Althoughl-3,4-dihydroxyphenylalanine (l-DOPA) remains the reference treatment of Parkinson's disease, its long-term beneficial effects are hindered byl-DOPA-induced dyskinesia (LID). In the dopamine (DA)-denervated striatum,l-DOPA activates DA D1receptor (D1R) signaling, including cAMP-dependent protein kinase A (PKA) and extracellular signal-regulated kinase (ERK), two responses associated with LID. However, the cause of PKA and ERK activation, their respective contribution to LID, and their relationship are not known. In striatal neurons, D1R activates adenylyl-cyclase through Gαolf, a protein upregulated after lesion of DA neurons in rats and in patients. We report here that increased Gαolflevels in hemiparkinsonian mice are correlated with LID after chronicl-DOPA treatment. To determine the role of this upregulation, we performed unilateral lesion in mice lacking one allele of theGnalgene coding for Gαolf(Gnal+/−). Despite an increase in the lesioned striatum, Gαolflevels remained below those of unlesioned wild-type mice. InGnal+/−mice, the lesion-inducedl-DOPA stimulation of cAMP/PKA-mediated phosphorylation of GluA1 Ser845 and DARPP-32 (32 kDa DA- and cAMP-regulated phosphoprotein) Thr34 was dramatically reduced, whereas ERK activation was preserved. LID occurrence was similar inGnal+/+andGnal+/−mice after a 10-dl-DOPA (20 mg/kg) treatment. Thus, in lesioned animals, Gαolfupregulation is critical for the activation byl-DOPA of D1R-stimulated cAMP/PKA but not ERK signaling. Although the cAMP/PKA pathway appears to be required for LID development, our results indicate that its activation is unlikely to be the main source of LID. In contrast, the persistence ofl-DOPA-induced ERK activation inGnal+/−mice supports its causal role in LID development.