Dendritic and Synaptic Plasticity of Neurons in the Human Age-Related Macular Degeneration Retina

To determine whether structural plasticity is evident in human retinal tissues in response to age-related macular degeneration (AMD). Remodeling events such as sprouting of neuronal processes and the reconnection of synapses are essential elements in repairing any damage to adult nervous tissues such as might occur in response to insults such as strokes or in AMD. The anatomic architecture of normal and AMD-affected human retinas was examined in the central, midperipheral, and far-peripheral regions. The retina, by virtue of its well-organized laminar structure, allows the identification and analysis of abnormal projections or connections of neuronal elements. In AMD-afflicted retinas, but not in normal aged human retinas, a large number of photoreceptor synapses across the entire retina retract into the outer nuclear layer. This event evokes the subsequent outgrowth of dendrites from the postsynaptic bipolar cells, again across the entire retina, and the subsequent reformation of synaptic contacts between photoreceptor and bipolar cells. These findings illustrate that there are anatomic changes in the AMD retina at all eccentricities, not just in the macular region. Aged human retinal neurons have the capacity to form new synapses, and this finding may be important when investigating possible means of repairing the damaged human retina.