The hippocampus is involved in the regulation of the autonomic nervous system, together with the hypothalamus and brainstem nuclei, such as the paraventricular nucleus and nucleus tractus solitarius. The vagus nerve-nucleus tractus solitarius pathway has an important role in cardiovascular reflex regulation. Myocardial ischemia has been shown to cause changes in the autonomic nervous system, affecting the dynamic equilibrium of the sympathetic and vagal nerves. However, it remains poorly understood how the hippocampus communicates with brainstem nuclei to regulate the autonomic nervous system and alleviate myocardial ischemic tissue damage. A rat model of acute myocardial ischemia (AMI) was made by ligating the left anterior descending branch of the coronary artery. Three days before ischemia, the hippocampal CA1 region was damaged. Then, 3 days after ischemia, electroacupuncture (EA) at Shenmen (HT7)-Tongli (HT5) was performed (continuous wave, 1 mA, 2 Hz, duration of 30 minutes). Cluster analysis of firing patterns showed that one type of neuron was found in rats in the sham and AMI groups. Three types of neurons were observed in the AMI + EA group. Six types of neurons were found in the AMI + EA + Lesion group. Correlation analysis showed that the frequency of vagus nerve discharge in each group was negatively correlated with heart rate (HR) (P < 0.05, r = -0.424), and positively correlated with mean arterial pressure (MAP) (P < 0.05, r = 0.40987) and the rate-pressure product (RPP) (P < 0.05, r = 0.4252). The total frequency of the nucleus tractus solitarius discharge in each group was positively correlated with vagus nerve discharge (P < 0.01, r = 0.7021), but not with hemodynamic index (HR: P > 0.05, r = -0.03263; MAP: P > 0.05, r = -0.08993; RPP: P > 0.05, r = -0.03263). Some neurons (Neuron C) were negatively correlated with vagus nerve discharge, HR, MAP and RPP in the AMI + EA group (vagus nerve discharge: P < 0.05, r = -0.87749; HR: P < 0.01, r = -0.91902; MAP: P < 0.05, r = -0.85691; RPP: P < 0.01, r = -0.91902). Some neurons (Neurons C, D and E) were positively correlated with vagus nerve discharge, HR, MAP and RPP in the AMI + EA + Lesion group (vagus nerve discharge: P < 0.01, r = 0.8905, P < 0.01, r = 0.9725, P < 0.01, r = 0.9054; HR: P < 0.01, r = 0.9347, P < 0.01, r = 0.9089, P < 0.05, r = 0.8247; MAP: P < 0.05, r = 0.8474, P < 0.01, r = 0.9691, P < 0.01, r = 0.9027; RPP: P < 0.05, r = 0.8637, P < 0.01, r = 0.9407, P < 0.01, r = 0.9027). These findings show that the hippocampus-nucleus tractus solitarius-vagus nerve pathway is involved in the cardioprotective effect of EA at the heart meridian. Some interneurons in the nucleus tractus solitarius may play a particularly important role in the cardiomodulatory process.
Keywords: Shenmen (HT7); Tongli (HT5); acute myocardial ischemia; autonomic nerve; electroacupuncture; hippocampus; nerve regeneration; neural regeneration; nucleus tractus solitarius; vagus nerve discharge.