An analysis of the effects of excitatory amino acid receptor antagonists on evoked field potentials in the olfactory bulb

Abstract

The effects of excitatory amino acid antagonists on extracellular field potentials in the olfactory bulb produced by lateral olfactory tract stimulation were analysed in vivo. The compounds tested D-2-amino-5-phosphonovalerate, L-(+)2-amino-4-phosphonobutyrate, gamma-D-glutamylglycine, L-glutamic acid diethylester and cis-2,3-piperidine dicarboxylic acid, were administered by brain dialysis. Of the compounds tested, only cis-2,3 piperidine-dicarboxylic acid and gamma-D-glutamylglycine were able to suppress the synaptic excitation of granule cells. This pharmacological profile suggests the involvement of non-N-methyl-D-aspartate receptors. However, the suppression was accompanied by a reduction in the amplitude of the presynaptic volley. A second finding was that D-2-amino-5-phosphono-valerate and gamma-D-glutamyl glycine attenuated granule cell mediated inhibition of mitral cells, suggesting the involvement of N-methyl-D-aspartate-sensitive receptors. The possibility that mitral cells and that either centrifugal fibres, or an intrinsic olfactory bulb feedback loop might use an excitatory amino acid as its neurotransmitter is therefore discussed.