibitory inputs are found, particularly for excitatory neurons in layers 2/3 and 5. This differs from earlier studies reporting that inhibitory cortical connections to excitatory neurons are generally localized within the same cortical layer. On the basis of the functional mapping assays, we conducted a quantitative assessment of both excitatory and inhibitory synaptic laminar connections to excitatory cells at single cell resolution, establishing precise layer-by-layer synaptic wiring diagrams of excitatory neurons in the visual cortex.

PMID:
26844927
PMCID:
PMC4818606
DOI:
10.1113/JP271891
[Indexed for MEDLINE]
Free PMC Article

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