FORWARD AND BACKWARD PROPAGATION OF DENDRITIC IMPULSES AND THEIR SYNAPTIC CONTROL IN MITRAL CELLS

The site of impulse initiation is crucial for the integrative actions of mammalian central neurons, but this question is currently controver sial. Some recent studies support classical evidence that the impulse always arises in the soma-axon hillock region, with back-propagation t hrough excitable dendrites, whereas others indicate that the dendrites are sufficiently excitable to initiate impulses that propagate forwar d along the dendrite to the soma-axon hillock. This issue has been add ressed in the olfactory mitral cell, in which excitatory synaptic inpu t is restricted to the distal tuft of a single primary dendrite. In ra t olfactory bulb slices, dual whole cell recordings were made at or ne ar the soma and from distal sites on the primary dendrite. The results show that the impulse can be initiated in either the soma-axon hilloc k or in the distal primary dendrite, and that the initiation site is c ontrolled physiologically by the excitatory synaptic inputs to the dis tal tuft and inhibitory synaptic inputs near the soma.