Abstract

The chemical synapse is a structure that permits information transfer from neuron to neuron via neurotransmitter release. Synapses of specialized cells in the retina and inner ear, e.g. retinal photoreceptor and bipolar cells or cochlear hair cells, have an extra electron-dense structure in comparison to ordinary synapses. This structure, called “ribbon”, plays a vital role on modulating vesicle release in response to time dependent input signals. This input, in the following investigation the terminal membrane voltage Vm of a retinal bipolar cell, is related to the variation of light intensity at a specific small region in the retina. Neurotransmitter release in axon terminals starts when the terminal membrane is depolarized which leads to open the voltage-gated calcium channels. Opening of calcium channels increases intracellular calcium concentration which triggers transient vesicle release. Transient vesicle release refers to contrast adaption (Oesch and Diamond, 2011). In case of long pulse stimulation, transient release is replaced by a tonic or sustained release, which occurs at slower rate and refers to luminance adaption (Oesch and Diamond, 2011). On the other hand, role of different periodic pulses on transient neurotransmitter release is investigated. The pulses make the terminal membrane depolarized in different levels which leads to different amount of neurotransmitter release.