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

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.

The correlation between the effects of propofol on the auditory brainstem response and the postsynaptic currents of the auditory circuit in brainstem slices in the rat / 대한마취과학회지

BACKGROUND: Although there have been reports showing the changes of the auditory brainstem response (ABR) waves by propofol, no detailed studies have been done at the level of brainstem auditory circuit. So, we studied the effects of propofol on the postsynaptic currents of the medial nucleus of the trapezoid body (MNTB)-lateral superior olive (LSO) synapses by using the whole cell voltage clamp technique and we compared this data with that obtained by the ABR. METHODS: 5 rats at postnatal (P) 15 days were used for the study of the ABR. After inducing deep anesthesia using xylazine 6 mg/kg and ketamine 25 mg/kg, the ABRs were recorded before and after intraperitoneal propofol injection (10 mg/kg) and the effects of propofol on the latencies of the I, III, and V waves and the I-III and III-V interwave intervals were evaluated. Rats that were aged under P11 were used in the voltage clamp experiments. After making brainstem slices, the postsynaptic currents (PSCs) elicited by MNTB stimulation were recorded at the LSO, and the changes of the PSCs by the bath application of propofol (100 microM) were monitored. RESULTS: We found small, but statistically significant increases in the latencies of ABR waves III and V and the interwave intervals of I-III and III-V by propofol. However, no significant changes were observed in the glycinergic or glutamatergic PSCs of the MNTB-LSO synpases by the application of propofol (100 microM). CONCLUSIONS: Glycinergic or glutamatergic transmission of the MNTB-LSO synapses might not contribute to the propofol-induced changes of the ABR.