Glutamate is the principal excitatory amino acid in the central nervous system and release of glutamate from axon terminals results in the activation of two distinct families of receptors. One of these families, the metabotropic glutamate receptors (mGluRs), coupled to a variety of GRP-binding (G) proteins and activate several second messenger pathways to regulate cell excitability and synaptic transmission. Because of the important roles of mGluRs in shaping net transmission at glutamatergic synapses, it is critical to understand the mechanisms involved in regulating mGluR responses. A new family of proteins termed RGS (regulators of G protein signaling) interact directly with G proteins to attenuate G protein-mediated responses and regulate G protein signaling. To date, the regulation of neurotransmitter responses by RGS proteins has not been addressed. It has recently been reported that the long-term application of agonists to mGluRs results in a form of long-term desensitization that is not accounted for by phosphorylation, or internationalization and degradation of the receptor. We hypothesize that RGS proteins may not only regulate G protein pathways in the central nervous system, but that long-term application of mGluR agonists may lead to the regulation of cellular levels of RGS proteins and the subsequent desensitization of receptor responses in neurons and glia. Thus the goal of this proposal is to determine the effects of RGS proteins on mGLuR- mediated responses and the effects of mGluR activation on the regulation of cellular levals of RGS proteins using a combination of molecular, biochemical and electrophysiological methods.
The specific aims are to: (1) determine the effects of RGS7 protein on mGluR responses in heterologous expression systems, (2) determine the effects of RGS proteins on mGluR responses in neuronal cells, (3) determine whether mGluR activation regulates the cellular levels of expression of RGS mRNA and protein in neurons and (4) determine whether mGluR activation regulates the cellular levels of expression of RGS mRNA and protein in glial cells. These studies will provide valuable insight into the cellular mechanisms involvedin mGluR signaling and could have important implications for the development of novel therapeutic agents for the treatment of a variety of central nervous system disorders.
