Involvement of basolateral amygdala in electroacupuncture induced alleviation of myocardial mitochondrial injury in rats with acute myocardial ischemia

To investigate the effect of electroacupuncture (EA) of the Heart Meridian on ischemic myocardial injury, left cardiac function, myocardial reactive oxygen species (ROS), and expression levels of mitochondrial injury related proteins and genes as mitofusin 2 (Mfn2), calcium/calmodulin-dependent protein kinase Ⅱ (CaMKⅡ), and dynamin-related protein 1 (Drp1) in rats with acute myocardial ischemia (AMI), and lesions of the anterior/posterior basolateral amygdala (a/pBLA), so as to assess its mechanisms underlying improvement of AMI and involvement of BLA in EA-induced alleviation of myocardial mitochondrial injury.

Male SD rats were randomly divided into sham operation, AMI model, EA, EA + aBLA lesion, and EA + pBLA lesion groups (n=12 in each group). The AMI model was established by occlusion of the left anterior descending (LAD) branch of the coronary artery. In the sham group, only a thoracotomy was performed without ligation of LAD. For rats of the amygdaloid lesion groups, microinjection of kainic acid (50 nL) into the pBLA and aBLA was conducted 3 d before the surgery to induce nucleus lesions. EA (2 Hz, 1—2 mA) was applied to“Shenmen”(HT7) to“Tongli”(HT5) segment of the Heart Meridian for 30 min, once daily, for a total of 3 d. Electrocardiography was used to record ST segment displacement of the standard limb lead Ⅱ (ECG-STⅡ) and low frequency/high frequency (LF/HF) ratio of the heart rate variability changes. Echocardiography was used to evaluate various indexes of cardiac function, including the left ventricular ejection fraction (LVEF), left ventricular fractional shortening (LVFS), left ventricular internal diameter in systole (LVIDs), and left ventricular internal diameter in diastole (LVIDd). The myocardial infarction area was measured after TTC staining. H.E. & Masson staining were used to examine histopathological changes of the myocardial tissue. Transmission electron microscopy was utilized to observe the ultrastructure of cardiomyocytes and mitochondria. Flow cytometry was used to detect ROS in cardiomyocytes. Real-time quantitative PCR was employed to measure the expression of Mfn2, CaMKⅡ, and Drp1 mRNA expressions in the myocardial tissue. Western blot was used to detect the expression of Mfn2, Drp1, phosphorylated(p)-Drp1, CaMKⅡ, and p-CaMKⅡ proteins in myocardial tissue.

Compared to the sham group, the model group had a significant increase in the levels of ECG-STⅡ, LF/HF ratio, LVIDs, LVIDd, proportion of myocardial infarction area, ROS fluorescence intensity, mRNA expression levels of Drp1 and CamkⅡ, and protein expression levels of p-Drp1 and p-CaMKⅡ (P<0.01), and a decrease in the levels of LVEF, LVFS and expression of Mfn2 protein and mRNA (P<0.01). In contrast to the model group, both the increase and decrease of the indexes mentioned above were reversed by both EA and EA+aBLA lesion (P<0.05, P<0.01), but not by EA+pBLA lesion. No significant differences were found between the EA and EA+aBLA lesion groups in the increased and decreased levels of the indexes mentioned above. The levels of ECG-STⅡ, LF/HF ratio, LVIDs, LVIDd, proportion of myocardial infarction area, ROS fluorescence intensity, expression of Drp1 and CaMKⅡ mRNAs, and p-Drp1 and p-CaMKⅡ proteins were significantly lower in the EA group than in the EA+pBLA lesion group (P<0.01, P<0.05), and the levels of LVEF, LVFS, expression of Mfn2 mRNA and protein were obviously higher in the EA group than in the EA+pBLA lesion group (P<0.01, P<0.05). H.E. & Masson staining showed swelling, rupture, necrosis, nuclear abnormal changes, inflammatory infiltration, increased collagen deposition and obvious fibrosis of the myocardial cells in the model group. Electron-microscopic observation showed sarcomere disorder, swollen mitochondria, disrupted cristae, with appearance of autophagosomes in cardiomyocytes in the model group. The damage severity of cardiomyocytes was relatively milder in both EA and EA+aBLA groups (including well demarcated mitochondria, reduction in the number of autophagosomes, etc.), but not in the EA+pBLA group.

EA can improve ischemic myocardial injury in rats with AMI, which may be related to its function in reducing endoplasmic reticulum stress level to improve mitochondrial dysfunction, and the BLA particularly the pBLA participates in EA-induced improvement of AMI.