Distinctive synaptic structural motifs link excitatory retinal interneurons to diverse postsynaptic partner types

Area of Science:

• Neuroscience
• Cell Biology
• Retinal Circuitry

Background:

• Neurons form synaptic connections with diverse partners, but the structural motifs of these synapses are not fully understood.
• Cone bipolar cells (CBCs) are crucial interneurons in the vertebrate retina, transmitting visual information from photoreceptors to downstream neurons.

Purpose of the Study:

• To investigate and compare the structural arrangements of output synapses from different cone bipolar cell types in the mouse retina.
• To determine if synaptic structural motifs vary based on the presynaptic bipolar cell type and its postsynaptic partners.

Main Methods:

• Serial electron microscopy was employed to reconstruct and analyze the three-dimensional structure of synaptic connections.
• Output synapses from various cone bipolar cell types in the mouse retina were meticulously mapped.

Main Results:

• Three primary presynaptic configurations were identified: single-ribbon, ribbonless, and multiribbon synapses.
• Mouse cone bipolar cells utilize a unique combination of these configurations, with at least six distinct synaptic motifs observed.
• Synaptic structures showed a bias towards specific motifs depending on the presynaptic CBC type and its postsynaptic partners.

Conclusions:

• Cone bipolar cells employ diverse and stereotypic synaptic strategies to modulate information flow.
• These distinct synaptic motifs contribute to the functional specialization of individual CBC types and retinal microcircuits.
• Understanding these structural variations is key to deciphering the complex processing of visual information in the retina.