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

<jats:title>ABSTRACT</jats:title><jats:p>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.</jats:p><jats:sec><jats:title>SIGNIFICANCE STATEMENT</jats:title><jats:p>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.</jats:p></jats:sec>

Hippocampal cAMP-dependent synaptic potentiation, ERK-dependent immediate-early gene activation, and context-dependent fear conditioning in mice are linked through dependence on the guanine nucleotide exchange factor RapGEF2

“…Both floxed and cKO mice could distinguish between training and novel contexts (Figure 2C 2 , Two-way ANOVA followed by post hoc Bonferroni t-test, context effect: F (1, 82) =66.802, p<0.001). Although RapGEF2 is ablated in BLA in cKO mice (Jiang et al, 2017, 2021), these mutant mice associate tone with the foot shock as did the floxed control mice, and did not differ from floxed controls in cued fear memory when tested 24 h after fear conditioning (Figure 2C 3 , Two-way ANOVA followed by post hoc Bonferroni t-test, to compare floxed and cKO mice during tone presentation. Conditioning effect: F (1, 82) =189.502, p<0.001; genotype effect: F (1, 82) =0.462, p=0.499; flox vs cKO after conditioning, p=0.351).…”

“…The dynamic changes of expression of immediate-early genes (IEGs), such as c-Fos and Egr-1, have been widely used as molecular markers for neuronal plastic changes measured in cell culture (Harada et al, 2001; Han et al, 2007; Adams et al, 2017) and in vivo ((Jiang et al, 2021) and references therein), especially in the context of genetic manipulation of hippocampal function required for memory formation (Liu et al, 2012; Ramirez et al, 2013; Liu et al, 2014; Gallo et al, 2018). Previous studies suggested that most neuronal ensembles encoding fear memory may simultaneously express various IEGs, however, to what extent IEG-positive ensembles overlap with each other and whether they are regulated separately in the same neurons, remains unclear.…”

“…Our rationale for consideration of RapGEF2 as such a candidate derives from our previous results that RapGEF2 is an obligate cAMP sensor in Gs-coupled GPCR initiation of neuritogenesis in neuroendocrine cells (Emery et al, 2013); that RapGEF2 is a specifically neuronal/neurendocrine signaling component in adult mammals (Jiang et al, 2017); that RapGEF2 is required for dopaminergic cAMP-dependent signaling to ERK underlying cocaine’s psychomotor stimulant effects on behavior (Jiang et al, 2021); and that RapGEF2-dependent signaling to ERK is required for cAMP-dependent induction of the immediate-early gene Egr1/zif268 (Jiang et al, 2017; Jiang et al, 2021), implicated in learning and memory mechanisms, along with ERK and cAMP, in hippocampus as well as other brain areas (Bozon et al, 2003).…”

“…LTP involves the mobilization of several immediate-early genes activated by both the cAMP and calcium pathways. Fos up-regulation can be either calcium- or cAMP-dependent, and that of other immediate early genes, such as Egr-1/Zif268, are cAMP-dependent (Sheng and Greenberg, 1990; Sheng et al, 1990; Ginty et al, 1992; Greenberg et al, 1992; Tai et al, 2001; Bozon et al, 2002; Bozon et al, 2003; Ravni et al, 2008; Gangarossa et al, 2011; Jiang et al, 2021). More controversial is the mode of regulation of fos initiated either by cAMP or calcium: this has been attributed both to a PKA-dependent, Rap1-independent activation of ERK, leading to MSK-1 activation and phosphorylation/activation of the transcription factor CREB, or to a CREB-dependent mechanism due CREB phosphorylation directly by PKA (Wong et al, 1999; Poser and Storm, 2001; Sindreu et al, 2007; Xia and Storm, 2012).…”

“…A signaling matrix in which cAMP activates cognitive kinases through parallel PKA-dependent and PKA-independent pathways is an attractive construct for better understanding of the molecular events controlling neuronal plasticity. In fact, we have recently proferred evidence that dopamine signaling through the D1 GsPCR activates both CREB and ERK phosphorylation in D1 dopaminoceptive neurons (Jiang et al, 2017), and that eliminating RapGEF2 from D1 medium spiny neurons (MSN) of the nucleus accumbens curtails cocaine-induced locomotor sensitization and conditioned place preference (Jiang et al, 2021), the latter a type of learning previously shown to require ERK-dependent D1-MSN neuroplasticity (Girault et al, 2007).…”