Spikelets in Pyramidal Neurons: Action Potentials Initiated in the Axon Initial Segment That Do Not Activate the Soma
Fig 5
Orthodromic and antidromic-like spikelets in a model cell with the axon attached to a basal dendrite.
A: Neuron model with fluctuating somatic inputs as in Fig 1 (red: excitatory, blue: inhibitory), except that the axon is attached to a basal dendrite. Additionally, the model cell was stimulated every 500 ms with a synaptic conductance gsyn located at the axon-carrying basal dendrite, distally to the AIS-connecting site (orange, see Methods). B: Left: example somatic spikelets; shown are 20 orthodromic (black, evoked with somatic inputs) and 20 antidromic-like spikelets(orange, evoked with dendritic input). Right: phase plots of the spikelets shown in the left panel. C: Spikelet-triggered averages for all orthodromic spikelets (N = 137, dashed lines) and all antidromic-like spikelets (N = 100, dotted lines) generated within 100 s of simulation. C1: Mean orthodromic (dashed black) and antidromic-like (dotted orange) spikelet, aligned to the voltage-threshold crossing at the AIS (as in Fig 1H). C2: Mean excitatory (red) and inhibitory (blue) conductances for orthodromic (dashed lines) and antidromic-like (dotted lines) spikelets. C3: Mean effective synaptic reversal potentials (as in Fig 1H) for the orthodromic (dashed line) and antidromic-like (dotted line) spikelets.