Synaptic and dendritic activity in Purkinje neurons generates spatially and temporally complex calcium (Ca) dynamics. Purkinje cells express high levels of many cellular constituents involved in Ca homeostasis, including IP3 receptors (IP3Rs) and ryanodine receptors (RyRs), which mediate Ca release from intracellular stores. The precise localization of these receptors is likely to be critical for determining Ca dynamics and function. Our previous physiological studies showed that Ca release by RyRs plays a substantial role in Ca signals generated by parallel fiber (PF) synaptic activity (Artinian and Finch, SFN abstract, 2003). In the present study we have used immunohistochemistry to analyze the localization of receptors, ion channels, and signaling molecules involved in Ca homeostasis in the cerebellum of rats at P16-24, the ages commonly used for electrophysiological and Ca imaging studies, and at P60. We find that IP3Rs, RyRs, and mGluRs are extensively colocalized in Purkinje cells. Although IP3Rs and...