Conditional Spike Transmission Mediated by Electrical Coupling Ensures Millisecond Precision-Correlated Activity among Interneurons In Vivo

Abstract

SummaryMany GABAergic interneurons are electrically coupled and in vitro can display correlated activity with millisecond precision. However, the mechanisms underlying correlated activity between interneurons in vivo are unknown. Using dual patch-clamp recordings in vivo, we reveal that in the presence of spontaneous background synaptic activity, electrically coupled cerebellar Golgi cells exhibit robust millisecond precision-correlated activity which is enhanced by sensory stimulation. This precisely correlated activity results from the cooperative action of two mechanisms. First, electrical coupling ensures slow subthreshold membrane potential correlations by equalizing membrane potential fluctuations, such that coupled neurons tend to approach action potential threshold together. Second, fast spike-triggered spikelets transmitted through gap junctions conditionally trigger postjunctional spikes, depending on both neurons being close to threshold. Electrical coupling therefore controls the temporal precision and degree of both spontaneous and sensory-evoked correlated activity between interneurons, by the cooperative effects of shared synaptic depolarization and spikelet transmission.

Closed-Loop Real-Time Imaging Enables Fully Automated Cell-Targeted Patch-Clamp Neural Recording In Vivo

“…By developing and using a bright pipette dye that has a fluorescence emission spectrum overlapping minimally (or ideally, not overlapping at all) with that of the target cells’ fluorescent marker, the high level of background fluorescence that results from multiple penetrations into the brain may have little or no effect on cell position detection and targeting by the imagepatcher, enabling many imagepatching trials and thus patch clamp recordings per animal. Further augmentation of the imagepatcher hardware (i.e., integration of multiple autopatcher control boxes, each linked to an individual pipette, with a single two-photon microscope) and refinement of the software (e.g., code development for simultaneous micromanipulator control in response to multiple pipette impedances and imaged positions of target neurons) may also enable multi-cell targeted patch clamp recordings in vivo (Jouhanneau et al, 2015; Pala and Petersen, 2015; van Welie et al, 2016), which will provide information on how cells communicate with each other in an intact brain network. Although we have not obtained patch clamp recordings in the awake brain using the imagepatcher, with an appropriate restraint habituation strategy (to reduce brain motion), a robust image analysis approach (which compensates for large motion artifacts), or a strategy for real-time switching of target cell identity (which enables targeting of an alternative cell, if present, when motion artifacts are large enough to displace the originally targeted cell out of the field-of-view), the imagepatcher may enable patch clamping of targeted neurons in awake animals.…”

“…The dura was then carefully removed to expose the brain surface. Right before starting an imaging or a patch clamp experiment, 1.5% (vol/w) agar in HEPES buffered artificial cerebrospinal fluid (ACSF, containing 145 mM NaCl, 5.4 mM KCl, 10 mM HEPES, 1.8 mM CaCl 2 , 1 mM MgCl 2 (Chen et al, 2015) or 150 mM NaCl, 2.5 mM KCl, 10 mM HEPES, 2 mM CaCl 2 and 1 mM MgCl 2 (van Welie et al, 2016); pH adjusted to 7.3 – 7.4 with NaOH) was applied on top of the brain to dampen pulsations caused by respiration and heartbeat, and then the craniotomy was covered with ACSF to keep the brain moist throughout the experiment. We took extra care to minimize bleeding throughout the surgery as blood on the cortical surface can greatly diminish optical clarity during two-photon imaging (Komai et al, 2006).…”

“…Targeted patch clamp recording of visually identified neurons (Dittgen et al, 2004; Kitamura et al, 2008; Margrie et al, 2003) is a powerful technique for electrophysiological characterization of cells of a given class in the living mammalian brain, and is in increasing demand for its ability to link a cell’s molecular and anatomical identity with its electrophysiological characteristics in the context of specific behaviors, states, and diseases (Chen et al, 2015; Li et al, 2015; Pala and Petersen, 2015; Runyan et al, 2010; van Welie et al, 2016). However, the manual labor and skill required to perform visually guided patching in vivo have limited widespread adoption of the technique.…”

Cx36, Cx43 and Cx45 in mouse and rat cerebellar cortex: species‐specific expression, compensation in Cx36 null mice and co‐localization in neurons vs. glia

“…In the case of neurons in the cerebellar cortex, it has been established ultrastructurally that gap junctions occur between Golgi cells, between stellate cells, between basket cells, and between stellate cells and basket cells (Sotelo & Llinas, ; Van Der Giessen et al ., ; Vervaeke et al ., ; Szoboszlay et al ., ). Correspondingly, electrophysiological analyses have firmly demonstrated electrical and/or dye‐coupling between these various neuronal populations and have extended understanding of the functional importance of electrical synapses in cerebellar interneuronal networks (Mann‐Metzer & Yarom, , ; Dugue et al ., ; Vervaeke et al ., , ; Hull & Regehr, ; Alcami & Marty, ; Kim et al ., ; Szoboszlay et al ., ; Van Welie et al ., ). Dye‐coupling of Purkinje cells with both basket cells and stellate cells has also been described (Middleton et al ., ), but gap junctions linking these cell types have not been found.…”

Synchrony and so much more: Diverse roles for electrical synapses in neural circuits

“…There have been very few attempts to directly measure the relationship between electrical synapses and synchrony in intact vertebrate brains. In an inspiring feat of electrophysiology, Van Welie et al () recently described paired whole‐cell recordings from cerebellar Golgi cells in anesthetized mice. Their data demonstrate, first, that Golgi cells in vivo are indeed electrically coupled, as in vitro work had suggested (Dugué et al, ); second, that electrical synapses in vivo can mediate spike synchrony with millisecond precision; and third, that synchrony depends on electrical synapses spreading both slow, subthreshold fluctuations across the Golgi network as well as fast, spike‐triggered electrical PSPs.…”