Glutamatergic Transmission Is Sustained at a Later Period of Development of Medial Nucleus of the Trapezoid Body–Lateral Superior Olive Synapses in Circling Mice

Abstract

Synaptic transmission between the medial nucleus of the trapezoid body (MNTB) and the lateral superior olive (LSO) was investigated in circling mice, an animal model for inherited deafness, using the voltage-clamp technique. In postnatal day 9 (P9)ϳP11 homozygous (cir/cir) circling mice, perfusion with 10 M DL-APV and 10 M CNQX reduced the 10 min average of postsynaptic currents (PSCs) to 8.8 Ϯ 3.0% compared with controls (n ϭ 6). In heterozygous (؉/cir) mice in the same age range, the 10 min PSCs average was reduced to 87.5 Ϯ 3.7% compared with controls (n ϭ 7). In P0ϳP2 homozygous (cir/cir) and heterozygous (ϩ/cir) mice, the 10 min PSCs averages were 11.0 Ϯ 2.6% (n ϭ 9) and 84.1 Ϯ 4.6% (n ϭ 11), respectively. The effects of a glutamate antagonist mixture were almost the same in single fiber stimulation of P9ϳP11 mice, reducing mean PSCs to 5.2 Ϯ 3.1% (homozygous (cir/cir) mice, n ϭ 8) and 78.3 Ϯ 4.3% (heterozygous (ϩ/cir) mice, n ϭ 12). Immunohistochemical study revealed that glycine receptor (GlyR) immunoreactivity in heterozygous (ϩ/cir) mice was more prominent than in homozygous (cir/cir) mice, while immunoreactivities of NR1 and NR2A-type NMDAR of P16 homozygous (cir/cir) mice were more prominent than in heterozygous (ϩ/cir) mice of the same age. No significant difference was found in the immunoreactivity of NR2B-type NMDAR. These results indicate that glutamatergic transmission is sustained at a later period of developing MNTB-LSO synapses in homozygous (cir/cir) mice.

Characteristics of K+Outward Currents in the Cochlear Outer Hair Cells of Circling Mice within the First Postnatal Week

“…The data presented were obtained from pups between P0 and P6. Genotypes were assessed by polymerase chain reaction analysis according to our previous report [ 8 ]. The Dankook University Institutional Animal Care and Use Committee (DUIAC) approved this study.…”

Immunohistochemical Localization of Calbindin D28k, Parvalbumin, and Calretinin in the Superior Olivary Complex of Circling Mice

“…In order to keep sustained sequences of MNTB neuron action potentials at high rates, rapid and potent Ca 2+ buffer may be necessary since MNTB neurons were almost constantly exposed to excitatory glutamate [Englitz et al, 2009]. In support of these data, glutamatergic transmission at MNTB-LSO synapses has persisted in cir / cir mice [Hong et al, 2008].…”

“…Heterozygous (+/ cir ) females were mated with homozygous (cir/cir) males, and their pups (P16) were used for this study. Details were described in a previous report [Hong et al, 2008]. Animals were provided a commercial diet and water ad libitum under controlled temperature, humidity, and lighting conditions (22 ± 2 ° C, 55 ± 5% humidity, and 12-h light/12-h dark cycle).…”

“…More than 6 SCO sections (from rostral to caudal) per mouse were randomly selected from each group and stained in a 6-well plate simultaneously to eliminate conflict between different experimental conditions. Immunohistochemistry was conducted in accordance with the free-floating method described earlier [Hong et al, 2008]. Briefly, polyclonal anti-rabbit CB (AB1778; Millipore, USA), polyclonal anti-rabbit PV (PV 25; Swant, Switzerland), and polyclonal anti-goat CR (AB1550; Millipore, USA) antibodies were used as primary antibodies for staining.…”

Vesicular glutamate transporter 3 is strongly upregulated in cochlear inner hair cells and spiral ganglion cells of developing circling mice

“…At least three animals were included in each experiment. The genotype of homozygous (cir/cir) mice was assessed with polymerase chain reaction analysis according to our previous report [9]. The animals were maintained at the Animal Facility of Dankook University.…”