Membrane-based gating mechanism for auditory information in the mouse inferior colliculus

Abstract

In order to analyse the intrinsic membrane-based mechanisms of neurons in the mouse inferior colliculus that are likely to contribute to the processing of acoustic signals, this study use whole cell patch clamp recordings in brain slices to characterize the dependence of depolarization evoked inward and outward currents on different prestimulus membrane potentials. Eighty-seven of one-hundred and one inferior colliculus neurons reacted during depolarizing voltage steps from a holding potential of −60 or −80 mV with a fast inactivating inward current followed by a slow inactivating outward current (type I neurons). Fourteen neurons showed outward currents but no inward currents during depolarizing voltage steps from a holding potential of −60 mV (type II neurons). However, these neurons reacted with TTX-sensitive fast inward currents, if the holding potential was set to −80 mV before the voltage steps occurred. The resting potential was not significantly different between type I (−64.3±3.5 mV) and type II (62.7±2.9 mV) neurons. If the neuronal behavior is the same in vivo, type II neurons must receive an inhibition which hyperpolarizes the membrane potential prior to the arrival of excitatory inputs to be able to generate action potentials. This finding suggests a further function for feedforward inhibition in the IC, namely to open a gate for transmission of excitatory information within a distinct time window. With this membrane based gating mechanism it is possible to detect time related information within an acoustic stimulus (e. g. coincidence) which is an essential task e. g. in the neuronal processing of speech.