Abstract
Author SummaryThe process of neurotransmission involves the conversion of electrical signals into the release of a chemical neurotransmitter from the neurons synaptic terminal, and the key trigger for this release is a rise in calcium concentration. Accordingly, the amplitude and speed of this calcium signal controls the amplitude and time-course of synaptic communication. Working on the synaptic terminals of fish retinal bipolar cells, we show that the presynaptic calcium signal and the subsequent neurotransmitter release are shaped by the basic property of synapse volume. Using a combination of experimental approaches and computational models, we found that large synapses are slow and adapt little during ongoing stimulation, while small synapses are fast and show more profound adaptation. This observation leads to a second key concept: since neurons usually have several presynaptic terminals that may vary in volume, a single neuron can, in principle, forward different synaptic signals to different postsynaptic partners. We provide direct evidence that this is the case for bipolar cells of the fish retina.
Highlights
The retina analyzes the visual world through a series of spatiotemporal filters that establish parallel representations for transmission to the brain [1,2,3,4]
The process of neurotransmission involves the conversion of electrical signals into the release of a chemical neurotransmitter from the neurons synaptic terminal, and the key trigger for this release is a rise in calcium concentration
Working on the synaptic terminals of fish retinal bipolar cells, we show that the presynaptic calcium signal and the subsequent neurotransmitter release are shaped by the basic property of synapse volume
Summary
The retina analyzes the visual world through a series of spatiotemporal filters that establish parallel representations for transmission to the brain [1,2,3,4]. The anatomical organization of these channels is established in the inner plexiform layer (IPL), which is organized into five to six distinct strata containing the dendrites of as many as 20 different types of retinal ganglion cell (RGC) [2]. Bipolar cells (BCs) with distinct filtering properties make excitatory synaptic connections with defined subsets of RGCs [5]. An answer might lie in reconsidering the fundamental neural element through which the visual signal is transmitted to the inner retina: individual BCs have diverse properties, their output is transmitted through a much more numerous and heterogeneous component of neural circuits–synapses [10]. The property we concentrate on is the volume of the terminal, which is expected to influence the amplitude and kinetics of the presynaptic calcium signal controlling neurotransmission [12]
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