Figure 8.
Contribution of the M-current to CCh effects on CA2 PN intrinsic properties. (A) Sample traces of AP firing in response to depolarizing current step injections recorded in whole-cell current-clamp configuration from a CA2 PN in control (A1, gray), 10 µM XE-991 (A2, purple), and 10 µM XE-991 and 10 µM CCh (A3, orange), expanded view of the first AP in each condition (A4); and corresponding phase plane plot (A5). (B–I) Summary graphs of CA2 PNs AP firing properties in control (gray), 10 µM XE-991 (purple), and 10 µM XE-991 and 10 µM CCh (orange; n = 15; individual cells shown as thin lines; population averages shown as thick lines; error bars represent SEM). (B) RM (before XE-991, 46 ± 2.6 MOhm; after XE-991, 53 ± 2.3 MOhm; after XE-991 and CCh = 79 ± 4.5 MOhm; Friedman ANOVA, P < 0.001). (C) AP threshold (before XE-991, −46.3 ± 0.9 mV; after XE-991, −47.9 ± 1.4 mV; after XE-991 and CCh, −47.7 ± 1.2 mV; Friedman ANOVA, P = 0.37). (D) AP width at half-maximal amplitude (before XE-991, 1.13 ± 0.03 ms; after XE-991, 1.06 ± 0.03 ms; after XE-991 and CCh, 1.17 ± 0.04 ms; repeated-measures ANOVA, P = 0.002). (E) AHP (before XE-991, 6.7 ± 0.7 mV; after XE-991, 9.1 ± 0.4 mV; after XE-991 and CCh, 8.0 ± 0.5 mV; repeated-measures ANOVA, P < 0.001). (F) Latency to fire first AP per current step as a function of current injection over rheobase (200 pA over rheobase: before XE-991, 100 ± 7.6 ms; after XE-991, 132 ± 14.0 ms; after XE-991 and CCh, 147 ± 19.7 ms; Friedman ANOVA, P = 0.006). (G) Number of APs fired per current step as a function of current injection over rheobase (200 pA over rheobase, before XE-991, 6 ± 1; after XE-991, 12 ± 2; after XE-991 and CCh, 15 ± 3; Friedman ANOVA, P = 0.27). (H) Instantaneous firing frequency of APs as a function of AP number during a current step of intensity chosen 1.5 times above rheobase (first couple of APs frequency, before XE-991, 18 ± 1.8 Hz; after XE-991, 20 ± 2.3 Hz; after XE-991 and CCh, 20 ± 2.4 Hz; repeated-measures ANOVA, P = 0.55). (I) AP amplitude as a function of AP number during a current step of intensity chosen 1.5 times above rheobase (first AP amplitude, before XE-991, 79 ± 2.0 mV; after XE-991, 84 ± 1.6 mV; after XE-991 and CCh, 78 ± 2.6 mV; repeated-measures ANOVA on first AP amplitude, P = 0.044). (J) Sample traces of the ADP following a depolarizing current step injection in a CA2 PN recorded in whole-cell current-clamp configuration in control (gray), 10 µM XE-991 (purple), and 10 µM XE-991 and 10 µM CCh (orange). (K) Summary graph of CA2 PNs ADP in control (gray), 10 µM XE-991 (purple), and 10 µM XE-991 and 10 µM CCh (orange; n = 14, before XE-991, 2.1 ± 0.3 mV; after XE-991, 0.5 ± 0.5 mV; after XE-991 and CCh, 5.8 ± 0.7 mV; Friedman ANOVA, P < 0.001; individual cells shown as thin lines; population averages shown as thick lines; error bars represent SEM). (L) Sample traces of voltage sag in response to hyperpolarizing current step injections recorded in whole-cell current-clamp configuration from a CA2 PN in control (gray), 10 µM XE-991 (purple), and 10 µM XE-991 and 10 µM CCh (orange). (M) Summary graphs of CA2 PN voltage sag following hyperpolarization to −100 mV in control (gray), 10 µM XE-991 (purple), and 10 µM XE-991 and 10 µM CCh (orange; n = 12, preXE991, 2.1 ± 0.2 mV; after XE-991, 3.5 ± 0.3 mV; after XE-991 and CCh, 4.2 ± 0.5 mV; Friedman ANOVA, P < 0.001; individual cells shown as gray lines; population averages shown as thick lines; error bars represent SEM). *, P < 0.05; **, P < 0.01; ***, P < 0.001.

