The olfactory system of vertebrates has become an increasingly important model for the study of processing of sensory information. The olfactory bulb and primary olfactory paleocortex are the major sites of sensory processing in this system. Although the anatomy and synaptic circuitry of this system have been studied extensively, the molecular events at olfactory synapses and within olfactory neurons mediating olfactory information processing, associative learning and memory have not been characterized. Glutamate couples to two classes of receptors: ligand-gated ion channels (ionotropic receptors), and those coupled to intracellular signalling pathways through guanyl nucleotide binding proteins or G proteins (metabotropic receptors). The latter group is potentially important in effects of glutamate involving calcium, kinases and modulation of synaptic strength. Expression of this class of receptors is remarkably prevalent in olfactory regions by physiologic and molecular studies, suggesting an essential role in glutamate signaling and information processing. However, the lack of specific pharmacologic tools has limited our understanding of the function of G protein-coupled glutamate receptors. This proposal will use Xenopus oocytes and neuronal cells that express cloned receptors to address three questions: 1) What are the structural features of different G protein-coupled receptors in the olfactory system that determine their pharmacology? 2) What are the cellular effects of G protein coupled glutamate receptors that determine their function in olfactory neurons? 3) How do G protein-coupled glutamate receptors in olfactory neurons contribute to the normal function of these neurons? The investigators will use cDNAs for metabotropic glutamate receptors and isolate others from olfactory bulb and olfactory cortex to test hypotheses about the features of these receptors that determine their pharmacology. This will be crucial to understand the receptors that mediate effects of known pharmacologic reagents and perhaps allow the development of more specific and effective pharmacologic tools. They will determine by patch-clamp recording of neuronal cell lines and primary neuronal cultures expressing the receptor cDNAs the effects of these receptors on gating and modulation of specific ion channels to determine how these receptors affect neuronal excitation. They will also determine the anatomic expression of these receptors mRNAs in olfactory neurons and use antisera to determine whether they are expressed in specific areas of the olfactory circuitry, including at olfactory synapses. They will also try to dissect the important signals that individual G protein-coupled glutamate receptors activate in olfactory neurons by combining physiologic and molecular studies in individual neurons and by blocking their expression of individual metabotropic receptors and measuring differences in glutamate effects on ion channel modulation and intracellular signaling pathways. By defining the precise pharmacology of these receptors, understanding their cellular effects in neurons and determining their pattern of expression in olfactory neurons and synapses, the investigators will begin to elucidate the molecular events underlying processing of olfactory sensory information.
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