The purpose of this work is to study calcium (Ca) dynamics and plasticity at excitatory synapses made onto the smooth dendrites of a class of inhibitory interneuron, cerebellar stellate cells (SC). Because interneurons play a crucial role in regulating neuronal circuits, it is important to understand the mechanisms underlying changes in the efficacy of their excitatory synapses. We are interested in addressing the following questions. First, does synaptic activation triggers calcium rises in SC dendrites? Second, what are the Ca sources? Third, how spatially restricted are the Ca increases? What are the mechanisms for any Ca compartmentalization in dendritic regions near excitatory synapses? Fourth, does Ca rises result in longterm synaptic plasticity? Finally, can SC synapses be independently modulated? These questions will be addressed by recording synaptic currents (EPSCs) and imaging Ca transients in whole-cell, voltage-clamped SC dendrites from acute cerebellar slices. EPSCs will be evoked by extracellular stimulation of the parallel fibers (PFs). Ca transients and sources will be identified using Ca indicators and the required pharmacology. Induction of plasticity will be performed via high frequency stimulation delivered to the PFs.