The metabotropic glutamate receptor subtype 1 (mGluR1) is highly expressed in cerebellar Purkinje cells and is crucial for cerebellar function. Synaptic activation of mGluR1 at parallel fiber synapses is followed by two G-protein-dependent processes: (1) production of inositol-trisphosphate (IP3) leading to release of Calcium ions from intracellular stores and (2) initiation of a slowly activating excitatory postsynaptic current (sEPSC). We recently reported that mGluR1-mediated synaptic transmission at the parallel fiber-Purkinje cell synapse requires the transient receptor potential channel (TRPC) subunit TRPC3 (Hartmann J. et al. 2008, Neuron 59, 392-398). Both the parallel fiber stimulation-evoked sEPSC and the inward currents evoked by local application of the mGluR-specific agonist dihydrophenylglycine (DHPG) are absent in TRPC3-deficient mice. By analyzing the pharmacological properties of mGluR1-dependent synaptic transmission in cerebellar slices of adult mice, we found that synaptically-evoked Calcium signals have two distinct components: a large Calcium signal component that is sensitive to cyclic piazonic acid (CPA), identifying it as a Calcium release signal from internal store, and an about 10-fold smaller component that is insensitive to CPA. We identified the small component as a Calcium entry signal through TRPC3 channels. Using two-photon Calcium imaging we analyzed the subcellular location of the two Calcium signaling components. We found that the Calcium release component is prominent in spines and has a fast rise time, while the Calcium influx signal has a slow onset and is more evenly distributed in spines and dendrites. The results also show that Calcium release from stores, but not Calcium entry is required for the induction of long-term synaptic depression in Purkinje cells. Thus, in conclusion, our results identify Calcium entry through TRPC3 channels as a novel postsynaptic response that is involved synaptic signaling but not in activity-dependent synaptic plasticity.