METABOTROPIC GLUTAMATE-RECEPTOR EXPRESSION IN OLFACTORY RECEPTOR NEURONS FROM THE CHANNEL CATFISH, ICTALURUS-PUNCTATUS

Metabotropic glutamate receptors (mGluRs) were identified in olfactory receptor neurons of the channel catfish, Ictalurus punctatus, by poly merase chain reaction. DNA sequence analysis confirmed the presence of two subtypes, mGluR1 and mGluR3, that were coexpressed with each othe r and with the putative odorant receptors within single olfactory rece ptor neurons. Immunocytochemical data showed that both mGluR subtypes were expressed in the apical dendrites and some cilia of olfactory neu rons. Pharmacological analysis showed that antagonists to each mGluR s ubtype significantly decreased the electrophysiological response to od orant amino acids. alpha-Methyl-L-CCG1/(2S,3S,4S)-2-methyl-2- (carboxy cyclopropyl )glycine (MCCG), a known antagonist to mGluR3, and (S)-4-c arboxyphenylglycine (S-4CPG), a specific antagonist to mGluR1, each si gnificantly reduced olfactory receptor responses to L-glutamate. S-4CP G and MCCG reduced the glutamate response to 54% and 56% of control, r espectively, which was significantly greater than their effect on a ne utral amino acid odorant, methionine. These significant reductions of odorant response by the antagonists, taken with the expression of thes e receptors throughout the dendritic and ciliated portions of some olf actory receptor neurons, suggest that these mGluRs may be involved in olfactory reception and signal transduction. (C) 1998 John Wiley & Son s, Inc.