Why can a fast-spiking interneuron fire at hundreds of hertz while a pyramidal cell slows down? · Lobeworks/17

Because of the potassium channels each one expresses.

Why can a fast-spiking interneuron fire at hundreds of hertz while a pyramidal cell slows down?

Because of the potassium channels each one expresses. Parvalbumin interneurons carry Kv3 channels (genes KCNC), which open and close very fast and do not inactivate: the spike is narrow, the membrane is reset at once and the next spike can follow almost immediately, with little adaptation. Most pyramidal cells instead carry slow calcium-activated potassium channels and the M-current, whose growing outward current IadaptI_{\text{adapt}}Iadapt​ makes each new spike harder, so their trains slow down.