Figure 9.
R420H subunit reduces the precision and amplitude of the startle response. A–C, Left panels show results from individual startle response assays performed on uninjected, EGFP-injected, or R420H + EGFP-injected animals: change in head trajectory (A), maximum C-start angle (B); maximum counterbend angle (C). In C, a negative counterbend angle indicates that the counterbend and the C-start were in the same direction. Mean change in head trajectory: uninjected, 193 ± 8° (n = 43 assays, conducted on 16 animals); EGFP-injected, 172 ± 5° (54 assays on 22 animals); R420H + EGFP-injected, 143 ± 6° (79 assays on 27 animals). Values are provided as mean ± SEM. R420H differed significantly from EGFP and uninjected, p < 0.001 by one-way ANOVA followed by Student's t test. Mean maximum C-start angle: uninjected, 252 ± 5° (42 assays); EGFP, 245 ± 5° (54 assays); R420H + EGFP, 213 ± 6° (79 assays). Values are provided as mean ± SEM. R420H differed significantly from EGFP and uninjected, p < 0.001 by one-way ANOVA followed by Student's t test. Mean maximum counterbend angle: uninjected, 111 ± 5° (38 assays); EGFP, 115 ± 4° (49 assays); R420H, 79 ± 8° (72 assays). R420H differed significantly from EGFP and uninjected, p < 0.01 by one-way ANOVA followed by Student's t test. There were fewer counterbend measurements because the head or the tail was sometimes out of frame during this phase of the response. In the right panels, results from startle response assays performed on EGFP-injected (open bars) or R420 + EGFP-injected (black bars) animals have been binned and plotted versus percentage of total responses: change in head trajectory (A), maximum C-start angle (B), maximum counterbend angle (C). In A and C, binned data have been fitted with Gaussian functions of the form y = (A/(w*))*exp(−2*((x − xc/w)⋀2), where A is area, w is width at half-maximal amplitude, and xc is center of the distribution. The fits are superimposed on the histograms: EGFP-injected, dashed line; R420H + EGFP-injected, solid line. The fitted distributions of change in head trajectory (A) and maximum counterbend angle (C) for EGFP- and R420H + EGFP-injected animals differed significantly, p < 0.01 using F test in Origin 7. Fitted parameters, change in head trajectory: EGFP, A = 100.6 ± 0.8, w = 1.59 ± 0.01, xc = 4.9 ± 0.01; R420H, A = 99.9 ± 2.8, w = 2.18 ± 0.07, xc = 4.4 ± 0.04. Fitted parameters, maximum counterbend angle: EGFP, A = 96.1 ± 2.8, w = 1.1 ± 0.04, xc = 5.9 ± 0.03; R420H, A = 96.5 ± 4.5, w = 1.9 ± 0.1, xc = 5.3 ± 0.05. Data in B, right panel, were not fitted because the R420H results were not well described by a normal distribution.