Investigation of Developmental Changes of Convergence Ratios of MNTB-LSO Synapses in Circling Mice

Kim, So Youn; Ahn, Seung Cheol

Abstract

The developmental changes of convergence ratios of medial nucleus of trapezoid body (MNTB) axons to single lateral superior olive (LSO) neuron were investigated using voltage clamp technique in homologous (cir/cir) circling mice, animal model for the congenital deafness with autosomal recessive inheritance. As the developmental reduction of convergence ratio reported in rats indicates the presence of synaptic refinement, we aimed to find out whether the similar reduction of convergence ratio also occurs in circling mice. Heterologous (+/cir) mice were used as control and mice younger than postnatal (P) day 4 or older than P9 were used. The convergence ratios of MNTB axons to single LSO neuron were 29.16+/-2.7 (n=12, P9) in homologous (cir/cir) mice, while they were 37.89+/-3.8 (n=9, P9) in heterozygous (+/cir) mice. The significant changes were observed only in heterozygous (+/cir) mice, which indicated that synaptic refinement of MNTBLSO synapses occurs in heterozygous (+/cir) mice, not in homozygous (cir/cir) mice. Considering homologous (cir/cir) mice being animal model for the congenital deafness, our data might contribute to the understanding of developmental changes of brain stem auditory circuits of congenitally deaf patients.