Expression of neuron-specific enolase in the developing rat retina as revealed by immunocytochemistry

Expression of neuron-specific enolase (NSE) in retinal neurons was immunocytochemically investigated during the development of the rat retina. At embryonic day 14 (E14), the first immunoreaction of NSE was identified in the pigment epithelium. NSE-positive ganglion cells occurred at the inner surface of the retina by E15. Horizontal cells and photoreceptor cells became stainable for NSE in the outer portion of the neuroblastic layer as early as E17. At E20, when the majority of ganglion cells were intensely positive for NSE, immunoreactive amacrine cells first appeared at the outer surface of the developing inner plexiform layer. It was not until postnatal day 7 (P7) that NSE-positive bipolar cells occurred in the middle of the inner nuclear layer. At this stage, most of the photoreceptor cells located in the outer nuclear layer were immunolabeled, whereas the ectopic photoreceptor cells in the inner nuclear layer were devoid of immunoreaction. Most identifiable retinal neurons became strongly immunostained for NSE by P14. Our results indicate that the NSE expression of retinal neurons occurs just after their migration to the final location and prior to establishing the synaptic structures. In this paper, the characteristic sequence in which different types of retinal neurons exhibit NSE immunoreaction is discussed in the light of certain autoradiographic data on the sequence of retinal cell genesis.