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Objective: To evaluate the nerve remodeling induced by 48 hours right atrial pacing in a canine model., Methods: Rapid right atrial pacing (600 beats/min) was performed in 6 mongrel dogs of either sex for 48 hours to induce sustained atrial fibrillation (AF). Six dogs without pacing served as controls. Cardiac nerves were immunocytochemically stained using anti-growth-associated protein 43 (GAP43) and anti-choline acetyltransferase (CHAT) antibodies to compare nerve sprouting and pneumogastric nerve remodeling between the 2 groups., Results: In dogs with AF, the GAP43-positive and CHAT-positive nerve densities in the left atrium, left auricular appendage, right atrium and right auricular appendage were significantly higher than in control animals (all P < 0.05). Moreover, nerve density was significantly higher in the right atrium than in the left atrium in dogs with AF. Microscopic examinations revealed an inhomogeneous distribution of cardiac nerves., Conclusion: Significant nerve sprouting and pneumogastric nerve remodeling were evidenced in the right and left atrium in a canine model of sustained AF induced by 48 hours right atrial pacing.

Objective: To test the hypothesis that regional sympathetic innervation in the atria and pulmonary veins are correlated with atrial fibrillation (AF)., Methods: Sixteen adult mongrel dogs underwent thoracotomy under general anesthesia. Bilateral cervical vagal trunks were decentralized. Multipolar catheters were placed into right atrial appendage (RAA), left atrial appendage (LAA), left atrium (LA), left superior pulmonary vein (LSPV), left inferior pulmonary vein (LIPV), right superior pulmonary vein (RSPV), and left inferior pulmonary vein (LIPV). The bilateral sympathovagal trunks were stimulated, S1S1 burst stimulation and S1S2 stimulation procedure were performed on different points of RAA, LAA, LA, LSPV, LIPV, RSPV, and LIPV. The TF thus induced was monitored. After that, the dogs were killed with their hearts and lungs were taken out. Immunocytochemical staining of cardiac nerves was performed using anti-tyrosine hydroxylase (TH) antibodies. The nerve fiber density was counted manually for each case and expressed as the mean number per slice., Results: Two dogs died during the experiment and the whole procedure was completed on 14 dogs. There was no significant difference in the AF induction rate among the most points, however, the AF induction rate of the RIPV was significantly lower than those of the other points (all P < 0.05). The levels of density of TH-positive nerves in the atria and atrial appendages were significantly higher than those in the pulmonary veins (P = 0.02). The density of TH-positive nerves in the dogs with AF was significantly higher than that in the dog without AF (P < 0.05). The innervation of sympathetic nerves in atria and pulmonary veins was highly correlated to the induction of atrial fibrillation (r = 0.83)., Conclusion: Regional sympathetic hyperinnervation plays an important role in atrial fibrillation induction.

Objective: To investigate the general pattern of cholinergic nerve distribution and M(2) receptors in adult rat heart., Methods: Karnovsky-Roots histochemical staining combining point counting method and immunochemical SABC method with image analysis were used to identify the cholinergic nerves and M(2) receptors, respectively, in adult rat heart., Results: Positive staining of cholinergic nerves and M(2) receptors was found in all regions of the rat heart, and the point count of cholinergic nerves in the atria was 4.6 times as much as that in ventricles, and the area of immunoreactive substance for M(2) receptors two-fold higher in the atria than in the ventricles. The point counts of the cholinergic nerves in the medial-layer myocardium were fewer than that in subepicardial and endocardial tissues of the left ventricular free wall. However, M(2) receptors were comparable among the 3 layers of the left free ventricular wall., Conclusion: Cholinergic nerves and M(2) receptors are located in both rat atria and ventricles, but their density is much higher in the atria than in the ventricles. Transmural heterogeneity characterizes cholinergic nerve innervation in the left ventricular free wall without significant differences in M(2) receptor density.