Internalization at glutamatergic synapses during development.

Glutamate receptors are internalized from the cell membrane via clathrin-coated pits. However, little is known about where this occurs - whether at or near the synapse or at some distance from it. In this study we used immunogold localization in the rat brain (mainly hippocampus) to show that clathrin-coated pits are found both at the edge of the synaptic active zone and at further postsynaptic distances, including on the sides of the spine; we also localize these pits specifically to glutamatergic synapses. In addition, we show that clathrin-coated pits can internalize both N-methyl-d-aspartate (in vivo) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (in vitro data only) receptors at extrasynaptic sites not associated directly with synapses. Also, caveolin might be prevalent at excitatory synapses, although it is not known whether it is involved in receptor internalization, receptor stabilization, or some other function.