Ribbon synapses compute temporal contrast and encode luminance in retinal rod bipolar cells.
Contrast is computed throughout the nervous system to encode changing inputs efficiently. The retina encodes luminance and contrast over a wide range of visual conditions and must adapt its responses to maintain sensitivity and to avoid saturation. We examined the means by which one type of adaptation allows individual synapses to compute contrast and encode luminance in biphasic responses to step changes in light levels. Light-evoked depletion of the readily releasable vesicle pool (RRP) at rod bipolar cell ribbon synapses in rat retina limited the dynamic range available to encode transient, but not sustained, responses, thereby allowing the transient and sustained components of release to compute temporal contrast and encode mean light levels, respectively. A release/replenishment model revealed that a single, homogeneous pool of synaptic vesicles is sufficient to generate this behavior and that a partial depletion of the RRP is the dominant mechanism for shaping the biphasic contrast/luminance response.
Synaptic Physiology Section, National Institute of Neurological Disorders and Stroke, US National Institutes of Health, Bethesda, Maryland, USA.
Nicholas W
NW
Oesch
Jeffrey S
JS
Diamond
D000818:Animals; D000831:Animals, Newborn; D055592:Biophysical Phenomena; D003198:Computer Simulation; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D066298:In Vitro Techniques; D008027:Light; D008959:Models, Neurological; D018408:Patch-Clamp Techniques / Q000379:methods; D010775:Photic Stimulation; D051381:Rats; D012160:Retina / Q000166:cytology*; D051245:Retinal Bipolar Cells / Q000502:physiology*; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology; D013569:Synapses / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology