G protein-coupled receptor 3 (GPR3) is highly expressed in various neurons and can constitutively activate the Gαs protein in the absence of ligands, thereby elevating the basal intracellular cAMP levels. We have shown that GPR3 is upregulated during neuronal differentiation and contributes to neurite outgrowth and neuronal survival. Meanwhile, GPR3 is rapidly induced in neurons, T cells, and mast cells upon stimuli; however, the potential mechanisms related to the rapid GPR3 induction remain elusive. In this study, we investigated the regulatory mechanism underlying GPR3 expression and its effect on downstream gene expression during neuronal differentiation in PC12 cells. PC12 cells stimulated using the cAMP activator forskolin strongly upregulated GPR3 mRNA as early as 1–2 h, declining thereafter. In addition, the GPR3 expression induced by forskolin was significantly augmented with the increased intracellular Ca²⁺ level produced by ionomycin. In addition, a luciferase-based promoter assay revealed that the cAMP response element in the 5'-flanking region of the rat GPR3 genome was associated with GPR3 transcription. Moreover, the upregulated GPR3 expression resulted in increased NR4A1 gene expression, further upregulating the expression of synapsin1, a downstream target of NR4A1. These results suggest that immediate early GPR3 upregulation by cAMP and Ca²⁺ stimuli may further enhance cAMP signaling, thereby modulating downstream gene expressions.