title: Spikes in retinal bipolar cells phase-lock to visual stimuli with millisecond precision.
abstract: BACKGROUND
  The conversion of an analog stimulus into the digital form of spikes is a fundamental step in encoding sensory information. Here, we investigate this transformation in the visual system of fish by in vivo calcium imaging and electrophysiology of retinal bipolar cells, which have been assumed to be purely graded neurons.
  
  
  RESULTS
  Synapses of all major classes of retinal bipolar cell encode visual information by using a combination of spikes and graded signals. Spikes are triggered within the synaptic terminal and, although sparse, phase-lock to a stimulus with a jitter as low as 2-3 ms. Spikes in bipolar cells encode a visual stimulus less reliably than spikes in ganglion cells but with similar temporal precision. The spike-generating mechanism does not alter the temporal filtering of a stimulus compared with the generator potential. The amplitude of the graded component of the presynaptic calcium signal can vary in time, and small fluctuations in resting membrane potential alter spike frequency and even switch spiking on and off.
  
  
  CONCLUSIONS
  In the retina of fish, the millisecond precision of spike coding begins in the synaptic terminal of bipolar cells. This neural compartment regulates the frequency of digital signals transmitted to the inner retina as well as the strength of graded signals.
authors: Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
authors: Tom
authors: T
authors: Baden
authors: Federico
authors: F
authors: Esposti
authors: Anton
authors: A
authors: Nikolaev
authors: Leon
authors: L
authors: Lagnado
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D006054:Goldfish / Q000502:physiology*; D008027:Light; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D010775:Photic Stimulation; D017729:Presynaptic Terminals / Q000502:physiology*; D012160:Retina / Q000737:chemistry / Q000166:cytology*; D051245:Retinal Bipolar Cells / Q000502:physiology*; D013997:Time Factors; D015027:Zebrafish / Q000502:physiology*
chemical_list: D002118:Calcium