Lateral olivocochlear (LOC) neurons of the mouse LSO receive excitatory and inhibitory synaptic inputs with slower kinetics than LSO principal neurons

We examined membrane properties and synaptic responses of neurons in the mouse lateral superior olivary nucleus (LSO). Two clear populations were identified consistent with: principal neurons which are involved in detecting interaural intensity differences (IIDs) and efferent neurons of the lateral olivocochlear (LOC) system which project to the cochlea. Principal neurons fired a short latency action potential (AP) often followed by an AP train during maintained depolarization. They possessed sustained outward K+ currents, with little or no transient K+ current (IA) and a prominent hyperpolarization-activated non-specific cation conductance, IH. On depolarization, LOC neurons exhibited a characteristic delay to the first AP. These neurons possessed a prominent transient outward current IA, but had no IH. Both LOC and principal neurons received glutamatergic and glycinergic synaptic inputs. LOC synaptic responses decayed more slowly than those of principal neurons; the mean decay time constant of AMPA receptor-mediated EPSCs was around 1 ms in principal neurons and 4 ms in LOC neurons. Decay time constants for glycinergic IPSCs were around 5 ms in principal neurons and 10 ms in LOC neurons. We conclude that principal cells receive fast synaptic responses appropriate for integration of IID inputs, while the LOC cells possess excitatory and inhibitory receptors with much slower kinetics.

Research highlights
► LOC neurons have membrane properties distinct from LSO principal neurons.
► LOC neurons in mouse LSO can be identified by their membrane properties.
► LOC neurons receive glutamatergic and glycinergic synaptic inputs.
► Synaptic responses in LOC neurons are smaller than in principal LSO neurons.
► Synaptic responses in LOC neurons are slower than in principal LSO neurons.