Parkinson’s disease (PD) is the second most common neurodegenerative disorder after Alzheimer’s disease. There is currently no cure for PD. Symptomatic drug therapy essentially relies on dopamine (DA) replacement therapy. The spectacular antiparkinsonian effect of levodopa in PD is however hampered by long-term complications, motor fluctuations and dyskinesia in all patients at some time during the disease course. The mechanisms of the maladaptive striatal plasticity leading to dyskinesia are not well understood. The aim of this project was to identify the dysregulations of signaling pathways in striatal projection neurons (SPN) in the absence of dopamine. We used a mouse model of lesion of DA neurons with 6-OHDA and virally transduced biosensors to monitor signaling pathways in live neurons with two-photon imaging of corticostriatal slices. We focused our attention on extracellular signal-regulated kinase (ERK), cAMP-dependent protein kinase (PKA) and Ca2+ which are known to be altered in the absence of DA. We first set up a reliable experimental model in adult mice, successfully combining 6-OHDA and viral vector in the same unilateral stereotactic injection into the dorsal striatum. In some experiments we targeted the biosensor expression to specific neuronal populations using Cre-dependent “flexed” biosensors. We used mice expressing Cre under the control of the D1 DA receptor (D1R) promoter to target specifically striatal projection neurons of the direct pathway (dSPNs) or the adenosine A2A receptor (A2AR) to target SPNs of the indirect pathway (iSPNs). We used fluorescence resonance energy transfer (FRET)-based biosensors EKAR-EV and AKAR-3 to monitor ERK and PKA activities, respectively. We also monitored cytosolic free Ca2+ with the genetically encoded calcium indicator GCaMP6S. We used pharmacological tools to modulate glutamate, DA, and adenosine receptors as well as phosphodiesterases (PDE) and kinases activities. We observed that the DA lesion increased ERK responsiveness to stimulation of D1R. Since ERK activation depends on both cAMP and Ca2+ signals, we then investigated these two pathways. We observed an increased activation of PKA in response to D1R but not A2AR. We explored the mechanism of this increased sensitivity using mice deficient for Gαolf, the G protein that couples striatal receptors to adenylyl cyclase. We provided evidence that increased levels of Gαolf contributed to enhanced D1 responses after 6-OHDA lesions and identified a deficit in PDE activity in D1 neurons that was likely to amplify this effect. By monitoring Ca2+ signals we showed an increased spontaneous activity of D1 neurons in lesioned mice. However, unexpectedly the Ca2+ responses to stimulation of AMPA glutamate receptors were increased in iSPNs and not dSPNs. In conclusion, our work using for the first time 2-photon biosensor imaging in the DA-depleted striatum of adult mice confirms and extends previous observations on signaling dysregulations in the absence of DA. It reveals distinct cell type-specific alterations of cAMP, Ca2+ and ERK responses in the two populations of SPNs and suggests possible mechanisms for these alterations.