Figure 1.

An insulin-like growth factor 1 receptor (IGF1R) antagonist JB1 induced the loss of ribbon synapses in cochlear explant cultures. Cochlear explants of P4 mice were exposed to JB1 at a concentration of 25, 50, 100, or 150 μg/ml for 24 h (A). (B–D) Maximal-intensity projection images with z-stack of ribbon synapses in control specimens that were cultured without JB1. Panels (E–J) are maximal-intensity projection images of the degeneration of ribbon synapses in specimens cultured with JB1 at concentrations of 50 and 150 μg/ml, respectively. Arrows show the postsynaptic receptor patches and dotted lines indicate the location of an IHC. (K) JB1 showed significant effects on both presynaptic ribbons (p < 0.001 by one-way ANOVA) and postsynaptic receptor patches (L; p = 0.004 by one-way ANOVA). Tukey’s post hoc test revealed significant losses at concentrations of 50 (p = 0.001), 100 (p < 0.001), and 150 μg/ml (p < 0.001) in the number of presynaptic ribbons, and at concentrations of 50 (p = 0.032) and 150 μg/ml (p = 0.002) in the number of postsynaptic receptor patches, in comparison with controls which were cultured without JB1. (M–R) No inner hair cell (IHC) or spiral ganglion neuron (SGN) loss was found at any JB1 concentrations (p = 0.428 by one-way ANOVA for IHC, p = 0.730 by one-way ANOVA for SGN). Scale bars: 10 μm. Data are expressed as mean (digits at the top of each bar) ± SD. The digits at the bottom of each bar represent the sample number. *p < 0.05; **p < 0.01 with Tukey’s post hoc test. P4, postnatal day 4; IHC, inner hair cell; SGN, spiral ganglion neuron; SD, standard deviation; ANOVA, analysis of variance.