Incubation of Cocaine Seeking following Brief Cocaine Experience in Mice Is Enhanced by mGluR1 Blockade

Abstract

The incubation of cocaine craving describes the time-dependent augmentation of cue-induced cocaine seeking during withdrawal from prolonged cocaine self-administration and requires time-dependent changes in neuroplasticity at the level of glutamatergic synapses in the nucleus accumbens (NAc). In contrast to most studies that use multiple cocaine-cue conditioning sessions, the present study tested mice with limited cocaine experience (i.e., a single conditioning session) in the incubation of cue-mediated cocaine seeking and its associated changes in the glutamate system. Mice that self-administered cocaine during a single session exhibited a time-dependent increase in their response for the drug-associated cue as compared to mice that self-administered saline. This behavior was associated with changes in AMPA and NMDA receptor binding characteristics. Furthermore, Group I metabotropic glutamate receptor (mGluR1) mRNA levels were altered in several brain regions, including the NAc. Because of the pivotal role of mGluR1 in the control of cocaine-induced plasticity, we investigated the role of mGluR1 in the formation of drug cue-mediated cocaine seeking. After prolonged withdrawal, mice in which an mGluR1 antagonist was administered following cocaine self-administration displayed increased cocaine seeking compared to vehicle-treated mice. These results suggest that limited cocaine experience is sufficient to induce neurobiological changes that enable an initially neutral cue to acquire motivational value that increases over time, an effect that likely involves glutamate signaling through mGluR1.