Olfactory nerve stimulation activates rat mitral cells via NMDA and non-NMDA receptors in vitro

THE neurotransmitter(s) and receptors mediating excitatory transmission at the mammalian olfactory nerve-mitral cell synapse were investigated using extracellular recordings in rat olfactory bulb slices. Single shocks applied to the olfactory nerve elicited both a short latency and a delayed excitatory response in mitral cells. Both responses were blocked after bath application of kynurenic acid, a broad-spectrum glutamate receptor antagonist, or DNQX, a preferential non-NMDA receptor antagonist. The specific NMDA receptor antagonist AP5 selectively attenuated the delayed, but not the initial excitation. These results suggest that glutamate is the major excitatory transmitter in the mammalian olfactory nerve, and excites mitral cells via NMDA and non-NMDA receptors.