Firing properties of GABAergic versus non-GABAergic vestibular nucleus neurons conferred by a differential balance of potassium currents

Neural circuits are composed of diverse cell types, the firing properties of which reflect their intrinsic ionic currents. GABAergic and non-GABAergic neurons in the medial vestibular nuclei, identified in GIN and YFP-16 lines of transgenic mice, respectively, exhibit different firing properties in brain slices. The intrinsic ionic currents of these cell types were investigated in acutely dissociated neurons from 3- to 4-wk-old mice, where differences in spontaneous firing and action potential parameters observed in slice preparations are preserved. Both GIN and YFP-16 neurons express a combination of four major outward currents: Ca²⁺-dependent K⁺ currents (I_KCa), 1 mM TEA-sensitive delayed rectifier K⁺ currents (I_1TEA), 10 mM TEA-sensitive delayed rectifier K⁺ currents (I_10TEA), and A-type K⁺ currents (I_A). The balance of these currents varied across cells, with GIN neurons tending to express proportionately more I_KCa and I_A, and YFP-16 neurons tending to express proportionately more I_1TEA and I _10TEA. Correlations in charge densities suggested that several currents were coregulated. Variations in the kinetics and density of I _1TEA could account for differences in repolarization rates observed both within and between cell types. These data indicate that diversity in the firing properties of GABAergic and non-GABAergic vestibular nucleus neurons arises from graded differences in the balance and kinetics of ionic currents.