Thalamocortical input onto layer 5 pyramidal neurons measured using quantitative large-scale array tomography.

Area of Science:

• Neuroscience
• Cell Biology
• Microscopy

Background:

• Synapse location on pyramidal neurons impacts dendritic integration and plasticity.
• Quantitative data on specific synaptic input distributions is limited.

Purpose of the Study:

• To quantitatively map thalamocortical (TC) synapse distribution on layer 5 pyramidal neurons using array tomography (AT).
• To assess the utility of AT for mapping synaptic connectivity.

Main Methods:

• Verified AT's synapse identification capability using electron microscopy.
• Employed large-scale array tomography (LSAT) to analyze TC synapse distribution in mouse somatosensory cortex.
• Quantified synapse distribution on L5 pyramidal neurons within a defined cortical volume.

Main Results:

• TC synapses predominantly target basal dendrites of layer 5 neurons and proximal apical dendrites in layer 4.
• TC inputs exhibit branch bias and significant clustering, with nearest neighbors within 5-15 μm.
• Demonstrated AT as a sensitive method for mapping synaptic input.

Conclusions:

• Array tomography provides a quantitative method for mapping specific synaptic inputs.
• Synapse clustering and distribution patterns offer insights into neural circuit organization.
• AT is a valuable tool for studying functionally relevant anatomical connectivity.