Abstract:
Neuronal processing is classically organized into dendritic input, somatic integration and axonal output. We found that in about half of all murine CA1 pyramidal cells the axon emerges from basal dendrites instead of the somatic compartment, directly coupling input to output and bypassing somatic integration. We show that active properties of these cells and the fine structure of the axon initial segment (AIS) are modified by axonal localization, implying that the efficiency of the AIS as the site of action potential generation is altered. Computer simulations predict that synaptic input on the axon-connected dendrite (AcD) is privileged over simple dendrites (SD) which are directly connected to the soma. We demonstrate by multi-photon glutamate uncaging that synaptic input to axon-connected dendrites generates action potentials with lower activation threshold as compared to SDs. Thus, our findings suggest that systematic variation of the axonal origin offers electrically privileged input channels within the hippocampal structure.