We identified the isoforms of Ca²⁺/calmodulin‐dependent protein kinase II (CaM kinase II) subunits in rat striatum. All four subunits of CaM kinase II α, β, γ and δ were detected including the isoforms of αB, γA, γA′, γA.B, δ3 and δ7 with nuclear localization signal. We established NG108‐15 cells with the stably expressed dopamine D2L receptor (D2LR, long form), which is an alternative splicing variant. The cells were termed NGD2L. Immunostaining demonstrated that D2LR was localized in plasma membranes. Calcium imaging with fluo‐3 AM revealed that quinpirole, a D2R agonist, increased the intracellular Ca²⁺, which was blocked by treatment with sulpiride and pertussis toxin in NGD2L cells, but not in mock cells. Furthermore, stimulation of D2LR with quinpirole in NGD2L cells activated the nuclear isoform of CaM kinase II. Stimulation of D2LR increased the expression of exon III‐ and IV‐BDNF mRNA. Overexpression of CaM kinase II δ3 increased exon IV‐ but not exon III‐BDNF mRNA. These results suggest that D2R is involved in the activation of the nuclear isoform of CaM kinase II and thereby in stimulation of gene expression through Ca²⁺ signaling.