Porcine intrinsic cardiac ganglia.

The gross, light, and electron microscopic anatomies of the porcine intrinsic cardiac nervous system were investigated in 26 pigs to facilitate functional studies in this model. Gross anatomy: Numerous ganglia and interconnecting nerves (ganglionated plexuses) were found to be concentrated in epicardial fat in five atrial and six ventricular regions. The five atrial ganglionated plexuses identified were (1) the ventral right atrial, (2) the right vena cava-right atrial, (3) the dorsal atrial, (4) the interatrial septal, and (5) the left superior vena cava-left atrial ones. Six ventricular ganglionated plexuses were identified in close proximity to the (1) roots of the aorta and pulmonary artery (craniomedial), extending along the left main coronary artery to the (2) ventral interventricular and (3) circumflex coronary arteries. (4) A ganglionated plexus was identified around the origin of the dorsal interventricular coronary artery, as well as the (5) right main and (6) right marginal coronary arteries. Isolated neurons were identified scattered throughout the cranial interventricular septum. Microscopic anatomy: Approximately 3,000 neuronal somata were estimated to compose this intrinsic cardiac nervous system. Some ganglia contained more than 100 neurons. Neuronal somata had dimensions of roughly 33.1 (short axis) by 46.3 (long axis) microm. Most were multipolar, a small population of unipolar neurons being identified in atrial and ventricular tissues. At the electron microscopic level, asymmetrical axodendritic synapses with small clear, round vesicles were identified, some containing large dense-cored vesicles. In summary, porcine intrinsic cardiac neurons are concentrated in 11 distinct atrial and ventricular ganglionated plexuses. These extensive plexuses, along with fewer scattered neurons, display varied neuronal morphology and synaptology that represent the anatomical substrate for complex information processing within the intrinsic cardiac component of the porcine cardiac neuronal hierarchy. These anatomical data provide a framework for physiological analyses of the porcine intrinsic cardiac nervous system.