Identification of zebrafish histamine H1, H2 and H3 receptors and effects of histaminergic ligands on behavior

Neuronal histamine regulates several functions in the vertebrate brain. The zebrafish brain contains a widespread histaminergic system and H(3) receptor ligand binding has been reported. In this study we provide evidence for the existence of histamine H(1), H(2) and H(3) receptor genes in zebrafish. Single copies of putative histamine H(1), H(2) and H(3) receptors were identified and cloned from the zebrafish brain. Expression analysis suggested that they are expressed in the brain and a few other tissues. Widespread distribution of zebrafish H(2) receptor binding sites was detected with [(125)I]iodoaminopotentidine in brain sections. Zebrafish larvae were exposed to 1, 10 or 100 microM of the H(1) ligand pyrilamine, the H(2) ligand cimetidine and the H(3) ligands thioperamide and immepip for 5 days. Significant decreases in swimming distance were observed with the highest dose of all ligands, whereas cimetidine gave a significant decrease also with 1 and 10 microM doses. These results provide the first molecular biological evidence for the presence of histamine receptors in zebrafish. These histamine receptors resemble those of higher vertebrates and they provide a useful model for pharmacological and behavioral studies for characterizing the functions of histamine in more detail.     

Discovery of a novel enzyme mediating glucocorticoid catabolism in fish: 20beta-hydroxysteroid dehydrogenase type 2

Hydroxysteroid dehydrogenases (HSDs) are involved in metabolism and pre-receptor regulation of steroid hormones. While 17beta-HSDs and 11beta-HSDs are extensively studied in mammals, only few orthologs are characterized in fish. We discovered a novel zebrafish HSD candidate closely related to 17beta-HSD types 3 and 12, which has orthologs in other species. The enzyme catalyzes the conversion of cortisone to 20beta-hydroxycortisone identified by LC-MS/MS. We named the new enzyme 20beta-HSD type 2. All 20beta-HSD type 2 orthologs localize in the endoplasmic reticulum. Zebrafish 20beta-HSD type 2 is expressed during embryonic development showing the same expression pattern as 11beta-HSD type 2 known to oxidize cortisol to cortisone. In adult tissues 20beta-HSD type 2 shows a ubiquitous expression pattern with some minor sex-specific differences. In contrast to other enzymes metabolizing C21-steroids and being mostly involved in reproduction we propose that novel type 2 20beta-HSDs in teleost fish are important enzymes in cortisol catabolism.     

Müller glia: Stem cells for generation and regeneration of retinal neurons in teleost fish

Adult zebrafish generate new neurons in the brain and retina throughout life. Growth-related neurogenesis allows a vigorous regenerative response to damage, and fish can regenerate retinal neurons, including photoreceptors, and restore functional vision following photic, chemical, or mechanical destruction of the retina. Müller glial cells in fish function as radial-glial-like neural stem cells. During adult growth, Müller glial nuclei undergo sporadic, asymmetric, self-renewing mitotic divisions in the inner nuclear layer to generate a rod progenitor that migrates along the radial fiber of the Müller glia into the outer nuclear layer, proliferates, and differentiates exclusively into rod photoreceptors. When retinal neurons are destroyed, Müller glia in the immediate vicinity of the damage partially and transiently dedifferentiate, re-express retinal progenitor and stem cell markers, re-enter the cell cycle, undergo interkinetic nuclear migration (characteristic of neuroepithelial cells), and divide once in an asymmetric, self-renewing division to generate a retinal progenitor. This daughter cell proliferates rapidly to form a compact neurogenic cluster surrounding the Müller glia; these multipotent retinal progenitors then migrate along the radial fiber to the appropriate lamina to replace missing retinal neurons. Some aspects of the injury-response in fish Müller glia resemble gliosis as observed in mammals, and mammalian Müller glia exhibit some neurogenic properties, indicative of a latent ability to regenerate retinal neurons. Understanding the specific properties of fish Müller glia that facilitate their robust capacity to generate retinal neurons will inform and inspire new clinical approaches for treating blindness and visual loss with regenerative medicine.     

Delivery of progenitor cells with injectable shear-thinning hydrogel maintains geometry and normalizes strain to stabilize cardiac function after ischemia

Objectives

The ventricle undergoes adverse remodeling after myocardial infarction, resulting in abnormal biomechanics and decreased function. We hypothesize that tissue-engineered therapy could minimize postischemic remodeling through mechanical stress reduction and retention of tensile myocardial properties due to improved endothelial progenitor cell retention and intrinsic biomechanical properties of the hyaluronic acid shear-thinning gel.