PICK1 Regulates Incorporation of Calcium-Permeable AMPA Receptors during Cortical Synaptic Strengthening

While AMPA-type glutamate receptors (AMPARs) found at principal neuron excitatory synapses typically contain the GluR2 subunit, several forms of behavioral experience have been linked to the de novo synaptic insertion of calcium-permeable (CP) AMPARs, defined by their lack of GluR2. In particular, whisker experience drives synaptic potentiation as well as the incorporation of CP-AMPARs in the neocortex. Previous studies implicate PICK1 (protein interacting with C kinase-1) in activity-dependent internalization of GluR2, suggesting one potential mechanism leading to the subsequent accumulation of synaptic CP-AMPARs and increased synaptic strength. Here we test this hypothesis by using a whisker stimulation paradigm in PICK1 knock-out mice. We demonstrate that PICK1 facilitates the surface expression of CP-AMPARs and is indispensable for their experience-dependent synaptic insertion. However, the failure to incorporate CP-AMPARs in PICK1 knock-outs does not preclude sensory-induced enhancement of synaptic currents. Our results indicate that synaptic strengthening in the early postnatal cortex does not require PICK1 or the addition of GluR2-lacking AMPARs. Instead, PICK1 permits changes in AMPAR subunit composition to occur in conjunction with synaptic potentiation.