1 2 3 4 5 Comparative post - hearing development of inhibitory inputs to the 6 lateral superior olive in gerbils and mice 7 8 9

41 Interaural intensity differences are analyzed in neurons of the lateral superior olive (LSO) by 42 integration of an inhibitory input from the medial nucleus of the trapezoid body (MNTB), activated by 43 sound from the contralateral ear, with an excitatory input from the ipsilateral cochlear nucleus. The 44 early postnatal refinement of this inhibitory MNTB-LSO projection along the tonotopic axis of the LSO 45 has been extensively studied. However, little is known to what extent physiological changes at these 46 inputs also occur after the onset of sound evoked activity. 47 Using whole-cell patch-clamp recordings of LSO neurons in acute brainstem slices we analyzed the 48 developmental changes of inhibitory synaptic currents evoked by MNTB fiber stimulation occurring 49 after hearing onset. We compared these results in gerbils and mice, two species frequently used in 50 auditory research. Our data show that neither the number of presumed input fibers nor the 51 conductance of single fibers significantly changed after hearing onset. Also the amplitude of miniature 52 inhibitory currents remained constant during this developmental period. In contrast, the kinetics of 53 inhibitory synaptic currents greatly accelerated after hearing onset. We conclude that tonotopic 54 refinement of inhibitory projections to the LSO is largely completed before the onset of hearing, 55 whereas acceleration of synaptic kinetics occurs to a large part after hearing onset and might thus be 56 dependent on proper auditory experience. Surprisingly, inhibitory input characteristics as well as basic 57 membrane properties of LSO neurons were rather similar in gerbils and mice.