Nuclear Ca2+ plays a critical role in many cellular functions although its mode (s) of regulation is unclear. Recently, we have shown that the metabotropic glutamate receptor, mGlu5, mobilizes nuclear Ca2+ independent of cytosolic Ca2+ regulation. Immunocytochemical, ultrastructural, and subcellular fractionation techniques revealed that the metabotropic glutamate receptor, mGlu5, was localized to nuclear membranes in heterologous cells as well as midbrain and cortical neurons. Nuclear mGlu5 receptors expressed in heterologous cell types could bind agonist and isolated nuclei responded to agonist with rapid, oscillatory [Ca2+] elevations that were blocked by antagonist. Because these results challenge existing paradigms as to the role of intracellular receptors and have important ramifications in intracellular signaling, they are applicable to the purpose of the R21 mechanism. The goal of the current application is to establish a native, physiological system with which to test these novel concepts further. Because preliminary results indicate that mGluR5 receptors are expressed on both nuclear and plasma membranes in striatal cultures, these preparations will be used to examine the hypothesis that nuclear mGlu5 receptors can regulate nuclear Ca2+ in neurons. Specifically, cultures will be loaded with a calcium indicator whose spatio-temporal distribution will be analyzed in the confocal microscope. Following treatment with specific agonists and antagonists, cultures will be fixed, stained, and field re-located to determine whether nuclear oscillatory responses, if any, are associated with nuclear mGlu5 receptors. Striatal nuclei, isolated in situ, will be analyzed in a similar fashion. Subsequent experiments will address what ligand is activating nuclear receptors and how it is doing so. Given that mGlu5 receptors play pivotal roles in synaptic plasticity, neuronal development and modulation of synaptic transmission, the mechanisms by which they do so are of critical importance. Direct nuclear calcium regulation represents a novel signaling strategy by which intracellular receptors such as mGlu5 may play a pivotal role in generating and shaping intracellular Ca2+ signals ? ?
