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Torten G, Fisher SK, Linberg KA, Luna G, Perkins G, Ellisman MH, Williams DS. Three-Dimensional Ultrastructure of the Normal Rod Photoreceptor Synapse and Degenerative Changes Induced by Retinal Detachment. J Neurosci 2023; 43:5468-5482. [PMID: 37414561 PMCID: PMC10376940 DOI: 10.1523/jneurosci.2267-22.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Revised: 05/08/2023] [Accepted: 06/19/2023] [Indexed: 07/08/2023] Open
Abstract
The rod photoreceptor synapse is the first synapse of dim-light vision and one of the most complex in the mammalian CNS. The components of its unique structure, a presynaptic ribbon and a single synaptic invagination enclosing several postsynaptic processes, have been identified, but disagreements about their organization remain. Here, we have used EM tomography to generate high-resolution images of 3-D volumes of the rod synapse from the female domestic cat. We have resolved the synaptic ribbon as a single structure, with a single arciform density, indicating the presence of one long site of transmitter release. The organization of the postsynaptic processes, which has been difficult to resolve with past methods, appears as a tetrad arrangement of two horizontal cell and two rod bipolar cell processes. Retinal detachment severely disrupts this organization. After 7 d, EM tomography reveals withdrawal of rod bipolar dendrites from most spherules; fragmentation of synaptic ribbons, which lose their tight association with the presynaptic membrane; and loss of the highly branched telodendria of the horizontal cell axon terminals. After detachment, the hilus, the opening through which postsynaptic processes enter the invagination, enlarges, exposing the normally sequestered environment within the invagination to the extracellular space of the outer plexiform layer. Our use of EM tomography provides the most accurate description to date of the complex rod synapse and details changes it undergoes during outer segment degeneration. These changes would be expected to disrupt the flow of information in the rod pathway.SIGNIFICANCE STATEMENT Ribbon-type synapses transmit the first electrical signals of vision and hearing. Despite their crucial role in sensory physiology, the three-dimensional ultrastructure of these synapses, especially the complex organization of the rod photoreceptor synapse, is not well understood. We used EM tomography to obtain 3-D imaging at nanoscale resolution to help resolve the organization of rod synapses in normal and detached retinas. This approach has enabled us to show that in the normal retina a single ribbon and arciform density oppose a tetrad of postsynaptic processes. In addition, it enabled us to provide a 3-D perspective of the ultrastructural changes that occur in response to retinal detachment.
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Affiliation(s)
- Gil Torten
- Departments of Ophthalmology and Neurobiology, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095
| | - Steven K Fisher
- Neuroscience Research Institute, University of California, Santa Barbara, Santa Barbara, California 93117
- Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California 93117
| | - Kenneth A Linberg
- Neuroscience Research Institute, University of California, Santa Barbara, Santa Barbara, California 93117
| | - Gabriel Luna
- Neuroscience Research Institute, University of California, Santa Barbara, Santa Barbara, California 93117
| | - Guy Perkins
- National Center for Microscopy and Imaging Research and Department of Neurosciences, University of California, San Diego, La Jolla, California 92093
| | - Mark H Ellisman
- National Center for Microscopy and Imaging Research and Department of Neurosciences, University of California, San Diego, La Jolla, California 92093
| | - David S Williams
- Departments of Ophthalmology and Neurobiology, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095
- Molecular Biology Institute, University of California, Los Angeles, Los Angeles, California 90095
- Brain Research Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095
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