Figure 3. E_GABAA effects upon residual membrane depolarization during synaptically-evoked spiking underlies differences in LTP induction between ZT3 and ZT15.

(A) Gramicidin recordings were used to monitor synaptically-evoked spike trains, whilst brief somatic current pulses (4 ms) were injected to modulate the membrane potential between spikes. (B) Linear fits to the residual depolarization. (C) Residual depolarization increased in the ZT3+Depolarization condition compared to ZT3 (control from Figure 2E; 5 neurons, 5 animals; **p=0.009, t-test; t=3.109; df=12; d=1.73). Depolarization was reduced in the ZT15+Hyperpolarization condition compared to ZT15 (control from Figure 2E; 5 neurons, 3 animals; **p=0.001, t-test; t=4.5; df=10; d=2.64). (D) Same stimulus train was used to induce LTP (four pulses at 100 Hz, repeated 100 times at 0.1 Hz). (E) LTP was enhanced at ZT3 by increasing the post-spike depolarization during induction (control from Figure 2G; 5 neurons, 5 animals; **p=0.003, t-test; t=3.64; df=12; d=2.03). LTP was attenuated at ZT15 by reducing the post-spike depolarization during induction (control from Figure 2G; 5 neurons, 3 animals; **p=0.003, Mann-Whitney; d=3.48). (F) Gramicidin recordings in KCC2 blocker (VU) at ZT3, or an NKCC1 blocker (Bume) at ZT15. (G) Linear fits to residual depolarization. (H) VU increased residual depolarization at ZT3 (5 neurons, 4 animals; *p=0.017, t-test; t=2.782; df=12; d=1.55). Bumetanide reduced residual depolarization at ZT15 (5 neurons, 4 animals; *p=0.018, t-test; t=2.816; df=10; d=1.65). (I) LTP population data. (J) LTP was enhanced by VU at ZT3 (5 neurons, 4 animals; **p=0.002, Mann-Whitney; d=1.88). LTP was attenuated by bumetanide at ZT15 (5 neurons, 4 animals; **p=0.003, Mann-Whitney; d=4.62).