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 GABAB receptor-mediated presynaptic inhibition of GABAergic and/or glycinergic synaptic transmission onto developing rat LSO neurons. MNTB-evoked GABAergic and/or glycinergic inhibitory postsynaptic currents (IPSCs) were recorded from LSO neurons of acute brain stem slices at postnatal (P) 2 to 20 day old rats divided in three groups (P2–6, P8–12, P16–20) using conventional whole-cell patch clamp technique. The pharmacological isolation of MNTB-evoked inhibitory transmission revealed a developmental switch from GABAergic to glycinergic IPSCs during these developmental stages. Bath application of baclofen, a selective GABAB receptor agonist, greatly reduced IPSC amplitude in neonatal (< P6) with a significant change in the paired-pulse ratio, and these effects were eliminated in the presence of GABAB receptor antagonist, suggesting that baclofen acts presynaptic GABAB receptors to reduce the release probability of GABA and/or glycine from presynaptic nerve terminals. However, the GABAB receptor-mediated presynaptic inhibition was gradually reduced with postnatal development so that baclofen had little effect on MNTB-evoked IPSCs recorded from P16–20 LSO neurons. Based on these results, the functional roles of presynaptic GABAB receptors in the development of LSO neurons will be further investigated and discussed. [Jpn J Physiol 55 Suppl:S132 (2005)]
