The data suggest the following model for postsynaptic membrane formation: Initially glycine receptors are diffusely distributed in the neuronal plasma membrane. Whenever receptors, encounter freely diffusing an active nerve terminal releasing the appropriate neurotransmitter, namely glycine, they open and the resulting ion flux generates a local change in membrane potential. This induces the opening of voltage-gated calcium channels. The resulting calcium influx triggers a second messenger cascade which together with additional presynaptic effectors causes the aggregation of gephyrin beneath the activated plasmamembrane. The aggregates of this peripheral membrane protein then act as a diffusion trap for additional glycine receptor polypeptides. This passive mechanism concentrates the receptors at the developing postsynaptic site.
In the forties, Donald Hebb postulated that the coincident activity of both pre- and
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