Distinct Synaptic Transfer Functions in Same-Type Photoreceptors
- University of Tuebingen, Germany, Germany
- University of Tübingen, Germany
- University of Sussex, UK, United Kingdom
- University of Sussex, United Kingdom
Abstract
Many sensory systems use ribbon-type synapses to transmit their signals to downstream circuits. The properties of this synaptic transfer fundamentally dictate which aspects in the original stimulus will be accentuated or suppressed, thereby partially defining the detection limits of the circuit. Accordingly, sensory neurons have evolved a wide variety of ribbon geometries and vesicle pool properties to best support their diverse functional requirements. However, the need for diverse synaptic functions does not only arise across neuron types, but also within. Here we show that UV-cones, a single type of photoreceptor of the larval zebrafish eye, exhibit striking differences in their synaptic ultrastructure and consequent calcium to glutamate transfer function depending on their location in the eye. We arrive at this conclusion by combining serial section electron microscopy and simultaneous “dual-colour” 2-photon imaging of calcium and glutamate signals from the same synapse in vivo. We further use the functional dataset to fit a cascade-like model of the ribbon synapse with different vesicle pool sizes, transfer rates and other synaptic properties. Exploiting recent developments in simulation-based inference, we obtain full posterior estimates for the parameters and compare these across different retinal regions. The model enables us to extrapolate to new stimuli and to systematically investigate different response behaviours of various ribbon configurations. We also provide an interactive, easy-to-use version of this model as an online tool. Overall, we show that already on the synaptic level of single neuron types there exist highly specialized mechanisms which are advantageous for the encoding of different visual features.
Data availability
Data is deposited on Data-dryad under Schroder, Cornelius et al. (2021), Distinct Synaptic Transfer Functions in Same-Type Photoreceptors, Dryad, Dataset, https://doi.org/10.5061/dryad.7wm37pvt0.
Article and author information
Author details
Funding
Wellcome Trust (220277/Z/20/Z)
- Tom Baden
European Research Council (677687)
- Tom Baden
BBSRC (BB/R014817/1)
- Tom Baden
German Ministry for Education and Research (01GQ1601,01IS18052C,01IS18039A)
- Philipp Berens
German Research Foundation (BE5601/4-1,EXC 2064 - 390727645)
- Philipp Berens
Leverhulme Trust (PLP-2017-005)
- Tom Baden
Lister Institute for Preventive Medicine (Fellowship)
- Tom Baden
Marie Curie Sklodowska Actions individual fellowship (748716)
- Takeshi Yoshimatsu
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Animal experimentation: All procedures were performed in accordance with the UK Animals (Scientific Procedures) act 1986 and approved by the animal welfare committee of the University of Sussex. All licensed procedures (in vivo 2-photon imaging of live zebrafish larvae) are covered by the Project License PPL PE08A2AD2 (to TB).
Copyright
© 2021, Schroeder et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Distinct Synaptic Transfer Functions in Same-Type Photoreceptors
eLife 10:e67851.
https://doi.org/10.7554/eLife.67851
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