Specific synapses develop preferentially among sister excitatory neurons in the neocortex.

Area of Science:

• Neuroscience
• Developmental Biology
• Cellular Neuroscience

Background:

• Mammalian neocortical neurons organize into functional columns with specific synaptic connections.
• Neocortical synaptic connectivity is sparse and specific, enabling independent information processing by adjacent neurons.
• The microcircuit construction underlying columnar architecture at the individual neuron level is not fully understood.

Purpose of the Study:

• Investigate if radial clones of excitatory neurons in the developing neocortex form the basis of specific microcircuits.
• Determine if sister neurons within radial clones establish preferential synaptic connections.

Main Methods:

• Labelled ontogenetic radial clones of excitatory neurons in mouse neocortex using enhanced green fluorescent protein (EGFP)-expressing retroviruses.
• Performed multiple-electrode whole-cell recordings to analyze synapse formation between sister neurons and non-siblings during postnatal development.

Main Results:

• Radially aligned sister excitatory neurons showed a propensity for forming unidirectional chemical synapses with each other.
• Synaptic connections between sister neurons exhibited the same interlaminar directional preference observed in mature neocortex.
• These connections were more prevalent between sister neurons than between sister neurons and adjacent non-siblings.

Conclusions:

• Specific microcircuits preferentially develop within radial clones of excitatory neurons in the developing neocortex.
• Ontogenetic radial clones serve as a substrate for the emergence of functional columnar microarchitectures.
• This finding sheds light on the cellular basis of neocortical columnar organization.