Fear potentiated startle increases phospholipase D (PLD) expression/activity and PLD-linked metabotropic glutamate receptor mediated post-tetanic potentiation in rat amygdala

•In the present study, we report on presynaptic cellular mechanisms involved in fear potentiated startle long-term memory (FPS LTM) by examining downstream elements of metabotropic glutamate receptor (mGluR) signaling in the thalamic–lateral amygdala (Th–LA) synaptic pathway.•Following fear potentiated startle behavior (FPS) in rats, proteomic analyses identified a 30% decrease in amygdala aldolase A, that immunoprecipitated with amygdala anti-phospholipase D1 and D2 isoform (PLD1/2) antibodies.•Amygdala aldolase A has a reverse profile to the expression of PLD, a downstream target of mGluR signaling.•Paired (PA) group PLD expression and activity increased significantly, attesting that our hypothesis of increased PLD (in response to aldolase A reduction) is important for storage mechanisms of FPS LTM.•The fEPSPs during baseline and long-term potentiation (LTP) maintenance remain unaltered, but the PPR ratios in the PA group are reduced compared to the unpaired (UNP) confirming an increased release probability in FPS.•Neither inhibition nor stimulation of mGluR signaling via PLD affected the PA group PPR ratios suggesting that the increased probability of release coupled to the increased PLD activity may contribute to multiple vesicular release resulting in a constant PPR.•High frequency stimulation (HFS) recruits PLD signaling since the first field excitatory post synaptic potential (fEPSP) and post-tetanic potentiation (PTP) are affected following block of PLD–mGluR signaling.•These effects are similar to those mediated through mGluR7, which is co-immunoprecipitated with PLD in the PA group.•Finally, blocking PLD signaling upstream at mGluR level attenuated the associative memory mechanism underlying FPS response, underscoring the importance of PLD–mGluR in cue-induced anxiety and fear in emotional learning.

Long-term memory (LTM) of fear stores activity dependent modifications that include changes in amygdala signaling. Previously, we identified an enhanced probability of release of glutamate mediated signaling to be important in rat fear potentiated startle (FPS), a well-established translational behavioral measure of fear. Here, we investigated short- and long-term synaptic plasticity in FPS involving metabotropic glutamate receptors (mGluRs) and associated downstream proteomic changes in the thalamic–lateral amygdala pathway (Th–LA). Aldolase A, an inhibitor of phospholipase D (PLD), expression was reduced, concurrent with significantly elevated PLD protein expression. Blocking the PLD–mGluR signaling significantly reduced PLD activity. While transmitter release probability increased in FPS, PLD–mGluR agonist and antagonist actions were occluded. In the unpaired group (UNP), blocking the PLD–mGluR increased while activating the receptor decreased transmitter release probability, consistent with decreased synaptic potentials during tetanic stimulation. FPS Post-tetanic potentiation (PTP) immediately following long-term potentiation (LTP) induction was significantly increased. Blocking PLD–mGluR signaling prevented PTP and reduced cumulative PTP probability but not LTP maintenance in both groups. These effects are similar to those mediated through mGluR7, which is co-immunoprecipitated with PLD in FPS. Lastly, blocking mGluR–PLD in the rat amygdala was sufficient to prevent behavioral expression of fear memory. Thus, our study in the Th–LA pathway provides the first evidence for PLD as an important target of mGluR signaling in amygdala fear-associated memory. Importantly, the PLD–mGluR provides a novel therapeutic target for treating maladaptive fear memories in posttraumatic stress and anxiety disorders.