Disruption of lateral olivocochlear neurons with a dopaminergic neurotoxin depresses spontaneous auditory nerve activity

- The neurotoxin MPTP disrupts lateral olivocochlear (LOC) neurons in the cochlea.
- Sound-evoked neural potentials were reduced in amplitude after MPTP.
- Spontaneous neural firing was also decreased by MPTP disruption of LOC neurons.
- The net effect of the LOC innervation on the auditory nerve is excitatory.
- Loss of LOC input decreases both spontaneous and sound-driven activity.

Neurons of the lateral olivocochlear (LOC) system project from the auditory brainstem to the cochlea, where they synapse on radial dendrites of auditory nerve fibers. Selective LOC disruption depresses sound-evoked auditory nerve activity in the guinea pig, but enhances it in the mouse. Here, LOC disruption depressed spontaneous auditory nerve activity in the guinea pig. Recordings from single auditory nerve fibers revealed a significantly reduced proportion of fibers with the highest spontaneous firing rates (SRs) and an increased proportion of neurons with lower SRs. Ensemble activity, estimated using round window noise, also decreased after LOC disruption. Decreased spontaneous activity after LOC disruption may be a consequence of reduced tonic release of excitatory transmitters from the LOC terminals in guinea pigs.