Rate thresholds determine the precision of temporal integration in principal cells of the ventral cochlear nucleus

Abstract

The three types of principal cells of the ventral cochlear nucleus (VCN), bushy, octopus, and T stellate, differ in the detection of coincidence among synaptic inputs. To explore the role of the action-potential-generation mechanism in the detection of coincident inputs, we examined responses to depolarizing currents that increased at varying rates. To fire an action potential, bushy cells, likely of the globular subtype, had to be depolarized faster than 4.8 ± 2.8 mV/ms, octopus cells faster than 9.5 ± 3.6 mV/ms, and T stellate cells fired irrespective of the rate of depolarization. The threshold rate of depolarization permitted definition of a time window over which depolarization could contribute to generating action potentials. This integration window differed between cell types. It was 5.3 ± 1.8 ms for bushy cells and 1.4 ± 0.3 ms for octopus cells. T Stellate cells fired action potentials in response to even slow depolarizations, showing that their integration window was unlimited so that temporal summation in these cells is limited by the time course of synaptic potentials. The rate of depolarization threshold in octopus and bushy cells was decreased by α-dendrotoxin while T stellate cells were largely insensitive to α-dendrotoxin indicating that low-voltage-activated K + conductances ( g KL) are important determinants of the integration window.