Figure 4

Motor Behavior Selectively Modulates Hair Cells Activated by Deflection in the Posterior Direction

(A–C) Three examples of synapses whose response was (A) unaffected, (B) suppressed during the entire stimulation episode, and (C) suppressed only during the initial part of the stimulus (shaded areas represent the SEM).

(D) The suppression index (SI), calculated on a point-by-point basis during mechanical stimulation (Equation 1). The red, blue, and green traces show synapses from three different hair cells, with the corresponding motor activity shown below. Glutamate release from the green synapse (A) was not significantly suppressed, with an SI ∼0 (negative values occur whenever the response during motor activity is larger than the average response in the absence of motor activity). Stimulated release from the red synapse (C) was nulled during motor activity (SI ∼1) but then recovered at the end of the burst of spikes. Glutamate release from the blue synapse (B) was reduced to below resting levels (SI > 1).

(E) Plot of the relation between the SI at each time point during a mechanical stimulus and the number of spikes in the motor nerve in the preceding 50-ms time interval. Only synapses classified as suppressed were analyzed. Collected results from 29 synapses in 6 fish are shown. The data could be described by a Hill equation of the form SI(N_s) = (SI_max^∗N_s)/(N_s + N_1/2), where N_s is the number of spikes, SI_max is the maximum SI (1.05 ± 0.08), and N_1/2 is the number of spikes coinciding with half-maximal suppression (1.12 ± 0.42). Error bars show SEM.

(F) The effects of motor activity on synaptic transmission from hair cells of opposing polarity. Column 1: the number of synapses activated by deflection in the posterior and anterior directions is shown. Measurements were made in a total of 41 synapses in 8 neuromasts in 6 fish. Column 2: the number of synapses suppressed during motor activity, classified as described in the STAR Methods, is shown. Column 3: the number of synapses unaffected by motor activity is shown.

(G) Comparison of the average magnitude of the suppression index during a swimming bout in hair cells polarized for anterior and posterior deflection. We also compared the maximal SI values during a swimming bout: these were also significantly different in hair cells of opposite polarity (p < 0.001; Mann-Whitney U test). Bars show SEM.