Extinction of Contextual Cocaine Memories Requires Ca1.2 within D1R-Expressing Cells and Recruits Hippocampal Ca1.2-Dependent Signaling Mechanisms.

Exposure to cocaine-associated contextual cues contributes significantly to relapse. Extinction of these contextual associations, which involves a new form of learning, reduces cocaine-seeking behavior; however, the molecular mechanisms underlying this process remain largely unknown. We report that extinction, but not acquisition, of cocaine conditioned place preference (CPP) in male mice increased Ca1.2 L-type Ca channel mRNA and protein in postsynaptic density (PSD) fractions of the hippocampus, a brain region involved in drug-context associations. Moreover, viral-mediated deletion of Ca1.2 in the dorsal hippocampus attenuated extinction of cocaine CPP. Molecular studies examining downstream Ca1.2 targets revealed that extinction recruited calcium/calmodulin (Ca/CaMK)-dependent protein kinase II (CaMKII) to the hippocampal PSD. This occurred in parallel with an increase in phosphorylation of the AMPA GluA1 receptor subunit at serine 831 (S831), a CaMKII site, along with an increase in total PSD GluA1. The necessity of S831 GluA1 was further demonstrated by the lack of extinction in S831A GluA1 phosphomutant mice. Of note hippocampal GluA1 levels remained unaltered at the PSD, but were reduced near the PSD and at perisynaptic sites of dendritic spines in extinction-resistant S831A mutant mice. Finally, conditional knock-out of Ca1.2 in dopamine D1 receptor (D1R)-expressing cells resulted in attenuation of cocaine CPP extinction and lack of extinction-dependent changes in hippocampal PSD CaMKII expression and S831 GluA1 phosphorylation. In summary, we demonstrate an essential role for the hippocampal Ca1.2/CaMKII/S831 GluA1 pathway in cocaine CPP extinction, with data supporting contribution of hippocampal D1R-expressing cells in this process. These findings demonstrate a novel role for Ca1.2 channels in extinction of contextual cocaine-associated memories. Continued drug-seeking behavior, a defining characteristic of cocaine addiction, can be precipitated by contextual cues, yet the molecular mechanisms required for extinction of these context-specific memories remain poorly understood. Here, we have uncovered a novel and selective role of the Ca1.2 L-type Ca channel and its downstream signaling pathway in the hippocampus that mediate extinction of cocaine conditioned place preference (CPP). We additionally provide evidence that supports a role of Ca1.2 within dopamine D1 receptor-expressing cells of the hippocampus for extinction of cocaine CPP. Therefore, these findings reveal a previously unknown role of Ca1.2 channels within the hippocampus and in D1 receptor-expressing cells in extinction of cocaine-associated memories, providing a framework for further exploration of mechanisms underlying extinction of cocaine-seeking behavior.