Inactivation of NMDAR and CaMKII signaling within the prelimbic cortex blocks incubated cocaine- and sucrose-craving

Abstract

The incubation of craving is a term coined to characterize the behavioral phenomenon wherein cue-elicited craving strengthens over a period of abstinence. Incubated cocaine-craving is mediated, at least in part, by increased glutamate release within the prelimbic cortex (PL). We hypothesized that this glutamate release stimulates NMDA-type glutamate receptors (NMDARs), leading to calcium-dependent activation of CaMKII signaling that drives incubated craving. To test this hypothesis, adult male and female Sprague-Dawley rats were trained to self-administer either intravenous cocaine or sucrose pellets (6 h/day × 10 days) and tested for cue-elicited cocaine- or sucrose-craving in early versus later (i.e., after incubation) withdrawal. Incubated cocaine-seeking was associated with increased CaMKII activity in the PL, but no change in NMDAR subunits. In contrast, incubated sucrose-craving was associated with many sex-dependent changes in both NMDAR subunit expression and CaMKII activation that were subregion-selective. An intra-PL infusion of the NMDA antagonist D-AP5 (2.5 or 7.5 µg/side) or the CaMKII inhibitor myr-AIP (10 pg/side) blocked both incubated cocaine- and sucrose-craving, with no effects detected in early withdrawal. Co-infusion of both D-AP5 and myr-AIP exerted a larger effect on incubated cocaine-craving than either antagonist alone. These data corroborate earlier evidence for distinct biochemical correlates within mPFC between incubated cocaine- and sucrose-craving and, for the first time, demonstrate that both NMDAR and CaMKII activation within the PL are common drivers of incubated craving of potential relevance to the design of anti-craving medications in the contexts of both drug and food reinforcers.