![]() Toluidine blue stainingĪfter fixation, retinal pieces taken from the central region of the retina were washed in 0.1 M phosphate buffer (PB), pH 7.4, dehydrated in a graded series of ethanol, infiltrated with propylene oxide, and embedded in Epon 812 (Polysciences, Warrington, PA). The posterior segments of the eyes were processed as previously described. The eyes were enucleated, and they were then cut along the anterior border of the ora serrata. Adult rats and their litters were killed by an intraperitoneal injection of 10% chloral hydrate (10 ml/100 g body weight). Tissue preparationĮight pregnant rats and their litters of pups (four of each age) at PD 5~14, and 28 were used. All experimental procedures performed on the animals were conducted with the approval of the Catholic Ethics Committee of the Catholic University of Korea (2013-0088-06) and were consistent with the United States National Institutes of Health Guide for the Care and Use of Laboratory Animals. In this study, we demonstrate that this plexiform layer-like structure, the transient intermediate plexiform layer (TIPL) temporarily exists in the middle of the INL, the border between the bipolar and amacrine sublayers in the INL, in the rat retina from postnatal day (PD) 6 to PD 12, during retinal development and further characterize it.Įight litters of Sprague Dawley rats were used for assessment of retinas in various developmental stages. A distinct plexiform-like structure was found within the INL in developing retina. Previously, Kang and Chung reported development of the substance P (SP) (so called neurokinin 1) receptor-immunoreactive amacrine cells in the rat retina. However, within the INL, bipolar cells are located in the distal half, while amacrine cells are located in the proximal half, without any demarcating border between them. In this way, the formation of the plexiform layer clearly delineates the position of the main retinal cell classes, although the position of the retinal cell classes is primarily thought to be programmed by intrinsic factors. The outer plexiform layer (OPL) is formed when horizontal cell processes are elaborated laterally, generating a demarcating border between photoreceptors in the outer nuclear layer (ONL) and bipolar cells in the INL. The inner plexiform layer (IPL) appears as ganglion cell dendrites grow, creating a demarcating border between amacrine cells in the inner nuclear layer (INL) and ganglion cells in the ganglion cell layer (GCL). During this process, two synaptic layers of the retina are formed and retinal cells are accurately positioned. A number of transcription factors or homeodomain proteins are known to be involved in retinal cell fate determination and differentiation. Ganglion cells are generated first, followed in overlapping phases by horizontal cells, cone photoreceptors, amacrine cells, rod photoreceptors, bipolar cells, and finally, Müller cells. Retinal cell differentiation proceeds in a highly conserved histogenic order. During maturation, it develops into a laminated tissue with five major neuronal cell classes (photoreceptors, bipolar, horizontal, amacrine, and ganglion cells), each of which occupies a characteristic position within the retina. ![]() ![]() The retina develops from an apparently homogeneous collection of cells in a single-layered neuroepithelium. The retina is a part of the central nervous system (CNS) that originates from the neural ectoderm during development. ![]()
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