Sights on cone geometry

Rather than merely point-to-point dispatches, synaptic messengers also make widespread broadcasts, as evidenced by Steven DeVries, Wei Li, and Shannon Saszik (Northwestern University, Chicago, IL). Messages are received both near and far, they show, to create transient and sustained responses.

The cone presynaptic terminal is highly invaginated, with ribbons of glutamate-containing vesicles above each invagination. Cones respond to changes in light with graded changes in membrane potential. Decreases in light intensity depolarize cones and increase glutamate release, which then activates a class of cells known as Off bipolar cells.

In the new report, DeVries et al. show that Off bipolar cell dendrites contact cone terminals at two sites. Most subtypes of Off bipolar cells contact the base of the cone terminal, ∼300 nm...