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A more mixed distribution of high- and low-threshold channel subtypes at the axon initial segment (AIS) of SST cells may lead to these differences.

The minimal activation voltage of axonal channels in SST was substantially higher (∼7 mV) than in PV cells, consistent with differences in AP thresholds. Patch-clamp recording from mouse prefrontal cortical slices showed that axonal but not somatic Na + channels exhibit different voltage-dependent properties. We focused on two predominant interneuron types in neocortex: parvalbumin (PV)- and somatostatin (SST)-expressing neurons. However, it remains unclear what determines AP initiation in different interneurons. Error bars represent s.e.m.Īction potential (AP) generation in inhibitory interneurons is critical for cortical excitation-inhibition balance and information processing. No significant difference was found between the control and α-DTx groups. (D) Voltage threshold changes of single APs induced by 2-ms current pulses in both neuronal types before and after α-DTx application. (Right) Voltage threshold changes of the first AP in both neuronal types before and after application of 100 nM α-DTx. Delay in SST neruons is the duration of the depolarizing ramp before the first AP. (C, Left) Averaged delay of the first AP in both neuronal types before and after application of 100 nM α-DTx.

The duration of the depolarizating ramp before the first AP was not affected. (Right) The same neuron after application of 100 nM α-DTx. (B, Left) V m responses of a SST neuron to 10-pA (threshold current) and 200-pA step current injections. The threshold current decreased to 100 pA, and the delay of the first AP (indicated by the gray bar) was diminished. (A, Left) V m responses of a PV neuron to 250-pA (threshold current) and 400-pA step current injections. Figure S1: Blocking K V1 does not change the threshold of APs evoked by brief and strong stimulation.