Mapping of excitatory and inhibitory postsynaptic potentials of neuronal populations in hippocampal slices using the GEVI, ArcLight

Abstract

To understand the circuitry of the brain, it is essential to clarify the functional connectivity among distinct neuronal populations. For this purpose, neuronal activity imaging using genetically-encoded calcium sensors such as GCaMP has been a powerful approach due to its cell-type specificity. However, calcium (Ca2+) is an indirect measure of neuronal activity. A more direct approach would be to use genetically encoded voltage indicators (GEVIs) to observe subthreshold, synaptic activities. The GEVI, ArcLight, which exhibits large fluorescence transients in response to voltage, was expressed in excitatory neurons of the mouse CA1 hippocampus. Fluorescent signals in response to the electrical stimulation of the Schaffer collateral axons were observed in brain slice preparations. ArcLight was able to map both excitatory and inhibitory inputs projected to excitatory neurons. In contrast, the Ca2+ signal detected by GCaMP6f, was only associated with excitatory inputs. ArcLight and similar voltage sensing probes are also becoming powerful paradigms for functional connectivity mapping of brain circuitry.

In VitroTesting of Voltage Indicators: Archon1, ArcLightD, ASAP1, ASAP2s, ASAP3b, Bongwoori-Pos6, BeRST1, FlicR1, and Chi-VSFP-Butterfly

“…2C, thick gray dashed line), consistent with the previously reported sigmoidal fluorescence-voltage relationship of ArcLight (Jin et al, 2012). Interestingly, ArcLight and two ASAP variants also gave proportionally the strongest optical signal at voltages more negative than À70 mV (neuronal resting membrane potential), suggesting that these three indicators may be useful for tracking hyperpolarizing (inhibitory) signals, consistent with the data obtained with ArcLightderived Bongwoori (Nakajima and Baker, 2018) (Fig. 2D, gray round markers).…”

“…In the cerebral cortex, hyperpolarizing potentials may provide important clues about the status of outward potassium currents (which are often influenced by important neuromodulators; Hoffman and Johnston, 1998;Dong et al, 2004), as well as the status of the GABAergic inhibitory signals (which are slower and do not require a fast response (Tremblay et al, 2016)). In an elegant study by Nakajima and Baker (2018), the spreading hyperpolarization, due to GABAergic inhibition, was optically monitored in hippocampal brain slices using GEVIs (Nakajima and Baker, 2018). Along these lines, specific mutations in the voltage-sensing domain have been shown to improve the sensitivity of the GEVI to hypopolarizing potentials (Dimitrov et al, 2007;Piao et al, 2015).…”

“…Furthermore, we found that Archon1 (red emission) and ASAP3b (green emission) are suitable for monitoring fast action potentials in individual cells, with ASAP being a slightly brighter and more forgiving probe. Our current data are potentially useful for guiding the practical choice of a GEVI indicator depending on the following: (1) biological application (e.g., cell body action potential; Abdelfattah et al, 2019); cell body UP state-a sustained ;20 mV depolarization (Adam et al, 2019;Villette et al, 2019), dendritic back-propagating action potential (Gong et al, 2015;Adam et al, 2019), dendritic subthreshold depolarization (Kwon et al, 2017), compound excitatory synaptic potential (Storace and Cohen, 2017;Song et al, 2018), and compound inhibitory (hyperpolarizing) synaptic potential (Nakajima and Baker, 2018);…”

Functional Connectivity Between the Trigeminal Main Sensory Nucleus and the Trigeminal Motor Nucleus

“…The slope and duration of the rising phase of the recorded calcium transients would then correspond to the spike frequency and firing duration, respectively (Yoshida et al, 2001). This comes from the fact that calcium transients from internal stores are not necessarily correlated with changes in membrane potential (Nakajima and Baker, 2018). Moreover, an increase in the frequency of spontaneous EPSPs was also induced, indicating a possible synaptic facilitation effect caused by the high-frequency stimulations.…”

Proton wires mediate the optical signal for ArcLight-type Genetically Encoded Voltage Indicators

“…GEVIs convert changes in membrane potential into changes in fluorescence intensity allowing simultaneous measurements at multiple locations from subcellular regions like the endoplasmic reticulum of a neuron (7) all the way to population signals in neuronal circuits (8,9).…”