An analysis of voltage noise in rod bipolar cells of the dogfish retina.

Abstract

1. The power spectral density of voltage noise in depolarizing rod bipolar cells was analysed during darkness and steady illumination. 2. The variance of the voltage fluctuations increased nearly linearly with dim light but was suppressed by bright light. 3. The spectrum in darkness and during illumination could be resolved into two components. One component was attributed to random quantal events arising from spontaneous or light‐induced isomerization of rhodopsin in the bipolar cell's rod pool. 4. The second component had a peaked spectrum and was attributed to synaptic noise. 5. A significant fraction of the noise variance in the dark arose from spontaneous thermal isomerization of rhodopsin, with a rate constant of 6 X 10(‐12) s‐1 or a half‐life for rhodopsin of 3700 years at 17 degrees C. 6. The peak amplitude of the single‐photon signal in the bipolar cell was about 200 microV, associated with a peak conductance increase of 200 pS. The spectral data suggest that there may be a random delay in the generation of these events. 7. It was concluded that the limitation to single‐photon detection in the dark‐adapted state may be the rate of spontaneous rhodopsin isomerization. Synaptic noise at the rod‐bipolar cell level would not seriously degrade the signal‐to‐noise ratio.

Regulation of ON bipolar cell activity

“…In 7 rod bipolar cell-AII amacrine cell pairs, the average size of the response to CPPG that failed to elicit an EPSC in the AII was 3.4±0.6 mV. By comparison, the single photon response, measured in voltage clamp, has been estimated to be between 5 and 10 pA in mouse (Field and Rieke, 2002;Berntson et al, 2004b), similar to the estimate of 8 pA in dogfish, obtained 20 years earlier (Ashmore and Falk, 1982) using sharp electrode recording and noise analysis. For a rod bipolar cell with an input resistance of 2 GΩ (Zhou et al, 2006;Oltedal et al, 2007), the single photon response would produce a depolarization of approximately 10-20 mV in the rod bipolar cell.…”

Neurotransmitter‐induced currents in retinal bipolar cells of the axolotl, Ambystoma mexicanum.

“…Ashmore & Copenhagen (1983) estimated that about 75 % of the light-suppressed voltage noise variance in turtle hyperpolarizing bipolar cells originated in presynaptic cones. Similarly, for dogfish depolarizing bipolar cells, Ashmore & Falk (1982) calculated that about 60% of the light-suppressed noise was transmitted from presynaptic rods. In both cases the remaining light-sensitive noise was assumed to be introduced during synaptic transmission, as fluctuations in quantal release and post-synaptic channel noise.…”

An analysis of transmission from cones to hyperpolarizing bipolar cells in the retina of the turtle.

“…A related analysis has been applied to the rod-bipolar system in the dogfish (Ashmore & Falk, 1982), but where the properties of the rods had to be inferred. In the turtle, both pre-and post-synaptic contributions to the noise can be recorded and can be used to separate synaptic mechanisms.…”

“…The continuous release of transmitter from the photoreceptor terminals in the dark leads to observable fluctuations in the bipolar cell membrane potential (Simon, Lamb & Hodgkin, 1975), and it is the analysis of such fluctuations which should characterize the nature of transmitter action and synaptic interactions at the outer plexiform layer. Noise analysis has been used to investigate transduction (Hagins, 1965; Schwartz, 1977;Lamb & Simon, 1977;Baylor, Matthews & Yau, 1980) as well as synaptic mechanisms in photoreceptors, (Ashmore & Copenhagen, 1980;Ashmore & Falk, 1982).…”