[Correlation between acupoint sensitization of body surface and pituitary adenylate cyclase activating polypeptide expression in myocardial ischemia mice].

Objectives: To explore the relationship between sensitization points of the body surface and the expression of pituitary adenylate cyclase activating polypeptides (PACAP) in myocardial ischemia (MI) mice, so as to reveal the underlying mechanisms of acupoint sensitization from the perspective of molecular biology.

Methods: Male C57BL/6J mice were randomly divided into control and model groups (28 mice/group). The MI-induced visceral pain model was established by intraperitoneal injection of isoprenaline (ISO, 160 mg/kg). The mice of the control group received intraperitoneal injection of the same dose of normal saline. Six days after modeling, the Evans blue (EB) dye was injected into the tail vein of mice to observe the distribution and quantity of the plasma extravasated EB points at the body surface. Meanwhile, the mechanical pain threshold (MPT) was measured to evaluate the level of pain sensitivity in the activated area on their body surface and left forelimb and hindlimb, respectively. Hematoxylin-eosin (H.E.) staining was used to evaluate the morphologic and pathological changes of the heart tissue in the two groups. Then, the expressions of PACAP in the thoracic (T)1-T5 dorsal root ganglia (DRGs), spinal cord and skin in the dominant area of body surface were detected by Western blot and immunofluorescence staining, respectively.

Results: Compared with the control group, the heart tissue of the model group was hypertrophic and the myocardial tissue showed obvious inflammatory cell infiltration and fibrosis. In addition to these pathologic changes, the number of EB exudation points on the body surface was significantly increased (<0.01), and was mainly distributed in the innervated region of T1-T5 segments of the spinal cord, and the MPT of these EB exudation points was lower than that of non-exudation points (<0.01). At the same time, the MPTs of left forelimb and hindlimb were significantly decreased in the model group (<0.001). More importantly, the level of protein and positive expression of PACAP were significantly higher in the model group than those in the control group, which was observed in the innervated body surface, spinal cord and its DRG neurons of T1-T5 segments (<0.01, <0.001, <0.05).

Conclusions: ISO injection resulted in histological lesions and cardiogenic referred pain on the body surface after the formation of MI in mice. The expression of PACAP in the body surface of the sensitization points, the corresponding T1-T5 segments of spinal cord and DRG neurons were significantly increased, which may partly explain the reason for acupoint sensitization in the animal model of visceral pain.