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 ^Ndnf generated slower postsynaptic currents that terminated plateaus more effectively than OLM ^α2 . Voltage-gated Ca ²⁺ channels (VGCCs) were necessary for plateaus, which were prolonged by blocking small-conductance Ca ²⁺ -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 ²⁺ influx, a positive feedback loop that was quasi-balanced by I _SK . 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 ²⁺ imaging showed that plateaus evoke large dendritic Ca ²⁺ 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 ²⁺ signals in CA1-PYRs.