Blockade of glutamate receptors substantially reduced both early and late spikes in some sustained units. A, NBQX completely eliminated all spikes in this unit. BF, 59.5 kHz; MT, 9 dB SPL; minimum latency, 7.7 ms. B, CPP eliminated nearly all early and late spikes in this unit, whereas NBQX did not reduce spikes relative to recovery. BF, 58.2 kHz; MT, 39 dB SPL; minimum latency, 15.1 ms. Drug application times and currents are as follows: in A, NBQX, 16 min, −40 nA; RECOVERY, 8 min; in B, CPP, 10 min, −40 nA; RECOVERY, 18 min; NBQX, 12 min, −60 nA. See Figure 2 for protocol. SPL, Sound pressure level.