Innervation of the Horse Pericardium Revealed by Immunostaining of Whole Mount Preparations with an Anti-Protein Gene Product 9.5 Serum

Abstract

The dense distribution of nerve fibers in the parietal pericardium suggests the pericardium's role as a sensory apparatus, in accordance with the findings of electrophysiological studies. The present immunohistochemical study of a neuron-specific protein, protein gene product (PGP) 9.5, revealed the overall innervation of the horse pericardium using whole mount preparations. PGP9.5-immunoreactive nerves formed two nerve plexuses extending horizontally on the cardiac and pleural sides of the pericardium. Nerve elements on the cardiac side ran submesothelially and branched into individual nerve fibers to form a randomized, but considerably regularly interlacing network. These nerves terminated in free nerve endings within the submesothelial connective tissue. On the pleural side, nerve fascicles were abundant, and individual nerve fibers ran along blood vessels or formed a coarse network. The density of nerves on both sides was highest over the atrioventricular grooves and was slightly lower over the atria, while there were few nerves over the ventriculi. The pericardial nerves may receive signals from mechanical stimuli such as extension of the pericardial sac and touching via the dense network of nerves on the pericardium.