Synaptic organization of vertebrate retina may lead to understanding of human retinal disease

Fort Lauderdale, FL-Samuel M. Wu, PhD, has spent much of his career at the Cullen Eye Institute, Baylor College of Medicine, Houston, investigating the molecular, cellular, and synaptic mechanisms underlying signal processing systems in the retina as well as the synaptic mechanisms underlying eye diseases.

“By understanding the general principles of the synaptic circuitry, not only will we be able to understand how animals and humans see and process information in the retina, but it may also give us some hints about retinal diseases,” Dr. Wu said. He noted that one form of retinitis pigmentosa involves rod-cone degeneration, that congenital stationary blindness may be related to some function of the post-synaptic channels, and that loss of retinal ganglion cell sensitivity, an early sign of glaucoma, may originate in the A2 amacrine cell system.

Dr. Wu was the 2009 recipient of the Friedenwald Award, which recognizes exceptional scientific research as applied to ophthalmology. He is professor of ophthalmology, professor of molecular physiology and biophysics, and professor of neuroscience at the Cullen Eye Institute, where he also holds the Camille and Raymond Hankamer Chair in ophthalmology.

During the Friedenwald Award lecture, he summarized the findings of his lab on the synaptic organization of the vertebrate retina. Although there are some species-specific variations among the vertebrates commonly used in scientific studies, more importantly, there are many common principles or features that are applicable to all vertebrates and also to people, Dr. Wu said. Grasping these principles eventually could lead to better understanding of retinal diseases in humans.

He described four principles of synaptic organization:

• Cell-cell coupling can be divided into homocellular, in which cells of the same type are coupled, or heterocellular, in which different types of cells are coupled.
• Retinal neurons seem to use voltage-gated and time-dependent channels to shape their light responses.
• In the bipolar cells, there seem to be common rules concerning the rod and cone input and axon terminal morphology.
• The fourth rule concerns center-surround receptive field organization and antagonism.