Contribution of the M-current to CCh effects on CA2 PN intrinsic properties. (A) Sample traces of AP firing in response to depolarizing current step injections recorded in whole-cell current-clamp configuration from a CA2 PN in control (A1, gray), 10 µM XE-991 (A2, purple), and 10 µM XE-991 and 10 µM CCh (A3, orange), expanded view of the first AP in each condition (A4); and corresponding phase plane plot (A5). (B–I) Summary graphs of CA2 PNs AP firing properties in control (gray), 10 µM XE-991 (purple), and 10 µM XE-991 and 10 µM CCh (orange; n = 15; individual cells shown as thin lines; population averages shown as thick lines; error bars represent SEM). (B) RM (before XE-991, 46 ± 2.6 MOhm; after XE-991, 53 ± 2.3 MOhm; after XE-991 and CCh = 79 ± 4.5 MOhm; Friedman ANOVA, P < 0.001). (C) AP threshold (before XE-991, −46.3 ± 0.9 mV; after XE-991, −47.9 ± 1.4 mV; after XE-991 and CCh, −47.7 ± 1.2 mV; Friedman ANOVA, P = 0.37). (D) AP width at half-maximal amplitude (before XE-991, 1.13 ± 0.03 ms; after XE-991, 1.06 ± 0.03 ms; after XE-991 and CCh, 1.17 ± 0.04 ms; repeated-measures ANOVA, P = 0.002). (E) AHP (before XE-991, 6.7 ± 0.7 mV; after XE-991, 9.1 ± 0.4 mV; after XE-991 and CCh, 8.0 ± 0.5 mV; repeated-measures ANOVA, P < 0.001). (F) Latency to fire first AP per current step as a function of current injection over rheobase (200 pA over rheobase: before XE-991, 100 ± 7.6 ms; after XE-991, 132 ± 14.0 ms; after XE-991 and CCh, 147 ± 19.7 ms; Friedman ANOVA, P = 0.006). (G) Number of APs fired per current step as a function of current injection over rheobase (200 pA over rheobase, before XE-991, 6 ± 1; after XE-991, 12 ± 2; after XE-991 and CCh, 15 ± 3; Friedman ANOVA, P = 0.27). (H) Instantaneous firing frequency of APs as a function of AP number during a current step of intensity chosen 1.5 times above rheobase (first couple of APs frequency, before XE-991, 18 ± 1.8 Hz; after XE-991, 20 ± 2.3 Hz; after XE-991 and CCh, 20 ± 2.4 Hz; repeated-measures ANOVA, P = 0.55). (I) AP amplitude as a function of AP number during a current step of intensity chosen 1.5 times above rheobase (first AP amplitude, before XE-991, 79 ± 2.0 mV; after XE-991, 84 ± 1.6 mV; after XE-991 and CCh, 78 ± 2.6 mV; repeated-measures ANOVA on first AP amplitude, P = 0.044). (J) Sample traces of the ADP following a depolarizing current step injection in a CA2 PN recorded in whole-cell current-clamp configuration in control (gray), 10 µM XE-991 (purple), and 10 µM XE-991 and 10 µM CCh (orange). (K) Summary graph of CA2 PNs ADP in control (gray), 10 µM XE-991 (purple), and 10 µM XE-991 and 10 µM CCh (orange; n = 14, before XE-991, 2.1 ± 0.3 mV; after XE-991, 0.5 ± 0.5 mV; after XE-991 and CCh, 5.8 ± 0.7 mV; Friedman ANOVA, P < 0.001; individual cells shown as thin lines; population averages shown as thick lines; error bars represent SEM). (L) Sample traces of voltage sag in response to hyperpolarizing current step injections recorded in whole-cell current-clamp configuration from a CA2 PN in control (gray), 10 µM XE-991 (purple), and 10 µM XE-991 and 10 µM CCh (orange). (M) Summary graphs of CA2 PN voltage sag following hyperpolarization to −100 mV in control (gray), 10 µM XE-991 (purple), and 10 µM XE-991 and 10 µM CCh (orange; n = 12, preXE991, 2.1 ± 0.2 mV; after XE-991, 3.5 ± 0.3 mV; after XE-991 and CCh, 4.2 ± 0.5 mV; Friedman ANOVA, P < 0.001; individual cells shown as gray lines; population averages shown as thick lines; error bars represent SEM). *, P < 0.05; **, P < 0.01; ***, P < 0.001.

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