Analysis of rod/cone gap junctions from the reconstruction of mouse photoreceptor terminals

Abstract

Electrical coupling, mediated by gap junctions, contributes to signal averaging, synchronization and noise reduction in neuronal circuits. In addition, gap junctions may also provide alternative neuronal pathways. However, because they are small and especially difficult to image, gap junctions are often ignored in large-scale 3D reconstructions. Here, we reconstruct gap junctions between photoreceptors in the mouse retina, using serial blockface-scanning electron microscopy (SBF-SEM), focused ion beam-scanning electron microscopy (FIB-SEM), and confocal microscopy for the gap junction protein Cx36. An exuberant spray of fine telodendria extends from each cone pedicle (including blue cones) to contact 40-50 nearby rod spherules at sites of Cx36 labeling, with approximately 50 Cx36 clusters per cone pedicle and 2-3 per rod spherule. We were unable to detect rod/rod or cone/cone coupling. Thus, rod/cone coupling accounts for nearly all gap junctions between photoreceptors. We estimate a mean of 86 Cx36 channels per rod/cone pair, which may provide a maximum conductance of ~ 1200 pS, if all gap junction channels were open. This is comparable to the maximum conductance previously measured between rod/cone pairs in the presence of a dopamine antagonist to activate Cx36, suggesting the open probability of gap junction channels can approach 100% under certain conditions.

Melatonin in the mammalian retina: Synthesis, mechanisms of action and neuroprotection

“…Note that rod/cone coupling is maximal (reaches the theoretical maximum conductance established in Ishibashi et al85 ) in the presence of the D 2 -like antagonist spiperone. The operating range of rod/cone coupling is [0-1200 pS] (from Jin et al84 ; Ishibashi et al85 ).…”

“…congenic mice at different times in the circadian cycle, or during subjective day, with or without the presence of a dopamine D 2 -like receptor agonist or antagonist, or during the day under bright light adaptation. Note that rod/cone coupling is maximal (reaches the theoretical maximum conductance established in Ishibashi et al85 ) in the presence of the D 2 -like antagonist spiperone. The operating range of rod/cone coupling is [0-1200 pS] (from Jin et al84 ; Ishibashi et al85 ).…”

“…We are now able to measure rod/cone coupling strength and quantify its daily changes (Figure 3B,C). In addition, we recently established the operating range of rod/cone coupling in mouse retina and found that coupling can reach its minimum (0‐50 pS) under light adaptation or activation of D 2 ‐like receptors and its maximum (1200 pS) under pharmacological blockade of D 2 ‐like receptors 84,85 . Using novel mouse models that lack rod/cone coupling, 84 we were able to demonstrate the profound impact of rod/cone coupling plasticity on the light responses of cones, 84 and subsequently second‐order 86 and third‐order neurons 87 .…”

“…In addition, we recently established the operating range of rod/cone coupling in mouse retina and found that coupling can reach its minimum (0-50 pS) under light adaptation or activation of D 2 -like receptors and its maximum (1200 pS) under pharmacological blockade of D 2 -like receptors. 84,85 Using novel mouse models that lack rod/cone coupling, 84 we were able to demonstrate the profound impact of rod/ cone coupling plasticity on the light responses of cones, 84 and subsequently second-order 86 and third-order neurons. 87 Remarkably, eliminating rod/cone coupling decreases the amplitude of pupillary light reflex under dim light, thereby revealing its functional importance in the performance of a visual function.…”

Neurexin 3 is Essential for the Specific Wiring of a Color Pathway in the Mammalian Retina

“…The transgenic Opn1sw -cre mouse was generated by the NEI Genetic Engineering Core by BAC insertion. Strain generation was identical to that of our previously described Opn1sw -venus mouse (Ishibashi et al, 2022), but with the cre recombinase sequence instead of venus. Cre expression is under control of the Opn1sw -promoter.…”