Different postsynaptic events in two types of retinal bipolar cell

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Abstract
The 1st synapse in the vertebrate visual system is made between the photoreceptors and the bipolar cells. Bipolar cells fall into 2 distinct classes according to whether the cell hyperpolarizes or depolarizes to small centered spots of light. Most evidence indicates that the light-induced hyperpolarization of the photoreceptors suppresses transmitter release from the synaptic terminals, and it is probable that the differences between the 2 bipolar cell classes results from the different actions of the photoreceptor transmitter. Analyzing the membrane potential fluctuations in both types of bipolar cell showed that the voltage noise spectra differ. It is to be expected that postsynaptic noise would be composed of the sum of noise generated in and transmitted from the cones and the noise arising from the statistical nature of synaptic transmission. Evidence is reported for 2 such components in the voltage noise spectra recorded from each type of bipolar cell. The differences in the frequency distribution of the presumed transmitter-related components indicate that the transmitter generates events of longer duration in the depolarizing bipolar cells.