title: The retina is a target for GnRH-3 system in the European sea bass, Dicentrarchus labrax.
abstract: The European sea bass expresses three GnRH (Gonadotrophin Releasing Hormone) forms that exert pleiotropic actions via several classes of receptors. The GnRH-1 form is responsible for the endogenous regulation of gonadotrophin release by the pituitary gland but the role of GnRH-2 and GnRH-3 remains unclear in fish. In a previous study performed in sea bass, we have provided evidence of direct links between the GnRH-2 cells and the pineal organ and demonstrated a functional role for GnRH-2 in the modulation of the secretory activity of this photoreceptive organ. In this study, we have investigated the possible relationship between the GnRH-3 system and the retina in the same species. Thus, using a biotinylated dextran-amine tract-tracing method, we reveal the presence of retinopetal cells in the terminal nerve of sea bass, a region that also contains GnRH-3-immunopositive cells. Moreover, GnRH-3-immunoreactive fibers were observed at the boundary between the inner nuclear and the inner plexiform layers, and also within the ganglion cell layer. These results strongly suggest that the GnRH-3 neurons located in the terminal nerve area represent the source of GnRH-3 innervation in the retina of this species. In order to clarify whether the retina is a target for GnRH, the expression pattern of GnRH receptors (dlGnRHR) was also analyzed by RT-PCR and in situ hybridization. RT-PCR revealed the retinal expression of dlGnRHR-II-2b, -1a, -1b and -1c, while in situ hybridization only showed positive signals for the receptors dlGnRHR-II-2b and -1a. Finally, double-immunohistochemistry showed that GnRH-3 projections reaching the sea bass retina end in close proximity to tyrosine hydroxylase (dopaminergic) cells, which also expressed the dlGnRHR-II-2b receptor subtype. Taken together, these results suggest an important role for GnRH-3 in the modulation of dopaminergic cell activities and retinal functions in sea bass.
authors.affiliation: Departamento de Biología, Facultad de Ciencias del Mar y Ambientales, Universidad de Cádiz, Campus de Excelencia Internacional del Mar (CEIMAR), E-11510 Puerto Real, Spain.
authors.forename: Arianna
authors.initials: A
authors.lastname: Servili
authors.forename: Patricia
authors.initials: P
authors.lastname: Herrera-Pérez
authors.forename: Olivier
authors.initials: O
authors.lastname: Kah
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Muñoz-Cueto
mesh_terms: D000818:Animals; D001492:Bass / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D008297:Male; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives*; D011966:Receptors, LHRH / Q000502:physiology; D012160:Retina / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D014446:Tyrosine 3-Monooxygenase / Q000502:physiology
chemical_list: D011966:Receptors, LHRH; C448022:gonadotropin-releasing hormone-III; D007987:Gonadotropin-Releasing Hormone; D014446:Tyrosine 3-Monooxygenase; D011761:Pyrrolidonecarboxylic Acid