Dendritic inhibition terminates plateau potentials in CA1 pyramidal neurons.

In CA1 pyramidal neurons (CA1-PYRs), plateau potentials control synaptic plasticity and the emergence of place cell identity. Here, we show that dendritic inhibition terminates plateaus in an all-or-none manner. Plateaus were initially resistant to inhibition but became increasingly susceptible to termination as they progressed. Between two distinct subtypes of dendrite-targeting interneurons, OLM generated slower postsynaptic currents that terminated plateaus more effectively than OLM. Voltage-gated Ca channels (VGCCs) were necessary for plateaus, which were prolonged by blocking small-conductance Ca-activated K channels (SK). A single-compartment model with these two conductances recapitulated core experimental findings and provided a mechanistic explanation for terminations. Plateaus arose from VGCCs maintained in the active state by sustained Ca influx, a positive feedback loop that was quasi-balanced by . Inhibition terminated plateaus by driving the membrane potential below a dynamic threshold to deactivate VGCCs and end the positive feedback loop. Lastly, two-photon Ca imaging showed that plateaus evoke large dendritic Ca transients that were graded by terminations. Overall, our results demonstrate how the feedback inhibitory circuit interacts with intrinsic cellular mechanisms to regulate plateau potentials and shape dendritic Ca signals in CA1-PYRs.