Figure 1.

Synaptic Conditioning Enhances High-Frequency Firing and Reduces Postsynaptic Excitability in MNTB Neurons

(A) Left view illustrates synaptically evoked 100 Hz (upper) and 800 Hz (lower) trains delivered before conditioning (Naive, black) showed failures after 4–6 APs at 800 Hz. Right view shows 100 and 800 Hz trains after synaptic conditioning at 10 Hz for 1 hr with Poisson-distributed ISIs (PC, red); note improved AP firing maintained through the 800 Hz train in contrast to Naive (black). (B) Summary of MNTB output/input ratios: Naive (black) and PC (red), PC resulted in improved fidelity at high frequencies (100 Hz: Naive 1 ± 0, PC 1 ± 0; 800 Hz: Naive 1.7 ± 0.8, PC 0.5 ± 0.4, p = 0.0089; 1 kHz: naive 0.06 ± 0.01, PC 0.4 ± 0.2, p < 0.0001). Inset shows orientation of slice, synaptic input, and stimulation (Stim) and recording (Rec) electrodes. (C) Left view is example traces for APs evoked by current injection in Naive (black), showing reduced excitability after PC (red). Right view is a frequency plot of current evoked APs; PC reduced postsynaptic excitability. (D) AP firing threshold is increased by synaptic conditioning or nitrergic signaling: Naive, control; NO, following NO-donor incubation (1 hr, 100 μM SNP or PapaNONOate); PC, synaptic conditioning. The threshold rise is suppressed by blocking glutamate receptors: PC+AP5/MK+CNQX (50 μM AP5 + 10 μM MK801 + 10 μM CNQX). Statistical significance was determined by one-way ANOVA with posttest; data tested versus Naive. Error bars are mean ± SEM. ^∗p < 0.01, n.s., not significant, unpaired data.