MOLECULAR CHARACTERIZATION OF GLUTAMATE RECEPTORS IN FRESHWATER SNAILS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Glutamate is a common neurotransmitter in both vertebrates, where it is involved primarily in excitatory neurotransmission, and invertebrate systems. In invertebrates, glutamate mediates behaviors through receptors that are less well characterized than vertebrate ones. For example, glutamate is known to control the feeding behavior in pulmonate mollusks such as the pond snails Lymnaea and Helisoma through receptors that mediate either excitation or inhibition, but the receptors responsible have only been partially characterized. Only one of two excitatory receptor subunits cloned from Lymnaea have been characterized physiologically. Since glutamate excites motor neurons controlling one phase of feeding in Helisoma, one or more similar receptor(s) is likely to be present. The pharmacology of these receptors suggests homology with the Lymnaea receptors, which have homology with rat brain receptors. The goal of this research is to clone and sequence excitatory glutamate receptors hypothesized to be present in the buccal ganglia of both Helisoma trivolvis, and a closely related species, Biomphalaria glabrata, chosen because of its medical importance as the intermediate host of Schistosoma mansoni. In the first two years of the grant, degenerate primer PCR was used to obtain short overlapping DNA sequences representing the transmembrane regions of two Helisoma excitatory glutamate receptors. RACE PCR was used to extend these sequences to the 3 end, and part of the way to the 5 end. Sequences obtained from AMPA receptor primers have significant sequence identity to the Lym-eGluR1 receptors. Sequences obtained with both AMPA and KA receptor primers are homologous to Aplysia GluR7. We plan to use the last 4 months of funding this year to finish these two clones and to obtain glutamate receptor sequences from Biomphalaria.