On the composition, properties and physiological roles of K+ currents found at a central auditory synapse

The medial nucleus of the trapezoid body (MNTB) forms part of the circuits involved in sound source localisation. It receives the synapse called the calyx of Held and rapidly transmits this information to other neurons in the circuit. This thesis characterises the composition and properties of the K+ channels found in the MNTB neuron and shows how they regulate action potential firing.;I have shown that a large K+ leak current (0.8nA at +10mV) contributes to the resting membrane potential and action potential repolarisation. Kv1 channels open with small depolarisations and prevent the MNTB from firing multiple action potentials in response to its giant synaptic input. Kv3 channels make a large contribution to the outward current and promote brief action potentials by rapid repolarisation. A smaller A-type current is also present (probably mediated by a Kv4 subunit). However this current is largely inactivated at rest.;I show that the major conductance contributing to the outward K + current in the MNTB is mediated by Kv2.2 containing channels. These channels are localised to the initial segment of the axon. Due to their slow kinetics, they contribute little to a single action potential. Rather their activity accumulates through high frequency trains, providing a hyperpolarisation of the inter-spike potential, necessary to promote recovery of Nav channels from inactivation. Thus the Kv2.2 channels facilitate sustained high frequency firing.