An intracellular study of dendrodendritic inhibitory synapses on mitral cells in the rabbit olfactory bulb.

Abstract

In the rabbit olfactory bulb, intracellular potentials were recorded from mitral cells and from neurons in the granule cell layer (GCL) following lateral olfactory tract (LOT) stimulation. Most recordings from mitral cells showed large (5-21 mV) and prolonged (60-650 ms) IPSP [inhibitory postsynaptic potential] subsequent to the antidromic spikes. These IPSP decreased in amplitude and then reversed in polarity by progressive increase in hyperpolarizing current applied intracellularly. They were accompanied by a prominent and long lasting (up to 100 ms) conductance increase of the mitral cell membrane. Reversed IPSP of mitral cells having quite different time courses from the original hyperpolarizing IPSP suggested that the inhibitory synapses are widely distributed on the soma and dendrites. E[excitatory]PSP could be recorded from GCL cells whose onset latency was approximately 0.6 ms shorter than that of mitral cell IPSP. Comparison of the behavior of EPSP in GCL cells and that of mitral cell IPSP under various conditions of LOT stimulation suggested that these GCL cells are the inhibitory interneurons mediating mitral cell inhibition. Apparently there are dendrodendritic pathways for activation of granule cells and subsequent inhibition of mitral cells.