| Somatostatin (SST) is a kind of cerebro-intestinal peptide, which is widely located in tissues such as the central nervous system, pancreas, digestive duct, and regulates physiological actions and pathological processes of some diseases acting as both neurotransmitter and neuromediator. SST has been increasely studied in the field of developmental biology. It has been demonstrated that SST is expressed widely during the development of nervous system, which has closely related to the differentiation and maturation of tissues and cells of the same region in terms of time and space. Previous studies have shown that in the rat retina the maturation of somatostatinergic systems encompasses late prenatal and early postnatal periods, suggesting a role of SST in maturative events of the retina. However, Based on previous reports, in the prenatal, postnatal and adult rat retina, there was no ganglion cells expressing SST mRNA except during the postnatal days from 7 to 14 when there was a part of ganglion cells expressing somatostatin peptide transiently. We observed that there were a lot of immunoreactive positive fibers in optic chiasma and optic tract when we studied the distribution of immunoreactive positive cells and fibers of hypothalamus in embryonic rats. We inferred that ganglion cell in the developing retina of rat could synthesize and transport SST into the superior visual center. Therefore, at first we studied the distribution of the positive fiber in developing optic chiasma and optic tract with immunohisto- chemistry. We then studied the expression of SST mRNA during the development of retina with in situ hybridization technique, especially the expression of SST mRNA in retinal ganglion cells. Secondly, we observed that the change of ganglion cell morphology and the conduct velocity of visual impulse by decreasing SST level during development with specificdepletor, and determined whether SST play an important role in genesis and differentiation of ganglion cells and formation and maturation of visual tract. The results is as following:1. The distribution of SST positive fibers in hypothalamus optic chiasma and optic tract initially existed in E16 and the density of positive fiber increased rapidly from E16 to E18, decreased in E19 and disappeared in E21.2. The distribution of SST mRNA during the development of retina: in E13, the positive cells became detectable in retinal ganglion cells layer (GCL), from E14 to E17, the number of cells expressing SST mRNA increased rapidly. The location of the positive cells in the developing GCL from the center to the periphery. At E17 most of the cells in the developing GCL expressed SST mRNA. From E18 to postnatal days the number of the positive cells decreased gradually. At postnatal day 15(PND15), the positive cells can be found only in the inner neuroblastic layer and in the GCL. At PND20 the distribution pattern and the number of the positive cell were essentially the same as that in adult rat.3. In the first group of rats with depletion of SST during the period of the embryo, we found that the ganglion cells arranged sparser, the number of cells decreased, the time of opening eye and the pupillary optic reflex delayed, the latency of visual evoked potential dramatically extended. In the second group of rats with depletion of SST during the period of the lactation, we found that the time of opening eye delayed, the pupillary optic reflex extended or disappeared, but ganglion cell layer and the latency of visual evoked potential did not change significantly. It is suggested the effects of SST on differentiation and development of ganglion cell was mainly in E16-19... |
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