Electron‐translucency and partial defects of synaptic basal lamina in the electrocyte synapse of an electric ray (Narke japonica) in 3D embedment‐free section electron microscopy

• Published in: Microscopy research and technique Vol. 87; no. 7; pp. 1647 - 1653
• Main Authors: Chomphoo, Surang, Kondo, Hisatake, Hipkaeo, Wiphawi
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.07.2024; Wiley Subscription Services, Inc
• Subjects: Animals; Basal lamina; Consistency; Defects; electric organ; Electrical Synapses - physiology; Electrical Synapses - ultrastructure; electron‐translucenty; embedment‐free TEM; Imaging, Three-Dimensional - methods; liquid–liquid phase separation; Membranes; Microscopy; Microscopy, Electron, Transmission - methods; Sol-gel processes; sol/gel transition; Synapses - ultrastructure; synaptic basal lamina; Synaptic Membranes - ultrastructure; Synaptic vesicles; Synaptic Vesicles - ultrastructure; torpedo; Transmission electron microscopy; Vesicles; torpedo; liquid–liquid phase separation; sol/gel transition; embedment‐free TEM; electron‐translucenty; electric organ; synaptic basal lamina
• ISSN: 1059-910X; 1097-0029; 1097-0029
• DOI: 10.1002/jemt.24534

The synaptic basal lamina of the electrocytes was disclosed to be electron‐translucent to some extent when viewed in an en‐face direction in embedment‐free section transmission electron microscopy (EFS‐TEM), and synaptic vesicles located close to the presynaptic membrane were seen through the synaptic basal lamina together with the presynaptic and postsynaptic membranes. This feature of translucency has the potential to analyze possible spatial interrelations in situ between bioactive molecules in the synaptic basal lamina and the synaptic vesicles in further studies. The synaptic basal lamina, appearing as an electron‐dense line sandwiched by two parallel lines representing the presynaptic and postsynaptic membranes in ultrathin sections cut right to the synaptic junctional plane in conventional TEM, was not fully continuous but randomly intermittent along its trajectory. Compatible with the intermittent line appearance, the en‐face 3D view in embedment‐free section TEM revealed for the first time partial irregular defects of the synaptic basal lamina. Considering the known functional significance of several molecules contained in the synaptic basal lamina in the maintenance and exertion of the synapse, its partial defects may not represent its rigid structural features, but its immature structure under remodeling or its dynamic changes in consistency such as the sol/gel transition, whose validity needs further examination. Research Highlights In embedment‐free section TEM, a 3D en‐face view of synaptic basal lamina in situ is reliably possible. The basal lamina en‐face is electron‐translucent, which makes it possible to analyze spatial interrelation between pre‐ and post‐synaptic components. Partial irregular defects in the basal lamina are revealed in Torpedo electrocytes, suggesting its remodeling or dynamic changes in consistency. In 3D embedment‐free TEM, the synaptic basal lamina of the electrocyte appeared translucent and was disclosed to have partial defects. Potential merits of its translucency and functional significance of its partial defects were discussed.