A Positive Feedback Synapse from Retinal Horizontal Cells to Cone Photoreceptors
<p>May 04, 2011 06:21 PM
 
pdf is free and online... from  Cal, Berk.
exclt article;
 
retina is exceptionally approachable
 
synapses btwn  HCs = horizontal cell and  CONE photoreceptos was of partic interest.
HC exerts  negative feedback on  cones.
 
HCs project laterally over hundreds of microns and integrates many rods and cones, so
negative feedback causes rods and cones to have an  antagonist  center-surround recep field.
 
This is first seen in bipolar cells and subseq cells  and 
results in  enhancing the neural repres of spatial contrast  and sharpening visual edge detection.
 
mechanism by which HC  causes  negative feedback to cones  has been controversial.
three proposals  1)  gaba  hyperpolariz  2)  ephaptic by elecric currents
3)  proton efflux.
 
Here,   BIG SURPRISNG DISCOVERY:  RETROGRADE signal from HCs to cones by
elevating  intracell Ca in cones and  ENHANCING neuroxmtr release in the cones.
 
(note:  mech is robust in intact retina but disrupted in slices.)
 
This POSITIVE feedback  which only occurs locally  offsets the negative feedback from the more distant
neighborhood.
 
used  anole lizards  (retina is ALL cone)
 
 
 
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