A biological blueprint for the axons of superficial layer pyramidal cells in cat primary visual cortex

Kevan A C Martin,Stephan Roth,Elisha S Rusch

doi:10.1007/s00429-017-1410-6

Kevan A C Martin, Stephan Roth + Show 1 more

Open Access

https://doi.org/10.1007/s00429-017-1410-6

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Abstract

Pyramidal cells in the superficial layers of neocortex of higher mammals form a lateral network of axon clusters known as the ‘daisy’ network. The role of these axon clusters remains speculative and we still lack a comprehensive quantitative description of the single neurons forming the daisy or their heterogeneity. We filled intracellularly 50 superficial layer pyramidal neurons in the cat primary visual cortex and reconstructed the axonal tree and their synaptic boutons in 3D. Individual bouton clusters were identified using an objective mean-shift algorithm. By parameterizing the morphology of these 50 axonal trees and the 217 bouton clusters they formed, we were able to extract one set of relatively constant parameters and another set of variable parameters. Both sets combined allowed us to outline a comprehensive biological blueprint of superficial layer pyramidal neurons. Overall, our detailed analysis supports the hypothesis that pyramidal neurons use their lateral clusters to combine differential contextual cues, required for context-dependent processing of natural scenes.

Highlights

The pyramidal cells of the superficial cortical layers form a distinctive network consisting of a circular arrangement of clusters of synaptic boutons arranged around a core of cells, dendrites, and axon (Rockland and Lund 1982)
The conventional view of neurons is in the transverse view of the dendrites and axon shown in Fig. 1a, which allows the laminar boundaries to be indicated
Since a bouton cluster is well-fitted with an ellipsoid, we explored the possibility that the elongation of the cluster was a reflection of the direction of outgrowth of the spoke

Summary

Introduction

The pyramidal cells of the superficial cortical layers form a distinctive network consisting of a circular arrangement of clusters of synaptic boutons arranged around a core of cells, dendrites, and axon (Rockland and Lund 1982). The network appears flower-like and has been referred to as the cortical ‘daisy’ (Douglas and Martin 2004) This daisy structure is made visible by extracellular injections of tracers. Binzegger et al (2007) demonstrated that such a relation is not just confined to the superficial layer pyramidal cells, but applies to all cell types examined in cat V1, including smooth neurons. These observations give encouragement to the notion that the cortical daisy emerges from elemental rules that govern the growth of all cortical neurons

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