Abstract
Purpose :
Previous studies have shown structural remodeling of rod photoreceptor synaptic terminals (rod spherules, RS) in response to experimental retinal detachment (RD, Erickson, et al., 1983, IOVS, 24: 927). However, these studies relied on conventional electron microscopy, which is limited for 3-D analyses. Here we used the advanced imaging capabilities of electron microscope tomography (EMT) to study the 3-D complexities of the RS in feline retina during remodeling after experimental RD. Our aim was to generate a high-resolution 3-D analysis of the time-course of RS remodeling, and thus enhance our understanding of this process and its potential for reversibility.
Methods :
All tissue used in this study was generated in previous studies of experimental RD (Erickson et al., 1983). Here we generated tomograms from RDs of 30min, 1hr, 24hr, 48hr, 72hr, 7d duration and from a control eye without RD. Tomograms were generated from imaging of either single 400nm sections, at 400KeV, or serial 200nm-thick sections, at 120KeV. 3D models were constructed using the software IMOD3D.
Results :
At 7d, the RS no longer form a solid layer of terminals across the outer plexiform layer (OPL). Those that remain show several signs of severe degeneration including their transformation into an elongated “teardrop” shape, loss of some post-synaptic processes, changes in the geometry of the synaptic invagination with enlargement of the opening (hilus) through which post-synaptic processes pass, fragmentation of synaptic ribbons, the accumulation of large cytoplasmic vesicles, and a loss of branches from horizontal cell axon terminals within the synaptic invagination. In addition, Müller cells show many ultrastructural changes associated with their hypertrophy throughout the OPL. Within 1hr of RD there is minor restructuring of the synaptic invagination and postsynaptic processes, and a severe loss of synaptic vesicles. The degenerative phenotype becomes more severe as the length of the RD increases.
Conclusions :
Our data indicate that RS undergo both pre- and post-synaptic changes that begin within 1hr after a RD. This is much earlier than previously thought. Clearly, it will now be critical to determine at what stage these early changes cease to be reversible, in order to understand the limitations of surgical reattachment for the return of vision in RD patients.
This is a 2021 ARVO Annual Meeting abstract.