, 2002 and Davie et al., 2008) and it is sensitive to activity-dependent changes (Hashimoto and Kano, 1998 and Maruta et al., 2007). Indeed, we found that the number of spikelets varied across physiologically relevant CF stimulation frequencies (Figure S2) paralleling the effects seen with the EPSC (Figure S1).
CpSs evoked by 2 Hz CF stimulation had fewer spikelets compared to those recorded during 0.05 Hz stimulation (Figures 6A and 6B; 2.8 ± 0.14 and 3.7 ± 0.12, respectively; n = 26; p < 0.0001). Individual spikelets were also altered during Quisinostat molecular weight 2 Hz stimulation in an unexpected manner (Figures 6C–6E). While the amplitude of the first spike was not different, the second and third spikelet amplitude increased with 2 Hz stimulation relative to the corresponding spikes at 0.05 Hz (by 1.5 ± 1.3%, 33.4 ± 7.3%, and 62.2 ± 16.8%, respectively; n = 26, 26, and 18; p > 0.05, p < 0.0001, and p < 0.01, one-sample t test). Similarly, the rate of rise for all spikelets during 2 Hz stimulation differed from the corresponding spikelets at 0.05 Hz (−8.2 ± 2.0%, 68.5 ± 32.2%, and 54.7 ± 13.9%, respectively; n = 26, 26, and 18; p < 0.001 each; one-sample t test). Lastly, the interspike interval (ISI) between the first and the second pair of spikelets was prolonged during 2 Hz stimulation (27.2 ± 4.2%
and 23.1 ± 4.6%; n = 26 and 18; p < 0.001 each; one-sample t test). Because increases in spike height, rising rate, and ISI are positively correlated with reliability of spikelet propagation in PC axons (Khaliq and Apoptosis Compound Library Raman, 2005 and Monsivais et al., 2005), this implies that frequency-dependent changes in the CpS waveform promote more efficient spikelet propagation to PC target neurons. We wondered whether the reduction in the synaptic charge that occurs with 2 Hz stimulation (Figure 1A) was sufficient to account for the activity-dependent changes in CpS waveform. To test this possibility, we used NBQX to reduce the EPSC charge to a similar degree as with 2 Hz stimulation. This strategy
allowed us to distinguish the contribution of amplitude versus kinetics to the CpS waveform because even at high concentrations NBQX application has no effect on the EPSC current time course (Figure S3). At 100 nM, NBQX inhibited the EPSC peak amplitude by ∼30% (Figure 6F, similar to Figure 3; unpaired t test; p > 0.05), resulting in a reduction of the current-time integral these of 30.0 ± 2.8% (n = 4) that is equivalent to the depression of the EPSC peak amplitude (∼30%) and significantly more than the decrease of the current-time integral (∼20%) caused by 2 Hz stimulation (Figure 1). However, application of 100 nM NBQX had no significant effect on the CpS evoked by 0.05 Hz stimulation (Figures 6G–6K). As expected, further inhibition of AMPARs with higher concentrations of NBQX (300 nM) reduced the number of spikelets (from 3.6 ± 0.4 to 2.4 ± 0.2; n = 5; p < 0.05) within each CpS (data not shown; see also Foster et al., 2002).