Abstract
The lateral superior olive (LSO) is the first auditory center that processes differences in the sound level between the two ears. Here we report the developmental changes in metabotropic glutamate receptor (mGluR)-mediated presynaptic inhibition of GABAergic/glycinergic synaptic transmission onto developing rat LSO neurons using conventional whole-cell patch clamp technique. In addition to a developmental switch of MNTB-LSO afferents from GABAergic to glycinergic IPSCs during development, immature MNTB-LSO synapses could release glutamate with GABA/glycine. Bath application of DCG IV, a selective mGluR 2/3 (group II) agonist, greatly reduced IPSC amplitude in neonatal (< P5) with a significant change in the paired-pulse ratio, which was eliminated in the presence of group II antagonist, suggesting that DCG IV acts presynaptic mGluR 2/3 leading to reduce the release probability of GABA and/or glycine release from presynaptic nerve terminals. However, the mGluR-mediated presynaptic inhibition was gradually reduced with postnatal development, in which DCG IV had little effect on MNTB-evoked IPSCs recorded from P16-18 LSO neurons. At P5 LSO neurons, presynaptic mGluR could be activated by endogenous glutamate released from the ipsilateral anteroventral cochlear nucleus (AVCN) afferent, but not from MNTB terminals. Based on these results, the functional roles of presynaptic mGluR in the development of LSO neurons will be further investigated and discussed. [J Physiol Sci. 2006;56 Suppl:S171]
