Metabotropic glutamate receptors (mGluRs) compromise a unique subfamily of G-protein couple receptors for which glutamate is the endogenous ligand. A number of physiological roles have been ascribed to mGluRs including ion channel modulation, regulation of neurotransmitter release, and participation in synaptic plasticity such as long-term potentiation and depression. Moreover, recent evidence suggests that mGluRs could play a role in pathological processes related to epilepsy, ischemia, excitotoxic neurodegenerative disorders, Alzheimer's Disease, and hypertension. Thus there is a substantial interest in defining the roles subserved by specific mGluR subtypes and developing subtype specific pharmacological agents. At present, the sequences for twelve mGluR subtypes (mGluR1-8 plus splice variants) have been elucidated. However, despite this wealth of primary sequence information, little is known about which specific mGluR subtypes modulate ion channels and synaptic transmission in neurons or the mechanisms involved in these actions. To address this void in our knowledge, we will examine the function, pharmacology, and signal transduction pathways of: 1) heterologously expressed mGluRs in sympathetic neurons (SPECIFIC AIMS 1 and 2), and 2) natively expressed mGluRs in CNS neurons (SPECIFIC AIMS 3 and 4). Accordingly, the SPECIFIC AIMS are: 1) Pharmacological characterization and signal transduction pathways of defined mGluR subtypes that inhibit N-type Ca2+ and M-type K+ channels. Molecularly defined mGluR subtypes will be heterologously expressed in mature rat sympathetic neurons to determine which subtypes modulate N-type Ca2+ and M-type K+ channels. 2) Molecular elements of mGluR structure/function. The structural domains of mGluRs which determine pharmacological profile and G-protein coupling specificity will be examined by expressing chimeric mGluR constructs in sympathetic neurons. 3) Identification and signal transduction pathways of mGluRs involved in Ca2+ and K+ channel modulation in isolated CNS neurons. The pharmacological (agonist and antagonist) profile and signal transduction characteristics of mGluR-mediated Ca2+ and K+ channel inhibition will be determined in acutely isolated hippocampal and cortical neurons. 4) Identification of mGluRs involved in modulation of synaptic transmission in CNS neurons. Glutamatergic synaptic transmission in brain slices will be examined to determine which mGluRs mediate modulate neurotransmitter release.
