Recent studies suggest that selective activators of specific subtypes of metabotropic glutamate receptors (mGluRs) have exciting potential for development of novel treatment strategies for a variety of psychiatric and neurological disorders, including Parkinson's disease, Alzheimer's disease, psychotic disorders, epilepsy, and others. Unfortunately, it has been difficult to develop compounds that act as selective agonists of specific mGluR subtypes that have properties that are likely to be suitable for development of therapeutic agents. However, over the past year, we and others have been highly successful in developing a novel approach to activation of mGluRs by developing highly selective allosteric potentiators of specific mGluR subtypes. These allosteric potentiators do not activate mGluRs directly but dramatically potentiate the response of these receptors, to glutamate. These compounds offer high selectivity for the targeted receptor and provide an exciting new approach to development of novel selective activators of specific mGluR or other G protein-coupled receptor subtypes. Interestingly, our preliminary studies suggest that multiple allosteric potentiators may interact with similar binding pockets that are conserved between mGluR subtypes. However, we have identified at least one novel potentiator of mGluRS that may act at a distinct site. Defining the precise domains of the receptors required for actions of these compounds and the mechanisms involved in allosteric potentiation of mGluRs will be important for further development of this approach to mGluR activation. Furthermore, a number of previous studies raise the possibility that allosteric potentiators could differentially regulate mGluR coupling to different signaling pathways or functional responses in different neuronal populations. However, the effects of allosteric potentiators on coupling of mGluRs to multiple signaling pathways and the physiological effects of these compounds have not been determined. We now propose a series of studies in which we will use site directed mutagenesis to rigorously define the domains and specific amino acids necessary for the function of allosteric potentiators at mGluR4 and mGluRS that we recently discovered. We will then perform a series of studies in which we determine the effects of these allosteric potentiators on coupling to different signaling pathways and electrophysiological responses to mGluR activation in native neuronal and glial cell populations. These studies will provide important information as to the impact of allosteric potentiators on mGluR function in different of neuronal circuits.
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