[Developmental changes of spontaneous excitatory postsynaptic currents mediated by AMPA receptor in layer 2 and 3 pyramidal neurons of rat visual cortex].

Objective: To investigate the modification function of visual experience onto synapses by recording developmental changes of spontaneous excitatory postsynaptic currents (sEPSC) in layer 2 and 3 pyramidal neurons of rat visual cortex, and to observe the spontaneous synaptic activities during the earlier postnatal period.

Methods: This was an experimental study. By combining infrared differential interference contrast (IR-DIC) technique and a CCD-camera system with visual patch clamp whole-cell recording technique, spontaneous EPSCs of P2 approximately 7, P8 approximately 14, P15 approximately 21 and P22 approximately 28 groups were observed and analyzed. The neurons were stained by adding 0.3% Lucifer yellow to the pipette solution simultaneously.

Results: The amplitude of sEPSC was enhanced when aging (F = 20.69, P < 0.01). The sEPSC frequency increased with age (F = 87.46, P < 0.01). There was no significant difference between P2 approximately 7 groups and P8 approximately 14 groups (P > 0.05). The electrophysiology and dendrite of neuron became mature whilst development.

Conclusions: During the early postnatal days neurons were relatively immature, and became mature during development. Visual experience played an important role in this process. In spite of most synapses were taken silent at early postnatal days, and NMDA receptor-mediated function was revealed exclusively, these results suggested that early AMPA receptor-mediated functional activities existed in layer 2 and 3 pyramidal neurons. Synapses were not completely silent, but had early spontaneous activities.