Ribbon synapses of the retina

Vision is a highly complex task that involves several steps of parallel information processing in various areas of the central nervous system. Complex processing of visual signals occurs as early as at the retina, the first stage in the visual system. Various aspects of visual information are transmitted in parallel from the photoreceptors (the input neurons of the retina) through their interconnecting bipolar cells to the ganglion cells (the output neurons). Photoreceptors and bipolar cells transfer information via the release of the neurotransmitter glutamate at a specialized synapse, the ribbon synapse. Although known from early days of electron microscopy, the precise functioning of ribbon synapses has yet to be explained. In this review, we highlight recent advances towards understanding the molecular composition and function of this enigmatic synapse.