Relationship between simultaneously recorded spiking activity and fluorescence signal in GCaMP6 transgenic mice
- Allen Institute for Brain Science, United States
Abstract
Fluorescent calcium indicators are often used to investigate neural dynamics, but the relationship between fluorescence and action potentials (APs) remains unclear. Most APs can be detected when the soma almost fills the microscope's field of view, but calcium indicators are often used to image populations of neurons, necessitating a large field of view, generating fewer photons per neuron, and compromising AP detection. Here we characterized the AP-fluorescence transfer function in vivo for 48 layer 2/3 pyramidal neurons in primary visual cortex, with simultaneous calcium imaging and cell-attached recordings from transgenic mice expressing GCaMP6s or GCaMP6f. While most APs were detected under optimal conditions, under conditions typical of population imaging studies only a minority of 1AP and 2AP events were detected (often <10% and ~20-30%, respectively), emphasizing the limits of AP detection under more realistic imaging conditions.
Data availability
All data generated and analyzed in this study are available at https://portal.brain-map.org/explore/circuits/oephys
Article and author information
Author details
Saskia E J de Vries
Funding
Allen Institute for Brain Science (program funds)
- Lawrence Huang
- Peter Ledochowitsch
- Ulf Knoblich
- Jérôme Lecoq
- Gabe J Murphy
- Clay Reid
- Saskia E J de Vries
- Christof Koch
- Hongkui Zeng
- Michael A Buice
- Jack Waters
- Lu Li
National Natural Science Foundation of China (NSFC31871055)
- Lu Li
Guangdong Science and Technology Department (2017B030314026)
- Lu Li
This work is funded by the Allen Institute for Brain Science. The funder had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Animal experimentation: Experimental procedures were conducted in accordance with NIH guidelines and approved by the Institutional Animal Care and Use Committee (IACUC) of the Allen Institute for Brain Science under protocol number 1509.
Copyright
© 2021, Huang 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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Relationship between simultaneously recorded spiking activity and fluorescence signal in GCaMP6 transgenic mice
eLife 10:e51675.
https://doi.org/10.7554/eLife.51675
Further reading
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Granule cells of the cerebellum make up to 175,000 excitatory synapses on a single Purkinje cell, encoding the wide variety of information from the mossy fibre inputs into the cerebellar cortex. The granule cell axon is made of an ascending portion and a long parallel fibre extending at right angles, an architecture suggesting that synapses formed by the two segments of the axon could encode different information. There are controversial indications that ascending axon (AA) and parallel fibre (PF) synapse properties and modalities of plasticity are different. We tested the hypothesis that AA and PF synapses encode different information, and that the association of these distinct inputs to Purkinje cells might be relevant to the circuit and trigger plasticity, similar to the coincident activation of PF and climbing fibre inputs. Here, by recording synaptic currents in Purkinje cells from either proximal or distal granule cells (mostly AA and PF synapses, respectively), we describe a new form of associative plasticity between these two distinct granule cell inputs. We show for the first time that synchronous AA and PF repetitive train stimulation, with inhibition intact, triggers long-term potentiation (LTP) at AA synapses specifically. Furthermore, the timing of the presentation of the two inputs controls the outcome of plasticity and induction requires NMDAR and mGluR1 activation. The long length of the PFs allows us to preferentially activate the two inputs independently, and despite a lack of morphological reconstruction of the connections, these observations reinforce the suggestion that AA and PF synapses have different coding capabilities and plasticity that is associative, enabling effective association of information transmitted via granule cells.
