Antimicrobial peptides (AMPs) are found widespread in nature and possess antimicrobial and immunomodulatory activities. Due to their multifunctional properties, these peptides are a focus of growing body of interest and have been characterized in several fish species. Due to their similarities in amino-acid composition and amphipathic design, it has been suggested that neuropeptides may be directly involved in the innate immune response against pathogen intruders. In this review, we report the molecular characterization of the fish-specific AMP piscidin1, the production of an antibody raised against this peptide and the immunohistochemical identification of this peptide and enkephalins in the neuroepithelial cells (NECs) in the gill of several teleost fish species living in different habitats. In spite of the abundant literature on Piscidin1, the biological role of this peptide in fish visceral organs remains poorly explored, as well as the role of the neuropeptides in neuroimmune interaction in fish. The NECs, by their role as sensors of hypoxia changes in the external environments, in combination with their endocrine nature and secretion of immunomodulatory substances would influence various types of immune cells that contain piscidin, such as mast cells and eosinophils, both showing interaction with the nervous system. The discovery of piscidins in the gill and skin, their diversity and their role in the regulation of immune response will lead to better selection of these immunomodulatory molecules as drug targets to retain antimicrobial barrier function and for aquaculture therapy in the future.

This article reports the morphological characteristics of the atrioventricular (AV) region of the teleost heart. A total of 29 teleost species belonging to 19 families and 10 orders were analyzed. The study includes hearts with entirely trabeculated ventricles and hearts possessing a ventricular compacta. In all cases, the AV region is formed by a ring of compact myocardium surrounded by a connective tissue ring. The myocardium contains vessels in most species having entirely trabeculated ventricles, and in all species possessing a compacta. The ring of connective tissue is rich in collagen and elastin, partially isolating the AV muscle from the surrounding musculature. Continuity between the AV muscle and the atrial and ventricular musculature is always observed. The AV muscle supports the AV valves, which are formed by two leaflets, lack papillary muscles, show a collagenous fibrosa on the atrial side, and present a variable number of cells and a variable amount of extracellular material. Ventricular trabeculae attach to the AV muscle. These trabeculae may help to bear the stress generated by ventricular contraction and may constitute a preferential pathway for the conduction of electrical impulses. In all teleosts studied, the AV region can be recognized as a distinct morphological segment interposed between the atrium and the ventricle. The morphological characteristics of the AV segment appear to be species specific. Anat Rec, 2011.

Sturgeons constitute a family of living “fossil” fish whose heart is related to that of other ancient fish and the elasmobranches. We have undertaken a systematic study of the structure of the sturgeon heart aimed at unraveling the relationship between the heart structure and the adaptive evolutionary changes. In a related paper, data were presented on the conus valves and the subendocardium. Here, the structure of the conus myocardium, the subepicardial tissue, and the conus‐aorta transition were studied by conventional light, transmission, and scanning electron microscopy. In addition, actin localization by fluorescent phalloidin was used. The conus myocardium is organized into bundles whose spatial organization changes along the conus length. The variable orientation of the myocardial cell bundles may be effective in emptying the conus lumen during contraction and in preventing reflux of blood. Myocardial cell bundles are separated by loose connective tissue that contains collagen and elastin fibers, vessels, and extremely flat cells separating the cell bundles and enclosing blood vessels and collagen fibers. The ultrastructure of the myocardial cells was found to be very similar to that of other fish groups, suggesting that it is largely conservative. The subepicardium is characterized by the presence of nodular structures that contain lympho‐hemopoietic (thymus‐like) tissue in the young sturgeons and a large number of lymphocytes after the sturgeons reach sexual maturity. This tissue is likely implicated in the establishment and maintenance of the immune responses. The intrapericardial ventral aorta shows a middle layer of circumferentially oriented cells and internal and external layers with cells oriented longitudinally. Elastin fibers completely surround each smooth muscle cell, and the spaces between the different layers are occupied by randomly arranged collagen bundles. The intrapericardial segment of the ventral aorta is a true transitional segment whose structural characteristics are different from those of both the conus subendocardium and the rest of the ventral aorta. Anat Rec 268:388–398, 2002.