Encoding light intensity by the cone photoreceptor synapse

Neuron. 2005 Nov 23;48(4):555-62. doi: 10.1016/j.neuron.2005.09.011.


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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Dose-Response Relationship, Radiation
  • Fluorescent Dyes / pharmacokinetics
  • Fluorescent Dyes / radiation effects
  • In Vitro Techniques
  • Light*
  • Lizards
  • Poisson Distribution
  • Pyridinium Compounds / pharmacokinetics
  • Pyridinium Compounds / radiation effects
  • Quaternary Ammonium Compounds / pharmacokinetics
  • Quaternary Ammonium Compounds / radiation effects
  • Retinal Cone Photoreceptor Cells / physiology*
  • Retinal Cone Photoreceptor Cells / radiation effects*
  • Synapses / physiology*
  • Synaptic Vesicles / metabolism
  • Synaptic Vesicles / physiology
  • Vision, Ocular / physiology*
  • Visual Pathways / physiology*


  • AM1-43 compound
  • FM1 43
  • Fluorescent Dyes
  • Pyridinium Compounds
  • Quaternary Ammonium Compounds