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. 1997 Oct 28;94(22):12198–12203. doi: 10.1073/pnas.94.22.12198

Figure 4.

Figure 4

Stable frequency shifts are caused by EPSP expression. (A) (a) Post-spike AHP size increases during oscillations either expressing EPSPs (and frequency shift) (•, n = 6) or not (○, n = 5). Data expressed as mean ± SEM. Shaded area represents AHP size seen immediately pre-frequency switch where present. (b) Mean EPSP size increases significantly, 100–400 ms, post-tetanus in runs showing frequency shift (•) but not in runs with no frequency shift (○). Shaded area represents EPSP amplitude immediately pre-frequency shift where present. (B) Example of AHP and EPSP amplitude increase associated with frequency shift after two-site tetanus. Two pyramidal cells were impaled in one area (separation c. 80 μm). (Upper) A pyramidal cell with RMP = −70 mV. (Lower) A neighboring pyramidal cell injected with hyperpolarizing current (RMP = −79 mV). [Scale bar, 100 ms, 50 mV (Upper) and 5 mV (Lower). Below are two somatic potential traces from the computer model. (Upper) Normal RMP. (Lower) A different pyramidal cell in the group hyperpolarized with current scaled to −3 nA. [Scale bars, 100 ms, 50 mV (Upper) and 10 mV (Lower). (C) Effects of pressure ejection of NBQX on EPSPs in hyperpolarized cells during oscillations subsequent to initial EPSP potentiation. (Upper) Control. (Lower) Same cell with NBQX ejected onto stratum oriens (dark bar). RMPs = −86 mV and −85 mV, respectively. (Scale bar = 200 ms, 8 mV.) (D) Action potentials generated in a pyramidal cell in site 1 (CA1c, Lower) can elicit an EPSP in a pyramidal cell in site 2 (CA1a, Upper) during the slower oscillation (i) but not afterward (ii). However, EPSPs are re-expressed during further tetanically induced oscillations (iii). All cells were at normal RMP (−65 to −70 mV). [Scale bar = 10 ms, 0.5 mV (CA1a), 180 mV (CA1c).] (E) Post-tetanic response in a cell containing QX314. Strong tetanus generates inhibitory gamma only (i). Subsequent control tetani generate few EPSPs (ii). Underlying oscillation is absent in cells impaled with QX314 and 200 μM picrotoxin (iii). Cells were injected with 0.3 nA depolarizing current to expose underlying IPSPs (RMPs = −55 mV i and ii, −57 mV iii). (Scale bar = 200 ms, 5 mV.)