Publications

Abstract

In the mouse brainstem cochlear nucleus, the auditory nerve to bushy cell synapse (endbulb of Held) is specialised for rapid, high-fidelity transmission. Development of this synapse is modulated by auditory nerve activity. Here we investigate the role of spontaneous auditory nerve activity in synaptic transmission using deafness (dn/dn) mutant mice that have abnormal hair cells and lack spontaneous auditory nerve activity. Evoked and miniature alpha amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor-mediated excitatory post-synaptic currents (eEPSCs, mEPSCs) were compared in deafness and normal mice before the age of hearing onset (postnatal day 7-11: P7-11) using variance-mean, miniature event and tetanic depression analyses. Amplitudes were significantly greater in deafness mice for eEPSCs (2.1-fold), mEPSCs (1.4-fold) and quantal amplitudes (1.5-fold). eEPSCs in deafness mice decayed more rapidly with increasing age, indicating an input-independent transition in post-synaptic AMPA receptor properties. A comparison of normal mice before and after the onset of hearing showed a change in synaptic parameters with an increase in eEPSC (1.7-fold), mEPSC (1.6-fold) and quantal amplitude (1.7-fold) after hearing onset while release probability remained constant (0.5). Overall, the results in deafness mice suggest that synaptic strength is altered in the absence of spontaneous auditory nerve activity.