Activation and inhibition of olfactory bulb neurones by anterior commissure volleys in the rabbit.

Abstract

In the rabbit olfactory bulb, analysis was carried out on intracellular potentials recorded from mitral cells and neurons in the granule cell layer (GCL cells) in addition to the extracellular field potentials in the olfactory bulb elicited by anterior commissure (AC) stimulation. Most mitral cell recordings showed IPSP [inhibitory postsynaptic potential] with latency of 7-11 ms following AC stimulation. These IPSP were similar to those evoked by lateral olfactory tract (LOT) stimulation in their sensitivity to internally applied current and showed asymmetrical reversal during application of the hyperpolarizing current. Volleys in the AC elicited E[excitatory]PSP in type 1 GCL cells whose characteristics were in agreement with those of inhibitory interneurons inferred from the analyses of mitral cell IPSP. These type 1 GCL cells may be the common inhibitory interneurons (presumably granule cells) mediating both AC-evoked and LOT-evoked IPSP in mitral cells. Conditioning AC stimulation depressed the test LOT-evoked IPSP in mitral cells and test LOT-evoked EPSP in type 1 GCL cells. Apparently LOT-evoked IPSP are mainly mediated by the dendrodendritic reciprocal synapses between mitral cell dendrites and peripheral processes of granule cells. The inhibitory mechanisms controlling mitral cell activity in the olfactory bulb were discussed.