Loss of mGluR1-LTD following cocaine exposure accumulates Ca2+-permeable AMPA receptors and facilitates synaptic potentiation in the prefrontal cortex.

Abstract

Addiction results from drug-elicited alterations of synaptic plasticity mechanisms in dopaminergic reward circuits. Impaired metabotropic glutamate receptor (mGluR)-dependent long-term depression (LTD) and accumulation of synaptic Ca²⁺-permeable AMPA receptors (CP-AMPARs) following drug exposure have emerged as important mechanisms underlying drug craving and relapse. Here we show that repeated cocaine exposure in vivo causes transient but complete loss of mGluR1- and mTOR (mammalian target of rapamycin)-dependent LTD in layer 5 pyramidal neurons of mouse prefrontal cortex (PFC), a major dopaminergic target in the reward circuitry. This mGluR1-LTD impairment was prevented by in vivo administration of an mGluR1 positive allosteric modulator (PAM) and rescued by inhibition of dopamine D1 receptors, suggesting that impaired mGluR1 tone and excessive D1 signaling underlie this LTD deficit. Concurrently, CP-AMPARs were generated, indicated by increased sensitivity to the CP-AMPAR inhibitor Naspm and rectification of synaptic AMPAR currents, which were reversed by PAM in cocaine-exposed mice. Finally, these CP-AMPARs mediate an abnormal spike-timing-dependent long-term potentiation enabled by cocaine exposure. Our findings reveal a mechanism by which cocaine impairs LTD and remodels synaptic AMPARs to influence Hebbian plasticity in the PFC. Failure to undergo LTD may prevent the reversal of drug-potentiated brain circuits to their baseline states, perpetuating addictive behaviors.HIGHLIGHTSA mGluR1- and mTOR-dependent LTD is present in the mouse medial prefrontal cortex.Repeated cocaine exposure in vivo temporally but completely abolishes prefrontal mGluR1-LTD.Impaired mGluR1 function and excessive D1 DA signaling likely underlie cocaine impairment of mGluR1-LTD.Ca²⁺-permeable AMPA receptors are generated by cocaine exposure, likely resulting from mGluR1-LTD impairment, and contribute to a cocaine-induced extended spike timing LTP.