Dopamine and BDNF Modulate LTP in the BLA Figure 3. Application of either the dopamine transport inhibitor, GBR12783, or the D1 receptor agonist, SKF38393 facilitated 5xHFS induced LTP in BLA principal neurons. A, B) Bath application of either the selective dopamine uptake inhibitor, GBR12783 (10 mM, n = 6, blue diamonds), or the selective D1 family receptor agonist, SKF38393 (50 mM, n = 5, blue diamonds), before and during 5xHFS enhanced the magnitude of LTP in principal neurons. The time of drug application is marked by the horizontal bar below the line plots. C) Raw data showing the effects of drug application on the PPR of evoked EPSCs in BLA principal neurons. D) Bar chart showing the group data for the effects of drug application on the PPR. ** P,0.01. Error bars indicate S.E.M. doi:10.1371/journal.pone.0026065.g003 significantly enhanced the magnitude of LTP compared to control (17564% of baseline, n = 5, 3 animals, P,0.01, Figure 3B, red squares; Figure 4, diagonal bar). Application of SKF38393 alone caused no enduring changes in membrane input resistance (F (10, 110) = 0.58, P = 0.8302, Two-way ANOVA). Similarly, no change was observed in the PPR at 10 or 30 min after LTP induction in the presence of either GBR12783 or SKF38393 (Figure 3D). As expected, prior application of SCH23390 fully blocked the SKF38393-induced facilitation of LTP, and markedly attenuated the induction of LTP compared to control (12264%, n = 5, 3 animals, P,0.001 Figure 4, hatched bar). Together these data suggested that release of endogenous dopamine and subsequent activation of D1 receptors was necessary for 5xHFS induction of LTP in BLA principal neurons, and that the magnitude of LTP was tightly regulated by the activity of the local dopamine- reuptake system. Finally, addition of the AC inhibitor to the patch recording solution significantly attenuated the ability of both SKF38393 (SKF38393:17969% of baseline, n = 5; SKF38393 + 29, 59- dideoxy-39-ATP: 13667% of baseline, n = 5; P,0.001) and GBR12783 (GBR12783: 208613% of baseline, n = 5; GBR12783 + 29, 59-dideoxy-39-ATP: 149610% of baseline, n = 5; P,0.001) to facilitate LTP. Similarly, intracellular applica- tion of the PKA inhibitor, KT5720 (100 nM), blocked not only the GBR12783 facilitated LTP (11665% of baseline, n = 6, 4 animals, Figure 5A, C), but also the SKF38393-induced facilitation of LTP (11369% of baseline, n = 5, 3 animals, Figure 5B, C). Hence, D1 receptor activation appeared to facilitate LTP by acting through activation of the classic AC – cAMP - PKA signaling cascade and that this response was itself scaled by the level of extracellular dopamine. The role of BDNF in 5xHFS induction of LTP in BLA principal neurons Like the dopaminergic system, a growing body of evidence suggests that fear learning is also dependent on local release of BDNF and subsequent activation of its cognate receptor, the TrkB receptor [14]. In the hippocampus, BDNF is released in response PLoS ONE | www.plosone.org 5 October 2011 | Volume 6 | Issue 10 | e26065