Differences in the dynamics of synaptic depression between neocortical and hippocampal neurons in culture. A, Sample traces of synaptic depression recorded from hippocampal (top traces) and neocortical (bottom traces) neurons in culture during 10 Hz stimulation (the first 10 responses and the 100th to 110th response are shown). B, Traces showing the average synaptic depression from a number of cells normalized to the amplitude of the first response (n = 21 cells and 8 cells for neocortex and hippocampus, respectively). Neocortical neurons depress significantly faster than hippocampal neurons in response to 10 Hz stimulation with significance (p < 0.01) emerging by the fifth response. C, Treatment with cyclothiazide (CTZ) to block AMPA receptor desensitization slightly (gray symbols) decreased the time constant of rapid depression in both neocortical (n = 4) and hippocampal (n = 8) cultures but maintained the difference in the rates of depression between the two cultures. Error bars indicate SE.