ERG Responses in Mice with Deletion of the Synaptic Ribbon Component RIBEYE

Abstract

Purpose To determine the influence of RIBEYE deletion and the resulting absence of synaptic ribbons on retinal light signaling by electroretinography. Methods Full-field flash electroretinograms (ERGs) were recorded in RIBEYE knock-out (KO) and wild-type (WT) littermate mice under photopic and scotopic conditions, with oscillatory potentials (OPs) extracted by digital filtering. Flicker ERGs and ERGs following intravitreal injection of pharmacological agents were also obtained under scotopic conditions. Results The a-wave amplitudes were unchanged between RIBEYE KO and WT mice; however, the b-wave amplitudes were reduced in KOs under scotopic, but not photopic, conditions. Increasing stimulation frequency led to a greater reduction in RIBEYE KO b-wave amplitudes compared with WTs. Furthermore, we observed prominent, supernormal OPs in RIBEYE KO mice in comparison with WT mice. Following intravitreal injections with l -2 amino-4-phosphonobutyric acid and cis -2,3 piperidine dicarboxylic acid to block ON and OFF responses at photoreceptor synapses, OPs were completely abolished in both mice types, indicating a synaptic origin of the prominent OPs in the KOs. Conversely, tetrodotoxin treatment to block voltage-gated Na + channels/spiking neurons did not differentially affect OPs in WT and KO mice. Conclusions The decreased scotopic b-wave and decreased responses to increased stimulation frequencies are consistent with signaling malfunctions at photoreceptor and inner retinal ribbon synapses. Because phototransduction in the photoreceptor outer segments is unaffected in the KOs, their supernormal OPs presumably result from a dysfunction in retinal synapses. The relatively mild ERG phenotype in KO mice, particularly in the photopic range, is probably caused by compensatory mechanisms in retinal signaling pathways.

Properties of multivesicular release from mouse rod photoreceptors support transmission of single-photon responses

“…Recent studies on mice in which synaptic ribbons have been eliminated by deleting the key ribbon protein, Ribeye, showed surprisingly modest deficits ( Fairless et al, 2020 ; Okawa et al, 2019 ) Multivesicular release in both salamander and mouse rods involves ribbon-associated vesicles ( Hays et al, 2020a ; Hays et al, 2020b ). One role of the ribbon may thus be to help organize vesicles to promote multivesicular release, implementing an Erlang process to improve the encoding of light responses near scotopic threshold ( Schein and Ahmad, 2005 ).…”

Photoreceptor Compartment-Specific TULP1 Interactomes

“…As expected, Ribeye knockout abolishes all photoreceptor synaptic ribbons and causes a loss of synaptic vesicles in the vicinity of the active zone of photoreceptor ribbon synapses [32]. However, phototransduction in the OSs is unaffected [63]. Whether Tulp1, Dynamin-1 and other Ribeye interacting proteins are present and correctly localized in Ribeye-/- photoreceptors has yet to be determined.…”

Properties of multi-vesicular release from rod photoreceptors support transmission of single photon responses

“…Recent studies on mice in which synaptic ribbons have been eliminated by deleting the key ribbon protein, Ribeye, showed surprisingly modest deficits (Fairless et al, 2020; Okawa et al, 2019) Multivesicular release in both salamander and mouse rods involves ribbon-associated vesicles (Hays et al, 2020b)(Hays et al, 2020a). One role of the ribbon may thus be to help organize vesicles to promote multivesicular release, implementing an Erlang process to improve the encoding of light responses near scotopic threshold (Schein and Ahmad, 2005).…”