Formation of new rod photoreceptor synapses onto differentiated bipolar cells in goldfish retina

摘要

AbstractIn goldfish new rods are continuously added to the entire retina at a rate that assures stable rod density, while the densities of other neurons decrease. Theb1bipolar, known to contact every rod within its dendritic domain, was used to determine the fate of these newly formed rods.Golgi‐stainedb1bipolars were sectioned serially at 0.5 μm in the plane of the receptor terminals and reconstructions of their rod and cone contacts were prepared from camera lucida drawings.The newly formed rods are accommodated within the dendritic trees of alreadyformedb1bipolars at a rate of about one new rod synapse/bipolar/month. During growth from about 6 months to 5 years of age the number of synapses onto eachb1bipolar increases by 50. Concomitantly the dendritic tree area increases by about 50, and the density of rod‐b1synapses remains constant at about one synapse/11 μm2.Assuming a dendritic coverage factor of 1, theb1bipolars will contact every retinal rod. The numbers of cones contacted and not contacted do not significantly change. The overall dimensions ofb1bipolars increase with retinal growth and new branches are added to their dendritic trees.These observations show that new rods added to adult goldfish retina form synapses with old bipolars. Some functional inferences are also