Figure 6.

Glutamate accumulation and spillover increase the firing rate of calyces. A, In an example calyx recording, during application of 200 μm TBOA, the membrane potential depolarized and the firing rate increased from 2.9 ± 0.7 spikes/s to 12.1 ± 7.3 spikes/s. In TBOA the membrane potential depolarized by ∼5 mV. B, The AP shape did not change during TBOA application (red). C, Comparison of changes in membrane potential during individual ATP applications (to increase release rate from hair cells) without (control) and with TBOA or KynA. Throughout the experiment, 2 μm TTX was applied to block AP generation. Inset (gray), Example EPSPs. Scale bar: 0.2 mV, 100 ms. In control, ATP causes depolarization mediated by P2X receptors on the calyx membrane. D, Most calyces were further depolarized during TBOA application compared with control (filled symbols above dashed unity line). Empty symbols: TBOA and NBQX application. E, During application of 10 μm NBQX, the effects of TBOA and KynA shown in C were blocked. Same calyx as in C. F, Most calyces showed less depolarization during KynA application compared with control (filled symbols below dashed unity line). Empty symbols: KynA and NBQX application.