Encoding light intensity by the cone photoreceptor synapse.
How cone synapses encode light intensity determines the precision of information transmission at the first synapse on the visual pathway. Although it is known that cone photoreceptors hyperpolarize to light over 4-5 log units of intensity, the relationship between light intensity and transmitter release at the cone synapse has not been determined. Here, we use two-photon microscopy to visualize release of the synaptic vesicle dye FM1-43 from cone terminals in the intact lizard retina, in response to different stimulus light intensities. We then employ electron microscopy to translate these measurements into vesicle release rates. We find that from darkness to bright light, release decreases from 49 to approximately 2 vesicles per 200 ms; therefore, cones compress their 10,000-fold operating range for phototransduction into a 25-fold range for synaptic vesicle release. Tonic release encodes ten distinguishable intensity levels, skewed to most finely represent bright light, assuming release obeys Poisson statistics.
Choi
Sue-Yeon
SY
Department of Molecular and Cell Biology and the Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, California 94720, USA.
Borghuis
Bart G
BG
Borghuis
Bart
B
Rea
Ruth
R
Levitan
Edwin S
ES
Sterling
Peter
P
Kramer
Richard H
RH
D000818:Animals; D004307:Dose-Response Relationship, Radiation; D005456:Fluorescent Dyes / Q000493:pharmacokinetics / Q000528:radiation effects; D066298:In Vitro Techniques; D008027:Light; D008116:Lizards; D016012:Poisson Distribution; D011726:Pyridinium Compounds / Q000493:pharmacokinetics / Q000528:radiation effects; D000644:Quaternary Ammonium Compounds / Q000493:pharmacokinetics / Q000528:radiation effects; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology* / Q000528:radiation effects*; D013569:Synapses / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism / Q000502:physiology; D014785:Vision, Ocular / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology*
C507005:AM1-43 compound; C073804:FM1 43; D005456:Fluorescent Dyes; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds