Synapses between cones and diffuse bipolar cells of a primate retina

Area of Science:

• Neuroscience
• Ophthalmology
• Cell Biology

Background:

• Understanding retinal circuitry is crucial for visual processing.
• Cone bipolar cells mediate communication between photoreceptors and retinal ganglion cells.
• Previous research has characterized various mammalian bipolar cell synaptic connections.

Purpose of the Study:

• To describe the photoreceptor synapses of three specific diffuse bipolar cell types (DB3, DB4, DB5) in the rhesus macaque retina.
• To classify bipolar cell types based on their synaptic connections with cones.
• To compare primate bipolar cell synaptic structures with those of other vertebrates.

Main Methods:

• Ultrastructural analysis of photoreceptor synapses at 3.5-4.0 mm eccentricity in the rhesus macaque retina.
• Identification and characterization of synaptic connections (basal, ribbon, invaginating) between cones and specific diffuse bipolar cell types (DB3, DB4, DB5).
• Classification of bipolar cells based on axon termination layers (a-layer and b-layer) in the inner plexiform layer.

Main Results:

• DB3 cells form basal synapses (70% triad-associated) with 11 cones.
• DB4 cells form ribbon synapses (52) and basal synapses (23) with eight cones.
• DB5 cells form invaginating synapses (57) with seven cones and few basal synapses.

Conclusions:

• Bipolar cells terminating in the a-layer (e.g., DB3) form only basal synapses.
• Bipolar cells terminating in the b-layer are postsynaptic at ribbon synapses, with DB4 showing both ribbon and basal connections.
• At least one primate bipolar cell type exhibits dual synaptic connections with cones, mirroring findings in other vertebrates.