Central auditory synapse alterations in mice with enhanced and suppressed medial olivocochlear efferent activity

CHEQUER D, WENQING H, GOMEZ-CASATI ME, HUA Y, ELGOYHEN AB AND DI GUILMI MN

San Luis

Congreso; XXXVIII Annual Meeting of the Argentine Society for Neuroscience; 2023

Sociedad Argentina de Investigacion en Neurociencias

Spontaneous activity in the immature inner ear plays a critical role in the development ofprecise connectivity in the central auditory system. This is modulated by the medialolivocochlear system (MOC). In mice with enhanced MOC activity (KI), synapticdysfunctions were observed in the medial nucleus of the trapezoid body (MNTB) (DiGuilmi et al., 2019). In the present work, we performed electrophysiological recordingsand morphological 3D reconstructions of the calyx of Held (CH)-MNTB synapse at P12-14 in three mouse models: WT, KI and KO (which lacks MOC activity). Short termsynaptic plasticity (STP) experiments displayed a significant higher rate of depression inthe KI than WT and KO (10Hz; �WT=2.99±0.21s, �KI=1.96±0.24s, �KO=3.42±0.56s, n=16,ANOVA, p=0,001; 100Hz; �WT=4.89±2.42s, �KI=2.32±0.98s, �KO=7.09±1.58s, n=16,ANOVA, p=0.013). Morphological analysis of CHs in WT and KI mice by volumetricreconstructions from serial electron microscopy images at P25 showed that the KI has alower proportion of complex CHs compared to WT (69% vs. 83%). Considering that theCH morphology determines the STP, the larger depression rate in the KI aligns with theobservation that principal MNTB neurons receive innervation from CHs with simplemorphologies (Grande & Wang, 2011). The present results suggest that the transientcochlear efferent innervation to IHCs during the critical period is involved in setting thecorrect synaptic transmission at central auditory nuclei.