Abstract
Neurons connect to each other through synapses. Synapse is the elemental information processing units of the brain. To reveal the mechanism of synaptogenesis is crucial to understand the development of neural circuitry .A cardinal feature of the formation of synapses is the accumulation of neurotrasmitter receptors at the postsynaptic site. Glutamatergic synapses mediate the main excitatory neural transmission in mammalian CNS. Glutamate receptor clustering in synapses has been studied in culture and slice. Here, I used immunocytochemical methods to investigate the distribution of two main glutamate receptors, AMPA and NMDA receptors, of cultured rat neocortical neurons in various developmentat stages.We found that between first and second weeks in vitro the subunit compositions of most synaptic AMPA receptors switched from GluR2-free to GluR2-containing receptors. In the same period, more NMDA receptors were recruited from extrasynaptic areas to synapses. We suggest that in the early development stage neurons express mainly Ca++ permeable AMPA receptors at synapses. Ca++ influxes through AMPA receptor may be related to a subtype switch from Ca++ permeable to Ca++ impermeable AMPA receptors and the targeting of NMDA receptors to synapses in the latter stages of development.