Functional maturation of excitatory synapses in layer 3 pyramidal neurons during postnatal development of the primate...

Area of Science:

• Neuroscience
• Developmental Neuroscience
• Primate Brain Research

Background:

• The primate dorsolateral prefrontal cortex (DLPFC) undergoes significant synaptic pruning during adolescence.
• This refinement of neural circuits is linked to improved working memory but its functional implications are unclear.
• Understanding which synapses are pruned is key to understanding adolescent brain maturation.

Purpose of the Study:

• To investigate the functional properties of excitatory synapses in the primate DLPFC during postnatal development.
• To determine if synapses eliminated during adolescence are functionally immature.
• To differentiate between maturation-dependent and maturation-independent synaptic pruning mechanisms.

Main Methods:

• Electrophysiological recordings were used to assess excitatory synaptic function in monkey DLPFC.
• Key synaptic properties studied included release probability, AMPA/NMDA ratio, and NMDA current duration.
• Sensitivity to NR2B subunit-selective antagonists was also examined.

Main Results:

• Early postnatal monkeys (3 months) exhibited immature synaptic properties (high release probability, low AMPA/NMDA ratio, prolonged NMDA currents).
• These immature properties were associated with greater sensitivity to ifenprodil, an NR2B antagonist.
• Synaptic inputs in preadolescent (15 months) and adult monkeys showed similar functional properties, indicating maturation before adolescence.

Conclusions:

• Functionally immature synapses are significantly reduced in the DLPFC before the onset of adolescence.
• Synaptic pruning during DLPFC adolescence may not involve widespread changes in synaptic strength.
• Adolescent circuit refinement in the DLPFC appears to prune synapses that have already matured or possess other maturation-independent characteristics.