Postnatal development of synaptic structure proteins in pyramidal neuron axon initial segments in monkey prefrontal...

Area of Science:

• Neuroscience
• Developmental Neuroscience
• Primate Brain Development

Background:

• The maturation of synaptic connections in the primate prefrontal cortex (PFC) is complex, particularly for gamma-aminobutyric acid (GABA) neurons.
• Proteins regulating GABA neurotransmission from chandelier interneurons to pyramidal neuron axon initial segments (AIS) change significantly during development in the monkey PFC.

Purpose of the Study:

• To investigate the molecular mechanisms underlying developmental refinements in primate PFC GABAergic synapses.
• To quantify the density, distribution, and length of AIS proteins (ankyrin-G, betaIV spectrin, gephyrin) in the developing monkey PFC.

Main Methods:

• Immunoreactivity for ankyrin-G, betaIV spectrin, and gephyrin was assessed in the PFC of rhesus monkeys across a wide age range.
• Quantification of AIS density, laminar distribution, and length was performed.

Main Results:

• Ankyrin-G and betaIV spectrin-labeled AIS decreased in density and length during the first six postnatal months, stabilizing thereafter.
• Gephyrin-labeled AIS remained stable until approximately 15 months, then significantly declined during adolescence.
• Distinct developmental trajectories were observed for proteins regulating AIS structure and GABAergic input.

Conclusions:

• Molecular components of GABA inputs to pyramidal neuron AIS exhibit distinct developmental timelines in the primate PFC.
• A two-phase developmental process governs GABAergic synaptic stability and neurotransmission at chandelier cell inputs.
• These developmental changes likely contribute to the protracted maturation of PFC-mediated behaviors.