Biochemical controls: specialized retinal synapses (Introduction)

by David Turell , Monday, June 19, 2023, 15:56 (521 days ago) @ David Turell

In specialized retinal cells:

https://medicalxpress.com/news/2023-06-uncovers-synaptic-intricacies-retina.html

"Cone synapses inside the eye's retina help the brain process changes in light. It's a unique synapse because it is has evolved to signal changes in light intensity, said Steven DeVries, MD, Ph.D., the David Shoch, MD, Ph.D., Professor of Ophthalmology.

"'Counterintuitively, cone neurotransmitter release is high in the dark and reduced by light. When the light's brighter, the reduction is larger. When the lights are dimmer, it's smaller; it operates differently from most synapses which use an increase in transmitter release to signal all-or-nothing, digital action potentials," DeVries said.

"Unlike most other synapses in the brain, each individual cone synapse is connected to more than a dozen different types of post-synaptic neurons, the bipolar cells, which relay information in parallel to the inner retina. In the inner retina, these parallel streams not only contribute to conscious vision but also to subconscious processes like gaze stabilization.

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"Using these techniques, the investigators showed that certain bipolar cell types respond to individual fusion events and total quanta while other types respond to degrees of locally coincident events, creating a nonlinear summation. These differences are caused by a combination of factors specific to each bipolar cell type, including diffusion distance, contact number, receptor affinity, and proximity to transporters.

"'The outer retina uses the same toolbox as elsewhere in the central nervous system, like vesicles, synaptic release zones and postsynaptic receptors, but organizes these elements in novel ways to accomplish a different, very localized type of processing. Analog processing is also found in the dendritic tree of central nervous system neurons, where the bulk of calculation, both linear and nonlinear, occurs," DeVries said.

"According to DeVries, one next step for his team includes using a new, more powerful type of super-resolution microscopy to determine the protein components that make up cone synapses.

"'One of the ways that the different bipolar cells divide the cone signal up is that some of them are very sensitive to small signals and others require strong signals to respond; the 'strong signal' or high threshold bipolar cell has a unique type of insensitive post-synaptic receptor. We would also like to identify this receptor," DeVries said."

comment: We know eyes evolved from light sensing spots of cells, but how this degree of intricate design developed implies a designer was necessary,