AMPA-type glutamate receptor (AMPAR) trafficking is essential for modulating synaptic transmission strength. Prior studies that have characterized signaling pathways underlying AMPAR trafficking have identified the cAMP/PKA-mediated phosphorylation of GluA1, an AMPAR subunit, as a key step in the membrane insertion of AMPAR. Inhibition of ERK impairs AMPAR membrane insertion, but the mechanism by which ERK exerts its effect is unknown. Dopamine, an activator of both PKA and ERK, induces AMPAR insertion, but the relationship between the two protein kinases in the process is not understood. We used a combination of computational modeling and live cell imaging to determine the relationship between ERK and PKA in AMPAR insertion. We developed a dynamical model to study the effects of phosphodiesterase 4 (PDE4), a cAMP phosphodiesterase that is phosphorylated and inhibited by ERK, on the membrane insertion of AMPAR. The model predicted that PKA could be a downstream effector of ERK in regulating AMPAR insertion. We experimentally tested the model predictions and found that dopamine-induced ERK phosphorylates and inhibits PDE4. This regulation results in increased cAMP levels and PKA-mediated phosphorylation of DARPP-32 and GluA1, leading to increased GluA1 trafficking to the membrane. These findings provide unique insight into an unanticipated network topology in which ERK uses PDE4 to regulate PKA output during dopamine signaling. The combination of dynamical models and experiments has helped us unravel the complex interactions between two protein kinase pathways in regulating a fundamental molecular process underlying synaptic plasticity.T he strength of synaptic transmission depends on the number of AMPA-type glutamate receptors (AMPARs) localized to the synaptic membrane. The regulated trafficking of AMPARs in and out of the postsynaptic membrane controls the number of synaptic AMPARs and is thought to underlie synaptic plasticity (1). AMPARs are composed of four subunits (GluA1-4), which assemble as homo-or hetero-tetramers to mediate excitatory transmissions in the brain. There are a number of intracellular pathways that regulate signal-initiated trafficking of GluA1-containing AMPARs. For instance, PKA and PKG, the cyclic nucleotide-activated kinases, phosphorylate GluA1 at S845 (2, 3). Phosphorylation of S845 is required for GluA1 synaptic insertion because mutation to A845 prevents GluA1 exocytosis (4). Dopamine, a modulatory neurotransmitter that increases cAMP/ PKA levels, promotes GluA1 phosphorylation at S845 and AMPAR insertion into the plasma membrane (3, 5, 6). Additional signaling pathways influence this process, but the role they play in dopamine-mediated AMPAR trafficking is not known. ERK, a downstream effector of dopamine, promotes AMPAR membrane insertion even though ERK does not directly phosphorylate GluA1 (7,8). The objective of this study was to identify the mechanism by which ERK regulates dopamine-mediated GluA1 membrane insertion. Based on our observation that ERK inhibition decreases dop...