Transient expression of somatostatin mRNA in developing ganglion cell layers of rat retina

Somatostatin (SOM) mRNA in developing ganglion cell layer (GCL) detected by in situ hybridization histochemistry anti SOM peptide in developing optic chiasma and optic tract detected by immunocytochemistry were monitored to e xplore whether ganglion cells expressing SOM project to the visual center. Most of these cells in the developing GCL expressed SOM transiently from em bryonic day 13 (E13) to E21. The cells expressing SOM mRNA initially follow ed a central-to-peripheral pattern of development. The cells expressing SOM mRNA in the retinas of fetuses became detectable at E13. From E14 to E17 t he number of cells expressing SOM mRNA increased rapidly. At E17 most of th e cells in the developing GCL expressed SOM mRNA. From E18 to postnatal day s the positive cells became sparse except at the postnatal day 0 (PND0) the positive cells decreased dramatically in comparison with that at the E21. At PND15, the positive cells only can be found in the inner neuroblastic la yer and in the ganglion cell layer. At PND20 the distribution pattern and t he number of the positive cells were essentially the same as that in adult rat. SOM immunoreactivity was detectable at E16 in the developing optic chi asma and optic tract; the majority of the fibers in these area were SOM pos itive. From E16 to E18 the density of the immunostaining increased rapidly, whereas from E19 to E21 the density decreased. At PND0 no positive fibers were seen. The transient presence of SOM in most of the ganglion cells in t he developing ganglion cell layer has prompted us to study the rc,le of SOM in generation and differentiation of the retinal ganglion cells, and forma tion of the retina-visual center projections. (C) 2001 Elsevier Science B.V . All rights reserved.