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.
Gen Comp Endocrinol. 2012 Feb 1;175(3):398-406. doi: 10.1016/j.ygcen.2011.11.007. Epub 2011 Nov 19.
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.
欧洲鲈鱼表达三种 GnRH（促性腺激素释放激素）形式，通过几类受体发挥多效作用。 GnRH-1 形式负责垂体腺内源性调节促性腺激素的释放，但 GnRH-2 和 GnRH-3 在鱼类中的作用仍不清楚。在之前在鲈鱼中进行的一项研究中，我们提供了 GnRH-2 细胞与松果体之间直接联系的证据，并证明了 GnRH-2 在调节这种光感受器官的分泌活性中的功能作用。在这项研究中，我们在同一物种中研究了 GnRH-3 系统与视网膜之间的可能关系。因此，我们使用生物素化葡聚糖胺示踪法，揭示了鲈鱼终神经中存在向视网膜细胞，该区域也含有 GnRH-3 免疫阳性细胞。此外，在核内和内丛状层之间的边界以及神经节细胞层内观察到 GnRH-3 免疫反应纤维。这些结果强烈表明，位于终神经区域的 GnRH-3 神经元代表该物种视网膜中 GnRH-3 神经支配的来源。为了阐明视网膜是否是 GnRH 的靶标，还通过 RT-PCR 和原位杂交分析了 GnRH 受体（dlGnRHR）的表达模式。RT-PCR 显示 dlGnRHR-II-2b、-1a、-1b 和 -1c 在视网膜中的表达，而原位杂交仅显示 dlGnRHR-II-2b 和 -1a 受体的阳性信号。最后，双重免疫组织化学显示，到达鲈鱼视网膜的 GnRH-3 投射与酪氨酸羟化酶（多巴胺能）细胞紧密接近，这些细胞也表达了 dlGnRHR-II-2b 受体亚型。总之，这些结果表明 GnRH-3 在调节鲈鱼多巴胺能细胞活性和视网膜功能方面具有重要作用。
