Horizontal cell connectivity in the anchovy retina-a 3D electron microscopic study.

Area of Science:

• Neuroscience
• Vision Science
• Comparative Anatomy

Background:

• Block-face scanning electron microscopy enables detailed neural network reconstruction.
• Anchovy retinas possess unique regions for color and polarization vision.
• Neural wiring for polarization contrast in anchovy retinas remains largely unknown.

Purpose of the Study:

• To elucidate the retinal connectomics of the European anchovy (Engraulis encrasicolus).
• To investigate the wiring rules of horizontal cells in relation to cone photoreceptors.

Main Methods:

• Volume electron microscopy was employed for dense neural reconstructions.
• Computer-aided reconstruction was used to map cellular connections.
• Analysis focused on horizontal cell types (H1, H2, H3) and their synaptic contacts.

Main Results:

• H1 cells connect to both polycone types; H2 cells connect to short cones; H3 cells connect to rods.
• A distinct double band of Müller fibers and H1 axon terminals were identified.
• Specific wiring patterns of horizontal cells with different photoreceptor types were clarified.

Conclusions:

• The polarization contrast system connects to a bichromatic color contrast mechanism.
• Anchovy polycones likely evolved from red and green cones.
• Blue single cones appear to have been lost in this retinal region.