Figure 3. Glutamate release probability varies among LC-NE inputs.

(A) Representative traces showing paired pulse ratios (PPR) at a 50 ms interstimulus interval (ISI) for LH (left; purple), PAG (center; orange), and PFC (right; green).

(B) Quantification of paired pulse ratios at a 50 ms ISI (mean ± SEM). Kruskal Wallis ANOVA with post-hoc Dunn’s Test, H(2) = 80.11, p < 0.0001; ***LH vs. PAG p < 0.0001, LH vs. PFC p = 0.87, ***PAG vs. PFC p < 0.0001.

(C) Scatter plots showing the relationship between PPRs and EPSC amplitudes; the size of the response did not significantly account for variability in PPR.

(D-F) Quantification (left) and representative traces (right) for trains of 5 pulses with 50 ms ISIs. For each input a RMANOVA with post hoc Tukey’s test was used to compare the ratio of pulse_n to pulse₁. (D) LH had a significantly lower ratio for pulses 4 and 5 as compared to pulse 2 (F(4,40) = 19.70, p < 0.0001). (E) PAG facilitated on all pulses with significant differences between them (F(4,28) = 1.83, p = 0.15). (F) PFC responses on average depressed for all pulses (F(4,56) = 2.72, p = 0.0383).

(G-I) Quantification (left) and representative traces (right) for PPRs of varying ISI (50 – 400 ms). For each input a RMANOVA with post hoc Tukey’s test was used to compare PPRs. (G) LH inputs depressed at all ISIs, with PPR₃₀₀ < PPR₅₀, PPR₄₀₀ < PPR₅₀, PPR₁₀₀, & PPR₂₀₀ (F(4,40) = 5.93, p = 0.0008). (H) PAG inputs facilitated at all ISIs except 200 ms, which was significantly less than 50 ms (F(4,28) = 2.95, p = 0.0376). (I) PFC inputs depressed for all frequencies with PPR₁₀₀ > PPR₃₀₀ and PPR₄₀₀ (F(4,60) = 5.60, p = 0.0007). Traces for each of the 5 ISIs are shown overlapped with their first peak normalized to 1; the shade of each trace corresponds to that in the bar graph, going from lightest to darkest with increasing ISI.

Summary data are mean ± SD. * = p < 0.05, *** = p < 0.001.