Distinct K currents result in physiologically distinct cell types in the inferior colliculus of the rat

The inferior colliculus (IC) processes auditory information ascending from the brainstem. The response of the IC to this information and its ability to transform it is partly determined by the types of ionic currents that generate the intrinsic discharge patterns of IC neurons and their susceptibility to changes in the external environment. We have used whole-cell patch-clamp techniques on IC neurons in rat brain slices to characterize the potassium currents present and to correlate them with the firing patterns observed. Neurons in the IC can be classified into six physiologically distinct cell types. Each of these cell types has a firing pattern that is generated by a unique potassium current and set of cellular parameters. Sustained-regular cells show mainly delayed rectifier K+ channels. Onset cells have a unique high-threshold tetraethylammonium-sensitive K+ current. Pause-build cells have an A-current. Rebound-regular cells have calcium-dependent rebound depolarizations. Rebound-adapting cells have both an apamin-sensitive calcium-dependent K+ current and a calcium-dependent rebound depolarization. Transient-rebound cells have a charybdotoxin-sensitive calcium-dependent K+ current and a calcium-dependent rebound. Our data suggest that there would be similarities as well as differences among IC neurons in their responses to excitatory or inhibitory inputs. Furthermore, some cells are likely to show little or no plasticity and behave as simple relays of temporal and intensity information, whereas others are likely to transform their inputs.