Cocaine-dependent acquisition of locomotor sensitization and conditioned place preference requires D1 dopaminergic signaling through a cyclic AMP, NCS-Rapgef2, ERK and Egr-1/Zif268 pathway

ABSTRACT Elucidation of the underlying mechanism of dopamine signaling to ERK that underlies plasticity in dopamine D1 receptor expressingneurons leadingto acquired cocaine preference is incomplete. NCS-Rapgef2 is a novel cAMP effector, expressed in neuronal and endocrine cells in adult mammals, that is required for D1 dopamine receptor-dependent ERK phosphorylation in mouse brain. In this report, we studied the effects of abrogating NCS-Rapgef2 expression on cAMP-dependent ERK→Egr-1/zif268 signaling in cultured neuroendocrine cells; in D1 medium spiny neurons (MSNs) of nucleus accumbens slices; and in mouse brain in a region-specific manner. NCS-Rapgef2 gene deletion in the nucleus accumbens (NAc) in adult mice, using AAV-mediated expression of cre recombinase, eliminated cocaine-induced ERK phosphorylation and Egr-1/Zif268 upregulation in D1-MSNs and cocaine-induced behaviors including locomotor sensitization and conditioned place preference (CPP). Abrogation of NCS-Rapgef2 gene expression in medium prefrontal cortex and basolateral amygdala, by crossing mice bearing a floxed Rapgef2 allele with a cre mouse line driven by calcium/calmodulin-dependent kinase IIα promoter also eliminated cocaine-induced phospho-ERK activation and Egr-1/Zif268 induction, but without effect on the cocaine-induced behaviors. Our results indicate that NCS-Rapgef2 signaling to ERK in dopamine D1-receptor expressing neurons in the NAc, butnotin corticolimbic areas, contributes to cocaine-induced locomotor sensitization and CPP. Ablation of cocaine-dependent ERK activation by elimination of NCS-Rapgef2 occurred with no effect on phosphorylation of CREB in D1 dopaminoceptive neurons of NAc. This study reveals a new cAMP-dependent signaling pathway for cocaine-induced behavioral adaptations, mediated through NCS-Rapgef2/phospho-ERK activation, independently of PKA/CREB signaling. SIGNIFICANCE STATEMENT ERK phosphorylation in dopamine D1 receptor expressing neurons exerts a pivotal role in psychostimulant-induced neuronal gene regulation and behavioraladaptation, including locomotor sensitization and drug preference in rodents. In this study, we examined the role of dopamine signaling through the D1 receptor via a novel pathway initiated through the cAMP-activated guanine nucleotide exchange factor NCS-Rapgef2 in mice. NCS-Rapgef2 in the nucleus accumbens is required for activation of ERK and Egr-1/Zif268 in D1 dopaminoceptive neurons after acute cocaine administration, and subsequentenhanced locomotor response anddrugseeking behavior after repeated cocaine administration. This novel component in dopamine signaling provides a potential new target for intervention in psychostimulant-shaped behaviors, and new understanding of how D1-MSNs encode the experience of psychomotor stimulant exposure.