Activation of Locus Coeruleus-Hippocampus Tyrosine Hydroxylase Projection Contributes to the Surgical Incision Pain-Induced Memory Consolidation Enhancement in Mice.

AIMS: The mechanism underlying postoperative post-traumatic stress disorder (PTSD) remains unclear. However, studies have shown that acute postoperative pain is an independent risk factor for PTSD, which is also closely related to memory consolidation enhancement. Preoperative patients often experience unpleasant traumatic events, and postoperative pain usually occurs in the memory consolidation stage of these events. Therefore, inquiring whether acute postoperative pain affects memory consolidation and its possible mechanism may help to explain the causes of postoperative PTSD.

METHODS AND RESULTS: In this study, we show that the surgical incision pain enhances the consolidation of emotional memory (in the passive avoidance test) and nonemotional memory (in the novel object recognition test) in mice. None of the behaviors evaluated were affected by anxiety or locomotor dysfunction (in the open-field test). Besides, we confirmed that surgical incision pain promotes memory enhancement by enhancing memory consolidation instead of memory retrieval. Furthermore, the consolidation of emotional memory and nonemotional memory was enhanced by the activation of the LC-HPC TH projection after surgical incision pain. Hippocampal CA1 dopamine receptors, rather than β adrenoceptors, mediate emotional and nonemotional memory consolidation enhancement after surgical incision pain.

CONCLUSION: Thus, our results indicate that surgical incision pain enhances the memory consolidation of emotional memory and nonemotional memory in mice. Activation of the LC-HPC TH projection may contribute to memory consolidation enhancement induced by surgical incision pain, which involves the activity of dopamine receptors in CA1.