Photoreceptor-bipolar cell transmission in the perfused retina eyecup of the mudpuppy

The hypothesis that a synaptic transmitter is released by photoreceptors in the dark is supported by experiments in which cobalt was used as a synaptic blocking agent, while intracellular recordings of receptors and neurons that are directly post-synaptic to receptors were maintained. In the dark the depolarizing bipolars are hyperpolarized, whereas the hyperpolarizing bipolars are depolarized.