Prenatal development of layer-specific local circuits in primary visual cortex of the macaque monkey

Area of Science:

• Neuroscience
• Developmental Neuroscience
• Cortical Circuitry

Background:

• Axonal arbors in mature macaque visual cortex (V1) exhibit high specificity for cortical layers and sublayers.
• Previous research indicates activity-independent cues guide the initial development of axonal arbors for main cortical layers.

Purpose of the Study:

• To investigate the prenatal development of laminar and sublaminar specificity in local circuits within macaque V1.
• To determine the precision of axonal targeting during early development compared to mature animals.

Main Methods:

• Intracellular labeling of 238 neurons in macaque V1 slices from prenatal animals (100-145 days postconception).
• Reconstruction of axonal and dendritic arbors to analyze their laminar and sublaminar relationships.
• Comparison of prenatal axonal targeting with known mature patterns.

Main Results:

• Developing neurons in layers 2-4B and layer 5 showed specific targeting to superficial and deep layers without aberrant branches in layer 4C.
• Layer 6 pyramidal neurons projecting to layer 4C did not show incorrect branching in layer 5.
• Prenatal development revealed imprecise sublayer-specific projections, including layer 4Cbeta neurons branching into layer 4B and layer 6 neurons projecting to both 4Calpha and 4Cbeta.
• Transient projections to the subplate and white matter were observed in most layers, except 4Cbeta.

Conclusions:

• Specific projections to main cortical layers develop with high selectivity, consistent across species.
• Sublayer-specific projections are not precisely established from the outset and undergo refinement.
• Elimination of exuberant axonal branches and activity-dependent mechanisms likely refine sublayer specificity, potentially guided by spontaneous prenatal activity patterns.