Article Figures & Data
Figures
- Figure 1.
Characterization of mixed CBA/CaJ x C57BL/6J genetic background mice. A, ABR thresholds (expressed as back-transformed least squares means) were not significantly different between ChR2-EYFP-positive (ChR2-EYFP+) and ChR2-EYFP-negative (ChR2-EYFP–) littermates. Error bars represent 95% confidence intervals of means. B, C, ChR2 expression in inhibitory IC central nucleus neurons. B, A low-magnification image shows that the majority of inhibitory cells labeled with anti-GAD67 antibody (red) also express ChR2-EYFP labeled with anti-GFP antibody (green). White arrows show examples of double-labeled cells. The blue arrow shows a rare example of a cell that labeled with the anti-GAD antibody but did not express EYFP. Scale bar: 20 μm. C, High-magnification images of double-labeled cells. Scale bar: 20 μm.
- Figure 2.
Example RLF fitted with a curve. The maximum firing rates, slopes, and thresholds were extracted from the fitted curves for subsequent data analyses.
- Figure 3.
The effect of topical mGluR2/3 agonist LY354740 application on RLFs’ peak firing rates (A1, B1, C1), slopes (A2, B2, C2), and thresholds (A3, B3, C3). A, At the population level (n = 31), MGluR2/3 activation significantly increased the peak firing rates, steepened the slopes, and lowered the thresholds. Neurons were then assigned to two groups: those which had RLFs affected by topical mGluR2/3 agonist LY354740 (B; n = 20), and those in which mGluR2/3 activation did not have a clear effect (C; n = 11). Each neuron’s mean pre-drug and mean post-drug values are connected by gray lines; population data are summarized with boxplots (the plot presents Box–Cox transformed data); NS p > 0.05, **p < 0.001, ***p < 0.0001.
- Figure 4.
The effect of topical mGluR2/3 agonist LY354740 application on neurons’ monotonicity. All pre-drug and post-drug MIs are plotted as cumulative distributions. A, Neurons from the drug effect group (n = 20) became significantly more monotonic after drug application. B, Monotonicity did not significantly change in neurons assigned to the no drug effect group (n = 11); *p < 0.05, NS p > 0.05.
- Figure 5.
Examples of RLFs before and after topical LY354740 application. A, B, Non-GABAergic neurons. C, D, GABAergic neurons. Pre-drug RLFs are plotted in solid black, blue, and gray lines in all panels (legend only shown in panel B). Post-drug RLFs are color coded yellow, green, pink, and orange to demonstrate drug effect over time; time after drug application is indicated for each individual RLF. Error bars represent ± SEM of 10 sound stimulus presentations at each sound level.
- Figure 6.
Association between the animals’ age, sex, drug dose and the effect of topical LY354740 application on RLFs. All neurons were split into two groups: those which had RLFs affected and unaffected by mGluR2/3 activation. No significant differences were found in age (A), sex (B), and drug dose (C) between these two neuron groups; NS p > 0.05.
- Figure 7.
Examples of RLFs before and after mGluR2/3 activation: iontophoretic LY354740 ejection (A) and topical LY379268 application (B). Pre-drug RLFs are plotted in solid black, blue, and gray lines in both panels; the legend is only shown in panel B. Post-drug RLFs are color coded yellow, green, pink, and orange to demonstrate drug effect over time; time after drug application is indicated for each individual RLF. Error bars represent ± SEM of 10 sound stimulus presentations at each sound level.
- Figure 8.
The effect of topical mGluR2/3 agonist LY354740 application on spontaneous firing rates. A, Spontaneous activity significantly increased in neurons assigned to the drug effect group (n = 20). B, Spontaneous activity did not significantly change in neurons assigned to the no drug effect group (n = 11). Each neuron’s pre-drug and post-drug means are connected by gray lines; population data are summarized with boxplots (the plot presents rank-transformed spontaneous firing rates); **adj. p < 0.01, NS adj. p > 0.05.
- Figure 9.
Example recording sites labeled with Fluoro-Gold (A), Neurobiotin 350 (B), and Neurobiotin 488 (C). Dashed lines indicate the boundaries of IC and its subregions: parts of the central IC nucleus, area 1 and area 2, as well as dorsal (d) and lateral (lc) cortex. Scale bar: 500 μm.
- Figure 10.
Successfully identified recording sites plotted on the schematic IC sections arranged from caudal to rostral. Numbers under each section indicate the approximate distance in μm from the caudal surface of the IC. Dashed lines indicate the boundaries of IC subregions: parts of the central IC nucleus, area 1 and area 2, as well as dorsal (d) and lateral (l) cortex (subdivisions are labeled only in the section at 350 μm from the most caudal IC part). GABAergic neurons are marked with blue dots, non-GABAergic with orange dots. The dots additionally marked with yellow indicate neurons assigned to the drug effect group.
Tables
- Table 1
The effect of topical LY354740 application on RLFs’ peak firing rates, slopes, and thresholds
Term Statistic p value Peak firing rate Overall ANOVA Drug F(1,253) = 80.8 <0.0001 Cluster F(2,28) = 2.8 0.07 Drug-cluster interaction F(2,253) = 44.3 <0.0001 Pairwise comparisons with clusters Cluster #1: pre-drug–post-drug t(253) = 10.7 <0.0001 Cluster #2: pre-drug–post-drug t(253) = 5.9 <0.0001 Cluster #3: pre-drug–post-drug t(253) = −1.8 0.07 Slope Overall ANOVA Drug F(1,253) = 13.9 <0.001 Cluster F(2,28) = 0.9 0.4 Drug-cluster interaction F(2,253) = 5.6 <0.01 Pairwise comparisons with clusters Cluster #1: pre-drug–post-drug t(253) = 2.5 <0.05 Cluster #2: pre-drug–post-drug t(253) = 4.3 <0.0001 Cluster #3: pre-drug–post-drug t(253) = −0.4 0.7 Threshold Overall ANOVA Drug F(1,253) = 47.0 <0.0001 Cluster F(2,28) = 0.8 0.4 Drug-cluster interaction F(2,253) = 11.1 <0.0001 Pairwise comparisons with clusters Cluster #1: pre-drug–post-drug t(253) = −6.6 <0.0001 Cluster #2: pre-drug–post-drug t(253) = −4.4 <0.0001 Cluster #3: pre-drug–post-drug t(253) = −0.5 0.6 The drug had a significant effect on all three dependent variables in clusters #1 and #2, but not in cluster #3, neurons. Significant p values are highlighted in bold.
- Table 2
Summary of GABAergic and non-GABAergic neurons that were affected by topical mGluR2/3 activation
Cell type
(number of neurons)Affected by mGluR2/3 activation
(number of neurons; percentage)Unaffected by mGluR2/3 activation
(number of neurons; percentage)GABAergic (n = 6) n = 5; 83% n = 1; 17% Non-GABAergic (n = 25) n = 15; 60% n = 10; 40%
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